Production of Benthic Macroinvertebrates in the New River at Sandstone Falls in 1987

Voshell, J; Hiner, SW; Christman, VD; Silvia, A

The secondary production of the dominant benthic macroinvertebrates was measured in the New River at Sandstone Falls from June through November 1987. The purpose of this study was to establish baseline data on the levels of production and the factors affecting production in a year without applications of Bti for black fly control. The results of this study are intended to serve as comparisons in future years when Bti is applied in the New River Gorge National River. Total production on the rock outcrops at Sandstone Falls was 30.8 g/m2. This level of production is similar to what has been reported for streams of about the same size as the New River. Production at Sandstone Falls was considerably lower than previous measurements at Bluestone Dam (330.7 g/m' in 1983 and 173.9 g/m^2 in 1986). Water temperature and the amount of habitat provided by the submerged macrophyte Podostemum were approximately the same at both sites. The most likely reason for lower production at Sandstone Falls was lower concentrations of seston (suspended particulate organic matter), which provides the major source of food for many of the organisms in the New River. Abundant quantities of energy-rich seston are released from Bluestone Lake, but this material probably settles out in pools or is consumed by the biota as it passes downstream. Of the total production at Sandstone Falls, mayflies accounted for 51%, chironomids 34%, caddisflies lo%, and black flies only 5%. At Bluestone Dam prior to treatment with Bti (1983), the relative contributions of the various taxa to total production was considerably different: chironomids 72%, caddisflies 20%, black flies 8%, and mayflies only <1%.

Production of Benthic Macroinvertebrates in the New River at Sandstone Falls in 1987

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