Multi-approach assessment of groundwater biogeochemistry: Implications for the site characterization of prospective spent nuclear fuel repository sites

초록

The disposal of spent nuclear fuel in deep subsurface repositories using multi-barrier systems is considered to be the most promising method for preventing radionuclide leakage. However the stability of the barriers can be affected by the activities of diverse microbes in subsurface environments. Therefore this study investigated groundwater geochemistry and microbial populations activities and community structures at three potential spent nuclear fuel repository construction sites. The microbial analysis involved a multi-approach including both culture-dependent culture-independent and sequence-based methods for a comprehensive understanding of groundwater biogeochemistry. The results from all three sites showed that geochemical properties were closely related to microbial population and activities. Total number of cells estimates were strongly correlated to high dissolved organic carbon; while the ratio of adenosine-triphosphate:total number of cells indicated substantial activities of sulfate reducing bacteria. The 16S rRNA gene sequencing revealed that the microbial communities differed across the three sites with each featuring microbes performing distinctive functions. In addition our multi-approach provided some intriguing findings: a site with a low relative abundance of sulfate reducing bacteria based on the 16S rRNA gene sequencing showed high populations during most probable number incubation implying that despite their low abundance sulfate reducing bacteria still played an important role in sulfate reduction within the groundwater. Moreover a redundancy analysis indicated a significant correlation between uranium concentrations and microbial community compositions which suggests a potential impact of uranium on microbial community. These findings together highlight the importance of multi-methodological assessments in better characterizing groundwater biogeochemical properties for the selection of potential spent nuclear fuel disposal sites. © 2024 Elsevier B.V.

키워드