Marsh

Lore & Background

Marshes provide habitats for many kinds of invertebrates, fish, amphibians, waterfowl and aquatic mammals. This biological productivity means that marshes contain 0.1% of global sequestered terrestrial carbon. Moreover, they have an outsized influence on climate resilience of coastal areas and waterways, absorbing high tides and other water changes due to extreme weather. Though some marshes are expected to migrate upland, most natural marshlands will be threatened by sea level rise and associated erosion. 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. 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 flooding. Marshes also provide the services of tourism, recreation, education, and research.

In Their Own Story

The three main types of marsh are salt marshes, freshwater tidal marshes, and freshwater marshes. Saltwater 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 at which the land level is sinking. Salt marshes are dominated by specially adapted rooted vegetation, primarily salt-tolerant grasses. Salt marshes are most commonly found in lagoons, 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. These marshes are slowly declining. Coastal development and urban sprawl have caused significant loss of these essential habitats. Although considered a freshwater marsh, the ocean tides affect freshwater tidal marshes. 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. 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 include wet meadows, vernal pools, and playa lakes. 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. 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. Large tracts of tidal marsh have been embanked and artificially drained. They are usually known by the Dutch name of polders. 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 Fens.

Reader's Guide

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 rhizomes for underground storage and reproduction. Common examples include cattails, sedges, papyrus and sawgrass. Aquatic animals, from fish to salamanders, 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. Hassocks or tussocks are firmer clumps of vegetation in marshy or boggy ground. 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.

Did You Know?

• Marshes contain 0.1% of global sequestered terrestrial carbon.
• Marshes are differentiated from swamps by being dominated by herbaceous plants rather than trees.
• The pH in marshes tends to be neutral to alkaline, as opposed to bogs where peat accumulates under more acid conditions.
• Some areas have already lost 90% of their wetlands, including marshes.
• Vernal pools are a type of marsh found only seasonally in shallow depressions; many amphibian species depend upon them for spring breeding because they are free from fish.