Bacterial and Archaeal Community Successions in Extremely High-Salinity Groundwater and Their Potential Impact on Arsenic Cycling

Abstract

Groundwater arsenic (As) contamination is a global issue involving complex biogeochemical processes. However, the arsenic cycling in extremely high-salinity groundwater environments remains unclear. In this study, we used hydrogeochemical and microbial techniques to investigate the impact of salinity on bacterial and archaeal community structures and their functional evolution in the Yellow River Delta (YRD), China, exploring how these dynamics influence arsenic enrichment. The results showed that bacterial richness and evenness were significantly reduced with increasing salinity, particularly in samples with TDS above 10 g/L, with a more pronounced reduction compared to archaea. Bacterial communities were dominated by Proteobacteria and Omnitrophica, with relative abundances fluctuating with salinity levels. Archaeal communities were predominantly composed of Halobacteria, which displayed higher tolerance to saline conditions. Microbial communities are actively involved in As-Fe-C-N-S redox cycling, displaying different cycling characteristics under varying salinity conditions. Microbe-mediated organic matter degradation, sulfate reduction, iron reduction, methanotrophy, and methanogenesis potentially contributed to As mobilization in low-salinity groundwater. In contrast, in extremely high-salinity groundwater, the processes of sulfur respiration, iron respiration, and nitrate respiration are more intense; however, methane oxidation and methanogenesis are inhibited, which also affects As cycling. This study highlights the critical role of salinity in shaping microbial community dynamics and functions in the YRD aquifers, enhancing our understanding of arsenic biogeochemical cycles in high-salinity environments.

Keywords: High-As groundwater, Biogeochemical cycling, Microbial diversity, Functional profiles, River Delta