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.