Quantifying the contribution of small and highly dynamic water bodies to methane emissions

Methane (CH4) is a potent greenhouse gas with a global warming potential 28 times higher than carbon dioxide over a 100-year time horizon. The importance of CH4 on a global scale is illustrated by the recent Global Methane Pledge, signed by 103 countries during COP26. Atmospheric concentrations of CH4 have been increasing in recent years. The mechanisms driving recent increases are unclear and could include increased anthropogenic emissions from natural gas extraction, increased natural emissions, and decreased atmospheric oxidative capacity, or a combination of all three. Inland aquatic ecosystems are important sources of methane and could be a driving part of increased natural emissions. Emissions from inland waters have been identified as a critical gap in understanding the global CH4 budget.

Uncertainty of emissions from inland waters comes from a lack of comprehensive spatial datasets and the multiple drivers of emissions in highly dynamic water bodies. The expansion of agriculture and urban areas has created a new water body that has remained relatively unexplored: small artificial waterbodies (SAWBs). These SAWBs (reservoirs, streams, ponds, and ditches) are highly variable in size and have been reported to provide nearly half of regional CH4 emissions. Despite the critical importance of SAWBs in CH4 emissions, their numbers, location, and area are unknown. This lack of information on SAWBs is largely due to challenges brought about by their presence in large numbers and small sizes. Earth Observation data represent a promising way to map the presence of SAWBs as they acquire data systematically over space and time. However, most prior research focusing on mapping SAWBs with EO data is based on medium-resolution satellite imagery (30m Landsat or 10m Sentinel 1 and 2), which is known to underestimate SAWBs.

To address the limitations of accurately mapping small artificial water bodies and quantifying their contribution to CH4 emissions, the overarching aim of this proposal is to provide better annual regional CH4 flux estimates from inland waters of the Southeastern US by constraining the spatial and temporal dynamics of small water bodies.

This is an ongoing project funded by a NASA Commercial Smallsat Data Scientific Analysis (Grant Number 80NSSC24K0053).