Recent Accretion and Subsidence Rates within High Marshes of Northern New England
Salt marshes are well known as specialized habitats that provide coastal populations with many ecosystem services and these systems can also build in elevation with low to moderate rates of sea level rise. Traditional methods of measuring elevation change (survey with rod) are only able to track salt marsh building over relatively long time periods and do not distinguish between accretion and change in elevation. In contrast, the Surface Elevation Table (SET) installed with marker horizons can measure accretion of sediment as well as elevation change in 3 to 5 years. SETs were installed and monitored in several tidal marshes in Massachusetts, New Hampshire and Maine in the period from 1994 to 2002. Data indicated elevations were keeping up with the approximately 2.0 mm/year of SLR, mostly by accretion, which was typically found to be slightly greater than elevation gain. In 2011-2012, we revisited these sites. Preliminary analysis of the data from three SETs in one marsh shows rapid elevation gains over the 2000 to 2011 period of 4.3 +/1.5 mm/year. Elevation gain in the marsh was even greater than new rapid global rates of SLR calculated from sea surface altimetry data (Church and White 2011), indicating that the marsh was likely keeping up with SLR, but also that the salt marsh may rovide a rapid, integrated estimate of recent SLR.