Seasonal variation and release of soluble reactive phosphorus in an agricultural upland headwater in central Germany. Rode, M., Tittel, J., Reinstorf, F., Schubert, M., Knöller, K., Gilfedder, B., Merensky-Pöhlein, F., & Musolff, A. Hydrology and Earth System Sciences, 27(6):1261–1277, March, 2023.
Seasonal variation and release of soluble reactive phosphorus in an agricultural upland headwater in central Germany [link]Paper  doi  abstract   bibtex   
Abstract. Soluble reactive phosphorus (SRP) concentrations in agricultural headwaters can display pronounced seasonal variability at low flow, often with the highest concentrations occurring in summer. These SRP concentrations often exceed eutrophication levels, but their main sources, spatial distribution, and temporal dynamics are often unknown. The purpose of this study is therefore to differentiate between potential SRP losses and releases from soil drainage, anoxic riparian wetlands, and stream sediments in an agricultural headwater catchment. To identify the dominant SRP sources, we carried out three longitudinal stream sampling campaigns for SRP concentrations and fluxes. We used salt dilution tests and natural 222Rn to determine water fluxes in different sections of the stream, and we sampled for SRP, Fe, and 14C dissolved organic carbon (DOC) to examine possible redox-mediated mobilization from riparian wetlands and stream sediments. The results indicate that a single short section in the upper headwater reach was responsible for most of the SRP fluxes to the stream. Analysis of samples taken under summer low-flow conditions revealed that the stream water SRP concentrations, the fraction of SRP within total dissolved P (TDP), and DOC radiocarbon ages matched those in the groundwater entering the gaining section. Pore water from the stream sediment showed evidence of reductive mobilization of SRP, but the exchange fluxes were probably too small to contribute substantially to SRP stream concentrations. We also found no evidence that shallow flow paths from riparian wetlands contributed to the observed SRP loads in the stream. Combined, the results of this campaign and previous monitoring suggest that groundwater is the main long-term contributor of SRP at low flow, and agricultural phosphorus is largely buffered in the soil zone. We argue that the seasonal variation of SRP concentrations was mainly caused by variations in the proportion of groundwater present in the streamflow, which was highest during summer low-flow periods. Accurate knowledge of the various input pathways is important for choosing effective management measures in a given catchment, as it is also possible that observations of seasonal SRP dilution patterns stem from increased mobilization in riparian zones or from point sources.
@article{rode_seasonal_2023,
	title = {Seasonal variation and release of soluble reactive phosphorus in an agricultural upland headwater in central {Germany}},
	volume = {27},
	copyright = {https://creativecommons.org/licenses/by/4.0/},
	issn = {1607-7938},
	url = {https://hess.copernicus.org/articles/27/1261/2023/},
	doi = {10.5194/hess-27-1261-2023},
	abstract = {Abstract. Soluble reactive phosphorus (SRP) concentrations in
agricultural headwaters can display pronounced seasonal variability at low
flow, often with the highest concentrations occurring in summer. These SRP
concentrations often exceed eutrophication levels, but their main sources,
spatial distribution, and temporal dynamics are often unknown. The purpose
of this study is therefore to differentiate between potential SRP losses and
releases from soil drainage, anoxic riparian wetlands, and stream sediments
in an agricultural headwater catchment. To identify the dominant SRP sources,
we carried out three longitudinal stream sampling campaigns for SRP
concentrations and fluxes. We used salt dilution tests and natural
222Rn to determine water fluxes in different sections of the stream,
and we sampled for SRP, Fe, and 14C dissolved organic carbon (DOC) to examine possible redox-mediated
mobilization from riparian wetlands and stream sediments. The results
indicate that a single short section in the upper headwater reach was
responsible for most of the SRP fluxes to the stream. Analysis of samples
taken under summer low-flow conditions revealed that the stream water SRP
concentrations, the fraction of SRP within total dissolved P (TDP), and DOC radiocarbon ages matched those in the groundwater
entering the gaining section. Pore water from the stream sediment showed
evidence of reductive mobilization of SRP, but the exchange fluxes were
probably too small to contribute substantially to SRP stream concentrations.
We also found no evidence that shallow flow paths from riparian wetlands
contributed to the observed SRP loads in the stream. Combined, the results of
this campaign and previous monitoring suggest that groundwater is the main
long-term contributor of SRP at low flow, and agricultural phosphorus is
largely buffered in the soil zone. We argue that the seasonal variation of
SRP concentrations was mainly caused by variations in the proportion of
groundwater present in the streamflow, which was highest during summer low-flow periods. Accurate knowledge of the various input pathways is important
for choosing effective management measures in a given catchment, as it is
also possible that observations of seasonal SRP dilution patterns stem from
increased mobilization in riparian zones or from point sources.},
	language = {en},
	number = {6},
	urldate = {2024-11-15},
	journal = {Hydrology and Earth System Sciences},
	author = {Rode, Michael and Tittel, Jörg and Reinstorf, Frido and Schubert, Michael and Knöller, Kay and Gilfedder, Benjamin and Merensky-Pöhlein, Florian and Musolff, Andreas},
	month = mar,
	year = {2023},
	pages = {1261--1277},
}
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