Wetland Functions
Aside from the richness and diversity of life that wetlands bring to our planet, they perform other very important roles in protecting both natural and human resources:
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Many different types of wildlife use wetlands at some time during their life cycles. Migratory birds use wetlands as stopovers. Nesting waterfowl take advantage of the cover provided by wetland vegetation. Many fish depend on wetlands for feeding and spawning, and as nursery areas for their young. Some species such as walleye, yellow perch and bluegill move from open lake waters to spawn in shallow water wetlands. Many of the commercial marine fish harvested along the Atlantic coast need coastal wetlands in order to survive and reproduce.
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Wetlands play several important roles in preserving water quality by removing pollutants from water:
Sedimentation can create water quality problems in freshwater systems by decreasing water clarity, adding excess phosphorous and by smothering aquatic insect larvae. Wetlands reduce the sediment loads of water entering rivers and streams. When water flows through a wetland, vegetation slows it down, allowing many of the sediments to settle out. As much as 80-90% of sediments in water may be removed as it moves through wetlands. This process results in cleaner, clearer water entering a larger waterbody.
Excess nutrients (phosphorous and nitrogen) also create water quality problems by promoting excessive algal growth. When large amounts of algae die, aerobic bacteria must use up massive amounts of dissolved oxygen during decomposition, robbing fish and other wildlife of necessary oxygen. Wetlands improve water quality by removing excess nutrients in runoff from agricultural lands or waste disposal. Wetland plants trap sediments containing nutrients, absorb some of these nutrients, and release nitrogen gas to the atmosphere.
Wetland plants have the ability to absorb and temporarily hold pesticides, heavy metals, and other toxics materials in their tissues. The thick organic soils of wetlands also help trap the harmful chemicals and heavy metals in runoff and prevent them from flowing into other surface waters.
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Estuaries and coastal marshes are among the most productive ecosystems in the world and play an important role in aquatic food webs. When wetland plants die, specialized bacteria and fungi break down the plant tissues into minute fragments of nutrient rich detritus. The tide flushes out these bits of decaying material, making them available to finfish, shellfish and invertebrates in the coastal and marine environments. These animals in turn can serve as food for larger wetland inhabitants such as herons and waterfowl.
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Wetlands are important groundwater discharge points, where springs and groundwater seep to the surface. The groundwater discharging into a wetland helps maintain minimum flows in many rivers and streams. The role of wetlands in recharging (or adding water) to groundwater supplies is less clear. Many wetlands are situated over impervious soils which prevent water from percolating down into the groundwater. However, if the wetland is hydrologically connected to the groundwater system, it may help replenish groundwater.
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Wetlands reduce flood damage by storing flood water and slowly releasing it into downstream areas, thus lowering flood peaks. The large surface area of wetlands allows precipitation and surface runoff to accumulate in a temporary holding basin. Wetland vegetation slows down water flowing toward a waterbody and prevents it from draining into the waterbody all at once.
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Wetlands often act as a buffer zone between open water and land areas. Vegetation, such as Spartina grasses in coastal wetlands helps stabilize the shoreline against erosion and helps protect it from the impact of waves and storms. In inland areas, wetland vegetation along rivers and streams also serves to stabilize the banks, filter nutrients and reduce erosion and the subsequent sedimentation.
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Wetlands are home to a number of protected species. Destruction of habitats, particularly aquatic habitats, is a major threat to plants and animals and to biodiversity. One third of the endangered species in North America rely on wetlands. The piping plover and roseate tern are listed as threatened and endangered respectively and depend upon the preservation of fragile coastal wetlands.
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Wetlands provide valuable aesthetic, educational and recreational assets. Anyone who has been boating, fishing, birdwatching, walking or photographing in wetland areas understands these aspects. Wetlands offer a rich and diverse landscape for education, research and enjoyment. Wetlands that are managed for preservation and education are often accessible to beginning and experienced naturalists.
Historically many of the functions of wetlands were neither recognized nor valued. However, more people are learning to see wetlands as productive and valuable ecosystems that perform important roles in the environment.