@article{ehnvall_topography_2024,
	title = {Topography and {Time} {Shape} {Mire} {Morphometry} and {Large}-{Scale} {Mire} {Distribution} {Patterns} in the {Northern} {Boreal} {Landscape}},
	volume = {129},
	copyright = {© 2024. The Authors.},
	issn = {2169-9011},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2023JF007324},
	doi = {10.1029/2023JF007324},
	abstract = {Peatlands are major terrestrial soil carbon stores, and open mires in boreal landscapes hold a considerable fraction of the global peat carbon. Despite decades of study, large-scale spatiotemporal analyses of mire arrangement have been scarce, which has limited our ability to scale-up mire properties, such as carbon accumulation to the landscape level. Here, we use a land-uplift mire chronosequence in northern Sweden spanning 9,000 years to quantify controls on mire distribution patterns. Our objectives include assessing changes in the spatial arrangement of mires with land surface age, and understanding modifications by upland hydrotopography. Characterizing over 3,000 mires along a 30 km transect, we found that the time since land emergence from the sea was the dominant control over mire coverage, especially for the establishment of large mire complexes. Mires at the youngest end of the chronosequence were small with heterogenous morphometry (shape, slope, and catchment-to-mire areal ratios), while mires on the oldest surfaces were variable in size, but included larger mires with more complex shapes and smaller catchment-to-mire ratios. In general, complex topography fragmented mires by constraining the lateral expansion, resulting in a greater number of mires, but reduced total mire area regardless of landscape age. Mires in this study area occurred on slopes up to 4\%, indicating a hydrological boundary to peatland expansion under local climatic conditions. The consistency in mire responses to spatiotemporal controls illustrates how temporal limitation in peat initiation and accumulation, and topographic constraints to mire expansion together have shaped present day mire distribution patterns.},
	language = {en},
	number = {2},
	urldate = {2024-03-26},
	journal = {Journal of Geophysical Research: Earth Surface},
	author = {Ehnvall, B. and Ratcliffe, J. L. and Nilsson, M. B. and Öquist, M. G. and Sponseller, R. A. and Grabs, T.},
	year = {2024},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2023JF007324},
	keywords = {Holocene, boreal, catchment, long-term development, mire morphometry, spatiotemporal drivers},
	pages = {e2023JF007324},
}

Peatlands are major terrestrial soil carbon stores, and open mires in boreal landscapes hold a considerable fraction of the global peat carbon. Despite decades of study, large-scale spatiotemporal analyses of mire arrangement have been scarce, which has limited our ability to scale-up mire properties, such as carbon accumulation to the landscape level. Here, we use a land-uplift mire chronosequence in northern Sweden spanning 9,000 years to quantify controls on mire distribution patterns. Our objectives include assessing changes in the spatial arrangement of mires with land surface age, and understanding modifications by upland hydrotopography. Characterizing over 3,000 mires along a 30 km transect, we found that the time since land emergence from the sea was the dominant control over mire coverage, especially for the establishment of large mire complexes. Mires at the youngest end of the chronosequence were small with heterogenous morphometry (shape, slope, and catchment-to-mire areal ratios), while mires on the oldest surfaces were variable in size, but included larger mires with more complex shapes and smaller catchment-to-mire ratios. In general, complex topography fragmented mires by constraining the lateral expansion, resulting in a greater number of mires, but reduced total mire area regardless of landscape age. Mires in this study area occurred on slopes up to 4%, indicating a hydrological boundary to peatland expansion under local climatic conditions. The consistency in mire responses to spatiotemporal controls illustrates how temporal limitation in peat initiation and accumulation, and topographic constraints to mire expansion together have shaped present day mire distribution patterns.

@article{skerlep_differential_2023,
	title = {Differential {Trends} in {Iron} {Concentrations} of {Boreal} {Streams} {Linked} to {Catchment} {Characteristics}},
	volume = {37},
	copyright = {© 2023. The Authors.},
	issn = {1944-9224},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2022GB007484},
	doi = {10.1029/2022GB007484},
	abstract = {Increasing iron (Fe) concentrations have been reported for freshwaters across northern Europe over the last decades. This increase, together with elevated concentrations of dissolved organic carbon (DOC), leads to browning of freshwaters, which affects aquatic organisms, ecosystem functioning, biogeochemical cycles, and brings challenges to drinking water production. However, how such increasing trends in stream Fe concentrations reflect the contribution of different catchment sources remains poorly resolved. Here, we explored how catchment characteristics, that is, mires and coniferous soils, regulate spatial and temporal patterns of Fe in a boreal stream network. For this, we determined Fe speciation in riparian and mire soils, and studied temporal Fe dynamics in soil-water and stream-water over a span of 18 years. Positive Fe trends were found in the solution of the riparian soil, while no long-term trend was observed in the mire. These differences were reflected in stream-water, where three headwater streams dominated by coniferous cover also displayed positive Fe trends, whereas the mire dominated stream showed no trend. Surprisingly, the majority of higher order streams showed declining Fe trends, despite long-term increases in DOC. In addition, we found that an extreme drought event led to a prolonged release of Fe and DOC from the riparian soils, that could have long-term effects on stream Fe concentrations. Our results show that riparian forest soils can be major contributors to ongoing increases in freshwater Fe concentrations and that drought can further promote the release of Fe from organic soils.},
	language = {en},
	number = {3},
	urldate = {2024-03-27},
	journal = {Global Biogeochemical Cycles},
	author = {Škerlep, M. and Nehzati, S. and Sponseller, R. A. and Persson, P. and Laudon, H. and Kritzberg, E. S.},
	year = {2023},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2022GB007484},
	keywords = {browning, catchment, iron, mire, riparian zone, stream},
	pages = {e2022GB007484},
}

Increasing iron (Fe) concentrations have been reported for freshwaters across northern Europe over the last decades. This increase, together with elevated concentrations of dissolved organic carbon (DOC), leads to browning of freshwaters, which affects aquatic organisms, ecosystem functioning, biogeochemical cycles, and brings challenges to drinking water production. However, how such increasing trends in stream Fe concentrations reflect the contribution of different catchment sources remains poorly resolved. Here, we explored how catchment characteristics, that is, mires and coniferous soils, regulate spatial and temporal patterns of Fe in a boreal stream network. For this, we determined Fe speciation in riparian and mire soils, and studied temporal Fe dynamics in soil-water and stream-water over a span of 18 years. Positive Fe trends were found in the solution of the riparian soil, while no long-term trend was observed in the mire. These differences were reflected in stream-water, where three headwater streams dominated by coniferous cover also displayed positive Fe trends, whereas the mire dominated stream showed no trend. Surprisingly, the majority of higher order streams showed declining Fe trends, despite long-term increases in DOC. In addition, we found that an extreme drought event led to a prolonged release of Fe and DOC from the riparian soils, that could have long-term effects on stream Fe concentrations. Our results show that riparian forest soils can be major contributors to ongoing increases in freshwater Fe concentrations and that drought can further promote the release of Fe from organic soils.

@article{mosquera_concentration-discharge_2023,
	title = {Concentration-{Discharge} {Patterns} {Reveal} {Catchment} {Controls} {Over} the {Stoichiometry} of {Carbon} and {Nutrient} {Supply} to {Boreal} {Streams}},
	volume = {128},
	copyright = {© 2023. The Authors.},
	issn = {2169-8961},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2022JG007179},
	doi = {10.1029/2022JG007179},
	abstract = {Carbon (C), nitrogen (N), and phosphorus (P) export from catchments is strongly regulated by interactions between hydrological flowpaths and their terrestrial use/storage. While concentration-discharge (c-Q) relationships have been widely used to understand this interplay for C, N, and P individually, how flow regulates the relative supply of these resources across spatial and temporal scales is not well documented. Here, we analyze c-Q relationships from 12 years of data to test how seasonal flow regulates the concentrations of inorganic N (Dissolved inorganic nitrogen [DIN]) and P (Dissolved inorganic phosphorus [DIP]), dissolved organic N (DON) and C (dissolved organic carbon [DOC]) and their respective ratios across 12 streams in a boreal landscape. We observed opposing c-Q relationships between organic and inorganic solutes. DOC and DON tended toward transport limitation with little year-to-year change, whereas ammonium (NH4) and DIP were increasingly source limited over time. These different c-Q relationships translated into large (up to three-fold) shifts in resource ratios (e.g., DOC:DIN) in response to changes in flow. Our results also highlight strong influences of catchment structure on c-Q patterns, regardless of solute, season, and longer-term directional changes. Here, the organic solute c-Q responses became less transport limited over time; while inorganic solute responses became less source limited with increasing mire/decreasing forest cover. Overall, differences in timing of catchment exports for C, N, and P, create dynamic variation in solute concentrations in streams with subsequent impacts on resource stoichiometry that is central to aquatic ecological processes.},
	language = {en},
	number = {8},
	urldate = {2024-03-26},
	journal = {Journal of Geophysical Research: Biogeosciences},
	author = {Mosquera, Virginia and Laudon, Hjalmar and Blackburn, Meredith and Hasselquist, Eliza Maher and Sponseller, Ryan A.},
	year = {2023},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2022JG007179},
	keywords = {boreal catchments, concentration-discharge relationships, dissolved organic carbon, nitrogen, nutrient stoichiometry, phosphorus},
	pages = {e2022JG007179},
}

Carbon (C), nitrogen (N), and phosphorus (P) export from catchments is strongly regulated by interactions between hydrological flowpaths and their terrestrial use/storage. While concentration-discharge (c-Q) relationships have been widely used to understand this interplay for C, N, and P individually, how flow regulates the relative supply of these resources across spatial and temporal scales is not well documented. Here, we analyze c-Q relationships from 12 years of data to test how seasonal flow regulates the concentrations of inorganic N (Dissolved inorganic nitrogen [DIN]) and P (Dissolved inorganic phosphorus [DIP]), dissolved organic N (DON) and C (dissolved organic carbon [DOC]) and their respective ratios across 12 streams in a boreal landscape. We observed opposing c-Q relationships between organic and inorganic solutes. DOC and DON tended toward transport limitation with little year-to-year change, whereas ammonium (NH4) and DIP were increasingly source limited over time. These different c-Q relationships translated into large (up to three-fold) shifts in resource ratios (e.g., DOC:DIN) in response to changes in flow. Our results also highlight strong influences of catchment structure on c-Q patterns, regardless of solute, season, and longer-term directional changes. Here, the organic solute c-Q responses became less transport limited over time; while inorganic solute responses became less source limited with increasing mire/decreasing forest cover. Overall, differences in timing of catchment exports for C, N, and P, create dynamic variation in solute concentrations in streams with subsequent impacts on resource stoichiometry that is central to aquatic ecological processes.

@article{ehnvall_landscape_2023,
	title = {Landscape constraints on mire lateral expansion},
	volume = {302},
	issn = {0277-3791},
	url = {https://www.sciencedirect.com/science/article/pii/S0277379123000094},
	doi = {10.1016/j.quascirev.2023.107961},
	abstract = {Little is known about the long-term expansion of mire ecosystems, despite their importance in the global carbon and hydrogeochemical cycles. It has been firmly established that mires do not expand linearly over time. Despite this, mires are often assumed to have expanded at a constant rate after initiation simply for lack of a better understanding. There has not yet been a serious attempt to determine the rate and drivers of mire expansion at the regional, or larger spatial scales. Here we make use of a natural chronosequence, spanning the Holocene, which is provided by the retreating coastline of Northern Sweden. By studying an isostatic rebound area we can infer mire expansion dynamics by looking at the portion of the landscape where mires become progressively scarce as the land becomes younger. Our results confirms that mires expanded non-linearly across the landscape and that their expansion is related to the availability of suitably wet areas, which, in our case, depends primarily on the hydro-edaphic properties of the landscape. Importantly, we found that mires occupied the wettest locations in the landscape within only one to two thousand years, while it took mires three to four thousand years to expand into slightly drier areas. Our results imply that the lateral expansion of mires, and thus peat accumulation is a non-linear process, occurring at different rates depending, above all else, on the wetness of the landscape.},
	urldate = {2024-03-26},
	journal = {Quaternary Science Reviews},
	author = {Ehnvall, Betty and Ratcliffe, Joshua L. and Bohlin, Elisabet and Nilsson, Mats B. and Öquist, Mats G. and Sponseller, Ryan A. and Grabs, Thomas},
	month = feb,
	year = {2023},
	keywords = {Boreal zone, Chronosequence, Holocene, Landscape ecology, Landscape wetness, Mire available areas, Mire lateral expansion, Non-linear, Peat accumulation},
	pages = {107961},
}

Little is known about the long-term expansion of mire ecosystems, despite their importance in the global carbon and hydrogeochemical cycles. It has been firmly established that mires do not expand linearly over time. Despite this, mires are often assumed to have expanded at a constant rate after initiation simply for lack of a better understanding. There has not yet been a serious attempt to determine the rate and drivers of mire expansion at the regional, or larger spatial scales. Here we make use of a natural chronosequence, spanning the Holocene, which is provided by the retreating coastline of Northern Sweden. By studying an isostatic rebound area we can infer mire expansion dynamics by looking at the portion of the landscape where mires become progressively scarce as the land becomes younger. Our results confirms that mires expanded non-linearly across the landscape and that their expansion is related to the availability of suitably wet areas, which, in our case, depends primarily on the hydro-edaphic properties of the landscape. Importantly, we found that mires occupied the wettest locations in the landscape within only one to two thousand years, while it took mires three to four thousand years to expand into slightly drier areas. Our results imply that the lateral expansion of mires, and thus peat accumulation is a non-linear process, occurring at different rates depending, above all else, on the wetness of the landscape.

@article{stanley_grimedb_2023,
	title = {{GRiMeDB} : the global river methane database of concentrations and fluxes},
	volume = {15},
	shorttitle = {{GRiMeDB}},
	url = {https://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-215374},
	doi = {10.5194/essd-15-2879-2023},
	abstract = {Despite their small spatial extent, fluvial ecosystems play a significant role in processing and transporting carbon in aquatic networks, which results in substantial emission of methane (CH4) into ...},
	language = {eng},
	number = {7},
	urldate = {2024-03-26},
	journal = {Earth System Science Data},
	author = {Stanley, Emily H. and Loken, Luke C. and Casson, Nora J. and Oliver, Samantha K. and Sponseller, Ryan A. and Wallin, Marcus B. and Zhang, Liwei and Rocher-Ros, Gerard},
	year = {2023},
	note = {Publisher: Copernicus Publications},
	pages = {2879--2926},
}

Despite their small spatial extent, fluvial ecosystems play a significant role in processing and transporting carbon in aquatic networks, which results in substantial emission of methane (CH4) into ...

@article{rocher-ros_global_2023,
	title = {Global methane emissions from rivers and streams},
	volume = {621},
	url = {https://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-213705},
	doi = {10.1038/s41586-023-06344-6},
	abstract = {Methane (CH4) is a potent greenhouse gas and its concentrations have tripled in the atmosphere since the industrial revolution. There is evidence that global warming has increased CH4 emissions fro ...},
	language = {eng},
	number = {7979},
	urldate = {2024-03-26},
	journal = {Nature},
	author = {Rocher-Ros, Gerard and Stanley, Emily H. and Loken, Luke C. and Casson, Nora J. and Raymond, Peter A. and Liu, Shaoda and Amatulli, Giuseppe and Sponseller, Ryan A.},
	year = {2023},
	note = {Publisher: Springer Nature},
	pages = {530--535},
}

Methane (CH4) is a potent greenhouse gas and its concentrations have tripled in the atmosphere since the industrial revolution. There is evidence that global warming has increased CH4 emissions fro ...

@article{rehn_long-term_2023,
	title = {Long-term changes in dissolved inorganic carbon across boreal streams caused by altered hydrology},
	volume = {68},
	url = {https://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-201749},
	doi = {10.1002/lno.12282},
	abstract = {A major challenge for predicting future landscape carbon (C) balances is to understand how environmental changes affect the transfer of C from soils to surface waters. Here, we evaluated 14 yr (200 ...},
	language = {eng},
	number = {2},
	urldate = {2024-03-26},
	journal = {Limnology and Oceanography},
	author = {Rehn, Lukas and Sponseller, Ryan A. and Laudon, Hjalmar and Wallin, Marcus B.},
	year = {2023},
	note = {Publisher: John Wiley \& Sons},
	pages = {409--423},
}

A major challenge for predicting future landscape carbon (C) balances is to understand how environmental changes affect the transfer of C from soils to surface waters. Here, we evaluated 14 yr (200 ...

@article{menden-deuer_cascading_2023,
	title = {Cascading, interactive, and indirect effects of climate change on aquatic communities, habitats, and ecosystems},
	volume = {68},
	url = {https://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-212501},
	doi = {10.1002/lno.12384},
	abstract = {Climate-change is rapidly and intensively altering aquatic communities and habitats. While previous work has focused on direct effects of potential drivers, indirect and interactive effects on orga ...},
	language = {eng},
	number = {S1},
	urldate = {2024-03-26},
	journal = {Limnology and Oceanography},
	author = {Menden-Deuer, Susanne and Mullarney, Julia C. and Boersma, Maarten and Grossart, Hans-Peter and Sponseller, Ryan A. and Woodin, Sarah Ann},
	year = {2023},
	note = {Publisher: John Wiley \& Sons},
	pages = {S1--S7},
}

Climate-change is rapidly and intensively altering aquatic communities and habitats. While previous work has focused on direct effects of potential drivers, indirect and interactive effects on orga ...

@article{mckie_long-established_2023,
	title = {A long-established invasive species alters the functioning of benthic biofilms in lakes},
	volume = {68},
	url = {https://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-214759},
	doi = {10.1111/fwb.14175},
	abstract = {Invasive species often transform environmental conditions, exclude native species and alter ecosystem functioning, including key ecosystem processes underpinning nutrient and energy cycles. However ...},
	language = {eng},
	number = {12},
	urldate = {2024-03-26},
	journal = {Freshwater Biology},
	author = {McKie, Brendan G. and Tattersdill, Kristina and Ecke, Frauke and Frainer, André and Sponseller, Ryan A.},
	year = {2023},
	note = {Publisher: John Wiley \& Sons},
	pages = {2068--2083},
}

Invasive species often transform environmental conditions, exclude native species and alter ecosystem functioning, including key ecosystem processes underpinning nutrient and energy cycles. However ...

@article{lupon_groundwater-stream_2023,
	title = {Groundwater-stream connections shape the spatial pattern and rates of aquatic metabolism},
	volume = {8},
	url = {https://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-204765},
	doi = {10.1002/lol2.10305},
	abstract = {A longstanding challenge in stream ecology is to understand how landscape configuration organizes spatial patterns of ecosystem function via lateral groundwater connections. We combined laboratory  ...},
	language = {eng},
	number = {2},
	urldate = {2024-03-26},
	journal = {Limnology and Oceanography Letters},
	author = {Lupon, Anna and Gómez-Gener, Lluís and Fork, Megan L. and Laudon, Hjalmar and Martí, Eugènia and Lidberg, William and Sponseller, Ryan A.},
	year = {2023},
	note = {Publisher: John Wiley \& Sons},
	pages = {350--358},
}

A longstanding challenge in stream ecology is to understand how landscape configuration organizes spatial patterns of ecosystem function via lateral groundwater connections. We combined laboratory ...

