How to avoid coastal eutrophication - a back-casting study for the North China Plain.

Eutrophication is a serious problem in Chinese seas. We explore possibilities to avoid coastal eutrophication without compromising food production in the North China Plain. We used the Model to Assess River Inputs of Nutrient to seAs (MARINA 1.0) for back-casting and scenario analysis. Avoiding coastal eutrophication by 2050 implies required reductions in river export of total nitrogen (TN) and phosphorus (TP) by 50-90% for the Hai, Huai and Huang rivers. We analyzed the potential to meet these targets in 54 scenarios assuming improvements in manure recycling, fertilizer application, animal feed and wastewater treatment. Results indicate that combining manure recycling while reducing synthetic fertilizer use are effective options to reduce nutrient inputs to seas. Without such options, direct discharge of manure are important sources of water pollution. In the 7-25 scenarios with the low eutrophication potential, 40-100% of the N and P in untreated manure is recycled on land to replace synthetic fertilizers. Our results can support the formulation of effective environmental policies to avoid coastal eutrophication in China.