Diffusive nitrous oxide (N2O) fluxes across the sediment-water-atmosphere interfaces in aquaculture shrimp ponds in a subtropical estuary: Implications for climate warming

Emissions of the potent greenhouse gas nitrous oxide (N2O) from aquaculture remain a large knowledge gap in the global N2O budget. The water column and the sediment of aquaculture ponds present very different environmental conditions, but their relative contributions to N2O production and emission are poorly resolved. We sampled three aquaculture ponds in the Min River Estuary in southeastern China monthly throughout the farming season. Based on the dissolved N2O concentrations within the water column and in sediment porewater, we calculated the diffusive N2O fluxes across the water-atmosphere interface (WAI) and sediment-water interface (SWI). The diffusive N2O flux averaged 216.9 nmol m- 2 h-1 across WAI and 16.0 nmol m- 2 h-1 across SWI. The estimated N2O production rate under steady-state condition was 0.13 nmol L-1 h-1 in the water column and 1.07 nmol L-1 h-1 in sediment porewater. Hence, the water column compartment and the sediment compartment of the aquaculture ponds played different roles in N2O dynamics. Based on our data, it is calculated that China's coastal aquacultural ponds would emit 0.2 Gg N2O yr- 1, or less than 1% of all aquaculture N2O emission in China. Therefore, coastal shrimp aquaculture has a relative minor climate impact compared to other aquaculture operations. Future studies should examine the role of N-cycling functional genes on N2O production and the mechanisms regulating N2O emission from aquaculture ecosystems.

Automated summary

Emissions of nitrous oxide (N2O) from aquaculture, particularly in China, are poorly understood. This study investigated N2O dynamics in aquaculture ponds in southeastern China and found that the water column and sediment contribute differently to N2O production and emission. The study estimates that China's coastal aquacultural ponds emit a relatively small amount of N2O compared to other aquaculture operations.