Dynamics and control of the Asiatic clam in the New River, Virginia

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Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University

The Asiatic clam, Corbicula fluminea, has invaded the New River at the rate of nine miles a year from the Kanawha River, which enters downstream from the Glen Lyn coal-powered generating plant in Virginia. During the period of investigation, October 1976-September 1978, clams were more numerous in the vicinity of the thermal discharge of the plant than they were in unheated waters, and their population fell sharply during the winter months, when the water temperature dropped to approximately 2°C. The temperature (35°C) of the heated discharge water in late summer did not adversely affect the clam. High mortality occurred at temperatures ~36°C in laboratory thermal tolerance studies.

The clam proved to be highly resistant to the conventional biocidal practice of intermittent chlorination and to exposure to heavy metals in both static and artificial stream bioassays. Copper was more toxic than either zinc or a combination of zinc and copper. Potassium was not an effective biocidal agent at low concentrations (< 100 mg/I).

Measurements of 42 elements in water, sediment, clam shell, and visceral tissue revealed that Corbicula was an efficient accumulator of many elements. Concentrations in all tissue samples were greater than those measured in river water. Fifteen elements were more concentrated in tissue samples than in river sediment, but the converse was true for 25 elements. Elements released from discharges at the Glen Lyn Plant did not limit the clam's development or ability to propagate.

Although only minor incidents of Corbicula infestation have been observed in the cooling system of the power plant, such infestation could become a serious problem if winter water temperatures rise. No effective means of controlling the clam's population has been developed.