Historically, the U.S. has had an abundance and diversity of wetlands. However, the wetlands that exist now may represent only 50% of those seen by pioneers as they advanced across the continent some 200 years ago. The loss of wetlands in this country is of extreme concern to wildlife managers because of the value the wetland ecosystem has for wildlife.
Just what are wetlands? A frequently used definition is “lowlands covered with shallow and sometimes temporary or intermittent waters.” Wetlands are ecotones, since they are transition zones from uplands to deep water aquatic systems. Over the years, many terms have been used for the coastal and inland wetlands in the US, for example:
- Swamp: Wetland dominated by trees or shrubs
- Marsh: Wetland dominated by herbaceous vegetation
- Pothole: Shallow marsh-like ponds, mainly found in the Prairie Region of the US
- Playa: Term used in Southwestern US for marsh-like ponds similar to potholes.
- Bottomlands or Riparian Wetlands: Lowlands along streams and rivers, usually on river or stream flood-plains, that are periodically flooded but are otherwise dry for varying portions of the growing season. These wetlands are often forested and referred to as Bottomland Hardwood Forests.
Characteristics of all Wetlands:
- Hydrology: Land is covered with water for a period of time
- Hydric Soils
- Hydrophytes: Vegetation adapted to wet conditions
Hydrology is probably the single most important determinant for the establishment and maintenance of specific types of wetlands and wetland processes.
The hydroperiod is the seasonal patter of water level of a wetland. It defines the rise and fall of a wetland’s surface and subsurface water. It is unique to each type of wetland, and its constancy from year-to-year ensures the stability for that wetland. Alter the hydroperiod and you can destroy the wetland!!
The hydroperiod of many bottomland hardwood forests is a sudden and relatively short seasonal flooding followed by a rapid drop of the water’s surface to well below ground – so a bottomland hardwood forest wetland may be “bone dry” for many months of the year!
A hydric soil is a soil that in its undrained condition is saturated, flooded, or ponded long enough during the growing season to develop anaerobic conditions (low or no oxygen) that favor the growth and regeneration of hydrophytic vegetation.
Hydrophytic vegetation are plants growing in water or on wet soil which have developed various adaptations to overcome being submerged and/or growing in anaerobic soils.
So what value does a wetland have for wildlife and people? Wetlands are nutrient sources, sinks, or transformers.
- Source: Exports nutrients to downstream or adjacent ecosystems
- Sink: Stores elements within the wetland (e.g., nitrogen and phosphorus)
- Transformer: Chemicals can be transformed (e.g., from inorganic to organic forms) often accomplished by the microbes found associated with wetlands.
Nutrients from wetlands are extremely important to vegetation and food webs within and outside the wetland system!
Wetlands are also important wildlife habitat as well as habitat for endangered animals (at least one-third of the nation’s endangered animals live in wetlands).
Wetlands also play a role in flood control and water quality. Wetlands store floodwaters and reduce downstream flooding. They also act as natural water filters, helping recharge the underground water table.
They also have a very high economic value – very large amounts of money are brought into local communities via waterfowl hunting, fishing, boating, etc.
A type of wetland important to the Southeast are Riparian Wetlands (such as the Bottomland Hardwood Forest we’ve been discussing). Riparian wetlands are unique because of their linear form along rivers and streams, and because they process large amounts of material coming from upstream or as runoff from the land.
The streamside or riparian forest (sometimes referred to as the “riparian zone“) is valuable to the many animals that seek its refuge, diversity of habitats, and abundant water – or use it as a corridor for migration.
Most nutrients in the nearby trees are not stored in the wood, but rather in the leaves. Litter falling into the stream provides a source of nutrients and food for aquatic invertebrates, which in turn are food for fish! When trees in the riparian forest die, or are carried downstream, the wood increases channel complexity by the water flowing over and under it. It also increases water velocity (increasing the water’s oxygen content), and logs form pools and become a source of cover for fish and amphibians.
And finally, riparian forest canopy helps shade a stream, keeping the stream cooler, which in turn keeps the oxygen level up, and avoiding the thermal stress that can negatively impact many fish species.
Wetlands are one, if not the, most important wildlife habitat, and disappearing at an alarming rate. Whatever you can do as a wildlife manager to protect these areas is of the highest priority.
Next post we’ll discuss wildlife and farming, and how many practices today are harmful to the areas we are trying to protect.