Research On The Characteristics Of Algal Bloom And Organic Pollution In Typical Stagnant Water

As an important surface water resource,the stagnant water body is different from deep-water lakes and reservoirs in that the water body flows slowly and has a long renewal period,so the water body is prone to eutrophication and algal blooms.At present,there are frequent water pollution problems in slow-flowing reservoirs in many cities,which seriously affect people’s production and life.As a typical stagnant water area,the Yuzigou Reservoir provides a reliable water source for the third water plant in Xixian New Area and scattered agricultural land.Its water quality is crucial to promoting the construction of ecological civilization in Qinhan New Town.In order to explore the characteristics of algal blooms and organic pollution in stagnant water,the water quality changes and algal community structure in the reservoir were analyzed and studied.This paper mainly includes the following three aspects:（1）The characteristics of water quality changes before and after the impoundment of the Yuzigou Reservoir and the succession characteristics of the algal population structure after the impoundment;（2）The composition and source of dissolved organic matter in the water body after the impoundment of the reservoir;（3）Small-scale study on pressure control of algae.The main conclusions are as follows:（1）The comprehensive nutritional status index（TLI）of the Yuzigou Reservoir was higher after impoundment,which indicated that the reservoir was in a state of eutrophication for a long time.A total of 79 species of algae in 5phyla,35 genera and 79 species were identified in the reservoir.The succession of dominant species in the algal community is greatly affected by temperature.In spring（March,April,May）in 2021,the proportion of green algae was35.7%～49.3%,mainly chlorella and cellulophyte;in summer（June,July,August）,cyanobacteria dominated（40.5%～49.2%）,mainly merismopedia,chromococcus and microcystis.A total of 15 phytoplankton functional groups were monitored in the water body:A,C,D,F,J,L0,M,MP,N,P,S1,W1,X1,X3,Y.Its spring and summer season changes are:A+F+M+D+X1+J in March→C+A+MP+X1 in April→J+X1+F+M+DinMay→L0+P+X1+MP+N+S1+Y+Din June→L0+J+F+X1+N+M+S in July→L0+J+F+X1+P+N+W1+S1 in August.The distribution of planktonic algae in the Yuzigou Reservoir is relatively uniform,and there is no stratification phenomenon.（2）After impoundment,the DOC concentration in each sampling area of the reservoir was basically the same over time,and the water temperature and UV₂₅₄had the greatest impact on the DOC content in the water body.Ultraviolet spectral characteristics showed that the CDOM concentrations in the surface water and bottom water of the reservoir were relatively consistent,and the relative concentration of CDOM in the spring water was significantly lower than that in summer.The PARAFAC technique was used to analyze the terrigenous humus C1,microbial humus C2 and tyrosine-like substance C3 in the Yuzigou reservoir.There was no significant difference in the content of dissolved organic matter in different areas of the reservoir,and the fluorescence intensity of each component showed a trend of increasing in summer.The three-dimensional fluorescence spectral indices（HIX,FI,BIX）showed that the self-sourced pollutants produced by the growth and reproduction of algae and water microorganisms in the reservoir had a greater impact on the DOM composition of the Yuzigou Reservoir.The correlation analysis shows that the three fluorescent components have homology.（3）The small-scale experiment of algae control under pressure showed that chlorella and microcystis under different pressure for 1 minute would have a certain inhibition on the chlorophyll fluorescence activity of algae,and the density of algae could be significantly reduced when cultured under dark conditions.Compared with unpressurized and 0.4MPa pressurized for 1minute,chlorella under 0.8MPa pressurization for 1minute had the highest superoxide dismutase（SOD）and hydrogen peroxide（CAT）enzyme activities during photoculturing,it was shown that pressurization had an effect on the activity of chlorella enzymes.The sedimentation experiments of microcystis after pressurization showed that the pressurization changed the sedimentation process of microcystis and adversely affected the photosynthesis of algal cells.