Research And Application Of Grid-Based Distributed Non-Point Source Pollution Model

With the effective control and treatment of point source pollution,the non-point source pollution from surface has become the most important water environmental issue worldwide.Compared with the point source pollution,non-point source pollution is difficult to control and prevent due to its complexity,randomicity,uncertainty,universality,and dispersibility.The traditional monitoring method and the artificial simulation experiment cannot satisfy non-point source pollution research on basin scale.Thus,the distributed non-point pollution models have been identified as the most effective tools to quantify and evaluate the non-point source pollution on basin scale.Jiaoyi watershed is the sub-basin on the upstream of the Huai River Basin,which is the important regional transit area of East Route Project and Middle Route Project of the South-to-North Water Diversion Project.The shortage of water resources and the serious of water pollution in Jiaoyi watershed not only constrain the sustainable development of social economy,but also definitely affect the South-to-North Water Diversion Project.Therefore,it is essential to develop the distributed non-point source pollution model suitable for regional characteristics in China.This model has an important theoretical significance and a high practical value for controlling and preventing the non-point source pollution,planning and managing the water environment in Jiaoyi watershed.In this paper,combined with the RS,GIS,and DEM techniques,a distributed non-point source pollution model,ESSI-2(infiltration Excess and Saturation excess Soil-water Integration model for non-point source pollution),is built based on regular grid of the DEM dataset.It abandoned the dependency of the traditional single runoff yielding scheme to watershed weather conditions,based on distributed hydrological model ESSI which adopted a dynamic water yielding mechanism.ESSI-2 model was calibrated and applied to the Jiaoyi watershed.A set of model parameters were established to simulate and predict water quantity and water quality in Jiaoyi watershed,and the applicability of ESSI-2 model in Jiaoyi watershed was verified.After the model calibration and validation,ESSI-2 model was applied to analyze and assess the non-point source pollution of Jiaoyi watershed.The results can provide scientific basis for solving water environment problem and effective decision support for water pollution control,water quality planning and environmental management in Jiaoyi watershed.The main conclusions of this research were followed as such:(1)ESSI-2 model was calibrated and validated in Jiaoyi watershed.The results of simulation showed that ESSI-2 model can describe and simulate the processes of rainfall-runoff,sediment transport as well as non-point source pollutant transport reasonably and accurately.Furthermore,it would also establish a good simulation and prediction platform for the spatial and temporal change analysis of water resource and non-point source pollution in Jiaoyi watershed.(2)ESSI-2 model was applied to evaluate water resources of Jiaoyi watershed in the period 2001-2009.Results displayed that the annual runoff correlated to the annual rainfall very well with a correlation coefficient of 0.878.However,the river runoff of Jiaoyi watershed could not be recharged effectively by the rainfall with the annual mean runoff coefficient was only 0.23.Additionally,in Jiaoyi watershed,the annual mean total runoff was mainly recharged by groundwater runoff(about 52.64%),then was supplied by interflow(about 29.47%),and the rest 17.89%was contributed by surface flow.The water resource of Jiaoyi watershed is extremely heterogeneous throughout the year.The mainly rainfall and runoff occur in June,July,and August,and the runoff is mainly concentrated in July,August,and September.(3)The soil erosion in Jiaoyi watershed was evaluated using ESSI-2 model in the period 2001-2009.Results showed that the annual soil erosion level of Jiaoyi watershed was mainly moderate erosion and below degree erosion,and the soil erosion area of intensity erosion level was smaller,which is mainly distributed in the east and the west sides of Jiaoyi watershed.While the total load of soil erosion belonged to extremely intensive and above erosion degree was 63.36%of the total load of soil erosion in Jiaoyi watershed.Furthermore,the soil erosion of Jiaoyi watershed was most intense in the area with the elevation of 200-300 meters,the slope above 25 degree,the rainfall between 830mm and 850mm,the cinnamon soil,and bare land.(4)The non-point source pollution loading in Jiaoyi watershed was assessed using ESSI-2 model in the period 2006-2009.The results showed that the non-point source ammonia nitrogen pollution load positively correlated to the annual runoff very well with a correlation coefficient of 0.84.About 93.25%of non-point source ammonia nitrogen pollution load was primarily produced in flood season.In addition,in view of the non-point source ammonia nitrogen pollution contribution rate,ammonia nitrogen pollution transported by groundwater runoff was mainly contributed to the total non-point source ammonia nitrogen pollution load,the next was ammonia nitrogen pollution transported by interflow,and ammonia nitrogen pollution transported by surface flow was the minimum contribution.Therefore,controlling the groundwater pollution is priority when controlling and treating the non-point source pollution for Jiaoyi watershed.