Non-tidal marshes are the most prevalent and widely distributed wetlands in North America. They are mostly freshwater marshes, although some are brackish or alkaline. Non-tidal marshes 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 marshes, like prairie potholes, may periodically dry out completely.
It is easy to recognize a non-tidal marsh by its characteristic soils, vegetation, and wildlife. Highly organic, mineral-rich soils of sand, silt, and clay underlie these wetlands, while characteristic plants, such as lily pads, cattails (see photo), reeds, and bulrushes in North American marshes, provide excellent habitat for waterfowl and other small mammals. In North America, these include red-winged blackbirds, great blue herons, otters, and muskrats. Prairie potholes, playa lakes, vernal pools, and wet meadows are all examples of non-tidal marshes.
Functions & Values
Due to their high levels of nutrients, freshwater marshes are among the most productive ecosystems on Earth. They can support diverse plant communities that in turn support a wide variety of wildlife. As a result, marshes often sustain an abundance of life that is out of proportion to their size. In addition to their considerable habitat value, non-tidal marshes serve to mitigate flood damage and filter excess nutrients from surface runoff.
Unfortunately, like many other wetland ecosystems, freshwater marshes have suffered major losses in area to human development. Some have been degraded by excessive deposits of nutrients and sediment from construction and farming. Severe flooding and nutrient deposition to downstream waters have often followed marsh destruction and degradation. Such environmental problems illustrate the vital roles these wetlands play. This realization has spurred enhanced protection and restoration of marsh ecosystems, such as the prairie potholes and the Everglades.
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