Multi-level Regionalization And Classification For Water Environment

Water environment regionalization is an important way to establish the response relationship between pollution sources and water quality,to achieve the spatial management of water environment,and to implement the management concept of "by region,by type,by grade,by stage" based on water quality target,which provides the technical support for fine management of watershed environment.In this study,taking Zhejiang Province as the research area,by selecting zoning indicators,a multi-level regionalization system for water environment was constructed and then aquatic ecoregions and water environment control units were divided.On the basis of recognizing the ecological service function and environmental characteristics of each control unit,control units were classified based on the management requirement of water quality target.Differentiated control strategies were proposed for different types of control units to support the fine water environment management in Zhejiang Province.The main research results were as follows:(1)The collected data including natural environment data,social economy data and water environment data,combined with the method of principal component analysis and correlation analysis,zoning indicators of different levels were selected to construct the multi-level regionalization indicator system of Zhejiang Province including indicators for aquatic ecoregion and water control unit delineation.First-level aquatic ecoregion indicators included elevation,annual average temperature and annual average precipitation;second-level aquatic ecoregion indicators included land use type,soil type,NDVI and population density.On the basis of aquatic ecoregion,primary tributary catchment area of eight major river systems and administrative boundary constituted the division indictors for primary control unit;secondary tributary catchment area of eight major river systems,administrative boundary,control section and water environmental function zoning were taken as the division indictors for secondary control unit.(2)According to the determined indicator system,based on the method of ISODATA spatial clustering and spatial overlay analysis,water environment regionalization was completed step by step.At the level of control regions,water areas and land areas were both taken into consideration to divide four first-level aquatic ecoregions and ten second-level aquatic ecoregions,which reflected the spatial differences of ecological characteristics.On this basis,73 primary water control units and 510 secondary water control units were divided to implement the fine water environment management.(3)Based on the division of control units,the ecological service value of each control unit was estimated by the method of modified equivalent value factor,four ecosystem service bundles were identified based on K-means clustering method and the dominant ecological service function of each bundle was determined.Bundle I included 169 contol units,located in the plain and mountainous hilly areas,and the dominant ecological service function was not prominent;Bundle II included 11 control units,distributed in the Qiandao Lake and the lower reaches of Qiantang River,with waste treatment and hydrological regulation as the dominant ecological service functions;Bundle III included 186 contol units,mainly distributed in the western and southwestern mountainous areas,with gas regulation,climate regulation and biodiversity maintenance as the dominant ecological service functions;Bundle IV included 144 control units,concentrated in the northern plain,the Jinqu basin and the southeastern coastal plain,with food production as the main function.The total ecological service value of the four bundles was in the order of bundle Ⅲ>bundle II>bundle I>bundle IV.(4)By analysing water environment characteristic of control units,444 contol units reached the standard,but 66 contol units did not,and the water quality tended to deteriorate from west to east and from south to north.According to pollution discharge,identified 104,98 and 101 contol units with high intensity emission of industrial pollution,farmland pollution and domestic pollution reletivvely,which mainly distributed in the northern plain,the Jinqu basin and the eastern plain of Zhejiang Province.(5)Superposed ecosystem service bundles,water quality classification and pollution discharge intensity classification,different types of control units were identified,including 93 priority protection units,accounting for 27.67%of the total area,mainly distributed in the upstream areas of each watershed;202 key control units,accounting for 25.21%of the total area,mainly concentrated in the northern plain,the Jinqu basin and the southeastern edge,and among them,79 units were industrial pollution control units,38 units were farmland pollution control units and 85 units were domestic pollution control units.The rest were general control units,totaling 215 units,accounting for 47.12%of the total area.(6)According to the classification of water environment control units,guided by the improvement of water quality target and combined with the ecological characteristics,the corresponding control countermeasures were put forward:①Priority protection units aimed at maintaining good water quality and promoting ecological service function,with ecological protection of water sources and wetlands as the core,and at the same time controlled rural non-point source pollution in the source areas.②The key control units aimed at improving water quality,with total pollution control and water ecological restoration as the core,should optimize industrial structure,strengthen industrial wastewater treatment,improve collection and trealtment level of domestic sewage,control the loss of nitrogen and phosphorus from fertilizer and promote water ecological restoration.③The general control units aimed at maintaining the overall stability of water quality and improving local water quality,with pollution prevention as the core and implemented the universal control requirements from the aspects of spatial layout,pollution control and risk prevention.