|Aerial view of Rainbow Bay.
Rainbow Bay is an isolated seasonal wetland located within the Rainbow
Bay Amphibian Reserve Set-Aside Area, in the center of the Savannah
River Site (SRS). This 87.5-acre Set-Aside Area includes Rainbow Bay,
a 200-meter forested buffer area, and a wedge-shaped corridor extending
to a tributary of Fourmile Creek. This corridor provides a forested
connection between the Rainbow Bay wetland, Bullfrog and Pickerel
Ponds, and the Fourmile Creek drainage, allowing amphibians to move
freely among these wetlands. Prior to the establishment of the SRS,
Rainbow Bay was surrounded completely by agricultural fields. In the
1950s, these fields were planted in slash and loblolly pine
by the U.S. Forest Service. The 200-meter buffer area surrounding
this wetland has not been subjected to clear-cutting or prescribed
fire for over twenty years.
SREL Research at Rainbow Bay....
The Savannah River Ecology Laboratory (SREL) began research in Rainbow
Bay in 1978, when this wetland was selected as a control site to examine
the ecological importance of Sun Bay, a wetland eliminated during
construction of the Defense Waste Processing Facility (DWPF). As part
of this research project, a drift fence was installed around Rainbow
Bay, allowing SREL researchers to census on a daily basis the amphibian
and reptiles that use the wetland and the surrounding terrestrial
habitat. Animals moving into and out of the wetland fall into buckets
located at regular intervals along both sides of the drift fence;
captured animals are identified, measured, and marked prior to their
release. This 20-year study is the longest running
project of its kind in the world and is considered to be a model for
the type of long-term studies that are required to understand the
effects of climatic fluctuations and habitat disturbances on natural
amphibian populations. Studies of Rainbow Bay fauna have resulted
in over 60 scientific research articles and countless articles in
the popular press. Such long-term intensive studies of a single natural
community have revealed that amphibian species can go through major
population fluctuations from year to year and that a species dominant
in some years may be almost absent in others, and vice versa. This
study was the basis for an article in the journal Science which concluded
that long-term studies are required to separate the effects of natural
climate-induced fluctuations in amphibian populations from human-induced
|Drift fence used at Carolina bays
to census amphibians and reptiles. Typical captures at
Rainbow Bay include ornate choruse frogs, tiger, mole, and marbled
salamanders, and narrowmouthed toads.
Other SREL studies have examined the species com-position and population
dynamics of zooplankton, bacterial diversity, and the relationship
between precip-itation and water chemistry in Rainbow Bay. Research
has determined that although the aquatic invertebrate community is
strongly influenced by the ponds hydroperiod, Rainbow Bay usually
holds water for long enough periods to support a diverse array of
zooplankton species, which serve as the primary food base for larval
salamanders. Surveys of cloned and sequenced bacterial DNA extracted
from Rainbow Bay sediments revealed that, of the 35 clones sequenced,
most were novel species. Other studies of the microbial community
at Rainbow Bay determined that SRS operations have not had a detectable
impact on antibiotic resistance expressed by the bacteria surveyed.
A study of the water chemistry in Rainbow Bay revealed that water
in this bay is soft and acidic (pH 4.0-5.9), with dissolved organic
matter ranging from 4-60 mg/L. Like other bays examined in this study,
atmospheric inputs of human-produced acids may influence the water
chemistry of Rainbow Bay.
What we've learned at Rainbow Bay...
- Hydroperiod (the number of days in a year that a wetland holds
water) is the single most important factor that influences what
species are successful at Rainbow Bay and how these
- No direct relationship could be detected between the pH of surface
water in Rainbow Bay and acidic rainfall entering the bay, suggesting
that the water quality in Carolina bays is influenced not only by
precipitation but also by shallow ground-water and potentially important
in-bay processes that are as yet poorly under-stood.
- Surveys of cloned and sequenced bacterial DNA extracted from Rainbow
Bay sediments revealed that most of the 35 clones sequenced represented
novel bacterial species.
|A 200-meter forested buffer
separates Rainbow Bay from a recent clear cut.
- The importance of hydroperiod is clearly evident in
the amphibian community. If the hydroperiod is too short, no species
reproduce successfully; if too long, then only a few species may
do well. The number of species successfully reproducing in the pond
and the number of young emerging from the pond appear to be highest
at intermediate hydroperiods.
- Conditions in the larval environment (the aquatic phase of the
life cycle) affect the traits of adults, such as body size, survival,
and age at maturity. The density experienced by larval salamanders
plays an important role in population regulation.
- Long-term daily censusing of amphibians indicated that any population
declines within a species were the result of drought conditions
and several years of unsuccessful reproduction. The unexplained
declines observed at other locations around the world have not occurred
in populations at Rainbow Bay.
- Data from long-term monitoring of Rainbow Bay suggest that it
may be difficult to distinguish natural population fluctuations
from human-caused declines.
- Statistical analyses show that, due to the extreme levels of natural
fluctuations in amphibian numbers, long time periods (greater than
20 years) may be necessary to identify population trends, especially
if changes are subtle.
Studies at Rainbow Bay
to Research Snapshots)