Concerns About Carbon If Wetlands Temporarily Dry Out

The Science

Wetlands are known for being natural methane sources because they have large amounts of organic matter submerged in water. This organic matter gets slowly broken down by microbes, and without oxygen, it produces methane, a greenhouse gas. At the Old Woman Creek National Estuarine Research Reserve, parts of the wetland underwent periods of flooding and then drying. When flooded, plants released more methane into the atmosphere, but plants also removed carbon dioxide from the atmosphere. When the wetland dried, less methane was released, but the wetland released carbon dioxide instead of storing it.

The Impact

Climate change is affecting meteorology, including rainfall, temperature, and evaporation. If climate change leads wetlands to dry out periodically, this can change the amount and type of greenhouse gas emitted to the atmosphere. Alternatively, if wetlands don’t flood, their plants may be unable to pull as much carbon dioxide from the atmosphere. Since wetlands are the largest natural source of methane, it is essential to understand how changing water patterns could affect these gas emissions.

Summary

A team of researchers sampled the Old Woman Creek National Estuarine Research Reserve wetland from July to October 2022 and measured methane and carbon dioxide fluxes in three areas with vegetation and three without vegetation from 7 AM to 7 PM once a month. In July, the wetland was completely flooded, but it dried out in August and slowly reflooded in September and October. When flooded in July, less oxygen was present in the water column, which supported more methane emissions. Most methane was emitted from plants since plants transport gas from the sediment to the atmosphere, bypassing the water barrier. However, flooding also allowed plants to take in more carbon dioxide from the atmosphere as the plants were, presumably, not water-limited for photosynthesis. Consequently, the greatest carbon dioxide uptake occurred during the afternoon at the height of photosynthetic activity. The wetland both emitted methane and sequestered carbon dioxide during flooding. After the wetland dried, plants were no longer taking in carbon dioxide at a rate faster than emission, so the wetland turned into a source of carbon dioxide. The methane emission rate also dropped since more oxygen converted methane to carbon dioxide during drier conditions. However, the wetland was still a source of both methane and carbon dioxide when the wetland was dry.

Principal Investigator

Timothy Morin
The State University of New York College of Environmental Science and Forestry
[email protected]

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This research was funded by the U.S. Department of Energy’s (DOE) Biological and Environmental Research program through award numbers DE-SC0022191, DE-SC0023084, and DE-SC0021067. Funding for the US-Old Woman Creek AmeriFlux core site was provided by DOE’s Office of Science.

Related Links

• ESS-DIVE Data Repository

References