8 - Tidal marshes

Abstract

Tidal marshes are common in temperate regions of the world. They are characterized by mixing of seawater and freshwater and by hydrologic pulsing driven by the astronomical tides and are among the most productive of wetlands, supporting high levels of plant and animal biomass. Many tidal marshes have been lost to shoreline development and urbanization and, sometimes, agriculture. Efforts to restore them consist of reintroducing tidal inundation by removing fill, dikes, levees, and tide gates and by managed realignment where coastal defenses are removed and marsh vegetation is allowed to reestablish. Because of the vigorous energy associated with tidal inundation, reestablishment of vegetation by natural colonization or seeding is slow and planting is often 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 abundant vegetated edge to facilitate access and use by nekton and wading birds.