Nitrous oxide emissions at aquaculture ponds in the coastal zone of the Bohai Rim Region of China: Impacts of eutrophication and feeding practice

The coverage of ponds has increased due to the rapid growth of coastal aquaculture, and the intense nitrogen accumulation from feeding input has generated inconstant nitrous oxide (N2O) emissions. Coastal aquaculture ponds are critical hotspots for global N2O emissions. Although it is crucial for developing mitigation solutions, little is known about the source-sink effects of N2O and key influencing factors in aquaculture ponds. This study analyzed water parameters, nutrient status, and coastal aquaculture pond features in the Bohai Rim Region to determine feeding and nutrient implications on N2O production and emissions. Results showed more than 80% of ponds were eutrophic and chlorophyll-driven. N2O concentrations varied spatiotemporally and most ponds were atmospheric N2O sources during mature development, while over half were sinks during dormancy. The emission fluxes of N2O at the water-air interface ranged from-442 to 1109 nmol m-2 h-1 in both periods. High salinity significantly suppressed N2O production, especially in the dormant period. Nitrification dominated N2O production, while denitrification prevailed in some oxygen-deficient ponds during the mature stage. Aquaculture density and species were the main reasons for the spatial differences in N2O concentrations in aquaculture ponds of the Bohai Rim Region. N2O concentrations correlated with contribution proportions of eutrophication factors and pond area. The mean EF5 values (0.0648 in mature stage, 0.0117 in dormant period) exceeded IPCC recommendations by 32 and 5.9 times, respectively, indicating potential underestimation of N2O emission in coastal aquaculture globally. This study highlighted importance of incorporating aquaculture in global N2O assessments and provided data to support sustainable management.