Washington Sea Grant researchers assessed the carbon stocks contained in regional tidal marshes and the rate at which they accumulate by estimating the amount of carbon sequestered following the restoration of a degraded marsh in Port Susan Bay. Researchers measured carbon in aboveground plant biomass and in sediment cores from five zones ranging from healthy, undisturbed marsh to a regenerating, rapidly accreting restoration zone. They will continue monitoring changes in surface elevation throughout the estuary to validate long-term accretion rates obtained from soil-core chemical analyses. The results will enable managers and planners to incorporate blue-carbon accounting in their climate adaptation and coastal restoration strategies.
Coastal wetlands play an important role in the global carbon budget. Because most of a wetland’s soil is submerged underwater, the decomposition of plant material takes place much more slowly than in other ecosystems, meaning wetlands can potentially store carbon for thousands of years. Quantifying exactly how much carbon is sequestered in Pacific Northwest wetlands could help resource managers valuate and plan wetland restoration projects as part of climate mitigation strategies.
The researchers found that the rate of carbon sequestration in the recently restored marsh is currently twice the rates found in the adjacent natural marshes. The restoration site is expected to accumulate approximately 4,500 to 9,000 tonnes of carbon before it reaches equilibrium with adjacent marshes, equivalent to removing 3,500 to 7,000 cars from the road for one year. Using the national average carbon offset price, this amount of carbon is worth $65,000 to $165,000. These findings indicate wetland restoration has significant and immediate benefits and could be a valuable tactic to help mitigate future climate change. The salt marshes adjacent to the delta distributary are also all accreting at rates that exceed the rate of sea level rise, indicating the additional potential of wetland restoration for climate resiliency.