Marsh

For other uses, see Marsh (disambiguation).

In geography, a marsh, also referred to as a morass, is a type of wetland defined as a low lying, poorly drained section of land, which is often if not always covered in water . It can normally be found at the edge of lakes and streams, and act as a transition between the aquatic and terrestrial ecosystems. They are dominated by grasses such as rushes and reeds, and have few to no woody areas. If woody plants are present they tend to be low-growing shrubs. This form of vegetation is what differentiates marshes from other types of wetland such as swamps, which are dominated by trees, and bogs, which are wetlands that have accumulated deposits of acidic peat .

Basic information

Marshes are a habitat to many types of plants and animals which have adapted to living in such a highly saturated area. This greatly limits the number and variety of its inhabitants. The plants must be able to survive in a highly saturated area and still be able to take in the necessary nutrients. The aquatic denizens are able to live with a low amount of oxygen in the water. Some have found ways to get their oxygen from the air instead, while others can live indefinitely without it. Marshes provide habitat for fish, waterfowl and a number of types of aquatic mammal . As well as this, they act to improve water quality by acting as a sink to filter pollutants and sediment from the water that flows through them. Also important is their function in flood control. Marshes and other wetlands are able to absorb water during periods of heavy rainfall and slowly release it into waterways and therefore reduce the magnitude of the flooding . The pH in marshes tends to be neutral to alkaline; as opposed to in bogs.

Types of marshes

There are a number of different types of marshes depending mainly on their location and salinity. Both of these factors greatly influence the range and scope of animal and plant life that can survive and reproduce in these environments. The three main types of marsh are salt marshes, freshwater tidal marshes, and freshwater marshes. These three can be found worldwide and each contains a different set of organisms specialized to survive in the harsh environment that it finds itself in.

Salt marshes

Main article: Salt marsh

Salt water marshes are found around the world in mid to high latitudes, wherever there are sections of protected coastline. They are located close enough to the shoreline that the motion of the tides affects them and, sporadically, they are covered with water. They flourish where the rate of sediment buildup is greater than the rate that the land level is sinking at. Salt marshes are dominated by specially adapted rooted vegetation, primarily salt-tolerant grasses. As the area has a high salinity, sporadically alternates between dry and submerged, and undergoes extreme daily and seasonal temperature fluctuations, the creatures inhabiting this type of marsh must be highly specialized to survive. At one time it was believed that the detritus that was carried out with each tide was eaten by the marine life in nearby estuaries. This, however, is not the case. Through numerous studies, it was found that very little of the salt marsh vegetation is eaten by animals. It is believed that the majority is in fact consumed by bacteria and converted back into nutrients usable by the marsh plants, therefore recycling the marshes nutrients. Salt marshes are most commonly found in lagoons, estuaries and on the sheltered side of shingle or sandspit. The currents there carry the fine particles around to the quiet side of the spit and sediment begins to build up. These locations allow the marshes to absorb the excess nutrients from the water running through them before they reach the oceans and estuaries. These marshes are slowly declining. Coastal development and urban sprawl has caused significant loss of these essential habitats. In the United States though, most states have enacted laws for the specific purpose of protecting and conserving the declining salt marshes.

Fresh water tidal marshes

This form of marsh is defined by the fact that although it is a freshwater marsh, it is still affected by the tides. Without the stresses of salinity that is undergone by its salt water counterpart, the diversity of the plants and animals that live in and use these marshes is much higher than any other form of marsh. Around the world, the locations of freshwater tidal marshes often have been claimed by humans as a favorable spot for habitation and eventually are over run by towns and cities. These spots are chosen because of their proximity to the sea while having a supply of fresh water. This is why, of all the wetland types, freshwater tidal marshes have been altered or destroyed by human civilizations the most. The most serious threats to this form of marsh are the increasing size and pollution of the cities surrounding them.

Fresh water marshes

Main articles: Wet meadow, Vernal pool, Dry lake, and Prairie Pothole Region

Freshwater marshes are the most diverse form of marsh in the three groups and range greatly in both size and geographic location. They make up the most common form of wetland in North America. Some examples of freshwater marsh types in North America are;

Wet meadows

Wet meadows are a type of freshwater marsh that is generally found in areas of poor drainage.

Vernal pools

Vernal pools are a type of marsh found only seasonally in shallow depressions in the land. This form of marsh only occurs on the West Coast.

Playa lakes

Playa lakes are a form of freshwater marsh that occurs in the southern high plains of the United States. They are only present at certain times of the year and occur as round hollows in the ground.

Prairie potholes

Prairie potholes are found in the northern parts of North America. This landscape was once covered by glaciers and as a result shallow depressions were formed in great numbers. These depressions fill with water in the spring. Some only occur seasonally while others retain enough water to be present all year.

The mineral rich soils have high organic components which make these one of the most productive ecosystems in the world. The mineral rich soils are made up of sand, silt and clay. This form of marsh is dominated by various forms of grasses, sedges, and other hydrophytes. As most of its productivity follows detrital pathways, the substrate in this form of marsh has a higher pH than the substrate of bogs. Freshwater marshes are being degraded along with all the other forms of marsh. Farming activities and construction have caused deposits of nutrients and sediment to build up in marshes past the normal level. Much of the marsh land has been destroyed and damaged because of human development, causing severe flooding and overwhelming nutrient deposits in the waters downstream. These excess nutrients can cause occurrences such as algal blooms, which in turn cause population decline of the animal life in the area.

See also

• Aquatic plant
• Bayou
• Biodiversity Action Plan
• Bog
• Fen
• Freshwater marsh

External links

• Marshes of the Lowcountry (South Carolina) -- Beaufort County Library
• General Information of Ibera Marshes (in English and Spanish)