Productivity, stability, and geomorphological evolution of New England salt marshes: Plum Island case study

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Coastal salt marshes are well recognized for their important ecological functions and societal values, providing great value as habitat and nursery grounds for commercially important fin and shellfishes, and as storm abatement. The Nation is currently losing much of its coastal marsh habitat. Several factors, including changes in sea-level-rise rates, influence salt-marsh growth and decline. However, changes in sediment supply caused by changing terrestrial land uses may have dominated the evolution of New England salt marshes in recent centuries. This project involves examination of sediment layers to investigate the hypothesis that the existing extensive marshes in this region developed recently and rapidly, in response to the increased sediment yield associated with colonial deforestation. If this hypothesis is true, it is possible that in this region (which now has less sediment washing off of reforested and developed landscapes) marshes are presently maintaining a precarious balance, relying on the continued sediment-trapping and stabilizing influences of marsh grasses. The vegetation influence helps the marsh surface gain elevation so that it does not disappear as sea level rises. However, accelerating rising sea level increases the amount of water that floods into and out of the marshes with the tides, increasing tidal currents and tending to cause erosion in the channel networks that intertwine through tidal marshes. Preliminary experiments with a simplified computer model suggest that if vegetation is disturbed in a marsh subjected to high rates of sea-level rise and/or reduced sediment delivery, this erosion could spread laterally, irreversibly converting marsh to open water. This project will employ field observations to further develop the model, and use it to explore how marshes and tidal networks evolve as vegetation influences, tidal currents, sea-level rise, and changing land use/sediment supply all interact. The results will have considerable broader impact across both scientific subdisciplines (ranging from landscape evolution to strictly ecological studies) and societal issues (ranging from storm abatement to land-use management).