By Grace Lovins
Beneath the serene surface of Oakland County’s 400 – 1,400 lakes lies a story millions of years in the making. Shaped by the powerful forces of retreating glaciers, these inland lakes are not just natural wonders but vital lifelines for local ecosystems.
Each lake, whether naturally formed or human-made, plays a crucial role in sustaining biodiversity and, especially in Michigan, supporting community. Uncovering the ecological significance of these waterbodies highlights their importance not just for the aquatic life and wildlife in and around them, but for the people that have grown to depend on all they have to offer.
The story of the basins and depressions that came to be Oakland County’s lakes began millions of years ago during the last ice age which covered most of North America in a sheet of ice. Explained by the Lakehead Region Conservation Authority, roughly two million years ago, the Earth had cooled to a point where glaciers were able to form.
During the last glacial period, known as the Wisconsinan Glaciation, the cold climate allowed the Laurentide Ice Sheet to form covering Canada and most of the United States. As temperatures began to rise again towards the end of the glacial period, the ice sheet retreated leaving depressions, or basins, in the ground that eventually filled with water, said Michigan State University Professor Emeritus of Ecosystem Ecology and Biogeochemistry Steve Hamilton.
A retreating ice sheet is responsible for thousands of lakes that Michiganders, and Oakland County residents, enjoy today, none more well-known than the five Great Lakes. What makes the formation of the Great Lakes different than the formation of the smaller lakes in Oakland County, according to Joel Edgerton of Kent State University, has to do with the movement of the tectonic plates below the lakes and the magnitude of the basins carved in the Earth by the ice sheet.
In the case of the Great Lakes, the immense weight and pressure of the ice sheet pushed down on the Earth’s crust effectively carved out enormous basins in the bedrock, a process partly supported by pre-existing rift valleys resulting from tectonic movement some millions of years prior. These basins filled with melting ice when the glaciers began to retreat, leading to the creation of the world’s largest freshwater lakes.
This process took thousands of years and the lakes, Edgerton explained, throughout that time transformed through different stages as the glaciers grew and receded.
Not all lakes were created equal. Inland lakes seen in Oakland County and scattered around the state, while having been formed by glaciers, did not go through as intense of a process as the one that formed the five Great Lakes. Rather, the retreating ice sheet left smaller depressions and basins that were eventually filled with water, becoming the state's inland lakes.
There are various types of inland lakes that were formed in the Great Lakes region after the last glaciation, including proglacial lakes, glacial outwash and glacial scour lakes, noted Edgerton.
Many of the naturally occurring lakes seen in Oakland County, explained Nicole Wagner, professor of biological sciences at Oakland University, are categorized as kettle lakes. These lakes form when a glacier recedes and a block of the ice breaks off, remaining in the same spot. As the ice melted, a depression formed in the land from the water and debris, creating a basin, known as the kettle, and eventually when it filled with the glacier water it became a lake.
Just as not all lakes were created equal, not all lakes were created by nature. Some lakes and waterways seen around Michigan, and all around the country for that matter, were created by humans, be it for recreation, industry or lakeshore development.
Wayne State University professor of civil and environmental engineering Carol Miller stated that manmade lakes are commonly a result of the desire for aesthetically pleasing areas and increased property value.
“Often homeowners will get together and say, ‘This land would be worth more if this was turned into a prominent wet area like a lake and if we could create a lake, then we have waterfront property for our home rather than just wet soils for our front yard,’” Miller said.
On top of boosting property values, the creation of artificial lakes can provide recreational opportunities for residents either living on the lake or around it.
Historically, however, lakes were artificially created for industries like logging during the 1860s to the early 1900s, said Jo Latimore, aquatic ecologist and outreach specialist in the department of fisheries and wildlife at Michigan State University’s College of Agriculture and Natural Resources. These artificial lakes can also be created for electricity production through hydroelectric dams, she explained. Because moving water can generate a lot of electricity, major dams were put on larger rivers in Michigan, which caused new lakes to form as a result of the water backing up behind the dam.
Lakes created by the water backing up behind a dam are called reservoirs. There are different types of artificial lakes but the most common one seen in Michigan, according to MSU professor emeritus Hamilton, is a reservoir.
“Many Michigan lakes have also been fundamentally changed as a result of water level regulation, typically in the form of a dam at the point of outflow to a stream or river. Often this entails stabilization of fluctuating water levels, and an increase in the water level to allow for boat recreation and lakeshore development,” Hamilton said.
“Given that most man-made lakes in Michigan are reservoirs, they differ from most of our lakes because they have a river flowing through them. Reservoirs are commonly flushed by river water flowing through them more than other lakes, and they are subject to fluctuating inflows,” he continued.
