Low threshold for nitrogen concentration saturation in headwaters increases regional and coastal delivery

Environmental Research Letters
By: , and 



River corridors store, convey, and process nutrients from terrestrial and upstream sources, regulating delivery from headwaters to estuaries. A consequence of chronic excess nitrogen loading, as supported by theory and field studies in specific areas, is saturation of the biogeochemically-mediated nitrogen removal processes that weakens the capacity of the river corridor to remove nitrogen. Regional nitrogen models typically assume that removal capacity exhibits first-order behavior, scaling positively and linearly with increasing concentration, which may bias the estimation of where and at what rate nitrogen is removed by river corridors. Here we estimate the nitrogen concentration saturation threshold and its effects on nitrogen export from the Northeastern United States, revealing an average 42% concentration-induced reduction in headwater removal capacity. The weakened capacity caused an average 10% increase in the predicted delivery of riverine nitrogen from urban and agricultural watersheds compared to estimates using first-order process assumptions. Our results suggest that nitrogen removal may fall below a first-order process at a low riverine threshold concentration of 0.5 mg N L-1. Threshold behavior indicates that even modest mitigation of nitrogen concentration in river corridors above the threshold can cause a self-reinforcing boost to nitrogen removal.

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Publication type Article
Publication Subtype Journal Article
Title Low threshold for nitrogen concentration saturation in headwaters increases regional and coastal delivery
Series title Environmental Research Letters
DOI 10.1088/1748-9326/ab751b
Volume 15
Issue 4
Year Published 2020
Language English
Publisher IOP Publishing
Contributing office(s) John Wesley Powell Center for Analysis and Synthesis, WMA - Earth System Processes Division
Description 044018, 10 p.
Country United States
State Connecticut, District of Columbia, Delaware, Massachusetts, Maryland, Maine, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Virginia, Vermont, West Virginia
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