Abstract
The downstream distribution of Cu, Cd, and Pb in fine-grained sediments and benthic insect larvae of the Clark Fork River, Montana is characterized. This river has been heavily con laminated as a result of past mining and smelling operations near its headwaters. Concentrations of all metals in bed sediments displayed a simple exponential downstream decrease through the upper 181 km of the river. The trend suggested metal contamination originated from source(s) in the headwaters, with physical dilution occurring downstream. Additional data suggested floodplain sediments also were contaminated by the original source(s). Secondary inputs from cutbanks in the floodplains may have extended the downstream influence of the contamination. The exponential model predicted that sediment contamination should extend at least 550 km downstream, a result that was verified with data from a separate, independent study. Metal contamination, as observed in all taxa of insect larvae collected from the upper Clark Fork. Concentrations in the insect larvae were highest in the upper 100 km of the river, but downstream trends were more complex than those of the sediments. Some differences in trends occurred among taxa and metals. Areas in the river of enhanced or reduced metal contamination also were apparent. Metal contamination, however, was still evident at 381 km, the most downstream station sampled. Metal concentrations in sediments and insects decreased at the confluences of uncontaminated tributaries, but the influence of tributaries on metal contamination in the Clark Fork River was localized, extending for only 1-2 kin below the confluences.
Start Date
20-4-1990 8:40 AM
End Date
20-4-1990 9:20 AM
Document Type
Presentation
Distribution of Trace Metals in Fine-grained Bed Sediments and Benthic Insects in the Clark Fork River, Montana
The downstream distribution of Cu, Cd, and Pb in fine-grained sediments and benthic insect larvae of the Clark Fork River, Montana is characterized. This river has been heavily con laminated as a result of past mining and smelling operations near its headwaters. Concentrations of all metals in bed sediments displayed a simple exponential downstream decrease through the upper 181 km of the river. The trend suggested metal contamination originated from source(s) in the headwaters, with physical dilution occurring downstream. Additional data suggested floodplain sediments also were contaminated by the original source(s). Secondary inputs from cutbanks in the floodplains may have extended the downstream influence of the contamination. The exponential model predicted that sediment contamination should extend at least 550 km downstream, a result that was verified with data from a separate, independent study. Metal contamination, as observed in all taxa of insect larvae collected from the upper Clark Fork. Concentrations in the insect larvae were highest in the upper 100 km of the river, but downstream trends were more complex than those of the sediments. Some differences in trends occurred among taxa and metals. Areas in the river of enhanced or reduced metal contamination also were apparent. Metal contamination, however, was still evident at 381 km, the most downstream station sampled. Metal concentrations in sediments and insects decreased at the confluences of uncontaminated tributaries, but the influence of tributaries on metal contamination in the Clark Fork River was localized, extending for only 1-2 kin below the confluences.