Date of Award

Fall 2021

Rights

Access is available to all users

Document Type

Thesis

Degree Name

Master of Science (MS) in Biology

Department

Biology

Abstract

This study documents the effects of beaver dam analogs (BDAs) on nutrient transport, fish community composition, macroinvertebrate drift, and benthic macroinvertebrate communities of Crab Creek, WA, USA. In 2019, the U.S. Fish and Wildlife Service (USFWS), and Natural Resource Conservation Service (NRCS) placed 25 BDAs in Crab Creek on a section of private land near Harrington, WA. Beaver dam analogs are structures placed in streams to mimic the ecosystem effects of beaver activity and are increasingly used as a stream restoration technique. The primary goals of placing these BDAs in the stream was to impound sediment and create a new floodplain at the currently incised stream channel. While BDAs are increasingly used as a stream restoration technique, there is limited research on their impacts on stream ecosystem function. Investigating how BDAs effect nutrient retention, macroinvertebrate communities, and fish community composition will help inform practitioners about the effectiveness of this restoration strategy. Crab Creek had a significantly higher density of red sided shiners (Richardsonius balteatus) (p=0.00175) in the BDA reach compared to control reaches. When comparing the BDA reach to the control sites, there were no significant differences in nutrient retention in the BDA site. Macroinvertebrate community response had limited statistically significant differences when compared to the control sites. However, there were significant changes from 2009 to 2020 when comparing benthic macroinvertebrate assemblages, probably in response to factors other than BDA installation. Altogether, few effects of BDA installation were detected for nutrient retention, macroinvertebrate communities, and fish community composition. BDAs are a process-based restoration technique that requires a significant change in physical ecosystem parameters before any changes are likely to be seen in the biological community or ecosystem processes. Changes to geomorphology of the stream could potentially take time, as these restoration techniques require stream energy to alter the physical parameters of the stream. Since BDA installation in Crab Creek, no significant high flow events have occurred. Without early spring flood events, changes in the nutrient dynamics, and macroinvertebrates communities could be subtle, or undetectable. This research will ultimately contribute to the current limited understanding of the effects of BDAs on stream ecosystem function.

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