Nutrient Impacts on Biogenic Chemical Flux in an End Pit Lake Reclamation Scenario

Ebullition of biogenic gases, primarily methane (CH4), might affect the trajectory of end pit lake (EPL) reclamation. We investigated the influence of nutrients (N with or without P) on methanogenesis and the resulting chemical flux from underlying fluid fine tailings (FFT) to cap water. Anaerobic 10 L columns were filled with FFT amended with a mixture of hydrocarbons (n-alkanes, iso-alkanes, and monoaromatics from C-6-C-10 ; HC columns) and capped with process water. Some amended FFT were further amended with N (HCN columns) or N and P (HCNP columns). A microbial community dominated by Desulfobacterota and Desulfotomaculales plus acetoclastic and hydrogenotrophic methanogens depleted hydrocarbons at different rates concomitant with CH4 production in the order HCN > HC > HCPN, indicating stimulation of methanogenesis by N and inhibition by P amendments. Microbial processes transformed FFT minerals (Fe-III to Fe-II minerals and dissolution of carbonates), mobilized ions, and trace elements (Ca2+, Mg2+, K+, HCO3-, Sr, and Ba) in FFT porewater and densified FFT and induced chemical flux to cap water. Other dissolved trace elements (As, Sb, and Mo) decreased in porewater and cap water during methanogenesis. The results provide novel information about nutrients' effect on methanogenesis and associated chemical flux to inform predictions about sustainable management of EPL.