| What are wetlands?
Types of wetlands
Why are wetlands important? |
We hear the term all the time, but what does "wetland" actually mean? Marshes, swamps, fens, and wet meadows are all wetlands, so how do you make sense of all these names? And even if you know a wetland when you see one, why are wetlands so important to us? Read on to learn the answers to these questions and more.
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What are Wetlands?
Swamps, bogs, fens, marshes, vernal pools, and wet meadows all have two things in common: they're all wetlands and they all perform vital functions that benefit people and wildlife.
A wetland is defined as an area of land that is saturated or flooded with water for a sufficient time to foster the growth of hydrophytic plants and the development of hydric soils.
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So what does hydrophytic mean?
Hydrophytic is a scientific term for "water-loving." Hydrophytic plants grow in water, or in soil that is frequently flooded with water. These plants are unique because they can grow in soils with low amounts of oxygen.
What about hydric soil?
A hydric soil is a soil that is saturated or frequently flooded with water. This saturation results in low oxygen conditions.
When you find water-loving plants, wet soils, and water at or near ground level for at least part of the year, you've probably found a wetland!
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Types of Wetlands
There are many different terms used to describe wetlands, depending on specific soil, water, and climatic characteristics. Michigan's wetlands fall into three general categories: marshes, swamps, and northern peatlands.
Marshes
A marsh is what most people think of when they hear the term wetland. Marshes feature shallow, standing or slow-moving water, often near ponds, rivers, streams, and lakes. Typical plants include rushes, reeds, sedges, cattails, and grasses. Wet meadows are a special type of marsh with grass-like vegetation and saturated soils, but little or no standing water. Many wet meadows occur in the former lake-plain of the Great Lakes, especially in southeast Michigan. Because many of these areas have been converted to farmland or have been developed, the remaining wet meadows are rare and contain some plant species found nowhere else in the world.
Marshes are one of the most biologically productive ecosystems in Michigan. They provide habitat and breeding grounds for water birds such as ducks, geese, swans, and herons. The common loon, bald eagle, and osprey use marshes for feeding and nesting, as do many songbirds. Marshes are also home to mammals such as muskrat and mink, and are important spawning grounds for many fish species.
Swamps
Swamps are forested wetlands. In southeast Michigan they are typically hardwood swamps, dominated by trees such as red maple, black ash, American elm, or balsam poplar. Swamps can also contain shrubs such as tag alder, willows, and dogwood. |
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Swamps can be located in the floodplain near lakes, rivers, or streams, but they also may occur far from open water, in areas where groundwater comes close to the surface. The soils in swamps are usually rich in nutrients and organic matter (created from the decomposition of dead trees and other vegetation). The dense vegetation and presence of water make swamps very important habitat for a wide array of wildlife, including deer, raccoons, bobcats, songbirds, frogs, and many other small animals.
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Northern Peatlands
Northern peatlands, also called bogs or fens, occur as thick peat deposits in old lake basins or as blankets of peat across the landscape. A combination of cool temperatures and rainfall create conditions that favor the accumulation of dead plant material, or peat. Bogs are isolated from ground or surface water and are dominated by sphagnum mosses, sedges, shrubs, and evergreen trees. Their primary source of water is rainfall, which is naturally slightly acidic. Many of the plants, animals, and microbes found in bogs have special adaptations to these acidic and somewhat nutrient-deficient conditions. For example, the pitcher plant obtains nutrients by capturing and "digesting" insects.
Fens, at the other end of the peatland spectrum, are fed by mineral-rich ground or surface water and are dominated by sedges and other grass-like vegetation. Plants that only grow in fens include grass of parnassus and shrubby cinquefoil.
Peatlands provide valuable safety cover for many birds and animals and are characterized by many unique plant species. The more acidic nature of bogs, however, makes them slightly less palatable than fens as a food source for wildlife.
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Why are wetlands important?
Wetlands are complex systems that serve vital ecological functions and provide many benefits to the communities in which they are found. As wetlands disappear in southeast Michigan, these functions and benefits become increasingly significant. The basic functions of wetlands can be divided into seven categories:
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Floral diversity and wildlife habitat
Approximately one-third of the nation's endangered and threatened plants and animals are wetlands species. Wetlands are extremely productive ecosystems and provide food, water, shelter, and nesting and breeding sites to a variety of insects, fish, amphibians, reptiles, mammals, and birds. Wetlands are important corridors for deer, migratory birds, and other wildlife. Such corridors are becoming scarce in southeast Michigan and should be preserved wherever possible.
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Fish and herpetile habitat
Wetlands, especially those connected to lakes and rivers, provide food, shelter and breeding habitat to the majority of Michigan's fish and herpetiles (reptiles and amphibians) during at least some part of their life cycle. Fish move into wetlands from deep water bodies daily and seasonally to use wetland resources. Wetland vegetation provides fish and herpetiles with aquatic insect larvae for food, spawning habitat, and refuge from predators and direct sunlight.
Flood and stormwater storage
Wetlands play a critical role in regulating the flow of water in a watershed. Floodwater storage is the process by which peak flows from runoff, surface flow, and precipitation are retained, reducing the danger of downstream flooding. This function is performed to varying degrees by almost all wetlands. Floodwater storage is extremely important in developing areas such as the Stony Creek watershed, because development increases the rate and volume of runoff delivered to surface waters. Protecting these wetlands will reduce the occurrence of flooding, erosion, and flood-related damages.
Runoff attenuation
Runoff attenuation refers to the ability of wetland vegetation to reduce the velocity of runoff. This has two positive impacts: first, runoff attenuation reduces erosion; second, it allows sediments carried in runoff to sink and be deposited in the wetland. Urban stormwater runoff and runoff from cultivated fields are rich in nutrients and sediments. Nitrogen and phosphorous absorbed by wetland vegetation prevents eutrophication (the overproduction of algae and aquatic plants due to excessive nutrients) in downstream lakes and rivers. Nutrients can also be trapped in sediments that are deposited in wetlands, thereby preventing them from degrading downstream water quality.
Water quality protection
Water quality protection refers to the ability of wetlands to remove and break down sediments, nutrients, and toxins. Heavy metals and hydrocarbons attach to sediment particles suspended in runoff. These may be deposited along with sediment when runoff enters a wetland. Once deposited, pollutants may be altered biologically, broken down by bacteria, or taken up by plants and deposited in wetland sediments when the plant dies. Toxins may also be immobilized or converted chemically to a less toxic form. This biological or physical entrapment is beneficial to aquatic life and downstream water quality. The filtering capacity of wetlands also protects groundwater by removing contaminants before they seep into the aquifer.
Shoreline and streambank protection
Wetlands along the edges of water bodies protect shorelines and streambanks by dissipating the erosive forces of wave action, currents and ice floes. Root systems of wetland vegetation bind soil at the water's edge, stabilize sediments, and reduce shoreline erosion by slowing wave velocity and current speed. The removal of wetland vegetation, coupled with boat traffic, dramatically increases shoreline and stream bank erosion. Wetlands alongside water bodies where development is occurring are therefore particularly important in providing shoreline and stream bank stabilization.
Aesthetic and recreation opportunities
Wetlands are a rich recreational resource for a variety of uses such as fishing, wildlife watching, walking, photography, hunting, and nature observation. The value of a wetland for aesthetic and recreational purposes is difficult to assess, due to the subjectivity of this function to personal interpretation. However, aesthetic and recreational value is important to many groups; over $10 billion per year is spent nationally to observe and photograph wetland-dependent birds.
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Last updated Saturday, August 05, 2006 by CRWC.
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