ScholarWorks at University of Montana

In the mid and late 1980' s, attached algae levels in the Clark Fork of the Columbia River varied from unnoticeable to extreme nuisance levels. Thi.5 study addressed the question: are P and N levels low enough long enough to limit algal growth and standing crop in this river? If so, river reaches with nuisance levels may improve if nutrient levels are lowered, and high quality reache.5 may worsen if nutrient levels are allowed to increase. Because the Clark Fork often exhibits N and P levels thought to saturate algal growth, there was doubt that nutrient management would affect algal levels. Through the use of artificial stream fertilization experiments, this study showed that the standing crop of these attached algal communities saturate at much higher nutrient levels than does growth. At most river sites from Sept.1987 to 1989, dissolved P and N were almost always below levels that saturate algal standing crop. The ratio of dissolved N:P in the water suggested that N limitation, P limitation or a balance between the two existed for significant periods of time at almost all sites. Hence management of both N and P may reduce nuisance levels (when other factors are not limiting) and are important to protecting high quality areas.

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.

Ceriodaphnia dubia, a small planktonic daphnid was used to biomonitor point sources of toxicity in wastewater and nonpoint source toxicity in stream samples obtained from the Clark Fork River Basin, MT. Brief descriptions, results and discussions are presented for studies of wastewater from a kraft mill near Frenchtown, MT and potential toxicity of water samples from 19 sites along the Clark Fork River in 1985. In 1987, dilutions of Missoula, MT municipal wastewater fortified with ammonia were tested, as was the wastewater before and after chlorination. Potential toxicity of water samples from eight sites along the upper Clark Fork River were also tested. All studies were cooperative efforts with the Montana Departments of Health and Environmental Sciences and Fish, Wildlife and Parks.

Ceriodaphnia appear to be indicators of toxicity in a variety of test conditions such as ammonia in wastewater and metals from past mining activities. The daphnids indicated toxicity from other substances in the wastewater or perhaps the influence of characteristics of the wastewater that increased ammonia toxicity. All example of nonpoint source effects was toxicity in samples from Silver Bow Creek MT, where impaired conditions to aquatic life resulting from the presence of metals have been reported for years. During some of the tests with wastewater, toxicological endpoints were observed using the actual number of daphnids that reproduced in a test, not the average number of young. There was circumstantial evidence in 1985 that copper alone was responsible for the toxicity in Silver Bow Creek. However, the later studies performed under different hydrological conditions found toxicity was probably due to a combination of metals, some of which had not been measurable earlier. For well-defined "control" of "standard" conditions during testing, there are indications that waters to be used as reference media for Ceriodaphnia need further research. Nevertheless, the use of daphnids to test the ambient conditions described in this paper should encourage environmental managers to consider approaches with this or similar species in the future.

Trout population densities decline dramatically in the Clark Fork River from nearly 2,000 catchable brown trout per mile just downstream of mine waste settling ponds to 50 trout Instream toxicity tests (1986-89), and analyses of metals in fish organs (1989) were conducted in various river reaches to try to understand how metals influence trout density patterns.

Instream toxicity tests with swim-up stage rainbow trout fry demonstrate that river water induces chronic mortality during spring runoff when metals concentration, particularly copper, exceed chronic criteria for protection of aquatic life. Concentration of copper in livers of adult brown trout (salmo trutta) are higher than those in laboratory fish populations exposed for several generations to chronically toxic concentrations of copper. Both acute and chronic stress from metals, particularly copper, are implicated as contributing to poor fish production in the Clark Fork.