NITROGEN CYCLING AND ESTUARINE INTERFACES: SOME CURRENT CONCEPTS AND RESEARCH DIRECTIONS. Kemp, W. M., Wetzel, R. L., Boynton, W. R., D'Elia, C. F., & Stevenson, J. C. In Estuarine Comparisons. 1982.
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The role of physical interfaces in estuarine nitrogen (N) dynamics is discussed. We consider here: four N-transformation processes (uptake, regeneration, de nitrification, nitrification) and five interfaces (water mass fronts and transitions, watershed-estuarine boundaries, the pycnocline of stratified estuaries, the sediment-water boundary, the redox discontinuity layer). Seven examples are presented. First, we show that phytoplankton production and, in turn, NH+4 recycling can be stimulated at interfaces where two water masses meet, with one being relatively clear and the other nutrient-rich. Second, data are provided to illustrate that N recycling rates tend to exceed (by 2–8 fold) inputs of “new” N entering across watershed-estuary boundaries, although annual net primary production is more a function of the latter. Third, we argue that periodic occurrences of high NH+4 concentrations in strongly stratified water columns reflect active NH+4 oxidation at the estuarine pynocline. Fourth, evidence is given to indicate that intensive remineralization of NH+4 occurs in the uppermost flocculent layer of sediments, and that fluxes estimated from diagenic modeling would tend to overlook this. Next, we show that denitrification, which is concentrated near the sediment redox discontinuity layer (RDL), may be a major component of estuarine N budgets (50–60% of NH+4 recycling). Sixth, we indicate that de nitrification can be fueled either by sediment nitrification just above the RDL or via NO−3 diffusion from overlying waters. Seventh, recent experimental results are considered to demonstrate the effects of macrophytic roots enhancing nitrification (and possibly denitrification) by transporting O2 and deepening the oxidized zone of sediments. Finally, we propose some generic properties of estuarine interfaces which may account for their importance in N cycling.
@incollection{kemp_nitrogen_1982,
	title = {{NITROGEN} {CYCLING} {AND} {ESTUARINE} {INTERFACES}: {SOME} {CURRENT} {CONCEPTS} {AND} {RESEARCH} {DIRECTIONS}},
	abstract = {The role of physical interfaces in estuarine nitrogen (N) dynamics is discussed. We consider here: four N-transformation processes (uptake, regeneration, de nitrification, nitrification) and five interfaces (water mass fronts and transitions, watershed-estuarine boundaries, the pycnocline of stratified estuaries, the sediment-water boundary, the redox discontinuity layer). Seven examples are presented. First, we show that phytoplankton production and, in turn, NH+4 recycling can be stimulated at interfaces where two water masses meet, with one being relatively clear and the other nutrient-rich. Second, data are provided to illustrate that N recycling rates tend to exceed (by 2–8 fold) inputs of “new” N entering across watershed-estuary boundaries, although annual net primary production is more a function of the latter. Third, we argue that periodic occurrences of high NH+4 concentrations in strongly stratified water columns reflect active NH+4 oxidation at the estuarine pynocline. Fourth, evidence is given to indicate that intensive remineralization of NH+4 occurs in the uppermost flocculent layer of sediments, and that fluxes estimated from diagenic modeling would tend to overlook this. Next, we show that denitrification, which is concentrated near the sediment redox discontinuity layer (RDL), may be a major component of estuarine N budgets (50–60\% of NH+4 recycling). Sixth, we indicate that de nitrification can be fueled either by sediment nitrification just above the RDL or via NO−3 diffusion from overlying waters. Seventh, recent experimental results are considered to demonstrate the effects of macrophytic roots enhancing nitrification (and possibly denitrification) by transporting O2 and deepening the oxidized zone of sediments. Finally, we propose some generic properties of estuarine interfaces which may account for their importance in N cycling.},
	booktitle = {Estuarine {Comparisons}},
	author = {Kemp, W. Michael and Wetzel, Richard L. and Boynton, Walter R. and D'Elia, Christopher F. and Stevenson, J. Court},
	year = {1982},
	doi = {10.1016/b978-0-12-404070-0.50018-1},
	keywords = {Environmental Interactions, Processes, and Modeling}
}

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