Changes in Fish and Benthic Macroinvertebrate Assemblages Along the Impounded Arkansas River

Abstract

In order to determine cumulative impacts of multiple impoundments on the Arkansas River, we collected forage fish, macroinvertebrate, and physical and chemical samples from stations upstream and downstream of four hypolimnial release reservoirs and from stations along unimpounded reaches between Florence, Colorado, and Bixby, Oklahoma. Dendrograms using Jaccard associations and polar ordinations indicated that distributional patterns of macroinvertebrates were dependent upon changes in substrate, total dissolved solids, alkalinity, and zinc and fish upon substrate and temperature. Only changes in IDS and alkalinity levels could be attributed to cumulative impacts of the series of impoundments. Substrate changes were localized effects downstream of each reservoir and influenced changes in proportions of functional groups of macroinvertebrates. This hydrologic effect supported predictions of serial discontinuity. Impoundments served as distributional barriers to fish communities rather than a river continuum resetting device.