Coastal Impacts, Adaptation, and Vulnerabilities - Climate ...

Adaptation and Mitigation 117The variety of ecosystem services and ecological, economic, and societal benefits ofhealthy coasts and estuaries are well-documented in a new report, Jobs and Dollars: BigReturns from Coastal Habitat Restoration (Restore America’s Estuaries, 2011). Our nationhas lost more than half of its wetlands in the past 200 years (Dahl & Johnson, 1991), andthe planet has lost a quarter of its salt marshes and freshwater tidal marshes and continuesto lose 1-2 percent per year, making these ecosystems some of the most threatened inthe world (Convention on Biological Diversity, 2010). Moreover, between 2004 and 2009,the U.S. lost 110,000 acres of coastal wetlands (Dahl, 2011).However, recent science has demonstrated that some of these same endangeredcoastal resources—coastal marshes, mangroves and sea grasses—may be able to sequesterand store large quantities of carbon dioxide (CO2) in plants and the soils below themin a process termed blue carbon (Crooks et al., 2011). In the first meter of coastal wetlandsediments alone, soil organic carbon averages 500 t CO2e/ha (tonnes of carbon dioxideequivalent per hectare) for sea grasses, 917 t CO2e/ha for salt marshes, 1060 t CO2e/ha forestuarine mangroves, and nearly 1800 t CO2e/ha for oceanic mangroves (Murray et al.,2011). If destroyed, degraded, or lost, these coastal ecosystems become globally significantsources of carbon dioxide emitted into the atmosphere and the ocean. For example,in California’s Sacramento/San Joaquin Delta, drainage of 1,800 kilometers 2 of wetlandshas released 0.9 giga tons, or billion tons, of carbon dioxide over the last century. An additional5 to 7.5 million tons of CO2continue to be released on average from this Deltaeach year (Crooks et al., 2011). Additionally, the stresses of climate change, increasingtemperature, sea-level rise, and acidification could challenge these ecosystems and leadto the release of this carbon.In addition to the loss of carbon stores, when wetlands are degraded or destroyed,the ongoing sequestration capacity of wetlands is lost as well. Coastal wetlands sequestercarbon at rates three to five times greater than global rates observed in mature tropicalforests: 6 to 8 t CO2e/ha compared to 1.8–2.7 t CO2e/ha (Murray et al., 2011). Althoughthe capacity of the systems to sequester carbon may be diminished when the systems arestressed by climate change. For example, when a coastal marsh is stressed due to risingsalinities associated with sea-level rise, the capacity for the wetland to store carbon maydiminish through time.Protecting the remaining coastal wetlands in the U.S. and globally and restoring thosethat have been degraded or destroyed (McLeod et al., 2011) may provide meaningfulcontributions to climate change mitigation strategies. Carbon storage, when consideredas an ecosystem service provided by coastal wetlands, could provide a strong incentivefor protection and restoration through payments for blue carbon (Sifleet et al., 2011).However many of these ecosystems have been shown to release greenhouse gases underthe conditions associated with climate change (Shindell et al., 2004; Vann & Megonigal,2003), indicating that the permanence of coastal carbon must be carefully evaluated. Furthermore,oceans and coastal ecosystems have not been part of the policy dialogue forreducing greenhouse gases (Nellemann et al., 2009).A key impediment to coastal conservation such as wetlands protection and restorationefforts is adequate assistance to undertake projects. In the U.S., the restorationcommunity is well established but has a backlog of high-priority, shovel-ready projectsthat amount to billions of dollars; for example, under the American Recovery and