Study On Water Environmental Function Zoning Of QingShui River Basin

Water shortage and water quality deterioration happened in the Qingshui river basin.Water quality indicators of Qingshui river were determined in April,July and November 2018.Data about types of natural utilization,remote sensing data,planning about basin development and utilization collected for water environment function zoning.BP neural network and survey method used for identify the type of land use and water use,single factor evaluation method and water quality index used for assessment of water qualitu status,vector model method and zero dimension water quality model index used for quantitatively analysis of the water environment bearing capacity of Qingshui River.To distinguish water function zoning of Qingshui river basin under the target that water quality meet requirement.The main achievements of this study are as follows:(1)Demand about water function in the basin mainly included drinking water and irrigation,requirement for drinking water was mainly located at the source of the trunk stream.Distribution of different types of land use was obviously different.Cities had built on the banks of river,there was a dense distribution of green land in the southern mountainous area.The proportion of bare land was largest,followed by cultivated land.The cultivated land occupied a wide area,accounted for 35.5%of the basin area.There were a wide area of cultivated land in the northern plain and the southwest of the basin,and the area of cultivated land in the area far from the river was smaller than the area close to river.(2)Water quality grade of Qingshui river depended on the concentration of total nitrogen(TN)and five-day biochemical oxygen demand(BOD5),and poor water quality happened under the single-factor assessment model,78%water quality monitoring sections are class V,and 12.5%of the sections are inferior class V.The proportion of cross river sections whose water quality belonged to class III under the comprehensive water quality index model was 81%.The comprehensive water quality of Qingshui river in April was best while was worst in July,2018.Water quality status was deterioring from the source in the upstream section,little change happened in middle reaches,and gradual improvement occurred in downstream.The enterprises who belonged to polluters were mainly distributed in the upstream and downstream of the trunk stream,while rarely distributed in the middle reaches and subbasin.The water quality of most areas can meet the requirements of water environment quality for agricultural use,and water quality in a few sections can meet the basic requirements for drinking.(3)Water environment capacity for different pollutants was unequal.Under the class V water quality target,The water capacity of Qingshui river for chemical oxygen demand(COD)is significantly larger than capacity for BOD5,the overall difference is about 4.5 times.The water capacity was large for ammonia nitrogen(NH3-N),while was small for TN and total phosphorus(TP).the capacity for pollutants in the downstream was stronger than that in the upstream,The pollution load of Qingshui River was appropriate and not overloaded only under the water quality target was class V.Environmental carrying capacity of Qingshui River was decreasing year by year,and it will still be at a low level in the next five years.Insufficient sewage treatment capacity in the river basin are the important reasons that affect the environmental carrying capacity of Qingshui River,the water environmental carrying capacity of the river basin will recover gradually after 2023.(4)Qingshui River was suitable to be divided into 14 water environment functional zones,four water environment functional types including natural protection area,drinking water source protection area,transition area and agricultural water use area.The pollutants load in most area of basin was overloaded,it was necessary to reduce the pollution load in the water environment function area.Agricultural water use areas in trunk stream need to reduce the BOD5 load by 73.84 t/a,and TN load by 30.90 t/a to meet requirement.Those acts including strengthening the control of non-point source pollution,reducing the pollution of point source,strengthening the water environment management in the urban reach,coordinating water environment management and recovery coulde be taken to improve water quality.