Skip to Content

Cross-scale methane dynamics at terrestrial-aquatic interfaces in temperate forests

Active Dates 9/1/2023-8/31/2026
Program Area Environmental Systems Science
Project Description
Interfaces between well-drained, upland soils and wetlands are critical sites for biogeochemical processing in temperate forests. The location of these interfaces fluctuates with water table depth, which is controlled by incoming precipitation, and small ephemeral and perennial wetlands are particularly dynamic. In many locations, including the Harvard Forest within the northeastern U.S., water table fluctuations are changing with more frequent extreme precipitation events, higher total precipitation, and more variation in total precipitation among years due to climate change. In the saturated zone below the water table, conditions are anaerobic, and methane is produced. Dissolved gas may diffuse or bubble up to the water table or escape to the atmosphere through plant roots and stems. In the unsaturated zone above the water table, conditions are oxic, carbon dioxide is produced, and methane is oxidized. The timing and location of these processes fluctuate with precipitation variation. Additionally, methane transported by ebullition and tree stems have high variation across the landscape and through time, and the mechanisms driving plant-mediated methane transport are not well understood. 

In this project, we will conduct cross-scale field measurements of methane dynamics at the Harvard Forest in Petersham, MA. We will collect new field measurements in uplands, ephemeral wetlands, and two small perennial wetlands: a ~14,000 year old forested peatland and a ~20 year old beaver-constructed wetland. We will leverage data and infrastructure from core AmeriFlux sites to add new ecosystem-scale measurements of methane and carbon dioxide exchange, and we will measure the lateral flow of carbon in gaged streams. At the process-scale, we will characterize rates of methane production, consumption, ebullition, and diffusion, and we will develop a novel reactive transport model to represent these processes. The model will use data from carbon dioxide and methane concentrations and stable carbon isotopes from soil porewater depth profiles. To quantify the magnitude and drivers of tree stem methane flux, we will deploy automated flux chambers on the stems of trees within wetlands and uplands that are co-located with soil porewater depth profiles.

We will synthesize our new field measurements within a spatiotemporal modeling framework that brings together process-based measurements with net methane flux constraints from eddy flux towers and lateral flow data in streams. Our model will be tested across sub-seasonal to interannual temporal scales to capture variation in precipitation during the study period. The observational design will facilitate understanding of the dynamics of methane within this complex ecosystem that dynamically changes across space and in time with precipitation. This will yield new insights for the spatial scaling of methane dynamics across dynamic terrestrial-aquatic interfaces within earth system models like the E3SM Land Model (ELM).
Award Recipient(s)
  • President and Fellows of Harvard College (PI: Matthes, Jaclyn)