**3.7 The North American Great Lakes and groundwater**

The Great Lakes in North America provide unique freshwater resources for humans, plants, and animals. Many small tributaries drain directly to a large lake, but in some geologic settings, groundwater discharges into Lake Michigan through

**Figure 7.**  *The location and scenery of the Bob Marshall Wilderness. Source: gravel.org.* 

 sedimentary rock and breach ridge sands. In Door County, Wisconsin (**Figure 8**), coastal springs and wetlands provide ecotones for rare species like the Hine's emerald dragonfly and unique orchids, such as lady's slipper. The Ridges Sanctuary was created in 1937 to sustain plant and wildlife in an area that was rapidly developing to accommodate tourist demands. Near-shore areas were being developed for lodging and food and drinking establishments. Given the high tourist value of Door County, Wisconsin, today, it was possible for people to love the place to death. Specifically, if groundwater recharge areas were paved and rain water redirected to streams, ecosystem services would have been lost. Fortunately, visionaries like Albert Fuller sounded the alarm to the general public and raised awareness to preserve an 18-Ha parcel of land from future development. Over time, studies in Door County, Wisconsin, have provided more information about the natural resources and the need for local government to place restrictions on land development. Groundwater flows from higher ground underlain by dolomite toward Lake Michigan at a rate approaching a cm/second [22]. The large lake waves can push water and sediment back unto the land; over time this process has created sand dunes. At the Ridges Sanctuary, there are a series of dunes with swales, between the dunes are wetlands that provide critical habitat for plants and animals.

Along the north shore of Lake Superior, the geology is metamorphic and gives rise to steep gradients within a kilometer of the shoreline, which differs from the relatively flat shoreline of Door County. The water that infiltrates the shallow soil

*Sustainability of Human, Plant, and Aquatic Life: A Theoretical Discussion from Recharge… DOI: http://dx.doi.org/10.5772/intechopen.86171* 

#### **Figure 8.**

*The location of Door County in Wisconsin, an aerial view of the Ridges adjacent to Lake Michigan and vegetation. Source: map.co.door.wi.us., mnnps.org.* 

and moves downgradient toward Lake Superior resurges where the soil becomes too thin over the bedrock. Glacial Lake Duluth left behind linear zones of sediment: some beach sands and other lacustrine silts and clays. In Amity Creek before branches converge, the valley slope flattens, and alluvial material creates an active flood plain over bedrock. In June of 2012, after a year of data collection from the stream and alluvial aquifer, a large magnitude storm event dropped over 15 cm of rainfall in a half-a-day. This event not only flushed channels; it displaced preexisting snowmelt water contained in the riparian aquifer [23]. We have further noted a complete groundwater flushing from the same storm event in the Cross River watershed [24]. The data gathered from these two watersheds indicate a lack of resilience to climate change. To maintain sustainability for the high-valued tourist region, infrastructure development along the north shore of Lake Superior must be constrained to prevent the loss of ecosystem services. All levels of government will need to agree on the vulnerability of the region.

 In the Nemadji River basin, lake sediment dominates the movement of groundwater (**Figure 9**). The west end of Lake Superior was formed by beach ridges laid upon coarse till, whereas the central part of the valley is composed of loose lacustrine silts and clays that settled when glacial Lake Duluth drained to the east. This sediment deposition pattern creates a unique groundwater flow system. Water recharges rapidly through sand and gravel in the headwaters but then builds up pressure as it tries to find a discharge path into the Nemadji River. Because there is over 25 meters head drop from the headwaters to the main valley, the valley walls are under hydrostatic pressure and ooze water through the lacustrine silts and clays. Bank and bluff geotechnical failure are a natural phenomenon that creates a continuous turbid water clarity in both discharging groundwater and surface water [25].

The loss of large perennial trees and conversion of land to managed grass crops altered the hydrologic evapotranspiration regime which, in turn, increased runoff and concordant river sediment regime. The Nemadji River system is the most productive trout fishery in Western Lake Superior, but channel bed downcutting has the potential to create fish barriers and block trout migration. Long-term aquatic

#### **Figure 9.**

*The location of Lake Duluth on the west end of Lake Superior and illustration of groundwater flow paths southeast of Lake Duluth, Minnesota, in the Nemadji basin [25]. Source: Google Images and Magner PowerPoint.* 

life sustainability will depend on land use management and then enhances evapotranspiration, reduces runoff, channels enlargement, and allows for fish passage culverts.

#### **3.8 Trapped groundwater: mining the Buffalo aquifer**

 Connate water is water that is not actively part of the water cycle but groundwater contained or trapped in the earth's crust from some previous time period. In the northern latitudes of North America, Europe, and Asia, this may be frozen groundwater or water left behind in a buried aquifer when glaciers retreated toward the Arctic region.

 Climate change in the Arctic region may be liberating frozen groundwater today that has been contained due to a lack of any hydraulic head to move the water toward discharge.

Magner and others [26] used isotopes to estimate the age of water contained in a buried sand and gravel aquifer embedded in the lake clays left behind by Glacial Lake Agassiz. The City of Moorhead, Minnesota (**Figure 10**), needed to expand their water supply and began pumping tests to determine the sustainability of the Buffalo aquifer. The results suggested the high-capacity water abstraction would lead to groundwater mining; thus, the city focused their water supply efforts toward the Red River of the North. Nevertheless, single-family homes with small domestic water demand could pull water from buried sand and gravel. Over a long *Sustainability of Human, Plant, and Aquatic Life: A Theoretical Discussion from Recharge… DOI: http://dx.doi.org/10.5772/intechopen.86171* 

**Figure 10.**  *The location of Moorhead, Minnesota, and domestic water. Source: claycountymn.gov and valleynewsalive.com.* 

 period of time, very slow-moving groundwater would likely replenish the buried aquifer water volume; however, this may take millennia. The city of Moorhead, Minnesota, made the right and sustainable decision; however, in California, parts of the Central Valley are sinking as both farms and cities pump harder and drill deeper wells to extract groundwater. The California groundwater is estimated to be 15,000–20,000 years old [27]. This is perhaps the best example of a truly unsustainable groundwater use in the world.
