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 production. 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 two 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, EM = 0.4 eV), compared to unfenced dams increasing by 275% (Q10 = 3.75, EM = 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 yr⁻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.

Methods
This research was conducted in temperate mainland south-eastern Australia (Fig. 1), covering the states of Victoria, New South Wales, and southern Queensland. The region spans approximately from –39.14° to –25.85° latitude and from 140.96° to 168.00° longitude, encompassing temperate zones across these states with diverse landscapes, including temperate grasslands, coastal plains, and montane environments, and has a temperate climate influenced by the Southern Ocean. Seasonal temperatures range from 25–30°C in summer (December–February), 20–25°C in autumn (March–May), 15–25°C in spring (September–November), and 6–10°C in winter (June–August). Annual rainfall, peaking in winter, typically varies from 400 to 1200 mm. Livestock grazing, particularly beef cattle and sheep, dominates the region’s agriculture. The study area spans 526,296 km2 and contains an estimated 249,305 farm dams, with an average total water surface area of about 24,000 hectares (ha) across 168 Local Government Authorities (LGAs) (Malerba et al., 2021).

Over a period of 24 months (October 2022–October 2024), we monitored 113 farm dams to analyse seasonal patterns of CH4 and CO2 emissions, their driving factors, and the effects of fencing to limit livestock access. These dams were spread across ten farming properties arranged along an approximately 1,498 km transect in temperate southeast Australia. Each property contained 2–25 farm dams, with treatments nearly balanced between fenced dams (n = 52; 685 monitoring days) and unfenced dams (n = 61; 963 monitoring days). Sampling spanned all four seasons, including summer, autumn, winter, and spring, with individual dams monitored for periods ranging from one week to four months in one or multiple seasons, yielding a total of 1,648 dam-day observations.