Phytoplankton Community Structure And Ecological Health Assessment Of Typical Landscape Lakes In Nanjing

Nanjing is an important birthplace of Chinese gardens,and water is the important element that plays a crucial role in gardens.Landscape lake is one of the most important in city,and also a business card that Nanjing people are proud of,so it is necessary to pay attention to the ecological health of the typical landscape lake in Nanjing.Phytoplankton community structure is sensitive to environmental changes and is widely used in aquatic ecological surveys.This study conducted a one-year ecological survey of Zixia Lake,Pipa Lake,Huashen Lake,Mochou Lake,Nan Lake,Yueya Lake,and Xuanwu Lake in Nanjing urban area from October 2021 to August 2022.The characteristics of phytoplankton community structure in these seven lakes were analyzed from the aspects of species,dominant species,density,biomass,functional groups and so on.Analysising the correlation between the phytoplankton and the water phy-chemical factors in order to obtaining the key factors that affect community structure.The density,biomass evaluation criteria,biodiversity index,the Q index,and phytoplankton biological integrity index（P-IBI）are used for biological assessment.The comprehensive trophic level index（TLI）and single factor evaluation index are also used for water quality assessment.Based on the results,proposed relevant suggestions for the restoration and management of the typical landscape lakes in Nanjing.The main results are as follows:（1）In this survey,a total of 108 species of phytoplankton were detected,with Chlorophyta taking the lead,followed by Diatoma.The dominant species are mainly Cyanophyta,followed by Chlorophyta,and exhibit heterogeneity in different time and space.The highest value of phytoplankton density and biomass occurred in summer and spring（August and April）,and the lowest values occurred in winter and autumn（December and October）.In space,the highest density appeared in Mochou Lake,followed by Xuanwu Lake,the lowest in Yueya Lake;The highest and lowest biomass values occurred in Xuanwu Lake and Yueya Lake,respectively.Both the Shannon-Wiener and the Margalef of phytoplankton indicate that the typical lakes of Nanjing are in moderate pollution,while the Pielou evaluation results are better（light～moderate pollution）.Phytoplanktons are divided into 28 functional groups,and the spatial and temporal distribution of dominant functional groups varies greatly in Nanjing urban area.The Q index evaluation results based on functional groups show that lakes are mainly in the moderate state.In space,the Q index manifested as Zixia Lake<Xuanwu Lake<Mochou Lake<Yueya Lake<Pipa Lake<Nan Lake<Huashen Lake.In terms of time,the best state mostly occurs in winter,while the worst state is mainly in summer.The states of various lakes vary greatly in spring and autumn.（2）Most environmental factors exhibit significant spatiotemporal heterogeneity.The single factor evaluation results show that the overall water quality is mainly Class III;The average TLI is 47.54,mainly in the mesotrophic and light eutropher state.In terms of time,it presents a phenomenon of high in spring and summer,and low in autumn and winter.In terms of space,Xuanwu Lake has the highest TLI（56.83）,and the lowest value occurs in Yueya Lake（41.13）.（3）WT、Cond、Tur、SD、SS、COD_Mn、TN、TP、NO₃^--N and NO₂^--N are the main environmental factors affecting the density of phytoplankton.In addition,DO、PO₄^3-、p H also affect the dominant functional groups of phytoplankton in various lakes to a certain extent.（4）The P-IBI evaluation results showed that the survey points were mainly in the good state,followed by the moderate.In space,Yueya Lake and Nan Lake have higher P-IBI values,while Xuanwu Lake has the lowest.In time,the highest and lowest values of P-IBI in various lakes mostly occur in winter and summer,which is relatively consistent with the Q index.（5）To achieve the ecological restoration of typical landscape lakes in Nanjing,the following suggestions are proposed:controlling sources and intercepting pollution,controlling pollutants entering the lakes;biological regulation,adjusting the food chain structure of lake ecosystems;vegetation restoration,inhibiting the growth of phytoplankton,reducing nutrient concentration,creating a visual landscape;artificial media,setting up ecological floating islands and biomimetic plants to purify water quality;strengthen management,improving management mechanisms;education and publicity,achieving common construction and sharing among the people.