| In recent years,due to the continuous interference of human activities,lakes in Yunnan Plateau have faced multiple environmental pressures,mainly including eutrophication,heavy metal pollution and fish invasion.As one of the nine biggest plateau lakes in Yunnan Province,Yangzong Lake used to be an important water source location for industrial,agricultural and drinking use in the watershed and its lower reaches.Owing to the leakage of industrial pollutants containing arsenic into water in 2008,arsenic pollution has become one of the most seriously environmental problems in Yangzong Lake.At the same time,with the increasement in nutrient input to the lake,the concentration of nutrients gradually increased,and the cyanobacterial bloom took place several times in the 1990 s.In addition,As an intermediate link in the food chain of lakes,Zooplankton plays an important role in material circulation and energy flow.Zooplankton,as a microorgsnism,has the peculiarity of short generation time and large population,and is also very sensitive to environmental changes,so it is often used as an important biological index to evaluate lake ecology.However,under the condition of arsenic pollution,little is known about how the zooplankton community in Yangzong Lake responds to a variety of biological and abiotic factors.Therefore,it is of great importance to understand the temporal and spatial characteristics of zooplankton community under arsenic pollution and to explore the factors affecting the changes of zooplankton.zooplankton community and water environment indicators in this lake were investigated from 2015 to 2019.the variation characteristics of zooplankton in different communities and the main environmental driving factors were determined through analysis of Pearson correlation,Analysis of variance(ANOVA),Cluster analysis,Redundancy analysis(RDA)and weighted averaging model.The results showed that:(1)From 2015 to 2019,33 zooplankton species in total were observed,including 26 Rotifera species,3 Cladocera species,and 4 Copepoda species.The zooplankton community were mainly dominated by Asplanchna priodonta,Keratella cochlearis,Keratella tropica,Keratella tecta,Bosimina fatalis,and Thermocyclops taihokuensis.(2)The abundance and biomass of zooplankton in Yangzong Lake were relatively low.In time scale,zooplankton abundance ranged from 1.9 to 105.1ind./L,with an average of 28.3ind./L(rotifers: 23.6ind./L,cladoceras: 0.2ind./L,copepods:4.5ind./L).In space scale,zooplankton abundance ranged from 8.1 to 36.9 ind./L,increasing from southwest to northeast.Total zooplankton biomass ranged from 1 to275.4μg/L,with an average of 33.2μg/L(rotifers: 4.8μg/L,cladoceras: 0.9μg/L,copepods: 29.4μg/L).The spatial zooplankton biomass ranged from 26.2 to 48μg/L,with little difference in the whole lake.(3)The body length of crustaceans was between 180-1780μm.The smallest body-sized species was Chydorus sphaericus,with an average body length of 276μm.The largest body-sized species was Phyllodiaptomus tunguidus,with an average body length of 1126 μm.From 2015 to 2019,the abundance of crustaceans over1 mm in body length showed a decreasing trend.(4)The redundancy analysis showed that the main environmental factors causing the change of zooplankton community structure in Yangzong Lake were total phosphorus,total nitrogen,As,water temperature,transparency and dissolved oxygen.In comparsion with the historical data of Yangzong Lake and related lakes,the zooplankton species(species composition or richness)in Yangzong Lake changed greatly with eutrophication,fish predation and arsenic pollution,and zooplankton abundance decreased significantly.Through monitoring zooplankton in Yangzong Lake for five consecutive years and combining with the existing historical data,I systematically analyzed the temporal and spatial changes of zooplankton,which will provide an important scientific basis for scientifically evaluating the health risks of arsenic pollution to zooplankton in Yangzong Lake and protecting lake ecological environment. |
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