Spatial Variations of N₂O Fluxes Across the Water-Air Interface of Mariculture Ponds in a Subtropical Estuary in Southeast China

While aquaculture ponds are potentially important sources of atmospheric N₂O, the magnitude and variability of N₂O concentrations and fluxes both within and across the ponds remain poorly understood. In this study, we examined the small-scale spatial variations of dissolved N₂O concentrations in water and N₂O fluxes across the water-air interface from three mariculture ponds in a subtropical estuary in southeast China. Our results showed that the dissolved concentrations and diffusive fluxes of N₂O in the shrimp ponds ranged between 2.3–19.2 nM and 16.4–589.7 nmol m⁻² hr⁻¹, respectively, over the culture period. Significant variations of N₂O concentrations and fluxes were observed within the ponds, with higher values being observed in the aeration area that could be attributed to the high rates of nitrification in the water column, as well as sediment N₂O production and diffusive flux into the overlying water. Also, N₂O concentrations and fluxes varied significantly among the three ponds as a result of the difference in N-NO₃⁻ and N-NH₄⁺ concentrations in the water column. The large fine-scale spatial variations of N₂O concentrations and fluxes observed in our aquaculture ponds suggested that management practices such as aeration and bait feeding could largely affect the extent that aquaculture activities have on N₂O emissions and climate change through their influence on the physicochemical environment (e.g., oxygen and N-NH₄⁺ concentrations) of the ponds.