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Marsh

earth science Maturity 11-13 Next article →

A marsh is a specific type of wetland characterized by its vegetation. While many people use the word for any low-lying, waterlogged land, ecologists define a marsh by its plants. Marshes are dominated by herbaceous plants, such as grasses, rushes, or reeds. This distinguishes them from swamps, which are dominated by trees. They also differ from mires, which are wetlands where acidic peat accumulates. If a marsh contains low-growing shrubs, it is sometimes called a carr.

Coastal marsh profile
Coastal marsh profile

Living in a marsh requires specialized biological adaptations. The soil is often wet mud with very low oxygen levels. To survive, many marsh plants have developed aerenchyma. These are internal channels within the stem that allow air to move from the leaves down to the rooting zone. Many plants also utilize rhizomes, which are underground structures used for both storage and reproduction.

Water Lily - geograph.org.uk - 483063
Water Lily - geograph.org.uk - 483063

Animals must also adapt to these conditions. Many fish, amphibians, and invertebrates can survive in water with low oxygen. Some species can even obtain oxygen directly from the air.

Marshes serve as vital ecosystems with massive global significance. They are incredibly productive, supporting high levels of biological activity. This productivity helps support global fisheries by providing habitats for fish, waterfowl, and aquatic mammals. Furthermore, marshes play a major role in the carbon cycle. They contain 0.1% of the world's sequestered terrestrial carbon. They also act as a natural sink, filtering pollutants and sediment from water to improve quality.

These wetlands also provide essential services for climate resilience. Marshes can absorb high tides and manage water changes caused by extreme weather. During periods of heavy rainfall, they absorb excess water and release it slowly into waterways. This process helps reduce the magnitude of flooding in nearby areas. Beyond these natural functions, marshes are also used by humans for tourism, recreation, education, and scientific research.

Marshes are categorized into three main types based on salinity and location. Salt marshes are found in protected coastlines at mid to high latitudes. They are located close enough to the shore to be affected by the motion of tides. These marshes flourish in areas where the rate of sediment buildup is greater than the rate at which the land sinks. They are commonly found in lagoons, estuaries, or on the sheltered sides of sandspits.

Culbin Salt Marsh - geograph.org.uk - 185128
Culbin Salt Marsh - geograph.org.uk - 185128

Freshwater tidal marshes are also influenced by ocean tides. However, they lack the high salinity of salt marshes. Because they do not face the same salt stress, they often support a much higher diversity of plants and animals. The third type is the freshwater marsh, which is the most common wetland in North America. These are highly diverse and include several distinct sub-types.

MeadowInBigBear
MeadowInBigBear

Specific freshwater marsh types include wet meadows and vernal pools. Wet meadows occur in shallow lake basins or depressions and are often dry during the summer. Vernal pools are seasonal marshes found in shallow depressions. In western North America, they often form in grasslands, while in the east, they appear in forested landscapes. These pools are critical for amphibians, such as the endangered gopher frog, because they provide breeding habitats free from fish.

VernalPool
VernalPool

Other unique freshwater formations include playa lakes and prairie potholes. Playa lakes are circular, shallow marshes found in the southern high plains of the United States. They only appear during certain times of the year. Prairie potholes are found in northern North America and were created by ancient glaciers. These depressions fill with water in the spring and provide vital breeding grounds for waterfowl.

Human activity has significantly impacted these environments. Some areas have lost 90% of their wetlands due to urban sprawl or drainage for agriculture. In some regions, marshes have been embanked and drained to create polders. However, many people are now working on restoration. This involves returning marshes to the landscape to replace what was lost, such as by allowing rivers to flood naturally in the spring.

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🖼️ Images & Media (9)
File:Meadowlands Lyndhurst.jpg
Meadowlands Lyndhurst.jpg
File:Coastal marsh profile.png
Coastal marsh profile.png
File:Water Lily - geograph.org.uk - 483063.jpg
Water Lily - geograph.org.uk - 483063.jpg
File:Xanthocephalus xanthocephalus -100 Mile House, British Columbia, Canada -male-8.jpg
Xanthocephalus xanthocephalus -100 Mile...
File:Jyväskylä - swamp 2.jpg
Jyväskylä - swamp 2.jpg
File:Culbin Salt Marsh - geograph.org.uk - 185128.jpg
Culbin Salt Marsh - geograph.org.uk - 185128.jpg
File:MeadowInBigBear.JPG
MeadowInBigBear.JPG
File:VernalPool.jpg
VernalPool.jpg
File:Prairie Pothole Wetlands.jpg
Prairie Pothole Wetlands.jpg
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