Relationship Between Phytoplankton Community Structure And Environmental Factors In Baishuimen Reservoir

Baishuimen Reservoir is located in the upstream of Baishuimen Stream in the Wujiang River Basin of Ganjiang River system,Jiangxi Province.It is the standby drinking water source of Yongfeng County,Ji ’an City.In the past,most of the water quality of Baishuimen Reservoir focused on the monitoring of physical and chemical indexes,and there was a lack of research on biological indexes.Phytoplankton can reflect the nutritional status of water bodies,so it is of great value to carry out researches on individual or community ecology of phytoplankton for scientific evaluation of water environmental quality in reservoirs.Based on this,this study set five representative sites in Baishuimen Reservoir from October 2021 to November 2022 for monthly sampling survey.The physical and chemical indicators and phytoplankton biological indicators were used to conduct a preliminary evaluation of the current water quality of the reservoir.Through the analysis of phytoplankton species and dominant species composition,the temporal and spatial succession characteristics of phytoplankton were explored.Pearson correlation analysis and redundancy analysis were used to study the correlation between phytoplankton and water environmental factors.The main research results are as follows:(1)During the investigation period,the temperature of water in Baishuimen Reservoir varied from 10.6℃ to 32.3℃.The average annual transparency of the reservoir is 0.65 m.The monthly variation range of dissolved oxygen was 8.18mg/L～10.28 mg/L,and the annual pH value was 7.43.The average annual permanganate index was 4.48 mg/L.The annual average of ammonia nitrogen concentration in nutrient salts was 0.62 mg/L,and the whole water body was in the poor Class V standard.The annual mean of total nitrogen was 1.25 mg/L,which was in Class IV standard water.The annual mean value of total phosphorus was 0.029 mg/L,which was in the standard Class Ⅲ water supply.(2)A total of 103 species of phytoplankton were detected in 8 phyla,among which Cyanophyta,Chlorophyta and Bacillariophyta were the main groups.The temporal variation of species number was more in winter and spring,but less in summer and autumn.There are more species in the upper and middle reaches of the reservoir than in the lower reaches.The seasonal variation of phytoplankton density was autumn >winter > summer > spring.Spatially,it is high in the middle of the reservoir area and low in the upstream.The temporal variation of phytoplankton biomass in the reservoir was higher in autumn and winter and lower in spring and summer.The biomass in the upper reaches of the reservoir was the lowest,and reached a peak in the transition area between the upper and middle reaches of the reservoir.(3)A total of 19 dominant species of phytoplankton were identified in each season,including 7 species of Chlorophyta,6 species of Cyanophyta,2 species of Bacillariophyta,3 species of Cryptophyta and 1 species of Euglenophyta.In spring,the dominant species were Chlorophyta,among which the main dominant species were Mougeotia and Sphaerocystis schroetri.In summer,the Lyngbya circumcreta was dominant.In autumn,the dominant species were Aphanocapsa,Merismopedia minima and Pseudoanabaena.In winter,Lyngbya circumcreta,Pseudoanabaena and Aphanizomenon.In terms of spatial distribution,the dominant species of phytoplankton in the reservoir were divided into Cyanophyta,Chlorophyta and Bacillariophyta in each sampling site.(4)Shannon-Wiener diversity index and Pielou evenness index were used to comprehensively evaluate the water quality in the reservoir area.It was found that the average values of the two indexes were 1.84 and 0.33 respectively,indicating that the water environment quality in Baishuimen Reservoir area was moderately polluted on the whole.From the perspective of seasons,the diversity indexes were higher in spring and winter than in summer and autumn.Spatially,the variation range of diversity index H’ was between 1.78 and 1.89,and the variation trend of Pielou evenness index was consistent among sampling points,with a low mean.(5)Pearson correlation analysis showed that the number of phytoplankton species in Baishuimen reservoir was negatively correlated with water temperature and transparency.Phytoplankton density was positively correlated with pH,permanganate index and ammonia nitrogen.Phytoplankton biomass was positively correlated with ammonia nitrogen and total nitrogen,and negatively correlated with water temperature and transparency.Redundancy analysis showed that the main environmental factors affecting phytoplankton distribution in Baishuimen reservoir were water temperature,ammonia nitrogen,total nitrogen and transparency.The ratio of ammonia nitrogen,total nitrogen and nitrogen phosphorus contributed more to the density change of Chlorophyta,Bacillariophyta and Cryptophyta,while the influence of permanganate index and pH on Cyanophyta was greater.