What do we need to assess the sustainability of the tidal salt marsh carbon sink?

Abstract

Tidal salt marshes provide a range of ecosystem services. The most recently recognized is their provision of highly effective sinks for atmospheric carbon dioxide, a characteristic they share with mangroves swamps which largely replace salt marshes in the intertidal zones of tropical regions. Efforts are emerging to use salt marsh preservation or restoration in carbon offset programs, similar to the REDD initiative for tropical forests, but a number of issues first must be addressed to determine if a site meets the requirements of these programs. As intertidal systems, both salt marshes and mangrove swamps are threatened by increasing rates of sea level rise, and it will be essential to determine their sustainability, thus meeting the requirement of permanence of the carbon sink. In many areas the vegetation responsible for marsh soil accretion may not survive increased flooding periods, resulting in submergence of the marsh in its present location or inability to restore a marsh at its previous elevation. However, the marsh and its carbon sink, may survive if allowed to migrate inland. Thus assessment of permanence requires a determination if inland migration will be hindered by barriers such as high slopes or development, i.e., if the ecosystem is in a coastal squeeze. Presently, the only technology that can provide elevation models at the required vertical accuracy is Lidar, which also is extremely valuable for assessing vulnerability of coastal communities to flooding. Yet, Lidar data is not available for all coastlines, even those in the developed world. To effectively plan for the future of our coastlines requires Lidar coverage on all sensitive coastlines and its free availability for impact assessments.