Lakeshore Living: Designing Lake Places and Communities in the Footprints of Environmental Writers

Chapter 1. Lake Parts

11 CHAPTER 1 Lake Parts It has been estimated that there are about three million lakes greater than 25 acres (0.1 square kilometers) on the planet. These lakes are not distributed evenly over the world’s landmasses. Earth’s north temperate zone, including North America, is lake rich; Minnesota is called the land of ten thousand lakes, and Finland is called the land of thousands of lakes. Canada has over thirty-one thousand large lakes, and about 9 percent of the country is covered by freshwater. In North America, the highest densities of lakes are in the northeast and areas associated with glaciation. The continent’s lakes are diverse in both size and character , ranging from small, fertile water bodies to the Great Lakes. People through the ages have been attracted to lakeshore living. We are attracted to lakes for food, home, and solace. PHYSICAL FEATURES OF LAKES Lakes are places. Lakes are made up of living and nonliving things. They are more than pools of water. Lakes are ecosystems that connect to other systems. Understanding lakes begins with understanding their basic elements. First, a lake includes a large amount of water, though what constitutes a large amount of water is arbitrary. The line between lakes and ponds is a fuzzy one. If you’ve spent time on Lake Superior, the world’s largest lake by surface area, your perspective may be different than someone who has never experienced big water. Ponds are often characterized by shallow water, where light penetrates to the bottom, and they lack waves. Using this definition of a pond, Henry David Thoreau’s Walden Pond, located in Concord , Massachusetts, is actually a lake. (Every New Englander might know that Walden Pond is a lake, but its name can confuse people from other areas.) Walden Pond is a deep (102 foot; 31 meter), small (61 acres; 25 hectares) lake formed by glaciers over ten thousand years ago. Most of the world’s lakes are small; however, about 9 percent of the lakes account for about 60 percent of the total lake surface area. Second, a lake’s boundary is defined by its shoreline. Shorelines are dynamic places. Waves smooth out irregularities and deposit fine sediment in quiet areas, and water levels rise and fall with changes in the hydrologic cycle. At the open shore, trees and shrubs fight to reach the sun and to hold the soil at their roots. Lakes in a glacial outwash plain may have sand and soft sediment shorelines, whereas lakes situated in areas of glacial till often have rocky shorelines. The length of a lake’s shoreline is dependent on the scale of measurement (measuring with a ruler produces an estimate larger than that measured with a yardstick), and based on the 12| North American Lakes mathematics of Benoit Mandlebrot, one could also say that the length of a lake’s shoreline is nearly infinite. With regard to fish and wildlife habitat, the shoreline generally refers to the narrow band around the lake centered on the land–water interface. Third, subsurface, surface, and atmospheric water systems contribute water to a lake and can be considered parts of a lake. Beginning with these basic elements, lakes have a rich set of physical features that we can explore. Lakes receive water from precipitation, inlets, and groundwater, and lose water by evaporation, transpiration, outlets, and seepage to groundwater . Hydrologists can determine a lake’s water balance by estimating inflow and outflow from all sources. Except for very large lakes, precipitation contributes generally only a small proportion of the water received by a lake. Drainage lakes, as their name implies, receive and lose most of their water from surface water inflows and outflows (inlets and outlets). Groundwater provides an important source of water for lakes in glacial till areas. Such lakes extend below the groundwater level, and the water seeps into the lake by percolating through the lake sediments or enters at discrete springs in the shallow water areas along the shore. Seepage lakes have no inlets and outlets and receive their water mostly from groundwater. Spring lakes are similar but have outlets that form the headwaters of a stream network. In their studies of productivity, nutrient cycling, and animal and plant communities, limnologists often divide the lake into zones. This defining of lake zones is based on light transmission. The amount of energy received by the lake is dependent on the angle of the light as it hits the water. Latitude, season, time...