Contrasting effects of aeration on methane (CH4) and nitrous oxide (N2O) emissions from subtropical aquaculture ponds and implications for global warming mitigation

The increasing number of small-hold aquaculture ponds for food production globally has raised concerns of their emission of greenhouse gases (GHGs) such as methane (CH4) and nitrous oxide (N2O). Aeration is commonly applied to improve oxygen supply for the farmed animals, but it could have opposite effects on GHG emission: It may inhibit anaerobic microbial processes that produce GHGs; it may also increase water-to-air GHG exchange via physical agitation. To resolve the overall effect of aeration on GHG emissions, this study analyzed and compared the monthly CH4 and N2O emissions from earthen shrimp ponds with and without aeration, in the farming period for two consecutive years, in an estuary in subtropical southeastern China. CH4 flux was mainly influenced by water temperature and dissolved oxygen, and it was significantly higher in non-aerated pond (7.6 mg m -2h- 1) than in aerated ponds (4.5 mg m -2h- 1), with ebullition accounting for >90 % of the emission. Conversely, non-aerated pond had ca. 50 % lower N2O flux than aerated ponds, and dissolved nitrate was the main driving factor. The combined CO2-equivalent emission in aerated ponds (avg. 10,829 kg CO2-eq ha-1 yr-1) was substantially lower than that in non-aerated pond (avg. 17,627 kg CO2-eq ha-1 yr -1). While aeration may increase diffusive flux of GHGs via physical agitation, it remains a simple and effective management practice to decrease the overall climate impact of aquaculture ponds.