Probing – 17 Grad Students Join In

Probing the Depths of Crater Lake: A Century of Scientific Research by Douglas Larson

University of Washington’s Weston submarine photometer (light meter). Photo courtesy of the National Park Service

Other OSU graduate students-Owen Hoffman, James Malick, and I were brought into Donaldson’s program during the summer of 1967. Donaldson, who had received a research grant from the U.S. Department of the Interior’s Office of Water Resources Research to classify Oregon’s lakes, saw Crater Lake as the ideal limnological bench mark with which to compare other Oregon lakes. Hoffman and Malick discovered new information about the lake’s zooplankton populations, including the observation that zooplankton migrated vertically through the water column, with Daphnia migrating from depths of more than two hundred feet during the day to the lake surface at night. I focused on the relationship among temperature gradients, sunlight penetration, and phytoplankton photosynthesis. I found that the maximum photosynthetic rates generally occurred between depths of 230 and 400 feet despite low temperatures of around 39 degrees F and low sunlight (about 4 percent of surface sunlight). This suggested that the lake’s deep phytoplankton populations were well adapted for extremely cold water and near-darkness conditions.

Donaldson and his students also provided field assistance and logistical support for visiting scientists conducting special studies at Crater Lake. During the summer of 1967, a team of scientists led by Herbert Volchok of the U.S. Atomic Energy Commission analyzed lake waters and sediments for radioactive isotopes. Team members included H. J. Simpson and W. S. Broecker of Columbia University’s Lamont- Doherty Geological Observatory, V. T. Bowen of Woods Hole Oceanographic Institution in Massachusetts, and W. E. Libby of the Institute of Geophysics at UCLA. The team recorded temperature gradients and collected water samples from the lake surface and from eight depths extending to 1,700 feet. They obtained sediment cores from deep regions of the lake with a free-falling coring device and analyzed water and sediment samples for tritium, strontium-90, and cesium-137.

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