The Nonpoint Sources and Transport of Baseflow Nitrogen Loading Across a Developed Rural?Urban Gradient

Nonpoint source urban nutrient loading into streams and receiving water bodies is widely recognized as a major environmental management challenge. A dominant research paradigm assumes that primarily derives from elevated stormwater. However, baseflow can account for large portion of total loading, especially low development intensity watersheds which comprise the largest areas. We investigated sources drivers nonpoint nitrogen across 27 headwater catchments in urbanized Piedmont region North Carolina, USA. Nitrate isotopes, predictors concentration-discharge (CQ) slopes, mean annual dissolved (TDN) suggest wastewater was developed likely contributing 61% nitrate septic served 49% sewer catchments. Our findings subsurface TDN abundant, largely transport limited, hydrogeomorphic position sanitary infrastructure strongly influences transport. an empirical model showing catchment increased with topographic wetness index location, convergent sloping land area, parcel density, residual agricultural landcover (R2 = 0.78). extended this to study region's 1,436 small (0.3–20.8 sq km) estimated up 92.7% comes medium catchments, wet areas landscape accounts 39% regional loading. indicates managing will require addressing lower infrastructure.