Study On Simulation Of Non-point Source Pollution Of Xiangtan Watershed In Sichuan Province

Due to the presence of slope cropland and the rapid development of livestock and poultry industry in the hilly agricultural area, non-point source pollution(NSP) has become an important factor restricting the sustainable development of economy and environment in Sichuan Province. With the fast development of 3S technology, many domestic experts and scholars use SWAT model to study NSP, while the hydrology and water quality data are relatively intact in most of the target drainage basins. In China, there is a gap in the study of NSP problems on predictions in ungauged basins(PUB). And it is expected that this paper can be great reference for research on NSP and water environment.This paper selected a typical hilly agricultural region, Xiangtan basin, as the object of study. Based on 3S technology, field investigation, laboratory experiment and other means, the study constructed the basis database of spatial and attribute information for SWAT(Soil and Water Assessment Tool) model. Then SWAT model as well as L-THIA(Long-Term Hydrologic Impact Assessment) model was used to estimate the NSP of the study area, under the circumstance of lacking true runoff data. On this basis, spatiotemporal distribution characteristics and influencing factors of NSP were analysed, and effective management measures were put forward to cut NSP output. In this paper, the main results were as follows:(1) On the basis of parameter sensitivity analysis, parameters of SWAT model were calibrated and validated. By contrasting the simulation accuracy of SWAT model, L-THIA model and L-THIA-SWAT coupled model, the precision of NSP simulation by L-THIASWAT coupled model proved the highest. Thus, the method that L-THIA-SWAT coupled model was used to simulated NSP, was suitable for the study basin.(2) Temporal distribution analysis indicated that, yearly changing trends of TN(Total Nitrogen) and TP(Total Phosphorus) output were similar, and NSP loads were concentrated in the rain season in a year. Furthermore, liner correlation analysis was respectively conducted between rainfall and TN load, TP load, and the R2 value was 0.86 and 0.86 respectively. The result concluded that rainfall impacted NSP seriously.Spatial distribution analysis showed that, TN load ranged from 20.4 kg/ha/moth to 97.7 kg/ha/moth and TP load was from 2.8 kg/ha/moth to 8.7 kg/ha/moth. According to the standard GB3838-2002, TN and TP concentration were both high. Even more specifically, TN concentration was over â…¤ standard and TP concentration was over â…£ standard in most of sub-basins.(3) Influencing factors analysis to NSP distribution showed that: for land use tupes, the main contributor were urban land and farmland, while woodland had certain inhibition to NSP; for soil types, paddy soil had a greater impact; for slope classes, NSP was mainly focused on relatively flat areas. On the basis of influencing factors analysis, some effective management measures, that could cut NSP output, were put forward, such as grain for green, balanced fertilization, standardized livestock and poultry breeding and so on.