Phytoplankton Community Structure And Water Quality Evaluation In Dongxihu Lake And Saiqiaohu Lake In Huangshi City

Dongxihu Lake and Saiqiaohu Lake are two natural lakes located in Yangxin County,Hubei Province.Phytoplankton is an important research object in the investigation of water ecological environment.Understanding the internal relationship between phytoplankton and water environment factors can provide a reference for lake management.In this paper,the phytoplankton and water quality of Dongxihu Lake and Saiqiaohu Lake were sampled in April,July,October,20021 and January 2022,and phytoplanktonic community structure of the two lakes were analyzed focusing on the aspects of species composition,abundance,and temporal and spatial changes of dominant species.The biological diversity index was used to evaluate the water quality of Saiqiaohu Lake and Dongxihu Lake.On the other hand,using the water quality index to evaluate the water health of Dongxihu Lake and Saiqiaohu Lake provides relevant scientific basis for maintaining the ecological environment balance of Dongxihu Lake and Saiqiaohu Lake and the construction of aquatic biological resources.The main results are as follows:1.A total of 178 species of phytoplankton were detected in the Dongxihu Lake,belonging to eight phyla and 66 genera.Chlorophyta has the largest number of species,followed by Diatoms,Euglena,Dinophyta,Cryptophyta,Xanthophyta,and Chrysophyta.By analyzing the biodiversity index and evenness of phytoplankton in the four seasons of Dongxihu Lake,the Shannon-Wiener diversity index is summer>spring>autumn>winter,the evennessindex is spring>summer>autumn>winter,and the Margalef index Autumn>spring>winter>summer;198 species of phytoplankton in Saiqiaohu Lake were identified,belonging to 69 genera in eight phyla.Among them,the number of green algae is the largest,followed by Diatoms,Cyanobacteria,Euglena,Dinophyta,Cryptophyta,and Chrysophyta.Shannon-Wiener diversity index of phytoplankton community in Saiqiaohu Lake spring>autumn>winter>summer,evenness index spring>summer>autumn>winter,Margalef index autumn>summer>winter>spring.Based on the diversity indicators of Dongxihu Lakes,the water bodies are in light-moderate pollution in spring,moderately-severely polluted in summer,moderately-severely polluted in autumn,and moderately-severely polluted in winter.According to the comprehensive three indexes,the water quality of Saiqiaohu Lake in spring is slightly polluted.The water quality in summer is mild to moderate pollution,and the water quality in autumn is mild to moderate pollution,while moderate-heavy pollution in winter.2.The seasonal differences of water environmental factors between Dongxihu Lake and Saiqiaohu Lake are significant.The average water temperature of Saiqiaohu Lake in spring,summer,autumn and winter is 20.46,31.11,20.15 and 7.49,respectively.The average water temperature of Dongxihu Lake in the four seasons was 20.5,33.25,20.15,and 9.56,respectively.The annual water temperature of the two lakes was significantly higher in summer than in other seasons.The average total phosphorus content of Saiqiaohu Lake in the four seasons of spring,summer,autumn and winter was 0.27 mg/L,0.28 mg/L,0.29 mg/L and 0.38 mg/L,respectively.The average total phosphorus content of Dongxihu Lake in the four seasons was 0.24 mg/L,0.22 mg/L,0.12 mg/L,and 0.34mg/L,respectively.The content of total phosphorus（TP）in the water body of two lakes in winter was higher than that in other seasons.The average total nitrogen content of Saiqiaohu Lake in spring,summer,autumn and winter was 0.92 mg/L,0.76 mg/L,0.3mg/L and 0.38 mg/L,respectively.The average total nitrogen concentration of Dongxihu Lake in the four seasons was 0.64 mg/L,0.31 mg/L,0.7 mg/L and 0.29 mg/L,respectively.The content of total nitrogen（TN）in water in winter in both lakes was significantly lower than that in other seasons.The p H of these two lakes is weakly alkaline throughout the year.The p H range of Saiqiaohu Lake ranges from 8.45 to 9.91,and the p H range of Dongxihu Lake ranges from 8.36 to 9.47.According to the surface water classification standard,Dongxihu Lake is class III-IV in winter,and class V water in other seasons.Saiqiaohu Lake is class III-IV in spring and summer,and class V water in autumn and winter.3.According to the RDA analysis results,the main abiotic factors affecting the phytoplankton in the Dongxihu Lake are WT,TP,and DO.WT,TP,NH₃-N were the main abiotic factors affecting the phytoplankton community structure in Saiqiaohu Lake.