THE EFFECT OF BIOMASS ON MARSH EDGE EROSION IN RELATION TO RISING SEA LEVELS

Recently, New England’s marshes have experienced stresses due to accelerating sea-level rise and encroaching suburban and urban development. One response to rising sea level is marsh edge erosion, which is occurring at a rate of 0 to > 1.0 m/yr. To better understand the factors that control the variability in retreat rates, peat samples were taken from the marsh surface and every 20 cm down the face of the marsh, at more than 70 locations in the Great Marsh in northern New England. These samples were dried and weighed to obtain bulk density. In addition, companion samples were rinsed over a 500-micron sieve to collect belowground biomass, and loss on ignition (LOI) was performed to measure total organic content. The results from these samples indicate that as the sample depth increases, so does the bulk density of the sample. This suggests that more dense sediment is present deeper in the marsh, while less dense biomass peat, such as that associated with Spartina alterniflora, is present closer to the surface. The presence of biomass can increase the integrity of the marsh edge, meaning that the lack of biomass at lower depths can result in a pattern of undercutting and erosion. Ultimately, these processes weaken the structure of the marsh edge and may accelerate slumping. Our study shows a correlation between peat biomass and marsh edge retreat. These results may help predict areas of lesser or greater marsh resiliency in northern New England marshes.