Recovery status of freshwater mussels (Bivalvia : Unionidae) in the North Fork Holston River, Virginia

To determine the degree of recovery of mussels from mercury (Hg) contaminat ion in the North Fork Holston River (NFHR) downstream of the Superfund site at Saltville, Virginia (NFHRM 80.3), 19 sites were sampled using catch-per -unit-effort (no./h) sampling method and 3 sites were surveyed with quadrat s (0.25 m(2)). Nine species of live freshwater mussels were observed in the river, and juveniles were noted at 5 sites (30 juveniles of 4 species). Th e first mussel assemblage, as defined by numerous animals of multiple speci es, was located at NFHRM 59.9, approximately 20.4 river miles downstream of Saltville. The greatest number of species was observed at NFHRM 11.0 (5 sp ecies), while the greatest mussel density (2.6 mussels/m(2)), the greatest number of juveniles (11), and the greatest species richness of juveniles (3 species) were observed at NFHRM 13.5. Random catch-per-unit-effort at surv eyed sites, as well as the number of juvenile species observed, were correl ated to total Hg, but not methylmercury content, as measured in Corbicula f luminea (Muller, 1774) from proximate sites. Based on the appearance of mul tiple species and age classes, as well, as the presence of juvenile mussels , recovery of freshwater mussels begins to occur roughly 20 river miles dow nstream of the Hg contaminated Superfund site at Saltville.