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Water: Wetlands


Wetland Types Overview | Marshes | Bogs | Swamps | Fens | References 


Tidal marsh along the Edisto River, South Carolina 


Marshes are defined as wetlands frequently or continually inundated with water, characterized by emergent soft-stemmed vegetation adapted to saturated soil conditions. There are many different kinds of marshes, ranging from the prairie potholes to the Everglades, coastal to inland, freshwater to saltwater. All types receive most of their water from surface water, and many marshes are also fed by groundwater. Nutrients are plentiful and the pH is usually neutral leading to an abundance of plant and animal life. For the purposes of this publication, we have divided marshes into two primary categories: non-tidal and tidal.


Common Cattail (Typha latifolia) is a freshwater and estuarine marsh species  

Functions & Values

Marshes recharge groundwater supplies and moderate streamflow by providing water to streams. This is an especially important function during periods of drought. The presence of marshes in a watershed helps to reduce damage caused by floods by slowing and storing flood water. As water moves slowly through a marsh, sediment and other pollutants settle to the substrate, or floor of the marsh. Marsh vegetation and microorganisms also use excess nutrients for growth that can otherwise pollute surface water such as nitrogen and phosphorus from fertilizer. This wetland type is very important to preserving the quality of surface waters. In fact, marshes are so good at cleaning polluted waters that people are now building replicas of this wetland type to treat wastewater from farms, parking lots, and small sewage plants.



 Muskrat (Ondatra zibethicus) next to its house in a cattail-dominated marsh.

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. 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 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 lily pads, cattails (see photo), reeds, and bulrushes provide excellent habitat for waterfowl and other small mammals, such as 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 one of 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, marshes sustain a diversity of life that is way out of proportion with its size. In addition to their considerable habitat value, non-tidal marshes serve to mitigate flood damage and filter excess nutrients from surface runoff.


 Mink (Mustela vison), a predator of the muskrat.


Pickerelweed (Pontederia cordata)


Unfortunately, like many other wetland ecosystems, freshwater marshes have suffered major acreage losses 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 prove 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.



The Clapper Rail of the saltmarshes, which is more commonly heard than seen.  

Tidal marshes can be found along protected coastlines in middle and high latitudes worldwide. They are most prevalent in the United States on the eastern coast from Maine to Florida and continuing on to Louisiana and Texas along the Gulf of Mexico. Some are freshwater marshes, others are brackish (somewhat salty), 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 tide. It is predominantly covered by the tall form of Smooth Cordgrass (Spartina alterniflora). The saline marsh is covered by water only sporadically, and is characterized by Short Smooth Cordgrass, Spike Grass,and Saltmeadow Rush (Juncus gerardii). Saline marshes support a highly specialized set of life adapted for saline conditions. Brackish and fresh tidal marshes are also associated with specific plants and animals, but they tend to have a greater variety of plant life than saline marshes.

Functions & Values
Tidal marshes serve many important functions. They buffer stormy seas, slow shoreline erosion, and are able to absorb excess nutrients before they reach the oceans and estuaries. High concentrations of nutrients can cause oxygen levels low enough to harm wildlife, such as the "Dead Zone" in the Gulf of Mexico. 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.


The Great Egret (Casmerodius albus) winters in the tidal marshes along the Gulf Coast.


Pressure to fill in these wetlands for coastal development has lead to significant and continuing losses of tidal marshes, especially along the Atlantic coast. Pollution, especially near urban areas, also remains a serious threat to these ecosystems. Fortunately, most states have enacted special laws to protect tidal marshes, but much diligence is needed to assure that these protective measures are actively enforced.

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