@article{vachon_controls_2023,
	title = {Controls on {Terrestrial} {Carbon} {Fluxes} in {Simulated} {Networks} of {Connected} {Streams} and {Lakes}},
	volume = {37},
	copyright = {© 2023. The Authors.},
	issn = {1944-9224},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2022GB007597},
	doi = {10.1029/2022GB007597},
	abstract = {Inland waters play a critical role in the carbon cycle by emitting significant amounts of land-exported carbon to the atmosphere. While carbon gas emissions from individual aquatic systems have been extensively studied, how networks of connected streams and lakes regulate integrated fluxes of organic and inorganic forms remain poorly understood. Here, we develop a process-based model to simulate the fate of terrestrial dissolved organic carbon (DOC) and carbon dioxide (CO2) in artificial inland water networks with variable topology, hydrology, and DOC reactivity. While the role of lakes is highly dependent on DOC reactivity, we find that the mineralization of terrestrial DOC is more efficient in lake-rich networks. Regardless of typology and hydrology, terrestrial CO2 is emitted almost entirely within the network boundary. Consequently, the proportion of exported terrestrial carbon emitted from inland water networks increases with the CO2 versus DOC export ratio. Overall, our results suggest that CO2 emissions from inland waters are governed by interactions between the relative amount and reactivity of terrestrial DOC and CO2 inputs and the network configuration of recipient lakes and streams.},
	language = {en},
	number = {3},
	urldate = {2023-07-20},
	journal = {Global Biogeochemical Cycles},
	author = {Vachon, Dominic and Sponseller, Ryan A. and Rosvall, Martin and Karlsson, Jan},
	year = {2023},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2022GB007597},
	keywords = {\#nosource, CO2 emission, DOC mineralization, aquatic network, carbon cycle, modeling},
	pages = {e2022GB007597},
}

Inland waters play a critical role in the carbon cycle by emitting significant amounts of land-exported carbon to the atmosphere. While carbon gas emissions from individual aquatic systems have been extensively studied, how networks of connected streams and lakes regulate integrated fluxes of organic and inorganic forms remain poorly understood. Here, we develop a process-based model to simulate the fate of terrestrial dissolved organic carbon (DOC) and carbon dioxide (CO2) in artificial inland water networks with variable topology, hydrology, and DOC reactivity. While the role of lakes is highly dependent on DOC reactivity, we find that the mineralization of terrestrial DOC is more efficient in lake-rich networks. Regardless of typology and hydrology, terrestrial CO2 is emitted almost entirely within the network boundary. Consequently, the proportion of exported terrestrial carbon emitted from inland water networks increases with the CO2 versus DOC export ratio. Overall, our results suggest that CO2 emissions from inland waters are governed by interactions between the relative amount and reactivity of terrestrial DOC and CO2 inputs and the network configuration of recipient lakes and streams.

@article{berggren_nutrient_2023,
	title = {Nutrient limitation masks the dissolved organic matter composition effects on bacterial metabolism in unproductive freshwaters},
	volume = {n/a},
	copyright = {© 2023 The Authors. Limnology and Oceanography published by Wiley Periodicals LLC on behalf of Association for the Sciences of Limnology and Oceanography.},
	issn = {1939-5590},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/lno.12406},
	doi = {10.1002/lno.12406},
	abstract = {Aquatic microbial responses to changes in the amount and composition of dissolved organic carbon (DOC) are of fundamental ecological and biogeochemical importance. Parallel factor (PARAFAC) analysis of excitation–emission fluorescence spectra is a common tool to characterize DOC, yet its ability to predict bacterial production (BP), bacterial respiration (BR), and bacterial growth efficiency (BGE) vary widely, potentially because inorganic nutrient limitation decouples microbial processes from their dependence on DOC composition. We used 28-d bioassays with water from 19 lakes, streams, and rivers in northern Sweden to test how much the links between bacterial metabolism and fluorescence PARAFAC components depend on experimental additions of inorganic nutrients. We found a significant interaction effect between nutrient addition and fluorescence on carbon-specific BP, and weak evidence for influence on BGE by the same interaction (p = 0.1), but no corresponding interaction effect on BR. A practical implication of this interaction was that fluorescence components could explain more than twice as much of the variability in carbon-specific BP (R2 = 0.90) and BGE (R2 = 0.70) after nitrogen and phosphorus addition, compared with control incubations. Our results suggest that an increased supply of labile DOC relative to ambient phosphorus and nitrogen induces gradually larger degrees of nutrient limitation of BP, which in turn decouple BP and BGE from fluorescence signals. Thus, while fluorescence does contain precise information about the degree to which DOC can support microbial processes, this information may be hidden in field studies due to nutrient limitation of bacterial metabolism.},
	language = {en},
	number = {n/a},
	urldate = {2023-07-20},
	journal = {Limnology and Oceanography},
	author = {Berggren, Martin and Ye, Linlin and Sponseller, Ryan A. and Bergström, Ann-Kristin and Karlsson, Jan and Verheijen, Hendricus and Hensgens, Geert},
	year = {2023},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/lno.12406},
	keywords = {\#nosource, ⛔ No INSPIRE recid found},
	pages = {1--11},
}

Aquatic microbial responses to changes in the amount and composition of dissolved organic carbon (DOC) are of fundamental ecological and biogeochemical importance. Parallel factor (PARAFAC) analysis of excitation–emission fluorescence spectra is a common tool to characterize DOC, yet its ability to predict bacterial production (BP), bacterial respiration (BR), and bacterial growth efficiency (BGE) vary widely, potentially because inorganic nutrient limitation decouples microbial processes from their dependence on DOC composition. We used 28-d bioassays with water from 19 lakes, streams, and rivers in northern Sweden to test how much the links between bacterial metabolism and fluorescence PARAFAC components depend on experimental additions of inorganic nutrients. We found a significant interaction effect between nutrient addition and fluorescence on carbon-specific BP, and weak evidence for influence on BGE by the same interaction (p = 0.1), but no corresponding interaction effect on BR. A practical implication of this interaction was that fluorescence components could explain more than twice as much of the variability in carbon-specific BP (R2 = 0.90) and BGE (R2 = 0.70) after nitrogen and phosphorus addition, compared with control incubations. Our results suggest that an increased supply of labile DOC relative to ambient phosphorus and nitrogen induces gradually larger degrees of nutrient limitation of BP, which in turn decouple BP and BGE from fluorescence signals. Thus, while fluorescence does contain precise information about the degree to which DOC can support microbial processes, this information may be hidden in field studies due to nutrient limitation of bacterial metabolism.

@article{truchy_responses_2022,
	title = {Responses of multiple structural and functional indicators along three contrasting disturbance gradients},
	volume = {135},
	issn = {1470-160X},
	url = {https://www.sciencedirect.com/science/article/pii/S1470160X21011791},
	doi = {10.1016/j.ecolind.2021.108514},
	abstract = {Ecosystem functioning and community structure are recognized as key components of ecosystem integrity, but comprehensive, standardized studies of the responses of both structural and functional indicators to different types of anthropogenic pressures remain rare. Consequently, we lack an empirical basis for (i) identifying when monitoring ecosystem structure alone misses important changes in ecosystem functioning, (ii) recommending sets of structural and functional metrics best suited for detecting ecological change driven by different anthropogenic pressures, and (iii) understanding the cumulative effects of multiple, co-occurring stressors on structure and function. We investigated variation in community structure and ecosystem functioning of stream ecosystems along three gradients (10–16 independent stream sites each) of increasing impact arising from agriculture, forestry and river regulation for hydropower, respectively. For each stream, we quantified variation in (i) the abiotic environment, (ii) community composition of four organism groups and (iii) three basal ecosystem processes underpinning carbon and nutrient cycling in streams. We assessed the responsiveness of multiple biodiversity, community structure and ecosystem functioning indicators based on variance explained and effect size metrics. Along a gradient of increasing agricultural impact, diatoms and fish were the most responsive groups overall, but significant variation was detected in at least one aspect of community composition, abundance and/or biodiversity of every organism group . In contrast, most of our functional metrics did not vary significantly along the agricultural gradient, possibly due to contrasting, antagonistic effects of increasing nutrient concentrations and turbidity on ecosystem process rates. The exception was detritivore-mediated litter decomposition which increased up to moderate levels of nutrient. Impacts of river regulation were most marked for diatoms, which were responsive to both increasingly frequent hydropeaking and to increasing seasonal river regulation. Among functional indicators, both litter decomposition and algal biomass accrual declined significantly with increasing hydropeaking. Few structural or functional metrics varied with forest management, with macroinvertebrate diversity increasing along the forestry gradient, as did algal and fungal biomass accrual. Together, these findings highlight the challenges of making inferences about the impacts of anthropogenic disturbances at the ecosystem level based on community data alone, and pinpoint the need to identify optimal sets of functional and structural indicators best suited for detecting ecological changes associated with different human activities.},
	urldate = {2024-03-27},
	journal = {Ecological Indicators},
	author = {Truchy, Amélie and Sponseller, Ryan A. and Ecke, Frauke and Angeler, David G. and Kahlert, Maria and Bundschuh, Mirco and Johnson, Richard K. and McKie, Brendan G.},
	month = feb,
	year = {2022},
	keywords = {Agriculture, Community structure, Ecosystem functioning, Forestry, Multiple stressors, River regulation},
	pages = {108514},
}

Ecosystem functioning and community structure are recognized as key components of ecosystem integrity, but comprehensive, standardized studies of the responses of both structural and functional indicators to different types of anthropogenic pressures remain rare. Consequently, we lack an empirical basis for (i) identifying when monitoring ecosystem structure alone misses important changes in ecosystem functioning, (ii) recommending sets of structural and functional metrics best suited for detecting ecological change driven by different anthropogenic pressures, and (iii) understanding the cumulative effects of multiple, co-occurring stressors on structure and function. We investigated variation in community structure and ecosystem functioning of stream ecosystems along three gradients (10–16 independent stream sites each) of increasing impact arising from agriculture, forestry and river regulation for hydropower, respectively. For each stream, we quantified variation in (i) the abiotic environment, (ii) community composition of four organism groups and (iii) three basal ecosystem processes underpinning carbon and nutrient cycling in streams. We assessed the responsiveness of multiple biodiversity, community structure and ecosystem functioning indicators based on variance explained and effect size metrics. Along a gradient of increasing agricultural impact, diatoms and fish were the most responsive groups overall, but significant variation was detected in at least one aspect of community composition, abundance and/or biodiversity of every organism group . In contrast, most of our functional metrics did not vary significantly along the agricultural gradient, possibly due to contrasting, antagonistic effects of increasing nutrient concentrations and turbidity on ecosystem process rates. The exception was detritivore-mediated litter decomposition which increased up to moderate levels of nutrient. Impacts of river regulation were most marked for diatoms, which were responsive to both increasingly frequent hydropeaking and to increasing seasonal river regulation. Among functional indicators, both litter decomposition and algal biomass accrual declined significantly with increasing hydropeaking. Few structural or functional metrics varied with forest management, with macroinvertebrate diversity increasing along the forestry gradient, as did algal and fungal biomass accrual. Together, these findings highlight the challenges of making inferences about the impacts of anthropogenic disturbances at the ecosystem level based on community data alone, and pinpoint the need to identify optimal sets of functional and structural indicators best suited for detecting ecological changes associated with different human activities.

@article{tiwari_emerging_2022,
	title = {The emerging role of drought as a regulator of dissolved organic carbon in boreal landscapes},
	volume = {13},
	copyright = {2022 The Author(s)},
	issn = {2041-1723},
	url = {https://www.nature.com/articles/s41467-022-32839-3},
	doi = {10.1038/s41467-022-32839-3},
	abstract = {One likely consequence of global climate change is an increased frequency and intensity of droughts at high latitudes. Here we use a 17-year record from 13 nested boreal streams to examine direct and lagged effects of summer drought on the quantity and quality of dissolved organic carbon (DOC) inputs from catchment soils. Protracted periods of drought reduced DOC concentrations in all catchments but also led to large stream DOC pulses upon rewetting. Concurrent changes in DOC optical properties and chemical character suggest that seasonal drying and rewetting trigger soil processes that alter the forms of carbon supplied to streams. Contrary to expectations, clearest drought effects were observed in larger watersheds, whereas responses were most muted in smaller, peatland-dominated catchments. Collectively, our results indicate that summer drought causes a fundamental shift in the seasonal distribution of DOC concentrations and character, which together operate as primary controls over the ecological and biogeochemical functioning of northern aquatic ecosystems.},
	language = {en},
	number = {1},
	urldate = {2024-03-27},
	journal = {Nature Communications},
	author = {Tiwari, Tejshree and Sponseller, Ryan A. and Laudon, Hjalmar},
	month = aug,
	year = {2022},
	note = {Publisher: Nature Publishing Group},
	keywords = {Carbon cycle, Environmental impact, Hydrology},
	pages = {5125},
}

One likely consequence of global climate change is an increased frequency and intensity of droughts at high latitudes. Here we use a 17-year record from 13 nested boreal streams to examine direct and lagged effects of summer drought on the quantity and quality of dissolved organic carbon (DOC) inputs from catchment soils. Protracted periods of drought reduced DOC concentrations in all catchments but also led to large stream DOC pulses upon rewetting. Concurrent changes in DOC optical properties and chemical character suggest that seasonal drying and rewetting trigger soil processes that alter the forms of carbon supplied to streams. Contrary to expectations, clearest drought effects were observed in larger watersheds, whereas responses were most muted in smaller, peatland-dominated catchments. Collectively, our results indicate that summer drought causes a fundamental shift in the seasonal distribution of DOC concentrations and character, which together operate as primary controls over the ecological and biogeochemical functioning of northern aquatic ecosystems.

@article{rulli_seasonal_2022,
	title = {Seasonal patterns in nutrient bioavailability in boreal headwater streams},
	volume = {67},
	copyright = {© 2022 The Authors. Limnology and Oceanography published by Wiley Periodicals LLC on behalf of Association for the Sciences of Limnology and Oceanography.},
	issn = {1939-5590},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/lno.12064},
	doi = {10.1002/lno.12064},
	abstract = {Changes in nutrient bioavailability due to increased loading of dissolved organic matter (DOM) may impact boreal freshwaters. Yet, the relative bioavailability of carbon (C), nitrogen (N), and phosphorus (P) associated with terrestrial DOM remains poorly understood. We applied short-term bioassays with natural bacterial inocula to determine seasonal variation in bioavailable organic nutrient pools from four boreal headwater streams in northern Sweden. Experiments were designed to exhaust bioavailable nutrients associated with DOM by inducing limiting conditions when all required resources except for the targeted nutrient (C, N, or P) are provided in excess. We hypothesized that the supply of different bioavailable nutrients to streams would reflect seasonal variations in terrestrial demand, hydrology, and temperature. The delivery of bioavailable DOM-associated resources from the four streams were, on average, 2\%, 11\%, and 38\% of the total dissolved organic C, N, and P, respectively, emphasizing the relatively low C bioavailability in these DOM-rich waters. Bioavailable N : P ratios peaked in autumn for all sites, with lower values in winter and spring. Both in terms of relative (\% of total) and absolute bioavailable organic nutrient concentrations, the seasonal pattern was characterized by systematically high values for the autumn period. Furthermore, links between bioavailable resources and temperature and hydrology varied across sites, time periods, and the different elements. Thus, elevated concentrations of bioavailable organic resources in autumn suggest the potential for leaf fall, as well as late season storms that rewet dry soils, to serve as considerable sources of C, N, and P to boreal aquatic ecosystems.},
	language = {en},
	number = {5},
	urldate = {2024-03-27},
	journal = {Limnology and Oceanography},
	author = {Rulli, Mayra P. D. and Bergström, Ann-Kristin and Sponseller, Ryan A. and Berggren, Martin},
	year = {2022},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/lno.12064},
	keywords = {\#nosource},
	pages = {1169--1183},
}

Changes in nutrient bioavailability due to increased loading of dissolved organic matter (DOM) may impact boreal freshwaters. Yet, the relative bioavailability of carbon (C), nitrogen (N), and phosphorus (P) associated with terrestrial DOM remains poorly understood. We applied short-term bioassays with natural bacterial inocula to determine seasonal variation in bioavailable organic nutrient pools from four boreal headwater streams in northern Sweden. Experiments were designed to exhaust bioavailable nutrients associated with DOM by inducing limiting conditions when all required resources except for the targeted nutrient (C, N, or P) are provided in excess. We hypothesized that the supply of different bioavailable nutrients to streams would reflect seasonal variations in terrestrial demand, hydrology, and temperature. The delivery of bioavailable DOM-associated resources from the four streams were, on average, 2%, 11%, and 38% of the total dissolved organic C, N, and P, respectively, emphasizing the relatively low C bioavailability in these DOM-rich waters. Bioavailable N : P ratios peaked in autumn for all sites, with lower values in winter and spring. Both in terms of relative (% of total) and absolute bioavailable organic nutrient concentrations, the seasonal pattern was characterized by systematically high values for the autumn period. Furthermore, links between bioavailable resources and temperature and hydrology varied across sites, time periods, and the different elements. Thus, elevated concentrations of bioavailable organic resources in autumn suggest the potential for leaf fall, as well as late season storms that rewet dry soils, to serve as considerable sources of C, N, and P to boreal aquatic ecosystems.

@article{mosquera_co-occurrence_2022,
	title = {Co-occurrence of browning and oligotrophication in a boreal stream network},
	volume = {67},
	url = {https://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-199209},
	doi = {10.1002/lno.12205},
	abstract = {The relative supply of carbon (C), nitrogen (N), and phosphorus (P) to freshwater ecosystems is of fundamental importance to aquatic productivity, nutrient cycling, and food web dynamics. In northe ...},
	language = {eng},
	number = {10},
	urldate = {2024-03-26},
	journal = {Limnology and Oceanography},
	author = {Mosquera, Virginia and Maher Hasselquist, Eliza and Sponseller, Ryan A. and Laudon, Hjalmar},
	year = {2022},
	note = {Publisher: John Wiley \& Sons},
	pages = {2325--2339},
}

The relative supply of carbon (C), nitrogen (N), and phosphorus (P) to freshwater ecosystems is of fundamental importance to aquatic productivity, nutrient cycling, and food web dynamics. In northe ...

@article{puts_landscape_2022,
	title = {Landscape determinants of pelagic and benthic primary production in northern lakes},
	volume = {28},
	url = {https://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-194518},
	doi = {10.1111/gcb.16409},
	abstract = {Global change affects gross primary production (GPP) in benthic and pelagic habitats of northern lakes by influencing catchment characteristics and lake water biogeochemistry. However, how changes  ...},
	language = {eng},
	number = {23},
	urldate = {2024-03-26},
	journal = {Global Change Biology},
	author = {Puts, Isolde C. and Ask, Jenny and Siewert, Matthias B. and Sponseller, Ryan A. and Hessen, Dag O. and Bergström, Ann-Kristin},
	year = {2022},
	note = {Publisher: John Wiley \& Sons},
	pages = {7063--7077},
}

Global change affects gross primary production (GPP) in benthic and pelagic habitats of northern lakes by influencing catchment characteristics and lake water biogeochemistry. However, how changes ...

@article{myrstener_resolving_2022,
	title = {Resolving the {Drivers} of {Algal} {Nutrient} {Limitation} from {Boreal} to {Arctic} {Lakes} and {Streams}},
	volume = {25},
	url = {https://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-194276},
	doi = {10.1007/s10021-022-00759-4},
	abstract = {Nutrient inputs to northern freshwaters are changing, potentially altering aquatic ecosystem functioning through effects on primary producers. Yet, while primary producer growth is sensitive to nut ...},
	language = {eng},
	urldate = {2024-03-26},
	journal = {Ecosystems (New York. Print)},
	author = {Myrstener, Maria and Fork, Megan L. and Bergström, Ann-Kristin and Puts, Isolde and Hauptmann, Demian and Isles, Peter D. F. and Burrows, Ryan M. and Sponseller, Ryan A.},
	year = {2022},
	note = {Publisher: Springer-Verlag New York},
	pages = {1682--1699},
}

Nutrient inputs to northern freshwaters are changing, potentially altering aquatic ecosystem functioning through effects on primary producers. Yet, while primary producer growth is sensitive to nut ...

