H-02 Constructed Wetland Studies: Amphibians and Plants
Amphibian Studies: Stacey Lance, David Scott, Wes Flynn, and Diana Soteropoulos
Vegetation Surveys: Rebecca Sharitz, Linda Lee, and Paul Stankus
The H-02 treatment wetland array associated with the H-Area facilities
Buckets at sampling location
Green treefrogs (Hyla cinerea
) on planted bulrush stems
Construction of the H-02 treatment wetlands adjacent to H-Area on the Savannah River Site (SRS) began during FY-2007. The Savannah River Ecology Laboratory (SREL) initiated ecological studies related to the operation of the H-02 constructed wetlands in May 2008. Constructed wetlands are one method to treat and improve water quality at regulated outfalls on the SRS. Heavy metals such as copper, lead, and zinc are removed by adsorption to organic matter and clay particles, and sulfate reducing bacteria enable the precipitation of metal ions in the anaerobic soils. Constructed treatment wetlands proved effective at the A-01 outfall on the SRS, with removal efficiencies > 80% for copper, mercury, and lead within four years. Systematic monitoring has revealed that water quality is improved prior to discharge into streams, but the extent to which these constructed treatment wetlands also serve other “natural wetland” functions, such as providing wildlife habitat, has not been documented.
Water chemistry is extremely important to the successful development of amphibian eggs and young. Of particular interest are factors such as pH, dissolved oxygen (DO) concentration, and concentrations of metal ions such as copper (Cu) and zinc (Zn). The H-02 wetlands, now in their early phase of establishment, exhibit large fluctuations in some of these parameters. Copper concentrations in the H-02 system can vary spatially throughout the system, ranging as high as 31-37 ppb in the influent in summer months to 7 ppb in the effluent exiting the treatment wetlands. Levels in portions of the retention pond have reached 340-590 ppb. These concentrations may be of concern for normal amphibian development. By assessing the response of amphibians to the water quality of the H-02 wetlands over time and comparing amphibian success in created versus natural wetlands, we will better understand the suitability of the H-02 created wetlands for wildlife habitat, especially amphibians. The H-02 wetlands were designed to comply with regulatory guidelines for process and storm water discharge from H-Area facilities, but they may also provide wildlife benefits.
The SREL began amphibian and vegetation surveys at the site in summer 2008. Ecological research conducted by SREL focuses primarily on four questions related to these treatment wetlands: 1) What amphibians, reptiles, and plants have become established in the wetlands? 2) Is there any evidence that elevated metals levels in the wetlands (e.g., copper and zinc) affect amphibian success? 3) How do the amphibian diversity and numbers compare to other, more natural, wetlands? 4) As the constructed wetlands age, how will changes in metal loads, as well as vegetation composition and structure, affect the amphibian community?
Permanent plots for monitoring vegetation and amphibians were established in each wetland cell in May 2008, and three partial 30-m drift fences were constructed adjacent to the area to determine amphibian use of the ponds as breeding sites. To date we have captured 24 species amphibians and reptiles, and documented successful production of juveniles by nine amphibian species. To date no salamander species have been recorded at the H-02 site. Our baseline vegetation sampling documented 23 vascular plant species plus algae in our plots.
In addition to monitoring amphibian and reptile use of the wetlands, we collected data on metal burdens of amphibians inhabiting the wetlands, and we are conducting field and laboratory tests on effects of Cu concentration on amphibian development in three species (the southern toad, Anaxyrus (Bufo) terrestris, the eastern narrowmouth toad, Gastrophryne carolinensis, and the southern leopard frog, Lithobates (Rana) sphenocephalus). We are also monitoring vegetation colonization and succession patterns, with a special interest in how vegetation structure, species richness, proportional abundances, and invasive species numbers change over time.
In previous years some of our findings include:
- Metamorphs from our laboratory experiments have Cu body burdens comparable to those in metamorphs from the H-02 wetlands, suggesting our lab conditions accurately approximate field exposures.
- Embryo and early hatchling survival is reduced by Cu exposure in three species: Lithobates (Rana) sphenocephalus, Anaxyrus (Bufo) terrestris, and Gastrophryne carolinensis.
- There is a lot of among species variation in sensitivity to Cu with L. sphenocephalus being the most tolerant and G. carolinensis the least tolerant.
- Preliminary data suggests there is also among and within population variation in tolerance.
Based on these findings our current objectives include: 1) further examining within and among population variation in tolerance, 2) examining genetic components of Cu exposure tolerance, 3) conducting mesocosm studies to explore more realistic exposure pathways, and 4) further examining G. carolinensis.
- Lance SL, Erickson MR, Flynn RW, Mills GL, Tuberville TD, and Scott DE. 2012. Effects of chronic copper exposure on development and survival in the southern leopard frog [Lithobates (Rana) sphenocephalus]. Environmental Toxicology and Chemistry 31:1587-1594. [pdf]
ACKNOWLEDGEMENTS: These studies of contaminant effects on amphibians are funded in part by the National Nuclear Security Administration (NNSA-DOE). Work was also partially supported by the Department of Energy under Award Number DE-FC09-07SR22506 to the University of Georgia Research Foundation.