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 (NAPIAF) and residential (NAPIR) systems for the upper Jiaojiang watershed in eastern China. Annual NAPIAF rose by 73% in 1980–1999 followed by a 41% decline in 2000–2011, while NAPIR 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 NAPIAF, NAPIR, 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 NAPIAF, NAPIR, 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 NAPIAF, NAPIR 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 NAPIAF, reduction of NAPIR was predicted to have a greater immediate impact on decreasing riverine TP fluxes. Changes in anthropogenic P input sources (NAPIAF vs. NAPIR), 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.