Assembly Mechanisms And Driving Factors Of Macroinvertebrate Community In The Impounding Lakes Along The Eastern Route Of The South-to-north Water Diversion Project

Community assembly is one of the core topics in ecological research and is mainly affected by niche processes and neutral processes.The relative importance of these two processes are usually with research scale,geographical area and species groups varies,as most of the groups in a restricted by diffusion from fully to completely restricted by ecological niche of the spectrum.Therefore,to clarify the distribution patterns of community and biodiversity and the drive behind the process is helpful to formulate scientific and effective strategies for biodiversity conservation.The operation of the South-to-North water diversion project(SNWDP)has brought a lot of uncertainties to the lake ecosystem."The Overall Plan of the South-to-North Water Diversion Project" clearly states:"Protecting the ecological environment is the basic premise and important goal of the planning and implementation of the SNWDP".The ecological and environmental safety of lakes is very important for the smooth implementation of the SNWDP.In this study,benthic community assembly and its driving mechanisms were studied in impounding lakes along the eastern route of the SNWDP,which can provide support for scientific management and biodiversity conservation in the lakes along the eastern route of the South-to-North Water Transfer Project.The main results are as follows:In terms of environmental factors,the compositions of physical and chemical factors of the lakes on the eastern route of the SNWDP were significantly different,especially between Gaoyou Lake and Hongze Lake near the water intake and Dongping Lake,Nansi Lake and Luoma Lake in the north.Water quality of the lakes along the eastern route of the SNWDP was best in spring and worst in summer.Water quality of Gaoyou and Hongze Lakes in spring,autumn and winter was better than that of other lakes and opposite was true in summer.Water in impounding lakes was mainly at mesotrophic and light-eutrophic levels.The runoff of the inflow rivers was the key factor affecting the physicochemical composition of the lakes.Especially in summer,the mass nutrients have the great influence on the water quality.We found that Compared with species diversity,functional and phylogenetic diversity were more sensitive to the response of lake eutrophication gradient.Changes of species,phylogenetic and functional diversity were consistent with trends of TLI,TLI(Chl-a),TLI(TN),TLI(TP),TLI(CODMn)and TLI(SD).For community assembly,Species and functional structure of benthic communities and diversity indices were significantly different among the impounding lakes.Spatial factors,environmental factors and their interactions had great effects on the benthic community and diversity,while climatic factors had relatively little effect on the diversity.At the same time,we found that the influence of spatial processes on the community construction increased with the increase of the study scale,and there were significant differences in the mechanism of the community assembling among different impounding lakes.Beta diversity was highest in species dimension,followed by phylogenetic dimension and lowest in functional dimension and dominated by the turnover component.Null model analysis showed that the functional and phylogenetic community assemblings were most likely to be dominated by random processes.Large spatial scale,the construction of cascade pump station and the weak mobility of benthic animals are the main factors leading to the diffusion limitation.Then,taking Weishan Lake as an example,we conducted a comparative study on the effects of inter-basin water transfer on benthic species and functional structure,and found that there were significant differences in the composition of benthic species and significant changes in community structure before and after the project operation.Compared with species structure,functional structure was more sensitive to habitat changes,and there were significant differences in the key factors driving the benthic community before and after water transfer.