In June of this year, Pickerel Lake was very clear with Secchi disc readings to 16 feet. On a calm day, the bottom of the lake and fish were easily visible. During July, the water turned cloudy, followed by days of thick green algae blooms, reducing clarity to near zero at times. What were the contributing factors for this dramatic change? During the spring we had several significant rainfall events, resulting in heavy runoff from the watershed. This provided the needed silicate to promote a significant diatom (think algae, phytoplankton) bloom, imparting a yellowish tint to the water. These diatoms were then consumed by a large population of zooplankton, which can completely filter the lake in an hour. That is when the lake became very transparent, allowing sunlight to to reach 50% of the water column. Warmer weather and more nutrient in runoff from continued rains, provided the perfect conditions for algae to grow in large portions of the lake. By this time, the younger fish had reduced the zooplankton population, leaving fewer to consume algae. If the lake then becomes nitrogen limited under these conditions, blue-green algae has an advantage over green algae since they can fix nitrogen (from the atmosphere) and grow very quickly. Blue-green algae give off a pungent, musty odor. These algae can then be pushed by the wind and form a thick sludge against the shoreline. When present, it is wise to stay out of the water, including family pets, as toxins can form. When algae decompose, the chlorophyll is lost, leaving a blue color and at times a milky-appearing scum as well. We have always had blue-green algae species in Pickerel Lake. The two species are microcystis and gleotrichia, which are both cyanobacteria. Microcystis is the species blooming right now. Gleotrichia has also occurred in the lake. This species causes swimmers rash or dermatitis. If the lake becomes nitrogen limited throughout the summer, blue greens will become the dominate species. For more information, click the EPA link on Cyanotoxins below. Many thanks to Dennis Skadsen for providing content.
CYANOTOXINS
