Study On Characteristics And Geographical Distribution Of Cladoceran Assemblages In Surface Sediments Of Lakes In Yunnan

As an important carrier of freshwater resources,lakes provide an important living environment for freshwater aquatic organisms.In recent decades,with the development of social economy,the ecological environment of the lakes in Yunnan has been greatly affected by human activities.For example,eutrophication,degradation of aquatic vegetation,disappearance of indigenous fish,lowering of water level,and so on.Due to over-exploitation of some lakes,experiencing the decrese in ecosystem functioning or even regime shifts.With the pressure of multiple environmental stresses,the evaluation of lake ecosystem health in Yunnan requires us to carry out a systematic study on biogeographic distribution and community structure response model of important components of lake system.Cladocera is an important part of zooplankton and it is located in the middle part of the lake food webs.It plays an important role in the material circulation and energy flow of the lake ecosystem,and is very sensitive to changes in the lake’s ecological environment.At the same time,because of its chitin structure,it can be completely preserved in the sediments.It has become one of the important indexes of paleolimnology and paleoecology.Here,we collected the surface sediments of 25 plateau lakes in Yunnan,and the related mathematical and statistical analysis methods were used to identify the spatial distribution characteristics of Cladocera community and the environmental driving factors of community construction,and the differences and causes of the composition of Cladocera community in the two regions of southeast and northwest Yunnan were discussed.The diversity of Cladocera and the body size of Bosmina were also discussed.The main results derived from this thesis include:(1)There are significant spatial differences in the geographical distribution ofthe Cladocera communities in the surface sediments of the lakes in Yunnan.Altitude,water depth and nutrient level are the main environmental factors that drove the spatial differences of Cladocera community in Yunnan lakes.The variation of Cladocera community was explained by 22.1%,8.7% and 3.9%,respectively.Dissolved oxygen,pH,calcium ions,As,etc.also have a certain influence on the spatial distribution of Cladocera communities.(2)The difference of the community of Cladocera in the lakes of northwest Yunnan and southeastern Yunnan is significant and the environmental factors leading to the difference are different.The community structure composition and spatial distribution of Cladocera species in lakes in northwestern Yunnan are mainly affected by elevations and water depth gradients,while the main driving factors for changes in the community structure of Cladocera species in the lakes in southeastern Yunnan are total phosphorus,arsenic,and lake water depth.The two results reflect different driving processes.The lakes in northwest Yunnan are more controlled by natural factors,while the lakes in southeast of Yunnan are dominated by human activities.(3)Cladocera diversity index(species richness,Shannon index and evenness index)showed that the α-diversity index of southeast Yunnan was slightly higher than that of northwestern Yunnan,and its β-diversity was lower in southeast than in northwestern Yunnan.Diversity was significantly correlated with altitude,pH,and water temperature.(4)The antennae length of B.longispina and B.longirostris,two species of Bosmina in the southeast of Yunnan,was significantly longer than that in the lake of northwest Yunnan.The temperature difference dominated by altitude may be an important reason for the significant difference in body size between the two regions.