Wetland functional values
Before the 1980s, wetlands were often viewed as wastelands, useful only when drained or filled. We now know that wetlands benefit people and the natural world in remarkable ways. They provide critical habitat for wildlife, water storage to prevent flooding and protect water quality, and recreational opportunities for wildlife watchers, anglers, hunters, and boaters. These are known as "wetland functional values."
Every wetland is unique. One wetland on the north edge of town may perform different functions than another on the south edge – even though they may appear at first glance to be very similar. A bog in northern Wisconsin may be valued for different reasons than a bog in southeastern Wisconsin. Wetland functional values are determined by a variety of different parameters including physical, chemical and biological components.
Values of wetlands
- When is a wetland a wetland?
- Wetlands in Wisconsin were defined by the State Legislature in 1978:
Wetland: An area where water is at, near or above the land surface long enough to be capable of supporting aquatic or hydrophytic (water–loving) vegetation and which has soils indicative of wet conditions.
- Apart from these essential common characteristics, wetlands – and wetland function – vary. This page describes the basic functions that can occur in a wetland. Whether a specific wetland performs these functions depends on many variables (including wetland type, size, and previous physical influences/natural or human-induced) and opportunity (including the location of the wetland in landscape and surrounding land use). Wetlands also change over time and may function differently from year to year or season to season. These are very dynamic ecosystems.
- Determining values
- Standardized assessment methods are used to evaluate the extent to which a specific wetland may perform any given function. The presence or absence of specific characteristics is used to determine the importance of each functional value for the site in question.
- These characteristics may or may not be obvious to the casual observer. The changing nature of wetlands can hide many of these traits. Migratory bird use, for example, is not always obvious except in spring and fall.
- And the occurrence of various wetland plants gives important, yet subtle, clues about habitat, water quality and biodiversity. These types of observations help us evaluate a wetland’s intrinsic value and overall importance to society.
- Floral diversity
- Wetlands can support an abundance and variety of plants, ranging from duckweed and orchids to black ash. These plants contribute to the earth’s biodiversity and provide food and shelter for many animal species at critical times during their life cycles. Many of the rare and endangered plant species in Wisconsin are found in wetlands.
- The importance of floral diversity in a particular wetland is usually related to two factors. First, the more valuable wetlands usually support a greater variety of native plants (high diversity), than sites with little variety or large numbers of non–native species. Second, wetlands communities that are regionally scarce are considered particularly valuable.
- Fish and wildlife habitat
- Many animals spend their whole lives in wetlands; for others, wetlands are critical habitat for feeding, breeding, resting, nesting, escape cover or travel corridors. Wisconsin wetlands are spawning grounds for northern pike, nurseries for fish and ducklings, critical habitat for shorebirds and songbirds and lifelong habitat for some frogs and turtles. Wetlands also provide essential habitat for smaller aquatic organisms in the food web, including crustaceans, mollusks, insects, and plankton.
- Some of the most valuable wetlands for fish and wildlife provide diverse plant cover and open water within large, undeveloped tracts of land. This function may be considered particularly important if the habitat is regionally scarce, such as the last remaining wetland in an urban setting.
- Flood protection
- Due to dense vegetation and location within the landscape, wetlands are important for retaining stormwater from rain and melting snow rushing toward rivers and lakes. Wetlands slow stormwater runoff and can provide storage areas for floods, thus minimizing harm to downstream areas.
- Preservation of wetlands can prevent needless expenses for flood and stormwater control projects such as dikes, levees, concrete-lined channels and detention basins.
- Wetlands located in the mid or lower reaches of a watershed contribute most substantially to flood control since they lie in the path of more water than their upstream counterparts. When several wetland basins perform this function within a watershed, the effect may be a staggered, moderated discharge, reducing flood peaks.
- Flood protection may be especially important in cities, where pavement contributes to runoff, and in areas with steep slopes or other land features which tend to increase stormwater amounts and velocity. These functional values can provide economic benefits to downstream property owners and taxpayers.
- Water quality protection
- Wetland plants and soils have the capacity to store and filter pollutants ranging from pesticides to animal wastes. Calm wetland waters, with their flat surface and flow characteristics, allow particles of toxins and nutrients to settle out of the water column. Plants take up certain nutrients from the water. Other substances can be stored or transformed to a less toxic state within wetlands. As a result, our lakes, rivers and streams are cleaner and our drinking water is safer.
- Larger wetlands and those which contain dense vegetation are most effective in protecting water quality. If surrounding land uses contribute to soil runoff or introduce manure or other pollutants into a watershed, the value of this function may be especially high.
- Wetlands that filter or store sediments or nutrients for extended periods may undergo fundamental changes. Sediments will eventually fill in wetlands and nutrients will eventually modify the vegetation. Such changes may result in the loss of this function over time.
- Shoreline protection
- Shoreland wetlands act as buffers between land and water. They protect against erosion by absorbing the force of waves and currents and by anchoring sediments. Roots of wetland plants bind lakeshores and streambanks, providing further protection. Benefits include the protection of habitat and structures, as well as land which might otherwise be lost to erosion. This function is especially important in waterways where boat traffic, water current and/or wind cause substantial water movement that would otherwise damage the shore.
- Trout streams and other high-quality waterways often depend on shoreland wetlands to protect their characteristic clear, cold waters. Without this wetland buffer, the shoreline becomes undercut and collapses. When this happens, streams often become wider, shallower and turbid. Water temperatures rise and habitat quality deteriorates.
- A wetland that reduces erosion can also reduce sedimentation to nearby waterways. If the waterway is a navigational channel, the reduction in sedimentation can help reduce the frequency of dredging to maintain the channel.
- Groundwater recharge and discharge
- Groundwater recharge is the process by which water moves into the groundwater system. Although recharge usually occurs at higher elevations, some wetlands can provide a valuable service of replenishing groundwater supplies. The filtering capacity of wetland plants and substrates may also help protect groundwater quality.
- Groundwater discharge is the process by which groundwater is discharged to the surface. Groundwater discharge is a more common wetland function and can be important for stabilizing stream flows, especially during dry months. Groundwater discharge through wetlands can enhance the aquatic life communities in downstream areas. It also can contribute toward high-quality water in lakes, rivers and streams. In some cases, groundwater discharge sites are obvious, through visible springs or by the presence of certain plant species.
- Aesthetics, recreation, education and science
- Do you like to canoe or cross–country ski? Watch birds or listen to bullfrogs? Wetlands are some of our favorite places to study, hike or just drive by. They provide peaceful open spaces in landscapes that are under development pressure and have rich potential for hunters and anglers, scientists and students.
- Wetlands provide exceptional educational and scientific research opportunities because of their unique combination of terrestrial and aquatic life and physical and chemical processes. Many species of endangered and threatened plants and animals are found in wetlands.
- Wetlands located within or near urban settings and those frequently visited by the public are especially valuable for the social and educational opportunities they offer. Open water, diverse vegetation, and lack of pollution also contribute to the value of specific wetlands for recreational and educational purposes and general quality of life.
- Functional value assessment
- Small wetlands provide important functional values, which are often difficult to measure if assessing a wetland in isolation from its landscape context. The report, Small Wetlands and the Cumulative Impacts of Small Wetland Losses (May 1998), presents literature relevant to assessing the functions of small wetlands including consideration of wetland complexes, local wetland scarcity, fragmentation and the cumulative impact of small wetland losses.