Report on the remedial investigation of Bear Creek Valley at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee. Volume 6: Appendix G -- Baseline ecological risk assessment report Page: 80 of 882
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G2-16
Toxicity in Reach 1 appears to be due to elevated concentrations of metals and calcium. Dissolved
metal concentrations were generally higher in Reach 1 than elsewhere in Bear Creek and previous studies
have identified nickel in water from BCK 12.36 as a major contributor to Ceriodaphnia toxicity (Kszos,
Stewart, and Taylor 1992). Also, Stewart et al. (in Hinzman et al. 1995) suggest that the high nitrate
concentrations in the S-3 discharges allow calcium to stay in solution at concentrations that are toxic.
Calcium is not generally toxic in ambient water because it occurs primarily as calcium carbonate and,
under most conditions, calcium carbonate is not soluble enough for calcium to reach toxic concentrations.
Based on their evaluation of the nitrate, carbonate, and calcium concentrations in upper Bear Creek, the
authors determined that calcium was likely to be present in a bioavailable form at concentrations
previously shown to be toxic to daphnids.
This conclusion is supported by the subsequent statistical analyses of the toxicity data for
May 19-26, 1994, and chemical data for filtered and unfiltered samples collected May 24, 1994. Linear
regression analyses revealed that the percent reduction in Ceriodaphnia fecundity relative to controls
was significantly positively correlated with dissolved calcium (a =0.0004, r2 = 0.81), but not with any
other COPEC. It is interesting to note that the percent reduction in Ceriodaphnia survival relative to
controls was significantly positively correlated with dissolved manganese (a = 0.0003, r2= 0.83), but
not with calcium or any other COPEC.
G.2.3.5 Biological Surveys
The fish community in Bear Creek does not appear to be degraded due to a contaminant effect. The
depauperate fish communities observed before 1989, especially at BCK 12.36, have increased in species
richness (Fig G.25) and total density (Fig G.26). The fish community in Reach 1 is composed of four
species. Only two species, the blacknose dace (Rhinichthys atratulus) and creek chub (Semotilus
atromaculatus) were found before the fall of 1988. Communities observed in 1993 were similar to those
observed in the reference headwater steams Gum Hollow Creek and Pinhook Branch. However, the
ability to discriminate between Bear Creek sites and reference sites is limited by the considerable
variability of fish densities at these locations. The number of species present in Reaches 2 and 3 have
fluctuated by one or two species per site, but demonstrated no consistent increasing or decreasing trends.
Density at BCK 9.91 was stable from 1988 through spring 1991, increased in fall 1991, and has
remained relatively stable and comparable to the reference streams. Species richness was greater at BCK
3.25 than at upstream sites (e.g., BCKs 7.87 and 9.40) because the weir at BCK 4.5 limits upstream
migration of some species (Fig. G.25). Density and biomass levels at BCK 3.25 have remained relatively
stable and comparable to the reference streams. Densities of all species at BCK 7.87 were lower from
the fall of 1989 through the spring of 1991 than during previous sampling periods, apparently due to the
gravel and fine sediments that have accumulated at this site (Fig.26). Siltation also is a contributing
factor to the changes observed at BCK 9.91.
The Tennessee dace population in Bear Creek does not appear to be degraded due to a contaminant
effect (Fig. G.27). Tennessee dace were not observed at BCK 12.36 before 1989. Densities in Reach 1
have increased to levels comparable to reference stream densities, though the year-to-year variability
precludes a definitive comparison. Also, the only reference streams with established Tennessee dace
populations are Gum Hollow Creek and Pinhook Branch, which were not evaluated before 1993.
Tennessee dace densities in Reach 3 at BCK 7.87 decreased by - 90% between the spring of 1989 (0.97
fish/m2) and the fall of 1990 (0.09 fish/m2). However, the density of Tennessee dace was higher in the
fall of 1994 than during the previous 6 years (0.92 fish/m2), and no known episodes of contamination
occurred that may have caused the observed changes. The habitat quality may have been degraded by
silt loading from activities in BCV. Tennessee dace prefer headwater streams and are not expected to
inhabit lower Reach 3 (BCK 3.25) and Reach 4 (BCK 0.7).
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Report on the remedial investigation of Bear Creek Valley at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee. Volume 6: Appendix G -- Baseline ecological risk assessment report, report, September 1, 1996; United States. (https://digital.library.unt.edu/ark:/67531/metadc675908/m1/80/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.