Marsh edge characteristics controlling the distribution and type of edge erosion

Salt marshes are key ecosystems, and pervasive marsh edge erosion is a major threat to their resiliency. Two major contributors to marsh edge erosion include wave erosion and soil creep. However, many eroding marsh edges occur where the channels are too small for significant wave impacts, and soil creep cannot solely account for the non-uniform distribution of peat blocks. Past studies have shown that vegetation alters the soil type and reduces wave erosion, while others suggest that a stronger soil and vegetation layer on the marsh platform can create unstable profiles and mass failure, increasing edge erosion. The present study mapped marsh edge erosion and measured soil characteristics along different bank profiles to explore possible relationships among marsh edge type, wave exposure, and soil properties in Great Marsh, MA. Marsh edges in the system were classified according to their overall character, which included slumping, abrading, stable to accretionary, and bedrock. In addition, bulk density, organic content, biomass, and shear strength were measured every 20 cm along vertical bank transects at 80 locations to investigate the relationship between erosion and various soil properties. The data show no correlation between marsh edge type and wave exposure. There was also no clear distinction between soil properties, depth, and type of erosion. However, stable/accretionary edges consistently had higher organic content and lower bulk density. Our study demonstrates that neither wave exposure nor soil properties is the driving force in controlling marsh edge dynamics, suggesting that other factors are responsible for edge erosion, such as wetting and drying cycles, freeze and thaw, ice wedging, or other processes.