Plankton Community Characteristics In Different Areas And Its Responses Of Hrdrological Connectivity In Dongting Lake

The eco-environment of floodplain lakes is considered to be among the most complex environments in the world,which is crucial for maintaining the biodiversity of the ecosystem.Hydrological connectivity is one of the important principal structuring factors of floodplain lake aquatic communities,which is greatly promoting the exchange of energy and matter between river and floodplain lake.As a river-connected lake,Dongting Lake is an important regulating and storage lake in the middle part of the Yangtze River.In recent years,affected by the upstream cascade development and maintenance of farmland,the river-lake relationship has changed,resulting in a significant decrease of natural hydrological connectivity and a longer water change cycle.In Dongting Lake,the lentic water and flowing water are scattered,and the water exchange rate in different regions is different,which determined the plankton community is different in different regions.Therefore,the study on the response mechanism of phytoplankton communities in lakes under different hydrological connectivity gradients is of great significance to the ecological protection and management of the river-connected Lake.In this study,hydrology,water environment and plankton community were systematically investigated in 10 areas with different hydrological connectivity in Dongting Lake in April(normal season)and October(dry season)in 2018.And,the hydrological connectivity of Dongting Lake is calculated(quantitative index is Turnover time),identified the key environmental factors influence community structure of the plankton.And,we tried to figure out the responses of phytoplankton and zooplankton community to the water exchange rate in different scales.In this study,a total of 157 species of phytoplankton belonging to 7 phyla and 51 genera were identified,and species number in April(105 species)and October(120 species)accounted for 66.9%and 76.4%of the total,respectively.Paired sample t test shows Margleft species index and Shannon-Winner index in spring is significantly higher than that in autumn and Pielou evenness index had no differences in the two seasons.PERMISP analysis shows that the beta diversity of phytoplankton in April is higher than that in October.The calculation of the relative contribution of environmental factors to the phytoplankton community indicates that the Turnover time is the dominant factor affecting the phytoplankton community.Regression analysis indicated that phytoplankton abundance and biomass increased with the increase of Turnover time,and the alpha diversity was the highest at the moderate hydrological connectivity,and the beta diversity was also predicted to reach the maximum at the moderate hydrological connectivity.And a total of 1 19 species of zooplankton belonging to 4 phyla were identified,and species numbers in April(91 species)and October(67 species)accounted for 76.5%and 56.3%.Paired sample t test shows Shannon-Winner index in spring is significantly higher than that in autumn and Pielou evenness index had no differences in the two seasons.PERMISP analysis shows that the beta diversity of zooplankton in April is higher than that in October.Regression analysis indicated zooplankton biomass increased with the increase of hydrological connectivity,and the distribution of beta diversity and Turnover time shows a monopeak curve.Except for zooplankton biomass and beta diversity,the abundance,Shannon-Wiener index,and Pielou evenness index had no significant relationship with Turnover time.