The Annual Fall Turnover Algae Bloom

by Richard D. Gainar, CEBS
Chairman, LMC

Did anyone notice the huge algae bloom during the last week of October? That’s because the lake “turned over”. “Turnover” is an annual phenomenon in deep, stratified lakes like ours. Cold, dense water holds at the bottom of the lake during warm weather while lighter, warm water floats nearer the surface above it. The fuel that spikes the algae bloom is phosphorus, the primary enemy of good water quality. While there was only 28 ug/L in the surface water before the turnover, the bottom water contained a much higher 490 ug/L. Phosphorus is released from the organic lake sediment (decayed weeds, leaves, dead algae, etc.) by de-oxygenated water and is held during summer months at the bottom of our lake by the denser water. Every year when the weather cools the top water to a temperature below that of the bottom water, the lake “turns over” mixing all that phosphorus throughout the water column giving algae that annual shot-in-the-arm resulting in a major bloom.

At our November 7th Association meeting a resident provided some test results that seemed to indicate that algal toxin levels in the waters of three coves were well above acceptable levels. However, the subsequent testing of the same waters by our consultants using official Ohio EPA sampling protocol indicated no detectable levels of toxins. It may be that a difference in sample collection techniques accounted for the difference. Nonetheless, residents need to understand that higher toxin levels may be associated with algae scum and should avoid coming in contact with it when possible.

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