Phytoplankton Community Composition And Its Relationship With Environmental Factors Of Typical Waters In The North And South Sides Of Qinling Mountains

Phytoplankton is the primary producer in the water environment,and plays an important role in starting the food chain.To some extent,it can also reflect the quality of water environment and the stability of water ecosystem.At present,the harm of Cyanophyta blooms has been reported all over the world.The large-scale propagation of Cyanophyta blooms has brought serious impact to fishing and breeding,and seriously affected the drinking water safety of residents around the water body.The investigation of phytoplankton community composition and its relationship with environmental factors will help us to understand the spatial and temporal distribution of phytoplankton and the competition mechanism between dominant species.At present,there are few studies on the spatiotemporal changes of phytoplankton and its relationship with environmental factors in Shaanxi,so this study takes North and South sides of Qin Ling mountains as the research area,chooses three typical water bodies as the research objects,?two urban landscape water bodies in Guanzhong Region?Juehe Wetland Park and Xiaoxihu Lake?,Weihe River?Shaanxi section?and hilly pond in southern Shaanxi Province?,through the exploration of drainage basin water environment quality and phytoplankton community,in order to enrich the investigation and research on the succession law of phytoplankton community and its relationship with relevant environmental factors in the water body of semi-humid and semi-arid areas.The main conclusions of this study are as follows:?1?From August 2017 to July 2018,two urban landscape waters?Juehe Wetland Park and Xiaoxihu Lake?were sampled and investigated.The results showed that the whole sampling period,phytoplankton communities in the two lakes are showing a significant seasonal and similar succession.Among them,Cyanophyta?Microcystis?dominated in August and September 2017 in the Juehe Wetland Park,and Bacillariophyta?Navicula?dominated from October to July 2017.From August to November in 2017,Cyanophyta?Microcystis?were dominant in the Xiaoxihu Lake.From December to July of the next year,Bacillariophyta?Synedra?were dominant.Redundancy analysis?RDA?results showed that the Cyanophyta and Bacillariophyta in the two lakes were positively correlated with temperature.Cyanophyta was positively correlated with total phosphorus?TP?,while Bacillariophyta was negatively correlated with TP.In addition,there was a close relationship between temperature?T?and TP in Microcystis,Navicula and Synedra in the two water bodies.Among them,Microcystis were positively correlated with TP,while Navicula and Synedra were negatively correlated with TP.?2?In August 2017,samples were collected along the Weihe river basin?Shaanxi section?,and the analysis results showed that Bacillariophyta?Nitzschia?was dominated in most sampling sites.When the levels of moderate and severe eutrophication were reached,the proportions of Chlorophyta?Pediastrum?and Cyanophyta?Microcystis?increased,and there was a tendency to replace Bacillariophyta?Nitzschia?as the main phyla.The results of RDA analysis showed that nitrate nitrogen?NO₃^—-N?,total dissolved phosphorus?TDP?,Total nitrogen?TN?and dissolved organic carbon?DOC?were closely related to phylum of phytoplankton.TDP,DOC,TN and TP were closely related to the succession of dominant phytoplankton species.?3?In August 2019,a sampling survey was conducted on the main ponds in southern Shaanxi,and the results showed that Bacillariophyta and Chlorophyta were the main phyla.Among them,the Nitzschia was dominant at most sampling sites.Cryptophyta and Euglenophyta were mainly concentrated in Xunyang County Ankang City to Hantai District,Hanzhong City?S15?S37?.Achnanthes is mainly distributed in Danfeng County Shangluo City to Langao County Ankang City?S3?S24?.The distribution of Navicula and Cymbella was relatively dispersed among the sampling sites.RDA analysis showed that TP,NO₃^—-N and TDN were closely related to phylum of phytoplankton.TP,ammonia nitrogen?NH₄⁺-N?and TN are closely related to the succession of dominant phytoplankton species.?4?Through the comparison of N,P concentration and dominant algae species in three typical water bodies in the northern and southern sides of Qinling mountains,it is found that Bacillariophyta?Nitzschia?was suitable for living with N concentration of 1?5 mg L^-1 and P concentration of 0.01?0.3 mg L^-1.Bacillariophyta?Navicula?was easy to dominate in water with N concentration of 1?3 mg L^-1 and P concentration of 0.01?0.1 mg L^-1.However,Cyanophyta?Microcystis?were more likely to reproduce in large numbers at higher N concentration(2?13 mg L^-1)and P concentration(0.02?0.1 mg L^-1),thus becoming dominant species.