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Diversity and relative abundance of preimpoundment freshwater mussel (Bivalvia: Unionidae) populations in the lower Holston River, Tennessee.

Article Excerpt
ABSTRACT -- A series of freshwater mussel valves was collected from six preimpoundment sites located along the lower Holston River between river mile 36 and 26, Jefferson and Grangier counties, Tennessee. Shell from two sites, the Loy Site and Cave T-11, reflect gathering activities by prehistoric Native Americans, while shell from the other four localities reflect normal river deposition and/or muskrat feeding activity. A total of 8,460 mussel valves, representing 49 species, was identified. Approximately 80 freshwater mussel species and subspecies have been reported from the Holston River. Today (2006) there appear to be about 18 living species remaining. Species represented in these six sites reflect this loss and serve to illustrate the differences among taxa represented in relatively close locales/beds in a stretch of river.

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The North Fork and South Fork Holston Rivers merge at Kingsport, Hawkins/Sullivan county lines, Tennessee, to form the Holston River proper. The river flows southwesterly for 228.4 km to the confluence with the French Broad River at Knoxville, Knox County, where they form the Tennessee River. The Holston River once flowed unobstructed from its source at Kingsport to its mouth at Knoxville. Construction of Cherokee Dam and Lake in 1941 flooded approximately one-third of the Holston River proper (Hughes, 1994). From the Cherokee Dam to its confluence with the French Broad River, the Holston River has an average gradient of 0.21 m/km (1.1 ft/mile), width of 91.5 m and a depth of 1.3 m. The substrate is composed of 15% bedrock, 5% boulders, 40% rubble, 25% gravel, and 15% sand and silt (Hill and Brown, 1980).

Construction of Cherokee Dam has produced large fluctuations in flow rate, water temperature and stream depth. These adverse environmental conditions appear to have brought about the nearly complete demise of the preimpoundment mussel fauna of this stretch of the Holston River. Analyses of shell deposits such as these provide insight into prehistoric and/or preimpoundment mussel species and abundance, and an evaluation of former and existing aquatic habitats relative to possible reintroduction of species.

MATERIALS AND METHODS

Shell recovered from two of the six study sites (Fig. 1) represent mussels collected and presumably utilized as food by Native Americans occupying these locations. The first, Cave Site T-22 situated above the right descending bank (RDB) at approximately Holston River Mile (HRM) 35.6, Grangier County, was excavated in the summer of 1963 by the late James H. Polhemus and Richard R. Polhemus. Excavation units consisted of five 1.5 m squares approximately 1 m in depth. A total of 1,172 valves, representing 36 species, was recovered (Table 1). This site was occupied by peoples of the Woodland culture, A.D. 200-600.

The second or Loy Site (40JE10), a Dallas phase Mississippian village (AD 1400) located above the RDB at HRM 24.7, Jefferson County, was excavated periodically by Richard R. Polhemus from 1986 to 1991. The majority of the 1,892 mussel valves (23 species) were recovered from three large aboriginal house floors, a total area of approximately 30 [m.sup.2]. Shell from the four remaining sites (Table 2) was deposited by muskrat (Ondatra...

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