Composition and Abundance of Stream Macroinvertebrates as a Determinant of Water Quality Up and Down Stream of the Imperial Dam, Saranac River, New York

Abstract

The removal of the Imperial Dam in Plattsburgh, New York is a subject being currently discussed by parties including city officials, Trout Unlimited and the New York Department of Environmental Conservation. One concern is the impact on water quality and stream benthos below the impoundment which may impact the fishery. This project investigated the hypothesis that the composition and abundance of aquatic stream invertebrates do not differ as a result of the change in water quality above and below the Imperial Dam on the Saranac River. Using a Hess sampler, stream invertebrates were collected, as well as associated physical characteristics (water depth, velocity, substrate size) from two different sites located up and down stream of the Imperial Dam. Aquatic stream invertebrates were identified to Genus or Family and the data were analyzed using various community diversity indices. Results show distinct community differences between the two sites with increased filter feeder abundance at the impounded reach and higher mayfly diversity and abundance at the open river reach. While impoundment has impacted aquatic biota in the Saranac River at Imperial Dam, recovery of the benthos to open river conditions is likely to occur rapidly from upstream colonization sources upon restoration of open river conditions at Imperial Dam.