By Jim Bloch
Michigan residents cherish their Great Lakes. The five lakes — Huron, Michigan, Superior, Erie and Ontario — make up the most expansive fresh water system on Earth. They contain 21 percent of the world’s fresh surface water and 84 percent of the fresh surface water in North America. The lakes are omnipresent in the state’s daily and cultural life. Michiganders are never more than six miles from a lake, river or stream and never more than 85 miles from a Great Lake. “The Great Lake State,” proclaims state license plates. Or: “Water Winter Wonderland.” Residents, regardless of political persuasion, uniformly support keeping the lakes drinkable, swimmable and fishable — keeping a Pure Michigan.
But underneath the seven states and two provinces the make up the Great Lakes watershed lies a body of groundwater large enough to fill Lake Michigan, nearly 1,200 cubic miles of fresh water.
Groundwater is critical to the health of Great Lakes and the health of the basin’s inhabitants.
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Groundwater in the Great Lakes Basin directly accounts for nearly three percent of the direct inflows to the lakes and 42 percent of the indirect flows. If properly protected, the long-term seepage of rain and snowmelt into deep underground aquifers functions to purify the water and keep the rivers and lakes it feeds clean and healthy.
Except for a relative handful of spots where it burbles to the surface in the form of springs, groundwater remains hidden from sight.
But beneath the backyards, sidewalks, roadways, farm fields and forests of the Great Lakes Basin lays enough groundwater to constitute a sixth Great Lake.
It may be impossible to walk on its beaches and discern a sunset over its horizon lines, but groundwater is the source of drinking water for about 45 percent of the Michigan population via public water systems — more than any state in the country, about nine percent — and private wells.
Groundwater is equally important globally.
Just over one percent of the world’s fresh water is held in lakes and rivers. But 30 percent of it is contained in groundwater. (More than two-thirds is bound up in glaciers and the ice caps.)
Groundwater is an endangered resource, according to “Groundwater: Michigan’s Sixth Great Lake,” a study published in June by For the Love of Water, a nonprofit organization dedicated to protecting public water resources in the Great Lakes region.
“In Michigan and across the U.S., groundwater is seriously polluted, threatened, and in some areas, entirely unusable,” said FLOW.
Groundwater and surface water are inextricably interlinked, each feeding the other in the overall water cycle that defines life on Earth. Surface water is protected by a variety of laws, perhaps most notably by the federal Clean Water Act.
There is no comparable legislation protecting groundwater, even though its poisoning can mean the poisoning of the streams, rivers and lakes it feeds.
Introduction to groundwater
When it rains and when snow melts, the water runs off the land into surface waters or it seeps into the ground, where it can sustain plants or evaporate. What’s left may find its way down to the water table, which lays above a layer of clay or porous rock and, in turn, feeds the soil and plant life.
Excess water, pulled by gravity, descends slowly into the crevices in the rock or clay. These water-imbued rock formations are known as an aquifers. Just below the water table, an unconfined aquifer may take days or years to recharge. Deeper down, glacial or drift aquifers consist of small organic materials, sand and gravel; it may take centuries to recharge, largely from precipation, about a third of which may reach the drift aquifers.
Below the glacial aquifers are bedrock aquifers where sandstone or limestone contain water; fed by glacial aquifers, bedrock aquifers may take thousands of years to recharge.
Helped along by gravity, water moves in a generally horizontal fashion through the aquifers in search of a lower, open body of water in which to discharge. In sand, water may move three to four feet per day; in clay, it may move inches per day. FLOW estimates that about 40 percent of the water tumbling through streams and rivers originates as groundwater.
In Michigan, groundwater feeds clean, cold water to trout streams like the Jordan, Au Sable and Manistee rivers, as well as natural springs and spring-fed lakes, such as Higgins Lake in Roscommon County.
Groundwater flows sometime create unusual natural phenomena such as fens.
“Fens are peat-forming wetlands that rely on groundwater input and require thousands of years to develop and cannot easily be restored once destroyed,” according to the U.S. Forest Service. “Fens are also hotspots of biodiversity. They often are home to rare plants, insects, and small mammals.”
The Nature Conservancy’s protected Grand River Fen, south of Jackson, is one source of the headwaters of the Grand River, Michigan’s longest river at 260 miles, which runs north through Lansing before heading west to Grand Rapids and emptying into Lake Michigan at Grand Haven.
To protect groundwater, it’s necessary to understand the threats to it. That’s where we head in Part II.
Jim Bloch is a freelance writer based in St. Clair, Michigan. Contact him at firstname.lastname@example.org.