Forest Preserve District of Cook County, Illinois
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The Life History of a Pond
Nature Bulletin No. 617    November 12, 1960
Forest Preserve District of Cook County
Daniel Ryan, President
Roberts Mann, Conservation Editor
David H. Thompson, Senior Naturalist

THE LIFE HISTORY OF A POND
In the Palos division of the Forest Preserve District there is an extraordinary number of ponds and sloughs Many were created by damming the outlets from wet places; some were originally farm ponds that we have restored. The largest and probably oldest pond is located in Swallow Cliff Woods, west of the picnic area in a grove of white pines planted about 40 years ago.

The pond is dying. Like most others, if undisturbed, after fifty years or so it will be forgotten because in its place there will be trees willows, cottonwoods, soft maples, and probably swamp white and bur oaks. Indeed, at one time it had already filled up until, after being drained by tile, corn was grown there.

Then we acquired the property and, about 30 years ago, built an earthen dam across the outlet -- a narrow ravine That restored the pond but, since no spillway had been provided for the overflows, most of the dam was washed away and the water became very shallow, with dense stands of cattails and other aquatic plants along the shores Now it is dry. There has been mighty little rain since July. We probed the bottom at several places with a 6-foot rod and easily pushed it down through the black muck until out of sight. Evidently this pond was far deeper when it was born.

At that spot, some ten or twelve thousand years ago when the last glacier melted away, a huge chunk of ice must have been left behind and surrounded by glacial drift: clay, boulders and debris When the chunk melted it left a deep pocket filled with water, in the moraine This lake found an outlet, possibly a low place in the rim of the pocket, where it overflowed northeasterly to the Sag valley.

As that outlet eroded and gouged a deep ravine through the moraine, the water level dropped. The sides of the pocket, thus exposed, also eroded and gradually became slopes. That material washed into the lake. As primitive plants and eventually trees covered the slopes, fallen leaves and other dead vegetation washed into it also decomposing animal matter. Thus, during the centuries, the bottom was covered with ever-thickening deposits of fertile material.

Meanwhile, aquatic plants had invaded the lake and that was the beginning of the end. They hastened the long slow process of filling in. The lake became smaller and shallower until it was a mere pond -- a dwindling pond.

First to appear were microscopic forms of plant and animal life, followed by filmy threads of algae, and these multiplied enormously. Then came submerged floating plants with no roots, notably hornwort or coontail and bladderworts. Each year, in its deep areas, a large pond produces tons of them in underwater meadows that sink to the bottom when winter comes Decomposing, they add to the fertility of the bottom but subtract from its depth.

Toward the shores of such ponds but in fairly deep water, tangled masses of submerged plants stream upward from their roots on the bottom: various kinds of pondweeds, eelgrass, and elodea or waterweed. In shallower water, about knee-deep, there may be tall slender bulrushes and plants with floating leaves: the yellow-flowered spatterdock and the white water lily Closest to the shore, in shallow water or in mud, are dense stands of plants such as reeds, arrowhead, sweet flag, pickerel weed, water plantain, and a host of different kinds of sedges and marsh grasses. Towering above them are the cattails. As a pond dies and becomes dry each summer, these shore plants take possession of it.

The Swallow Cliff pond is unique. To preserve its scenic and educational values we must deepen it and build an adequate dam, with a spillway at the outlet.


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