Effect of wastewater discharge on greenhouse gas fluxes from mangrove soils

The effects of wastewater on atmospheric fluxes of three greenhouse gases, nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) from mangrove soils were investigated, and the differences among shrimp pond wastewater (SP), livestock wastewater (LS) and municipal (S) sewage were compared. The gas emissions from mangrove soils were significantly enhanced after wastewater irrigation and the highest emission of N2O and CO2 were obtained from SP. High N2O emission was also found in S treatment, where fluxes varied from 13.42 to 16.78 μmol m−2 h−1, but the CH4 and CO2 fluxes were as low as the control irrigated with tap water. Results of soil analyses indicated that the high N2O emissions from mangrove soils receiving SP and S treatments were attributed to the denitrification and nitrification processes, respectively. The highest CH4 flux was recorded in LS treatment (186.14–762.40 μmol m−2 h−1), which also had the highest CO2 flux. The fluxes measured during the non-irrigation period were lower than those measured 4 h after irrigation.

Research highlights
► Wastewater discharge significantly increased greenhouse gas fluxes from soil.
► Shrimp pond wastewater (SP) induced the highest N2O flux due to denitrification.
► Nitrification was the main mechanism for N2O flux in municipal sewage treatment.
► Livestock wastewater treatment had low N2O as the control but highest CH4 flux.
► SP had high organic matter content but the CH4 flux was as low as the control.