Discontinuities in fish assemblages and efficacy of thermal restoration in Toxaway River, NC

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Title: Discontinuities in fish assemblages and efficacy of thermal restoration in Toxaway River, NC
Author: Robinson, Jason Lesley
Advisors: Peter Rand, Committee Chair
Tom Kwak, Committee Co-Chair
Kenneth Pollock, Committee Member
Abstract: Biogeographical studies in the Toxaway and Horsepasture Rivers, (Transylvania County, NC) were initiated along with the creation of a state park in the area. This region is noted for extreme topographic relief, high annual rainfall totals and many rare and endemic plants and animals. The study area encompasses a portion of the Blue Ridge Escarpment and the associated Brevard Fault Zone. These geologic features are important factors in determining the distribution of stream habitats and organisms. I hypothesize that major waterfalls and cascade complexes have acted to discourage invasion and colonization by fishes from downstream. This hypothesis is supported by longitudinal fish assemblage patterns in study streams. Fish species richness in Toxaway River increased from 4 to 23 between Lake Toxaway and Lake Jocassee, a distance of 10 river kilometers. No species replacement was observed in the study area, but additions of up to 7 species were observed in assemblages below specific waterfalls. A second component of the research examines the efficacy of a rapid bioassessment procedure in detecting thermal and biological changes associated with a reservoir mitigation project in an upstream site on Toxaway River. The mitigation project began in the winter of 2000 with the installation of a hypolimnetic siphon to augment the overflow release with cooler water during summer months. I record a greater summer temperature difference on Toxaway River below Lake Toxaway (comparison of pre- vs. post-manipulation), relative to control sites. The cooling effect of the mitigation decreases in magnitude with increasing distance from the dam. I offer a critique of the mitigation effort based on a mismatch between the longitudinal extent of thermal restoration and the distribution of target organisms that were expected to benefit from the manipulation.. Secondly, I highlight some of the important limitations in drawing inferences from data collected using a rapid bioassessment approach. I conclude with suggestions on how to improve future research efforts in this area. I emphasize the importance of implementing process-oriented field work that could provide insights into mechanisms responsible for biological changes downstream from reservoir ecosystems.
Date: 2003-07-29
Degree: MS
Discipline: Zoology
URI: http://www.lib.ncsu.edu/resolver/1840.16/2295


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