Summary
This study assessing methane emissions of agricultural ponds in the United States and Australia finds that these ponds emit twice as much methane than is accounted for by national greenhouse gas inventories. Using maps of these ponds, which consist of agricultural runoff (e.g. fertilizer contamination), over the two nations and previous aggregate data, the study quantifies their methane emissions and adjusts their impact in the context of predicted temperature increases. A strength of the study is the inclusion of agricultural ponds associated with raising animals for meat, and weakness is seen in the uncertainty around the parameters of the model (e.g. average methane flux) due to the small sample sizes. As agricultural ponds have some of the highest methane emissions per area among freshwater ecosystems, the study implies a need for management solutions and agriculture regulations that can reduce nutrient pollution in these areas.
Agricultural ponds have some of the highest methane emissions per area among freshwater systems, and these anthropogenic emissions should be included in national greenhouse gas inventories. Here we deliver a continental-scale assessment of methane emissions from agricultural ponds in the United States and Australia. We source maps of agricultural ponds, compile a meta-analysis for their emissions and use published data to correct for temperature and the relative contributions of two methane fluxes (diffusion and ebullition). In the United States, 2.56 million agricultural ponds cover 420.9 kha and emit about 95.8 kt year^−1 of methane. In Australia, 1.76 million agricultural ponds cover 291.2 kha and emit about 75.1 kt year^−1 of methane. Despite large uncertainties, our findings suggest that small water bodies emit twice as much methane than is currently accounted for in national inventories. Managing these systems can reduce these emissions while benefiting productivity, ecosystem services, and biodiversity.