Factors controlling phosphorus export from agricultural/forest and residential systems to rivers in eastern China, 1980-2011

This study quantified long-term response of riverine total phosphorus (TP) export to changes in land-use, climate, and net anthropogenic phosphorus inputs to agricultural/forest (NAPI(AF)) and residential (NAPI(R)) systems for the upper Jiaojiang watershed in eastern China. Annual NAPI(AF) rose by 73% in 1980-1999 followed by a 41% decline in 2000-2011, while NAPI(R) continuously increased by 122% over the 1980-2011 period. Land-use showed a 63% increase in developed land area (D%) and a 91% increase in use of efficient drainage systems on agricultural land area (AD%) over the study period. Although no significant trends were observed in annual river discharge or precipitation, the annual number of storm events rose by 90% along with a 34% increase in the coefficient of variation of daily rainfall. In response to changes of NAPI(AF), NAPI(R), land-use and precipitation patterns, riverine TP flux increased 16.0-fold over the 32 year record. Phosphorus export via erosion and leaching was the dominant pathway for P delivery to rivers. An empirical model incorporating annual NAPI(AF), NAPI(R), precipitation, D%, and AD% was developed (R-2 = 0.96) for apportioning riverine TP sources and predicting annual riverine TP fluxes. The model estimated that NAPI(AF), NAPI(R) and legacy P sources contributed 19-56%, 16-67% and 13-32% of annual riverine TP flux in 1980-2011, respectively. Compared to reduction of NAPI(AF), reduction of NAPI(R) was predicted to have a greater immediate impact on decreasing riverine TP fluxes. Changes in anthropogenic P input sources (NAPI(AF) vs. NAPI(R)), land-use, and precipitation patterns as well as the legacy P source can amplify P export from landscapes to rivers and should be considered in developing P management strategies to reduce riverine P fluxes. (C) 2015 Elsevier B.V. All rights reserved.