Assessment Of Pollution Load And Identification Of Critical Pollution Sources In Daqing River Basin

Water is a basic condition for human survival and an important material basis for national economic and social development.Studying the characteristics of watershed water quality in the face of anthropogenic disturbances can provide a strong scientific basis for regional water environmental governance.In this paper,we collected data through field surveys,statistical yearbook data and other methods to construct a SWAT(Soil and Water Assessment Tool)model of water pollution in the Daqinging River basin,analyzed the spatio-temporal distribution characteristics and main sources of pollution load in the basin,identified critical source areas in combination with the emission coefficient method,and proposed some countermeasures to reduce pollution.The specific contents and results of the study are as follows.(1)The SWAT model of the Daqing River basin was constructed,and the parameters were validated.First but not least,the basin pollution source data and basic data such as digital elevation model(DEM),river,land use,soil type,meteorological information,hydrological sites,water quality monitoring sections and natural geographic information of the basin were collected to build the model database.Then,divided the basin into sub-basins using the topographic and river network analysis tools,which were further subdivided into a number of hydrological response units(HRUs).Each HRU had a unique combination of soil and land use types.After model construction had been completed,a parametric sensitivity analysis,calibration and verification was performed.(2)Pollution load calculation and contribution were accounted.Simulation of the runoff and pollutant loadings at different times in the basin could support the analysis of their spatio-temporal characteristics and structural changes.The analysis of the sources of pollution exported from the basin outlet showed that the pollution load of total nitrogen(TN),total phosphorus(TP)in the Daqing River Basin mainly came from domestic sources,followed by industrial sources and agricultural sources.In terms of time,the pollution load of TN and TP in the whole catchment of Daqing River increased rapidly during the flood season(July-September)and after the flood season,while other months were mainly from domestic sources.Spatially,the main pollution-producing areas of TN and TP in the Daqing River basin were concentrated near the Baiyangdian precipitation area.The annual average output load of TN and TP in the basin reached 55499 t and 1488 t,and the average output concentration of pollutant load was 1.50 t/km~2 and 40.67 kg/km~2,with Baoding contributing the most to the pollutant output,accounting for 46.34%and 41.13%of the total load of TN and TP,respectively,while the highest output concentration of TN and TP was found in Hejian city.(3)Identified of critical source areas(CSAs)for sedimentation.The SWAT model and the emission coefficient method were coupled to caculate the contribution of different spatial units and different production activities to the TN and TP into the Baiyangdian lake,and to identify the CSAs.The results show that the total amount of TN and TP pollution into the lake generated by the basin was 41128.39 and 1086.40 t/a,respectively,and the main source of pollution was domestic sewage discharged from domestic sewage treatment facilities,which accounted for about half of the total pollutant load.The CSAs were the counties along the river,mainly including Lianchi District,Xushui District,Jingxiu District,Anxin County,Shunping County and Mancheng District.Units located in different spatial locations had different hydrographic characteristics,and the final amount of pollutants into the lake varied,so there were CSAs that contributed significantly to water pollution into the lake.the pollutant content and structure produced by different human activities also had obvious differences under the same external conditions due to different production attributes.The identification of CSAs and heavy pollution production activities played an important role in controlling the entry of pollutants into the Baiyangdian lake.In this paper,the emission coefficient method was combined with the SWAT model to synthesized the advantages of both methods,namely,the utility and completeness of the SWAT model in simulating pollution generation and migration processes,and the advantages of the emission coefficient method in classifying pollution sources for statistical purposes,to propose a quantitative analysis method applicable to the evaluation of pollution loadings in watersheds and the identification of CSAs.And using the Daqing River basin as an example,the effectiveness of the method was demonstrated,which provided a reference for the pollution evaluation of other lake basins in China.