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Fifth National Climate Assessment - Read the Report

Field, lab, and remote sensing studies assess greenhouse gas fluxes from drowning and restored wetlands

A researcher with a chamber used to measure greenhouse gas absorption by and emissions from marsh soils and vegetation. Source: EPA.

Coastal salt marshes, found on every coast in the United States, are essential for healthy fisheries, coastlines, and communities. They serve as important habitats, maintain water quality, and sequester carbon from the atmosphere, while also providing protection from storm surge and erosion. As sea level rise accelerates, salt marshes are increasingly vulnerable to drowning and loss, affecting their ability to provide ecosystem services, particularly carbon sequestration. Sediment placement in degraded, low-elevation marshes, typically using nearby dredged sediment, is one option to increase elevation and extend the lifespan of the marsh, increasing resilience to sea level rise. 

EPA scientists are collaborating with NOAA, the National Estuarine Research Reserves, Save the Bay, and academic scientists to track how much carbon dioxide and other greenhouse gases are absorbed or emitted from marsh soils and vegetation in drowning coastal marshes and recently restored marshes in Rhode Island. Marshes were previously restored by adding clean dredged sediments to increase elevation and improve resilience (Raposa et al., 2022). In field and lab experiments, researchers examined greenhouse gas and sediment accretion responses to the sediment enhancement techniques. This research effort will improve understanding of carbon sequestration recovery following application of dredged sediments to drowning marshes.

Coupled with greenhouse gas flux measurements will be marsh recovery metrics, such as plant recolonization and soil characteristics at each site. These measurements are a part of a monitoring program, which also includes measures of fish and crustaceans, birds, sediment accretion, and marsh elevation. The project’s overall goal is to evaluate the performance of marsh restoration efforts and to better inform assessment of marsh health in a changing environment.

Over the past decade, USGS has integrated field- and remote sensing-based studies to quantify the impacts of climate and land use change on carbon sequestration in both coastal and inland wetlands and to inform and assess impacts of wetland restoration efforts on federal lands. USGS has worked on and co-funded these studies with a wide range of partners from federal agencies (including USDA, DoD, NSF, SI, NPS, and USFWS), state agencies, academia, non-governmental organizations, and local entities. In 2022, USGS published results of several key studies. For example, one study demonstrated that hydrologic restoration of coastal wetlands produced elevation gains and enhanced carbon burial capacity (Eagle et al., 2022). Another study showed that restoration of tidal exchange in coastal wetlands dominated by invasive Phragmites (a non-native reed grass) limits methane emissions and enhances their climate regulating benefits (Sanders-DeMott et al., 2022). By quantifying the effects of land use and wetlands restoration on carbon sequestration, the USGS and agency partners are working to support climate action planning at the local, state, Tribal, and national scales.