Analysis of microbial and chemical exchange processes at the groundwater–surface water interaction zone
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Abstract
This essay examines the hydrological, chemical, and microbial interactions coupled with each other that occur at the interface of groundwater and surface water (hyporheic zone). The aim is to learn the role of hydrological connectivity and redox gradients in controlling the dynamics of microbial communities and nutrient conversion, which in turn affects the quality of water and ecosystem processes. A transect sampling method was used to sample the interaction zone to obtain surface water and groundwater samples. On-site measurements were done to measure physicochemical parameters (temperature, pH, dissolved oxygen, electrical conductivity, and redox potential). The structure of microbial communities was studied by ATP analysis and 16S rRNA gene sequencing. The standard laboratory methods were used to determine the chemical components (nutrients and dissolved organic carbon). The processes of hydrology and geochemistry were assessed based on the law of Darcy, the advection-dispersion equation, and numerical modeling, with the help of statistical techniques such as correlation and principal component analysis. The findings indicated that there were high hydraulic connectivity values with gradients between 0.002 and 0.015, which are indicative of active exchange processes. Surface water was oxic (DO: 6.8 mg/L; redox: +120 mV) and groundwater was suboxic to anoxic (DO: 3.2 mg/L; redox: -50 mV). The electrical conductivity of groundwater (780 µS/cm) was greater than that of surface water (420 µS/cm). The Firmicutes and Actinobacteria were the most dominant microbial communities (28–46%), and the diversities of the hyporheic zone were the highest. The occurrence of the processes of nitrification and denitrification was evidenced by the occurrence of the nutrient gradient, indicating high concentrations of nitrate in the surface waters (8.5 mg/L) and ammonium in groundwater (4.6 mg/L). The paper shows that the groundwater surface water interface represents a dynamic biogeochemical reactor wherein hydrological flow, redox, and microorganisms work together to balance nutrient cycling and contaminant conversion. These observations show the importance of such an interface in maintaining water quality and the need to have integrated monitoring and modeling systems.
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