Abstract
The Montana DHES conducts aquatic macroinvertebrate surveys as part of its environmental surveillance of the Clark Fork River. Since 1986, annual collections have consisted of four modified Hess samples from each of 25 stations between the headwaters of Silver Bow Creek and Thompson Falls Reservoir. The purpose of these studies are to monitor the integrity of macroinvertebrate assemblages in the river, to detect changes in water quality and to provide information useful for water-quality management decisions.
Macroinvertebrates provided assessments of metals and organic pollution as well as cumulative environmental stress in the Clark Fork drainage. Metals pollution remained the principle agent of perdition in Silver Bow Creek while degradation from both metals and organic pollution were widespread in the upper reaches of the Clark Fork River. The biological impacts of heavy metal contamination were significantly reduced below the Warm Springs Ponds compared with conditions in Silver Bow Creek. Nevertheless, metals clearly limited the number of macroinvertebrate species in the Clark Fork River downstream at least as far as Bonita. Impacts attributable to metals were relatively uniform in the upper river from Warm Springs Creek to the confluence of the Little Blackfoot River. Further downstream, proximity to "clean water" tributaries appeared to be an important factor influencing the extent of metals impacts. Biologically significant metals pollution was not detected downstream from the Clark Fork River' s confluence with Rock Creek. Metals-related stress appeared more severe in 1987 than in other years. Among all river reaches, the healthiest benthic fauna was found from Milltown Dam to the confluence of the Bitterroot River. Downstream from the Bitterroot, nutrient enrichment impacted the aquatic community.
The 1988 drought appeared to accentuate biological responses to organic and nutrient enrichment. Symptoms of organic pollution were more distinct and widespread than in previous years. Macroinvertebrate densities during August 1988 were, on average, double those in 1986 and 87. Impacts attributed to organic enrichment were widespread with the greatest effects in the upper river below the Warm Springs Ponds, at Deer Lodge, Bonita and Turah and, in the lower river, from Harper's B ridge downstream to Alberton. The response of the fauna and the ability of Silver Bow Creek to assimilate organics was limited by the prevailing toxic environment.
Start Date
20-4-1990 10:40 AM
End Date
20-4-1990 11:00 AM
Document Type
Presentation
Aquatic Macroinvertebrate Surveys in the Clark Fork River, 1986 to 1988
The Montana DHES conducts aquatic macroinvertebrate surveys as part of its environmental surveillance of the Clark Fork River. Since 1986, annual collections have consisted of four modified Hess samples from each of 25 stations between the headwaters of Silver Bow Creek and Thompson Falls Reservoir. The purpose of these studies are to monitor the integrity of macroinvertebrate assemblages in the river, to detect changes in water quality and to provide information useful for water-quality management decisions.
Macroinvertebrates provided assessments of metals and organic pollution as well as cumulative environmental stress in the Clark Fork drainage. Metals pollution remained the principle agent of perdition in Silver Bow Creek while degradation from both metals and organic pollution were widespread in the upper reaches of the Clark Fork River. The biological impacts of heavy metal contamination were significantly reduced below the Warm Springs Ponds compared with conditions in Silver Bow Creek. Nevertheless, metals clearly limited the number of macroinvertebrate species in the Clark Fork River downstream at least as far as Bonita. Impacts attributable to metals were relatively uniform in the upper river from Warm Springs Creek to the confluence of the Little Blackfoot River. Further downstream, proximity to "clean water" tributaries appeared to be an important factor influencing the extent of metals impacts. Biologically significant metals pollution was not detected downstream from the Clark Fork River' s confluence with Rock Creek. Metals-related stress appeared more severe in 1987 than in other years. Among all river reaches, the healthiest benthic fauna was found from Milltown Dam to the confluence of the Bitterroot River. Downstream from the Bitterroot, nutrient enrichment impacted the aquatic community.
The 1988 drought appeared to accentuate biological responses to organic and nutrient enrichment. Symptoms of organic pollution were more distinct and widespread than in previous years. Macroinvertebrate densities during August 1988 were, on average, double those in 1986 and 87. Impacts attributed to organic enrichment were widespread with the greatest effects in the upper river below the Warm Springs Ponds, at Deer Lodge, Bonita and Turah and, in the lower river, from Harper's B ridge downstream to Alberton. The response of the fauna and the ability of Silver Bow Creek to assimilate organics was limited by the prevailing toxic environment.