Fencing farm ponds to limit livestock access reduces nitrous oxide and methane emissions

Farm ponds are globally abundant features in agricultural landscapes and are increasingly recognised as important sources of greenhouse gases. However, greenhouse gas assessments of these systems have largely focused on methane (CH 4 ), while nitrous oxide (N 2 O) emissions remain poorly understood. Furthermore, it remains unclear whether management interventions that reduce CH 4 emissions also reduce N 2 O emissions. Here, we quantified carbon dioxide (CO 2 ), CH 4 , and N 2 O fluxes from 54 fenced and unfenced farm ponds across 495 km in southeastern Australia, amounting to 16,773 hourly greenhouse gas measurements, to assess the effects of livestock exclusion on multi-gas emissions. Fenced ponds exhibited 44% lower N 2 O and 52% lower CH 4 emissions than unfenced ponds, resulting in 44% lower total CO 2 -eq emissions. In contrast, CO 2 fluxes did not differ between treatments. Reductions in CH 4 and N 2 O emissions were not consistently coupled across sites, with only 52% of sites showing concurrent reductions in both gases. Measured water-quality variables did not strongly explain greenhouse gas variability, suggesting that standard water-quality metrics alone may be insufficient to predict mitigation outcomes. Despite contributing little to total emissions in mass units, N 2 O accounted for more than three-quarters (76.7%) of total CO 2 -eq emissions owing to its high global warming potential. Together, our findings show that livestock exclusion can reduce CH 4 and N 2 O emissions from farm ponds, but mitigation outcomes are strongly context-dependent and cannot be inferred from single-gas responses alone.