Tidal Flats and Salt Marshes

Salt marshes are important coastal ecosystems and this chapter describes the broader tidal-flat setting in which these landforms occur. The tidal-flat surface may comprise various surface morphologies and sedimentary structures. Those surfaces that are exposed for long periods of time develop desiccation cracks. Coastal salt marsh is a significant ecosystem occupying the upper margins of the intertidal zone. Salt marshes are commonly divided into low marsh and high marsh on the basis of elevation and plant zonation. The lower limit of low marsh is defined as the seaward margin of vegetation within the intertidal zone. The upper limit of high marsh is commonly marked by a sharp elevation change between the marsh vegetation and the hinterland, or artificial structures, such as roads or buildings. Despite our incomplete knowledge of tidal-flat and salt marsh behaviour and dynamics, these systems have been extensively modified by human activity.