We have been busy during our drawdown, with a city project in Blue Heron to replace a sewer line, an our dredge activity in Oswego Canal. The lake had a bit of a cyanobacteria bloom last week, and a bloom still persists in some parts of the lake. Also, a lake resident shared a photo of a blue film on the shore that did not look normal. When this happens it is thought to be a paint spill, but actually it is the remnants of a cyanobacteria bloom.
Cyanobacteria contains phycocyanin, which is a part of a light harvesting structure that allows cyanobacteria to grow under lower light conditions than algae that rely on chlorophyll alone. The color imparted by the structure is what gives cyanobacteria its common name – blue-green algae. When a large bloom washes ashore this blue pigment is left behind after the cyanobacteria dies. This will eventually wash away in the rain, but in the mean time keep your dog away so it does not get it on its paws to be licked off later.
Lake Temperature
The lake is isothermal, or the same temperature from top to bottom now. This will last until spring when sunlight provides enough energy to warm the top layer of water again. The reduced water volume during our drawndown means the lake will cool more rapidly this winter. However, it also means that any nutrients carried from the watershed will mean a higher concentration in the reduced volume. This is likely why we had a persistent cyanobacteria bloom this fall.
Secchi
All the sediment exposed during our drawdown does not help with water clarity. When it rains the exposed shoreline is rinsed into the lake, reducing visibility into the water column. In addition, storm outfalls and the creeks carve a channel in the exposed lake bed, transporting material out into the lake. You can see an example of this in the Water Quality News post from today.
Phytoplankton biovolume in Lakewood Bay has decreased a lot since September 11. There is only five percent cyanobacteria present, with 84% of the biomass diatoms, and a 75% decrease in overall biovolume. Diatoms will be the dominant population until next summer when conditions favor cyanobacteria again. We are not collecting any more data from Lakewood Bay until we refill and the bay returns.
Phytoplankton biovolume in Main Lake has decreased quite a bit from August and September. Although the overall concentration is low, the majority of the biomass is cyanobacteria. This will shift more towards diatoms as winter progresses.
West Bay is the only location that saw cyanobacteria biovolume increase during the September 25 sampling, but since the increase was from four to eleven percent the bay continued to be dominated by diatoms. We are not collecting any more data from West Bay until we refill and the bay returns.