Fisheries biologist with the Michigan Department of Natural Resources Cleyo Harris explained that, while most of the county’s lakes are formed naturally – including Cass Lake, Orchard Lake, Union Lake, Deer Lake and Maceday Lake – there are a large number of lakes in Oakland County that have a manmade water level control structure, such as a dam that keeps the water levels at an elevated state. Some of these dams are large enough that they expanded the dimensions of the original natural lake, Harris said, citing Lake Oakland as an example.
Few true reservoirs exist in Oakland County where the dam has caused the creation of a lake, but there are some, including Kent Lake and Stony Creek Lake, he said.
Although the creation of artificial lakes may have a positive impact for humans, that’s not always the case when it comes to the ecosystem. The creation of artificial lakes can have drastic impacts on the aquatic life and wildlife around it as the entire ecosystem is effectively being changed from a marsh, swamp or field into a lake.
WSU's Miller explained that some of the methods used to create artificial lakes – groundwater augmentation and well augmentation – can create issues in terms of overuse of some individuals’ water supply.
“Using groundwater to maintain the artificial lakes levels can be damaging to the environment because groundwater is used in some rural areas for drinking water,” Miller said.
On top of this, she noted that the flooding of areas to create an artificial lake can drown out vegetation and trees, causing the natural fauna to die off which leaves the wildlife without a source of food or a habitat.
“Obviously, the wildlife changes, whether it be rattlesnakes and frank that maybe used to be in the smaller swamps or marshes in an area that now have a fully flooded area. I’ve seen that happen before, so there will be changes to the land surface of maybe a region that is sort of a damp soil region to one that’s a lake area,” she said.
Miller also acknowledged that there can be ecological differences between artificial lakes and naturally occurring lakes depending on the type of water. She explained that lakes mostly fed by rainfall and surface runoff have a certain water quality and a certain pH level, whereas a lake relying on groundwater, such as an artificial lake, being pumped up to the surface may be more brackish. This could create a discrepancy in the types of fish and wildlife that the lakes are able to support.
Lakes, both naturally occurring and artificial, go through an evolutionary cycle, or life cycle, from formation to youth asnd maturity, then old age and a process that ultimately ends with the “death” of the lake.
Latimore of MSU's Department of Fisheries and Wildlife explained that when these lakes were first formed thousands of years ago, during the very young stages of the lake’s life, there wouldn’t be a lot of life, meaning the water would look clear and there would not be much, if any, organisms growing just yet.
“Our natural soils and geology in Michigan have enough nutrients to feed the primary producers, things that photosynthesize algae and plants, so between the photosynthesis they would do from sunlight and the naturally occurring nutrients in our soils, you would get plant life starting to arise,” Latimore said.
According to Hamilton, over the course of thousands of years since the glaciers retreated, many of the lake’s basins have also gradually filled with sediment from the watershed, organic matter that is produced in the lake and marl – a calcium carbonate that is precipitated out of the lake’s water which is important in groundwater fed lakes. Ultimately, he said, a lake basin that starts off relatively shallow may fill in to the point where it essentially becomes a wetland that supports aquatic life.
Once plant life is able to be supported, the lake would then be able to support microscopic animals, like plankton, that can feed invertebrates and smaller fish which leads to bigger fish being able to thrive. At this point, an entire ecosystem could initially form, explained Latimore.
This process is by no means quick. “The aging of lakes since the retreat of the glaciers has been a slow process taking over thousands of years,” Hamilton noted.
During the aging process, lakes experience a natural ebb and flow of short-term changes. While we likely won’t be around to witness the eventual old age and “death” of the state’s lakes, we certainly can have a hand in speeding up the process.
The experts – Wagner, Latimore, Miller and Hamilton – each explained that human influence has had a negative impact on the natural evolution of lakes. Land conversion, lakeshore development and runoff can hinder the natural evolution of lakes and cause premature aging.
“Soil erosion in Michigan was probably most important in the late 19th and early 20th centuries resulting from deforestation and poor agricultural practices,” Hamilton pointed out. During this time, the addition of organic matter like manure and fertilizer intended to help increase the production and health of crops seeped into the waterways from rain and irrigation.
A group of researchers with the Michigan Applied Public Policy Research Program, through the Institute for Public Policy and Research, also reports that pesticides and other toxins that make their way into lakes and waterways from agricultural areas impacts the growth of aquatic organisms and the quality of the lake water. Over time, these poor practices have been identified and reduced, but not completely removed from the equation. Additionally, as areas become more established, growing in population, the need for more houses and businesses grew. This created issues between the natural landscape and the increased in human development.
“Where the problem really is, is land use and how we’re developing the landscape, and in most cases in Michigan, that means converting what once was forest or potentially grassland into residential areas or businesses,” Latimore said.
Disturbances in the shoreline and the runoff of pollutants and sediment from surrounding developments, the main culprit being fertilizer, that make their way into the water may lead to quicker eutrophication of the lake. This in turn accelerates the lakes life cycle leading to a quicker “death.”
