GSA Annual Meeting in Seattle, Washington, USA - 2017

Paper No. 360-6
Presentation Time: 9:00 AM-6:30 PM


DAS-TOKE, Shyam, Department of Geology, Oregon State University, 104 Wilkinson Hall, 2601 SW Orchard Avenue, Corvallis, OR 97331, JUNGERS, Matthew Cross, Department of Geosciences, Denison University, F.W. Olin Science Hall, Granville, OH 43023, PERSICO, Lyman P., Department of Geology, Whitman College, 345 Boyer Avenue, Walla Walla, WA 99362, GRANKE, Sarah B., Department of Geology, Pomona College, Pomona, CA 91711 and O'BRYAN, Spencer, Carleton College, 1 North College Street, Northfield, MN 55057,

Beavers are ecosystem engineers that significantly influence reach-scale fluvial morphology through dam construction. They determine which parts of a stream are conducive to calmer stream flow and build dams in those areas, thus creating ponds. Our goal is to understand what geomorphic characteristics make those reaches suitable for beaver. Working on Panther Brook, an upland catchment in the Adirondack Mountains of New York, this study uses stream profile surveys, Wolman pebble counts, and measurements of hydraulic geometry to characterize the geomorphic parameters that beaver favor when selecting dam sites. We then use these field measurements and digital terrain analyses to calculate shear stress and stream power, two parameters shown to be good predictors of beaver habitability.

We find that beaver live in reaches with gradients ranging from 0.001-0.025, median grain sizes of 0.05 cm – 0.9 cm, total bank-full shear stress from 0 Pa –143 Pa, and bank-full stream power values from 1.0 W/m – 514 W/m. The values in beaver habitat are compared to those in reaches without beaver, through a two-sample t-test. This test shows significant differences between the two environments. Beaver-reaches have fine sediment, low gradients, low shear stress and low stream power values because beaver dams create ponds with lower stream velocity. This allows fine grained sediment to aggrade, which in turn further decreases gradient and lowers the stream’s total shear stress and stream power.

After beaver have chosen a reach, they further modify the geomorphic properties of that area. By selecting calmer stream reaches, beaver avoid areas with high risks of dam washouts. These calm areas also allow the species to swim from one part of the pond to another when foraging, without facing turbulent water. The information about suitable geomorphic characteristics from Panther Brook can be used to identify areas of possible beaver habitat in the broader Adirondack region.

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