Sustainable management of farm dams: Addressing ebullitive and diffusive methane emissions

Fencing farm dams to exclude livestock has recently emerged as a promising management strategy for reducing aquatic methane emissions by half as well as mitigating sedimentation. Farm dams are an important but underestimated contributor to Australia?s methane budget. However, existing literature tends to examine short time series of methane data that focus on diffusion and do not effectively capture interactions from weather. This study trialled a novel method of assessing farm dam emissions by deploying a greenhouse gas sensor (Pondi) tailor-made for long-term monitoring of aquatic systems. This device captures continuous data from both ebullitive and diffusive methane pathways and carbon dioxide. Fourteen farm dams across seven different cattle properties in the outskirts of Greater Melbourne were measured. A paired experiment tested the hypothesis that installing fences to exclude livestock could reduce both total methane emissions and sedimentation in farm dams. The continuous greenhouse gas data was coupled with meteorological data to explore the relationship between environmental variables and carbon fluxes. The results found that fencing significantly reduced daily methane emissions from both diffusive and ebullitive processes by over half (54.7%). The study explored specific interactions between weather variables and aquatic greenhouse gas emissions, and found that higher amounts of rainfall significantly increased methane emissions, while greater humidity was linked to heightened carbon dioxide emissions from farm dams. Fencing significantly reduced sediment entering farm dams, but found no evidence of its effect on the rate of organic carbon sequestration. The results demonstrate that a simple management strategy such as fencing has the potential to mitigate substantial greenhouse gas emissions from hundreds of thousands of farm dams across Australia.