Distribution Characteristics Of Phytoplankton Functional Groups And Biological Evaluation Of Water Quality In Taihu Basin

The study area was located in Taihu Basin and spanned three provinces(Jiangsu,Zhejiang,Anhui)and the Shanghai Administrative Region,China.The basin was located in the lower reaches of the Yangtze River and had a developed water system.Its water quality was related to the water safety of residents.Phytoplankton,primary producers in aquatic ecosystems,are sensitive to environmental changes and often used in water quality monitoring and assessment.We sampled 85 sites in Taihu Basin in August and September 2019,including lakes,rivers,streams and reservoirs,to investigate the distribution characteristics of phytoplankton functional groups and water quality.Three functional group classification methods,FG(Functional Group),MFG(Morpho-Functional Group)and MBFG(Morphology-Based Functional Group),were used to classify phytoplankton.We analyzed the differences in phytoplankton community composition among water bodies and the spatial distribution pattern of Taihu Basin,and discussed the applicability of the three functional groups in different water bodies,to evaluate the contribution of spatial and environmental factors and identify the key environmental factors affecting the spatial distribution of phytoplankton functional groups.The water quality was evaluated by various indexes,including the comprehensive trophic level index(TLI),the diversity indexes,and Functional Group with Q index.The results were expected to provide basic information on phytoplankton community structure and diversity in Taihu Basin,and a theoretical basis for comprehensive management and sustainable development of water quality in the basin.The main results were:1.In total,250 phytoplankton taxa,belonging to nine phyla,13 classes,28 orders,57 families and 110 genera were,for the first time,identified by artificial intelligence image recognition technology,combined with traditional microscopy.The phytoplankton species composition was dominated by Chlorophyta(45.6%),followed by Bacillariophyta(19.2%)and Cyanophyta(16.4%).There were differences in phytoplankton community composition among the four water bodies,but Chlorophyta,Bacillariophyta and Cyanophyta were the main phytoplankton species.Rivers had the largest number of phytoplankton species(224 species),followed by lakes(166 species),reservoirs(83 species)and streams(34 species).The number of phytoplankton species was the lowest in streams in the western part of the basin,followed by Lake Taihu and river inlets along the Yangtze River,and the greatest number was found in the river network in the central plain.2.The average phytoplankton biomass was 7.63 mg/L during the study period,fluctuated between 0.02 and 233.10 mg/L,and was dominated by Cyanophyta(71.41%),Bacillariophyta(11.74%)and Chlorophyta(10.8%).There were differences in phytoplankton biomass among the four water bodies,but Cyanophyta,Bacillariophyta and Chlorophyta were still dominant.Average biomass in rivers was the highest(9.76±34.12 mg/L),followed by lakes(6.57±6.36 mg/L),reservoirs(3.17±0.33 mg/L)and streams(0.25±0.18 mg/L).The spatial pattern of phytoplankton biomass was lowest in streams in the western part of the basin;this was followed by Lake Taihu,river networks in the central plain and river inlets along the Yangtze River(except for the northern part of Lake Taihu);and was highest in the northern part of Taihu Lake and coastal areas of it.3.According to the functional group classification methods,31 FG functional groups were identified:C,D,E,F,G,H1,J,K,LM,Lo,M,MP,N,P,Q,S1,S2,SN,T,TB,TC,TD,W0,W1,W2,WS,X1,X2,X3,Xph,Y groups;24 MFG functional groups:1a,1b,1c,2c,2d,3a,3b,4,5a,5b,5c,5d,5e,6a,6b,6c,7a,8a,9a,9b,10a,10b,11a,11b groups;and seven MBFG functional groups:?,?,?,?,V,?and?.During the study period,15 FG dominant functional groups were divided into M,S1,C,D,Y,G,MP,P,J,SN,F,TB,K,H1 and W1;13 MFG dominant functional groups were divided into 1b,1c,2d,3b,5a,5b,5e,6a,6b,7a,8a,11a and 11b;and there were six MBFG dominant functional groups:?,?,?,V,?and?.Analysis of similarities showed that only FG could significantly represent the differences in phytoplankton functional groups in the four water bodies(P<0.05).FG clustering analysis and similarity percentage analysis showed that the distribution of functional groups of phytoplankton in Taihu Basin had some spatial heterogeneity,and three cluster groups were found.The corresponding species composition types were Cyanophyta,Cyanophyta–Chlorophyta–Bacillariophyta and Chlorophyta–Bacillariophyta–Cyanophyta.The dominant groups were M,S1 groups,M,S1,P,j groups,and P,S1,J,D,C groups.The Mantel test showed that the similarity in the composition of FG functional groups decreased as geographic distance increased.4.There were significant differences among water bodies and environmental factors based on FG functional groups in Taihu Basin(P<0.05).Principal component analysis(PCA)and redundancy analysis(RDA)showed that the main environmental factors affecting the distribution of FG,MFG and MBFG in Taihu Basin were COD_Mn,nitrate nitrogen(NO₃^--N),total nitrogen(TN),transparency(SD),p H value and dissolved oxygen(DO).FG functional groups can better respond to the changes in environmental factors in Taihu Basin.Variation partitioning showed that both spatial factors and environmental factors independently explained the changes in phytoplankton functional groups,but spatial factors had a greater impact.In small local areas,the changes in phytoplankton functional groups were mainly explained by environmental factors.5.We evaluated the water quality of Taihu Basin using various analytical methods.Its water quality was assessed as mildly eutrophic,based on the comprehensive trophic level index(TLI);use of the phytoplankton diversity indexes revealed the water quality to be mildly to moderately polluted;and the phytoplankton Functional Group with Q index evaluated it to be medium.We used these water quality assessment methods to make a preliminarily evaluation that the water quality of Taihu Basin in the wet season of2019 was generally moderately polluted,and the nutritional state was mildly eutrophic.Of the four water bodies,the water quality of reservoirs was the best,followed by rivers and lakes.