Ecology of Greenhouse Gas Emissions from Coastal Wetlands

Science Center Objects

Wetlands have the potential to absorb large amounts of carbon dioxide via photosynthesis, and flooded soils have low oxygen levels which decrease rates of decomposition to promote the retention of soil carbon. However, the type of greenhouse gases emitted from wetlands varies by wetland type and soil condition. A suite of approaches are being used to assess  fluxes of greenhouses gases, like methane, carbon dioxide, and nitrous oxide. 

Elevated CO2 Facility, WARC, Lafayette, LA, USA
Elevated CO2 facility, WARC, Lafayette, Louisiana

The Science Issue and Relevance: Wetlands provide a particularly good environment for carbon sequestration, which has elevated them as potential hotspots for ameliorating increased CO2 and CH4 concentrations in the atmosphere. Not only does healthy wetland vegetation have the potential to take up large amounts of CO2 through photosynthesis, but also flooded soils have low oxygen levels which reduce rates of decomposition to promote retention of soil carbon. However, mass fluxes of carbon are only part of the story; while some wetlands can store large amounts of carbon, the biogeochemical state of the soil affects the balance among the types of greenhouse gases emitted. Some types of gases have greater radiative forcing and are more deleterious than others. For example, greater amounts of CH4 are often emitted from freshwater wetlands, and CH4 is much more persistent in the atmosphere than CO2. Thus, along with understanding the net ecosystem exchange of carbon, it is also critical that the primary suite of greenhouse gases (CO2, CH4, N2O) are considered together along environmental gradients. While many studies of greenhouse gas emissions are underway, our group is particularly interested in assessing fluxes accurately through combinations of various techniques and describing the nuances associated with each assessment.

Methodologies for Addressing the Issue: Greenhouse gases are emitted from the soil, belowground roots, and soil-emergent plant structures, while CO2 is taken up by photosynthetic tissue. The scale selected for greenhouse gas assessments matter tremendously. We use a suite of approaches to assess greenhouse gas fluxes, including dark static flux chambers, clear static flux chambers, infrared gas analyzers, laboratory-based and portable gas chromatography, and eddy covariance systems. We also measure greenhouse gas fluxes from a range of wetland types differing in natural and managed hydrology, salinity, latitude, and geography in order to understand how greenhouse gas emissions are regulated in each environment (e.g., water level, soil temperature, river discharge, etc.) and to determine mass fluxes of greenhouse gases on a molar, molecular, elemental, and global warming potential basis, depending on application.

Salvador WMA, Louisiana, USA
Salvador WMA, Louisiana

Future Steps: This project builds on a number of different funding sources, and we anticipate that our greenhouse gas research will become increasingly more applied. Projects are currently underway in created salt marshes of North Carolina, drained tall Pocosin wetlands in Virginia, natural marshes in Louisiana, and managed marshes in China.