Land Use and Environmental Effects on Greenhouse Gas Emissions and Carbon Sequestration in Pacific Northwest Tidal Wetlands - NERRS/NSC(NERRS Science Collaborative)

By bridging scientific inquiry and climate policy implementation, this project filled key regional blue carbon data gaps and expanded blue carbon data accessibility to facilitate the development of climate mitigation strategies.

The Project
Blue carbon refers to the carbon sequestered and stored in tidal wetlands such as tidal swamps, salt marshes, and seagrass meadows (and mangrove forests at tropical and subtropical latitudes). Blue carbon ecosystems are especially effective at capturing and storing carbon, often storing disproportionately large amounts of carbon on a per acre basis. However, tidal wetlands can also emit varying amounts of greenhouse gases (GHGs)-including carbon dioxide, methane, and nitrous oxide-which can reduce or offset their net climate benefit.

To fill regional data gaps associated with GHG emissions and carbon accumulation rates in Pacific Northwest (PNW) tidal wetlands and investigate how net ecosystem carbon balance differs among wetland types and land uses, a project team of PNW Blue Carbon Working Group members partnered with two National Estuarine Research Reserves and other collaborators to plan and implement this project. This project was built on partnerships developed through previous Science Collaborative efforts and addressed key data gaps and research priorities identified in those earlier projects (see: 2016 Collaborative Research and 2018 Catalyst Project).

Through new data collection across five estuaries and continued engagement with partners, the project team examined how net ecosystem carbon balance differs among wetland types and land uses, quantified blue carbon-ecosystem driver relationships, expanded the regional blue carbon database, and provided new data to the Smithsonian's Coastal Carbon Research Coordination Network working group to help validate a national methane emissions model.

Significant findings included:

Most project sites with salinity >2-3 ppt showed reduced methane fluxes.
Highest methane emissions occurred in wet pastures and restored marshes, especially those with low salinity and high water table.
Carbon accumulation rates were highest in restored marshes, somewhat lower in least-disturbed marshes and swamps, and lowest in diked pastures.
Carbon accumulation rates varied within wetland categories, primarily due to local differences in growing season water table level.