Concentrations and sources of trace metals in water and sediments of the South Fork New River, Ashe County, North Carolina, and their potential effects on aquatic biota

WCU Author/Contributor (non-WCU co-authors, if there are any, appear on document)
Xaviera Watkins (Creator)
Western Carolina University (WCU )
Web Site:
Cynthia Atterholt

Abstract: The Ore Knob Copper Mine located near Jefferson, North Carolina, operated from 1850 to 1962;mine tailings from the mine were disposed of behind an earthen dam located in the headwaters of Ore Knob Branch, a tributary to Peak Creek. As a result of groundwater contamination, the EPA placed the mine on the National Priority List in 2009. The erosion of mine tailings also released toxic trace metals to Peak Creek, where they were transported to the South Fork New River, an important recreational and ecological resource. The objectives of this study were to determine the source of metals in the South Fork New River and their potential impact(s) on aquatic biota by (1) documenting metal concentrations, and their spatial variations, in water and sediment along the river to locate potential sources, and (2) comparing these metal concentrations to previously developed aquatic effect criteria. Geochemical analyses included the determination of both total and bioavailable concentrations of aluminum, cobalt, copper, iron, and zinc in channel bed sediment as well as their dissolved and total recoverable concentrations in water along a 33km reach of the South Fork New River. Water and sediment samples were also collected from surrounding tributaries, including Peak Creek. Metal concentrations in Peak Creek, below the mine, were relatively high and decreased downstream, indicating that some metals were delivered to the South Fork New River. However, metal concentrations in both water and sediment varied significantly along the river and did not abruptly increase downstream of Peak Creek. These spatial trends suggest that the Ore Knob mine and Peak Creek (which was once devoid of fish) no longer contribute significant quantities of metals to the South Fork New River. Downstream variations in sediment-associated metal concentrations appear to reflect, in part, localized fine-grain sediment deposition, differences in organic carbon content, and the exposure of bedrock outcrops from which sulfidic minerals can be eroded. Comparison of dissolved metal concentrations in water to EPA guidelines found that no sampling sites exceeded acute nor chronic limits. In contrast, numerous (56 %, 94%) of the sampling sites exceeded the NCDEQ total recoverable concentration limits (120 ppb, 7 ppb) for Zn and Cu, respectively. A total of two sites exceeded the threshold effect concentration (TEC) for sediments compiled for Zn by MacDonald et al., whereas 3 sites exceed the TEC for Cu. The various criteria used herein suggest differing potential impacts of the metals on aquatic biota along the South Fork New River. However, the bioavailability of the metals is an important consideration. Dissolved concentrations in water, which indicated limited potential impacts, represent highly bioavailable metals. In contrast, metals attached to sediments both on the channel bed and within the water column may in part, be non-bioavailable, particularly given that the metals are largely derived from sulfidic mineral layers in the bedrock. Thus, the impacts to aquatic biota is likely to be limited.

Additional Information

Language: English
Date: 2020
contamination ecological, South Fork New River
River sediments--Quality
Copper mines and mining

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