Lake and reservoir methane (CH4) emissions – an underground past, a rising present, and scenarios for the future

During the last two decades, our perception of lake and reservoir methane (CH₄) emissions have changed from being peripheral to increasingly important in global CH₄ budget and source attribution discussions. This is reflected by a 10-fold increase in the number of related scientific publications per year from 2001 to 2020. Earlier research provided a strong foundation that has been developed further. As a result of expanding reserach in the field, some of the early bottlenecks are getting resolved, while others remain, and new challenges have emerged.

It is now clear that lakes and reservoirs jointly contribute in the order of 5 -15 % och the global CH₄ emissions to the atmosphere, and thereby cannot be ignored if we want to understand the atmospheric CH₄ development. This has added challenges regarding data needs and methodologies to make more accurate large-scale CH₄ flux estimates. Key questions also include how lake and reservoir emissions are influenced by environmental change including climate. Critical challenges are nested across a range of scales, from microscale process regulation that shape spatiotemporal variability at the whole-system scale, in turn generating measurement challenges and data constraints influencing global assessments. 

This presentation aims to provide a brief overview, highlighting some learnings and challenges. In addition, predictions of future global lake and reservoir CH₄ emissions will be presented, exploring a data-driven approach to integrate existing knowledge on spatiotemporal flux variability with consideration of multiple emission pathways and their seasonal regulation and long-term response to climate change, as well as to projected changes in inland water area and nutrient load. The relative impacts of different potential flux change drivers was also investigated. Overall, the predicted future emission scenarios illustrate the sensitivity of one of the largest sources of atmospheric CH₄ to the ongoing global change.