8 - Tidal Marshes

Abstract

Saline, brackish, and freshwater tidal marshes are common in temperate regions of the coastal zone. They are characterized by hydrologic pulsing driven by the astronomical tides and are among the most productive of wetlands, supporting high levels of plant and animal biomass. Saline and brackish marshes are inundated with seawater diluted by freshwater from rivers and terrestrial landscapes. Tidal freshwater marshes are located in upper reaches of river-dominated estuaries where astronomical tides penetrate but saline water does not. Many tidal marshes have been lost to shoreline development and urbanization and, sometimes, agriculture. Efforts to restore tidal marshes consist of reintroducing tidal inundation by removing fill, dikes, levees, and tide gates. Reintroduction of saline water alters soil chemical properties by increasing salinity and alkalinity. Because of the vigorous energy associated with tidal inundation, reestablishment of vegetation by natural colonization or seeding is slow and planting often is required. Development of heterotrophic food webs depends on establishing good coverage of vegetation and accumulation of soil organic matter and nitrogen (N). Keys to successful restoration include selecting sites with large tidal range to support a wide expanse of vegetation, gentle slope to limit waterlogging, and enhancing connectivity by creating tidal creeks and vegetated edge to facilitate access and use by nekton and wading birds.