Some effects of abandoned manganese strip mines in Smyth County, Virginia on stream ecology

Abandoned manganese strip mines in Smyth County, Virginia have for many years contributed pollution to the streams draining them. Streams in the Cripple Creek drainage area were sampled during the summer of 1967 to determine the nature and extent of pollution in them, and to evaluate the reclamation work being done by the United States Forest Service. Affected streams were compared with control streams on the basis of physical, chemical and biological properties.

Manganese levels in all streams sampled were found to be below one part per million. A controlled experiment with Mn(NO₃)₂ showed that the median tolerance limit for rainbow trout fingerlings is about 16 ppm Mn which, together with stream sampling data, indicates that manganese is not present in toxic concentrations in the study streams.

Killinger Creek, which drains a partially reclaimed area, was found to support fewer species of fish and benthic fauna than Crigger Creek, a comparable control stream. Siltation is probably the main contributing factor. Bedload was much greater in affected streams than in control streams. Although volume of bedload was high in Blue Spring Creek, which drains a reclaimed area, particle size distribution of the bedload indicates that much of the finest silt has been flushed from the upper portion of this stream. Blue Spring Creek supports an abundant population of aquatic insects and fish fauna, indicating that reclamation has been effective on this watershed. It was also found that rainbow trout are spawning successfully in this stream.