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January 4, 2018
To quote Eli Sprenkle, fisheries biologist at Tuttle Creek State Park, “algae and blue-green algae are everywhere.” Including our Bayer Pond. Some would say the same for ticks and mosquitoes. Blue-green algae are now considered to be a form of bacteria (cyano-bacteria) possessing chlorophyll and capable of photosynthesis. Thus, like green algae, they, as a by-product of their photosynthesis, release oxygen back into air or water. Both organismal types, especially the green algae, can occur in many forms, from free-living, single-celled organisms to the filamentous “pond scum” we commonly see on our ponds and lakes. Under a microscope, this scum looks like a dense mass of fine, green threads. Seaweeds, including the giant kelps, are green algae. Some greens, e.g., the kelps, among others, even develop roots and anchor themselves.
Thousands of species of both green algae and cyano-bacteria have been described. Did you ever wonder why our state waters are almost never “mountain trout-stream” clear? A drop of “clear” (but verdant) Kansas stream or lake water will reveal many types of microscopic green algae and cyano-bacteria. But we rarely notice them in Kansas unless they cause a problem, e.g., pond scum and aesthetic appearance. And sometimes, during a warm, sunny summer, with the pond or lake receiving lots of nitrogen and phosphorus in rain runoff from fields, one or more species of cyano-bacteria can develop into a bloom and release neuro-toxic chemicals into the water. Milford Lake sometimes has this problem. Biologist Sprinkle said that dogs are especially sensitive to these toxins, but other animals, as cattle, have been poisoned. Sprenkle says “Do not drink such water!” An evolutionary adaptation is evident in the fish in our natural waters: fish in these poisoned waters do take up the toxins in their brain, liver, and eye tissues, but they have a low sensitivity to the toxins. We do see summer fish kills—from very heavy cyano-bacteria toxic blooms.
Another (rare) path to warm weather fish kills is if conditions are such that much of the algae and such in a body of water die. Microbes always move in to decompose dead organic matter; in this case, dead algae no longer doing photosynthesis and producing oxygen. The microbes will use oxygen from the water for their own respiration, and the supply for fish can become low enough to be lethal. Because they can gulp air from the surface, carp are about the last fish to succumb in a fish kill. Sprenkle said he never has seen a garfish victim in a fish kill. These fish also can come to the surface and gulp air. The gars, tough and adaptable, are one of the three very ancient fish types we can see in Kansas. But that is another story.
Winter fish kills usually occur when snow covers an ice-coated pond or lake long enough to shut off sunlight sufficient for the algae, cyano-bacteria, and other water plants to survive. This sets up the same scenario of microbial decomposition of the dead biomass and of oxygen depletion described above. Have you hugged your green algae today?
2121 Meadowlark Road
Manhattan, KS 66502