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Assessing the Ecological Health of the D-Area Ash Plume Wetland


David Scott, Brian Metts, Tracey Tuberville, and Bill Hopkins

 

In recent years the Ash Plume Wetland (APW) and surrounding area in D-Area on the Savannah River Site (SRS) have been targeted for ecological studies due to the release of coal combustion wastes to the ecosystem several decades ago. High concentrations of trace metals (e.g., arsenic, selenium, and cadmium) in the waste may threaten the environmental health of the APW, especially for organisms such as amphibians that use both aquatic and terrestrial habitats during their life cycle. Our study builds on previous work by SREL scientists that examined the distribution of coal ash wastes in APW and adjacent floodplain, as well as concentrations of metals in soil, plants, invertebrates, and amphibians.

Although trace element uptake and accumulation has been well documented in different species and life stages of amphibians at the APW, potential biological effects have been little studied. Earlier sampling of the amphibian and reptile community revealed that the assemblage of species at the site is similar to a nearby reference site (Ellenton Bay); i.e., the number of species found at the APW is comparable to the “expected” number. However, with the exception of the leopard frog (Rana sphenocephala), newly metamorphosed individuals of amphibians were not found in earlier studies, possibly indicating that the APW is not suitable for successful egg and larval development of some pond-breeding amphibians. If the APW is an ecological trap, rather than a source pond for many species, the lack of recruitment of juveniles into the population may be connected to the elevated trace metal concentrations.

We combined aquatic and drift fence sampling with artificial mesocosm studies to 1) determine the species utilizing the APW and 2) assess biological effects of the APW environment on focal species of pond-breeding amphibians. The study began in mid-March 2008 and continued (primarily mesocosm studies) through 2011. We observed newly metamorphosed juveniles of five species at the APW: R. sphenocephala, Bufo terrestris (southern toad), Pseudacris crucifer (spring peeper), P. brimleyi (Brimley’s chorus frog), and Ambystoma opacum (marbled salamander) In contrast, at the reference site during the same time frame four additional species (P. ornata, ornate chorus frog; A. tigrinum, tiger salamander; A. talpoideum, mole salamander; Scaphiopus holbrookii, spadefoot toad) reproduced successfully, at least in part due to its longer hydroperiod and absence of fish.

We initially (2008) conducted egg hatching studies on five species (S. holbrookii; P. nigrita, southern chorus frog; B. terrestris; R. sphenocephala; and Gastrophryne carolinensis, eastern narrowmouth toad). The general protocol for these egg studies was: 1) collection of sediment from the APW and an uncontaminated reference site (Ellenton Bay), 2) preparation of 0.5-L containers with ~10 cm of sediment from each treatment, 3) introduction of pond water to the containers, and 4) introduction of known numbers of eggs to containers. Each treatment was replicated five times. Different numbers of clutches were used depending upon species average clutch size and the availability of eggs. We observed 100% hatching success in the APW trial for all five species; results for Ellenton Bay trials were nearly the same (4 of 5 species had 100% hatching success), with only B. terrestris showing reduced success (64%). Thus, to date we have seen no evidence that the APW environment affects hatching success for the amphibian species tested.

In subsequent years we conducted larger, full-scale mesocosm studies to assess effects of the APW environment on a greater variety of response variables, such as embryonic and larval malformations, larval performance, and overall viability. These results are currently being summarized by Brian Metts, who earned his doctorate from UGA for this work.

 

The ash plume wetland (APW).

 

The APW received coal combustion wastes from a breach in a receiving basin in the 1970s.

 

Several trace metals are elevated in sediments of the APW area, including arsenic, selenium, strontium and copper.

 
 
sediment containers

Eggs of five species were allowed to develop in containers with APW vs. reference site sediments.

mesocosms

Larvae of four species were reared in APW vs. reference site small-scale mesocosms.

results figure

Observed results indicate no significant impact of the APW environment on larval survival.

In these pilot studies we did not observe any difference between the APW and reference site treatments on our response variables, egg and larval survival. In 2009 we plan similar, full-scale studies to assess effects of the APW environment on a wider array of species and a greater variety of response variables, such as embryonic and larval malformations, larval performance, and overall viability.

ACKNOWLEDGEMENTS: We would like to thank the Area Completions Project of Savannah River Nuclear Solutions for funding this study; work was also partially supported by the Department of Energy under Award Number DE-FC09-07SR22506 to the University of Georgia Research Foundation.

 
 
 
 
 
 
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