Chapter 3 - Temperate Coastal Wetlands: Morphology, Sediment Processes, and Plant Communities

Abstract

Temperate coastal wetlands include a large variety of environments, from tidal flats and salt marshes to nontidal wetlands at the landward edge, whose hydrology is still influenced by mean sea level. Salt marsh evolution and accretion depends on several factors, and different models aim to reproduce the physical and ecological processes driving marsh evolution by using different levels of simplification. In response to the environmental gradients imposed by elevation, salt marsh plants commonly exhibit clear patterns of shore-parallel zonation of species. In low marsh areas, salinity is comparatively low because of regular tidal flushing, but soil salinity levels vary across marsh elevations. In humid warm regions, freshwater input from rain and upland sources moderates salinity at the terrestrial border, but salts can concentrate by evaporation at intermediate marsh elevations. In humid climates, the upper salt marsh commonly grades into freshwater communities. In arid climates, salt flats devoid of vascular vegetation develop near the upland boundary. Typical patterns of salt marsh plant zonation present substantial differences among major geographic regions, largely reflecting rainfall amount and seasonality, along with the biogeographic distribution of species. In addition, human activities have also exerted profound changes in coastal wetlands, and the processes of wetland loss and degradation have been quite variable in space and time, leading to major regional differences in the extent and ecological integrity of remaining wetland areas. Major human impacts are associated with land claims and alterations of fluvial sediment transport.