Meaning of Marshland
Marshland is a treeless land in which the water table is at, above, or just below the surface of the ground. It is dominated by grasses, reeds, sedges, and cattails. These plants typify emergent vegetation, which has its roots in soil covered or saturated with water and its leaves held above water.
Marshes may be freshwater or saltwater. Freshwater marshes develop along the shallow margins of lakes and slow-moving rivers, forming when ponds and lakes become filled with sediment. Salt marshes occur on coastal tidal flats. Inland salt marshes occupy the edges of saline lakes. The nature of a marsh – its plant composition, species richness, and productivity – is strongly influenced by its relationship to surrounding ecosystems. They affect the supply of nutrients, the movement of water, and the type and deposition of sediment.
In the prairie pothole country of glaciated central North America, freshwater marshes undergo a cyclic renewal that is induced by periodic drought and dependent on the feeding habits of muskrats. The cycle begins with a nearly dry marsh in which seeds of aquatic plants germinate in the mud. When the marsh fills, the aquatic plants grow densely. Muskrats eat large areas of the emergent vegetation, creating patches of open water. This causes the shallow-water emergent to decline, but the submerged and floating species persist. When the next drought comes, the cycle begins again.
Salt marshes are best developed on the Atlantic coasts of North America and Europe. In eastern North America the low marsh is dominated by a single species, salt – marsh cord grass. The high marsh consists of a short cord grass called hay, spike grass, and glasswort. Glasswort is the dominant plant of Pacific Coast salt marshes.
Water and Vegetation Patterns of Marshes
In some marshes, such as the saw-grass wetlands of the Everglades or in salt marshes that are swept twice daily by tidal floods, water flows like a sheet across the surface, and the terrain is typically dominated by one or two species of emergent vegetation. In other marshes the water flows in channels rather than in sheets, flooding only at times of snowmelt and heavy precipitation and bringing in nutrients and sediment. Such irregular deposition of sediments provides variations in water depth, thus creating conditions favourable for a variety of wetland species. Deep marsh water is colonized by aquatic submerged plants (pond weeds) and floating plants (pond lilies). Shallower water supports reeds and wild rice. Very shallow water supports sedges, bulrushes, and cattails.
As sediments and organic deposits raise the bottom of a marsh above the water table, aquatic vegetation is gradually replaced by shrubs and eventually by a terrestrial ecosystem of upland grasses or forest trees.
Importance of Freshwater Marshes
Freshwater marshes provide nesting and wintering habitats for waterfowl and shorebirds, muskrats, frogs, and many aquatic insects (see Freshwater Life). Salt marshes are wintering grounds for snow geese and ducks, a nesting habitat for herons and rails, and a source of nutrients for estuarine waters (see Estuary). Marshes are important in flood control, in sustaining high-water tables, and as settling basins to reduce pollution downstream. Despite their great environmental value, marshes are continually being destroyed by drainage and filling.
Characteristics of Marshland
- Marshes are low-lying wetlands covered under shallow waters for long periods of time.
- They are usually formed in lowlands and plains near lakes and creeks, river banks or river mouths where water drainage is poor.
- They consist of grass-like vegetations which is able to grow in a waterlogged soil.
- Due to abundance of nutrients and mineral present in the water, marshes are breeding and nursing grounds for wide variety of organisms.
- The relative humidity in the atmosphere over the habitat is usually high.
- The water bodies usually contain much decaying organic matter.
- The decay of organic matter takes place on a large scale in a marsh and this causes a decrease in the oxygen content of the water. Under the mainly anaerobic conditions in the water or soil, foul smelling gases may be produced in which hydrogen sulphide and methane may be present. The products of this decomposition change the chemical properties of the marsh. For instance, some marshes are very strongly acidic.
Types of Marshes
Marshes may be either saltwater or freshwater marshes. In Nigeria, salt water marshes are found along the Atlantic coast, which is influenced by the tides. Usually, freshwater flowing down the river, which empty into the sea, mixes with tidal sea water in the estuaries, creeks and lagoons. However, in the dry season, the volume of river water is relatively small, and large in the rainy season. This large volume of river water mixes together with tidal seawater in estuaries, creeks, and lagoons, filling them up and causing them to overflow their banks.
The water that floods the land near the estuaries, creeks and lagoons is a mix of fresh and salt water; hence the marshes are called saltwater marshes.
Freshwater marshes occur inland, just beyond the limits of the saltwater marshes and beyond the areas influenced by tides. In this zone, only the freshwater of the rivers overflows the river banks to flood the adjoining lowland, forming freshwater marshes.
Plants and Animals in the Marshes
Plants found in saltwater marshes include various grasses and also algae that float on the water surface. Major animals include mangrove crab, lagoon crab, hermit crab, mudskipper fish, bloody calm (Arcasenillis), oysters, barnacles and angel-fish.
Freshwater marshes also have floating plants in standing water like algae, water lettuce, Lemna and Salvinia (water arum), various ferns and varieties of sword grass. The animals include frogs and toads, as well as fishes and birds that wade into the water to feed on fish for example, the heron.
Adaptive Features of Plants and Animals in Marshes
The varying conditions of the marsh makes the organisms ready to adapt to all kinds of condition:
Adaptive Features of Plants in Marshes
- A soft muddy bottom that provides little support and anchorage;
- Low oxygen levels or an anaerobic environment in the soil;
- High salinity in salt marshes and
- Change in water levels due to the ebb and flow of tides.
Adaptive Features of Animals in Marshes
- Invertebrates such as clams, shellfishes, shrimps and oysters;
- Reptiles like the salt marsh snakes and diamondback turtles;
- Amphibians such as frogs and salamanders;
- Birds like the great blue herons and clapper rails and
- Mammals such as muskrats, racoons, rabbits, and river otters.
In saltwater marshes, all the organisms have to be able to tolerate the salinity of the soil or water. They also have to tolerate the low oxygen concentration in the soil and water.
In freshwater marshes, the plants show adaptations similar to those of freshwater plants. Saprophytic organisms such as bacteria, which live on the dead organic matters in marshes, have to adapt to the mainly anaerobic conditions here.