[Output characteristics of non-point phosphorus from a typical small watershed in Yimeng mountainous area under the special rainfall].

The relationships between pollutant concentrations and precipitation-runoff combined with the first and maximum intensity natural rainfall events were monitored at the outlets of the Menglianggu watershed in 2010. The results showed that dissolved organic phosphorus (DOP), dissolved inorganic phosphorus (DIP), total dissolved phosphorus (DP), total particle phosphorus (PP) and total phosphorus (TP) concentrations in the first rainfall were higher than those in the maximum intensity rainfall which was the largest average rainfall intensity, but the output of phosphorusin the first rainfall was all higher than that in the maximum intensity rainfall except dissolved organic phosphorus. The DOP, DIP, DP, PP and TP in two special rainfall events contributed 48%, 81%, 70%, 87% and 81% of the total output of rainy season. DP and TP were mainly composed by DIP and PP respectively. The two special rainfalls have the first flush effect and the maximum intensity rainfall was stronger than the first rainfall, so the analysis of M (V) curve showed that the priority should be given to the interception of corresponding phosphorus under special events. The regression analysis results showed that a linear relation existed between runoff and nutrient output, but there were some differences which the slope of the linear equation of the first rainfall was higher than that of the maximum intensity rainfall. Reducing agricultural practices such as tillage and fertilization during special rainfall period and building canals, ponds are effective ways for mitigating agricultural non-point source pollution.