Hidden contribution of shrimp farming effluents to greenhouse gas emissions from mangrove soils

Abstract

In the present study, we evaluated CO2, CH4, and N2O fluxes in mangrove soils that receive shrimp farming effluents. Soil and gas samples were collected from a mangrove that receives the discharge of shrimp pond effluents and another mangrove forest free of the effluent impacts. CO2 and N2O emissions were significantly higher in the mangrove soil affected by the shrimp effluents (51.4 mg m2 h−1 and 90.9 μg m−2 h−1, respectively) than in the mangrove soil free of the effluents (26.5 mg m−2 h−1 and 40.4 μg m−2 h−1, respectively). No significant differences in CH4 emissions were observed between the two mangroves soils (mean values ranging from 0.2 to 0.8 mg m−2 h−1). Suboxic conditions govern nitrification-denitrification and mineralization processes and control CO2 and N2O emissions from the soil; however, CH4 fluxes were not affected. The highest emissions from the impacted soil (93% higher for CO2 and 125% higher for N2O) were attributable to the high content of organic carbon, total nitrogen, and potentially mineralizable nitrogen, which reduce the role of the mangrove in mitigating greenhouse gas emissions.