Once plentiful in the United States, wetlands are in serious decline now because of their loss to agriculture
and commercial development. The United States has lost more than half
of its original wetland areas. Even though development in wetlands is
now regulated by the federal government, more than 300,000 acres are lost
annually. But because people are realizing the important and valuable
functions of wetlands, recent efforts have focused on restoring some of
these lost resources. But wetland restoration is a complex and lengthy
process. Ecologists are just beginning to learn about the effectiveness
of various restoration strategies.
Wetlands have numerous functions. Among them are:
1. Flood control: Wetlands, often called natural sponges, help control
flood waters by absorbing water during heavy rainfall, then slowly releasing
2. Water quality and availability: Wetlands help purify water by processing
nutrients, suspended materials and other pollutants. Wetlands also increase
the availability of water by absorbing and storing water in wet seasons,
then gradually releasing it during dry periods.
3. Erosion control: Because they are often located between water bodies
and high ground, wetlands buffer shorelands against erosion. Wetland plants
also bind soil with their roots and help to absorb the impact from wave
4. Fish and wildlife habitat: Most fish and shellfish eaten by humans
live in wetlands when they are young. Wildlife also migrate through wetlands,
and many endangered species, such as the wood stork, live there, as do
many other birds, amphibians, reptiles and mammals.
5. Recreation: Wetlands attract hunters, fishermen, hikers and boaters.
Wetlands are also havens for bird watchers and provide scenic inspiration
for artists and writers.
Swamp Forest Restoration
Experiments with various flood-tolerant tree species
and various planting methods have allowed Savannah River Ecology Laboratory
researchers to accelerate by decades the recovery of a portion of the
delta of Four Mile Creek, which was damaged
by 30 years of nuclear reactor discharges at the U.S. Department
of Energy's Savannah River Site near Aiken, S.C. Hot water destroyed 227 acres of the swamp forest.
The delta no longer receives these discharges because the reactor was
shut down in 1985.
In 1991, a DOE-funded mitigation program began funding research by the
Ecology Laboratory, which conducted a dozen experiments with more than
4,500 trees of 24 different species. Researchers found that two flood-tolerant
tree species, bald cypress and water tupelo, are suitable for all areas
of the delta.
In sites that are not frequently flooded, additional species can survive:
green ash, water hickory, overcup oak and nuttall oak. In the highest
and less flooded areas, swamp chestnut oak, water oak and willow oak can
become established. Researchers also found that the survival of the least
expensive planting stock, bareroot saplings, was almost as high as the
most expensive stock. And the use of plastic tube tree shelters prevent
tree seedling destruction by beavers.
Carolina Bay Restoration
Many Carolina bay wetlands have been
degraded or converted to non-wetland use. Restoration efforts have focused
largely on restoring a bay's hydrology, or capability to hold water. But
scientists at Savannah River Ecology Laboratory believe restoration is
not successful until studies show that the replacement ecosystems are
functioning at least equally as well.
So in 1994, they began a comprehensive study of the restoration of a 9-acre Carolina bay wetland on the U.S.
Department of Energy's Savannah River Site near Aiken, S.C. The bay had
been drained by a ditch for agricultural use sometime before 1951.
With scientists from the USDA Forest Service, researchers divided the
bay into four sections and applied several experimental treatments. They
were: logging only (mostly loblolly pine), burning only, logging and burning,
and a control area with no treatment. Since the treatments were applied,
researchers have been collecting and analyzing data related to the bay's
vegetation, soil chemistry, water chemistry and aquatic invertebrates.
The collective results from these four study areas will indicate the success
of the restoration project.
In 1996, researchers found the wetland vegetation that once lived there
had begun returning. The number of wetland and non- wetland plant species
increased greatly -- compared to a pre- restoration study -- in the first
year after workers closed a drainage ditch that emptied the bay, removed
woody species and burned portions of the wetland. As the water level rose
during the second growing season, the relative abundance of plant species
shifted toward those that were more flood tolerant. An examination of
the seed bank (seeds deposited in the soil underlying the bay) revealed
that germinating wetland species were an important component of the initial
vegetation response to the restoration efforts.
Did You Know?
- Wetlands are the second most endangered habitat
worldwide, according to the World Wildlife Fund. The most endangered
one is tropical forests. Although wetlands are threatened by the effects
of climate change, such as sea-level rise, their biggest enemy is habitat
destruction by humans, ecologists say.
- Recovery of a swamp forest is a slow process
because established seedlings can take 10 to 20 years to produce seeds
that ultimately sustain the habitat type.
- Most studies of wetland restoration are short
term -- about two years -- and are driven by laws requiring mitigation,
the replacement of altered or destroyed wetlands. Many of these projects
have failed in the long term, say researchers at the Savannah River
Ecology Laboratory. At the Savannah River Site, ecologists are studying
a protected wetland site undergoing restoration. It is not labor intensive
-- they are not planting species. They are simply studying effects of
four experimental treatments on the wetland. This restoration strategy
is very cost effective, though the results are not immediate, researchers
- One of the biggest threats to the regeneration
of Four Mile Creek's swamp forest and others throughout the United States
is upstream dams on the nation's rivers, say researchers at the Savannah
River Ecology Laboratory. Management of the water level for flood control
is, over time, changing the distribution of animal and plant communities
in swamp forests. This is a hidden cost, not usually considered in the
analysis of whether to build a dam, researchers say.