The Study On Composition Of Phytoplankton Communities And Their Response To Environmental Factors In Typical Freshwater Lakes Of Southeastern Hubei

At present,the eutrophication of freshwater lakes in southeastern Hubei is becoming more and more serious.Eutrophication in lakes can disrupt the normal pattern of phytoplankton diversity in the water column and cause harm to freshwater ecosystems.Phytoplankton are important primary producers in lakes,and can be classified into micro（20-200μm）,nano（5-20μm）and pico（0.7-5μm）based on particle size.Changes in the particle-level structure of phytoplankton can reflect changes in nutritional levels of lakes,making them an important basis for monitoring and assessing trends in water environment quality.In this study,the phytoplankton samples from the typical freshwater lakes in southeastern Hubei,including Cihu Lake,Baoan Lake,Qingshan Lake and Xiandao Lake in 2021,were analyzed using field ecological surveys,high performance liquid chromatography（HPLC）and Chemical Taxonomy to obtain the trophic status of the typical freshwater lakes in southeastern Hubei and their influencing factors.The phytoplankton community structure and its succession were also studied,and redundancy analysis（RDA）was carried out to investigate the key factors affecting the phytoplankton community structure of typical freshwater lakes in southeastern Hubei.The results are as follows:The nutrient status of the typical freshwater lakes in southeastern Hubei,Cihu Lake,Baoan Lake,Qingshan Lake and Xiandao Lake,were light eutropher,mesotropher,light eutrophic and oligotropher respectively.Turbidity（Turb）,chemical oxygen demand(COD_Mn),total nitrogen（TN）,total phosphorus（TP）and phosphate(PO₄^3-)were the main factors affecting the nutrient status of typical freshwater lakes in southeastern Hubei.Xiandao Lake was phosphorus-limited in spring.Baoan Lake and Xiandao Lake were significantly nitrogen-limited（TN/TP<9）in summer and winter,while Cihu Lake and Qingshan Lake were jointly nitrogen-phosphorus-limited in all seasons.Fucoxanthin（Fuco）,Neoxanthin（Neox）,Lutein（Lute）,Alloxanthin（Allo）,Chlorophyll b（Chl b）and Chlorophyll a（Chl a）were the most important characteristic photosynthetic pigments in typical freshwater lakes in southeastern Hubei.The phytoplankton photosynthetic pigments were strongly correlated with dissolved oxygen（DO）,Turb,p H,TN,TP and PO₄^3-at all grain levels.The phytoplankton photosynthetic pigments of micro,nano,and pico phytoplankton all showed significant positive correlations with Turb,TN,TP and PO₄^3-.The main characteristic photosynthetic pigments of small phytoplankton all showed negative correlations with DO.The phytoplankton community of typical freshwater lakes in southeastern Hubei was mainly consisted of Euglenophytes,Diatoms,Cryptophytes and Chlorophytes,and mainly dominated by nano and pico phytoplankton.The redundancy analysis revealed that COD_Mn,WT and TP were the key factors influencing the changes of phytoplankton communities at all grain levels in typical freshwater lakes in southeastern Hubei.PO₄^3-was one of the key factors influencing the changes of micro and pico phytoplankton communities in typical freshwater lakes in southeastern Hubei.The results of the study provided a systematic understanding of the trophic state,photosynthetic pigment composition,community composition of phytoplankton at various grain levels and their response to environmental factors in typical freshwater lakes in southeastern Hubei.And the results could provide ideas for the environmental management of lakes,and also provide a working basis and methodological ideas for the study of phytoplankton biodiversity in shallow lakes,lake environmental protection,eutrophication prevention and monitoring.