Net anthropogenic phosphorus inputs and riverine phosphorus fluxes in highly populated headwater watersheds in China

Riverine phosphorus (P) levels in headwaters are a worldwide concern for environmental management due to the sensitivity of freshwater ecosystems to phosphorus loads. Here, we evaluate P in the Huai River Basin of China, a watershed with one of the highest intensities of human-activity in the world. Estimates of net anthropogenic phosphorus inputs (NAPI) were obtained by accounting for the main anthropogenic phosphorus inputs in each watershed of the basin, including fertilizer application, net food and feed import, non-food P and seeding P. Multi-year average (2003-2010) anthropogenic inputs of P to the entire basin were 2700 kg P km(-2) year(-1), with an average amount of 1800 kg P km(-2) year(-1) entering its 17 headwater watersheds. Fertilizer application was the largest source of new P across the headwater watersheds (about 70 % of NAPI), followed by P content of imported food and feed (24 %) and non-food P (6 %). Riverine total phosphorus (TP) fluxes showed a significant linear relationship with NAPI, with an average 3.2 % of NAPI exported as riverine TP flux. Our result indicates that NAPI could be a good indicator for assessing the risk of regional P loss, as well as an excellent potential predictor of riverine TP flux. A comparison of our results with other similar analyses suggests that around 3 % of NAPI would be exported as riverine TP loads, although fractional export of P may vary significantly regionally. Corresponding P management should be targeted at the main anthropogenic sources and hot-spot areas.