Determination of Point and Nonpoint Source Toxicity in the Clark Fork River Basin Using the Daphnid, Ceriodaphnia Dubia

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