Probing the Depths of Crater Lake: A Century of Scientific Research by Douglas Larson
After 1971, limnological research at Crater Lake was discontinued for seven years, probably because the Park Service was either unwilling or unable to provide any funding. In June 1978, I returned to the lake to conduct an independent research program. The National Park Service loaned me a two-person rubber dinghy and a park employee to operate the boat’s three-horsepower outboard motor. We lowered water-sampling gear and various instruments into the lake with a homemade wooden winch and cable reel containing 2,000 feet of rope, which had been built for me by my father, Gunnard Larson. I used the dinghy and winch system for four summers, from 1978 through 1981, sometimes during storms that whipped up waves large enough to nearly swamp the tiny boat as we crossed the lake. In 1982, after someone in the Park Service finally realized that a rubber dinghy crammed with two people and limnological equipment was unsafe on Crater Lake, I received a twenty-four-foot aluminum pontoon vessel that was powered by a thirty-five-horsepower outboard motor. This boat, faster and more durable, was the first one ever purchased by the Park Service for research on Crater Lake.
|In July 1968, John Donaldson, James Malick, and Owen Hoffman prepare to go down the Cleetwood trail with their limnological equipment loaded on a motorized trail packer. Photo by D. W. Larson|
I returned to Crater Lake to learn more about the abundance, vertical distribution, and species composition of phytoplankton, all of which were poorly understood at the time. I also wanted to continue the research that I had begun with Donaldson, Malick, and Hoffman ten years earlier. Between 1978 and 1983, approximately nine hundred water samples were collected for phytoplankton analysis. Stan Geiger, a Portland algae expert, examined the samples and identified more than one hundred species of phytoplankton, roughly 75 percent of which were diatoms. Three species were dominant-two diatoms (Nitzschia gracilis, Stephanodiscus hantzschii) and yellow-green algae (Tribonema affine). Living phytoplankton were found at depths extending to nearly one thousand feet, although 95 percent of the phytoplankton was concentrated in the lake’s upper five hundred feet. During summer, Nitzschia gracilis became increasingly abundant in the lake’s surface waters, usually reaching maximum numbers by late August. The vertical distribution of phytoplankton in Crater Lake is analogous to a tropical rain forest in which communities of organisms aggregate into vertically distinct, environmentally disparate zones down through the forest canopy In Crater Lake, the three predominant species of phytoplankton are distributed in distinct depth zones. This three-tier structure, in which the phytoplankton live at different depths, is not common among lakes. In most lakes, especially shallow ones, the phytoplankton are more or less distributed homogeneously.