| In the lake wetland, water environment plays a important role in the protection work of ecological system, researchs on water quality evaluation, temporal and spatial distribution characteristics of pollutants are important preconditions to protect this kind of ecosystem. Phytoplankton and macrobenthos are respectively primary producer and primary consumer of aquatic ecosystem, the effects of internal and external factors on species and diversity characteristics are more obvious, and it also impacts on structure and function of the ecosystem, therefore, there has special meaning for regional protection by taking further discussion on species diversity change law and relationship with habitats. Caohai Lake,located on the Guizhou karst plateau,is one of the three great plateau freshwater lakes in China and it plays an important role in the Caohai Wetland ecosystem. A seasonal investigation was carried out to reveal the change law between biodiversity and water pollution, master the interactions and risk state of Caohai lake. Samples of water, phytoplankton, macrobenthos were collected once during each season(August and November,2014 and January and April,2015) at 15 sampling sites, and complete laboratory analysis. The main results are as follows:1. Spatial- temporal variation of water quality in Caohai lake: the resulting data was used to assess spatial-temporal variations of Caohai water quality using GIS analysis. Results show:(1)Concentrations of TN,TP,CODMn and C hl-a were higher in spring than the other seasons: 0.98 mg/l,0.03 mg/l, 6.30 mg/l and 0.025 mg/l,respectively. Spatially,TN,TP,CODMn and Chl-a concentrations decreased gradually from east to west,being generally higher at the inlet and wharf than other area of the lake.(2)Overall,the trophic status of Caohai lake is mesotrophic,but the 15 sampling sites fell into three groups according to the average comprehensive trophic status index(TLI) across four seasons. Area A includes the inlet and tourists wharf of northeastern Caohai,which remained eutrophic throughout the year(53.9?TLI?63.0) and water quality remained at the level of ? to?. Area B,including the areas located near Weining County and water inlet,is mesotrophic which seasonally eutrophic conditions(41.2?TLI?46.6). Area C,from the center of the lake to the outlet near Yangguang mountain,is oligo- mesotrophic(35.8?TLI?39.7). Water quality in areas B and C are both level ?.(3) Chl-a and TN were the major contributors to the TLI scores in all three areas.2. The species diversity characteristic of phytoplankton in different pollution areas of Caohai lake. Analysing community characteristics and relation with distribution to environmental factors of phytoplankton, result showed that:(1) the investigation of four surveys were total identified 7 phyla, 250 species, including 145 kinds of C hlorophyta, accounting for 58.00% of the whole phytoplankton species, Chlorell vulgaris, belongs to Chlorophyta, and Euglena caudate,belongs to Euglena, were the dominant populations in all three areas;(2) endemic species to area A included Dictyosphaerium pulchellum, Ankistrodesmus falcatus, Chlorobotrys, Dactylococcopsis acicularis, Navicula rhynchocephala, area B included Crucigenia quadrata, Characium, Phacus osillans, Pleurocapsa fuliginosa, Merismopedia tenuissima, Oscillatoria tenuis, Characiopsis sublinearis, Amphora ovalis, and no specific dominant species in area C;(3) There were significant difference of abundance and biomass between regional(P?0.05) and seasonal(P?0.05), area A was eutrophic state, were 39.53 cell×106 ind/L, 16.29mg/L respectively, higher than the area B, mesotrophic status, were 32.36 cell ×106 ind/L, 13.86mg/L respectively, and oligo- mesotrophic status of area C, were 30.08 cell ×106 ind/L, 12.68mg/L respectively; abundance mainly constitute was Chlorophyta, the maximum value,area A and B, appeared in autumn, area C in summer, the minimum value of the three areas is present in winter;(4)during spring and winter, Shannon-Wiener index, Pielou index, Margalef index, diversity thresholdin three area showed C >A > B; during summer and autumn, four categories index showed C> B> A;(5) the environment factors which had effects on phytoplankton abundance were different between seasons, DEP and Chl-a in summer, C hl-a and DO in autumn, CODMn and DO in winter, p H and DO in spring.3. The species diversity characteristic of macrobenthos in different pollution area of Caohai lake. Analysis community characteristics and relation with distribution to environmental factors of macrobenthos, research showed that:(1) the investigation of four surveys were totally identified 3 phyla, 21 species, in terms of density and biomass, Molluscs were the main types in this lake, Hippeutis cantor and Chironomidae were the dominant species in each season distributed in each area;(2) endemic species to area A included Earthworm ? Bellamya aeruginosa ? Novaculina chinensis, area B included Alocinma longicornis, area C included Dragonfly, Novaculina chinensis;(3) There were significant differences in density among regional(P?0.05) and seasonal(P?0.05),and biomass among seasonal(P?0.05), and no significant differences in biomass among regional(P?0.05), area A was eutrophic state, were 640.07ind/m2, 86.90g/m2 respectively, higher than the area B, mesotrophic status, were 158.50ind/m2, 41.54g/m2 respectively, oligo- mesotrophic status of area C, were 433.50ind/m2,38.83g/m2 respectively; density mainly constitute was Mollusca, the maximum value,area A and area B in winter, area C in summer, the minimum value, area A and area B in summer, area C in winter;(4)during summer and autumn, Shannon-Wiener index, Pielou index, Margalef index in three area showed B >C > A, A >B > C respectively, minimum value of three categories index during areas were areaC;(5) the environment factors effect macrobenthos abundance were different between seasons, TP and Chl-a in summer and winter, TP and CODMn in autumn,WT and Chl-a in spring.4.Risk assessment and early warning of water quality and biological diversity during different areas in Caohai. By screening method of correlation analysis etl, selecting nine indicators included SD, DO, TP, TN, Chl-a, Phy-H ', Phy-J ', Ben-H', Ben-D ' to establish a risk assessment system. Based on entropy method to value-determined, according to calculation method of ecosystem risk comprehensive index(EHCI × 100), reference to classification standard, carried out risk assessment and warning for lake water quality and biological in samples and areas of Caohai wetlands. Research showed that:(1) water quality and biological diversity risk of Caohai wetland was 53.57 as a whole, belonged to intermediate warning level;(2) the annual average of risk assessment value in area A was 42.82, belonged to intermediate level warning, in spring, summer, autumn and winter were 38.25, 50.85, 44.42, 37.77 respectively;(3) the annual average of risk assessment value in area B was 58.09, belonged to intermediate level warning, each season were 56.67, 76.28, 46.55, 52.58 respectively;(4) risk assessment value in area C was 59.80, belonged to intermediate warning level, each season were 54.69, 72.26, 56.01, 56.26 respectively;5. The recommendations to water and biodiversity diversity protection of Caohai lake. The risk value was determined by both water pollution situation and aquatic organisms, unicipal wastewater was the principal cause of poor water quality in area A and agricultural non-point source was the principal nutrient source to area B. Therefore,suggestions on area A was controlling municipal wastewater discharge and management over-use of chemical fertilizers, pesticide application in regional around lakes, the source of water pollution could be decreased, setting constructed wetland of half-subsurface flow, to construct an artificial wetland ecosystem from different plants,which contains floating plants, meadow plants, submerged macrophyte, aquatic macrophyte etl. Suggestions on area B and area C were building many relevant water projects, adding water supply to reduce pollution difference caused by different seasonal changes of water, and increasing fry collecting volume of phytophage type which could adapt this ecosystem, and improve the biological composition for both internal and external, format a comparatively rich and perfect food chain, forming a virtuous circle of ecosystem. |
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