Lake Life Cycle

By Timothy S. Dmoch staff writer

Like living creatures, lakes are born, mature, decline in their old age and eventually disappear.

But while living organisms complete their life-cycle in the span of a few decades at the outside, the life-cycle of most lakes stretches across several millennia. Since their creation by glaciers thousands of years ago, Oakland’s lakes have continued along an evolutionary trek toward death called eutrophication, the natural aging process that all lakes undergo.

The eutrophication process begins when algae blooms, weeds, and other organic matter decay and settle to the bottom of a lake. Combined with dust and mineral deposits, the decaying vegetation builds up from the lake bottom forming sediments. As the lake slowly fills up around its edges, it becomes smaller and smaller until it has been filled in completely.

According to Dr. Clifford Humphrys, professor emeritus in the Department of Resource Development at Michigan State University, the state had as many as four million lakes following the last period of glaciation. But the slow process of natural eutrophication has filled in most of those lakes, creating swamps and wetlands that now tinge the landscape.

Dr. Wally Fusilier, a freelance limnologist (lake scientist), agrees that most of the wetlands existing across Oakland County and the state are the remnants of ancient lakes.

“We know that the process of eutrophication has been occurring in Michigan over millions of years,” Fusilier said. “Essentially, all the wetlands that you find were lakes at one time, formed thousands of years ago by glaciers. We know that most wetlands were once lakes by drilling deep beneath the wetlands and looking at the native soil and glacial till below them.”

Humphrys said inland lakes in general began as sterile, shallow basins void of any significant plant life. Gradually, algae began to bloom along the lakeshore in shallow water. When this first generation of vegetation that grew around the lake’s perimeter died, the process of eutrophication began.

“The plants began to die and withered into the water,” Humphrys said. “The vegetation began to decompose in the warm, shallow water. The warm water around the lakeshore also encouraged the growth of bacteria, which also accelerated the decomposition of organic matter.”

But Fusilier said while bacteria help speed up the decay of organic matter, they also consume most, if not all of the oxygen in the water and eventually halt the decomposition of dead vegetation.

“Bacteria thrive in warm water. Their production rate will double with every 10 degree centigrade increase in temperature,” Fusilier said.

“With all those bacteria working like bastards, they depleted oxygen from the shallow water. The lack of oxygen in the water prevented the organic matter from completely decomposing, so it settled at the bottom of the lakeshore.”

The partially decayed organic matter served as an excellent fertilizer, which encouraged the growth of a greater number and size of plant life, according to Humphrys. Eventually the rooted vegetation also died and slumped into the water, and the process of partial decomposition and formation of another layer of sediment on the lake bottom began.

“Once enough plants die and partially decompose to fertilize the lake bed, the process of eutrophication really begins to accelerate,” Humphrys said. “But we’re still talking about a process that takes about 5,000 to 10,000 years to complete.”

Fusilier said repeated cycles of plants growing, dying and then partially decomposing around a lake’s edges, a sort of vicious circle, will continue over thousands of years until the lake has been transformed into a wetland. For reasons that -limnologists still don’t understand, the eutrophication process begins to slow to a snail’s pace when the lake reaches the wetland stage.

“We still don’t know exactly how the wetland makes it to a dry land stage,” Fusilier said. “Once the lake has become a wetland, it stays that way for a very long period of time. It seems that organic decomposition and plant reproduction in the wetland stage are at an equal rate. Thus a balance is maintained, and the wetland is filled in very, very slowly?’

The final stage of eutrophication is the deposit of wind-blown dust into the wetland, according to Fusilier. Humphrys agreed that dust, leaves from nearby trees and other organic material make up the final layer of sediments that eventually cause the wetland to disappear.

While the previous detailed eutrophication process is the way lakes in general slowly fade away, Humphrys and Fusilier said many lakes of southeastern lower Michigan, including many of the lakes that were once in Oakland County, vanished in a slightly different way.

Fusilier said in the mid-1980s he discovered that most of the lakes that disappeared in southeastern Michigan and Oakland County were characterized by significant calcium carbonate deposits. He said he stumbled onto the discovery while visiting a friend who was digging out a wetland to create a lake near Dexter, Mich.

“The first layer on the top of the wetland appeared to be Houghton muck; pure organic material forming muck from top to bottom,” Fusilier said. This first layer of muck was about 10 to 12 feet deep. But below that initial layer of muck was a layer of pure white calcium carbonate. This layer was also about 10 to 12 feet deep. The final layer beneath the surface of the wetland was native glacial till that was deposited about 10,000 years ago.”

While some of the lakes in the area certainly followed the previously described eutrophication process, Fusilier believes that many of the lakes in the county that eventually vanished were given a head-start in the normal eutrophication process by their calcium carbonate deposits.

“The calcium carbonate deposits came from the soils surrounding the original lake basing’ Fusilier said. “These calcarious barns (soil) had carbonates in them that were dissolved by groundwater and transported to the sterile lakes.”

Over a period of approximately 7,000 to 10,000 years, Fusilier said many of the county’s former lakes began to fill in around the edges with calcium carbonate deposits. He said it’s these deposits that created the “drop-offs” in the lakes that still exist today.

Fusilier says “the purpose of lakes is to disappear," but he warns lakefront property owners that they shouldn’t be able to detect a change in their lake water quality during their lifetime. He said eutrophication is supposed to be something that occurs on a geological time scale, not over a few decades.

Humans can greatly accelerate the process of euthrophication by adding unnatural levels of nutrients to a lake’s water and Fusilier said the most common way of turning up the eutrophication burners is allowing fertilizer to run off into a lake.

“Once the nutrients enter the lake, they just stay there and can never be removed,” Fusilier said. “The nitrogen and phosphorus in fertilizer runoff causes weeds to grow and algae blooms to develop, which will eventually die and settle to the bottom of the lake. When these forms of vegetation decay, they consume oxygen from the lower depths of the lake. Without oxygen, the bacteria that decompose organic material can’t survive, and partially decomposed vegetation will form the sediments that start to fill in the lake.”