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

Interfaces between well-drained, upland soils and wetlands

wetland

An area of land that is periodically saturated with water, which influences the types of plants and animals that can live there. Wetlands include swamps, marshes, bogs, and other similar areas.

Source: A student's guide to Global Climate Change Source

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.

climate change

A change in the average conditions — such as temperature and rainfall — in a region over a long period of time.

Source: NASA Climate Kids Source

In the saturated zone below the water table, conditions are anaerobic, and methane

methane

A hydrocarbon that is a primary component of natural gas. Methane is also a greenhouse gas (GHG), so its presence in the atmosphere affects the earth’s temperature and climate system

Source: EPA Source

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

carbon dioxide (CO2)

An important heat-trapping gas, also known as a greenhouse gas, that comes from the extraction and burning of fossil fuels (such as coal, oil, and natural gas), from wildfires, and natural processes like volcanic eruptions.

Source: NASA Source

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

peatland

Located within a terrestrial wetland environment where plant material cannot entirely decompose due to the presence of water.

Source: International Peatland Society Source

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

flux

The amount of some type of particle or energy crossing a unit area per unit time.

Source: NRC Library Source

chambers on the stems of trees within wetlands and uplands that are co-located with soil porewater depth profiles.

We will synthesize

synthesis

The process of combining a number of things into a coherent whole to form a theory or system.

Source: National Library of Medicine Source

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

ecosystem

A natural community of plants, animals, and other living organisms and the physical environment in which they live and interact.

Source: A student's guide to Global Climate Change Source

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

earth system model (ESM)

A model that simulates how chemistry, biology, and physical forces work together. These models are similar to, but much more comprehensive than, global climate models.

Source: U.S. Department of Energy Source

like the E3SM

Energy Exascale Earth System Model (E3SM)

The Energy Exascale Earth System Model (E3SM) project includes Earth System Models, simulations, and predictions to investigate energy-relevant science using code optimized for DOE's advanced supercomputers.

Source: NVCL Web Page Source

Land Model (ELM).