Annual CO2 and CH4 fluxes in coastal earthen ponds with Litopenaeus vannamei in southeastern China

Small-scale aquaculture operation is increasing rapidly in the world, particularly in developing countries, but the greenhouse gas (GHG) dynamics and fluxes from small aquaculture ponds are still poorly assessed.In this study, dissolved concentrations and fluxes of CO2 and CH4 were determined in three coastal earthen shrimp ponds over one whole year, including both farming and non-farming periods, in the Min River Estuary, southeastern China.Different from many previous studies, both ebullitive and diffusive CH4 fluxes were measured.The average concentrations of dissolved CO2 and CH4 in water column in the farming period varied between 18.1±0.1 and 79.6±1.1 µmol L -1 , and 1.3±0.1 and 55.9±3.2 µmol L -1 , respectively.Averaged across the whole year, the mean CO2 and CH4 fluxes from the ponds were -18.4±7.4 and 22.6±6.9mg m -2 h -1 , respectively, suggesting that the shrimp ponds worked as a CO2 sink and a CH4 source.Based on the sustained-flux global warming potential (SGWP) and sustained-flux global cooling potential (SGCP) models, the annual warming potential was estimated to be 7.1×10 3 g CO2-eq m -2 yr -1 , with approximately 90% from the farming period.Ebullition was the dominant emission pathway for CH4, accounting for over 90% of the total CH4 emission during the farming period.The full-year study improves the understanding of carbon cycling in coastal aquaculture ponds and provides scientific basis for updating GHG inventories.