Dying Lakes

Far out on Douglas Lake in northern Michigan, a crew of limnologists (the fresh-water equivalent of oceanographers) in a boat raised core samples from the bottom and tested the oxygen content of the deep. The results, carefully evaluated in the laboratory on shore, were disturbing. At 10,000 years of age, Douglas Lake was past its prime, and slowly dying. In a few more thousand years--a mere split-second in geological time--this haunt of fishermen will be gone, with nothing but a bog to mark its grave.

In the view of Indiana University Limnologist David Frey, 45, who last week passed sentence on Douglas Lake, almost every fresh-water lake in the world awaits the same unhappy fate. Like humans, says Frey, lakes grow old and inevitably die, in a predictable life span that man himself is abbreviating.

Phantoms in the Depths. Most of the earth's fresh-water lakes were deposited by glaciers 10,000 years ago. In their youth they were clear, silt-free and oxygen-rich. But with the passing of centuries came the infirmities of age. Land erosion, the death of billions upon billions of microscopic organisms inexorably added silt to the lake beds at a measurable (though varying) rate of some 18 in. a century. Summer heat warmed the upper layers of water, upsetting the normal turbulence that sends life-giving oxygen to the deepwater fish and other life.

In this cumulative process, Frey predicts, the oxygen content eventually will fall past the point--three parts oxygen to one million parts water--below which deepwater fish cannot survive. Limnologist Frey has discovered evidence of this in an increasing population of the red "blood" midge, a mosquitolike larva that can get along fine on far less oxygen than its more demanding green and brown brothers. In Douglas Lake, Frey's crew also brought up a few "phantom" midges, near-transparent larvae that can reach adult stage without any oxygen at all for long periods at a time. As the air supply decreases, the rate of muck deposited increases, eventually suffocating the lake in a tangle of vegetation.

Man himself contributes to the morbidity of his lakes by dumping in prodigious quantities of sewage and other wastes, which not only themselves increase sedimentation, but are rich in phosphates and nitrates--favorite food of algae and underwater vegetation whose accelerated growth hastens the end.

Another Glacier. The aging process can be checked, but at high cost. Near Detroit, senile Long Lake, which has silted in spots to within 2 ft. of the surface, is being dredged to 14 ft.--at a cost of $100,000 for a lake only 146 acres in size. Outside Indianapolis, Bacon Swamp, which once was a lake, is getting similar dredging treatment. Algaecides are also helpful, says Frey, and so is bubbling-in oxygen during a lake's stagnant summer months. But such processes are expensive, and practical only on small lakes.

"Unless means are found to arrest or reverse the aging process." says Frey, "we may have to depend on the arrival of another glacier to produce a fresh crop."

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