Influence Of Biogeochemical Characteristics On Migration And Transformation Of Arsenic In Aquifer Of Kuitun River Basin

Arsenic is a trace non-metallic element,toxic and carcinogenic,widely distributed in rocks and minerals,affected by biochemical conditions,will migrate into groundwater.Long term drinking high arsenic groundwater(arsenic concentration?10?g·L^-1)can cause skin cancer,bladder cancer,liver cancer,lung cancer and other diseases.Microorganisms play an important role in the migration and transformation of arsenic in groundwater.By analyzing the characteristics of microbial community structure and diversity in groundwater and sediment,exploring the impact of microbial community structure and function on geochemical environmental change has become a research hotspot.In this paper,the chemical components and microbial communities in aquifers of Kuitun River Basin were studied.The biogeochemical characteristics of these samples were analyzed by mathematical statistics,high-throughput sequencing,microbial analysis and other methods.The influencing factors of microbial community structure were determined,and the role of microorganisms in the biochemical migration and transformation of arsenic was identified.The main conclusions are as follows:(1)As and NO₃^-in groundwater exceeded the standard seriously and showed great spatial variability in the vertical direction.The over standard areas of as are mainly distributed in the plain area to the north of Wuyi highway,and the mass concentration of as in groundwater increases from south to north;the over standard areas of NO₃^-are mainly distributed in the South and middle and upper reaches of the plain area,and the mass concentration of NO₃^-gradually decreases with the direction of groundwater runoff.In the middle and upper reaches of the plain area,under the violent human activities and precipitation leaching,the microorganisms related to nitrogen cycle(nitrification and denitrification)in groundwater have a great impact on the migration and transformation of arsenic.(2)There are significant differences in microbial communities between high arsenic groundwater and low arsenic groundwater.The main microorganisms in high arsenic groundwater are Actintobacter,Aquabacterium,and Sphingomonas and Pseudomonas in low arsenic groundwater.Aquabacterium and Acinetobacter participate in the desorption and competitive adsorption of arsenic in groundwater,resulting in the increase of arsenic concentration in groundwater;Pseudomonas mainly promotes the release of arsenic from mineral surface to dissolved state through As(V)reduction,Sphingomonas can oxidize As(III),so that arsenic in groundwater can be adsorbed on rock mineral surface,resulting in the decrease of arsenic concentration in groundwater.(3)Proteobcatia was the most abundant phylum in sediment samples,followed by Actinobacteria,Firmicutes,Bacteroidetes and Chloroflex,which accounted for more than 88.5%of the total phylum level abundance.At genus classification level,the most abundant species are Arthrobacter,Acinetobacter,Pseudomonas,Novosphingobium and Hydrogenophaga.Arthrobacter increases the concentration of arsenic in the sediments by adsorbing dissolved arsenic in groundwater and coexisting iron-manganese minerals in the sediments.Actinobacteria can decompose organic materials,which contain sulfur bacteria,which can cause SO₄^2-reduction in groundwater,leading to further accumulation of arsenic in groundwater.In the process of reducing nitrate in the soil,Pseudomonas uses As(?)as the electron acceptor to generate solid Fe(?)oxide,which fixes the arsenic on the surface of the oxide.With the enhancement of the oxidation environment in the sediments,Hydrogenophaga oxidizes As(?)in groundwater,and the dissolved arsenic becomes solid arsenic and exists in the sediments.(4)The chemical components in groundwater and sediments have a great impact on the microbial community.In groundwater,the main environmental factors that affect the microbial community are sampling depth,groundwater p H,TDS,DO,EC,As,Fe,NH₄⁺,HCO₃^-.Bacteroidetes have a greater impact on the competitive adsorption of HCO₃^-and As.Nitrospirae can promote NH₄⁺to form a reducing environment and dissolve solid arsenic into groundwater;Chloroflexi has the effect of evaporation and concentration to further enrich arsenic in groundwater.Ca,Mg,Mn,Cu,As are the main environmental factors affecting the microbial community in sediments.Ca is significantly negatively correlated with Hydrogenophaga,Novosphingobium,and Aquabacterium,and Mn is significantly positively correlated with Nocardioides.Under the action of groundwater runoff,the arsenic-containing minerals in the sediments enter the groundwater under the action of microorganisms,which reduces the adsorbed arsenic in the sediments.When the sampling depth is large,Hydrogenophaga can produce NO₃^-through nitrification,which promotes the desorption of arsenic adsorbed on the surface of minerals into the groundwater.