Determining the temporal variation of microbial communities in groundwater systems is essential to improve our understanding of hydrochemical dynamics in aquifers, particularly as it relates to the fate of redox-sensitive contaminants like arsenic (As). Therefore, a high-resolution hydrobiogeochemical investigation was conducted in the As-affected alluvial aquifer systems of the Jianghan Plain. In two 25 m-deep monitoring wells, the seasonal variation in the composition of groundwater microbial communities was positively correlated with the change in groundwater level (R = 0.47 and 0.39 in NH03B and NH05B, respectively, P < 0.01), implying that the latter could be a primary driver of the seasonal microbial dynamics. In response to the fluctuating groundwater level, iron (Fe) reducers within the Desulfuromonadales were dominant (9.9 ± 4.7% among different sampling sites) in groundwater microbial communities during the monsoon season and associated with high concentrations of Fe(II) and As, while the predominance (16.7 ± 15.2% among different sampling sites) of iron-oxidizers the Gallionellaceae was accompanied by low Fe(II) and As in the non-monsoon season. These results suggest that microbially-mediated iron reduction/oxidation may have governed the seasonal mobilization/scavenging of As in groundwater. Our results provide new insights into mechanisms responsible for seasonal variations in groundwater As concentrations in similar aquifer systems.
Keywords: Groundwater level fluctuation; Iron redox cycling; Microbial community dynamics; Seasonal variation; Yangtze River Basin.
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