Water Chemistry And Bacterioplankton Community Characteristics Of The Le'an River

To understand the characteristics of the hydrochemistry and the phytoplankton community in the Le'an River,and to explore the effects of hydrochemistry and geographic distance on the bacterioplankton community,we collected surface water samples from 15 sampling sites in the Le'an River in the dry season?December 2016?and the wet season?July 2017?.We tested the concentrations of Na⁺?K⁺?Mg²⁺?Ca²⁺?Cl^-?SO₄^2-?HCO₃^-?NO₃^--N?NH₄⁺-N?TP?TOC?Cu?Zn and other hydrochemistry parameters.The characteristics of the bacterioplankton community by using high-throughput sequencing technology.Non-metric Multidimensional Scale?NMDS?Analysis of sampling sites based on Bray-Curtis distance was used to explore the bacterioplankton community structure.The t-test was used to compare the differences of water hydrochemistry parameters and bacterioplankton community diversity indexes in different seasons.One-way analysis of variance was used to analyze the differences of hydrochemistry and bacterioplankton communities in different reaches.We analyzed the relationships between water hydrochemistry,geographic distance?length of the river,mean dendritic stream length,cumulative dendritic stream length and basin area?and bacterioplankton community by Mantel Test.Variance partitioning was used to separate the impact of water chemistry and geographic distance on bacterioplankton community structure.The results showed that:?1?The highest concentration anion in the Le'an River was SO₄^2-,and the highest concentration cation was Ca²⁺.The water ions in different reaches of Le'an River were controlled by natural weathering of rock and anthropogenic activities,and the water hydrochemistry type was significantly different.The upstream was HCO₃-Ca,the middlestream was SO₄-Mg-Ca,and the downstream was SO₄-Ca-Na.?2?The concentrations of NO₃^--N,NH₄⁺-N and TOC in the dry season were higher than those in the wet season.Spatially,NO₃^--N and NH₄⁺-N in the downstream were significantly higher?p<0.05?than those in the upstream by the mines and agricultural activities.The concentrations of NH₄⁺-N and TP were increased from upstream to downstream gradually.The concentrations of TOC between different reaches was not significant,and the middle reach was higher than the other reaches.?3?The average concentration of trace metal elements in the Le'an river was Zn>Cu>As>Cr>Pb>Cd.The concentrations of Cr,Cu,Zn,Cd and Pb in the dry season were significantly higher than those in the wet season?p<0.05?.Spatially,because of the mines?e.g.Dexing Copper Mine?,the concentrations of Cr,Cu,Zn and As was highest in the middlestream.The concentrations of Cu and As were significantly higher in the upstream than that in the middlestream and downstream?p<0.05?.?4?The bacterioplankton community's richness and diversity in the Le'an River were higher in the wet season than those in the dry season.The richness increased along the flow direction and the diversity was highest in the downstream and the lowest in the middle stream.?5?The highest abundance of bacterioplankton community in the dry season was Proteobacteria,followed by Bacteroidetes and Actinobacteria.The abundance of Proteobacteria in the middle and lower reaches was significantly higher than that in the upper reach;the abundance of Bacteroidetes in the middle and lower reaches were significantly lower than that in the upstream;and the abundance of Actinobacteria in the upstream was higher unsignificantly than that in the middle and lower reaches.The highest abundance of bacterioplankton community in the wet season was Actinobacteria,followed by Proteobacteria and Cyanobacteria.The abundance of Actinobacteria firstly decreased and then increased along the flow direction,and was significantly lower in the midstream than that in the downstream.The abundance of Proteobacteria decreased along the flow direction gradually.The abundance of Cyanobacteria reached the highest in the midstream and was significantly higher than that in the downstream.?6?The average proportion of non-freshwater bacteria in Le'anjiang during the wet season was 62.94%,which was significantly higher than that in the dry season?49.33%??p=0.001?.it is continuously affected by human activities along the river.The abundance of non-freshwater bacteria in the dry season is gradually increasing.However,it was highest in the middlestream,followed by the upstream and the downstream during the wet season.?7?NO₃^--N was the best index among water chemistry variables explaining the dynamics of bacterioplankton community,and the length of the river was the best index among geographic distance variables.Both water chemistry and geographic distance affected the distribution of bacterioplankton community in the Le'an River.The affect of water chemistry was higher than the geographic distance.The variance variation of 54% and 51% was explained by water chemistry in the dry and wet season,respectively,and the geographic distance was 2% and 12%,respectively.The variance variation explained by water chemistry and geographic distance together was 28%in dry season and 20% in the wet season.