Year-long real-time monitoring of methane emissions from a sub-tropical reservoir show the persistence of ebullition

Methane emissions from reservoirs are dominated by ebullition, which accounts for up to 88 % of global methane emissions from reservoirs. Due to the sporadic nature of ebullition, it is difficult to measure its persistence through an annual cycle. Short-term manual sampling approaches, often consisting of 24-hour floating chamber deployments, cannot adequately capture the long-term patterns and variability in these emissions rates. This induces higher uncertainty when scaled to system-wide total emissions estimates. To address this, three low-cost automated real-time floating chambers, the Monitub system, were deployed in the Borumba Creek inflow arm of Lake Borumba, a sub-tropical reservoir in Queensland, Australia, to monitor emissions over an annual cycle. Monitoring of chlorophyll, temperature and bed pressure was also conducted to explore links to flux rates.

This long-term high temporal resolution data has revealed the presence of ebullition year-round, rather than it being dependent on seasonality. Statistical analysis of the hourly and daily averages shows rates follow a log-normal distribution. Preliminary results show the fit stabilises 6 – 8 months after deployment. This finding provides insight into minimum deployment timelines required for more accurate characterisation of temporal emission patterns.

These insights would not be attainable through traditional manual sampling techniques, but rather a long-term automated monitoring system is required. These systems can capture sporadic events, reduce required labour, and provide higher statistical understanding of methane emissions. These advances can improve total emissions estimates and inform future monitoring programs, which will lead to higher understanding of the contribution of ebullitive rates.