Dissolved inorganic phosphorus enrichment in groundwater of phosphate mining areas driven by multiple biogenic pathways.

The role of microbial mediation in the enrichment of phosphorus (P) is often mentioned but has rarely been explored, particularly regarding microbially mediated P cycling in P-contaminated groundwater within phosphate rock mining areas. To bridge this gap, this research explored the multiple biogenic pathways involved in dissolved inorganic phosphorus (DIP) enrichment by an approach combining comprehensive field investigations with hydrochemical and molecular biological analyses. Hydrochemical characteristics revealed that carbonate mineral dissolution and dissolved organic matter (DOM) degradation were the two key pathways controlling DIP enrichment in karstic water. Moreover, correlations between functional genes and DIP revealed that the indirect biological pathway involving CO2-driven carbonate weathering and the direct biological pathway mediated by gcd-governed gluconic acid acidification exhibited the strongest associations with DIP enrichment. Intense water-rock interaction drove the differentiation of inorganic P dissolution pathways and enabled the gcd pathway to dominate microbial DIP mobilization. Next were the direct biological pathways mediated by phosphatases encoded by the ppa and ppx genes, as well as the organic P mineralization pathway utilizing high O/C (≥ 0.4) unsaturated and aromatic P-containing compounds as core substrates. Substrate concentration and species might control the dominant pathways of DIP release, given the overwhelming dominance of inorganic P over organic P. These findings provide new insights into P enrichment in groundwater from a microbial perspective and offer valuable implications for the P management and remediation in phosphate mining areas.