Executive Summary

Blue carbon ecosystems are vegetated coastal habitats that have considerable potential to be managed for greenhouse gas benefits provided that policy, regulatory, and financial structures are in place to support management activities. Such structures are developing for marshes, mangroves, and seagrass ecosystems and are under research and development for kelp and mudflat ecosystems. However, in the United States, there is a great deal of state-to-state variation in the quantity, quality, and spatial representativeness of the data that is required to implement Blue Carbon projects. Here we assess the availability and quality of Blue Carbon ecosystem data in select U.S. states as captured by the most extensive database available, the Coastal Carbon Atlas, which is curated by the Smithsonian Environmental Research Center and focuses on soil data because these are generally the largest carbon pools in Blue Carbon ecosystems.

The Pew Charitable Trusts (herein Pew) identified a subset of states with attributes that make them potentially attractive for climate mitigation projects in Blue Carbon ecosystems because of state-level commitments to greenhouse gas reduction goals through the U.S. Climate Alliance, including California, Maine, Maryland, Massachusetts, New Jersey, New York, Oregon, Virginia, and Washington. The Coastal Carbon Atlas is a map interface for the Coastal Carbon Library, a open-source coastal soils synthesis dataset made up of 5,784 soil profiles from all continents except Antarctica, and for the major blue carbon habitat types (marshes, mangroves, seagrasses, tidal swamps and scrub/shrub). We developed four new metrics that synthesize key features of the Coastal Carbon Atlas and are broadly relevant to management activities. Data quantity is the number of soil profiles available in the Atlas; data quality captures the utility of the data for use cases ranging from advanced inventorying to carbon sequestration modeling; spatial representativeness considers whether the observations are well distributed across the geography of the state; and habitat representativeness does the same for habitat types found in a given state. The average of these provided a composite score.

Pacific coast states (CA, OR, WA) generally scored higher than Atlantic coast states (FL, ME, MD, MA, NJ, NY, VA) because the data is extensive compared to the area of these ecosystems and is of comparatively high quality. Thus, there are data to support a wide variety of Blue Carbon activities in the Pacific coast states. Atlantic coast states with robust Blue Carbon data are MA and FL, although the large and diverse variety of Blue Carbon habitats in FL demands better spatial coverage. Most of the remaining states where Pew focused are in the mid-Atlantic region, all of which had deficiencies in Blue Carbon data compared to other states. Deficiencies vary from data quantity (ME, MD, NJ), data quality (MD, ME, NY, VA), and spatial or habitat representativeness (ME, NJ).

Tidal marshes are generally well represented in the Atlas, reflecting a relatively long history of academic research on these habitats with respect to carbon cycling. Seagrasses, tidal swamps, and tidal scrub/shrub ecosystems are generally under-represented in the Atlas but in most cases the consequences of this for our metrics is relatively minor because of the limited areas of these habitats. Our analysis of seagrass habitat representativeness is limited by the quality of the habitat maps used in this analysis, which did not distinguish between seagrass, algal mats, and kelp beds. Improved seagrass habitat maps exist for FL, MD, and VA, and efforts underway promise to improve seagrass maps globally. Kelp beds are not presently represented in most Blue Carbon policies because these organisms do not build large in situ carbon stocks; however, this is an active area of research that is likely to yield new policy options in the next decade. Such policy will be especially helpful in states with large areas of these habitats such as CA and ME.

The Pew analysis did not focus on Gulf-coast states outside the gulf coast of FL, but analyses that encompassed all contiguous U.S. coastal states (CONUS) showed high scores for LA, TX and AL which collectively represent the largest fraction of Blue Carbon ecosystems in CONUS. GA, MD, NC, and VA are among states with large Blue Carbon habitat areas but relatively low composite scores and a long history of coastal wetland research. We suspect that data gaps in these states could be closed quickly by making public legacy data that resides with individual scientists.