The effects of the lampricide, TFM, on the benthic macroinvertebrates in the Rouge River, a hardwater tributary to Lake Ontario was examined at 1 untreated and 2 treated sites over a 7 month period . Drift samples were collected from one one of the treated sites during the 5 days bracketing treatment . Significant decreases in relative abundance attributable to TFM were recorded for Chimarra sp ., Dugesia sp. and Tubificoidea 2-19 d following treatment . Large reductions were also (l hibited by Caenis sp . and Lumbricidae. Two-thirds of the Chironomidae genera and Nematoda tended to decline in abundance 2 d after treatment at only one of the treated sites, probably due to a 2 .5 h longer treatment . This decline was followed by a significant increase to greater than pretreatment abundances 17 d later undoubtedly as a result of an upward migration of macroinvertebrates from within the hyporheos . Partial recolonization of the TFM-sensitive benthic taxa was evident 19 d after lampricide treatment with complete recolonization 6 .5 months later. With
The effect of the lampricide, 3-trifluoromethyl-4-nitrophenol (TFM), on the benthic macroinvertebrates within the hyporheic region of Dam Creek, Ontario was investigated . Organisms were regularly found to a depth of 70 cm in the substrate throughout the study period . Of the eight major taxa found at both the treated and untreated sites only Tubificoidea exhibited a decrease in abundance attributable to TFM .One day after treatment, TFM concentrations were greatest at a depth of 55 cm, the greatest depth to which water samples were taken . The movement of TFM into the hyporheic region during the present study may be due to the large convective forces created by the rapid decrease in surface water temperature . These convective forces are usually greatest in the late fall and winter when TFM is not applied . The greater part of TFM stream treatments are carried out during the summer when surface water temperatures remain fairly constant . It is suggested that the hyporheic region may act as a refuge zone for benthic macroinvertebrates against the lampricide during most of the TFM application season .
The effects of the lampricide, TFM, on the abundance of macroinvertebrates in the benthos of Wilmot Creek, a hardwater tributary to Lake Ontario, was examined over 1 year. Drifting macroinvertebrates were also collected before, during and after TFM treatment. Significant decreases in benthic abundance were exhibited by Dolophilodes sp., Tubificoidea, Cricotopus sp. and Macrotendipes sp. throughout the 350 days following treatment. Only the decrease in abundance of Dolophilodes sp. and lbbificoidea could be attributed to TFM treatment. Increases in drift abundance observed during treatment were generaIly an accurate indicator of TFM-sensitive macroinvertebrates. The most sentive taxa (Dolophilodes sp., Dugesia sp. and Tubificoidea) responded immediately following the introduction of TFM. Branchiobdellida, Diamesa sp., Dicranota sp., Lumbricidae and Nemouridae exhibited increases in drift abundance 8-10 h after the introduction of TFM, however, were considered less sensitive than the former taxa because a decline in their abundance in the benthos was not detected.The response of the benthic invertebrates found in this hardwater creek was similar to those observed during studies of softwater streams. Only the most severely affected taxa were not present in the benthos 350 days after treatment.
Diatom colonies were established on glass slides in Rouge River and Wilmot Creek before application of the lamprecide 3-trifluoromethyl-4-nitrophenol and their abundance was monitored for 21 and 55 d, respectively, after treatment. A total of 105 species of diatoms were identified from the Rouge River; of these, 23 were particularly abundant. Samples from Wilmot Creek yielded 80 species, of which 21 were dominant. Growth of the diatom community at the treated sites of Rouge River declined following chemical treatment, 8.7 mg 3-trifluoromethyl-4-nitrophenol per litre, but recovered within 21 d. Community structure and abundance in Wilmot Creek were not significantly altered by the addition of 5.3–6.7 mg 3-trifluoromethyl-4-nitrophenol per litre. No species identified from either stream exhibited particular sensitivity to the concentrations of 3-trifluoromethyl-4-nitrophenol applied. Temporal and spatial patterns of change are discussed.
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