Wetlands are defined by the EPA as areas where water covers the soil or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season. The degree of saturation largely determines how the soil develops and the types of plant and animal communities living in and on the soil. Wetlands may support both aquatic and terrestrial species. The prolonged presence of water creates conditions that favor the growth of specially adapted plants and promotes the development of characteristic wetland soils.
Wetlands are found from the tundra to the tropics and on every continent except Antarctica. They vary widely because of regional and local differences in soils, topography, climate, hydrology, water chemistry, vegetation and other factors, including human disturbance. Two general categories of wetlands are recognized: coastal or tidal wetlands and inland or non-tidal wetlands.
Non-tidal marshes are the most prevalent and widely distributed wetlands in North America. They are mostly freshwater marshes, although some are brackish (somewhat salty) or alkaline. They frequently occur along streams in poorly drained depressions and in the shallow water along the boundaries of lakes, ponds and rivers. Water levels in these wetlands generally vary from a few inches to two or three feet, and some non-tidal marshes, like prairie potholes, may periodically dry out completely.
Due to their high levels of nutrients, freshwater marshes are among the most productive ecosystems on earth. They can sustain a vast array of plant communities that in turn support a wide variety of wildlife within this vital wetland ecosystem. As a result, even small marshes may sustain an extensive diversity of life. Unfortunately, like many other wetland ecosystems, freshwater marshes have suffered major acreage losses due to human development.
Tidal marshes can be found along protected coastlines in middle and high latitudes worldwide. They are most prevalent in the U.S. on the eastern coast from Maine to Florida, and continuing to Louisiana and Texas along the Gulf of Mexico. Some are freshwater marshes, others are brackish and still others are saline (salty), but they are all influenced by the motion of ocean tides. Tidal marshes are normally categorized into two distinct zones, the lower or intertidal marsh and the upper or high marsh.
In saline tidal marshes, the lower marsh is normally covered and exposed daily by the ebbing tide. It is predominantly covered by the tall form of smooth cordgrass (Spartina alterniflora). The saline upper marsh is covered by water only sporadically and is characterized by short, smooth saltmeadow cordgrass (Spartina patens), spike grass (Distichlis spicata) and saltmeadow rush (Juncus gerardii). Saline marshes support a highly specialized suite of species adapted for salt conditions.
Tidal marshes serve many important functions. They buffer stormy seas, slow shoreline erosion and can absorb excess nutrients before they reach oceans and estuaries. Tidal marshes also provide vital food and habitat for clams, crabs and juvenile fish, as well as offering shelter and nesting sites for several species of migratory waterfowl. We recommend a visit to the Land Alliance’s Shore Road Sanctuary (formerly ExxonMobil) in Cold Spring Harbor to see these marshes in action.