A productivity study of the Roanoke River above Niagra Dam in Virginia

Deterioration of the water quality in the upper end of the Roanoke River of Smith Mountain Lake due to eutrophication has caused much concern. The Smith Mountain Lake impoundment was constructed in 1965 as a pump storage facility to generate electrical energy and has served as a major recreational area for Southwestern Virginia. Eight sampling stations were established along the length of the Roanoke River from an agricultural area in Montgomery County through the urban area of Roanoke-Salem to Niagra Dam above Smith Mountain Lake. On 12 different occasions, approximately once a month, grab samples. were taken at the sampling stations. Samples were analyzed for general chemical parameters and for nitrogen and phosphorus. The Algal Assay Procedure Bottle Test [Environmental Protection Agency, 1971] was conducted with the samples, and in addition, with samples in which phosphorus and/or nitrogen spikes were added to determine potential productivity and to determine which element was limiting productivity. ResuIts of this investigation demonstrate that the algal assay bottle test is usefuI in correlating phosphorus concentrations with algal growth rate. Phosphorus was found to limit the algal growth in the Roanoke River above the Roanoke wastewater treatment plant for Selenastrum capricornutum and Anabaena flos-aquae, the two algal species used in this study. Maximum specific growth rates tended to increase with in- creasing phosphorus concentration.