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Date Permissions Signed
Date of Award
Master of Science (MS)
Mitchell, Robert J. (Geologist)
Matthews, Robin A., 1952-
Nutrient enrichment presents a common problem in lakes and streams by promoting algae growth and the depletion of dissolved oxygen. Lake Whatcom in northwestern Washington State is subject to a Total Maximum Daily Load (TMDL) to limit phosphorus input. The 20-km2 lake is supported by runoff from numerous perennial streams in a steep, 125-km2, moderately developed, forested watershed. Much of the phosphorus entering the lake is adsorbed to suspended sediment in streams and is transported to the lake during storm events. Understanding sediment and phosphorus transport to the lake is important for managing the TMDL and for maintaining water quality in general because the lake serves as the drinking water source for about 100,000 people. My objectives were to calculate sediment and phosphorus fluxes into Lake Whatcom and examine relationships among precipitation, discharge, sediment concentrations, and phosphorus concentrations. I collected a series of water samples near the mouth of Smith Creek in the Lake Whatcom watershed during 22 storm events between February 2013 and January 2014. The samples were analyzed for total suspended solids and total phosphorus. I used data from Smith Creek and four other streams to examine the effects of varying basin features on loading and to develop sediment-discharge and phosphorus-discharge models to estimate loading to the lake during the 2013 water year. Relationships among sediment, phosphorus, and discharge varied temporally and spatially in the watershed. During most storm events, the sediment peak preceded the discharge peak, indicating that transport was limited by sediment availability. In Smith Creek, the magnitude of hydrograph rise was the best predictor of the maximum sediment concentration during the event. Among the five streams studied, sediment yields ranged from 11.5 to 143 tonnes/km2/year. The steep, forested Smith Creek basin yielded the most sediment per area. Phosphorus yields ranged from 25.7 to 68.5 kg/km2/year, with the highest phosphorus yield coming from a small, low-relief basin containing 29% residential development. My sediment and phosphorous yields were comparable to estimates from similar streams in the Puget Sound region. Total suspended solids and total phosphorus were significantly correlated to discharge in most streams in the watershed, but variability within and among storm events resulted in uncertainty when calculating fluxes based on discharge. Continuous turbidity monitoring could allow for improved models and flux estimates.
Western Washington University
Whatcom, Lake (Wash.)
Copying of this thesis in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.
Beeler, Katherine, "Sediment and phosphorus inputs from perennial streams to Lake Whatcom, northwestern Washington State" (2014). WWU Graduate School Collection. 380.