Effects Of Hydrological Connectivity On The Macrobenthos Community In West Dongting Lake

Hydrology is a key environmental factor affecting aquatic ecosystems.The aquatic organisms in the floodplain wetlands have formed a life history characteristic that adapts to hydrological changes.However,due to the development of water conservancy projects and the excessive use of resources,floodplain wetlands biodiversity is seriously threatened.Since the operation of the Three Gorges Dam,hydrological regime in the middle and lower reaches of Yangtze River has undergone great change.As a result,flooding regime also changed for lakes that with free flow to river,and tidal flats emerge more days which led to the decrease in hydrological connectivity among habitats,and thus,drive macrobenthos community change.Under this background,a key scientific question to be answered for biodiversity conservation in the middle reaches of Yangtze river is how hydrological connectivity affect the spatial and temporal patterns of macrobenthos communities.In this study,West Dongting was selected as the research area,and Yuan River,Li River,high-connectivity lakes,medium-connectivity lakes,and low-connectivity mudflats were set up based on hydrological connectivity and human disturbance gradients.During the water rising period(April),high water period(July),and water withdraw period(October),macrobenthos sampling and environmental factors survey were done to analyze the impact of hydrological connectivity on the spatial and temporal pattern of macrobenthos communities.1)The species richness and abundance in river channel was highest during flood retreat period,whereas for lakes,the highest species richness and abundances were in flood emerging and flood peaking period.These two parameters for low connectivity mudflats remained lowest in all season.The species richness of high connectivity lakes decreased with time gradient.Medium connectivity lakes always supported the highest species abundance.Hemiptera,Ephemeroptera,and Odonata mainly appeared in low-connectivity mudlats during water rising periods,high connectivity lakes during high water periods,and low-connectivity mudflats during water withdraw periods2)The Shannon-wiener index,Simpson index and Margalef index of rivers,middle-connectivitylakes and low-connectivity mudflats were all higher in the water withdraw period,lowest in the high water period,and highest in the withdraw period.The Shannon-wiener index,Simpson index and Margalef index of high-connectivity lakes were all higher in the water rising and lower in the high water period and the withdrawal period.The ? diversity of the low-connectivity mudflats remained lowest in all three periods.3)The spatial ? diversity of each habitat was lower during the water rising period,highest during the high water period,and higher during the water withdraw period.During the water rising period,the? diversity of the low-connectivity mudflats was the lowest,and 50% of the ? diversity was a nested component,whereas the ? diversity of other habitats was high,the nested component was only about3%.NMDS showed the community in low connectivity mudflats is not similar to other habitats.During the high water period,the ? diversity of each habitat were high,90% was composed of turnover components.NMDS showed that the mudflats community had similarities with other habitats.During the water withdraw period,the ? diversity of high connectivity lakes and low connectivity mudflats were the lowest,about 22% were nested components,whereas the? diversity in other habitats was relatively high,and the nested components were only about 3%.NMDS showed that there was similarity between the low connectivity mudflats and the high connectivity lake community.Along the time gradient,the low connectivity mudflats had the highest temporal ? diversity,followed by the Yuan River,and the middle-connected lakes had the lowest temporal ? diversity.Studies have shown that extreme flow(floods)enhanced the dispersal potential of macrobenthos and reduced the species richness and abundance at each plot.During the high water period,the water surface area increased.The higher the spatial variability,the greater the ? diversity,and the higher the proportion of species turnover.However,high flow velocity inhibited the species richness,abundance and alpha diversity of the river.channel.The low connectivity of the mudflats limited the entry of species and recharge of water bodies.Under the drought risk environment of the high-connectivity lake during the water withdraw period,the poorly-tolerance species were not easy to survive,which resulted the decrease in species richness and alpha diversity and increase in the nested components.It reflected the non-random process of species disappearance due to niche differentiation in an unfavorable environment.Medium-connectivity lakes always maintained a certain water area,which supported the complete life history of macrobenthos and the highest species abundance.This study found thatmoderately connectivity is most beneficial to maintain the diversity of macrobenthos in the middle reaches of the Yangtze River wetland.However,our study was limited to a one-year field survey,which fails to explore the inter-annual changes of different hydrological connectivity to macrobenthos communities in the region.