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A comparison of NEWS and SPARROW models to understand sources of nitrogen delivered to US coastal areas
Citation:
McCrackin, M. L., J. A. Harrison, AND J. E. COMPTON. A comparison of NEWS and SPARROW models to understand sources of nitrogen delivered to US coastal areas . BIOGEOCHEMISTRY. Springer, New York, NY, 114:281-297, (2013).
Impact/Purpose:
Nitrogen (N) loading to water bodies can result in eutrophication-related hypoxia and degraded water quality.
Description:
The relative contributions of different anthropogenic and natural sources of in-stream nitrogen (N) cannot be directly measured at whole-watershed scales. Hence, source attribution estimates beyond the scale of small catchments must rely on models. Although such estimates have been accomplished using individual models, there has not yet been a comparison of N source attribution predictions at large spatial scales. We compared results from two models applied to the continental US: Nutrient Export from WaterSheds (NEWS) and SPAtially Referenced Regressions On Watersheds (SPARROW). NEWS and SPARROW predictions for total N delivery to the US coastal zone were 373 and 429 kg N km−2 year−1, respectively, for the contemporary period. Despite differences in how inputs were represented and defined by the models, NEWS and SPARROW both identified the same single-largest N sources for 67 % of the surface area that drains to the US coastal zone. When only anthropogenic sources were considered, agreement increased to 78 % of surface area. Fertilizer and crop N-fixation were dominant in the Mississippi River Basin, where the bulk of agricultural lands are located. Sewage and population-related sources were most important in urban areas and natural N (primarily N-fixation on non-agricultural land) was most important in the Pacific Northwest. Attribution to fertilizer plus crop N-fixation, atmospheric deposition, and sewage and population-related sources was generally greater by SPARROW than NEWS, and the reverse was true for manure and natural sources. Nonetheless, both models agreed in attributing 62–81 % of N delivered to the coastal zone in the continental US to human activities.
