Fencing the Flux: Seasonal Trends, Environmental Drivers, and Mitigation Opportunities of Methane Emissions From Farm Dams

Farm dams are significant methane (CH₄) sources in agricultural landscapes. Fencing them to limit livestock access reduces organic matter and nutrient inputs, thereby limiting CH₄ emissions. However, existing studies on the benefits of fencing are constrained by short durations, omission of ebullitive fluxes, limited spatial and temporal coverage, and small sample sizes. Here, we report a large-scale, multi-season assessment of total CH₄ (diffusive + ebullitive) and carbon dioxide (CO₂) fluxes from fenced and unfenced farm dams, along key environmental drivers. We monitored 113 farm dams in temperate mainland south-eastern Australia over 2 years, amounting to 39,552 and 45,408 hourly observations of total CH₄ and CO₂ fluxes, respectively. We integrated field-measured emissions with Sentinel-2 indices, topo-climate variables, and geostatistical models to identify flux drivers, quantify temperature sensitivity, and spatially extrapolate mitigation potential across Local Government Authorities (LGAs). We found that fencing reduced CH₄ fluxes by 66%-82% across seasons while also significantly lowering the temperature sensitivity of CH₄ fluxes, slowing the exponential rise in emissions under warming conditions. Specifically, CH₄ fluxes in fenced dams increased by 71% per 10°C warming (Q₁₀ = 1.71, E_M = 0.4 eV), compared to unfenced dams increasing by 275% (Q₁₀ = 3.75, E_M = 0.98 eV). CH₄ fluxes were driven by temperature, rainfall, and hydrological proxies (Modified Normalized Difference Water Index, MNDWI; Floating Algae Index, FAI), while CO₂ fluxes responded to rainfall and Normalized Difference Water Index (NDWI). Extrapolating our findings across the study area (~526,296 km²), fencing all farm dams could cut CH₄ fluxes by 1.16-1.35 kt year^-1. By combining high-resolution emission data with scalable management strategies, this study offers a framework to improve greenhouse gas inventories and guide targeted climate mitigation in agriculture.