ContentsPutah and Cache: Clear Lake or Lypoyomi

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Horseshoe Bend

Pete Richerson and Scott Richerson

At the spot where the road from the Buckingham Point returns to the lake, pull across to the small parking space on the shoulder. Cautiously, for the road is narrow, walk until you can see down to Horseshoe Bend, a cove where the point intersects the mainland. If a bluegreen algal bloom is on, you will clearly see the thick scums. The water within 10 to 20 yards of shore will be conspicuously greener or redder than the water further out because the prevailing northwesterly winds blow the algae into embayments. Patches of algae a few millimeters thick sometimes float on the water surface here like olive drab paint.

Since the 1930's, blooms have caused problems for recreation on the lake. Usually most of the bluegreens are suspended in the water and are not particularly noxious. Scattered patches of scums cause localized problems, especially at sites where the prevailing wind causes drifting scums to accumulate. The worst bloom on record was The Great Microcystis Bloom of 1990, when packed mats of algae 4 feet thick collected in places like Horseshoe Bend. The buoyancy of the algae lifted the top inch or two of the mass above water, forming a dry crust. Beneath the crust, algae died and decayed, giving off odors redolent of a poorly run fish cannery. The smell rising from Horseshoe Bend was like a wall, and forced many residents of the Buckingham subdivision to move into motels.

Bluegreen algae are fascinating organisms. Some of the oldest fossils known, dating back 3 billion years, are bluegreens. These simple creatures of the lake are some 20 times older than the oldest rocks in our bioregion! As their technical name suggests, "cyanobacteria" are giant photosynthetic bacteria. Their individual cells are ten to a thousand times larger than typical bacteria, easily visible in a light microscope, and live in colonies of hundreds to thousands of cells that reach the size of pinheads. For a billion years or so these were the dominant photosynthetic organisms on earth, producing oxygen that was consumed by the sulfur and iron in the earth's oceans for perhaps two and a half billion years. Then photosynthesis finally tipped the balance and created an oxidizing environment in which animal life was possible.

Buoyant, nitrogen-fixing bluegreens are well positioned to take advantage of the eutrophic phosphorous-rich conditions of Clear Lake. Taking their nitrogen from the air, they float upward into the light waters, shading out their competitors. More "advanced" eukaryotic algae can't match the ancient cyanobacteria under nitrogen-poor eutrophic conditions.

But there are drawbacks. The floating strategy requires huge cell aggregations by bacterial standards and needs to be cleverly executed lest the colony become stranded at the surface and cooked by the sun. The trick is to float up at night and then become heavier than water by midmorning. That way colonies spend the heat of the day in the top two or three feet of water. This layer is heated by the sun and doesn't mix downward until late afternoon. Surface scums that persist later often do so because they are starved for nutrients and cannot manufacture enough heavy carbohydrates to sink. Sunlight towards midmorning then damages the photosynthetic apparatus and cells begin to die. Dead cells in turn release their water-soluble pigments and become pale, bleached hulls.

As ugly as bluegreen scums may be, if you chance upon a good bloom consider yourself lucky to see such wonderful complexity. The humble, ancient cyanobacteria offer one of the best opportunities in our otherwise very youthful bioregion to meditate on deep time. Without the eons of hard work by bluegreens, it really wouldn't matter if you held your nose or not; the gas-chamber atmosphere would kill you in moments.

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