Abstract
Concentrations of total recoverable copper, iron, and zinc in water were measured weekly between early April and mid-July 1984 in various segments of the Clark Fork River drainage upstream of Milltown Dam; stream discharge measurements were also recorded. Fourteen locations were sampled including eight in the mainstem and six in tributaries. All three metals were sometimes present in the Clark Fork River at concentrations that exceeded criteria for protection of aquatic life. Exceedances occurred at all mainstem stations, although conditions appeared to be least favorable for aquatic life between Deer Lodge and the confluence with Rock Creek. Of the metals measured, copper was present at the highest concentrations relative to its toxicity and is probably the most limiting. Copper concentrations in gills of brown trout collected after a fish kill indicated lethal exposure to copper, confirming the biological significance of copper to the river. Alternatively, cadmium concentrations found in gills were well below lethal thresholds, suggesting that cadmium is relatively less significant than copper in the Clark Fork.
Water entering the Clark Fork from the Little Blackfoot River and Rock Creek is low in metals. Consequently, metals concentrations in the Clark Fork are measurably lower downstream of these tributaries.
Fish population data for various segments of the river (although limited) correlate well with water quality; i.e., lower fish numbers correspond to more severe metals conditions. Direct flow of untreated Silver Bow Creek water into the Clark Fork River resulted in an extremely high peak metals concentration that was observable at all of the mainstem stations sampled. During the bypass. the highest metals concentrations occurred at Warm Springs. A more prolonged period of elevated metals concentrations occurred in the reach of river between Deer Lodge and Rock Creek and is apparently owing to erosion into tailings deposited in the flood plain. This prolonged exposure appears to damage fish populations.
Limited measurement of pH in various portions of the drainage indicate that pH is higher in the Warm Springs vicinity than in downstream reaches. If this observation is characteristic of the rest of the year, the implication is that metals are less soluble and probably less toxic near Warm Springs than downstream.
Start Date
19-4-1985 12:00 AM
End Date
19-4-1985 12:00 AM
Document Type
Presentation
Relationships Among Fish Populations, Metal Concentrations, and Stream Discharge in the Upper Clark Fork River
Concentrations of total recoverable copper, iron, and zinc in water were measured weekly between early April and mid-July 1984 in various segments of the Clark Fork River drainage upstream of Milltown Dam; stream discharge measurements were also recorded. Fourteen locations were sampled including eight in the mainstem and six in tributaries. All three metals were sometimes present in the Clark Fork River at concentrations that exceeded criteria for protection of aquatic life. Exceedances occurred at all mainstem stations, although conditions appeared to be least favorable for aquatic life between Deer Lodge and the confluence with Rock Creek. Of the metals measured, copper was present at the highest concentrations relative to its toxicity and is probably the most limiting. Copper concentrations in gills of brown trout collected after a fish kill indicated lethal exposure to copper, confirming the biological significance of copper to the river. Alternatively, cadmium concentrations found in gills were well below lethal thresholds, suggesting that cadmium is relatively less significant than copper in the Clark Fork.
Water entering the Clark Fork from the Little Blackfoot River and Rock Creek is low in metals. Consequently, metals concentrations in the Clark Fork are measurably lower downstream of these tributaries.
Fish population data for various segments of the river (although limited) correlate well with water quality; i.e., lower fish numbers correspond to more severe metals conditions. Direct flow of untreated Silver Bow Creek water into the Clark Fork River resulted in an extremely high peak metals concentration that was observable at all of the mainstem stations sampled. During the bypass. the highest metals concentrations occurred at Warm Springs. A more prolonged period of elevated metals concentrations occurred in the reach of river between Deer Lodge and Rock Creek and is apparently owing to erosion into tailings deposited in the flood plain. This prolonged exposure appears to damage fish populations.
Limited measurement of pH in various portions of the drainage indicate that pH is higher in the Warm Springs vicinity than in downstream reaches. If this observation is characteristic of the rest of the year, the implication is that metals are less soluble and probably less toxic near Warm Springs than downstream.