Wetland Carbon Cycling: Monitoring and Forecasting in a Changing World

Science Center Objects

WARC's wetland carbon cycle science team is working to improve model parameterizations and formulations and reduce forecast uncertainty in ecosystem modeling.

The Science Issue and Relevance: Wetlands are critical ecosystems for understanding the carbon budgets of landscapes and potential nature-based climate solutions. While covering only 3-8% of land surfaces, wetlands have a disproportionate impact on regional carbon budgets, thanks to the high capacity for carbon storage in flooded soils and their position at the terrestrial-aquatic interface. Wetlands present challenges when monitoring and forecasting carbon cycle responses to external drivers, such as climate change, sea-level rise, and human activities. Our work on wetland carbon cycling is conducted at three primary scales: ecophysiological fluxes at a fine scale, ecosystem fluxes at a larger scale, and regional to global ecosystem models of wetland carbon fluxes and storage at regional and national scales.

Measuring ecosystem-atmosphere carbon exchange

Measuring ecosystem-atmosphere carbon exchange at the leaf-level (left) using a porometer and at the ecosystem-level (right) using eddy covariance.

(Credit: Sergio Merino, USGS WARC. Public domain.)

At a fine scale, the ecophysiology of wetland plants and microbes include adaptations to the unique environmental conditions presented by wetland hydrology and soils, which may lead to different responses to global change drivers than commonly found in terrestrial plants. At a larger scale, wetland ecosystem fluxes exchange carbon both vertically with the atmosphere and laterally with hydrologically connected ecosystems, in ways not often examined for terrestrial ecosystems. At regional and national scales, ecosystem models of wetlands need to confront hydrological and land cover changes with relevant data to project changes in carbon cycling under multiple future scenarios that address human activities, changing climates, sea-level rise, and stochastic disturbances such as tropical storms and polar vortices.

 

Methodology for Addressing the Issue: At the ecophysiological scale, our work focuses on key processes identified as uncertainties in global models of wetland carbon cycling, such as leaf-level photosynthetic responses of wetland plants to nutrient loading, elevated carbon dioxide (CO2), and increased temperatures, or the belowground response of root function and productivity under increased flooding and salinity with sea-level rise. These responses are then coupled with observations of ecosystem level fluxes (Fig. 1) and pools of carbon to provide carbon budgets at scales relevant to regional and global ecosystem models and management. Using model-data assimilation techniques (Fig. 2), models are systematically confronted with novel observations and mechanistic responses that improve models’ parameterizations and formulations, reduce forecast uncertainty, and identify unresolved uncertainties that may be targeted by future ecophysiology and ecosystem studies.

LUCAS model

Model-data assimilation workflow for Land Use and Carbon Scenario Simulator (LUCAS) model in coastal “blue carbon” ecosystems of Louisiana. (Public domain.)

 

Future Steps: Wetland carbon cycle science is by necessity a collaborative effort, with contributions from field scientists, laboratory scientists, ecosystem modelers, and data scientists. Our wetland carbon cycle science team’s efforts contribute not just to interdisciplinary collaborations within USGS (such as our efforts in understanding mangrove’s carbon cycling response to nutrient loading in “Ding” Darling NWR, large-scale hydrological restoration projects in coastal marshes of Louisiana, and the carbon implications of tidal freshwater forested wetland decline with increasing flooding and salinity in the Gulf and Atlantic coasts), but also larger multi-institutional efforts such as the Powell Center’s Wetland FLUXNET Synthesis for Methane, Oak Ridge National Laboratory’s Spruce and Peatland Responses Under Changing Environments (SPRUCE) project, and the North American Carbon Program.