| This paper takes Chaohu Lake as the research object.The purpose of the work is to study the environmental factors of water bloom outbreaks and to identify the key factors controlling the bloom of Chaohu Lake.First,the spatial and temporal distribution characteristics and influencing factors of cyanobacteria in Chaohu Lake were studied;the temporal and spatial changes of cyanobacterial GV content and its main influencing factors were investigated,and the phosphorus-limited lake Erhai was used as a comparison to explore the distribution,GV content and cyanobacteria in different nutrient states.The main experimental method is to monitor the water quality and algae indicators of 12 monitoring points in Chaohu from August 2019 to January 2020,which are biological indicators:chlorophyll（Chla）,algae density;physical and chemical indicators of water quality:water temperature,p H,dissolved oxygen（DO）,transparency,conductivity;water quality nutrition indicators:total nitrogen（TN）,total phosphorus（TP）,ammonia nitrogen（NH4+-N）,nitrate nitrogen（NO3--N）,dissolved total nitrogen（DTN）,Dissolved Total Phosphorus（DTP）;Algae Physiological and Ecological Indicators:GV content,floating percentage,vertical migration rate.The main results achieved in this paper are as follows:（1）This article uses field sampling and monitoring techniques to clarify Chaohu Lake’s bloom characteristics and the dominant algal population structure during the experiment,describes the temporal and spatial distribution characteristics of chlorophyll a concentration in the whole lake and monitoring points.Using water quality physical and chemical indicators and water quality nutrient indicators to measure the correlation between the concentration of chlorophyll a in Chaohu Lake and environmental factors,it was found that the main environmental factors that have a significant driving effect on Chaohu bloom are TP concentration,TN concentration and p H.（2）The GV content of cyanobacteria in Chaohu Lake has obvious spatial and temporal distribution characteristics.The time-varying characteristics of cyanobacterial GV content are:from August 2019 to January 2020,the content of cyanobacteria GV at12 points in the surface water showed a trend of increasing first and then decreasing,and a small peak appeared in September（Average:23.1μm3/cell）.This is similar to the time-varying curve of algae density,indicating that the formation of cyanobacterial blooms is related to the volume of GV.The larger the volume of GV,the greater the buoyancy and the easier it is to form surface blooms.The GV content was significantly positively correlated with the concentration of TP in the water;positively correlated with the concentration of NH4+-N,DTP and DTN in the water;negatively correlated with the ratio of nitrogen to phosphorus in the water.（3）The significant difference in phosphorus concentration led to differences in the distribution and buoyancy characteristics of cyanobacteria in Chaohu Lake and Erhai Lake.The biomass of cyanobacteria in the surface water of Chaohu Lake is about 15.75times that of Erhai Lake,and the content of pseudo-air cells of cyanobacteria is about1.12 times that of Erhai Lake.Studies have shown that nitrogen and phosphorus have an important influence on the growth of cyanobacteria and the bloom of cyanobacteria,and under the condition of sufficient nitrogen and phosphorus,the pseudo-empty cell content of cyanobacteria is higher than that under the restriction of nitrogen and phosphorus.In this study,the nitrogen and phosphorus in the water of Chaohu Lake were 2.6 times and 5.3 times that of Erhai Lake,respectively,and the sufficient supply of nutrients made the cyanobacteria biomass of Chaohu Lake significantly higher than that of Erhai Lake.Erhai Lake acts as a phosphorus-limited lake,and the lack of ATP in the cells inhibits the synthesis of pseudoalveolar cyanobacteria.This paper has 54 figures,6 tables and 109 references. |
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