Wetlands protect water quality by trapping sediments and retaining excess nutrients and other pollutants such as heavy metals. These functions are especially important when a wetland is connected to groundwater or surface water sources, such as rivers and lakes, and used by humans for drinking, swimming, fishing, or other activities. These same functions are critical for fish and other wildlife.
Trapping and holding pollutants
Sediments, nutrients, and toxic chemicals enter wetlands primarily by surface water runoff. Runoff is the rain, melting snow, and stormwater that travels over urban, industrial, suburban, and rural lands on its way to storm drains, streams and other water bodies. In urban areas, runoff washes over buildings, parking lots, lawns, driveways, and streets in industrial, commercial, and residential areas. Runoff water picks up pollutants and carries them to water bodies such as Puget Sound.
In rural areas, agricultural and forest practices can affect runoff. For instance, runoff might carry too much sediment if it drains through a freshly-plowed field or clear-cut area. Runoff can carry pesticides and fertilizers if these have been applied to the land.
Sediments settle into the gravel of stream beds, disrupting or preventing fish from spawning, and even smothering fish eggs. Other pollutants — notably heavy metals — are often attached to sediments and may further contaminate water. Wetlands remove these pollutants by trapping sediments and holding them. The slow movement of water through wetlands allows sediments to settle where wetland plants can hold them in place.
Removing excess nutrients
Runoff often carries nutrients that can cause water quality problems such as algae blooms. Besides aesthetic problems associated with algae blooms such as a green, smelly slime, they can deplete oxygen levels in the water, killing fish and other aquatic life.
Some algae release toxins when they bloom that can kill pets and livestock. Wetlands protect surface waters from the problems of nutrient overload by removing excess nutrients. Some of these chemicals are taken up and used by wetland plants, and converted to less harmful chemical forms in the soil.
Protecting plants and animals from toxic chemicals
Toxic chemicals flushed into surface waters pose a threat for disease, death, or other problems for plants and animals (including humans). In a function similar to nutrient removal, wetlands trap and bury these chemicals or may even convert some of them to less harmful forms.Scientists continue to study what happens to toxic chemicals when they enter wetlands. They warn us that even if the toxins are buried, they are still potentially dangerous. Disrupting wetland soils could release toxins back into the aquatic environment.
Wetlands that occur along the shoreline of lakes or banks of rivers and streams help protect shoreline soils from erosion caused by the forces of waves and currents. Plants in wetland act as a buffer by dissipating the water's energy and providing stability to the soils with their extensive root systems.
Aquifers and groundwater are recharged or replenished by surface water or rain water or snow melt that seeps into the ground. Wetlands connected to underground sources of water are important because they retain water and provide time for it to filter down into aquifers.
Groundwater provides water for drinking, irrigation, and keeping water flowing in our streams, rivers, lakes and reservoirs. During periods of low stream flows or lake levels, the slow discharge of groundwater to surface waters often helps maintain minimum water levels. In addition, wetlands help maintain streams, lakes, and reservoirs by releasing stored water directly into these systems. The many intricate connections with groundwater, stream flows, and lake and reservoir water levels, make wetlands essential for a proper-functioning hydrologic cycle.
Almost any wetland can provide some measure of flood protection by holding excess water after a storm, and then releasing it slowly. The size, shape, location, and soil type of a wetland determine its ability to reduce local and downstream flooding.
While wetlands cannot prevent flooding, they do lower the severity by temporarily holding water and slowing its velocity. Wetland soil acts as a sponge, holding much more water than other soil types. Even isolated wetlands can reduce local flooding. If wetlands were not here to hold stormwater runoff, more backyards and basements might end up underwater.
Many species of birds, fish, mammals, reptiles, and amphibians rely on wetland habitat for breeding, foraging, and shelter. Wetlands provide unique habitats for species that cannot survive elsewhere. Migratory birds depend on wetlands, and many endangered and threatened animal species require wetlands during part of their life cycle. The incredibly high rate of wetlands loss has contributed to their demise.
Wetland plants and small animals, especially insects, are essential links at the lowest levels of the food chain. A wetland environment supports these plants and animals which, in turn, support wildlife that feed on them. While an otter or a trout may be a more attractive to protect than an insect or plant, the latter are no less important in the overall ecosystem.
There are significant economic benefits associated with wetlands. For example, if a community had to build flood control or water treatment systems to replace the functions provided by wetlands, the costs could far outweigh the expense of preserving the natural wetland systems. Similarly, when wetlands lose their value as fish habitat, it's difficult to replace, and the losses trickle down to recreational and commercial fishing industries.
There is no precise formula to determine the dollar value per acre of wetland but the more we learn about wetlands, the higher that value becomes.
An independent study found fresh water wetlands in the Puget Sound region alone could be worth more than $10 billion to Washington’s economy. A copy of the report can be found at http://www.eartheconomics.org/.
