Every year for many years I have been exploring a pond near school with my students. Though we look at the physical features of this small body of water, we concentrate on the critters that live here. To be more thorough and to get a complete picture of the pond, we visit it during different seasons. In May, we go to see the pond in spring. During October, we look at the same pond in fall. And, in January, we view this wetland during the cold season of winter.
Each time, we scoop out water to take back to the classroom to examine more closely. This is easy to do when the pond is open -- during this season our collecting is a bit different. Recently, we took our winter pond walk.
The pond is covered by snow and ice as expected; this year it was also holding a layer of slush as is seen on many regional lakes. We used ice augers to go through the ice into the aquatic world below. The ice thickness of 12 inches that we found is not as much as some other years, but ample to hold our entire class. Nearly a foot of snow and slush was over the ice.
Once we penetrated the ice, water came up to the surface with a strong odor of methane and hydrogen-sulfide. These gases are created by anaerobic decay of muck on the pond's floor. Such odors get trapped under the ice, but were freed when we drilled through.
Conditions in the pond do not look good for anything living here. The environment is cold and dark with little food or oxygen. Most wintering critters go into a dormant stage among the pond detritus.
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We collect these decaying leaves from deep in the pond. Back in the classroom, we take a closer look. Despite the less-than-desirable conditions, we find many kinds of animals living here. Most abundant are the immature insects. We saw them in the fall; they'll mature next spring and we find them here now, too.
We found the young of five species of insects.
Broad and stocky were the inch-long dragonflies' larvae (sometimes called "nymph"). Their cousins, the damselfly youth, are thinner, with three tail-like gills. Larvae of the moth-like caddisflies construct a home in a hollow twig or make one of leaves for their protection in the pond. The red worm-like larvae of midges, often called "bloodworms," stay in the muck in the bottom. Only the strange-looking transparent phantom-gnat young are actually swimming in these cool waters.
Besides the insects, we find minute snails, clams, worms, water mites and water fleas. As always, there is a large and diverse population of organisms beneath the ice of the January pond, showing us how healthy the pond is and letting us look forward to our spring visit.
Larry Weber is author of several books that are available now: "Butterflies of the North Woods," "Spiders of the North Woods" and "Fascinating Fungi of the North Woods." He lives in Carlton County and teaches natural science at Duluth's Marshall School.
