Geogenic Phosphorus Enrichment in Groundwater due to Anaerobic Methane Oxidation-Coupled Fe(III) Oxide Reduction.

Accumulation of geogenic phosphorus (P) in groundwater is an emerging environmental concern, which is closely linked to coupled processes involving FeOOH and organic matter under methanogenic conditions. However, it remains unclear how P enrichment is associated with methane cycling, particularly the anaerobic methane oxidation (AMO). This study conducted a comprehensive investigation of carbon isotopes in dissolved inorganic carbon (DIC), CO, and CH, alongside Fe isotopes, microbial communities, and functions in quaternary aquifers of the central Yangtze River plain. The study found that P concentrations tended to increase with Fe(II) concentrations, δFe, and δC-DIC, suggesting P accumulation due to the reductive dissolution of FeOOH under methanogenic conditions. The positive correlations of gene abundance versus δC-CH and Fe concentrations versus δC-CH, and the prevalent presence of , jointly demonstrated the potential significance of Fe(III)-mediated AMO process (Fe-AMO) alongside traditional methanogenesis. The increase of P concentration with δC-CH value, gene abundance, and Fe concentration suggested that the Fe-AMO process facilitated P enrichment in groundwater. Redundancy analysis confirmed this assertion, identifying P concentration as the primary determinant and the cooperative influence of Fe-AMO microorganisms such as and on P enrichment. Our work provided new insights into P dynamics in subsurface environments.