@article{costello_global_2022,
	title = {Global {Patterns} and {Controls} of {Nutrient} {Immobilization} on {Decomposing} {Cellulose} in {Riverine} {Ecosystems}},
	volume = {36},
	issn = {1944-9224},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2021GB007163},
	doi = {10.1029/2021GB007163},
	abstract = {Microbes play a critical role in plant litter decomposition and influence the fate of carbon in rivers and riparian zones. When decomposing low-nutrient plant litter, microbes acquire nitrogen (N) and phosphorus (P) from the environment (i.e., nutrient immobilization), and this process is potentially sensitive to nutrient loading and changing climate. Nonetheless, environmental controls on immobilization are poorly understood because rates are also influenced by plant litter chemistry, which is coupled to the same environmental factors. Here we used a standardized, low-nutrient organic matter substrate (cotton strips) to quantify nutrient immobilization at 100 paired stream and riparian sites representing 11 biomes worldwide. Immobilization rates varied by three orders of magnitude, were greater in rivers than riparian zones, and were strongly correlated to decomposition rates. In rivers, P immobilization rates were controlled by surface water phosphate concentrations, but N immobilization rates were not related to inorganic N. The N:P of immobilized nutrients was tightly constrained to a molar ratio of 10:1 despite wide variation in surface water N:P. Immobilization rates were temperature-dependent in riparian zones but not related to temperature in rivers. However, in rivers nutrient supply ultimately controlled whether microbes could achieve the maximum expected decomposition rate at a given temperature. Collectively, we demonstrated that exogenous nutrient supply and immobilization are critical control points for decomposition of organic matter.},
	language = {en},
	number = {3},
	urldate = {2022-05-04},
	journal = {Global Biogeochemical Cycles},
	author = {Costello, David M. and Tiegs, Scott D. and Boyero, Luz and Canhoto, Cristina and Capps, Krista A. and Danger, Michael and Frost, Paul C. and Gessner, Mark O. and Griffiths, Natalie A. and Halvorson, Halvor M. and Kuehn, Kevin A. and Marcarelli, Amy M. and Royer, Todd V. and Mathie, Devan M. and Albariño, Ricardo J. and Arango, Clay P. and Aroviita, Jukka and Baxter, Colden V. and Bellinger, Brent J. and Bruder, Andreas and Burdon, Francis J. and Callisto, Marcos and Camacho, Antonio and Colas, Fanny and Cornut, Julien and Crespo-Pérez, Verónica and Cross, Wyatt F. and Derry, Alison M. and Douglas, Michael M. and Elosegi, Arturo and de Eyto, Elvira and Ferreira, Verónica and Ferriol, Carmen and Fleituch, Tadeusz and Follstad Shah, Jennifer J. and Frainer, André and Garcia, Erica A. and García, Liliana and García, Pavel E. and Giling, Darren P. and Gonzales-Pomar, R. Karina and Graça, Manuel A. S. and Grossart, Hans-Peter and Guérold, François and Hepp, Luiz U. and Higgins, Scott N. and Hishi, Takuo and Iñiguez-Armijos, Carlos and Iwata, Tomoya and Kirkwood, Andrea E. and Koning, Aaron A. and Kosten, Sarian and Laudon, Hjalmar and Leavitt, Peter R. and Lemes da Silva, Aurea L. and Leroux, Shawn J. and LeRoy, Carri J. and Lisi, Peter J. and Masese, Frank O. and McIntyre, Peter B. and McKie, Brendan G. and Medeiros, Adriana O. and Miliša, Marko and Miyake, Yo and Mooney, Robert J. and Muotka, Timo and Nimptsch, Jorge and Paavola, Riku and Pardo, Isabel and Parnikoza, Ivan Y. and Patrick, Christopher J. and Peeters, Edwin T. H. M. and Pozo, Jesus and Reid, Brian and Richardson, John S. and Rincón, José and Risnoveanu, Geta and Robinson, Christopher T. and Santamans, Anna C. and Simiyu, Gelas M. and Skuja, Agnija and Smykla, Jerzy and Sponseller, Ryan A. and Teixeira-de Mello, Franco and Vilbaste, Sirje and Villanueva, Verónica D. and Webster, Jackson R. and Woelfl, Stefan and Xenopoulos, Marguerite A. and Yates, Adam G. and Yule, Catherine M. and Zhang, Yixin and Zwart, Jacob A.},
	year = {2022},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2021GB007163},
	keywords = {\#nosource, cotton strip assay, ecological stoichiometry, nitrogen, nutrient cycling, organic matter, phosphorus},
	pages = {e2021GB007163},
}

Microbes play a critical role in plant litter decomposition and influence the fate of carbon in rivers and riparian zones. When decomposing low-nutrient plant litter, microbes acquire nitrogen (N) and phosphorus (P) from the environment (i.e., nutrient immobilization), and this process is potentially sensitive to nutrient loading and changing climate. Nonetheless, environmental controls on immobilization are poorly understood because rates are also influenced by plant litter chemistry, which is coupled to the same environmental factors. Here we used a standardized, low-nutrient organic matter substrate (cotton strips) to quantify nutrient immobilization at 100 paired stream and riparian sites representing 11 biomes worldwide. Immobilization rates varied by three orders of magnitude, were greater in rivers than riparian zones, and were strongly correlated to decomposition rates. In rivers, P immobilization rates were controlled by surface water phosphate concentrations, but N immobilization rates were not related to inorganic N. The N:P of immobilized nutrients was tightly constrained to a molar ratio of 10:1 despite wide variation in surface water N:P. Immobilization rates were temperature-dependent in riparian zones but not related to temperature in rivers. However, in rivers nutrient supply ultimately controlled whether microbes could achieve the maximum expected decomposition rate at a given temperature. Collectively, we demonstrated that exogenous nutrient supply and immobilization are critical control points for decomposition of organic matter.

@article{bastias_seasonal_2022,
	title = {Seasonal variation in the coupling of microbial activity and leaf litter decomposition in a boreal stream network},
	volume = {67},
	issn = {1365-2427},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/fwb.13883},
	doi = {10.1111/fwb.13883},
	abstract = {Most stream networks are characterised by spatial and temporal variability in the physico-chemical conditions that regulate microbial processing of particulate organic matter. How these patterns control the turnover of particulate organic matter via altered activity of leaf-associated microbes has rarely been studied in high-latitude landscapes, particularly throughout long (i.e., up to 6 months) ice- and snow-covered periods. We investigated development of fungal biomass, enzyme activity, microbial respiration, and birch leaf litter decomposition from autumn to early summer in 11 nested streams in a boreal catchment that encompass a gradient in wetland (mire) cover. We observed relatively low variability in decomposition rates across the network, despite differences in key physical and chemical variables (e.g. temperature, pH, and dissolved organic carbon [DOC] concentrations) over time and space. Microbial enzymatic activity and respiration were positively related to leaf litter decomposition rates during early stages of decomposition (i.e., up to c. 30\% loss of initial ash-free dry mass). Thereafter, variation in microbial activity and respiration was decoupled from leaf litter mass loss, as enzymatic activity and respiration instead became positively related to DOC concentrations and upstream mire (wetland) cover among streams. Our results suggest that leaf-associated microbes increase their reliance on external sources of energy over time. This switch in resource use was more evident in streams with higher DOC concentration, which in boreal landscapes is largely determined by mire cover. Hence, variation in DOC concentration, linked to landscape configuration, or from intensified land use and climate change, could affect how different carbon sources are used by stream microbial communities, with consequences for overall carbon cycling in boreal headwaters.},
	language = {en},
	number = {5},
	urldate = {2022-05-04},
	journal = {Freshwater Biology},
	author = {Bastias, Elliot and Sponseller, Ryan A. and Bundschuh, Mirco and Jonsson, Micael},
	year = {2022},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1111/fwb.13883},
	keywords = {\#nosource, Krycklan Catchment Study, birch, cellobiohydrolase, extracellular enzyme activity, leaf-use efficiency},
	pages = {812--827},
}

Most stream networks are characterised by spatial and temporal variability in the physico-chemical conditions that regulate microbial processing of particulate organic matter. How these patterns control the turnover of particulate organic matter via altered activity of leaf-associated microbes has rarely been studied in high-latitude landscapes, particularly throughout long (i.e., up to 6 months) ice- and snow-covered periods. We investigated development of fungal biomass, enzyme activity, microbial respiration, and birch leaf litter decomposition from autumn to early summer in 11 nested streams in a boreal catchment that encompass a gradient in wetland (mire) cover. We observed relatively low variability in decomposition rates across the network, despite differences in key physical and chemical variables (e.g. temperature, pH, and dissolved organic carbon [DOC] concentrations) over time and space. Microbial enzymatic activity and respiration were positively related to leaf litter decomposition rates during early stages of decomposition (i.e., up to c. 30% loss of initial ash-free dry mass). Thereafter, variation in microbial activity and respiration was decoupled from leaf litter mass loss, as enzymatic activity and respiration instead became positively related to DOC concentrations and upstream mire (wetland) cover among streams. Our results suggest that leaf-associated microbes increase their reliance on external sources of energy over time. This switch in resource use was more evident in streams with higher DOC concentration, which in boreal landscapes is largely determined by mire cover. Hence, variation in DOC concentration, linked to landscape configuration, or from intensified land use and climate change, could affect how different carbon sources are used by stream microbial communities, with consequences for overall carbon cycling in boreal headwaters.

@article{laudon_legacy_2021,
	title = {From legacy effects of acid deposition in boreal streams to future environmental threats},
	volume = {16},
	issn = {1748-9326},
	url = {https://dx.doi.org/10.1088/1748-9326/abd064},
	doi = {10.1088/1748-9326/abd064},
	abstract = {Few environmental issues have resulted in such a heated policy-science controversy in Sweden as the 1990s acidification debate in the north of the country. The belief that exceptionally high stream acidity levels during hydrological events was caused by anthropogenic deposition resulted in a governmentally funded, multi-million dollar surface-water liming program. This program was heavily criticized by a large part of the scientific community arguing that the acidity of northern streams was primarily caused by naturally occurring organic acids. Here, we revisit the acid deposition legacy in northern Sweden two decades after the culmination of the controversy by examining the long-term water chemistry trends in the Svartberget/Krycklan research catchment that became a nexus for the Swedish debate. In this reference stream, trends in acidic episodes do show a modest recovery that matches declines in acid deposition to pre-industrial levels, although stream acidity continues to be overwhelmingly driven by organic acidity. Yet there are legacies of acid deposition related to calcium losses from soils, which are more pronounced than anticipated. Finally, assessment of these trends are becoming increasingly complicated by new changes and threats to water resources that must be recognized to avoid unnecessary, expensive, and potentially counterproductive measures to adapt and mitigate human influences. Here we make the argument that while the acidification era is ending, climate change, land-use transitions, and long-range transport of other contaminants warrant close monitoring in the decades to come.},
	language = {en},
	number = {1},
	urldate = {2024-03-27},
	journal = {Environmental Research Letters},
	author = {Laudon, Hjalmar and Sponseller, Ryan A. and Bishop, Kevin},
	month = jan,
	year = {2021},
	note = {Publisher: IOP Publishing},
	keywords = {\#nosource},
	pages = {015007},
}

Few environmental issues have resulted in such a heated policy-science controversy in Sweden as the 1990s acidification debate in the north of the country. The belief that exceptionally high stream acidity levels during hydrological events was caused by anthropogenic deposition resulted in a governmentally funded, multi-million dollar surface-water liming program. This program was heavily criticized by a large part of the scientific community arguing that the acidity of northern streams was primarily caused by naturally occurring organic acids. Here, we revisit the acid deposition legacy in northern Sweden two decades after the culmination of the controversy by examining the long-term water chemistry trends in the Svartberget/Krycklan research catchment that became a nexus for the Swedish debate. In this reference stream, trends in acidic episodes do show a modest recovery that matches declines in acid deposition to pre-industrial levels, although stream acidity continues to be overwhelmingly driven by organic acidity. Yet there are legacies of acid deposition related to calcium losses from soils, which are more pronounced than anticipated. Finally, assessment of these trends are becoming increasingly complicated by new changes and threats to water resources that must be recognized to avoid unnecessary, expensive, and potentially counterproductive measures to adapt and mitigate human influences. Here we make the argument that while the acidification era is ending, climate change, land-use transitions, and long-range transport of other contaminants warrant close monitoring in the decades to come.

@article{vachon_integrating_2021,
	title = {Integrating carbon emission, accumulation and transport in inland waters to understand their role in the global carbon cycle},
	volume = {27},
	copyright = {© 2020 The Authors. Global Change Biology published by John Wiley \& Sons Ltd},
	issn = {1365-2486},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.15448},
	doi = {10.1111/gcb.15448},
	abstract = {Inland waters receive a significant quantity of carbon (C) from land. The fate of this C during transit, whether it is emitted to the atmosphere, accumulated in sediments or transported to the ocean, can considerably reshape the landscape C balance. However, these different fates of terrestrial C are not independent but are instead linked via several catchment and aquatic processes. Thus, according to mass conservation, any environmental change inducing a shift in a particular C fate should come at the expense of at least one other fate. Nonetheless, studies that have investigated C emission, accumulation and transport concertedly are scarce, resulting in fragmented knowledge of the role of inland waters in the global C cycle. Here, we propose a framework to understand how different C fates in aquatic systems are interlinked and covary under environmental changes. First, to explore how C fates are currently distributed in streams, rivers, reservoirs and lakes, we compiled data from the literature and show that ‘C fate allocation’ varies widely both within and among inland water systems types. Secondly, we developed a framework that integrates C fates in any inland water system by identifying the key processes underlying their linkages. Our framework places the partitioning between the different C forms, and how this is controlled by export from land, internal transformations and hydrology, as central to understanding C fate allocation. We argue that, by focusing on a single fate, studies could risk drawing misleading conclusions regarding how environmental changes will alter the role of inland waters in the global C cycle. Our framework thus allows us to holistically assess the consequences of such changes on coupled C fluxes, setting a foundation for understanding the contemporary and future fate of land-derived C in inland water systems.},
	language = {en},
	number = {4},
	urldate = {2024-03-27},
	journal = {Global Change Biology},
	author = {Vachon, Dominic and Sponseller, Ryan A. and Karlsson, Jan},
	year = {2021},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1111/gcb.15448},
	keywords = {\#nosource, carbon cycle, conceptual framework, coupled fluxes, global change, inland waters, terrestrial carbon fate},
	pages = {719--727},
}

Inland waters receive a significant quantity of carbon (C) from land. The fate of this C during transit, whether it is emitted to the atmosphere, accumulated in sediments or transported to the ocean, can considerably reshape the landscape C balance. However, these different fates of terrestrial C are not independent but are instead linked via several catchment and aquatic processes. Thus, according to mass conservation, any environmental change inducing a shift in a particular C fate should come at the expense of at least one other fate. Nonetheless, studies that have investigated C emission, accumulation and transport concertedly are scarce, resulting in fragmented knowledge of the role of inland waters in the global C cycle. Here, we propose a framework to understand how different C fates in aquatic systems are interlinked and covary under environmental changes. First, to explore how C fates are currently distributed in streams, rivers, reservoirs and lakes, we compiled data from the literature and show that ‘C fate allocation’ varies widely both within and among inland water systems types. Secondly, we developed a framework that integrates C fates in any inland water system by identifying the key processes underlying their linkages. Our framework places the partitioning between the different C forms, and how this is controlled by export from land, internal transformations and hydrology, as central to understanding C fate allocation. We argue that, by focusing on a single fate, studies could risk drawing misleading conclusions regarding how environmental changes will alter the role of inland waters in the global C cycle. Our framework thus allows us to holistically assess the consequences of such changes on coupled C fluxes, setting a foundation for understanding the contemporary and future fate of land-derived C in inland water systems.

@article{rocher-ros_metabolism_2021,
	title = {Metabolism overrides photo-oxidation in {CO2} dynamics of {Arctic} permafrost streams},
	volume = {66},
	copyright = {© 2020 The Authors. Limnology and Oceanography published by Wiley Periodicals LLC. on behalf of Association for the Sciences of Limnology and Oceanography.},
	issn = {1939-5590},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/lno.11564},
	doi = {10.1002/lno.11564},
	abstract = {Global warming is enhancing the mobilization of organic carbon (C) from Arctic soils into streams, where it can be mineralized to CO2 and released to the atmosphere. Abiotic photo-oxidation might drive C mineralization, but this process has not been quantitatively integrated with biological processes that also influence CO2 dynamics in aquatic ecosystems. We measured CO2 concentrations and the isotopic composition of dissolved inorganic C (δ13CDIC) at diel resolution in two Arctic streams, and coupled this with whole-system metabolism estimates to assess the effect of biotic and abiotic processes on stream C dynamics. CO2 concentrations consistently decreased from night to day, a pattern counter to the hypothesis that photo-oxidation is the dominant source of CO2. Instead, the observed decrease in CO2 during daytime was explained by photosynthetic rates, which were strongly correlated with diurnal changes in δ13CDIC values. However, on days when modeled photosynthetic rates were near zero, there was still a significant diel change in δ13CDIC values, suggesting that metabolic estimates are partly masked by O2 consumption from photo-oxidation. Our results suggest that 6–12 mmol CO2-C m−2 d−1 may be generated from photo-oxidation, a range that corresponds well to previous laboratory measurements. Moreover, ecosystem respiration rates were 10 times greater than published photo-oxidation rates for these Arctic streams, and accounted for 33–80\% of total CO2 evasion. Our results suggest that metabolic activity is the dominant process for CO2 production in Arctic streams. Thus, future aquatic CO2 emissions may depend on how biotic processes respond to the ongoing environmental change.},
	language = {en},
	number = {S1},
	urldate = {2024-03-27},
	journal = {Limnology and Oceanography},
	author = {Rocher-Ros, Gerard and Harms, Tamara K. and Sponseller, Ryan A. and Väisänen, Maria and Mörth, Carl-Magnus and Giesler, Reiner},
	year = {2021},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/lno.11564},
	keywords = {\#nosource},
	pages = {S169--S181},
}

Global warming is enhancing the mobilization of organic carbon (C) from Arctic soils into streams, where it can be mineralized to CO2 and released to the atmosphere. Abiotic photo-oxidation might drive C mineralization, but this process has not been quantitatively integrated with biological processes that also influence CO2 dynamics in aquatic ecosystems. We measured CO2 concentrations and the isotopic composition of dissolved inorganic C (δ13CDIC) at diel resolution in two Arctic streams, and coupled this with whole-system metabolism estimates to assess the effect of biotic and abiotic processes on stream C dynamics. CO2 concentrations consistently decreased from night to day, a pattern counter to the hypothesis that photo-oxidation is the dominant source of CO2. Instead, the observed decrease in CO2 during daytime was explained by photosynthetic rates, which were strongly correlated with diurnal changes in δ13CDIC values. However, on days when modeled photosynthetic rates were near zero, there was still a significant diel change in δ13CDIC values, suggesting that metabolic estimates are partly masked by O2 consumption from photo-oxidation. Our results suggest that 6–12 mmol CO2-C m−2 d−1 may be generated from photo-oxidation, a range that corresponds well to previous laboratory measurements. Moreover, ecosystem respiration rates were 10 times greater than published photo-oxidation rates for these Arctic streams, and accounted for 33–80% of total CO2 evasion. Our results suggest that metabolic activity is the dominant process for CO2 production in Arctic streams. Thus, future aquatic CO2 emissions may depend on how biotic processes respond to the ongoing environmental change.

