Characterization of Contaminant Levels in the P-Area Wetland System
Biota: David Scott, Larry Bryan, David Kling, and Stacey Lance
Soils: John Seaman and Julian Singer
Fresh ash at D-Area
The Savannah River Ecology Laboratory (SREL) has a strong research history on the ecological effects of contaminants on the Savannah River Site (SRS), including the effects of coal combustion wastes (CCW). Coal-fired facilities have been in operation on the SRS since the early 1950s and there are multiple associated ash basins, as well as areas of CCW spills. Acceptable clean-up and closure of CCW sites on the SRS requires knowledge of contaminant levels and quantification of the diversity and success of the biota inhabiting these areas.
Most SREL CCW research has focused on the D-Area settling basins where contaminant levels are highest. Research in the settling basins demonstrated that amphibians and other wildlife inhabiting the basins and discharge streams can accumulate elevated concentrations of trace elements that cause adverse effects on survival, growth and development, energy acquisition and allocation, behavior or performance, and recruitment (reviewed in Rowe et al. 2002). However, potential impacts of CCW in other habitats, such as the ash plumes in D-Area and P-Area that extend into natural wetlands, are largely unknown. For example, a CCW release occurred more than 35 years ago at a portion of the D-Area Savannah River floodplain (D-Area Ash Plume Wetland, DAPW); currently the DAPW appears to have a normal amphibian community diversity (19 documented species, comparable to a nearby uncontaminated reference site; Roe et al. 2005), and the DAPW forest also exhibits species richness and basal area typical for a forest its age. Trace element concentrations in the floodplain surface soils are generally lower than in the more recent CCW of the settling basins—concentrations in tissue from several amphibian species are also lower compared to more recent CCW.
In this study we examined the distribution of trace elements in soils and biota at a portion of Dunbarton Bay (DB), a large wetland complex at the head of the Meyer’s Branch valley on the SRS. Dunbarton Bay is down gradient from the P-Area Ash Basin, and an historic release of CCW deposited ash (up to 1 m) over approximately 18.2 ha in one of the smaller wetlands within DB known as Bay 96. [Note: On the SRS GIS wetlands layer, Bay 96 includes additional area that did not receive CCW. For the purposes of this report, we use Bay 96 synonymously with the CCW plume area of the wetland.] Bay 96 appears to function as a seasonal wetland, and may be similar in key respects to the DAPW. The makeup of CCW at the two sites may vary due to differences in parent coal composition, combustion technology, and disposal method. As a consequence, the CCW in the P-Area system may differ from CCW deposits elsewhere on the SRS – it has not been established whether data from one basin can be applied to another. This report summarizes our findings from the P-Area system; we include limited data on the D-Area system for direct comparison.
Contaminants of potential concern (COPC) to aquatic receptor species have been identified in preliminary P-Area wetland surveys and SRS ecological risk models. We determined COPC levels in soil cores and biota from the affected area of Bay 96, as well as from a nearby uncontaminated wetland reference site (Bay 100). Soil cores were collected from ten sampling locations, seven within the ash depositional area and three outside the ash deposition zone, as well as two additional background wetland sampling locations within Bay 100. The metal levels in the seven sites impacted by ash deposition were elevated when compared to the three sites outside the ash deposition zone and background metal concentration for SRS upland soils. In Bay 96 soils, the levels of arsenic (As), copper (Cu), nickel (Ni), selenium (Se), and strontium (Sr) were elevated relative to the reference wetland—lead (Pb) and mercury (Hg) were higher at Bay 100. Within Bay 96, the soil levels of As, barium (Ba), beryllium (Be), cadmium (Cd), cobalt (Co), Cu, Pb, Ni, Se, and zinc (Zn) were elevated for the ash-impacted sampling sites compared to the three non-ash-impacted sites. Although the two Bay 100 background soils display rather minor levels of As (~ 1.1-1.7 mg kg-1), a major contaminant found in CCW, they exceed “upland” soil background thresholds (i.e., 2 times the mean background value) for Ba, Be, Cu, Pb, Ni, and Zn. However, elevated trace element concentrations observed in Bay 100 compared to upland soils likely reflect the higher clay and organic matter (OM) contents observed in wetland soils.
Site remediation decisions require an assessment of the potential ecosystem-level risk of trace element contaminants to organisms, including: 1) a species list (biological survey) for the habitat of interest for comparison to reference sites, 2) species-specific estimates of trace element concentrations (body burdens), and 3) the measurement of endpoints that reflect the individual and population-level consequences of elevated trace element body burdens (population effects). In our study, we conducted biological surveys of Bay 96, Bay 100, and select D-Area sites for comparison, and determined trace element tissue concentrations in a variety of organisms. Given the time and funding constraints, we were not able to conduct extensive population demography studies or experimentally assess chronic sub-lethal effects at the observed trace metal concentrations in Bay 96. Consequently, we are relying on prior experiments at CCW levels in the D-Area system to speculate about potential CCW impacts on biota in P-Area.
In general, the biota we examined at Bay 96 had elevated As, Se, and Sr tissue concentrations compared to animals from Bay 100. Despite these differences, concentrations in Bay 96 fauna were relatively low (e.g., As, 3-6 mg/kg dry mass; Se, 0.8-3 mg/kg) compared to those captured at the D-Area Primary Ash Settling Basin (As, 3-7 mg/kg; Se, 15-46 mg/kg) and D-Area Ash Plume Wetland (As, 1.6-3.4 mg/kg; Se, 6-22 mg/kg). Tissue concentrations were highly correlated with soil concentrations for As, Se, and Sr, and soil concentrations of these COPC were elevated in the D-Area system compared to P-Area (Bay 96).
For amphibians, both the contaminated site (Bay 96) and the reference site (Bay 100) were similar in species richness and composition. Greater numbers of captures occurred at Bay 100, but we think this was primarily due to 1) the presence of water for portions of the sample period at Bay 100 but not at Bay 96, and 2) a difference in configuration of our sampling fences that were likely sampling animals during their breeding migration at Bay 100 but only resident animals at Bay 96. Thus, any population-level differences between the two sites were more likely due to between-site hydroperiod differences rather than any direct effects of elevated COPC at Bay 96.
Project Report (pdf)
ACKNOWLEDGEMENTS: We would like 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.