Study on relationship between agricultural nonpoint source pollution output and rainfall runoff in the typical small watershed of the three Gorges Reservoir Area

Based on long term observation, the relationship between agricultural nonpoint source pollution output and rainfall runoff has been studied in Chenjiagou small basin (8 km²) and Daijiagou small watershed (0.67 km²)of the Three Georges Reservoir Area in Chongqing, southwest of China. The results showed that: a) The peak rainfall and runoff performed the similar variation trace in both of catchments in 2009 and the runoff played a major role in the output of nonpoint source pollution; b) Total nitrogen (TN) and total phosphorus (TP) concentration varied with consistent trend, but TN was more changeable with rainfall runoff than TP; c) TN losses was fluctuation in real time by rainfall runoff, however, TP losses showed a trend of increasing month by month, in addition, both of TN and TP are less changeable and less sensitively in Chenjiagou small basin than both of them in Daijiagou small watershed.; d) Variation of nitrogen to phosphorus ratio was similar to the TN concentration, and showed a good coupling relationship with the runoff fluctuation, TN played an important role in the nonpoint source pollution output in both of catchments; e) Significantly difference appeared in cumulative percentage between rainfall runoff peak time and TN and TP in 2009, and it´s suggesting that nonpoint source pollution has a larger random and dispersion, there is no strict correspondence between them; f)The cumulative percentage of rainfall with runoff, TN with TP showed a good common features, what´s more TN and TP changed significantly affected by the rainy season.