Dynamic phosphorus budget for lake-watershed ecosystems

Lake eutrophication caused by excess phosphorus(P) loading from point sources(PS) and nonpoint sources(NPS) is a persistent and serious ecological pro blem in China. A phosphorus budget, based on material flow analysis(MFA) and sys tem dynamic(SD), is proposed and applied for the agriculture-dominated Qionghai Lake watershed located in southwestern China. The MFA-SD approach will not only cover the transporting process of P in the lake-watershed ecosystems, but also c an deal with the changes of P budget due to the dynamics of watershed. P inflows include the fertilizer for agricultural croplands, soil losses, domestic sewage discharges, and the atmospheric disposition such as precipitation and dust sink ing. Outflows are consisted of hydrologic export, water resources development, f ishery and aquatic plants harvesting. The internal P recycling processes are als o considered in this paper. From 1988 to 2015, the total P inflows for Lake Qio nghai are in a rapid increase from 35.65 to 78.73 t/a, which results in the risi ng of P concentration in the lake. Among the total P load 2015, agricultural los s and domestic sewage account for 70.60% and 17.27% respectively, directly relat ed to the rapid social-economic development and the swift urbanization. Future m anagement programs designed to reduce P inputs must be put into practices in the coming years to ensure the ecosystem health in the watershed.