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), CO2, and CH4, 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,
δ56Fe, and δ13C-DIC, suggesting
P accumulation due to the reductive dissolution of FeOOH under methanogenic
conditions. The positive correlations of pmoA gene
abundance versus δ13C–CH4 and Fe
concentrations versus δ13C–CH4,
and the prevalent presence of Candidatus_Methanoperedens, jointly demonstrated the potential significance of Fe(III)-mediated
AMO process (Fe-AMO) alongside traditional methanogenesis. The increase
of P concentration with δ13C–CH4 value, pmoA 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 Candidatus_Methanoperedens and Geobacter on P enrichment. Our work provided
new insights into P dynamics in subsurface environments.