The Water Environment Evolution And Ecological Risk Assessment Of Chagan Lake Wetland

Water environment is an important component of the wetlandecosystem, is also the key factor for wetland formation, development,succession, death and regeneration. Global climate change andhigh-intensitive human activities deteriorate the water environmentthrough changing the water level, water flow and water qualities ofwetlands, bring potential risks to the structure and function of ecosystem.Chagan Lake wetland, the important ecological barrier in west Jilin, wastaken as the research object. Through analyzing of the evolutionalcharacteristics and laws of the water level and qualities in Chagan Lakewetland, combined with the multivariate analysis of the relationshipsbetween the changing environment and the structure, abundance andbiomass of plankton, a reasonable comprehensive index system wasestablished to assess and classify the ecological risk of Chagan Lakewetland. We proposed corresponding protection and managementstrategies of water environment, which has great theoretic and realisticsignificance to maintain the stability and healthy of the ecosystem.Through the above research, we mainly obtained the followingconclusions:(1) Analysis of evolutional characteristics of water environment ofChagan Lake wetlandAnalyzing the evolutional characteristics of the water environmentwill provide a scientific basis for the protection of the water environmentsecurity. The evolvement of water environment was comprehensivelystudied through analyzing the water level data from1982to2011and the water quality data in1985to2011. Carlson trophic state index (TSI) andthe fuzzy comprehensive evaluation method were used to assess theeutrophication level and the water quality. The results showed the waterlevel was recovered and stabilized at129.8-130.3m after the operation ofthe channel transferring water from Songhua river to Chagan Lake. Watersalinization, eutrophication, organic pollution were mitigated and thewater environment improved considerably in the late1980s, but the trendof alkalization and organic pollution has became serious since2006andthe water quality evolved from Ⅲ category to IV category. The trend ofeutrophication has been relieved since2006. Agriculture drainage hasrelieved the water salinization and hasn‘t aggravated the level ofeutrophication in Chagan Lake temporarily. The water quality of ChaganLake is interactive affected by terrestrial emissions in the catchment,endogenous releases and hydrological regimes and exhibits a remarkablephosphorus limited middle nutrition. Sewage and surface runoff pollutionshould be controlled to protect the water environment health.(2) Ecological effects of the changing water environment in ChaganLake wetlandThe study identified a total of127phytoplankton species (belongingto53genera and5phyla, mainly were Bacillariophyta and Chlorophyta)and46zooplankton species (belonging to26genera and4phyla, Rotiferawere in absolute advantage). This study investigated the biodiversity,abundance and community structures of plankton and their relations withenvironmental factors combining field investigations with cluster analysis,multi-dimensional scaling (MDS), redundancy analysis (RDA), canonicalcorrespondence analysis (CCA), and applying diversity indices in ChaganLake during the intermediate (May) and rainy season (September) in2012. Consisting of two connected parts (the main lake body and Xinmiao wetland), Chagan Lake was found to sustain significanttemporal-spatial variations of plankton populations. The abundance ofplankton in the intermediate season was considerably higher than that inthe rainy season. Because plankton abundance and biomass were affectedby salinity, nutrient, flow rate et al., abundance and biomass in Xinmiaowetland was lower than that in the main lake. the Results showedphytoplankton abundance was influenced by pH, water salinity,phosphate (PO3-4), total nitrogen (TN) and5-day biological oxygendemand (BOD5), while pH, water temperature (T), phosphate (PO3-4),whereas salinity, CODMnand BOD5were the key factors influencedzooplankton abundance. When plankton was used as a bio–indicator inwater quality evaluation, the results revealed that water quality in ChaganLake was in β-moderately-polluted category.(3) Ecological risk assessment of Chagan Lake wetlandPhysical and chemical indexes, nutrient state indicators, organicpollution indexes and ecological factors were selected to evaluate theecological risk in Chagan Lake wetland based on entropy weight.Ecological risk evolution characteristics from2006to2011and spatialclassification of ecological risk were analyzed in May and September,2012and in September,2013. The result showed: Chagan Lake wetlandwere facing an increasingly serious ecological risk during2006to2011,belonged to a moderate level risk; the status in intermediate season wasserious than in rainy season,2012. The major risk area distributed in thesouth and west of Chagan Lake besided Xinmiao wetland; the ecologicalcondition in September,2013was much more stable than in September,2012. Altogether ecosystem status in2013from2012, altogether stable,but out of respect for the ecological effect of water environment, leadingto a single index of entropy is too large, leading to the ecological riskassessment results polarized phenomenon. But without any consideration of ecological index, the entropy of a single index was enlarged, which ledto a polarized phenomenon of the ecological risk assessment results.Protection and management strategies of water environment wereproposed according to the ecological risk classification for Chagan Lakewetland, they are the guarantee of the water supply, control of agriculturalnon-point source pollution, construction of artificial wetland and waterecological system. The serious situation of eco-environment will beeffectively improved through controlling pollutant sources, increasing theadsorption during pollutant transport, combining with biologicaltreatment as well.