Ecological Health Assessment Of Dianchi Lake Water Based On P-IBI And Z-IBI

Water ecological health evaluation is the basis of water ecological function zoning and ecological management.The evaluation of water ecological health in our country lacks the evaluation of biological and completeness,and cannot reflect the integrity of water environment comprehensively,which restricts the protection and management of water ecological environment in various basins in our country.In order to realize the water environment management goal that the evaluation of rivers and lakes during the 14 th FiveYear Plan period has gradually changed from "water environment quality evaluation" to "water ecosystem health evaluation",to implement the research content of the national key research and development plan "Yangtze River water ecosystem integrity degradation and restoration mechanism",the Dianchi Lake,a typical plateau lake in the Yangtze River Basin,was selected as the research object.By collecting water samples and aquatic organisms,the physical and chemical factors of the water environment and the characteristic structure of aquatic organisms community were analyzed.Taking zooplankton and phytoplankton as biological objects,phytoplankton index of biotic integrity(P-IBI),zooplankton index of biotic integrity(Z-IBI)and index of ecological integrity(IEI)were established to assess the water ecological health status of Dianchi Lake.The results are as follows:(1)The results of the ecological investigation on the water quality of Dianchi Lake showed that:(1)The main pollution indicators were chemical oxygen demand and total nitrogen,and the comprehensive nutritional state was mild eutrophication.The main pollution indicators of 7 surrounding rivers was total nitrogen.(2)Plankton survey in Dianchi Lake: 28 species of phytoplankton and 21 species of zooplankton were identified.Cyanobacteria was the dominant species in lake and river with high density.Cladoceras and copepods were the dominant species in the Dianchi lake.The surrounding rivers were dominated by protozoa.The number of species and the diversity index were low.(2)The application of IBI in Dianchi Lake water ecological health evaluation showed that IBI was effective and applicable,and the evaluation results were accurate and could better describe the health status of the lake ecosystem compared with a single physical and chemical index and biological index evaluation.(1)The five core parameters screened by the P-IBI evaluation system were: Margalef richness index,total phytoplankton density,proportion of chlorophyta density,proportion of cyanobacteria and chlorophyta density,and proportion of cyanobacteria biomass.The results showed that the average P-IBI value of all sites was 2.49,and the evaluation grade was general.The water ecological status of 54.5%sites was healthy or sub-healthy,9.1% sites was general,and 36.4% sites was poor.The healthy areas was mainly distribute in the southern part of Dianchi Lake,the poor areas was mainly distribute in the central and eastern part of Dianchi Lake and the outlet river,and the other areas are generally in sub-health and general state.(2)The three core parameters selected by Z-IBI evaluation system were Shannon diversity index,Margalef richness index,and the density of the top three dominant species.The results showed that the average Z-IBI value of all survey sites was 2.11,the evaluation grade was general.The water ecological status of 54.5% sites was healthy or sub-healthy,18.2% was general,and 27.3% was poor.The healthy area mainly distributed in the south and north of Dianchi Lake,the poor area mainly in the central and western regions,and the other areas were generally in sub-health and general.(3)IEI was used to evaluate the integrity of Dianchi Lake ecosystem,including biological and abiotic factors,to make up for the deficiencies of IBI evaluation system.By comparing and analyzing the evaluation results of IEI,P-IBI and Z-IBI,it was found that IEI can avoid the errors of individual point site evaluation results caused by the single biological limitation of P-IBI and Z-IBI to a certain extent,which indicated that IEI has certain advantages in the evaluation of Dianchi Lake water ecological health,and was effective and applicable.The three types of 14 core parameters screened by IEI evaluation system were:(1)physical parameters: suspended matter;(2)chemical parameters: total nitrogen,total phosphorus,ammonia nitrogen,chlorophyll a,and permanganate index;(3)biological parameters: phytoplankton Margalef richness index,total phytoplankton density,proportion of chlorophyta density,sum proportion of cyanobacteria and chlorophyta density,proportion of cyanobacteria biomass,Shannon diversity index of zooplankton,Margalef richness index of zooplankton,and density of the top three dominant species of zooplankton.The evaluation results showed that the hierarchy was relatively clear by IEI.The average value of IEI was0.57,and the evaluation level was sub-health.The water ecological status of 54.5% sites was healthy and sub-health,36.4% was general,and 9.1% was poor.The healthy areas mainly distributed in the south and north of Dianchi Lake,while the poor areas mainly distributed in the middle.In general,the water ecology in the central area of Dianchi Lake has been damaged to different degrees.The research results verified the applicability and effectiveness of the evaluation system,and provided technical support for constructing water ecological health evaluation system in our country.Meanwhile,the evaluation results obtained by P-IBI,Z-IBI and IEI also provided scientific basis for restoring and improving water ecological environment in Dianchi Basin.