Document Title:

Sediment Quality within the Impounded Reaches of Cape Fear River Locks and Dams

Tom Augspurger Christopher G. Ingersoll James L. Kunz Sara E. Ward N. E. Kemble

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This report documents an evaluation of chemical contaminants in, and toxicity of, sediments collected from impoundments created by locks and dams on the Cape Fear River in Bladen and Cumberland Counties, North Carolina. Twelve whole-sediment samples from within the impounded reaches of the three locks and dams were collected in November 2006. All samples were analyzed for elemental contaminants and polycyclic aromatic hydrocarbons (PAHs), and a subset of nine of the samples were used in toxicity tests. Whole sediments had no significant effect on survival or growth in 28-d toxicity tests with Hyallela azteca (freshwater amphipod) or in 10-d tests with Chironomus dilutus (freshwater midge). In 2-d sediment elutriate (waterextractable fraction) tests with Ceriodaphnia dubia (freshwater cladoceran), statisticallysignificant reductions in survival occurred in four of the nine exposures. Pairwise correlation analyses indicated several whole-sediment and elutriate water chemistry variables were significantly and negatively correlated with C. dubia survival. Of the correlated variables, elutriate manganese had among the strongest correlation (r2 = 0.79, p = 0.0006) and the most plausible biological association with reduced C. dubia survival because some elutriate manganese concentrations exceeded published lethal concentrations for C. dubia in water exposures. All elemental contaminants for which published freshwater whole-sediment threshold effects concentrations (TECs, concentrations of contaminants in whole sediment below which adverse effects to sensitive aquatic organisms are not expected to occur) are available were less than their corresponding TECs and are therefore considered toxicologically insignificant. Sediment PAHs with published freshwater whole-sediment TECs were in excess of TECs at two of the 12 sampling stations (river mile 112.9 near Fayetteville and river mile 88.5 about 0.2 miles upstream of Tar Heel Landing Road). Five individual PAHs exceeded TECs at these locations, but no samples exceeded the probable effects concentrations (PECs, concentrations of contaminants in whole sediment above which adverse effects to sedimentdwelling organisms may be expected). Based on review of existing data (Tier 1) and results of sediment chemistry and toxicity tests (Tier 2 and 3), contamination in surface sediments behind Cape Fear River locks and dams is unlikely to be a concern in-place. Mobilization of sediments may be a short-term water column concern based on the elutriate toxicity test results. While sediment re-suspension and contaminant release in the elutriate tests may be near a worst case simulation of actual conditions following sediment disturbing activities, additional synthesis is needed to characterize the nature and magnitude of this issue. In particular, data regarding the modeled or measured sediment re-suspension caused by specific sediment disturbing activities (e.g., dredging, dam alterations, etc.) will help put the elutriate test results in context for normal sediment management practices. Sediment disturbing activities proposed for the Cape Fear River would benefit from development of a sediment management plan to address these issues.



U.S. Fish and Wildlife Service - Raliegh, North Carolina, Ecological Services Field Office

Last updated: June 12, 2015