Chemical characterization of sediments and pore water from the upper Clark Fork River and Milltown Reservoir, Montana

Environmental Toxicology and Chemistry
By: , and 

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Abstract

The upper Clark Fork River basin in western Montana is widely contaminated by metals from past mining, milling, and smelting activities As part of a comprehensive ecological risk assessment for the upper Clark Fork River, we measured physical and chemical characteristics of surficial sediment samples that were collected from depositional zones for subsequent toxicity evaluations Sampling stations included five locations along the upper 200 km of the river, six locations in or near Milltown Reservoir (about 205 km from the river origin), and two tributary reference sites Concentrations of As, Cd, Cu, Mn, Pb, and Zn decreased from the upper stations to the downstream stations in the Clark Fork River but then increased in all Milltown Reservoir stations to levels similar to uppermost river stations Large percentages (50 to 90%) of the total Cd, Cu, Pb, and Zn were extractable by dilute (3 n) HCl for all samples Copper and zinc accounted for greater than 95% of extractable metals on a molar basis Acid-volatile sulfide (AVS) concentrations were typically moderate (0 6 to 23 μmol/g) in grab sediment samples and appeared to regulate dissolved (filterable) concentrations of Cd, Cu, and Zn in sediment pore waters Acid volatile sulfide is important in controlling metal solubility in the depositional areas of the Clark Fork River and should be monitored in any future studies Spatial variability within a sampling station was high for Cu, Zn, and AVS, therefore, the potential for toxicity to sediment dwelling organisms may be highly localized.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Chemical characterization of sediments and pore water from the upper Clark Fork River and Milltown Reservoir, Montana
Series title Environmental Toxicology and Chemistry
DOI 10.1002/etc.5620131211
Volume 13
Issue 12
Year Published 1994
Language English
Publisher Wiley
Contributing office(s) Columbia Environmental Research Center
Description 13 p.
First page 1971
Last page 1983