| Water,which covers 71 percent of the earth’s surface,has been called the source of life.China is one of the 21 countries with poor water and the most water shortage in the world.With the acceleration of urbanization,water consumption for industry,agriculture and domestic use is still increasing.As a gathering place for human survival and development,the river basin has added environmental attributes from the original single ecological attributes.Excessive exploitation of fresh water resources and water pollution are two main problems in water environment management.At present,the point source pollution has been widely controlled in China,and the main source of water environment pollution has changed to the non-point source pollution.China feeds 19%of the world’s population with 6%of the world’s fresh water and 9%of the world’s arable land.In the process of advancing to an agricultural power country,excessive use of pesticides and fertilizers has aggravated the surface pollution of agriculture.The rapid development of livestock and poultry breeding has also brought environmental pollution and water resources destruction.In China,arsenic is widely used in chemical pesticides,phosphorus fertilizer has a very high content of heavy metals,and animal feed additives contain copper,zinc and other heavy metals.Heavy metal pollution can cause soil and water degradation and ecosystem failure,enter the food chain,and pose a threat to human and animal health.In September 2019,a major plan was made for ecological protection and high-quality development of the Yellow River Basin.Huangshui River as an important tributary of the upper reaches of the Yellow River,the Huangshui River basin is the most developed area of industry and transportation on the Qinghai-Tibet Plateau,with a vast area of arable land,developed livestock and poultry breeding,and rich mineral resources.However,the amount of water resources in the basin only accounts for 12.3%of Qinghai province,while the utilization rate of water resources is more than 40%.The self-purification capacity of water body is poor and the ecosystem is fragile.The water quality of section of Huangshui River is not up to standard in dry season.At present,there are a series of problems in the comprehensive assessment of water environment quality and the pollutant source apportionment of watershed.First,the selection of comprehensive evaluation index and weight determination method of water quality are subjective.Second,typical water pollutant traceability models are missing,and the pollution sources inventory has not yet been established.Thirdly,the evaluation of water environment quality in the Huangshui River basin is one-sided,and the research on the impact of plateau agriculture and animal husbandry on water environment has not been carried out.This study took Huangshui watershed as the research area,typical water pollutants as the research object,and water environment quality control as the research objective.The water environment quality of Huangshui River was evaluated synthetically and typical water pollutants were traced.The main research contents and conclusions are as follows.(1)Taking the whole index method as the measurement standard,the accuracy of Delphi method and multivariate statistical analysis method in the process of index selection is compared,and the entropy method is applied in the process of index weighting,and the MSAEWM WQI technology is established.Through the comprehensive evaluation of groundwater potable ability of Dawu water source,the WQI innovative technology was verified.The results show that the evaluation results of WQI technology are more scientific and reasonable by using multivariate statistical analysis method to determine the evaluation index and entropy method to assign weight.(2)MSA-EWM WQI technique was used to evaluate water quality in Huangshui River Basin.HRA human health risk assessment technique was used to assess the impact of typical pollutants on human health.This paper expanded the connotation of water environment quality,established the comprehensive evaluation model of water environment quality including water quality evaluation and health evaluation,and determined the main pollution factors and potential risk factors in Huangshui watershed.The results of water quality evaluation showed that the scores of 4 and 5 categories accounted for 26.67%.The results of human health evaluation showed that the heavy metals in Huangshui River had non-carcinogenic and carcinogenic risk to infants,but no risk to children,adolescents and adults.The comprehensive evaluation results show that the water environmental quality of Huangshui River is general,and the main pollution factors are COD,TN,TP and Hg,and the concentration exceeds the limit of class III surface water standard.The potential risk factors are As,Cr,Cd and Ni.Although the heavy metal content in water is very low,it has carcinogenic and non-carcinogenic risks for infants at some points.Managers should pay attention to it in daily heavy metal control work.(3)A universal pollutant source tracing model is constructed.For general pollutants such as COD,NH3-N,TP and TN in water bodies,point sources in the basin are analyzed by statistical data method and point sources are analyzed by output coefficient method.PMF technology was used to analyze the source of heavy metal pollutants in water.The results show that the point source pollution of the general pollutants in the Huangshui River basin has been basically controlled,and the proportion of non-point source pollutants in the total emissions is more than 80%.COD and NH3-N mainly come from livestock and poultry breeding and rural domestic wastewater discharge,while TN and TP mainly come from livestock and poultry breeding and agricultural cultivation.Heavy metals in water mainly come from natural processes,traffic tail gas and atmospheric deposition,agricultural cultivation,industrial wastewater discharge and livestock and poultry breeding.As for the main pollution factors and potential risk factors,the effects of planting and livestock breeding on Hg and As were close to 60%and 80%,respectively.The contribution of planting to Ni was more than 70%,and that of livestock breeding to Cd was more than 90%.Agriculture and animal husbandry in the watershed and plateau have great influence on the discharge of typical water pollutants.(4)Based on the results of pollutant traceability,source contribution was classified and calculated according to the land use type where the pollution source is located,and the spatial distribution of source contribution was carried out by combining with GIS technology,so as to construct the spatial pollution source contribution list of Huangshui River basin,providing a theoretical basis for regional differentiated management of water environment management in the watershed.The results show that the main sources of COD and NH3-N are along the river,the upper and middle reaches of the basin,the sources of TN,Cr and Hg are evenly distributed in the whole basin.TP,Ni,Co,As and Pb are mainly from the middle and lower reaches of the basin.The main contributing sources of elements Cu and Zn are concentrated along the river.Element Cd mainly comes from the upper and middle reaches of the basin.The sources of pollutants are differentiated in regional distribution,and managers should focus on different pollutants in different regions.(5)Based on the theory of circular economy,the countermeasures for the control of typical water pollutants in the Huangshui River basin were studied,and the suggestions for the whole process including "source emission reduction-process control-end treatment" were put forward.The water environment management of Huangshui River basin should be carried out from three aspects."Source cleaner production" mainly includes five source control measures in rural life,agricultural planting,livestock and poultry breeding,industrial and urban life,and traffic exhaust."Process supervision and management" should carry out process supervision from four aspects:routine monitoring,real-time monitoring,joint control of law enforcement and river chief system."Terminal risk prevention and control" should do a good job in emergency prevention and control on the basis of laws and policies,further improve the concept of environmental protection,speed up personnel training,and make contributions to the water environment management of the basin. |
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