Study Of Non-point Source Pollution In Jialing River Watershed And Its Effects On Water In The City Zone Of Chongqing

High concentration of total nitrogen (TN) and total phosphorus (TP) are the basic cause of water eutrophication. With the change in hydrological conditions since the impoundment of Three Gorges reservoir, potential issue of eutrophication becomes an important problem to solve. Non-point source of TN and TP pollution become a major potential threat of eutrophication to Three Gorges reservoir under the condition of point source pollution have been controlled gradually. Jialing River is the biggest tributary of the Three Gorges Reservoir, and also one of the biggest implicit inputs of TN and TN pollution to it. To improve water quality and protect water environment in the Three Gorges reservoir area, researches on spatial and temporal changes and control measures of non-point source of TN and TP pollution are of important theoretical significance and practical value.As a result of randomness, intensive and uncertainty characteristics of non-point source pollution,the quantitative research of its load and taking control measures on it are both very difficult. Therefore, simulation study of its production and the transport process by establishing mathematic models is an important method of quantifying non-point source pollution load and evaluating management effectiveness at present. In order to control effectively the non-point source pollution in the Jialing River watershed and improve the reservoir water quality, simulation method was taken to study the tempotal and spatial variation of non-point source pollution of TN and TP as well as its environmetal effect on receiving water. At first, based on the distributed hydrological model SLURP, a model of dissolved non-point source pollution load from land-uses, rural life, livestock and poultry raising was established. Then, a new dynamic estimation methods which can reflect yearly sediment yield change of Jialing River watershed was proposed based on the RUSLE model and by proposing a comprehensive influence factor which can reflect the effect of hydrology condition and human activities on sediment yield as well as by considering the space and time differences of sediment delivery ratio from the aspect of delivery route. Then, a non-point source pollution annual load model of particulate TN and TP of Jialing River watershed was established. On this basis, a dynamic non-point source pollution load model of Jialing River watershed was established by organic coupling of the sub-models in the GIS platform. The established load model has been verified by observation data. By the established model, the temporal and spatial distribution of non-point source TN and TP pollution generated by land-uses, rural living, domestic animal raising, water and soil loss in the Jialing River watershed range from 1990 to 2007. And the contribution rate of pollution from different sources, the pollution form, the key "Contribution Zones" were analysed quantitatively. In terms of results of the analysis, the district with serious pollution needed to put much emphasis on controlling was pointed out and the corresponding best management measures were suggested. In order to study of the transport and conversion feature of non-point source pollution in the receiving water, an ecological dynamic model was combined with the established non-point source pollution load model to form a model system. By the ecological dynamic model, the hydrodynamic characteristics, nitrogen and phosphorus concentration and chlorophyll a concentration in Jialing River in the city zone of Chongqing were simulated and analysised.In this paper, the main research results are as follow:â‘ Introducing SLURP hydrological model for the first time in the simulation study of non-point source pollution to replaces the SCS-CN statistic model which majority of non-point source pollution models used, making use of its advantages of physical mechanism, applicable for large-scale mountain watershed, taking different land-use types as hydrological response unit, through parameters optimization and certification, the simulation accuracy of rainfall runoff which is driving forces of non-point source pollution was increased. As a result, the estimation accuracy of non-point source pollution load was increased.â‘¡The annual sediment yield at the watershed outlet was not only influenced by hydrological condition, but also influenced by "the key water and soil conservation project in Yangtse River watershed ". Thus, the annual runoff and sediment yield at the Jialing River outlet not only changed with the precipitation conditon but also to remarkably reduced since the implementation of the project in 1989. So, the RUSLE equation which is generally used to prediction the average annual soil erosion can't satisfy the study requirement. To solve this problem, a dynamic model of annual sediment yield was proposed based on the RUSLE equation and by introducing a comprehensive influence factor which can reflect the effect of hydrological conditions and human activities on sediment yield as well as by considering the spatial distribution of sediment delivery ratio from the aspect of the delivery route. Based on the proposed dynamic model of sediment yield, the non-point source pollution load model of adsorbed TN and TP was established. Using the established dynamic model, the spatial and temporal distribution of soil erosion, sediment yield and non-point source pollution of adsorbed TN and TP were simulated.â‘¢During the establishment of sediment yield dynamic model at the watershed outlet, it was difficult for us to carry out dynamic monitoring of each impact factors in the whole basin, because it was a long time research and was in very large-scale watershed. Taking into account the interannual variability of sediment yield mainly affected by hydrological conditions of rainfall - runoff and underlaying surface changes caused by soil conservation measures, a combined influence factor which is related to surface runoff modulus and the implementation time of the water and soil conservation project was proposed for the first time. Furthermore, its specific expression was determined through dimensional analysis and non-linear regression multianalysis.â‘£According to the features of hydrology, climate and terrain of Jialing River watershed, an ecological dynamic model of Jialing river in city zone of Chongqing was established. In view of the significant effect of hydrodynamic condition on algae growth confirmed by measured data in studied river reach, a hydrodynamic factor was introduced in the ecological dynamic model. The expression of the hydrodynamic factor was proposed and the concrete parameters in the expression were also determined by measured data. The ecological dynamic model was coupled organically with non-point source pollution load model and a model system of non-point source polltuion model which can not only simulate overland non-point source pollution loas but also can assess its environmental effect on receiving water was formed.