A global research project, led by UAB scientist Ariane Arias-Ortiz and published in Global Change Biology, has studied methane gas emissions in more than a hundred tidal wetlands and marshes across the USA. This research has pinpointed significant environmental factors influencing methane output and has generated a comprehensive collection of standardized data on greenhouse gas emissions from these ecosystems. The findings can enhance the precision of greenhouse gas accounting and refine climate models.
Tidal wetlands play a crucial environmental role. They not only help conserve biodiversity, protect against erosion, and promote fishing activities but also assist in absorbing carbon dioxide from the atmosphere and slowing down the breakdown of organic matter in oxygen-poor, waterlogged soils.
Nonetheless, these conditions also lead to the release of methane—a greenhouse gas that is much more potent than carbon dioxide in trapping heat in the atmosphere. This release can undermine the carbon dioxide absorption capabilities of these wetlands, making it vital to accurately determine and forecast methane emissions to understand the climate impacts of restoring or degrading these natural habitats.
Under Ariane Arias-Ortiz from the UAB Department of Physics and a member of the Marine and Environmental Biogeosciences research group at ICTA-UAB, the study analyzed methane flux data from 109 US tidal wetlands, examining aspects such as climate, vegetation, and the chemical makeup of sediment-bound water. This is the first instance where such an extensive dataset on these emissions has been made available in a standardized format for the scientific community.
The research uncovered important spatial and temporal factors that influence methane emissions, highlighting interactions among various environmental variables for the first time. Salinity emerged as a key influencer; wetlands with higher salinity emitted lower levels of methane, whereas freshwater marshes displayed variable emissions. Freshwater marshes with warmer temperatures produced more methane, while those located above the floodplain, and thus less flooded, emitted less.
Additionally, the study revealed that seasonal changes in methane emissions within the same ecosystem highly depend on temperature—the higher the temperature, the more methane is emitted—as well as on plant carbon absorption and photosynthesis. Unlike inland wetlands, tidal marshes exhibit substantial daily variations in methane release, affected by plant activity, which can enhance root exudation during active photosynthesis and stimulate methane-producing microbes or help transport gas through the plant’s tissue. Furthermore, regions with pronounced tidal influences recorded peak emissions, mainly as intermittent discharges of stored gas following each low tide. Utilizing the study’s data could lead to enhanced models for predicting methane emissions and simulating these dynamics within tidal wetlands amid climate change.
“Methane emissions significantly affect climate change, and their variability in tidal wetlands complicates efforts to ascertain the total greenhouse gas production from these ecosystems. Predicting these emissions is crucial for meeting environmental goals and refining climate models,” explains Ariane. “This research provides valuable data and methodologies that can enhance the accuracy of methane emission assessments in tidal wetlands and improve national and global greenhouse gas inventories.” Over the past ten years, interest in restoring coastal wetlands to combat climate change has surged, as these tidal marshes can sequester more carbon dioxide per unit area than ecosystems like terrestrial forests. Ariane emphasizes that “the implications of this research are important for enhancing the accuracy of methane emission forecasts in tidal wetlands and for evaluating how restoring these ecosystems can aid in climate change mitigation.”
This research presents practical guidelines for determining whether methane emissions from a specific marsh are, or could be, significant enough to be included in greenhouse gas inventories for emission-reduction initiatives. The findings offer “more precise estimates of methane fluxes in these ecosystems than the global figures provided by the IPCC,” she notes. Understanding the mechanisms driving the observed emissions “is essential for accurately forecasting methane emissions in upcoming climate scenarios, particularly as tidal wetlands confront the escalating pressures of human activity and climate change consequences like rising sea levels and global warming,” she concludes.
