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Microorganisms are widely involved in the transformation process of physical and chemical properties in the geological and hydrogeological environment. Active participation of microorganisms is important features of the biogeochemical reactions during groundwater exploiting along the riverbank filtration. Hydrodynamic condition has a direct or indirect difference control of the biological effectiveness, chemical activity and mobility of the pollution components, which can affect biogeochemical process. In different biogeochemistry, there will be some exclusive functional bacteria, which is of great significance to understand the biogeochemical mechanism of river water infiltration. This study confirms that there are two main different flow paths from river to the center of the depression cone due to different hydrodynamic conditions and spatial characteristics and scaling effects of redox zonation during riverbank filtration. In different flow paths, the microbial abundance shows obvious spatial heterogeneity. The microbial abundance and species similarity degree of the riverbed and deep flow path sediments has significant correlation. There is a significant correlation between the dominant bacteria and the environmental factors in different hydrodynamic conditions on a spatial scale. This study is the first to reveal the response of microbial community structure to water chemical evolution during riparian filtration. Due to significant positive correlation between the Fe/Mn and As, it brings the potential danger for drinking water. [ABSTRACT FROM AUTHOR]

Groundwater exploitation along a river bank can not only induce the river water infiltrating but also affect the biogeochemical reactions in the riverbank infiltration zone. Due to the differences in water chemistry in river water and groundwater, there are obvious physical, chemical and biological gradients in the riverbank infiltration zone, resulting in a series of strong and complex biogeochemical processes. In this study, Huangjia groundwater source area along the Liao River is selected as the case study area. To explore the REDOX environment in the infiltration zone induced by groundwater exploitation, and to deduce the major geochemical reactions of release arsenic and iron in aquifer to groundwater under different REDOX environment during bank infiltration. A number of highlighted conclusions has been obtained through this study: arsenic and iron in the sediments are mainly released to groundwater through desorption and reductive dissolution of iron minerals. The content of exchangeable and iron-manganese oxides bound state changes significantly. Co-evolution characteristics of As and Fe release processes are strongly correlated with the variation of REDOX environment, the oxidation of organic matter bound iron minerals under weak oxidizing condition also played an important role in promoting the release of As and Fe. [ABSTRACT FROM AUTHOR]

Intensive groundwater extraction causes many environmental problems globally. Reducing groundwater extraction is a primary method for alleviating these problems. However, this reduction may create new pollution issues because of an increase in groundwater vulnerability. A case study was done using the DRAOTIC evaluation method (an improved DRASTIC method for organic pollutant in aquifer vulnerability; soil (S factor) has been updated by organic matter (O factor) in the method) for the Hun River Basin, northeastern China, where groundwater intensive extraction had caused serious environmental and hydrogeological problems. The assessment results show that moderate vulnerability level is the main vulnerability level in the Hun River Basin; high vulnerability level and low vulnerability level categories occupy a smaller area; while very high and very low vulnerability categories occupy the smallest area. By combining the predicted groundwater level distribution and DRAOTIC model, the responses of groundwater vulnerability to different groundwater extraction reductions could be studied. The results show that groundwater vulnerability levels increased as groundwater extraction was reduced; this is because the rising groundwater levels make it easier for pollution coming from the surface to reach the aquifer. The more the reduction in groundwater extraction, the greater the increase in the area with higher vulnerability levels, and the greater the increase in pollution risk. [ABSTRACT FROM PUBLISHER]