Modeling increased riverine nitrogen export: Source tracking and integrated watershed-coast management

The global NEWS model was calibrated and then used to quantify the long term trend of dissolved inorganic nitrogen (DIN) export from two tributaries of Jiulong River (SE China). Anthropogenic N inputs contributed 61-92% of river DIN yield which increased from 337 in 1980s to 1662 kg N km− 2 yr− 1 in 2000s for the North River, and from 653 to 3097 kg N km− 2 yr− 1 for the West River. North River and West River contributed 55% and 45% respectively of DIN loading to the estuary. Rapid development and poor management driven by national policies were responsible for increasing riverine N export. Scenario analysis and source tracking suggest that reductions of anthropogenic N inputs of at least 30% in the North River (emphasis on fertilizer and manure) and 50% in the West River (emphasis on fertilizer) could significantly improve water quality and mitigate eutrophication in both river and coastal waters.