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) contamination 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 quadrats (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). The first mussel assemblage, as defined by numerous animals of multiple species, 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 species), 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 surveyed sites, as well as the number of juvenile species observed, were correlated to total Hg, but not methylmercury content, as measured in Corbicula fluminea (Muller, 1774) from proximate sites. Based on the appearance of multiple species and age classes, as well, as the presence of juvenile mussels, recovery of freshwater mussels begins to occur roughly 20 river miles downstream of the Hg contaminated Superfund site at Saltville.