Nonpoint source nutrient Ioad from a subcatchm ent with a rice cultivation and m ultipond system

A small subwatershed of Chaohu Lake was chosen for research on the relationships of landuse，nonpoint source pollution and its prevention．The distributions of nitrogen and phosphorus in the different land use types were shown by monitoring N and P in water samples from rainfall，surface runoff,ponds，a stream and the lake，and in soil samples from rice fields，nonirrigated land and mountain forests．A multi-pond agroecosystem was found to prevent the nonpoint source pollutants and sediment loading to eutrophic Chaohu Lake from its catchment area，because this multi-pond system can effectively keep water and nutrients inside the catchment area and be reused to irrigate the rice field．It requires only a Small investment and energy consumption．and that is suitable for this large under-development agricultural watershed．