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Master of Science (MS) in Biology
Incised streams are disconnected from their floodplains and no longer store water effectively. This leads to diminished ecosystem function, loss of critical riparian and aquatic habitats, and reduced biodiversity. Beaver dams improve incised streams by raising surface and groundwater levels, leading to reconnected floodplains. When beaver establishment is not feasible, Beaver Dam Analogs (BDAs) may be used to mitigate damage from stream incision and facilitate beaver establishment. However, it is unclear how effective BDAs are at mimicking natural beaver dams, especially on streams affected by high-intensity wildfires. The objective of my research is to collect baseline data needed to assess BDA effectiveness in comparison to natural beaver dam complexes. I hypothesized that beaver dam sites would have lower channel incision, higher accumulation of fine sediment, higher abundance of wetland species, greater water storage, and higher soil moisture compared to non-beaver sites, and that BDA installation would make the BDA sites more similar to beaver sites. I used a Before-After-Control-Reference-Impact study design to compare five BDA restoration sites with paired control sites and three natural beaver dam complexes. In the summer of 2021, pre-restoration data was collected on 1) channel morphology using a laser level and stadia rod, 2) riparian vegetation accounting for riparian landform using the line-intercept method, 3) sediment composition using a Wolman pebble count, and 4) water storage using a salt drip to measure water travel time. In the summer of 2022, I assessed soil moisture above the stream channel (floodplain for beaver sites and terrace for non-dammed sites) one month after BDAs were installed on one restoration site. Overall, I found that beaver sites had width-to-depth ratios and floodplain widths over twice as large as non-beaver sites indicating they were less incised. They also had finer sediment, greater water travel times indicating greater water storage, and higher soil moisture that lasted through the summer months. Compared to beaver and control sites, pre-BDA sites had the lowest cover of wetland species. My study has shown that beaver dams effectively trap fine sediment, recharge soil moisture in floodplains, and increase the cover of wetland species. I have also provided critical baseline data needed to assess the impacts of BDAs over time after installation is complete to determine whether they effectively mimic beaver dams.
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Killoy, Katelin, "Baseline data for assessing beaver dam analogs as a restoration tool in fire-affected tributaries of the Methow and Okanogan watersheds" (2023). EWU Masters Thesis Collection. 865.