ABSTRACT
This study quantified nonpoint nitrogen (NPS-N) sources and sinks across the 14,582 km2 Neuse River Basin (NRB) located in North Carolina, to provide tabular data summaries and graphic overlay products to support the development of management approaches to best achieve established N reduction goals. First, a remote sensor–derived land-cover classification was performed to support modeling needs. Modeling efforts included the development of a mass balance modeling to quantify potential N sources and sinks, followed by a precipitation event–driven hydrologic modeling to effectively transport excess N across the landscape to individual stream reaches to support subsequent labeling of transported N values corresponding to source origin. Results indicated that agricultural land contributed 55% of the total annual NPS-N loadings, followed by forested land at 23% (background), and urban areas at 21%. Average annual N source contributions were quantified for agricultural (1.4 kg/ha), urban (1.2 kg/ha), and forested cover types (0.5 kg/ha). NPS-N source contributions were greatest during the winter (40%), followed by spring (32%), summer (28%), and fall (0.3%). Seasonal total N loadings shifted from urban and forest-dominated sources during the winter, to agricultural sources in the spring and summer. A quantitative assessment of the significant NRB land-use activities indicated that high (>70% impervious) and medium (>35% impervious) density urban development were the greatest contributors of NPS-N on a unit area basis (1.9 and 1.6 kg/ha/yr, respectively), followed by row crops and pasture/hay cover types (1.4 kg/ha/yr).
