Towards a Predictive Understanding of Coastal Wetland Response to Sea Level Rise: Synthesis of Data to Test a Model of Tidal Marsh Accretion

Goals: Tidal wetlands provide important ecosystem services (disturbance regulation, biological productivity, waste treatment) to the more than 50% of the world's population that lives in the coastal zone (Craft et al. 2009). They are highly susceptible to rising sea level caused by global warming and there is concern that they may not persist if sea level rises too quickly. Tidal wetlands maintain the elevation of their respective habitats within a relative narrow portion of the intertidal zone by trapping sediment and adding organic matter to the soil. Their long-term stability is controlled by the interactions among sea level, soil surface elevation, plant productivity and sediment deposition. Morris et al. (2002) showed that salt marshes along the south Atlantic (SC) coast have an optimal surface elevation at which plant productivity is maximized (i.e. the "low" marsh). But, below this elevation, the plants are unable to grow and the system becomes unstable. Based on this work, a model was developed to predict how coastal wetlands will respond to rising sea level. Knowledge of long-term changes in marsh surface elevation, elevation of the marsh platform relative to NAVD88, depth of inundation, above-ground biomass and suspended sediment concentrations are required as model inputs. The Morris et al. (2002) model was developed using data collected at North Inlet (SC) but has yet to be tested in other environments that vary in tidal range and sediment supply. The stability of tidal marshes in the coming century is of great concern to managers who oversee the natural and "built" resources of the coastal zone and to the public at-large that live in these areas. The goal of the workshop is to develop a general, predictive understanding of marsh stability in the face of rising sea level that is applicable marshes of the entire U.S. coast. We propose two workshops to synthesize data from four coastal LTER sites (PIE, VCR, GCE, FCE) and from four non-LTER sites with the goal of developing a proposal to validate the Morris et al. (2002) model describing tidal marsh response to sea level rise. Participants will consist of the four LTER Atlantic coast sites where SET's have been deployed for eight years or more. Participants who oversee long-term SET datasets from non-LTER sites along the Atlantic (North Inlet SC), Gulf of Mexico (coastal LA) and Pacific coasts (San Francisco Bay, Puget Sound) will also be invited. Participants and sites represent a broad range of tidal regimes (micro- to meso-) and sediment supply (low- to high-). Inputs to the model include long-term changes in soil surface elevation collected using sedimentation-erosion tables (SET's), marsh surface elevation relative to NAVD88, depth of inundation, aboveground biomass and suspended sediment concentration. See Supporting Data for list of sites, participants and availability of data for the model. We request $12,000 to support the workshops. Activities: Prior to the workshop, participants will synthesize results of their long-term SET datasets to identify trends in elevation relative to current rates of sea level rise at their respective sites and will compile supporting data that serve as inputs to the Morris et al. (2002) model.