Overlooked in carbon counting: Ground-breaking method estimates agricultural pond methane emissions in Australia

Published in a recent paper, the innovative method utilises open-access satellite imagery and sophisticated modelling to provide accurate estimations of methane emissions, facilitating targeted mitigation strategies.

Agricultural ponds, often overlooked in carbon accounting, have emerged as significant contributors to methane emissions, amplifying anthropogenic climate change. These small water bodies, covering approximately 7,500 kilo hectares worldwide, exhibit some of the highest methane emissions among man-made aquatic systems. However, their emissions are frequently neglected in national GHG inventories, highlighting the urgency for enhanced monitoring and reporting mechanisms.

Probing the ponds​

The study, led by a team of experts — from Deakin University, the Australian Department of Climate Change and Western Australia’s Department of Primary Industries and Regional Development, Sustainability and Biosecurity — introduced a remote sensing approach that considers various factors influencing methane emissions from agricultural ponds.

By analysing monthly fluctuations in surface area, historical accumulation rates, and temperature dependence of methane emissions, the method is said to offer unprecedented insights into the dynamics of GHG emissions.

As a case study, the method was applied to inform the 2024 National Greenhouse Gas Inventory reports submitted by the Australian government, aligning with commitments under the Paris Agreement. Subsequently, the findings revealed a staggering 58% increase in total annual methane emissions from agricultural ponds in Australia between 1990 and 2022.

This surge was closely tied to the expansion of water surfaces, with an average of 16,000 new ponds built annually, contributing to a yearly increase of methane-emitting surfaces by 1,230 hectares. Furthermore, these findings revealed that Australian agricultural ponds covered approximately 173,000 hectares and emitted around 41 kilo tonnes of methane annually.

At the same time, the researchers compared emissions from agricultural ponds to established reservoirs, revealing higher methane emissions per area from ponds despite occupying less surface area. These findings highlighted the need for improved understanding and mitigation strategies for methane emissions from agricultural ponds.

Compared to previous editions of the national GHG inventory, the study indicated a smaller water surface area for agricultural ponds, mainly due to accounting for partially covered ponds. Additionally, methane flux predictions using the Boltzmann–Arrhenius relationship showed intermediate values compared to previous editions.

The study also highlighted the importance of accurately representing historical changes in methane emissions for setting emission reduction targets. It noted a 44% increase in pond surface area and a 58% increase in total emissions since 1990. Notably, mission reduction targets for agricultural ponds in the 2024 edition of Australia’s national GHG inventory are aiming to return to 1990 levels.

Addressing uncertainties in the model, the study identified research priorities, such as developing remote sensing tools and improving the parameter for the temperature sensitivity of methanogenesis. By enhancing understanding of greenhouse gas emissions from agricultural ponds, the researchers aimed to promote innovative mitigation strategies and attract investments through carbon credit and bio-diversity finance schemes.

Breaking new global ground?​

The study marked a milestone in the quest for effective climate action, emphasising the importance of integrating small-scale emissions sources into national GHG inventories. Following the 2019 Refinement of IPCC guidelines, nations have been encouraged to account for methane emissions from small constructed waterbodies in their GHG inventory reports.

This study, focused on informing Australia's 2024 edition of the national GHG inventory, introduced several improvements in methodology. These included accounting for monthly fluctuations in pond surface area, historical accumulation rates of agricultural ponds, and the temperature dependency of methane emissions.

In shedding light on the significant contribution of agricultural ponds to methane emissions and outlining methods to accurately estimate these emissions from small constructed waterbodies (particularly agricultural ponds), the researchers hope to encourage nations to include them in their National Greenhouse Gas Inventory Reports.

By leveraging high-resolution satellite data and advanced modelling techniques, countries can gain a comprehensive understanding of methane emissions from agricultural ponds, paving the way for targeted mitigation efforts.

Policymakers are also urged to capitalise on these insights to develop tailored strategies aimed at curbing methane emissions from agricultural ponds. Financial incentives, such as carbon or bio-diversity credits, hold the potential to mobilise investments in emissions reduction initiatives while enhancing the ecological and environmental value of these water bodies.

With the novel data and modelling tools introduced in this study having been made available on a free cloud-based platform, countries worldwide are empowered to embrace this innovative approach, driving collective efforts towards a sustainable future.

Source: ​ACS Publications​

“​Including Methane Emissions from Agricultural Ponds in National Greenhouse Gas Inventories”​

https://doi.org/10.1021/acs.est.3c08898​

Authors: ​Martino E. Malerba, et al​.