| As primary producer in aquatic ecosystems,the changes of phytoplankton community structure can reflect the variations of water environment.Phytoplankton community structure and environmental characteristics at 15 sampling sites in Liuye Lake(L1～L9),Chuanzi River(C1～C3)and Yuan River(Y1～Y3)were quarterly investigated from March to December,2018.The trophic level index was used to evaluate the eutrophication status in the water body.At the same time,the phytoplankton community structure and environmental characteristics of the three types of water bodies were compared and analyzed,and the importance of water body connectivity was discussed.The main results are as follows:The annual average trophic level index values were 54.58,53.44 and 42.56 in Liuye Lake,Chuanzi River and Yuan River,respectively.The Yuan River has the good water quality,followed by Liuye Lake,and Chuanzi River has the poor quality.The Liuye Lake was transformed from light eutrophic in spring and summer to mesotrophic in autumn and winter.The trophic status of the Chuanzi River was mesotrophic in summer,and middle eutrophic in spring,autumn and winter.The trophic status of the Yuan River was light eutrophic in summer,and mesotrophic in other seasons.The species richness of phytoplankton was the highest in Liuye Lake,followed by Chuanzi River,and Yuan River.The three types of water bodies were similar in phytoplankton composition.Cyanophyta,Chlorophyta and Bacillariophyta were the main species.The number of species in Chuanzi river and Liuye Lake was the highest in summer,and in the Chuanzi River was the highest in spring.During the investigation,105 species of phytoplankton were identified in Liuye Lake,82 species of phytoplankton identified in Chuanzi River,and 56 species of phytoplankton identified in the Yuan River.The dominant species in the Liuye Lake and Chuanzi River are similar,with Cyanophyta as the main species.The dominant species in Yuan River were mainly Bacillariophyta.The dominant species of phytoplankton were Merismopedia tenuissima,Aphanizomenon sp.,Melosira ambigua and Cryptomonas ovata in Liuye Lake.The dominant species of the phytoplankton were Melosira granulata,Melosira ambigua,Cryptomonas ovata,Merismopedia tenuissima and Aphanizomenon sp.in Chuanzi river.The dominant species of phytoplankton are Melosira granulata,Melosira ambigua,Melosira varians and Cryptomonas ovata in Yuan River.During the investigation,the average abundance of phytoplankton was highest in the Chuanzi River,followed by Liuye Lake,and Yuan River.The annual abundance of phytoplankton ranged from 0.44×106 to 13.59×106 cells/L in Liuye Lake.The phytoplankton abundance was highest in summer and lowest in winter The phytoplankton community structure was Chlorophyta-Bacillariophyta type in spring,Chlorophyta-Cyanophyta type in summer,Cyanophyta type in autumn,and Cyanophyta-Chlorophyta-Bacillariophyta type in winter The annual abundance of phytoplankton ranged from 1.04×106 to 32.22×106 cells/L in the Chuanzi River,and the phytoplankton abundance is the highest in autumn and lowest in winter The phytoplankton community structure is Cyanophyta-Chlorophyta type in spring and summer,Cyanophyta-Bacillariophyta type in autumn,and Bacillariophyta-Cryptophyta type in winter The annual abundance of phytoplankton ranged from 0.02×106 to 0.91 ×106 cells/L,and the phytoplankton abundance was the highest in spring and lowest in winter The phytoplankton community structure is Bacillariophyta type in spring,Cyanophyta-Bacillariophyta type in summer and autumn,and Bacillariophyta-Chlorophyta-Cryptophyta type in winter.The results of redundancy analysis revealed that the most significant environmental factors influencing phytoplankton community were dissolved oxygen,transparency,chemical oxygen demand and chlorophyll a in Liuye Lake,total nitrogen in Chuanzi River,water depth,chlorophyll a and total phosphorus in Yuan River.This study showed that the connection among Chuanzi River and Liuye Lake and Yuan River had a certain impact on the variations of phytoplankton community structure.The water quality index and phytoplankton abundance were both high in Liuye Lake,showing a trend of eutrophication.Therefore,tourism management should be strengthened and control the discharge of domestic sewage from the land source.The urban area of Chuanzi River was greatly affected by human activities,and the water quality index and the phytoplankton abundance were high,showing a trend of eutrophication.Therefore,the management of sewage outlets and rainwater pumping stations should be strengthened.As the main river flowing through Changde city,the control of pollutants to Yuan River is crucial to maintaining the health of river ecosystem and human being. |
