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Disaggregating Landscape‐Scale Nitrogen Attenuation Along Hydrological Flow Paths
Author(s) -
Jawitz J.W.,
Desormeaux A.M.,
Annable M.D.,
Borchardt D.,
Dobberfuhl D.
Publication year - 2020
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2019jg005229
Subject(s) - attenuation , environmental science , hydrology (agriculture) , vadose zone , nonpoint source pollution , watershed , aquifer , drainage basin , soil science , surface runoff , groundwater , geology , geography , soil water , ecology , geotechnical engineering , cartography , computer science , machine learning , biology , physics , optics
Evaluating how nitrogen (N) sources are attenuated throughout the landscape is critical to further our understanding of catchment‐scale N budgets. We developed a catchment‐scale N budget for a mixed land use karst springshed using in situ measurements (nitrate leaching fluxes and attenuation) and long‐term records (surface N inputs and spring exports) to estimate 20‐year average landscape‐scale N loading, attenuation, and export. We introduce a conceptual model framework to compute N export that can be applied consistently for point or nonpoint sources. The model is based on the product of only four components for each N source: population density or proportion of land cover, P ; specific load, L ; anthropogenic attenuation, A ; and natural attenuation, N . The product of these components is computed for each N source and then integrated at the basin scale. The concise PLAN model framework predicted attenuation of 90% ± 3% of N inputs, in close agreement with the estimate based on measured spring mass discharge (87% ± 3%). Further, when this attenuation is disaggregated along the hydrological flow path, we estimate that 64% of inputs are lost in the surface soil, 20% in the vadose zone, and 6% in the aquifer. Livestock and human wastes were estimated to be the dominant contributors to spring N export, which was independently supported by isotopic data. The PLAN model is a simple, transferable framework that supports systematically computing N export based on proportioning of load and attenuation. Identifying the main sources of N ultimately contributing to discharged N loads is a critical step toward source‐related water‐quality management.