@article{myrstener_nutrients_2021,
	title = {Nutrients influence seasonal metabolic patterns and total productivity of {Arctic} streams},
	volume = {66},
	copyright = {© 2020 The Authors. Limnology and Oceanography published by Wiley Periodicals LLC on behalf of Association for the Sciences of Limnology and Oceanography.},
	issn = {1939-5590},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/lno.11614},
	doi = {10.1002/lno.11614},
	abstract = {The seasonality of gross primary production (GPP) in streams is driven by multiple physical and chemical factors, yet incident light is often thought to be most important. In Arctic tundra streams, however, light is available in saturating amounts throughout the summer, but sharp declines in nutrient supply during the terrestrial growing season may constrain aquatic productivity. Given the opposing seasonality of these drivers, we hypothesized that “shoulder seasons”—spring and autumn—represent critical time windows when light and nutrients align to optimize rates of stream productivity in the Arctic. To test this, we measured annual patterns of GPP and biofilm accumulation in eight streams in Arctic Sweden. We found that the aquatic growing season length differed by 4 months across streams and was determined largely by the timing of ice-off in spring. During the growing season, temporal variability in GPP for nitrogen (N) poor streams was correlated with inorganic N concentration, while in more N-rich streams GPP was instead linked to changes in phosphorus and light. Annual GPP varied ninefold among streams and was enhanced by N availability, the length of ice-free period, and low flood frequency. Finally, network scale estimates of GPP highlight the overall significance of the shoulder seasons, which accounted for 48\% of annual productivity. We suggest that the timing of ice off and nutrient supply from land interact to regulate the annual metabolic regimes of nutrient poor, Arctic streams, leading to unexpected peaks in productivity that are offset from the terrestrial growing season.},
	language = {en},
	number = {S1},
	urldate = {2024-03-26},
	journal = {Limnology and Oceanography},
	author = {Myrstener, Maria and Gómez-Gener, Lluís and Rocher-Ros, Gerard and Giesler, Reiner and Sponseller, Ryan A.},
	year = {2021},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/lno.11614},
	keywords = {\#nosource},
	pages = {S182--S196},
}

The seasonality of gross primary production (GPP) in streams is driven by multiple physical and chemical factors, yet incident light is often thought to be most important. In Arctic tundra streams, however, light is available in saturating amounts throughout the summer, but sharp declines in nutrient supply during the terrestrial growing season may constrain aquatic productivity. Given the opposing seasonality of these drivers, we hypothesized that “shoulder seasons”—spring and autumn—represent critical time windows when light and nutrients align to optimize rates of stream productivity in the Arctic. To test this, we measured annual patterns of GPP and biofilm accumulation in eight streams in Arctic Sweden. We found that the aquatic growing season length differed by 4 months across streams and was determined largely by the timing of ice-off in spring. During the growing season, temporal variability in GPP for nitrogen (N) poor streams was correlated with inorganic N concentration, while in more N-rich streams GPP was instead linked to changes in phosphorus and light. Annual GPP varied ninefold among streams and was enhanced by N availability, the length of ice-free period, and low flood frequency. Finally, network scale estimates of GPP highlight the overall significance of the shoulder seasons, which accounted for 48% of annual productivity. We suggest that the timing of ice off and nutrient supply from land interact to regulate the annual metabolic regimes of nutrient poor, Arctic streams, leading to unexpected peaks in productivity that are offset from the terrestrial growing season.

@article{myrstener_nitrogen_2021,
	title = {Nitrogen supply and physical disturbance shapes {Arctic} stream nitrogen uptake through effects on metabolic activity},
	volume = {66},
	issn = {0046-5070},
	url = {https://doi.org/10.1111/fwb.13734},
	doi = {10.1111/fwb.13734},
	abstract = {Abstract Climate change in the Arctic is altering the delivery of nutrients from terrestrial to aquatic ecosystems. The impact of these changes on downstream lakes and rivers is influenced by the capacity of small streams to retain such inputs. Given the potential for nutrient limitation in oligotrophic Arctic streams, biotic demand should be high, unless harsh environmental conditions maintain low biomass standing stocks that limit nutrient uptake capacity. We assessed the drivers of nutrient uptake in two contrasting headwater environments in Arctic Sweden: one stream draining upland tundra and the other draining an alluvial valley with birch forest. At both sites, we measured nitrate (NO3?) uptake biweekly using short-term slug releases and estimated rates of gross primary production (GPP) and ecosystem respiration from continuous dissolved oxygen measurements. Catchment characteristics were associated with distinct stream chemical and biological properties. For example, the tundra stream maintained relatively low NO3? concentrations (average: 46 µg N/L) and rates of GPP (0.2 g O2 m?2 day?1). By comparison, the birch forest stream was more NO3? rich (88 µg N/L) and productive (GPP: 1.7 g O2 m?2 day?1). These differences corresponded to greater areal NO3? uptake rate and increased NO3? use efficiency (as uptake velocity) in the birch forest stream (max 192 µg N m?2 min?1 and 96 mm/hr) compared to its tundra counterpart (max 52 µg N m?2 min?1 and 49 mm/hr) during 2017. Further, different sets of environmental drivers predicted temporal patterns of nutrient uptake at these sites: abiotic factors (e.g. NO3? concentration and discharge) were associated with changes in uptake in the tundra stream, while metabolic activity was more important in the birch forest stream. Between sites, variation in uptake metrics suggests that the ability to retain pulses of nutrients is linked to nutrient supply regimes controlled at larger spatial and temporal scales and habitat properties that promote biomass accrual and thus biotic demand. Overall, constraints on biotic potential imposed by the habitat template determined the capacity of these high latitude streams to respond to future changes in nutrient inputs arising from climate warming or human land use. ?},
	number = {8},
	urldate = {2023-07-22},
	journal = {Freshwater Biology},
	author = {Myrstener, Maria and Thomas, Steven A. and Giesler, Reiner and Sponseller, Ryan A.},
	month = aug,
	year = {2021},
	note = {Publisher: John Wiley \& Sons, Ltd},
	keywords = {Arctic, catchment, metabolism, nutrient uptake, tundra},
	pages = {1502--1514},
}

Abstract Climate change in the Arctic is altering the delivery of nutrients from terrestrial to aquatic ecosystems. The impact of these changes on downstream lakes and rivers is influenced by the capacity of small streams to retain such inputs. Given the potential for nutrient limitation in oligotrophic Arctic streams, biotic demand should be high, unless harsh environmental conditions maintain low biomass standing stocks that limit nutrient uptake capacity. We assessed the drivers of nutrient uptake in two contrasting headwater environments in Arctic Sweden: one stream draining upland tundra and the other draining an alluvial valley with birch forest. At both sites, we measured nitrate (NO3?) uptake biweekly using short-term slug releases and estimated rates of gross primary production (GPP) and ecosystem respiration from continuous dissolved oxygen measurements. Catchment characteristics were associated with distinct stream chemical and biological properties. For example, the tundra stream maintained relatively low NO3? concentrations (average: 46 µg N/L) and rates of GPP (0.2 g O2 m?2 day?1). By comparison, the birch forest stream was more NO3? rich (88 µg N/L) and productive (GPP: 1.7 g O2 m?2 day?1). These differences corresponded to greater areal NO3? uptake rate and increased NO3? use efficiency (as uptake velocity) in the birch forest stream (max 192 µg N m?2 min?1 and 96 mm/hr) compared to its tundra counterpart (max 52 µg N m?2 min?1 and 49 mm/hr) during 2017. Further, different sets of environmental drivers predicted temporal patterns of nutrient uptake at these sites: abiotic factors (e.g. NO3? concentration and discharge) were associated with changes in uptake in the tundra stream, while metabolic activity was more important in the birch forest stream. Between sites, variation in uptake metrics suggests that the ability to retain pulses of nutrients is linked to nutrient supply regimes controlled at larger spatial and temporal scales and habitat properties that promote biomass accrual and thus biotic demand. Overall, constraints on biotic potential imposed by the habitat template determined the capacity of these high latitude streams to respond to future changes in nutrient inputs arising from climate warming or human land use. ?

@article{maher_hasselquist_moving_2021,
	title = {Moving towards multi-layered, mixed-species forests in riparian buffers will enhance their long-term function in boreal landscapes},
	volume = {493},
	issn = {03781127},
	url = {https://linkinghub.elsevier.com/retrieve/pii/S037811272100342X},
	doi = {10.1016/j.foreco.2021.119254},
	abstract = {Riparian buffers are the primary tool in forest management for protecting the habitat structure and function of streams. They help protect against biogeochemical perturbation, filter sediments and nutrients, prevent erosion, contribute food to aquatic organisms, regulate light and hence water temperature, contribute deadwood, and preserve biodiversity. However, in production forests of Sweden and Finland, many headwater streams have been straightened, ditched, and/or channelized, resulting in altered hydrology and reduced natural disturbance by floods, which in turn affects important riparian functions. Furthermore, in even-aged management systems as practiced in much of Fennoscandia, understory trees have usually been cleared right up to the stream’s edge during thinning operations, especially around small, headwater streams. Fire suppression has further favored succession towards shade tolerant species. In the regions within Fennoscandia that have experienced this combination of intensive management and lack of natural disturbance, riparian zones are now dominated by single-storied, native Norway spruce. When the adjacent forest is cut, thin (5 - 15m) conifer-dominated riparian buffers are typically left. These buffers do not provide the protection and subsidies, in terms of leaf litter quality, needed to maintain water quality or support riparian or aquatic biodiversity. Based on a literature review, we found compelling evidence that the ecological benefits of multi-layered, mixed-species riparian forest with a large component of broadleaved species are higher than what is now commonly found in the managed stands of Fennoscandia. To improve the functionality of riparian zones, and hence the protection of streams in managed forest landscapes, we present some basic principles that could be used to enhance the ecological function of these interfaces. These management actions should be prioritized on streams and streamside stands that have been affected by simplification either through forest management or hydrological modification. Key to these principles is the planning and managing of buffer zones as early as possible in the rotation to ensure improved function throughout the rotation cycle and not only at final felling. This is well in line with EU and national legislation which can be interpreted as requiring landscape planning at all forest ages to meet biodiversity and other environmental goals. However, it is still rare that planning for conservation is done other than at the final felling stage. Implementing this new strategy is likely to have long-term positive effects and improve the protection of surface waters from negative forestry effects and a history of fire suppression. By following these suggested management principles, there will be a longer time period with high function and greater future management flexibility in addition to the benefits provided by leaving riparian buffers at the final felling stage.},
	language = {en},
	urldate = {2021-09-03},
	journal = {Forest Ecology and Management},
	author = {Maher Hasselquist, Eliza and Kuglerová, Lenka and Sjögren, Jörgen and Hjältén, Joakim and Ring, Eva and Sponseller, Ryan A. and Andersson, Elisabet and Lundström, Johanna and Mancheva, Irina and Nordin, Annika and Laudon, Hjalmar},
	month = aug,
	year = {2021},
	keywords = {\#nosource},
	pages = {119254},
}

Riparian buffers are the primary tool in forest management for protecting the habitat structure and function of streams. They help protect against biogeochemical perturbation, filter sediments and nutrients, prevent erosion, contribute food to aquatic organisms, regulate light and hence water temperature, contribute deadwood, and preserve biodiversity. However, in production forests of Sweden and Finland, many headwater streams have been straightened, ditched, and/or channelized, resulting in altered hydrology and reduced natural disturbance by floods, which in turn affects important riparian functions. Furthermore, in even-aged management systems as practiced in much of Fennoscandia, understory trees have usually been cleared right up to the stream’s edge during thinning operations, especially around small, headwater streams. Fire suppression has further favored succession towards shade tolerant species. In the regions within Fennoscandia that have experienced this combination of intensive management and lack of natural disturbance, riparian zones are now dominated by single-storied, native Norway spruce. When the adjacent forest is cut, thin (5 - 15m) conifer-dominated riparian buffers are typically left. These buffers do not provide the protection and subsidies, in terms of leaf litter quality, needed to maintain water quality or support riparian or aquatic biodiversity. Based on a literature review, we found compelling evidence that the ecological benefits of multi-layered, mixed-species riparian forest with a large component of broadleaved species are higher than what is now commonly found in the managed stands of Fennoscandia. To improve the functionality of riparian zones, and hence the protection of streams in managed forest landscapes, we present some basic principles that could be used to enhance the ecological function of these interfaces. These management actions should be prioritized on streams and streamside stands that have been affected by simplification either through forest management or hydrological modification. Key to these principles is the planning and managing of buffer zones as early as possible in the rotation to ensure improved function throughout the rotation cycle and not only at final felling. This is well in line with EU and national legislation which can be interpreted as requiring landscape planning at all forest ages to meet biodiversity and other environmental goals. However, it is still rare that planning for conservation is done other than at the final felling stage. Implementing this new strategy is likely to have long-term positive effects and improve the protection of surface waters from negative forestry effects and a history of fire suppression. By following these suggested management principles, there will be a longer time period with high function and greater future management flexibility in addition to the benefits provided by leaving riparian buffers at the final felling stage.

@incollection{jonsson_role_2021,
	address = {Cham},
	title = {The {Role} of {Macroinvertebrates} on {Plant} {Litter} {Decomposition} in {Streams}},
	isbn = {978-3-030-72854-0},
	url = {https://doi.org/10.1007/978-3-030-72854-0_10},
	abstract = {Macroinvertebrate detritivores (i.e., shredders) in freshwaters are often a main driver of decomposition rates of terrestrial plant litter. Yet, the extent to which shredders drive this process depends on the specific functional traits and species present in the shredder community, which in turn are determined by the broader species pool, as well as a range of local environmental conditions, such as pH, substrate characteristics, water chemistry, water temperature, and current velocity. Projected global change will modify several of these environmental conditions, with potential consequences for litter decomposition rates and overall carbon cycling in freshwaters. In this chapter, we describe how a range of freshwater environmental conditions determines the presence of certain species (i.e., functional traits) and the characteristics of shredder communities (i.e., species composition and richness). We then discuss how these characteristics in turn may influence interactions among shredders, and between shredders and other freshwater organisms, to determine their influence on litter decomposition in streams.},
	language = {en},
	urldate = {2021-09-03},
	booktitle = {The {Ecology} of {Plant} {Litter} {Decomposition} in {Stream} {Ecosystems}},
	publisher = {Springer International Publishing},
	author = {Jonsson, Micael and Sponseller, Ryan A.},
	editor = {Swan, Christopher M. and Boyero, Luz and Canhoto, Cristina},
	year = {2021},
	doi = {10.1007/978-3-030-72854-0_10},
	keywords = {\#nosource},
	pages = {193--216},
}

Macroinvertebrate detritivores (i.e., shredders) in freshwaters are often a main driver of decomposition rates of terrestrial plant litter. Yet, the extent to which shredders drive this process depends on the specific functional traits and species present in the shredder community, which in turn are determined by the broader species pool, as well as a range of local environmental conditions, such as pH, substrate characteristics, water chemistry, water temperature, and current velocity. Projected global change will modify several of these environmental conditions, with potential consequences for litter decomposition rates and overall carbon cycling in freshwaters. In this chapter, we describe how a range of freshwater environmental conditions determines the presence of certain species (i.e., functional traits) and the characteristics of shredder communities (i.e., species composition and richness). We then discuss how these characteristics in turn may influence interactions among shredders, and between shredders and other freshwater organisms, to determine their influence on litter decomposition in streams.

@article{gomez-gener_global_2021,
	title = {Global carbon dioxide efflux from rivers enhanced by high nocturnal emissions},
	volume = {14},
	copyright = {2021 The Author(s), under exclusive licence to Springer Nature Limited},
	issn = {1752-0908},
	url = {https://www.nature.com/articles/s41561-021-00722-3},
	doi = {10.1038/s41561-021-00722-3},
	abstract = {Carbon dioxide (CO2) emissions to the atmosphere from running waters are estimated to be four times greater than the total carbon (C) flux to the oceans. However, these fluxes remain poorly constrained because of substantial spatial and temporal variability in dissolved CO2 concentrations. Using a global compilation of high-frequency CO2 measurements, we demonstrate that nocturnal CO2 emissions are on average 27\% (0.9 gC m−2 d−1) greater than those estimated from diurnal concentrations alone. Constraints on light availability due to canopy shading or water colour are the principal controls on observed diel (24 hour) variation, suggesting this nocturnal increase arises from daytime fixation of CO2 by photosynthesis. Because current global estimates of CO2 emissions to the atmosphere from running waters (0.65–1.8 PgC yr−1) rely primarily on discrete measurements of dissolved CO2 obtained during the day, they substantially underestimate the magnitude of this flux. Accounting for night-time CO2 emissions may elevate global estimates from running waters to the atmosphere by 0.20–0.55 PgC yr−1.},
	language = {en},
	number = {5},
	urldate = {2021-09-03},
	journal = {Nature Geoscience},
	author = {Gómez-Gener, Lluís and Rocher-Ros, Gerard and Battin, Tom and Cohen, Matthew J. and Dalmagro, Higo J. and Dinsmore, Kerry J. and Drake, Travis W. and Duvert, Clément and Enrich-Prast, Alex and Horgby, Åsa and Johnson, Mark S. and Kirk, Lily and Machado-Silva, Fausto and Marzolf, Nicholas S. and McDowell, Mollie J. and McDowell, William H. and Miettinen, Heli and Ojala, Anne K. and Peter, Hannes and Pumpanen, Jukka and Ran, Lishan and Riveros-Iregui, Diego A. and Santos, Isaac R. and Six, Johan and Stanley, Emily H. and Wallin, Marcus B. and White, Shane A. and Sponseller, Ryan A.},
	month = may,
	year = {2021},
	note = {Bandiera\_abtest: a
Cg\_type: Nature Research Journals
Number: 5
Primary\_atype: Research
Publisher: Nature Publishing Group
Subject\_term: Carbon cycle;Ecosystem ecology;Limnology
Subject\_term\_id: carbon-cycle;ecosystem-ecology;limnology},
	keywords = {\#nosource},
	pages = {289--294},
}

Carbon dioxide (CO2) emissions to the atmosphere from running waters are estimated to be four times greater than the total carbon (C) flux to the oceans. However, these fluxes remain poorly constrained because of substantial spatial and temporal variability in dissolved CO2 concentrations. Using a global compilation of high-frequency CO2 measurements, we demonstrate that nocturnal CO2 emissions are on average 27% (0.9 gC m−2 d−1) greater than those estimated from diurnal concentrations alone. Constraints on light availability due to canopy shading or water colour are the principal controls on observed diel (24 hour) variation, suggesting this nocturnal increase arises from daytime fixation of CO2 by photosynthesis. Because current global estimates of CO2 emissions to the atmosphere from running waters (0.65–1.8 PgC yr−1) rely primarily on discrete measurements of dissolved CO2 obtained during the day, they substantially underestimate the magnitude of this flux. Accounting for night-time CO2 emissions may elevate global estimates from running waters to the atmosphere by 0.20–0.55 PgC yr−1.

@article{lupon_discrete_2020,
	title = {Discrete groundwater inflows influence patterns of nitrogen uptake in a boreal headwater stream},
	volume = {39},
	issn = {2161-9549},
	url = {https://www.journals.uchicago.edu/doi/abs/10.1086/708521},
	doi = {10.1086/708521},
	abstract = {Dissolved organic carbon (DOC) influences stream nitrogen (N) dynamics by regulating the nutrient demand of heterotrophic microbes and mediating their interactions with nitrifiers. However, DOC supply to streams is dynamic in space and time, which may create variability in N dynamics as a result of shifts between heterotrophic and chemoautotrophic influences. To test this, we measured spatial and temporal variation in concentrations and net uptake of dissolved organic nitrogen (DON), ammonium (NH4+), and nitrate (NO3−) along a 1.4-km boreal stream fed by 4 discrete groundwater inflow zones. We also performed constant rate additions of NH4+, with and without acetate, to test the influence of labile DOC availability on N cycling. Groundwater N supply did not drive spatial patterns in N concentrations. However, we observed high rates of net NH4+ uptake at the sub-reach with the greatest groundwater DOC inputs, whereas net nitrification occurred where such inputs were negligible. At the reach scale, net DON and NH4+ uptake increased with greater groundwater discharge, DOC∶DIN, and ecosystem respiration, whereas net nitrification increased with greater DOC aromaticity. Finally, constant rate additions showed that, under increased DOC availability, NH4+ uptake increased 2×, whereas the proportion of NH4+ nitrified decreased from 42 to 15\%. Together, these observations suggest that nitrification rivals heterotrophic uptake when aromatic DOC promotes heterotrophic carbon limitation. Discrete groundwater inflows and periods of elevated discharge can partially alleviate this limitation by supplying labile DOC from riparian soils. Hence, accounting for these land–water connections, over both time and space, is critical for understanding N dynamics in boreal streams.},
	number = {2},
	urldate = {2024-03-27},
	journal = {Freshwater Science},
	author = {Lupon, Anna and Denfeld, Blaize A. and Laudon, Hjalmar and Leach, Jason and Sponseller, Ryan A.},
	month = jun,
	year = {2020},
	note = {Publisher: The University of Chicago Press},
	keywords = {\#nosource, dissolved organic carbon, dissolved organic nitrogen, groundwater inputs, Krycklan, metabolism, net nitrogen uptake, nitrification},
	pages = {228--240},
}

Dissolved organic carbon (DOC) influences stream nitrogen (N) dynamics by regulating the nutrient demand of heterotrophic microbes and mediating their interactions with nitrifiers. However, DOC supply to streams is dynamic in space and time, which may create variability in N dynamics as a result of shifts between heterotrophic and chemoautotrophic influences. To test this, we measured spatial and temporal variation in concentrations and net uptake of dissolved organic nitrogen (DON), ammonium (NH4+), and nitrate (NO3−) along a 1.4-km boreal stream fed by 4 discrete groundwater inflow zones. We also performed constant rate additions of NH4+, with and without acetate, to test the influence of labile DOC availability on N cycling. Groundwater N supply did not drive spatial patterns in N concentrations. However, we observed high rates of net NH4+ uptake at the sub-reach with the greatest groundwater DOC inputs, whereas net nitrification occurred where such inputs were negligible. At the reach scale, net DON and NH4+ uptake increased with greater groundwater discharge, DOC∶DIN, and ecosystem respiration, whereas net nitrification increased with greater DOC aromaticity. Finally, constant rate additions showed that, under increased DOC availability, NH4+ uptake increased 2×, whereas the proportion of NH4+ nitrified decreased from 42 to 15%. Together, these observations suggest that nitrification rivals heterotrophic uptake when aromatic DOC promotes heterotrophic carbon limitation. Discrete groundwater inflows and periods of elevated discharge can partially alleviate this limitation by supplying labile DOC from riparian soils. Hence, accounting for these land–water connections, over both time and space, is critical for understanding N dynamics in boreal streams.

