In ecology, a marsh is a wetland that is dominated by rather than by .[Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p] More in general, the word can be used for any low-lying and seasonally waterlogged terrain. In Europe and in agricultural literature low-lying meadows that require draining and embanked are also referred to as marshes or marshland.
Marshes can often be found at the edges of lakes and streams, where they form a transition between the aquatic and terrestrial ecosystems. They are often dominated by Poaceae, Juncaceae or reeds.
Marshes provide for many kinds of Invertebrate, fish, Amphibian, Anseriformes and Aquatic mammal.
Basic information
Marshes provide a habitat for many species of plants, animals, and insects that have adapted to living in flooded conditions or other environments.
The plants must be able to survive in wet mud with low oxygen levels. Many of these plants, therefore, have
aerenchyma, channels within the stem that allow air to move from the leaves into the rooting zone.
Marsh plants also tend to have
for underground storage and reproduction. Common examples include
Typha,
sedges,
Cyperus papyrus and
Cladium. Aquatic animals, from fish to
, are generally able to live with a low amount of oxygen in the water. Some can obtain oxygen from the air instead, while others can live indefinitely in conditions of low oxygen.
The pH in marshes tends to be neutral to
alkaline, as opposed to
bogs, where peat accumulates under more acid conditions.
Values and ecosystem services
Marshes provide
for many kinds of invertebrates,
fish, amphibians, waterfowl and aquatic mammals.
Marshes have extremely high levels of biological production, some of the highest in the world, and therefore are important in supporting fisheries.
Marshes also improve water quality by acting as a sink to filter pollutants and sediment from the water that flows through them. Marshes partake in water purification by providing nutrient and pollution consumption.
Types of marshes
Marshes differ depending mainly on their location and
salinity. 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
, and
.
These three can be found worldwide, and each contains a different set of organisms.
Salt marshes
Saltwater marshes are found around the world in mid to high
, wherever there are sections of protected coastline. They are located close enough to the shoreline that the motion of the
affects them, and, sporadically, they are covered with water. They flourish where the rate of sediment buildup is greater than the rate at which the land level is sinking.
Salt marshes are dominated by specially adapted rooted vegetation, primarily salt-tolerant grasses.
[Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p.]
Salt marshes are most commonly found in , estuaries, and on the sheltered side of a 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.[B.R. Silliman, E.D. Grosholz, and M.D. Bertness (eds.) 2009. Human Impacts on Salt Marshes. A Global Perspective. University of California Press, Berkeley, California.]
Freshwater tidal marshes
Although considered a freshwater marsh, the
ocean tides affect this form of marsh. However, without the stresses of salinity at work in its saltwater counterpart, the diversity of the plants and animals that live in and use freshwater tidal marshes is much higher than in salt marshes. The most severe threats to this form of marsh are the increasing size and pollution of the cities surrounding them.
Freshwater marshes
Ranging greatly in size and geographic location, freshwater marshes make up North America's most common form of wetland. They are also the most diverse of the three types of marsh. Some examples of freshwater marsh types in North America are:
Wet meadows
Wet meadow occur in shallow lake basins, low-lying depressions, and the land between shallow marshes and upland areas. They also happen on the edges of large lakes and rivers. Wet meadows often have very high plant diversity and high densities of buried seeds.
[Keddy, P.A. and A. A. Reznicek. 1986. Great Lakes vegetation dynamics: the role of fluctuating water levels and buried seeds. Journal of Great Lakes Research 12: 25–36.] They are regularly flooded but are often dry in the summer.
Vernal pools
Vernal pool are a type of marsh found only seasonally in shallow depressions in the land. They can be covered in shallow water, but in the summer and fall, they can be completely dry. In western North America, vernal pools tend to form in open grasslands,
[Bauder, E. T. 1989. Drought stress and competition effects on the local distribution of Pogogyne abramsii. Ecology 70: 1083–9.] whereas in the east, they often occur in forested landscapes.
[Calhoun, A.J.K. and P.G. deMaynadier. 2008. Science and the Conservation of Vernal Pools in Northeastern North America. CRC Press, Boca Raton, Florida.] Further south, vernal pools form in pine savannas and
flatwoods. Many amphibian species depend upon vernal pools for spring breeding; these ponds provide a habitat free from fish, which eat the eggs and young of amphibians.
An example is the endangered
gopher frog.
[Richter, S. C. and Seigel, R. A. 2002. Annual variation in the population ecology of the endangered gopher frog, Rana sevosa Goin and Netting. Copeia, 2002, 962–72.] Similar temporary ponds occur in other world ecosystems, where they may have local names. However, vernal pool can be applied to all such temporary pool ecosystems.
Playa lakes
are a form of shallow freshwater marsh in the southern high plains of the United States.
[Smith, L. M. 2003. Playas of the Great Plains. Austin, TX: University of Texas Press.] Like vernal pools, they are only present at certain times of the year and generally have a circular shape.
As the playa dries during the summer, conspicuous plant zonation develops along the shoreline.
[Bolen, E. G., Smith, L. M., and Schramm, H. L., Jr. 1989. Playa lakes: prairie wetlands of the southern High Plains. BioScience 39: 615–23.]
Prairie potholes
Prairie potholes are found in northern North America, such as the Prairie Pothole Region. Glaciers once covered these landscapes, and as a result, shallow depressions were formed in great numbers. These depressions fill with water in the spring. They provide important breeding habitats for many species of waterfowl. Some pools only occur seasonally, while others retain enough water to be present all year.
[van der Valk, A. G. 1989. Northern Prairie Wetlands. Ames, IA: Iowa State University Press.]
Riverine wetlands
Many kinds of marsh occur along the fringes of large rivers. The different types are produced by factors such as water level, nutrients,
ice scour, and waves.
[Day, R., P.A. Keddy, J. McNeill and T. Carleton. 1988. Fertility and disturbance gradients: a summary model for riverine marsh vegetation. Ecology 69: 1044–1054]
Embanked marshlands
Large tracts of tidal marsh have been embanked and artificially drained. They are usually known by the Dutch name of
. In Northern Germany and Scandinavia they are called
Marschland,
Marsch or
marsk; in France
marais maritime. In the Netherlands and Belgium, they are designated as
marine clay districts. In
East Anglia, a region in the East of England, the embanked marshes are also known as
The Fens.
Restoration
Some areas have already lost 90% of their wetlands, including marshes. They have been drained to create agricultural land or filled to accommodate
urban sprawl. Restoration is returning marshes to the
landscape to replace those lost in the past.
Restoration can be done on a large scale, such as by allowing rivers to flood naturally in the spring, or on a small scale by returning wetlands to urban landscapes.
See also
External links
