Phytoplankton Community Structure And Ecological Health Assessment In Danjiangkou Reservoir

The abundance,species composition and diversity of phytoplankton populations are the most important indicators of the health of water bodies,and the seasonal changes in the structure of phytoplankton populations are the result of the combined effects of physical,chemical and climatic factors in water bodies.The ecological health evaluation based on the index(P-IBI)has gradually entered people's attention.Danjiangkou Reservoir is the water source area of the middle line of the South-to-North Water Transfer Project,and its water quality is directly related to the safety of water transfer.In order to grasp the current health status of the water ecosystem in Danjiangkou Reservoir,this study conducted a two-year quarterly survey of phytoplankton communities and environmental factors at 19sites in Danjiangkou Reservoir from October 2019 to July 2021.On the basis of analyzing the changes of phytoplankton community structure,the evaluation system of phytoplankton biological integrity index(P-IBI)was established in Danjiangkou Reservoir,and the correlation between P-IBI and comprehensive trophic status index and environmental factors was analyzed to determine This evaluation of the health status of the reservoir ecosystem can provide a basic scientific basis for the management and protection of the water ecology in the Danjiangkou Reservoir.The main findings are as follows:1.The sample points in Danjiangkou Reservoir in different seasons can be clustered well,the difference between spring and summer is not obvious,and the clustering phenomenon is obvious in autumn and winter.On the time scale,water temperature,p H,Cond,ORP,DO,TOC,COD,TN,TP and NH₄⁺-N showed obvious seasonal variation characteristics(p<0.05);on the spatial scale,Cond,SD,COD_Mn,TN,NO₃^--N and Chl.a had significant spatial differences(p<0.05).The overall TLI(?)value of Danjiangkou Reservoir is 37.62,and the water quality is in a mesotrophic state.The overall nutrient status index(TLI)is lower in spring and summer and higher in autumn and winter.From the spatial scale analysis,TLI(?)value The order is Dankusummer>spring>winter in time,and in space it shows library>inlet>Hanku>Danku;Margalef richness index shows summer>spring>autumn>in time In winter,in the space,it shows the warehouse entrance>exit entrance>Hanku>Danku,and the Pielou uniformity index shows in time autumn>summer>spring>winter,and spatially shows the warehouse entrance>inbound entrance>Hanku>Dan Library.3.The Danjiangkou Reservoir is at a healthy level as a whole,and only a few sites are at a sub-healthy level.In spring,the sites of Langhekou,Songgang and Shiqiao were in a sub-healthy state,and the other 13 sites were in a healthy state.It is in a healthy state;in autumn,it is in a sub-healthy state in Baxiandong,Lijiagou,Qushou,Shiqiao and Zhangying,and in the other 13 sites,it is in a healthy state;in winter,it is in Bashang,Lijiagou,Songgang,Shi Qiao and Zhang Ying showed sub-health status,and the remaining 13 sites were healthy.Spring p H was negatively correlated with P-IBI score,Cond,TN,NO₃^--N,TLI(?)were positively correlated with P-IBI score;Autumn TLI(?)was negatively correlated with P-IBI score.