@article{denfeld_heterogeneous_2020,
	title = {Heterogeneous {CO2} and {CH4} patterns across space and time in a small boreal lake},
	volume = {10},
	issn = {2044-2041},
	url = {https://doi.org/10.1080/20442041.2020.1787765},
	doi = {10.1080/20442041.2020.1787765},
	abstract = {Small boreal lakes emit large amounts of carbon dioxide (CO2) and methane (CH4) to the atmosphere. Yet emissions of these greenhouse gases are variable in space and time, in part due to variable within-lake CO2 and CH4 concentrations. To determine the extent and the underlying drivers of this variation, we measured lake water CO2 and CH4 concentrations and estimated associated emissions using spatially discrete water samples collected every 2 weeks from a small boreal lake. On select dates, we also collected groundwater samples from the surrounding catchment. On average, groundwater draining a connected peat mire complex had significantly higher CO2 and CH4 concentrations compared to waters draining forest on mineral soils. However, within the lake, only CH4 concentrations nearshore from the mire complex were significantly elevated. We observed little spatial variability in surface water CO2; however, bottom water CO2 in the pelagic zone was significantly higher than bottom waters at nearshore locations. Overall, temperature, precipitation, and thermal stratification explained temporal patterns of CO2 concentration, whereas hydrology (discharge and precipitation) best predicted the variation in CH4 concentration. Consistent with these different controls, the highest CO2 emission was related to lake turnover at the end of August while the highest CH4 emission was associated with precipitation events at the end of June. These results suggest that annual carbon emissions from small boreal lakes are influenced by temporal variation in weather conditions that regulate thermal stratification and trigger hydrologic land–water connections that supply gases from catchment soils to the lake.},
	number = {3},
	urldate = {2024-03-27},
	journal = {Inland Waters},
	author = {Denfeld, Blaize A. and Lupon, Anna and Sponseller, Ryan A. and Laudon, Hjalmar and Karlsson, Jan},
	month = jul,
	year = {2020},
	note = {Publisher: Taylor \& Francis
\_eprint: https://doi.org/10.1080/20442041.2020.1787765},
	keywords = {\#nosource, carbon dioxide, carbon emissions, groundwater, lakes, methane, mire},
	pages = {348--359},
}

Small boreal lakes emit large amounts of carbon dioxide (CO2) and methane (CH4) to the atmosphere. Yet emissions of these greenhouse gases are variable in space and time, in part due to variable within-lake CO2 and CH4 concentrations. To determine the extent and the underlying drivers of this variation, we measured lake water CO2 and CH4 concentrations and estimated associated emissions using spatially discrete water samples collected every 2 weeks from a small boreal lake. On select dates, we also collected groundwater samples from the surrounding catchment. On average, groundwater draining a connected peat mire complex had significantly higher CO2 and CH4 concentrations compared to waters draining forest on mineral soils. However, within the lake, only CH4 concentrations nearshore from the mire complex were significantly elevated. We observed little spatial variability in surface water CO2; however, bottom water CO2 in the pelagic zone was significantly higher than bottom waters at nearshore locations. Overall, temperature, precipitation, and thermal stratification explained temporal patterns of CO2 concentration, whereas hydrology (discharge and precipitation) best predicted the variation in CH4 concentration. Consistent with these different controls, the highest CO2 emission was related to lake turnover at the end of August while the highest CH4 emission was associated with precipitation events at the end of June. These results suggest that annual carbon emissions from small boreal lakes are influenced by temporal variation in weather conditions that regulate thermal stratification and trigger hydrologic land–water connections that supply gases from catchment soils to the lake.

@article{fork_dissolved_2020,
	title = {Dissolved organic matter regulates nutrient limitation and growth of benthic algae in northern lakes through interacting effects on nutrient and light availability},
	volume = {5},
	copyright = {© 2020 The Authors. Limnology and Oceanography Letters published by Wiley Periodicals LLC on behalf of Association for the Sciences of Limnology and Oceanography.},
	issn = {2378-2242},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/lol2.10166},
	doi = {10.1002/lol2.10166},
	abstract = {Widespread increases in dissolved organic matter (DOM) concentration across northern lakes can alter rates of primary production by increasing nutrient availability and decreasing light availability. These dual effects of DOM generate a unimodal relationship in pelagic primary production and primary producer biomass among lakes over a gradient of DOM concentration. However, the responses of benthic algae to variation in DOM loading are less clear because of their potential to access sediment nutrients. We tested algal production and nutrient limitation along a DOM gradient in northern Sweden. Without added nutrients, benthic algal production showed a unimodal relationship with DOM, similar to reported pelagic responses. Nutrient addition revealed widespread nitrogen limitation, with decreasing severity in lakes with higher DOM. Because the majority of northern Swedish lakes currently fall below the inflection point in this unimodal relationship, moderate increases in DOM have the potential to increase benthic primary production, particularly for epilithic algae.},
	language = {en},
	number = {6},
	urldate = {2024-03-26},
	journal = {Limnology and Oceanography Letters},
	author = {Fork, Megan L. and Karlsson, Jan and Sponseller, Ryan A.},
	year = {2020},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/lol2.10166},
	keywords = {\#nosource},
	pages = {417--424},
}

Widespread increases in dissolved organic matter (DOM) concentration across northern lakes can alter rates of primary production by increasing nutrient availability and decreasing light availability. These dual effects of DOM generate a unimodal relationship in pelagic primary production and primary producer biomass among lakes over a gradient of DOM concentration. However, the responses of benthic algae to variation in DOM loading are less clear because of their potential to access sediment nutrients. We tested algal production and nutrient limitation along a DOM gradient in northern Sweden. Without added nutrients, benthic algal production showed a unimodal relationship with DOM, similar to reported pelagic responses. Nutrient addition revealed widespread nitrogen limitation, with decreasing severity in lakes with higher DOM. Because the majority of northern Swedish lakes currently fall below the inflection point in this unimodal relationship, moderate increases in DOM have the potential to increase benthic primary production, particularly for epilithic algae.

@article{fork_changing_2020,
	title = {Changing {Source}-{Transport} {Dynamics} {Drive} {Differential} {Browning} {Trends} in a {Boreal} {Stream} {Network}},
	volume = {56},
	copyright = {© 2020 The Authors.},
	issn = {1944-7973},
	url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019WR026336},
	doi = {10.1029/2019WR026336},
	abstract = {Dissolved organic carbon (DOC) concentrations are increasing in freshwaters worldwide, with important implications for aquatic ecology, biogeochemistry, and ecosystem services. While multiple environmental changes may be responsible for these trends, predicting the occurrence and magnitude of “browning” and relating such trends to changes in DOC sources versus hydrologic transport remain key challenges. We analyzed long-term trends in DOC concentration from the two dominant landscape sources (riparian soils and mire peats) and receiving streams in a boreal catchment to evaluate how browning patterns relate to land cover and hydrology. Increases in stream DOC were widespread but not universal. Browning was most pronounced in small, forested streams, where trends corresponded to twofold to threefold increases in DOC production in riparian soils and increases in annual DOC export from a forested headwater. By contrast, DOC did not change in mire peats or streams draining catchments with high lake or mire cover, nor did we observe trends in DOC export from a mire-dominated headwater. The distinct long-term trends in DOC sources also altered concentration-discharge relationships, with a forested headwater shifting from transport-limited toward chemostasis, and a mire outlet stream shifting from chemostasis to source-limitated. Modified DOC supply to headwaters, together with altered seasonal hydrology and differences in the dominant water source along the stream network gave rise to predictable browning trends and consistent concentration-discharge relationships. Overall, our results show that the sources of DOC to boreal aquatic ecosystems are responding to environmental change in fundamentally different ways, with important consequences for browning along boreal stream networks.},
	language = {en},
	number = {2},
	urldate = {2020-03-19},
	journal = {Water Resources Research},
	author = {Fork, Megan L. and Sponseller, Ryan A. and Laudon, Hjalmar},
	year = {2020},
	note = {\_eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2019WR026336},
	keywords = {\#nosource, DOC, brownification, concentration-discharge, flux, riparian, wetland},
	pages = {e2019WR026336},
}

Dissolved organic carbon (DOC) concentrations are increasing in freshwaters worldwide, with important implications for aquatic ecology, biogeochemistry, and ecosystem services. While multiple environmental changes may be responsible for these trends, predicting the occurrence and magnitude of “browning” and relating such trends to changes in DOC sources versus hydrologic transport remain key challenges. We analyzed long-term trends in DOC concentration from the two dominant landscape sources (riparian soils and mire peats) and receiving streams in a boreal catchment to evaluate how browning patterns relate to land cover and hydrology. Increases in stream DOC were widespread but not universal. Browning was most pronounced in small, forested streams, where trends corresponded to twofold to threefold increases in DOC production in riparian soils and increases in annual DOC export from a forested headwater. By contrast, DOC did not change in mire peats or streams draining catchments with high lake or mire cover, nor did we observe trends in DOC export from a mire-dominated headwater. The distinct long-term trends in DOC sources also altered concentration-discharge relationships, with a forested headwater shifting from transport-limited toward chemostasis, and a mire outlet stream shifting from chemostasis to source-limitated. Modified DOC supply to headwaters, together with altered seasonal hydrology and differences in the dominant water source along the stream network gave rise to predictable browning trends and consistent concentration-discharge relationships. Overall, our results show that the sources of DOC to boreal aquatic ecosystems are responding to environmental change in fundamentally different ways, with important consequences for browning along boreal stream networks.

@article{rocherros_stream_2020,
	title = {Stream metabolism controls diel patterns and evasion of {CO} $_{\textrm{2}}$ in {Arctic} streams},
	volume = {26},
	issn = {1354-1013, 1365-2486},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.14895},
	doi = {10.1111/gcb.14895},
	abstract = {Streams play an important role in the global carbon (C) cycle, accounting for a large portion of CO2 evaded from inland waters despite their small areal coverage. However, the relative importance of different terrestrial and aquatic processes driving CO2 production and evasion from streams remains poorly understood. In this study, we measured O2 and CO2 continuously in streams draining tundra-dominated catchments in northern Sweden, during the summers of 2015 and 2016. From this, we estimated daily metabolic rates and CO2 evasion simultaneously and thus provide insight into the role of stream metabolism as a driver of C dynamics in Arctic streams. Our results show that aquatic biological processes regulate CO2 concentrations and evasion at multiple timescales. Photosynthesis caused CO2 concentrations to decrease by as much as 900 ppm during the day, with the magnitude of this diel variation being strongest at the low-turbulence streams. Diel patterns in CO2 concentrations in turn influenced evasion, with up to 45\% higher rates at night. Throughout the summer, CO2 evasion was sustained by aquatic ecosystem respiration, which was one order of magnitude higher than gross primary production. Furthermore, in most cases, the contribution of stream respiration exceeded CO2 evasion, suggesting that some stream reaches serve as net sources of CO2, thus creating longitudinal heterogeneity in C production and loss within this stream network. Overall, our results provide the first link between stream metabolism and CO2 evasion in the Arctic and demonstrate that stream metabolic processes are key drivers of the transformation and fate of terrestrial organic matter exported from these landscapes.},
	language = {en},
	number = {3},
	urldate = {2020-03-19},
	journal = {Global Change Biology},
	author = {Rocher‐Ros, Gerard and Sponseller, Ryan A. and Bergström, Ann‐Kristin and Myrstener, Maria and Giesler, Reiner},
	month = mar,
	year = {2020},
	keywords = {\#nosource},
	pages = {1400--1413},
}

Streams play an important role in the global carbon (C) cycle, accounting for a large portion of CO2 evaded from inland waters despite their small areal coverage. However, the relative importance of different terrestrial and aquatic processes driving CO2 production and evasion from streams remains poorly understood. In this study, we measured O2 and CO2 continuously in streams draining tundra-dominated catchments in northern Sweden, during the summers of 2015 and 2016. From this, we estimated daily metabolic rates and CO2 evasion simultaneously and thus provide insight into the role of stream metabolism as a driver of C dynamics in Arctic streams. Our results show that aquatic biological processes regulate CO2 concentrations and evasion at multiple timescales. Photosynthesis caused CO2 concentrations to decrease by as much as 900 ppm during the day, with the magnitude of this diel variation being strongest at the low-turbulence streams. Diel patterns in CO2 concentrations in turn influenced evasion, with up to 45% higher rates at night. Throughout the summer, CO2 evasion was sustained by aquatic ecosystem respiration, which was one order of magnitude higher than gross primary production. Furthermore, in most cases, the contribution of stream respiration exceeded CO2 evasion, suggesting that some stream reaches serve as net sources of CO2, thus creating longitudinal heterogeneity in C production and loss within this stream network. Overall, our results provide the first link between stream metabolism and CO2 evasion in the Arctic and demonstrate that stream metabolic processes are key drivers of the transformation and fate of terrestrial organic matter exported from these landscapes.

@article{gomez-gener_drought_2020,
	title = {Drought alters the biogeochemistry of boreal stream networks},
	volume = {11},
	copyright = {2020 The Author(s)},
	issn = {2041-1723},
	url = {https://www.nature.com/articles/s41467-020-15496-2},
	doi = {10.1038/s41467-020-15496-2},
	abstract = {High latitude droughts are increasing, but their effects on freshwater systems are poorly understood. Here the authors investigate Sweden’s most severe drought in the last century and show that these dry conditions induce hypoxia and elevated methane production from streams.},
	language = {en},
	number = {1},
	urldate = {2020-04-23},
	journal = {Nature Communications},
	author = {Gómez-Gener, Lluís and Lupon, Anna and Laudon, Hjalmar and Sponseller, Ryan A.},
	month = apr,
	year = {2020},
	note = {Number: 1
Publisher: Nature Publishing Group},
	keywords = {\#nosource},
	pages = {1--11},
}

High latitude droughts are increasing, but their effects on freshwater systems are poorly understood. Here the authors investigate Sweden’s most severe drought in the last century and show that these dry conditions induce hypoxia and elevated methane production from streams.

@article{truchy_habitat_2020,
	title = {Habitat patchiness, ecological connectivity and the uneven recovery of boreal stream ecosystems from an experimental drought},
	volume = {26},
	issn = {1365-2486},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.15063},
	doi = {10.1111/gcb.15063},
	abstract = {Ongoing climate change is increasing the occurrence and intensity of drought episodes worldwide, including in boreal regions not previously regarded as drought prone, and where the impacts of drought remain poorly understood. Ecological connectivity is one factor that might influence community structure and ecosystem functioning post drought, by facilitating the recovery of sensitive species via dispersal at both local (e.g. a nearby habitat patch) and regional (from other systems within the same region) scales. In an outdoor mesocosm experiment, we investigated how impacts of drought on boreal stream ecosystems are altered by the spatial arrangement of local habitat patches within stream channels, and variation in ecological connectivity with a regional species pool. We measured basal ecosystem processes underlying carbon and nutrient cycling: (i) algal biomass accrual, (ii) microbial respiration and (iii) decomposition of organic matter, and sampled communities of aquatic fungi and benthic invertebrates. An eight-day drought event had strong impacts on both community structure and ecosystem functioning, including algal accrual, leaf decomposition and microbial respiration, with many of these impacts persisting even after water levels had been restored for 3.5 weeks. Enhanced connectivity with the regional species pool and increased aggregation of habitat patches also affected multiple response variables, especially those associated with microbes, and in some cases reduced the effects of drought to a small extent. This indicates that spatial processes might play a role in the resilience of communities and ecosystem functioning, given enough time. These effects were however insufficient to facilitate significant recovery in algal growth before seasonal die-back began in autumn. The limited resilience of ecosystem functioning in our experiment suggests that even short-term droughts can have extended consequences for stream ecosystems in the world’s vast boreal region, and especially on the ecosystem processes and services mediated by algal biofilms.},
	language = {en},
	number = {6},
	urldate = {2020-03-18},
	journal = {Global Change Biology},
	author = {Truchy, Amélie and Sarremejane, Romain and Muotka, Timo and Mykrä, Heikki and Angeler, David G. and Lehosmaa, Kaisa and Huusko, Ari and Johnson, Richard K. and Sponseller, Ryan A. and McKie, Brendan G.},
	month = mar,
	year = {2020},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1111/gcb.15063},
	keywords = {\#nosource, Algal production, Detritivores, Drought, Ecosystem processes, Habitat patch, Hyphomycete fungi, Meta-ecosystem, Spatial connectivity},
	pages = {3455--3472},
}

Ongoing climate change is increasing the occurrence and intensity of drought episodes worldwide, including in boreal regions not previously regarded as drought prone, and where the impacts of drought remain poorly understood. Ecological connectivity is one factor that might influence community structure and ecosystem functioning post drought, by facilitating the recovery of sensitive species via dispersal at both local (e.g. a nearby habitat patch) and regional (from other systems within the same region) scales. In an outdoor mesocosm experiment, we investigated how impacts of drought on boreal stream ecosystems are altered by the spatial arrangement of local habitat patches within stream channels, and variation in ecological connectivity with a regional species pool. We measured basal ecosystem processes underlying carbon and nutrient cycling: (i) algal biomass accrual, (ii) microbial respiration and (iii) decomposition of organic matter, and sampled communities of aquatic fungi and benthic invertebrates. An eight-day drought event had strong impacts on both community structure and ecosystem functioning, including algal accrual, leaf decomposition and microbial respiration, with many of these impacts persisting even after water levels had been restored for 3.5 weeks. Enhanced connectivity with the regional species pool and increased aggregation of habitat patches also affected multiple response variables, especially those associated with microbes, and in some cases reduced the effects of drought to a small extent. This indicates that spatial processes might play a role in the resilience of communities and ecosystem functioning, given enough time. These effects were however insufficient to facilitate significant recovery in algal growth before seasonal die-back began in autumn. The limited resilience of ecosystem functioning in our experiment suggests that even short-term droughts can have extended consequences for stream ecosystems in the world’s vast boreal region, and especially on the ecosystem processes and services mediated by algal biofilms.

