Research On Temporal And Spatial Response Of Pollutants In Multi-rivers Basins Based On SPARROW Model

Water pollution is always an intractable international environment problem.Our country attaches great importance to water environmental protection,the water environment management has been developed for decades,and has made profound progress in terms of laws and regulations and management security.In order to further satisfy our growing water environment management needs,we will use the model to study the spatial and temporal distribution characteristics of water pollution in the basin scale,analyze the influence mechanism,and make feasible measures to make it necessary and deliberate.The watershed model is an effective tool for solving the problem of water environment management,and SPAtially Referenced Regressions on Watershed attributes(SPARROW)is a watershed model developed by the U.S.Geological Survey(USGS)for spatial analysis.Compared with other watershed models,the SPARROW model is used to consider the transport of pollutants in the basin,which is applied by scholars at home and abroad.It is a hybrid(statistical and mechanistic)model,which has high applicability in the simulation of non-point sources pollution.In addition,the Bayesian method is an important branch of statistics,which can analyze the uncertainty of the model while estimating the model parameters,and also have a wide application in the hydrological and watershed model.The main research object of this paper is SPARROW model,which can meet the current data situation and the management requirements of our country.Firstly,the model were established in the typical watersheds of the southern and northern China,i.e.the Poyang Lake Basin and the Haihe River Basin,to simulate Ammonia Nitrogen and COD.And then the comparison of the model results was made to validate the applicability of the SPARROW model in our country,and to find the shortcomings of the model.Secondly,considered the disadvantages of the SPARROW model,the separated land-to-water coefficients of sub-watersheds were estimated by introducing the Bayesian hierarchical method to improve the spatial heterogeneity of the model.Thirdly,based on the above improvements,the model framework was further improved by considering the variable associated with time and modifying the original model coefficients to improve the time resolution of the model,and to analyze the monthly pollution of the watershed.Finally,combined the established SPARROW model and the method of Mathematical programming,the spatial optimization of land use is carried out to find the prior regions needed to take measures,in order to provide the management projects meeting certain requirements.The comparison of the two models in China’s southern and northern regions shows that the SPARROW model has high applicability in China(the simulation results of the Poyang Lake basin,NSE=0.89;the simulation results of the Haihe Lake basin,NSE=0.53).However,due to the large area of HRB(320000 km~2),as well as the flat area of the HRB,and the relative small number of monitoring stations in the model building process(144),it is difficult for SPARROW model to distinguish the spatial differences between sub-watersheds based on the single parameter,which may influence the accuracy of the model,therefore,the spatial difference of the model is need to be improved,to enhance the accuracy of the model.Based on the problems encountered in the studies above,this paper enhanced the spatial differences of the SPARROW model by introducing the Bayesian hierarchical method,and improved SPARROW model was used in the PLB and HRB.The results show that the improved SPARROW model is more accurate and stable than the original SPARROW model(the simulation results of the Poyang Lake basin,NSE=0.93;the simulation results of the Haihe Lake basin,NSE=0.93).Meanwhile,the improved model fully expressed the spatial differences of different sub-watersheds,making the structure of the model more reasonable,and it is convenient for the comparison of the transport characteristics of different regions.After the improvement of the spatial heterogeneity of SPARROW model,this paper also made some improvements to its time resolution,by adding the monthly variable,so that the SPARROW model became a watershed model,which could simulated pollutants loads in different month.The application of the improved model in the PLB proved that the study of the temporal-spatial response relationship in the multi-watershed basins was carried out.After the model is changed in time,the time resolution is significantly improved,as well as the auxiliary ability of the SPARROW model for management decision.In the end,the paper combined the SPARROW model established above and the mature Mathematical programming method to optimize the land use,considered the environmental benefit as the target function.Through this method,we can find the prior control area of land use in the basins,and provide important support for the elaborate management.In summary,the bayesian hierarchcal method is introduced in this paper to estimate the land-to-water transport coefficients of different subbasins in SPARROW model.Based on the modification,monthly variables are introduced to simulate the pollution in different months.Compared with previous studies,this study can conduct more detailed simulation of water pollution in space and time scale,and has good innovation.At the same time,combined SPARROW model and mathematical programming method was used to optimize land use distribution,which provided scientific guidance for watershed management measures and had guiding significance for promoting watershed management in China.