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

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dc.contributor.authorSchmadel, Noah M.en
dc.contributor.authorHarvey, Judson W.en
dc.contributor.authorAlexander, Richard B.en
dc.contributor.authorBoyer, Elizabeth W.en
dc.contributor.authorSchwarz, Gregory E.en
dc.contributor.authorGomez-Velez, Jesus D.en
dc.contributor.authorScott, Durelle T.en
dc.contributor.authorKonrad, Christopher P.en
dc.contributor.departmentBiological Systems Engineeringen
dc.date.accessioned2020-05-05T19:12:12Zen
dc.date.available2020-05-05T19:12:12Zen
dc.date.issued2020-04en
dc.description.abstractRiver 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 watersheds, 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 annual 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 rate process as riverine concentration increases above a threshold 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.en
dc.description.notesThe US Geological Survey (USGS) River Corridor Working Group developed the project idea in their meetings at the JohnWesley Powell Center with support from the USGS and the National Science Foundation Hydrologic Sciences Program. NMS, JWH, RBA, GES, and CPK also received support from the USGS Water Resources Availability Program. NMS was additionally supported by a USGS Mendenhall Postdoctoral Fellowship. EWB and DS received support from the US Department of Agriculture National Institute of Food and Agriculture. JDGV received support from the US Department of Energy Subsurface Biogeochemistry Research Program as part of Pacific Northwest National Laboratory's scientific focus area. DS also received support from the Virginia Agricultural Experimental Station. The SPARROW source code is also publicly available (https://water.usgs.gov/nawqa/sparrow/). Expressions and equations in the Methods section can be used to reproduce the results. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US Government. The authors declare no competing interests.en
dc.description.sponsorshipUSGSUnited States Geological Survey; National Science Foundation Hydrologic Sciences ProgramNational Science Foundation (NSF)NSF - Directorate for Geosciences (GEO); USGS Water Resources Availability Program; USGS Mendenhall Postdoctoral FellowshipUnited States Geological Survey; US Department of Agriculture National Institute of Food and AgricultureUnited States Department of Agriculture (USDA); US Department of Energy Subsurface Biogeochemistry Research Program, Pacific Northwest National Laboratory's scientific focus area; Virginia Agricultural Experimental Stationen
dc.format.mimetypeapplication/pdfen
dc.identifier.doihttps://doi.org/10.1088/1748-9326/ab751ben
dc.identifier.issn1748-9326en
dc.identifier.issue4en
dc.identifier.orcidScott, Durelle T. [0000-0002-5792-789X]en
dc.identifier.other44018en
dc.identifier.urihttp://hdl.handle.net/10919/97974en
dc.identifier.volume15en
dc.language.isoenen
dc.rightsCreative Commons Attribution 4.0 Internationalen
dc.rights.urihttp://creativecommons.org/licenses/by/4.0/en
dc.subjectregional nitrogen budgeten
dc.subjectnitrogen concentration saturationen
dc.subjectheadwatersen
dc.subjectriver corridoren
dc.titleLow threshold for nitrogen concentration saturation in headwaters increases regional and coastal deliveryen
dc.title.serialEnvironmental Research Lettersen
dc.typeArticle - Refereeden
dc.type.dcmitypeTexten
dc.type.dcmitypeStillImageen
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