ContentsPutah and Cache: Clear Lake or Lypoyomi

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Clear Lake State Park

Pete Richerson and Scott Richerson

In another five miles look for the turn off into Clear Lake State Park, whose facilities include campsites, a life-guarded swimming beach, and boat launching facilities. Inside the visitor center is a display of some of the wildlife in and around the lake. There you can buy a bird checklist and other pertinent natural history information. The three-mile long Dorn Nature Trail gives an excellent introduction to the plants and animals of the region. The park is also a good place to observe the lakeside plant community. Valley oaks dominate the deep alluvial seasonally flooded soils while willows, cottonwoods and buttonwillows grow in abundance along the lake's margins. California wild grapes, blackberries, and poison oak form a thick undergrowth where they are not cleared. The hills are home to mountain lions, deer, elk, and black bears. Badgers, skunks, mountain quail, foxes and coyote move through the underbrush, while blue-bellied western fence lizards and long, slick, lanky, alligator lizards hide among the rocks. In and above the trees live great horned owls, flickers, hummingbirds, doves and woodpeckers. The lake itself supports mink, river otters, raccoons and a considerable variety of waterfowl.

Human disturbance has severely affected many populations of fish-eating wildlife at Clear Lake. Some populations have been recovering. Numbers of bald eagles remain small. The grizzly bear may be gone for good. The most serious single human disturbance was the repeated mass application of DDD, a chlorinated hydrocarbon pesticide related to DDT. It was used to control swarms of the Clear Lake gnat. Gnat larvae live in the lake, floating in the water column at night to hunt the small crustaceans that a eutrophic lake provides, and hiding in the mud during the day to avoid fish predation. These elegant, nearly transparent little creatures use gas bubbles to regulate their buoyancy in the water. Blind, they remain absolutely still until they sense the wake of a passing prey, which they follow and then attack.

Historically, swarms detracted greatly from the tourist experience. Although the adults do not bite, they sometimes hatch in huge numbers during the summer. Attracted to lights, dead gnats would sometimes accumulate three feet deep under streetlights, or so legend has it. Outdoor activities after dark were impossible, and even behind their screens, residents were unnerved by the high-pitched whine of thousands of gnats at every window screen. In the late 1930s, the Federal Government sent a team of biologists to find a way to control the Clear Lake gnat. Their work, halted by the outbreak of World War II, is the earliest sustained scientific investigation of Clear Lake. After the war, gnat researchers resumed their work, armed with the new tools of synthetic pesticides. As one member of the team, Garth Murphy, relates, the scientists aimed to be cautious with these powerful killers. They built a series of small ponds and stocked them with a suitably diverse selection of lake biota and tried several different pesticides. DDD controlled the gnats at levels that were non-toxic to other biota. They made a trial DDD application in the small Lower Blue Lake, controlling gnats without untoward side effects. The researchers were proud of their thorough and conservative analysis of the hazards of pesticide use. Three massive, lakewide applications of DDD followed in 1949, 1954, and 1957. The first application yielded complete and effective gnat control for several years, but the subsequent application was less successful; the third failed to achieve adequate control. The few gnats that could survive in the presence of a little DDD had most of the lake to themselves. Complete resistance evolved in less than ten years. The Mosquito Abatement District switched to Parathion, a different class of pesticide.

In the meantime, western grebes, the most abundant fish-eating bird at Clear Lake, suffered a reproductive collapse. Other fish-eating birds, such as osprey, diappeared entirely. Investigations by California Department of Fish and Game biologists turned up high levels of DDD in grebe tissues and found that DDD accumulated in food chains. Chlorinated hydrocarbons are stored in fat and metabolized to harmless substances at very slow rates. They also break down in the environment very slowly. Aquatic animals accumulate these compounds from the water and from their food, and pass them on to their predators. Longer-lived species higher up the food chain have progressively higher concentrations. Fish-eating birds at the top of the food chain become the inadvertent focus of the re-concentrated DDD. DDD harms them mainly by thinning eggshells to the point where they do not survive incubation. Clear Lake thus became one of the first two well-documented cases of food chain accumulation of chlorinated hydrocarbon pesticides, garnering more than a page of discussion in Rachel Carson's famous Silent Spring. The behavior of chlorinated hydrocarbons is one of the 20th Century's most striking lessons in the role of uncertainty in environmental management. Unanticipated processes like food chain accumulation and eggshell thinning often surprise even thorough and conservative scientists. In the 1980s Parathion treatments have stopped as well, but gnat numbers remain low. The introduced fish, Mississippi silversides, may be controlling gnat populations, although evidence is equivocal. Despite major efforts by Mosquito Abatement investigators, important aspects of gnat population biology are still concealed behind a veil of uncertainty.

Luckily, ecosystems are usually resilient. When UC Davis investigators began intensive Environmental Protection Agency funded studies there in the early 1990s, about ten pairs of osprey nested at the lake. Successful nests averaged about one and a half fledglings, a number experts consider sufficient for a growing population. By 1999, 20 pairs successfully nested. In 1999 a bald eagle pair nested at the lake and there were unconfirmed reports of a second nest. Grebes are typically present at Clear Lake in considerable numbers; Audubon Society members have found as many as 10,000 in the Christmas bird count. UC Davis investigators' work on western grebes shows that they currently carry hardly more than the regional background levels of chlorinated hydrocarbons. A massive amount of DDD remains in the lake, but is buried under 30 or 40 cm of lake sediment. It is now out of reach of the burrowing creatures that formerly introduced it into the bottom of the food chain. Grebe reproduction on the lake has been sporadic in recent years, most likely due to human activity around their tule marsh-nesting habitat. Most of the remaining tule marsh on Clear Lake grows in narrow strips that are exposed to boaters, who should take care to stay well away from tule stands where grebes show any signs of nesting.

If you are lucky or patient you may get a chance to observe the mating display of the western grebe, one of the most dramatic of any species. The pair begins with a vigorous display of synchronized head bobbing, then take off half flying, half running side-by-side across the water with heads held high for 50 yards or more before, still in perfect synchrony, abruptly diving beneath the water. Bird behavior doesn't get much more breathtaking. Other fish-eating birds that are now common on the lake include other species of grebes, double crested cormorants, white pelicans, belted kingfishers, and great blue herons. A considerable variety of ducks winter at Clear Lake. Mink and otter are common. The abundance of all this spectacular wildlife is one of the chief payoffs of a eutrophic lake.

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