Mitigating greenhouse gas emissions in nitrogen-enriched aquaculture ponds using calcium-based amendments.

Aquaculture ponds with high nitrogen loading emit substantial CH4 and N2O due to anoxic sediments. This study assessed the effects of calcium hydroxide [Ca(OH)2], calcium sulfate (CaSO4), and calcium silicate (CaSiO3) on greenhouse gas (GHG) emissions in 45-day anoxic incubations of sediments from conventional and broad bean-fed ponds. At 20 mmol kg-1, Ca(OH)2 and CaSiO3 reduced CO2 (38-53 %), CH4 (17-66 %), and N2O (43-62 %) emissions by elevating pH (8.5-8.9), enhancing mineral-associated organic carbon, and suppressing functional genes (nirK, norB, nosZ, and mcrA). CaSO4 lowered CH4 (48-56 %) and N2O (49-58 %), likely by stimulating sulfate-reducing genes (aprA and dsrA), but increased CO2 emissions and decreased Fe-bound organic carbon. Structural equation modeling revealed pH, sulfate competition, and microbial community shifts as key mediators. Ca(OH)2 and CaSiO3 offer broad-spectrum GHG mitigation and SOC stabilization, while CaSO4 provides targeted CH4/N2O control. These findings inform calcium-based strategies for climate-smart aquaculture.