CHARACTERISTICS OF A RESILIENT NEW ENGLAND SALT MARSH

The goal of this project is to determine the stability of a New England salt marsh by integrating biotic factors and erosional features. In 2014 and 2015 mosquito-ditched and un-ditched areas in Barn Island Wildlife Management Area, Connecticut were compared by repeat surveys. We studied both marsh edge stabilizing grasses and the mussel species Geukensia demissa. Although there were no major tropical storms this year, the marsh suffers from increased tidal inundation due to a local sea level rise of 2.58 ± 0.23 mm/y.

Our measurements indicate the edge of un-ditched marsh is relatively stable and dominated by a normal profile. The un-ditched edge has exclusively the low marsh grass Spartina alterniflora and 100-200 mussels/m². In contrast, the ditched marsh edge is less stable and dominated by overhanging profiles. One area of ditched marsh lost 2 m on its seaward edge and showed significant increase in high marsh grasses on its edge between 2014 and 2015. The ditched marsh headlands bordered on one side by a natural channel have high densities of mussels (3,000 mussels/m²). The areas of the ditched marsh with no adjacent natural channel had the most change in erosional state in the study year, with a surprising number of overhangs dislodging into islands.

Quantifying the changes in a year with no major tropical storm event will aid prediction of marsh resiliency against sea level rise and storms. Mosquito-ditched marshes without the sediment supply of a natural channel and the edge-stabilizing S. alterniflora and G. demissa will likely show increased deterioration as sea-level rise increases.