Term of Award

Fall 2014

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Department

Department of Biology

Committee Chair

Checo Colon-Gaud

Committee Member 1

Ray Chandler

Committee Member 2

Lance Durden

Abstract

Beaver were at the brink of extinction in the early 20th century, but over the past century populations have been rebounding. This increase in range and population size has raised new concerns over possible impacts on aquatic ecosystems. Beaver are considered ecosystem engineers because they change the physical structure of aquatic systems through the construction of dams, which turn naturally flowing sections of rivers and streams into standing water. Such changes are known to influence habitat heterogeneity, influence organic matter transport and storage, and consequentially influence biological diversity. To my knowledge, no studies of the effects of beaver impoundments on benthic invertebrate assemblages and benthic organic matter standing stocks have been conducted in the SE Coastal Plain ecoregion. Furthermore, few studies have explored the influence of beaver dams during drought conditions. The goal of this study was to assess the effects of beaver dams on organic matter standing stocks and benthic invertebrate assemblages in a Southeastern Coastal Plain stream during extreme to severe drought conditions. This goal was addressed by comparing stream reaches currently impacted by beaver activity (i.e., presence of dams) with segments where no beaver activity was evident (i.e., reference reaches), and comparing upstream and downstream segments within impacted reaches. Beaver impacted reaches retained significantly higher standing stocks of several major organic matter categories, including fine particulates (250 µm) ranged from 29-154 g ash free dry mass (AFDM) m¯² at beaver impacted reaches compared to 9-67 g AFDM m¯² at reference reaches (P=0.004), and coarse particulates (>1 mm) ranged from 473-1,540 g AFDM m¯² at impacted sites compared to 206-1335 g AFDM m¯² at reference sites (P=0.04). Furthermore, there were no differences in benthic organic matter standing stocks within impacted reaches (i.e., upstream and downstream of beaver dams). Benthic macroinvertebrate abundance or biomass did not differ between impacted reaches and reference reaches, or within impacted reaches. Taxonomic diversity as calculated by the Shannon-Wiener Index (H’) was significantly higher (P=0.03) at reference reaches (H’=1.16) over impacted reaches (H’=0.99), but did not differ within impacted reaches (P=0.30). Collector-gatherers consistently dominated macroinvertebrate assemblages accounting for more than half (65-91%) of the total community. In conclusion my study suggests that beaver activity can have an effect on the retention of organic materials in streams, with impacted sites retaining and storing significantly higher levels of benthic organic matter. In contrast with other studies, my results indicate that beaver dams had little effect on macroinvertebrate assemblages, at least during low flow conditions in SE Coastal Plain streams.

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