Probing – 21 Optical Deterioration

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

 When reports about the lake’s possible optical deterioration finally reached the public, concerns were raised that the tourists who crowded the park each summer were the culprits. Between 1902 and 1940, fewer than 3 million people had visited Crater Lake National Park. Following World War 11, however, the park’s summertime visitation rate rose dramatically, and close to six hundred thousand people visited the park each summer throughout the 1970s. Between 1970 and 1982, the Park Service counted 8 million visitors to the park.

Although there was no firm explanation for the decrease in the lake’s clarity, some scientists believed that it was related to an unusual abundance of phytoplankton inhabiting the lake’s waters to a depth of about one hundred and fifty feet. Researchers who had studied the lake speculated that the phytoplankton had become more abundant because of an unnatural increase in concentrations of essential plant nutrients, especially nitrogen. We had found that nitrogen concentrations in Crater Lake were extremely small and that additions of nitrogen from anthropogenic sources, such as sewage, could greatly stimulate the growth of phytoplankton and other lake algae. The source of this nutrient enrichment, researchers suspected, was the park’s sewage disposal facilities on the caldera rim, specifically the septic tank-drainfield system that processed an estimated 16 million gallons of raw sewage every summer. This system had been designed in the mid-1940s to accommodate about two hundred thousand visitors each summer. It was improved in 1975 shortly after the park’s main source of drinking water, a springfed creek, had become grossly contaminated with sewage, causing more than a thousand cases of diarrhea and other waterborne ailments among park tourists and staff.

The news media picked up the story about Crater Lake’s diminishing water clarity in 1981. On December 20, 1981, the Oregonian reported that scientists suspected that sewage was the cause and that they were frustrated by the scarcity of historical lake data, which was needed to determine if the loss of clarity was a new condition or a recurrent one. The Oregonian quoted James Rouse, superintendent of Crater Lake National Park, who said that “the only sewage that could get into the lake would have to come from either two outhouses on the lake’s Wizard Island, or from two sewage lagoons which are about 200 feet higher than, but two miles removed from the lake.”(42)  Oddly, Superintendent Rouse failed to mention the park’s main sewage facility on the rim, located only a few hundred feet from the lake and consisting of a septic tank and drainfield that handled millions of gallons of raw sewage each summer. Shortly after, Congressman Denny Smith, a Republican from Salem, sponsored an amendment to a bill in Congress directing the National Park Service to study the clarity problem at Crater Lake and “to immediately implement such actions as may be necessary to assure retention of the lake’s pristine water quality” Smith’s amendment became Public Law 97-250 in September 1982, authorizing a boundary modification of Crater Lake National Park and a ten year monitoring program to investigate possible lake pollution.

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