Impacts Of Hydrological Regulation And Climate Environment Fluctuation On Cladoceran Communities In Lakes Of Northwest Yunnan

Lake is an important part of inland waters,the ecosystem of lakes is of great significance for providing habitats for plants and animals,improving local climate and maintaining biodiversity.With the persistence of climate change and human disturbance,the stress of environmental on lake ecosystem health is increasing.For nearly a century,climate warming and exogenous inputs caused by human activities are transforming the ecological systems on global scale.Even alpine lakes at high altitudes,which are not directly affected by human activities,are also experiencing much stronger environmental pressures than ever before.There are numerous and diverse lakes in Yunnan,the stereoscopic natural geographical environment differences gives birth to various typical lakes in northwest Yunnan region.Crustacean zooplankton paly a central role in energy transfer along lake food weds because of their intermediate trophic level.However,few studies is kown on how human hydrologic regulation and climate change affect community organization and succession of cladoceran in northwest Yunnan.In order to explore the ecological response pattern of cladoceran to human hydrogical regulation and climate change on the spatio-temporal scale,this study selected three lakes in northwest Yunnan as the research objects.Based on the lake modern survey,monitoring data,literature records and analysis of surface and core sediments,the time series of changes of three lakes environments and cladoceran communities were established,and also constructed spatial and temoral change patterns of environment changes and cladoceran communities along water level gradient in Haixi Lake.Furthermore,the characteristics of ecological environment change among different lakes were compared and analyzed by various statistical analysis methods,and the environmental driving factors affecting the community structure of cladoceran were identified,so as to reveal the the ecological evolution process and mechanisms of typical lakes with different types and different degrees of human influence in northwest Yunnan.This study manily obtains the following research results:(1)Spatial survey of surface sediments in Haixi Lake showed that the physicochemical indicators show some environmental differences in water depth gradient.When the water depth is greater than 8 m,surface sediments had smaller particle sizes and higher TOC and TN values,and vice versa.In the past two centuries,the environmental characteristic of lakes in Haixi Lake changed significantly in 1957 and 1990,and the deposition rate of core sediment,median grain size,TOC,sediment C/N and benthic taxa of cladoceran all showed peaks in the two hydrological regulation periods.(2)There is a threshold water depth(~ 8 m)that affects the cladoceran community construction in both spatial and temporal scale,which possibly linked to lake water thermal stability and littoral habitat coverage.The planktonic species,Bosmina,was dominant and the benthic species were less in the spatio-temporal of cladoceran communities.In terms of spatial distribution,the antennule size of Bosmina din’t change signidicantly in the water depth gradient,however,the size of Bosmina’s antennule decreased with the water depth increased on the time scale.For the Haixi Lake,which is obviously influenced by anthropogenic hydrologic regulation,water level serves as a significant factor in affecing zooplankton species construction,including community structure,diversity and individual size,which are closely related to water depth.(3)Taiji Lake and Tiancai Lake are shallow alpine lakes,and their sediment cladoceran communities are mainly dominated chydoridate(Alona and Chydorus),with higher benthic abundance ratio.Sediment Chla-a,TC and TN in Taiji Lake and Tiancai Lake increased significantly in recent decades,while C/N value continued to decrease,indicating the increase of lake primary productivity and endogenous organic matter.Water TOC and sediment carbonates in Taiji Lake have been decreasing since 1820,indicating that increased atmospheric nitrogen deposition has caused in acidification of lake water.The cladoceran communities and environmental drivers of two alpine lakes in the same basin showed differences,but the increasing of nutrients(Nr)and regional climate warming were significant environmental drivers.(4)The comparative analysis of the three study lakes shows that Haixi Lake under the continuous influence of hydrologic regulation and alpine lakes in the natural state show different environmental changes and ecological response patterns.In Taiji Lake and Tiancai Lake,TN and TC in the sediments had higher background values than that in Haixi Lake,but the content of Chl-a and fluxes of cladocran in sediments were significantly lower than in Haixi Lake.Since 1960,nutrient and primary productivity increased in the three northwest Yunnan lakes.In conclusion,the changes of lake hydrological conditions,climate change in the watershed,the increase of nutrient and their interactions have significantly changed the biogeochemical cycle,biological community structure and diversity,and the functional health of lake ecosystem.Thus,the management of water resources in lakes and reservoirs should be carried out within its ecological threshold.Furthermore,the alpine lakes in the natural state are generally in poor nutrient level,but regional warming and nitrogen deposition have significantly affected the characteristics of water environment and the distribution of biological communities,so it is necessary to take active measures to alleviate the long-term ecological effects of water level decline and water acidification.