Abstract:

The Chenxi Reservoir (now Xijian lake) is a unique surface water resource of Chuzhou city.The nonpoint source pollution is the main reason of its water quality deterioration.Distributed nonpoint source pollution modelling in its watershed can identify the critical source areas.It can be taken as the grounds on making decision for protection of drinking water source and control of source pollution in the Chenxi Reservoir.
Based on the pattern of Land use/cover (LULC),a model was established to simulate the quantity of nonpoint source pollution exported to aquatic environment and retained by the different LULC on each cell according to these theories that the generation,retaining,flow accumulation and relative source and sink theory of nonpoint source pollution.This study chose phosphorus as an example and did a simulation in the watershed of the Chenxi Reservoir.The results showed that the region beside the riverway in the middle of watershed and the Xiaosha River feeding the reservoir were the high hydraulic connectivity area.In 2000 and 2010,total phosphorus exported to the reservoir by LULC in watershed was 2 58038 and 2 46120 kg/a,respectively.The Institute of Agricultural Science,Chengjiao Residents Committee,the Institute of Aquaculture as well as Taiping Village in northwestern of watershed were the critical source areas (CSA).Most of the exported phosphorus were effectively retained by the different LULC in the process of flow accumulation.In 2000 and 2010,total phosphorus retained by LULC in watershed was 5 77449 and 5 42236 kg/a,respectively.It occupied 691% and 68.8% of the total phosphorus loads.The abilities of phosphorus retention by forestland and grassland were not brought into full play due to the irrational distribution of existing LULC.Although the ability of phosphorus retention by paddy fields is relative weak,the average phosphorus retained was the highest because the paddy fields were mainly distributed in the hydrological sensitive area (HSA).Total phosphorus retained by the paddy fields in watershed was 3 84724 and 3 54168 kg/a,respectively.It occupied 666% and 653% of the total phosphorus retention.
Trees and shrubs should be planted along the shore and on the intersection of runoff.The grassland should have a banding distribution nearby the gentle slope of farmland.Therefore,it can largely improve the ecosystem services efficiency of forestland and grassland by setting vegetation buffer zones.