Distribution Patterns Of Phytoplankton Community And Its Impact Factors In Huaihe River Basin

Huaihe River is one of seven major rivers in China and it forms a geographical separation between northern and southern China.The population in the basin surpasses all other large basins together in China,and the basin has thus a history of disastrous pollution events and deterioration of aquatic ecosystems.Phytoplankton is the main primary producer in the river ecosystems,which plays an important role for maintaining the aquatic ecosystem,but there are few studies about the phytopalntkon distribution patterns in the Huaihe river basin.In this study we analyzed the phytoplankton community in Huaihe River Basin in 2013 and 2014,we studied the phytoplankton distribution patterns in different river systems,each stream order and distinct seasons and discussed the impact factors such as environmental factors,basin structure and dam on the phytoplankton community.This study is to provide the scientific evidence for the management of river ecosystem and water quality monitoring.1.The distribution patterns of phytoplankton community in Huaihe River Basin:green algae and diatom were major groups upon the species number.244 taxa species of phytoplankton belonging to 104 genera 8 divisions were identified,of which the most abundant are Chlorophyta(101 species of 41 genera),followed by Bacillariophyta(53 species of 29 genera),Cyanophyta(39 species of 18 genera),Euglenophyta(36 species of 5 genera),Chrysophyta(6 species of 5 genera),Dinophyta(5 species of 3 genera),Cryptophyta(3 species of 2 genera),and Xanthophyta(1 species of 1 genera).Fewer species richness was observed in the small streams and the pathway to the sea,while more in the middle of the river.Less phytoplankton biomass was found in the lower or higher stream order,higher biomass in the medium stream order.The average phytoplankton biomass was 3.93 mg/L,ranging from 0.04 mg/L to 83.62 mg/L.The relative biomass of Bacillariophyta was higher in the upstream.and with the increase of stream order,the relative biomasses of Cryptophyta,Dinophyta and Euglenophyta went up.The relative biomass of Cyanophyta and Chlorophyta were higher in downstream of the river.The dominant species in Huaihe River Basin were Cryptomonas erosa,Chroomonas acuta,Ceratium hirundinella and Cyclotella meneghiniana,whose relative biomasses were higher than 5%,respectively.2.Comparisons of the phytoplankton community in different river systems:the phytoplankton community was compared in Shahe River,Jialu River,Nansihu Lakes and Lixiahe River.The lowest species number(84)was in Shahe River and the highest in Nansihu Lakes(100).The green algae and diatom were dominant groups upon the species number in different river systems.Shahe River had the highest phytoplankton biomass(7.01 mg/L),where Dinophyta contributed 85.02%of total biomass.The lowest biomass(0.98 mg/L)occurred in Lixiahe River,where Bacillariophyta and Cryptophyta were major groups,contributing 29.47%and 26.53%of total biomass,respectively.The mean phytoplankton biomass in Jialu River was 3.32 mg/L,Bacillariophyta and Cyanophyta were major groups and contributed 48.8%and 21.99%of total biomass,respectively.The mean phytoplankton biomass in Nansihu Lakes was 2.45 mg/L and major group were Bacillariophyta,Cryptophyta and Cyanophyta,contributed 26.94%?20.41%? 20.41%of total biomass,respectively.The common dominant species in the four river systems were Cyclotella meneghiniana,Nitzschia palea,Cryptomonas erosa and Chroomonas acuta.Phormidum tenus and Synedra acus were the dominant species in Jialu River and Nansihu Lakes.Cymbella tropi'ca and Ceratium hirundinella dominated in Shahe River.Euglena oxyuris was the only dominant species in Lixiahe River.Chlamydomonas globosa was dominnt species in Lixiahe River and Nansihu Lakes.3.The distribution patterns of phytoplankton community in each stream order:we compared the phytoplankton community in each stream order of Yinghe River.The abundant species(96)was observed in the third stream order,with the major groups of green algae(36)and diatoms(30).Low species richness(12)was found in the first stream order and similarly green algae(2)and diatoms(10)constituted the major groups.With the increase of stream order,the species richness of diatoms declined,however the species number of green algae increased.The highest biomass(11.85mg/L)occurred in the fourth stream order,Dinophyta and Cryptophyta contributed for 75.53%and 14.43%,respectively.In contrast,the lowest biomass(0.131 mg/L)occurred in the first stream order,and the contribution of Bacillariophyta was 99.23%.Based on the biomass composition,the first stream order was represented by Bacillariophyta,the second and third stream order by Dinophyta and Bacillariophyta,the forth stream order by Dinophyta and Cryptophyta,the fifth stream order by Bacillariophyta,Dinophyta and Cryptophyta,and the reservoir by Euglenophyta,Bacillariophyta and Cyanophyta.There was a longitudinal gradient from benthic diatom to flagellate algae then to planktonic diatom and flagellate algae with the increased stream order.4.The variations of phytoplankton community in different seasons:174 taxa were identified in 2014,while 124 taxa in 2013,and the green algae and diatoms were major groups based on the species number.The species numbers of Cyanophyta,Euglenophyta and Chlorophyta were higher in 2014 than those in 2013.The average biomass of phytoplankton in 2014 was 4.84 mg/L,Dinophya,Bacillariaphyta,Euglenophya and Cyanophyta contributed more for the total phytoplankton biomass.In contrast,the average biomass in 2013 was 4.59 mg/L,Dinophya and Bacillariaphyta contributed more for the total phytoplankton biomass.The dominant species in 2014 were Cyclotella meneghiniana,Cryptomonas erosa and Pseudanabaena sp.;in 2013,however,it dominated by Ceratium hirundinella,Cyclotella meneghiniana,and Cryptomonas erosa.5.The variations of elevation,water depth,water width and NO3-N were significant in different stream order(one-way ANOVA,p<0.01),the variations of conductivity,transparency,total nitrogen and the ratio of total nitrogen and total phosphorus in different stream order(one-way ANOVA,p<0.05).The Canonical Correspondence Analysis(CCA)indicated that the main variables controlling the phytoplankton community structure were physical variables and nutrients.Cyclotella meneghiniana can be used as an indicator species for the water acidification,Nitzschiapalea for water turbidity,while Phromidium tenue for organic pollution.6.The model that reprensents water directionality(AEM)further better explained the community variations,which suggested that the spatial dynamics of phytoplankton community were mainly confined to the river network and influenced by the prevailing water flow.Procrustes analysis indicated that dams/sluices have significant effects on the hydrological variables and phytoplankton community.7.The idenfied phytoplankton associations by applying the Market Basket Analysis,based on phytoplankton community in 2013,could capture the ecological preferences of phytoplankton.The RDA indicated that the associations of flagellate algae displayed positively with turbidity and stream width,and the associations of flagellate algae and diatoms have a positive relationship with turbidity and TN.