On the other hand, while disturbances to the lakeshore as a result of land development and pollutants from development and industry can accelerate a lake’s natural aging process, Latimore said. However human use of the lake for recreational activities, like swimming or kayaking, does not have a great impact on the aging of the lake.
“In extreme cases, for example, if there’s a lot of high-speed wake boats operating in shallow areas that cause a lot of disturbance to the lake bottom and get stirred up and muddy looking, stuff like that could release more nutrients into the water column which leads to more algae and plants and moves things around,” Latimore said. “But most of our behaviors or recreation is not the problem.”
Latimore also explained that it’s incredible difficult to know exactly how much time a lake’s life cycle is being decreased by as a result of human activity. Given that the natural aging process of a lakes takes thousands upon thousands of years, human interference has only been present for a very small fraction of the lake’s actual life span.
As lakes mature over time, moving closer to the end of their life cycle, there are observable differences in the aquatic life, lake depth, temperature and water quality among other characteristics.
The National Geographic Society explains that a lake’s plants and algae will slowly die and float to the upper layers of the lake where they will decompose and sink back down to the bottom of the lake basin. They note that dust and other mineral deposits on the bottom of the lake will combine with plant matter to form sediment which, coupled with sediment from rainwater runoff like pebbles and the remains of fish and other animals piled at the bottom of the lake, which causes the lake to shrink.
MSU's Hamilton stated the depth of the waterbody can have an impact on how long this process takes. The same is true for the water quality and aquatic life found within a lake. Runoff from homes and agriculture such as fertilizer can cause the plant life inside the lakes to grow at an accelerated speed, which in turn accelerates the buildup of sediment.
The Michigan Inland Lakes Partnership, based out of Michigan State University, writes that the most natural factors in the aging process of a lake are constantly fluctuating. Plant growth is not always consistent, and neither is the population of fish and other organisms. However, the actual state of a lake’s life cycle is determined by recognizing the overall long-term changes in lake productivity.
The “death” of lakes comes when the waterbody has reached a point of eutrophication, noted Wagner of Oakland University, which is caused by an overabundance of nutrients like nitrogen and phosphorus. National Geographic explained that these natural processes will cause the lakes to become smaller and smaller, starting from the shorelines and working inward towards the middle, until they eventually become some type of wetland like a marsh, bog or swamp.
With the most commonly seen lake in Oakland County being a reservoir, MSU's Hamilton said, pollution can happen quickly depending on how long the water remains in the reservoir itself, which accelerates the natural timeline.
“If the water spends more than a week or so in a reservoir and if the river carries high concentrations of nutrients from human sources, reservoirs can be extremely productive and as a result they often present problems with eutrophication,” he continued.
While this doesn’t mean that a lake's “death” is imminent, not being mindful of how human interference can negatively impact the surrounding waterbodies can certainly accelerate the process.
Human interference doesn’t just pertain to development and runoff. Some artificially constructed interventions, such as dams that formed lakes behind them, can have long-term consequences. Unless carefully maintained or redone, these structures will eventually begin to crumble, potentially leading to a sudden influx of harmful pollutants into the waterbody.
“Ultimately, all dams will have to be removed or rebuilt, and the presence of decades and accumulation in the reservoir can make this a very costly endeavor,” Hamilton said. The cost only increases if there are contaminants which form historical water pollution, he said, as is often the case in areas where there was industrial activity.
Aside from cost and pollution as long-term implications of these artificial structures, artificial lakes themselves can have significant long-term consequences relating to changes in the nutrient cycle, erosion, water quality and hydrology.
As Professor Miller of Wayne State University previously stated, some artificial lakes are created by tapping into groundwater in order to flood an area that has been excavated. This can lead to groundwater depletion over time, affecting the water table and creating issues for surrounding vegetation, ecosystems and people that depend on groundwater or well water for drinking. These artificial waterbodies may also create problems with water quality as a result of increased nutrient levels and potential contamination, she said. If these lakes are potentially contaminated but are used for recreation, this may create health concerns.
Likewise, polluted water in a lake can cause the plants and aquatic life within the water to suffer. On top of the biodiversity impacts, in the long term this can create issues with species composition, Miller said.
It can be overwhelming to think about all the ways that human activity can negatively impact the natural world around us, especially when it comes to such complex ecosystems like lakes. However, recognizing the implications of our practices is the first step to becoming good stewards of our land and resources.
“It’s fun to think about what we know about how lakes are formed and how they function and how we can translate that to being better stewards of our lakes and taking better care of them,” Latimore, the aquatic ecologist, said.
By understanding the history and science behind Oakland County’s lakes, we can appreciate their importance and work towards preserving their health for future generations. While the lakes provide recreational opportunities, boost property values and support local communities, they also face threats from pollution, land development and, of course, the changing climate. Finding the balance between humans and lake ecology, with informed stewardship, can help to maintain the natural beauty and utility of our lakes.
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