@article{einarsdottir_particles_2020,
	title = {Particles and aeration at mire-stream interfaces cause selective removal and modification of dissolved organic matter},
	volume = {n/a},
	copyright = {This article is protected by copyright. All rights reserved.},
	issn = {2169-8961},
	url = {http://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JG005654},
	doi = {10.1029/2020jg005654},
	abstract = {Peatlands are dominant sources of dissolved organic matter (DOM) to boreal inland waters and play important roles in the aquatic carbon cycle. Yet, before peat-derived DOM enters aquatic networks, it needs to pass through peat-stream interfaces that are often characterized by transitions from anoxic or hypoxic to oxic conditions. Aeration at these interfaces may trigger processes that impact the DOM pool, and its fate downstream. Here, we experimentally assessed how the aeration of iron- and organic-rich mire-waters influences biodegradation, particle-formation, and modification of DOM. In addition, we investigated how suspended peat-derived particles from mires may influence these processes. We found that within five days of aeration, 20\% of the DOM transformed into particulate organic matter (POM). This removal was likely due to combination of mechanisms including co-precipitation with oxidized iron, aggregation, and DOM-adsorption onto peat-derived particles. Peat-derived particles promoted microbial activity, but biodegradation was a minor loss mechanism of DOM removal. Interestingly, microbial respiration accounted for only half of the oxygen loss, suggesting substantial non-respiratory oxygen consumption. The differences observed in DOM characteristics between anoxic and aerated treatments suggest that hydrophilic, aromatic DOM co-precipitated with iron oxides in aerated samples, and the corresponding C:N analysis of generated POM revealed that these organic species were nitrogen-poor. Meanwhile, POM formed via adsorption onto peat-derived particles generated from non-aromatic DOM and more nitrogen-rich species. Hence, selective removal of DOM, dissolved iron, and thus oxygen may be important and overlooked processes in mire-dominated headwater systems.},
	language = {en},
	number = {n/a},
	urldate = {2020-11-20},
	journal = {Journal of Geophysical Research: Biogeosciences},
	author = {Einarsdóttir, Karólína and Attermeyer, Katrin and Hawkes, Jeffrey A. and Kothawala, Dolly and Sponseller, Ryan A. and Tranvik, Lars J.},
	year = {2020},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2020JG005654},
	keywords = {\#nosource, CN, Co-precipitation, DOM, Iron, POM, Particle adsorption},
	pages = {e2020JG005654},
}

Peatlands are dominant sources of dissolved organic matter (DOM) to boreal inland waters and play important roles in the aquatic carbon cycle. Yet, before peat-derived DOM enters aquatic networks, it needs to pass through peat-stream interfaces that are often characterized by transitions from anoxic or hypoxic to oxic conditions. Aeration at these interfaces may trigger processes that impact the DOM pool, and its fate downstream. Here, we experimentally assessed how the aeration of iron- and organic-rich mire-waters influences biodegradation, particle-formation, and modification of DOM. In addition, we investigated how suspended peat-derived particles from mires may influence these processes. We found that within five days of aeration, 20% of the DOM transformed into particulate organic matter (POM). This removal was likely due to combination of mechanisms including co-precipitation with oxidized iron, aggregation, and DOM-adsorption onto peat-derived particles. Peat-derived particles promoted microbial activity, but biodegradation was a minor loss mechanism of DOM removal. Interestingly, microbial respiration accounted for only half of the oxygen loss, suggesting substantial non-respiratory oxygen consumption. The differences observed in DOM characteristics between anoxic and aerated treatments suggest that hydrophilic, aromatic DOM co-precipitated with iron oxides in aerated samples, and the corresponding C:N analysis of generated POM revealed that these organic species were nitrogen-poor. Meanwhile, POM formed via adsorption onto peat-derived particles generated from non-aromatic DOM and more nitrogen-rich species. Hence, selective removal of DOM, dissolved iron, and thus oxygen may be important and overlooked processes in mire-dominated headwater systems.

@article{lupon_groundwater_2019,
	title = {Groundwater inflows control patterns and sources of greenhouse gas emissions from streams},
	volume = {64},
	copyright = {© 2019 Association for the Sciences of Limnology and Oceanography},
	issn = {1939-5590},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/lno.11134},
	doi = {10.1002/lno.11134},
	abstract = {Headwater streams can be important sources of carbon dioxide (CO2) and methane (CH4) to the atmosphere. However, the influence of groundwater–stream connectivity on the patterns and sources of carbon (C) gas evasion is still poorly understood. We explored these connections in the boreal landscape through a detailed study of a 1.4 km lake outlet stream that is hydrologically fed by multiple topographically driven groundwater input zones. We measured stream and groundwater dissolved organic C (DOC), CO2, and CH4 concentrations every 50 m biweekly during the ice-free period and estimated in-stream C gas production through a mass balance model and independent estimates of aquatic metabolism. The spatial pattern of C gas concentrations was consistent over time, with peaks of both CH4 and CO2 concentrations occurring after each groundwater input zone. Moreover, lateral C gas inputs from riparian soils were the major source of CO2 and CH4 to the stream. DOC mineralization and CH4 oxidation within the stream accounted for 17–51\% of stream CO2 emissions, and this contribution was the greatest during relatively higher flows. Overall, our results illustrate how the nature and arrangement of groundwater flowpaths can organize patterns of stream C concentrations, transformations, and emissions by acting as a direct source of gases and by supplying organic substrates that fuel aquatic metabolism. Hence, refined assessments of how catchment structure influences the timing and magnitude of groundwater–stream connections are crucial for mechanistically understanding and scaling C evasion rates from headwaters.},
	language = {en},
	number = {4},
	urldate = {2024-03-26},
	journal = {Limnology and Oceanography},
	author = {Lupon, Anna and Denfeld, Blaize A. and Laudon, Hjalmar and Leach, Jason and Karlsson, Jan and Sponseller, Ryan A.},
	year = {2019},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/lno.11134},
	keywords = {\#nosource},
	pages = {1545--1557},
}

Headwater streams can be important sources of carbon dioxide (CO2) and methane (CH4) to the atmosphere. However, the influence of groundwater–stream connectivity on the patterns and sources of carbon (C) gas evasion is still poorly understood. We explored these connections in the boreal landscape through a detailed study of a 1.4 km lake outlet stream that is hydrologically fed by multiple topographically driven groundwater input zones. We measured stream and groundwater dissolved organic C (DOC), CO2, and CH4 concentrations every 50 m biweekly during the ice-free period and estimated in-stream C gas production through a mass balance model and independent estimates of aquatic metabolism. The spatial pattern of C gas concentrations was consistent over time, with peaks of both CH4 and CO2 concentrations occurring after each groundwater input zone. Moreover, lateral C gas inputs from riparian soils were the major source of CO2 and CH4 to the stream. DOC mineralization and CH4 oxidation within the stream accounted for 17–51% of stream CO2 emissions, and this contribution was the greatest during relatively higher flows. Overall, our results illustrate how the nature and arrangement of groundwater flowpaths can organize patterns of stream C concentrations, transformations, and emissions by acting as a direct source of gases and by supplying organic substrates that fuel aquatic metabolism. Hence, refined assessments of how catchment structure influences the timing and magnitude of groundwater–stream connections are crucial for mechanistically understanding and scaling C evasion rates from headwaters.

@article{truchy_partitioning_2019,
	title = {Partitioning spatial, environmental, and community drivers of ecosystem functioning},
	volume = {34},
	issn = {1572-9761},
	url = {https://doi.org/10.1007/s10980-019-00894-9},
	doi = {10.1007/s10980-019-00894-9},
	abstract = {Community composition, environmental variation, and spatial structuring can influence ecosystem functioning, and ecosystem service delivery. While the role of space in regulating ecosystem functioning is well recognised in theory, it is rarely considered explicitly in empirical studies.},
	language = {en},
	number = {10},
	urldate = {2020-03-19},
	journal = {Landscape Ecology},
	author = {Truchy, Amélie and Göthe, Emma and Angeler, David G. and Ecke, Frauke and Sponseller, Ryan A. and Bundschuh, Mirco and Johnson, Richard K. and McKie, Brendan G.},
	month = oct,
	year = {2019},
	keywords = {\#nosource},
	pages = {2371--2384},
}

Community composition, environmental variation, and spatial structuring can influence ecosystem functioning, and ecosystem service delivery. While the role of space in regulating ecosystem functioning is well recognised in theory, it is rarely considered explicitly in empirical studies.

@article{tiwari_contrasting_2019,
	title = {Contrasting responses in dissolved organic carbon to extreme climate events from adjacent boreal landscapes in {Northern} {Sweden}},
	volume = {14},
	issn = {1748-9326},
	url = {https://iopscience.iop.org/article/10.1088/1748-9326/ab23d4},
	doi = {10.1088/1748-9326/ab23d4},
	language = {en},
	number = {8},
	urldate = {2020-03-19},
	journal = {Environmental Research Letters},
	author = {Tiwari, Tejshree and Sponseller, Ryan A and Laudon, Hjalmar},
	month = jul,
	year = {2019},
	keywords = {\#nosource},
	pages = {084007},
}

@article{rocherros_landscape_2019,
	title = {Landscape process domains drive patterns of {CO2} evasion from river networks},
	volume = {4},
	copyright = {© 2019 The Authors. Limnology and Oceanography published by Wiley Periodicals, Inc. on behalf of Association for the Sciences of Limnology and Oceanography.},
	issn = {2378-2242},
	url = {https://aslopubs.onlinelibrary.wiley.com/doi/abs/10.1002/lol2.10108},
	doi = {10.1002/lol2.10108},
	abstract = {Streams are important emitters of CO2 but extreme spatial variability in their physical properties can make upscaling very uncertain. Here, we determined critical drivers of stream CO2 evasion at scales from 30 to 400 m across a 52.5 km2 catchment in northern Sweden. We found that turbulent reaches never have elevated CO2 concentrations, while less turbulent locations can potentially support a broad range of CO2 concentrations, consistent with global observations. The predictability of stream pCO2 is greatly improved when we include a proxy for soil-stream connectivity. Catchment topography shapes network patterns of evasion by creating hydrologically linked “domains” characterized by high water-atmosphere exchange and/or strong soil-stream connection. This template generates spatial variability in the drivers of CO2 evasion that can strongly bias regional and global estimates. To overcome this complexity, we provide the foundations of a mechanistic framework of CO2 evasion by considering how landscape process domains regulate transfer and supply.},
	language = {en},
	number = {4},
	urldate = {2019-08-30},
	journal = {Limnology and Oceanography Letters},
	author = {Rocher‐Ros, Gerard and Sponseller, Ryan A. and Lidberg, William and Mörth, Carl-Magnus and Giesler, Reiner},
	year = {2019},
	keywords = {\#nosource},
	pages = {87--95},
}

Streams are important emitters of CO2 but extreme spatial variability in their physical properties can make upscaling very uncertain. Here, we determined critical drivers of stream CO2 evasion at scales from 30 to 400 m across a 52.5 km2 catchment in northern Sweden. We found that turbulent reaches never have elevated CO2 concentrations, while less turbulent locations can potentially support a broad range of CO2 concentrations, consistent with global observations. The predictability of stream pCO2 is greatly improved when we include a proxy for soil-stream connectivity. Catchment topography shapes network patterns of evasion by creating hydrologically linked “domains” characterized by high water-atmosphere exchange and/or strong soil-stream connection. This template generates spatial variability in the drivers of CO2 evasion that can strongly bias regional and global estimates. To overcome this complexity, we provide the foundations of a mechanistic framework of CO2 evasion by considering how landscape process domains regulate transfer and supply.

@article{sponseller_headwater_2018,
	title = {Headwater {Mires} {Constitute} a {Major} {Source} of {Nitrogen} ({N}) to {Surface} {Waters} in the {Boreal} {Landscape}},
	volume = {21},
	issn = {1435-0629},
	url = {https://doi.org/10.1007/s10021-017-0133-0},
	doi = {10.1007/s10021-017-0133-0},
	abstract = {Nutrient exports from soils have important implications for long-term patterns of nutrient limitation on land and resource delivery to aquatic environments. While plant–soil systems are notably efficient at retaining limiting nutrients, spatial and temporal mismatches in resource supply and demand may create opportunities for hydrologic losses to occur. Spatial mismatches may be particularly important in peat-forming landscapes, where the development of a two-layer vertical structure can isolate plant communities on the surface from resource pools that accumulate at depth. Our objectives were to test this idea in northern Sweden, where nitrogen (N) limitation of terrestrial plants is widespread, and where peat-forming, mire ecosystems are dominant features of the landscape. We quantified vertical patterns of N chemistry in a minerogenic mire, estimated the seasonal and annual hydrologic export of organic and inorganic N from this system, and evaluated the broader influence of mire cover on N chemistry across a stream network. Relatively high concentrations of ammonium (up to 2 mg l−1) were observed in groundwater several meters below the peat surface, and N was routed to the outlet stream along deep, preferential flowpaths. Areal estimates of inorganic N export from the mire were several times greater than from an adjacent, forested catchment, with markedly higher loss rates during the growing season, when plant N demand is ostensibly greatest. At broader scales, mire cover was positively correlated with long-term concentrations of inorganic and organic N in streams across the drainage network. This study provides an example of how mire formation and peat accumulation can create broad-scale heterogeneity in nutrient supply and demand across boreal landscapes. This mismatch allows for hydrologic losses of reactive N that are independent of annual plant demand and potentially important to receiving lakes and streams.},
	language = {en},
	number = {1},
	urldate = {2024-03-27},
	journal = {Ecosystems},
	author = {Sponseller, Ryan A. and Blackburn, M. and Nilsson, M. B. and Laudon, H.},
	month = jan,
	year = {2018},
	keywords = {\#nosource, boreal, mire, nitrogen, peat, peatlands, watershed biogeochemistry},
	pages = {31--44},
}

Nutrient exports from soils have important implications for long-term patterns of nutrient limitation on land and resource delivery to aquatic environments. While plant–soil systems are notably efficient at retaining limiting nutrients, spatial and temporal mismatches in resource supply and demand may create opportunities for hydrologic losses to occur. Spatial mismatches may be particularly important in peat-forming landscapes, where the development of a two-layer vertical structure can isolate plant communities on the surface from resource pools that accumulate at depth. Our objectives were to test this idea in northern Sweden, where nitrogen (N) limitation of terrestrial plants is widespread, and where peat-forming, mire ecosystems are dominant features of the landscape. We quantified vertical patterns of N chemistry in a minerogenic mire, estimated the seasonal and annual hydrologic export of organic and inorganic N from this system, and evaluated the broader influence of mire cover on N chemistry across a stream network. Relatively high concentrations of ammonium (up to 2 mg l−1) were observed in groundwater several meters below the peat surface, and N was routed to the outlet stream along deep, preferential flowpaths. Areal estimates of inorganic N export from the mire were several times greater than from an adjacent, forested catchment, with markedly higher loss rates during the growing season, when plant N demand is ostensibly greatest. At broader scales, mire cover was positively correlated with long-term concentrations of inorganic and organic N in streams across the drainage network. This study provides an example of how mire formation and peat accumulation can create broad-scale heterogeneity in nutrient supply and demand across boreal landscapes. This mismatch allows for hydrologic losses of reactive N that are independent of annual plant demand and potentially important to receiving lakes and streams.

@article{myrstener_persistent_2018,
	title = {Persistent nitrogen limitation of stream biofilm communities along climate gradients in the {Arctic}},
	volume = {24},
	copyright = {© 2018 John Wiley \& Sons Ltd},
	issn = {1365-2486},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.14117},
	doi = {10.1111/gcb.14117},
	abstract = {Climate change is rapidly reshaping Arctic landscapes through shifts in vegetation cover and productivity, soil resource mobilization, and hydrological regimes. The implications of these changes for stream ecosystems and food webs is unclear and will depend largely on microbial biofilm responses to concurrent shifts in temperature, light, and resource supply from land. To study those responses, we used nutrient diffusing substrates to manipulate resource supply to biofilm communities along regional gradients in stream temperature, riparian shading, and dissolved organic carbon (DOC) loading in Arctic Sweden. We found strong nitrogen (N) limitation across this gradient for gross primary production, community respiration and chlorophyll-a accumulation. For unamended biofilms, activity and biomass accrual were not closely related to any single physical or chemical driver across this region. However, the magnitude of biofilm response to N addition was: in tundra streams, biofilm response was constrained by thermal regimes, whereas variation in light availability regulated this response in birch and coniferous forest streams. Furthermore, heterotrophic responses to experimental N addition increased across the region with greater stream water concentrations of DOC relative to inorganic N. Thus, future shifts in resource supply to these ecosystems are likely to interact with other concurrent environmental changes to regulate stream productivity. Indeed, our results suggest that in the absence of increased nutrient inputs, Arctic streams will be less sensitive to future changes in other habitat variables such as temperature and DOC loading.},
	language = {en},
	number = {8},
	urldate = {2024-03-27},
	journal = {Global Change Biology},
	author = {Myrstener, Maria and Rocher-Ros, Gerard and Burrows, Ryan M. and Bergström, Ann-Kristin and Giesler, Reiner and Sponseller, Ryan A.},
	year = {2018},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1111/gcb.14117},
	keywords = {\#nosource, Arctic, Bioassay, Biofilm, Climate Change, Co-limitation, Nitrogen limitation, Nutrient addition, Stream productivity, bioassay, biofilm, climate change, colimitation, nitrogen limitation, nutrient addition, stream productivity},
	pages = {3680--3691},
}

Climate change is rapidly reshaping Arctic landscapes through shifts in vegetation cover and productivity, soil resource mobilization, and hydrological regimes. The implications of these changes for stream ecosystems and food webs is unclear and will depend largely on microbial biofilm responses to concurrent shifts in temperature, light, and resource supply from land. To study those responses, we used nutrient diffusing substrates to manipulate resource supply to biofilm communities along regional gradients in stream temperature, riparian shading, and dissolved organic carbon (DOC) loading in Arctic Sweden. We found strong nitrogen (N) limitation across this gradient for gross primary production, community respiration and chlorophyll-a accumulation. For unamended biofilms, activity and biomass accrual were not closely related to any single physical or chemical driver across this region. However, the magnitude of biofilm response to N addition was: in tundra streams, biofilm response was constrained by thermal regimes, whereas variation in light availability regulated this response in birch and coniferous forest streams. Furthermore, heterotrophic responses to experimental N addition increased across the region with greater stream water concentrations of DOC relative to inorganic N. Thus, future shifts in resource supply to these ecosystems are likely to interact with other concurrent environmental changes to regulate stream productivity. Indeed, our results suggest that in the absence of increased nutrient inputs, Arctic streams will be less sensitive to future changes in other habitat variables such as temperature and DOC loading.

@article{metcalfe_patchy_2018,
	title = {Patchy field sampling biases understanding of climate change impacts across the {Arctic}},
	volume = {2},
	copyright = {2018 The Author(s), under exclusive licence to Springer Nature Limited},
	issn = {2397-334X},
	url = {https://www.nature.com/articles/s41559-018-0612-5},
	doi = {10.1038/s41559-018-0612-5},
	abstract = {Effective societal responses to rapid climate change in the Arctic rely on an accurate representation of region-specific ecosystem properties and processes. However, this is limited by the scarcity and patchy distribution of field measurements. Here, we use a comprehensive, geo-referenced database of primary field measurements in 1,840 published studies across the Arctic to identify statistically significant spatial biases in field sampling and study citation across this globally important region. We find that 31\% of all study citations are derived from sites located within 50 km of just two research sites: Toolik Lake in the USA and Abisko in Sweden. Furthermore, relatively colder, more rapidly warming and sparsely vegetated sites are under-sampled and under-recognized in terms of citations, particularly among microbiology-related studies. The poorly sampled and cited areas, mainly in the Canadian high-Arctic archipelago and the Arctic coastline of Russia, constitute a large fraction of the Arctic ice-free land area. Our results suggest that the current pattern of sampling and citation may bias the scientific consensuses that underpin attempts to accurately predict and effectively mitigate climate change in the region. Further work is required to increase both the quality and quantity of sampling, and incorporate existing literature from poorly cited areas to generate a more representative picture of Arctic climate change and its environmental impacts.},
	language = {en},
	number = {9},
	urldate = {2024-03-27},
	journal = {Nature Ecology \& Evolution},
	author = {Metcalfe, Daniel B. and Hermans, Thirze D. G. and Ahlstrand, Jenny and Becker, Michael and Berggren, Martin and Björk, Robert G. and Björkman, Mats P. and Blok, Daan and Chaudhary, Nitin and Chisholm, Chelsea and Classen, Aimée T. and Hasselquist, Niles J. and Jonsson, Micael and Kristensen, Jeppe A. and Kumordzi, Bright B. and Lee, Hanna and Mayor, Jordan R. and Prevéy, Janet and Pantazatou, Karolina and Rousk, Johannes and Sponseller, Ryan A. and Sundqvist, Maja K. and Tang, Jing and Uddling, Johan and Wallin, Göran and Zhang, Wenxin and Ahlström, Anders and Tenenbaum, David E. and Abdi, Abdulhakim M.},
	month = sep,
	year = {2018},
	note = {Publisher: Nature Publishing Group},
	keywords = {\#nosource, Climate change, Environmental sciences, Research data},
	pages = {1443--1448},
}

Effective societal responses to rapid climate change in the Arctic rely on an accurate representation of region-specific ecosystem properties and processes. However, this is limited by the scarcity and patchy distribution of field measurements. Here, we use a comprehensive, geo-referenced database of primary field measurements in 1,840 published studies across the Arctic to identify statistically significant spatial biases in field sampling and study citation across this globally important region. We find that 31% of all study citations are derived from sites located within 50 km of just two research sites: Toolik Lake in the USA and Abisko in Sweden. Furthermore, relatively colder, more rapidly warming and sparsely vegetated sites are under-sampled and under-recognized in terms of citations, particularly among microbiology-related studies. The poorly sampled and cited areas, mainly in the Canadian high-Arctic archipelago and the Arctic coastline of Russia, constitute a large fraction of the Arctic ice-free land area. Our results suggest that the current pattern of sampling and citation may bias the scientific consensuses that underpin attempts to accurately predict and effectively mitigate climate change in the region. Further work is required to increase both the quality and quantity of sampling, and incorporate existing literature from poorly cited areas to generate a more representative picture of Arctic climate change and its environmental impacts.

