Microbial Effects On Arsenic Redox In Alternating Wet And Dry Conditions In A Coastal Wetland

Arsenic(As)is one of the typical metal elements with high toxicity.It is widely distributed in coastal soil and wetland and its content increases.Due to tidal action,there are regular alternations of wet and dry in coastal wetland,which not only affects the physical and chemical reactions of wetland environment,but also has a close relationship with the composition of microbial community in sediments.These two factors affect the redox potential and migration release of arsenic in coastal tidal flat wetlands.In this study,a combination of laboratory simulation culture experiment and in-situ measurement experiment was used,and a longitudinal comparison was made between film gradient diffusion technology(DGT)and traditional slice collection method,aiming to explore the longitudinal trends of arsenic,iron and other elements above and below the water and soil interface,as well as the analysis of various forms of arsenic in soil.At the same time,q PCR technology and 16 s RNA microbial technology were used to study the changes of microbial community composition and arsenic related genes in sediments,and combined with the results of arsenic indexes in water and soil,to analyze the effects of microorganisms on the redox potential and migration release of arsenic under the condition of dry and wet alternately.The purpose of this study is to provide scientific basis for the ecological treatment of arsenic pollution in coastal tidal wetlands through the in-depth study on the mechanism of arsenic migration and transformation at the water and soil interface.The main research results of this subject are as follows:(1)In the case of long-term flooding,iron minerals in the soil in the early stage were reduced and dissolved,resulting in an increase in arsenic concentration in the water.In the later stage,due to the formation of ferrous minerals,part of arsenic in the water was adsorbed to the surface of minerals and precipitated in the soil.The concentration of available arsenic in soil increased with depth.As(Ⅲ)was the main valence state of arsenic in soil.Fusibacter and Sva1033 were the dominant bacteria,and anaerobic microorganisms accounted for a relatively high proportion.The abundance of ars C and arr A genes in arsenic related genes in soil was higher,which reduced As(V)to As(Ⅲ)in soil.Both the water body and the sediment are in anaerobic state,and the reducibility is strong.(2)Simulated semilunar tide,from flooded state to dry state,the water environment presented aerobic state,arsenic concentration in water decreased rapidly,arsenic concentration in soil increased,and most arsenic in water was absorbed into minerals.The proportion of microorganisms Fusibacter,Sva1033,Celeribacter and Vibrionimonas increased after drying,and the anaerobic bacteria still accounted for the main part.The deep soil still maintained environment.Compared with the semilunar tide,the arsenic concentration in the diurnal tide simulation test water did not fluctuate significantly,maintaining a relatively low concentration,and the higher fulminic acid component in the organic matter in the water promoted the release of arsenic.The activities of urease and dehydrogenase were promoted at low arsenic concentration in soil.Alkaline phosphatase was negatively correlated with arsenic concentration,while aryl sulfatase was little affected by arsenic concentration.Among the microorganisms,Salinimicrobium,Pseudomonas and Erythrobacter are the dominant bacteria;Salinimicrobium is the aerobic bacteria,and Pseudomonas can oxidize As(Ⅲ)to As(V).(3)Compared with the field test and the laboratory test,the similar continuous flooding group in the subtidal zone was always flooded,and the similar diurnal tide simulation group in the intertidal zone alternated between dry and wet.In general,arsenic concentration was very low at the coastal water and soil interface,but high below the interface.The total arsenic concentration in the field water in the intertidal zone is lower than that in the subtidal zone,and the residual arsenic phase in the subtidal zone is relatively high.The arsenic adsorption in the soil pore water is less,and the concentration is lower but increases with the depth.The arsenic form of good type iron and aluminum in intertidal zone is positively correlated with the concentration of total arsenic and As(Ⅲ),so the trend of arsenic concentration in soil is similar to the proportion of iron,aluminum and arsenic form.The concentration is higher at 2-4cm depth and 6-8cm depth,and decreases at 6cm depth.At this depth,arsenic precipitated in minerals and less arsenic in pore water.Desulfobacterota is predominant on a microbial level with Proteobacteria,Chloroflexi,Acidobacteriota and Desulfobacterota.Restrial_group of Woeseia,SBR1031 and BD2-11_terrestrial_group are restrial_restrial_group...