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Trace metal contamination due to acid rock drainage and its impacts on the fish-bearing Pennask Creek watershed in British Columbia Walls, Lisa Dawn

Abstract

Acid rock drainage (ARD) and associated metal leaching (ML) is a major pollution problem throughout the world, adversely affecting both surface and ground waters. The elevated concentrations of metals in the water column due to ARD/ML can be transferred to abiotic and biotic components of an ecosystem and adversely affect the health of aquatic life. The Pennask Creek watershed, one of the most important rainbow trout-producing environments in British Columbia (BC), has been contaminated with ARD/ML as a result of highway construction. This study was designed to comprehensively examine the Pennask Creek watershed ARD/ML problem and its environmental impacts by combining existing and newly gathered information. The overall objectives were to determine the extent of metal contamination of the water and sediments, the potential biological impacts of this contamination, the influence of local geology, and to estimate the potential risk to aquatic organisms. Results show that metal concentrations in the water and sediments downstream of the ARD/ML source are higher than concentrations elsewhere in the watershed. Analysis of historical water quality data indicates that the concentrations of these metals have decreased markedly since 2004, due to remediation efforts. Metals of concern include Al, As, Cu, Mn, Ni and Zn. Rock cuts along Highway 97C are generating ARD characterized by a low pH and high metal concentrations. Rock samples collected from the stream beds and banks were not found to be potentially acid-generating. However, these rock samples contained significant levels of metals of concern, which could continue to be leached under acidic conditions for many years to come. Al, Cu, and Zn levels consistently exceeded BC and Canadian water and sediment quality guideline values for the protection of aquatic life, indicating that adverse biological effects are probable at sites downstream of the ARD/ML source. Benthic invertebrate monitoring over a ten year period shows low abundance and diversity, and a complete absence of sensitive taxa at downstream sites. Risk quotients indicate a likelihood of adverse biological effects for aquatic organisms, including rainbow trout, due to metal contamination in the watershed.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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