Some effects of the introduction of hard water into Carvin Cove Reservoir, Virginia

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Virginia Polytechnic Institute and State University

In November, 1966, Tinker Creek, a hard water stream was introduced into Carvin cove Reservoir, a very infertile, water-supply reservoir. This provided an excellent opportunity to study some of the interactions between fish productivity and water quality.

Physicochemical conditions were monitored in the reservoir from 1965 to 1968 by the Roanoke City Water Department. These records demonstrated that a significant water quality alteration resulted from the addition of Tinker Creek water.

Total hardness and alkalinity were seen to increase from 10 - 20 ppm in 1965 and 1966 to 50 - 60 ppm by the end of 1968. Hydrogen ion concentrations, which averaged about 6.8 before the hard water introduction, had increased to about 7.6 in 1968.

The hard water introduction caused variations in the physicochemical conditions of different areas of the reservoir during 1968. Waters nearest the hard water inflow ranged somewhat higher in dissolved nutrients.

Bottom fauna distribution and abundance was affected. Greater concentrations of macrobenthic organisms were found in the area nearest the Tinker Creek inflow. High concentrations of fish, especially gizzard shad and white suckers, were found in the area near the hard water inflow.

Length-weight relationships and condition indices suggest that bluegills and bullheads were in better physical shape in 1968 than they were in 1951.

An age and growth study on the white sucker, Catostomus commersoni, indicated that growth rates had doubled in the sucker after the Tinker Creek water was added.