Photo Credit

Courtesy photo by Aaron Weiskittel.

Trees and downed woody debris at Howland Forest in Maine.

Soils can act both as a source and a sink for methane, a greenhouse gas that ranks second to carbon dioxide in terms of its impact on climate change. Many methane studies have been conducted in wetland environments that are known to release methane to the atmosphere. Less is known about the magnitude of methane fluxes from drier, forested upland areas. Upland forest soils are typically thought of as methane sinks, however, as regional climates become warmer and wetter, their ability to sequester methane could diminish or even lead some upland soils to become methane sources. Greater knowledge of methane fluxes in forested ecosystems will improve Earth System Models that can predict methane production under current and future climate scenarios.

This study combines field observations, laboratory analyses, and modeling of methane in a sub-boreal forest in Maine. Specifically, this research will:

1. Identify the roles of soil microbial communities in driving methane fluxes across environmental gradients
2. Compare methane fluxes under wet vs. dry conditions in aboveground and belowground components of a forest
3. Integrate field and laboratory findings to improve process-based models 

This research will occur at the Howland Research Forest in Maine. Howland Research Forest is currently a methane sink, but with precipitation increasing in the northeastern United States over time, the forest may become a methane source.

Approach

This study combines field observations, laboratory analyses, and process-based modeling. Field research is conducted at the Howland Research Forest in Maine, where scientists have been measuring fluctuations in methane since 2012. Howland Research Forest is a sub-boreal forest that acts as a sink for methane but may transition into a source of methane as precipitation continues to increase in the northeastern United States.  

Photo Credit

Courtesy photo by Aaron Weiskittel.

Eddy covariance tower at Howland Research Forest in Maine.

Researchers are measuring methane gas fluxes produced by different components on the ecosystem, including soil and downed woody debris, in a moisture-gradient experiment installed near the base of an eddy covariance tower, which measures carbon fluxes in the atmosphere above the forest canopy. They also measure a suite of other environmental characteristics that may help explain differences in methane flux in wet and dry environments.

The researchers are also conducting a series of laboratory analyses. These laboratory analyses include moisture manipulation experiments and microbial analyses, which provide insights on the characteristics of soil microbes in the forest and how they influence methane production. Conducting this research in a controlled environment helps reveal potential mechanisms that could explain observations made in the field.

With insights gained from several years of field observations and from laboratory analyses, researchers can inform process-based models that are used to predict methane fluxes under different climate conditions. Incorporating these findings improves our ability to predict the effects of climate change.

Expected Outcomes

• Field and laboratory analyses will fill knowledge gaps related to methane in upland and lowland landscapes and reveal mechanisms that can explain the transition from methane sink to methane source.
• Findings will be used to improve process-based models that simulate methane under different climate scenarios.
• This research will improve our ability to forecast the effects of global climate change by accounting for methane in areas that might become methane sources in the future.
• Outreach activities will share this information with other researchers and students.