@article{ledesma_towards_2018,
	title = {Towards an {Improved} {Conceptualization} of {Riparian} {Zones} in {Boreal} {Forest} {Headwaters}},
	volume = {21},
	issn = {1435-0629},
	url = {https://doi.org/10.1007/s10021-017-0149-5},
	doi = {10.1007/s10021-017-0149-5},
	abstract = {The boreal ecoregion supports about one-third of the world’s forest. Over 90\% of boreal forest streams are found in headwaters, where terrestrial–aquatic interfaces are dominated by organic matter (OM)-rich riparian zones (RZs). Because these transition zones are key features controlling catchment biogeochemistry, appropriate RZ conceptualizations are needed to sustainably manage surface water quality in the face of a changing climate and increased demands for forest biomass. Here we present a simple, yet comprehensive, conceptualization of RZ function based on hydrological connectivity, biogeochemical processes, and spatial heterogeneity. We consider four dimensions of hydrological connectivity: (1) laterally along hillslopes, (2) longitudinally along the stream, (3) vertically down the riparian profile, and (4) temporally through event-based and seasonal changes in hydrology. Of particular importance is the vertical dimension, characterized by a ‘Dominant Source Layer’ that has the highest contribution to solute and water fluxes to streams. In addition to serving as the primary source of OM to boreal streams, RZs shape water chemistry through two sets of OM-dependent biogeochemical processes: (1) transport and retention of OM-associated material and (2) redox-mediated transformations controlled by RZ water residence time and availability of labile OM. These processes can lead to both retention and release of pollutants. Variations in width, hydrological connectivity, and OM storage drive spatial heterogeneity in RZ biogeochemical function. This conceptualization provides a useful theoretical framework for environmental scientists and ecologically sustainable and economically effective forest management in the boreal region and elsewhere, where forest headwaters are dominated by low-gradient, OM-rich RZs.},
	language = {en},
	number = {2},
	urldate = {2024-03-27},
	journal = {Ecosystems},
	author = {Ledesma, José L. J. and Futter, Martyn N. and Blackburn, M. and Lidman, Fredrik and Grabs, Thomas and Sponseller, Ryan A. and Laudon, Hjalmar and Bishop, Kevin H. and Köhler, Stephan J.},
	month = mar,
	year = {2018},
	keywords = {\#nosource, catchment biogeochemistry, catchment heterogeneity, forest management, hydrological connectivity, redox, riparian buffer, soil organic matter, terrestrial–aquatic interface, water quality},
	pages = {297--315},
}

The boreal ecoregion supports about one-third of the world’s forest. Over 90% of boreal forest streams are found in headwaters, where terrestrial–aquatic interfaces are dominated by organic matter (OM)-rich riparian zones (RZs). Because these transition zones are key features controlling catchment biogeochemistry, appropriate RZ conceptualizations are needed to sustainably manage surface water quality in the face of a changing climate and increased demands for forest biomass. Here we present a simple, yet comprehensive, conceptualization of RZ function based on hydrological connectivity, biogeochemical processes, and spatial heterogeneity. We consider four dimensions of hydrological connectivity: (1) laterally along hillslopes, (2) longitudinally along the stream, (3) vertically down the riparian profile, and (4) temporally through event-based and seasonal changes in hydrology. Of particular importance is the vertical dimension, characterized by a ‘Dominant Source Layer’ that has the highest contribution to solute and water fluxes to streams. In addition to serving as the primary source of OM to boreal streams, RZs shape water chemistry through two sets of OM-dependent biogeochemical processes: (1) transport and retention of OM-associated material and (2) redox-mediated transformations controlled by RZ water residence time and availability of labile OM. These processes can lead to both retention and release of pollutants. Variations in width, hydrological connectivity, and OM storage drive spatial heterogeneity in RZ biogeochemical function. This conceptualization provides a useful theoretical framework for environmental scientists and ecologically sustainable and economically effective forest management in the boreal region and elsewhere, where forest headwaters are dominated by low-gradient, OM-rich RZs.

@article{laudon_how_2018,
	title = {How landscape organization and scale shape catchment hydrology and biogeochemistry: insights from a long-term catchment study},
	volume = {5},
	copyright = {© 2017 Wiley Periodicals, Inc.},
	issn = {2049-1948},
	shorttitle = {How landscape organization and scale shape catchment hydrology and biogeochemistry},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/wat2.1265},
	doi = {10.1002/wat2.1265},
	abstract = {Catchment science plays a critical role in the protection of water resources in the face of ongoing changes in climate, long-range transport of air pollutants, and land use. Addressing these challenges, however, requires improved understanding of how, when, and where changes in water quantity and quality occur within river networks. To reach these goals, we must recognize how different catchment features are organized to regulate surface chemistry at multiple scales, from processes controlling headwaters, to the downstream mixing of water from multiple landscape sources and deep aquifers. Here we synthesize 30-years of hydrological and biogeochemical research from the Krycklan catchment study (KCS) in northern Sweden to demonstrate the benefits of coupling long-term monitoring with multi-scale research to advance our understanding of catchment functioning across space and time. We show that the regulation of hydrological and biogeochemical patterns in the KCS can be decomposed into four, hierarchically structured landscape features that include: (1) transmissivity and reactivity of dominant source layers within riparian soils, (2) spatial arrangement of groundwater input zones that govern water and solute fluxes at reach- to segment-scales, (3) landscape scale heterogeneity (forests, mires, and lakes) that generates unique biogeochemical signals downstream, and (4) broad-scale mixing of surface streams with deep groundwater contributions. While this set of features are perhaps specific to the study region, analogous hierarchical controls are likely to be widespread. Resolving these scale dependent processes is important for predicting how, when, and where different environmental changes may influence patterns of surface water chemistry within river networks. WIREs Water 2018, 5:e1265. doi: 10.1002/wat2.1265 This article is categorized under: Science of Water {\textgreater} Hydrological Processes Science of Water {\textgreater} Water and Environmental Change Science of Water {\textgreater} Methods},
	language = {en},
	number = {2},
	urldate = {2024-03-27},
	journal = {WIREs Water},
	author = {Laudon, Hjalmar and Sponseller, Ryan A.},
	year = {2018},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/wat2.1265},
	keywords = {\#nosource},
	pages = {e1265},
}

Catchment science plays a critical role in the protection of water resources in the face of ongoing changes in climate, long-range transport of air pollutants, and land use. Addressing these challenges, however, requires improved understanding of how, when, and where changes in water quantity and quality occur within river networks. To reach these goals, we must recognize how different catchment features are organized to regulate surface chemistry at multiple scales, from processes controlling headwaters, to the downstream mixing of water from multiple landscape sources and deep aquifers. Here we synthesize 30-years of hydrological and biogeochemical research from the Krycklan catchment study (KCS) in northern Sweden to demonstrate the benefits of coupling long-term monitoring with multi-scale research to advance our understanding of catchment functioning across space and time. We show that the regulation of hydrological and biogeochemical patterns in the KCS can be decomposed into four, hierarchically structured landscape features that include: (1) transmissivity and reactivity of dominant source layers within riparian soils, (2) spatial arrangement of groundwater input zones that govern water and solute fluxes at reach- to segment-scales, (3) landscape scale heterogeneity (forests, mires, and lakes) that generates unique biogeochemical signals downstream, and (4) broad-scale mixing of surface streams with deep groundwater contributions. While this set of features are perhaps specific to the study region, analogous hierarchical controls are likely to be widespread. Resolving these scale dependent processes is important for predicting how, when, and where different environmental changes may influence patterns of surface water chemistry within river networks. WIREs Water 2018, 5:e1265. doi: 10.1002/wat2.1265 This article is categorized under: Science of Water \textgreater Hydrological Processes Science of Water \textgreater Water and Environmental Change Science of Water \textgreater Methods

@article{jonsson_catchment_2018,
	title = {Catchment properties predict autochthony in stream filter feeders},
	volume = {815},
	issn = {1573-5117},
	url = {https://doi.org/10.1007/s10750-018-3553-8},
	doi = {10.1007/s10750-018-3553-8},
	abstract = {Stream ecological theory predicts that the use of allochthonous resources declines with increasing channel width, while at the same time primary production and autochthonous carbon use by consumers increase. Although these expectations have found support in several studies, it is not well known how terrestrial runoff and/or inputs of primary production from lakes alter these longitudinal patterns. To investigate this, we analyzed the diet of filter-feeding black fly and caddisfly larvae from 23 boreal streams, encompassing gradients in drainage area, land cover and land use, and distance to nearest upstream lake outlet. In five of these streams, we also sampled repeatedly during autumn to test if allochthony of filter feeders increases over time as new litter inputs are processed. Across sites, filter-feeder autochthony was 21.1–75.1\%, did not differ between black fly and caddisfly larvae, was not positively related to drainage area, and did not decrease with distance from lakes. Instead, lake and wetland cover promoted filter-feeder autochthony independently of stream size, whereas catchment-scale forest cover and forestry reduced autochthony. Further, we found no seasonal increase in allochthony, indicating low assimilation of particles derived from autumn litter fall. Hence, catchment properties, rather than local conditions, can influence levels of autochthony in boreal streams.},
	language = {en},
	number = {1},
	urldate = {2024-03-27},
	journal = {Hydrobiologia},
	author = {Jonsson, Micael and Polvi, Lina E. and Sponseller, Ryan A. and Stenroth, Karolina},
	month = jun,
	year = {2018},
	keywords = {\#nosource, Allochthony, Aquatic insects, Autochthony, Land cover, Land use, Stream},
	pages = {83--95},
}

Stream ecological theory predicts that the use of allochthonous resources declines with increasing channel width, while at the same time primary production and autochthonous carbon use by consumers increase. Although these expectations have found support in several studies, it is not well known how terrestrial runoff and/or inputs of primary production from lakes alter these longitudinal patterns. To investigate this, we analyzed the diet of filter-feeding black fly and caddisfly larvae from 23 boreal streams, encompassing gradients in drainage area, land cover and land use, and distance to nearest upstream lake outlet. In five of these streams, we also sampled repeatedly during autumn to test if allochthony of filter feeders increases over time as new litter inputs are processed. Across sites, filter-feeder autochthony was 21.1–75.1%, did not differ between black fly and caddisfly larvae, was not positively related to drainage area, and did not decrease with distance from lakes. Instead, lake and wetland cover promoted filter-feeder autochthony independently of stream size, whereas catchment-scale forest cover and forestry reduced autochthony. Further, we found no seasonal increase in allochthony, indicating low assimilation of particles derived from autumn litter fall. Hence, catchment properties, rather than local conditions, can influence levels of autochthony in boreal streams.

@article{hasselquist_identifying_2018,
	title = {Identifying and assessing the potential hydrological function of past artificial forest drainage},
	volume = {47},
	issn = {1654-7209},
	url = {https://doi.org/10.1007/s13280-017-0984-9},
	doi = {10.1007/s13280-017-0984-9},
	abstract = {Drainage of forested wetlands for increased timber production has profoundly altered the hydrology and water quality of their downstream waterways. Some ditches need network maintenance (DNM), but potential positive effects on tree productivity must be balanced against environmental impacts. Currently, no clear guidelines exist for DNM that strike this balance. Our study helps begin to prioritise DNM by: (1) quantifying ditches by soil type in the 68 km2 Krycklan Catchment Study in northern Sweden and (2) using upslope catchment area algorithms on new high-resolution digital elevation models to determine their likelihood to drain water. Ditches nearly doubled the size of the stream network (178–327 km) and 17\% of ditches occurred on well-draining sedimentary soils, presumably making DNM unwarranted. Modelling results suggest that 25–50\% of ditches may never support flow. With new laser scanning technology, simple mapping and modelling methods can locate ditches and model their function, facilitating efforts to balance DNM with environmental impacts.},
	language = {en},
	number = {5},
	urldate = {2024-03-27},
	journal = {Ambio},
	author = {Hasselquist, Eliza Maher and Lidberg, William and Sponseller, Ryan A. and Ågren, Anneli and Laudon, Hjalmar},
	month = sep,
	year = {2018},
	keywords = {\#nosource, DEM, Flow accumulation model, Hydrology, LiDAR, Peatland, Terrain-based prediction},
	pages = {546--556},
}

Drainage of forested wetlands for increased timber production has profoundly altered the hydrology and water quality of their downstream waterways. Some ditches need network maintenance (DNM), but potential positive effects on tree productivity must be balanced against environmental impacts. Currently, no clear guidelines exist for DNM that strike this balance. Our study helps begin to prioritise DNM by: (1) quantifying ditches by soil type in the 68 km2 Krycklan Catchment Study in northern Sweden and (2) using upslope catchment area algorithms on new high-resolution digital elevation models to determine their likelihood to drain water. Ditches nearly doubled the size of the stream network (178–327 km) and 17% of ditches occurred on well-draining sedimentary soils, presumably making DNM unwarranted. Modelling results suggest that 25–50% of ditches may never support flow. With new laser scanning technology, simple mapping and modelling methods can locate ditches and model their function, facilitating efforts to balance DNM with environmental impacts.

@article{kupryianchyk_industrial_2018,
	title = {Industrial and natural compounds in filter-feeding black fly larvae and water in 3 tundra streams},
	volume = {37},
	copyright = {© 2018 SETAC},
	issn = {1552-8618},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/etc.4267},
	doi = {10.1002/etc.4267},
	abstract = {We report concentrations of polychlorinated biphenyls, polybrominated diphenyl ethers, novel flame retardants, and naturally occurring bromoanisoles in water and filter-feeding black fly (Simuliidae) larvae in 3 tundra streams in northern Sweden. The results demonstrate that black fly larvae accumulate a wide range of organic contaminants and can be used as bioindicators of water pollution in Arctic streams. Environ Toxicol Chem 2018;37:3011–3017. © 2018 SETAC},
	language = {en},
	number = {12},
	urldate = {2024-03-26},
	journal = {Environmental Toxicology and Chemistry},
	author = {Kupryianchyk, Darya and Giesler, Reiner and Bidleman, Terry F. and Liljelind, Per and Lau, Danny Chun Pong and Sponseller, Ryan A. and Andersson, Patrik L.},
	year = {2018},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/etc.4267},
	keywords = {\#nosource, Arctic streams, Bioaccumulation, Emerging pollutants, Fate and transport, Legacy contaminants, Long-range transport, bioaccumulation, emerging pollutants, fate and transport},
	pages = {3011--3017},
}

We report concentrations of polychlorinated biphenyls, polybrominated diphenyl ethers, novel flame retardants, and naturally occurring bromoanisoles in water and filter-feeding black fly (Simuliidae) larvae in 3 tundra streams in northern Sweden. The results demonstrate that black fly larvae accumulate a wide range of organic contaminants and can be used as bioindicators of water pollution in Arctic streams. Environ Toxicol Chem 2018;37:3011–3017. © 2018 SETAC

@article{denfeld_carbon_2018,
	title = {Carbon {Dioxide} and {Methane} {Dynamics} in a {Small} {Boreal} {Lake} {During} {Winter} and {Spring} {Melt} {Events}},
	volume = {123},
	copyright = {©2018. American Geophysical Union. All Rights Reserved.},
	issn = {2169-8961},
	url = {https://onlinelibrary.wiley.com/doi/abs/10.1029/2018JG004622},
	doi = {10.1029/2018JG004622},
	abstract = {In seasonally ice-covered lakes, carbon dioxide (CO2) and methane (CH4) emission at ice-off can account for a significant fraction of the annual budget. Yet knowledge of the mechanisms controlling below lake-ice carbon (C) dynamics and subsequent CO2 and CH4 emissions at ice-off is limited. To understand the control of below ice C dynamics, and C emissions in spring, we measured spatial variation in CO2, CH4, and dissolved inorganic and organic carbon from ice-on to ice-off, in a small boreal lake during a winter with sporadic melting events. Winter melt events were associated with decreased surface water DOC in the forest-dominated basin and increased surface water CH4 in the mire-dominated basin. At the whole-lake scale, CH4 accumulated below ice throughout the winter, whereas CO2 accumulation was greatest in early winter. Mass-balance estimates suggest that, in addition to the CO2 and CH4 accumulated during winter, external inputs of CO2 and CH4 and internal processing during ice-melt could represent significant sources of C gas emissions during ice-off. Moreover, internal processing of CO2 and CH4 worked in opposition, with production of CO2 and oxidation of CH4 dominating at ice-off. These findings have important implications for how small boreal lakes will respond to warmer winters in the future; increased winter melt events will likely increase external inputs below ice and thus alter the extent and timing of CO2 and CH4 emissions to the atmosphere at ice-off.},
	language = {en},
	number = {8},
	urldate = {2024-03-26},
	journal = {Journal of Geophysical Research: Biogeosciences},
	author = {Denfeld, B. A. and Klaus, M. and Laudon, H. and Sponseller, R. A. and Karlsson, J.},
	year = {2018},
	note = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2018JG004622},
	keywords = {\#nosource, carbon cycle, carbon dioxide, emissions, ice-covered lake, methane, winter limnology},
	pages = {2527--2540},
}

In seasonally ice-covered lakes, carbon dioxide (CO2) and methane (CH4) emission at ice-off can account for a significant fraction of the annual budget. Yet knowledge of the mechanisms controlling below lake-ice carbon (C) dynamics and subsequent CO2 and CH4 emissions at ice-off is limited. To understand the control of below ice C dynamics, and C emissions in spring, we measured spatial variation in CO2, CH4, and dissolved inorganic and organic carbon from ice-on to ice-off, in a small boreal lake during a winter with sporadic melting events. Winter melt events were associated with decreased surface water DOC in the forest-dominated basin and increased surface water CH4 in the mire-dominated basin. At the whole-lake scale, CH4 accumulated below ice throughout the winter, whereas CO2 accumulation was greatest in early winter. Mass-balance estimates suggest that, in addition to the CO2 and CH4 accumulated during winter, external inputs of CO2 and CH4 and internal processing during ice-melt could represent significant sources of C gas emissions during ice-off. Moreover, internal processing of CO2 and CH4 worked in opposition, with production of CO2 and oxidation of CH4 dominating at ice-off. These findings have important implications for how small boreal lakes will respond to warmer winters in the future; increased winter melt events will likely increase external inputs below ice and thus alter the extent and timing of CO2 and CH4 emissions to the atmosphere at ice-off.

