Masters Thesis

The effect of beaver (Castor canadensis) dam removal on total phosphorus concentration in Taylor Creek and Wetland, South Lake Tahoe, California

Taylor Creek is located in the Lake Tahoe basin and drains into Lake Tahoe. A beaver colony in Taylor Wetland has built 14 dams along Taylor Creek and in the wetland, creating nine beaver ponds upstream. All of the dams in the main channel of Taylor Creek are destroyed annually in early fall by United States Department of Agriculture Forest Service to allow kokanee salmon (Onchorynchus nerka) to spawn. In addition, flows from Fallen Leaf Dam, located upstream of Taylor Wetland, are increased to supply ample flows for spawning (United States Department of Agriculture 1981). To determine whether beaver activity, specifically the creation of beaver dams and ponds, improve water clarity by reducing the amount of total phosphorus entering Lake Tahoe, water samples were taken before and after beaver dam removal at sites upstream from beaver influence (control sites) and downstream from beaver pond sites (impacted sites). Results were analyzed using multiple linear regression models and mixed-effect models with site random effects for intercept and covariate coefficients. The mean total phosphorus concentration for control sites before and after dam removal was 51.0μg/l and 64.5μg/l, respectively. The impacted sites increased from 70.4 μg/l to 170.5μg/l (p = 0.1517). This study implies that the presence of beaver ponds in Taylor Creek could improve water quality by reducing the phosphorus load entering Lake Tahoe when flows are increased from Fallen Leaf Dam.

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