Phosphorus loss and its estimation in a small watershed of the Yimeng mountainous area, China

Non-point source pollution is severe in the Yimeng Mountainous Area of China. Few studies have been conducted to identify and predict phosphorus loss at a watershed scale in this region. The objectives of this study were to identify the characteristics of phosphorus loss and further to develop regression models to estimate phosphorus losses of different forms based on the dataset of measured rainfall, runoff, and sediment of 24 rainfall events during the period of 2010–2011 in a typical small watershed from Yimeng Mountainous Area. The results revealed that phosphorus (P) loss differed considerably with phosphorus forms. The dissolved inorganic phosphorus (DIP) was the dominant form of the total dissolved phosphorus (TDP) loss by runoff, accounting for 72 %. The ratio of particulate phosphorus (PP) to total phosphorus (TP) was 65 %, which indicated that most of phosphorus loss was transported by eroded sediment. Similar to soil loss, rainfall properties influenced phosphorus loss greatly and most of the phosphorus loss was produced by only a few heavy storms. The concentrations of different phosphorus forms during a rainfall event varied with similar trends and reached the maxima prior to the peak runoff. Phosphorus losses of different forms were influenced by rainfall kinetic energy, runoff volume, and sediment loss significantly. DIP, TDP, and TP could be predicted with rainfall kinetic energy and runoff volume satisfactorily (NSE ≥ 0.92). PP was estimated with rainfall kinetic energy, runoff volume, and sediment loss of rainfall event well (NSE = 0.90). Further studies are necessary to assess the performance of the developed models under different conditions.