@article{jonsson_land_2017,
	title = {Land use influences macroinvertebrate community composition in boreal headwaters through altered stream conditions},
	volume = {46},
	issn = {1654-7209},
	url = {https://doi.org/10.1007/s13280-016-0837-y},
	doi = {10.1007/s13280-016-0837-y},
	abstract = {Land use is known to alter the nature of land–water interactions, but the potential effects of widespread forest management on headwaters in boreal regions remain poorly understood. We evaluated the importance of catchment land use, land cover, and local stream variables for macroinvertebrate community and functional trait diversity in 18 boreal headwater streams. Variation in macroinvertebrate metrics was often best explained by in-stream variables, primarily water chemistry (e.g. pH). However, variation in stream variables was, in turn, significantly associated with catchment-scale forestry land use. More specifically, streams running through catchments that were dominated by young (11–50 years) forests had higher pH, greater organic matter standing stock, higher abundance of aquatic moss, and the highest macroinvertebrate diversity, compared to streams running through recently clear-cut and old forests. This indicates that catchment-scale forest management can modify in-stream habitat conditions with effects on stream macroinvertebrate communities and that characteristics of younger forests may promote conditions that benefit headwater biodiversity.},
	language = {en},
	number = {3},
	urldate = {2024-03-27},
	journal = {Ambio},
	author = {Jonsson, Micael and Burrows, Ryan M. and Lidman, Johan and Fältström, Emma and Laudon, Hjalmar and Sponseller, Ryan A.},
	month = apr,
	year = {2017},
	keywords = {\#nosource, Aquatic insects, Biodiversity, Forestry, Functional traits},
	pages = {311--323},
}

Land use is known to alter the nature of land–water interactions, but the potential effects of widespread forest management on headwaters in boreal regions remain poorly understood. We evaluated the importance of catchment land use, land cover, and local stream variables for macroinvertebrate community and functional trait diversity in 18 boreal headwater streams. Variation in macroinvertebrate metrics was often best explained by in-stream variables, primarily water chemistry (e.g. pH). However, variation in stream variables was, in turn, significantly associated with catchment-scale forestry land use. More specifically, streams running through catchments that were dominated by young (11–50 years) forests had higher pH, greater organic matter standing stock, higher abundance of aquatic moss, and the highest macroinvertebrate diversity, compared to streams running through recently clear-cut and old forests. This indicates that catchment-scale forest management can modify in-stream habitat conditions with effects on stream macroinvertebrate communities and that characteristics of younger forests may promote conditions that benefit headwater biodiversity.

@article{soares_new_2017,
	title = {New insights on resource stoichiometry: assessing availability of carbon, nitrogen, and phosphorus to bacterioplankton},
	volume = {14},
	issn = {1726-4189},
	shorttitle = {New insights on resource stoichiometry},
	url = {http://www.biogeosciences.net/14/1527/2017/},
	doi = {10.5194/bg-14-1527-2017},
	abstract = {Boreal lake and river ecosystems receive large quantities of organic nutrients and carbon (C) from their catchments. How bacterioplankton respond to these inputs is not well understood, in part because we base our understanding and predictions on total pools, yet we know little about the stoichiometry of bioavailable elements within organic matter. We designed bioassays with the purpose of exhausting the pools of readily bioavailable dissolved organic carbon (BDOC), bioavailable dissolved nitrogen (BDN), and bioavailable dissolved phosphorus (BDP) as fast as possible. Applying the method in four boreal lakes at base-flow conditions yielded concentrations of bioavailable resources in the range 105–693 µg C L−1 for BDOC (2 \% of initial total DOC), 24–288 µg N L−1 for BDN (31 \% of initial total dissolved nitrogen), and 0.2–17 µg P L−1 for BDP (49 \% of initial total dissolved phosphorus). Thus, relative bioavailability increased from carbon (C) to nitrogen (N) to phosphorus (P). We show that the main fraction of bioavailable nutrients is organic, representing 80 \% of BDN and 61 \% of BDP. In addition, we demonstrate that total C : N and C : P ratios are as much as 13-fold higher than C : N and C : P ratios for bioavailable resource fractions. Further, by applying additional bioavailability measurements to seven widely distributed rivers, we provide support for a general pattern of relatively high bioavailability of P and N in relation to C. Altogether, our findings underscore the poor availability of C for support of bacterial metabolism in boreal C-rich freshwaters, and suggest that these ecosystems are very sensitive to increased input of bioavailable DOC.},
	number = {6},
	urldate = {2017-03-28},
	journal = {Biogeosciences},
	author = {Soares, A. R. A. and Bergström, A.-K. and Sponseller, R. A. and Moberg, J. M. and Giesler, R. and Kritzberg, E. S. and Jansson, M. and Berggren, M.},
	month = mar,
	year = {2017},
	note = {00005},
	keywords = {\#nosource},
	pages = {1527--1539},
}

Boreal lake and river ecosystems receive large quantities of organic nutrients and carbon (C) from their catchments. How bacterioplankton respond to these inputs is not well understood, in part because we base our understanding and predictions on total pools, yet we know little about the stoichiometry of bioavailable elements within organic matter. We designed bioassays with the purpose of exhausting the pools of readily bioavailable dissolved organic carbon (BDOC), bioavailable dissolved nitrogen (BDN), and bioavailable dissolved phosphorus (BDP) as fast as possible. Applying the method in four boreal lakes at base-flow conditions yielded concentrations of bioavailable resources in the range 105–693 µg C L−1 for BDOC (2 % of initial total DOC), 24–288 µg N L−1 for BDN (31 % of initial total dissolved nitrogen), and 0.2–17 µg P L−1 for BDP (49 % of initial total dissolved phosphorus). Thus, relative bioavailability increased from carbon (C) to nitrogen (N) to phosphorus (P). We show that the main fraction of bioavailable nutrients is organic, representing 80 % of BDN and 61 % of BDP. In addition, we demonstrate that total C : N and C : P ratios are as much as 13-fold higher than C : N and C : P ratios for bioavailable resource fractions. Further, by applying additional bioavailability measurements to seven widely distributed rivers, we provide support for a general pattern of relatively high bioavailability of P and N in relation to C. Altogether, our findings underscore the poor availability of C for support of bacterial metabolism in boreal C-rich freshwaters, and suggest that these ecosystems are very sensitive to increased input of bioavailable DOC.

@article{lidman_composition_2017,
	title = {Composition of riparian litter input regulates organic matter decomposition: {Implications} for headwater stream functioning in a managed forest landscape},
	volume = {7},
	issn = {2045-7758},
	shorttitle = {Composition of riparian litter input regulates organic matter decomposition},
	url = {http://onlinelibrary.wiley.com/doi/10.1002/ece3.2726/abstract},
	doi = {10.1002/ece3.2726},
	abstract = {Although the importance of stream condition for leaf litter decomposition has been extensively studied, little is known about how processing rates change in response to altered riparian vegetation community composition. We investigated patterns of plant litter input and decomposition across 20 boreal headwater streams that varied in proportions of riparian deciduous and coniferous trees. We measured a suite of in-stream physical and chemical characteristics, as well as the amount and type of litter inputs from riparian vegetation, and related these to decomposition rates of native (alder, birch, and spruce) and introduced (lodgepole pine) litter species incubated in coarse- and fine-mesh bags. Total litter inputs ranged more than fivefold among sites and increased with the proportion of deciduous vegetation in the riparian zone. In line with differences in initial litter quality, mean decomposition rate was highest for alder, followed by birch, spruce, and lodgepole pine (12, 55, and 68\% lower rates, respectively). Further, these rates were greater in coarse-mesh bags that allow colonization by macroinvertebrates. Variance in decomposition rate among sites for different species was best explained by different sets of environmental conditions, but litter-input composition (i.e., quality) was overall highly important. On average, native litter decomposed faster in sites with higher-quality litter input and (with the exception of spruce) higher concentrations of dissolved nutrients and open canopies. By contrast, lodgepole pine decomposed more rapidly in sites receiving lower-quality litter inputs. Birch litter decomposition rate in coarse-mesh bags was best predicted by the same environmental variables as in fine-mesh bags, with additional positive influences of macroinvertebrate species richness. Hence, to facilitate energy turnover in boreal headwaters, forest management with focus on conifer production should aim at increasing the presence of native deciduous trees along streams, as they promote conditions that favor higher decomposition rates of terrestrial plant litter.},
	language = {en},
	number = {4},
	urldate = {2017-11-17},
	journal = {Ecology and Evolution},
	author = {Lidman, Johan and Jonsson, Micael and Burrows, Ryan M. and Bundschuh, Mirco and Sponseller, Ryan A.},
	month = feb,
	year = {2017},
	note = {00000},
	keywords = {\#nosource, boreal, introduced species, land use, litter quality, priming effect},
	pages = {1068--1077},
}

Although the importance of stream condition for leaf litter decomposition has been extensively studied, little is known about how processing rates change in response to altered riparian vegetation community composition. We investigated patterns of plant litter input and decomposition across 20 boreal headwater streams that varied in proportions of riparian deciduous and coniferous trees. We measured a suite of in-stream physical and chemical characteristics, as well as the amount and type of litter inputs from riparian vegetation, and related these to decomposition rates of native (alder, birch, and spruce) and introduced (lodgepole pine) litter species incubated in coarse- and fine-mesh bags. Total litter inputs ranged more than fivefold among sites and increased with the proportion of deciduous vegetation in the riparian zone. In line with differences in initial litter quality, mean decomposition rate was highest for alder, followed by birch, spruce, and lodgepole pine (12, 55, and 68% lower rates, respectively). Further, these rates were greater in coarse-mesh bags that allow colonization by macroinvertebrates. Variance in decomposition rate among sites for different species was best explained by different sets of environmental conditions, but litter-input composition (i.e., quality) was overall highly important. On average, native litter decomposed faster in sites with higher-quality litter input and (with the exception of spruce) higher concentrations of dissolved nutrients and open canopies. By contrast, lodgepole pine decomposed more rapidly in sites receiving lower-quality litter inputs. Birch litter decomposition rate in coarse-mesh bags was best predicted by the same environmental variables as in fine-mesh bags, with additional positive influences of macroinvertebrate species richness. Hence, to facilitate energy turnover in boreal headwaters, forest management with focus on conifer production should aim at increasing the presence of native deciduous trees along streams, as they promote conditions that favor higher decomposition rates of terrestrial plant litter.

@article{burrows_seasonal_2017,
	title = {Seasonal resource limitation of heterotrophic biofilms in boreal streams},
	volume = {62},
	issn = {1939-5590},
	url = {http://onlinelibrary.wiley.com/doi/10.1002/lno.10383/abstract},
	doi = {10.1002/lno.10383},
	abstract = {Unraveling the potentially shifting controls over microbial activity among habitats and across seasonal transitions is critical for understanding how freshwater ecosystems influence broader elemental cycles, and how these systems may respond to global changes. We used nutrient-diffusing substrates to investigate seasonal patterns and constraints on microbial activity of biofilms in streams draining distinct landscape features of the boreal biome (forests, mires, and lakes). Microbial respiration (MR) largely mirrored spatial and temporal variation in water temperature. However, limitation by labile carbon (C) was a constraint to microbial activity during ice-covered periods, when MR of control nutrient-diffusing substrates fell below rates predicted from stream temperature alone. Variation in C limitation among the study streams was reflective of putative organic C availability, with C limitation of biofilms weakest in the dissolved organic C (DOC)-rich, mire-outlet stream and greatest in the relatively DOC-poor, forest stream. Incidences of nutrient limitation were only observed during warmer months. Our study illustrates how variation in processes mediated by heterotrophic biofilms and seasonal shifts in resource limitation can emerge in a stream network draining a heterogeneous landscape. In addition, our results show that, for a large portion of the year, heterotrophic processes in boreal streams can be strongly limited by the availability of labile C, despite high DOC concentrations. Metabolic constraints to dissolved organic matter processing at near-freezing temperatures, coupled with hydrological controls over the delivery of more labile organic resources to streams (e.g., soil freezing and flooding), have potentially strong influences on the productivity of boreal streams.},
	language = {en},
	number = {1},
	urldate = {2017-11-17},
	journal = {Limnology and Oceanography},
	author = {Burrows, Ryan M. and Laudon, Hjalmar and McKie, Brendan G. and Sponseller, Ryan A.},
	month = jan,
	year = {2017},
	note = {00000},
	keywords = {\#nosource, Boreal forest, Dissolved organic carbon, Metabolism, Microbial processing, Resource limitation, Wetlands},
	pages = {164--176},
}

Unraveling the potentially shifting controls over microbial activity among habitats and across seasonal transitions is critical for understanding how freshwater ecosystems influence broader elemental cycles, and how these systems may respond to global changes. We used nutrient-diffusing substrates to investigate seasonal patterns and constraints on microbial activity of biofilms in streams draining distinct landscape features of the boreal biome (forests, mires, and lakes). Microbial respiration (MR) largely mirrored spatial and temporal variation in water temperature. However, limitation by labile carbon (C) was a constraint to microbial activity during ice-covered periods, when MR of control nutrient-diffusing substrates fell below rates predicted from stream temperature alone. Variation in C limitation among the study streams was reflective of putative organic C availability, with C limitation of biofilms weakest in the dissolved organic C (DOC)-rich, mire-outlet stream and greatest in the relatively DOC-poor, forest stream. Incidences of nutrient limitation were only observed during warmer months. Our study illustrates how variation in processes mediated by heterotrophic biofilms and seasonal shifts in resource limitation can emerge in a stream network draining a heterogeneous landscape. In addition, our results show that, for a large portion of the year, heterotrophic processes in boreal streams can be strongly limited by the availability of labile C, despite high DOC concentrations. Metabolic constraints to dissolved organic matter processing at near-freezing temperatures, coupled with hydrological controls over the delivery of more labile organic resources to streams (e.g., soil freezing and flooding), have potentially strong influences on the productivity of boreal streams.

@article{lucas_long-term_2016,
	title = {Long-term declines in stream and river inorganic nitrogen ({N}) export correspond to forest change},
	volume = {26},
	issn = {1939-5582},
	url = {http://onlinelibrary.wiley.com/doi/10.1890/14-2413/abstract},
	doi = {10.1890/14-2413},
	abstract = {Human activities have exerted a powerful influence on the biogeochemical cycles of nitrogen (N) and carbon (C) and drive changes that can be a challenge to predict given the influence of multiple environmental stressors. This study focused on understanding how land management and climate change have together influenced terrestrial N storage and watershed inorganic N export across boreal and sub-arctic landscapes in northern Sweden. Using long-term discharge and nutrient concentration data that have been collected continuously for over three decades, we calculated the hydrologic inorganic N export from nine watersheds in this region. We found a consistent decline in inorganic N export from 1985 to 2011 over the entire region from both small and large watersheds, despite the absence of any long-term trend in river discharge during this period. The steepest declines in inorganic N export were observed during the growing season, consistent with the hypothesis that observed changes are biologically mediated and are not the result of changes in long-term hydrology. Concurrent with the decrease in inorganic N export, we report sustained increases in terrestrial N accumulation in forest biomass and soils across northern Sweden. Given the close communication of nutrient and energy stores between plants, soils, and waters, our results indicate a regional tightening of the N cycle in an already N-limited environment as a result of changes in forest management and climate-mediated growth increases. Our results are consistent with declining inorganic N efflux previously reported from small headwater streams in other ecosystems and shed new light on the mechanisms controlling these patterns by identifying corresponding shifts in the terrestrial N balance, which have been altered by a combination of management activities and climate change.},
	language = {en},
	number = {2},
	urldate = {2017-02-01},
	journal = {Ecological Applications},
	author = {Lucas, Richard W. and Sponseller, Ryan A. and Gundale, Michael J. and Stendahl, Johan and Fridman, Jonas and Högberg, Peter and Laudon, Hjalmar},
	month = mar,
	year = {2016},
	note = {00011},
	keywords = {\#nosource, Boreal forest, Sweden, climate-mediated growth increases, forest management, soil N storage, terrestrial N retention, terrestrial biogeochemistry},
	pages = {545--556},
}

Human activities have exerted a powerful influence on the biogeochemical cycles of nitrogen (N) and carbon (C) and drive changes that can be a challenge to predict given the influence of multiple environmental stressors. This study focused on understanding how land management and climate change have together influenced terrestrial N storage and watershed inorganic N export across boreal and sub-arctic landscapes in northern Sweden. Using long-term discharge and nutrient concentration data that have been collected continuously for over three decades, we calculated the hydrologic inorganic N export from nine watersheds in this region. We found a consistent decline in inorganic N export from 1985 to 2011 over the entire region from both small and large watersheds, despite the absence of any long-term trend in river discharge during this period. The steepest declines in inorganic N export were observed during the growing season, consistent with the hypothesis that observed changes are biologically mediated and are not the result of changes in long-term hydrology. Concurrent with the decrease in inorganic N export, we report sustained increases in terrestrial N accumulation in forest biomass and soils across northern Sweden. Given the close communication of nutrient and energy stores between plants, soils, and waters, our results indicate a regional tightening of the N cycle in an already N-limited environment as a result of changes in forest management and climate-mediated growth increases. Our results are consistent with declining inorganic N efflux previously reported from small headwater streams in other ecosystems and shed new light on the mechanisms controlling these patterns by identifying corresponding shifts in the terrestrial N balance, which have been altered by a combination of management activities and climate change.

@article{hotchkiss_sources_2015,
	title = {Sources of and processes controlling {CO2} emissions change with the size of streams and rivers},
	volume = {8},
	issn = {1752-0894},
	doi = {10.1038/NGEO2507},
	abstract = {Carbon dioxide (CO2) evasion from streams and rivers to the atmosphere represents a substantial flux in the global carbon cycle(1-3). The proportions of CO2 emitted from streams and rivers that come from terrestrially derived CO2 or from CO2 produced within freshwater ecosystems through aquatic metabolism are not well quantified. Here we estimated CO2 emissions from running waters in the contiguous United States, based on freshwater chemical and physical characteristics and modelled gas transfer velocities at 1463 United States Geological Survey monitoring sites. We then assessed CO2 production from aquatic metabolism, compiled from previously published measurements of net ecosystem production from 187 streams and rivers across the contiguous United States. We find that CO2 produced by aquatic metabolism contributes about 28\% of CO2 evasion from streams and rivers with flows between 0.0001 and 19,000 m(3) s(-1). We mathematically modelled CO2 flux from groundwater into running waters along a stream-river continuum to evaluate the relationship between stream size and CO2 source. Terrestrially derived CO2 dominates emissions from small streams, and the percentage of CO2 emissions from aquatic metabolism increases with stream size. We suggest that the relative role of rivers as conduits for terrestrial CO2 efflux and as reactors mineralizing terrestrial organic carbon is a function of their size and connectivity with landscapes.},
	language = {English},
	number = {9},
	journal = {Nature Geoscience},
	author = {Hotchkiss, E. R. and Hall, R. O. and Sponseller, R. A. and Butman, D. and Klaminder, J. and Laudon, H. and Rosvall, M. and Karlsson, J.},
	month = sep,
	year = {2015},
	keywords = {\#nosource, aquatic ecosystems, budget, carbon-dioxide, cycle, inland waters, metabolism, temporal variability, united-states},
	pages = {696--+},
}

Carbon dioxide (CO2) evasion from streams and rivers to the atmosphere represents a substantial flux in the global carbon cycle(1-3). The proportions of CO2 emitted from streams and rivers that come from terrestrially derived CO2 or from CO2 produced within freshwater ecosystems through aquatic metabolism are not well quantified. Here we estimated CO2 emissions from running waters in the contiguous United States, based on freshwater chemical and physical characteristics and modelled gas transfer velocities at 1463 United States Geological Survey monitoring sites. We then assessed CO2 production from aquatic metabolism, compiled from previously published measurements of net ecosystem production from 187 streams and rivers across the contiguous United States. We find that CO2 produced by aquatic metabolism contributes about 28% of CO2 evasion from streams and rivers with flows between 0.0001 and 19,000 m(3) s(-1). We mathematically modelled CO2 flux from groundwater into running waters along a stream-river continuum to evaluate the relationship between stream size and CO2 source. Terrestrially derived CO2 dominates emissions from small streams, and the percentage of CO2 emissions from aquatic metabolism increases with stream size. We suggest that the relative role of rivers as conduits for terrestrial CO2 efflux and as reactors mineralizing terrestrial organic carbon is a function of their size and connectivity with landscapes.