Read an Excerpt
LAKESHORE LIVING
Designing Lake Places and Communities in the Footprints of Environmental Writers
By Paul J. Radomski, Kristof Van Assche Michigan State University Press
Copyright © 2014 Paul J. Radomski and Kristof Van Assche
All rights reserved.
ISBN: 978-1-61186-118-1
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 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 of day, and wave action all affect the angle. A substantial portion of the energy is often reflected. On a clear summer day, about 6 percent of the total radiant energy is reflected. The light that enters the water is either scattered or absorbed. The infrared portion of the energy spectrum is absorbed primarily by the first three feet of lake water, so only the top of the water column becomes sun-warmed. Turbid and dark-stained (from humic acids) water have higher absorption rates and thus lower transmission and transparency. Algae and other aquatic plants use the scattered, diffuse light to create their own food in the process of photosynthesis- a process that releases oxygen as a waste product. Aquatic plant production is reduced with increasing water turbidity, and algae production can limit water transparency. In 1865, Angelo Secchi, an Italian scientist, developed a simple index of a lake's transparency of light. He lowered a white disk into the lake and recorded the depth at which it was no longer visible. While photometers for measuring transmission of light through water are readily available today, the Secchi disk is still used. A common standardized Secchi disk method for lakes uses an eight-inch (twenty-centimeter) disk with black and white quadrants that is lowered from the shaded side of the boat during midday. The observer records the mean depth of the point at which the disk disappears during lowering and the point at which it reappears upon raising. Secchi disk observations range from a few inches in very turbid waters to over one hundred feet (thirty meters) in crystal clear waters.
The lake zones often used by scientists include the littoral, profundal, and pelagic zones. In the littoral zone, light is available for aquatic plant growth. The pelagic zone is the free open-water area of a lake, and the profundal zone is that part of the basin where light does not penetrate. Most of the lake productivity occurs in the littoral zone. The profundal zones are areas of decay and provide scientists with abundant information on lake chemical and historical characteristics. The pelagic zone is where offshore plankton, fast boats, and kids on tubes hang out.
The littoral zone is also highly influenced by wave action. Waves result from the force of wind and the friction of the water. As wind pushes the water, the water moves in the orbit of the wave but not in the direction of the wave. The maximum height of waves on a lake is a function of the fetch, or the uninterrupted distance across water in the direction of the down. As waves enter the littoral zone's shallow water, their speed decreases due to drag on the lake bottom. As the wave slows, the wave height increases and the wave becomes unstable, resulting in a wave break. The energy in the wave is now directed to the lake bottom and the shore. In areas with glacial till, the erosion at the foot of the shoreline bank brings additional rock down to shore. The process continues and the bank slowly moves landward, which creates a horizontal bed of rock alongshore. Natural beaches exist where sand is exposed by waves or where the wind and waves deposit the sand they have carried. Along high-energy shores, waves keep the beach clear of finer sediments and the sand in constant motion. These high-energy shorelines are often lacking in aquatic vegetation, as the continual wind and waves make it difficult for aquatic plants to colonize. Where gravel and rock are present in deepwater lakes, high-energy shorelines provide important spawning habitat for walleye, white sucker (Catostomus commersoni), cisco (Coregonus artedi), lake whitefish (Coregonus clupeaformis), lake trout (Savelinus namaycush), and burbot (Lota lota).
Lakes may also be divided into zones based on temperature and chemical composition. The sun warms the water close to the surface. Wind mixes this top water, creating a layer of uniformly warm water across the lake for a considerable depth. Below this is a pool of cooler water. This phenomenon of temperature variation with depth is called thermal stratification. The transition from warm to cool water, which is often abrupt, is known as a thermocline. Swim down into the depths of a deep lake in midsummer and you will soon realize when you have entered that cool, nonmixing pool of water. In deep lakes this thermal stratification lasts all summer. In shallow lakes the stratification may break down with high winds, only to return during calm periods (polymictic lakes). Many lakes circulate twice a year (dimictic lakes), in the spring and in the fall. A lake is said to turn over when the entire volume of lake water circulates.
The mixing of water, or lack thereof, can have a profound impact on dissolved oxygen concentrations in the water. This is important, as dissolved oxygen is vital to aquatic organisms from fish to bacteria. Oxygen diffuses in water from the air and from algae and aquatic plant photosynthesis. In lakes with very low nutrient concentrations and organic matter production, the oxygen concentration remains close to the saturation point at all water depths. In more productive lakes, the oxygen concentration progressively decreases in the deeper water after spring turnover. Bacteria in the bottom sediments consume the oxygen as they eat the accumulated organic matter on the lake bottom, converting much of the dead tissue into carbon dioxide gas and water vapor. In very productive, or eutrophic, lakes, dissolved oxygen can be depleted enough to create an anaerobic condition for much of the summer. This anaerobic condition allows the release of phosphorus, iron, and manganese from the lake sediments. Fish need high dissolved oxygen concentrations, so they spend most of their time living at depths where they find this. When oxygen is depleted at the lake bottom, aerobic bacteria are replaced with anaerobic bacteria and decomposition rates slow down. Anaerobic bacterial decomposition produces methane and carbon dioxide gases. In the summer, as methane diffuses up from the lake bottom into oxygenated waters, aerobic bacteria consume the methane and produce carbon dioxide gas as a waste product. Sometimes one can observe a mass release of methane and carbon dioxide gas: enter a muck-filled bay during an extended calm period, disturb the lake bottom, and witness the gas bubble to the surface.
Caused by wind or temperature gradients in the water, currents in the lake surface water are common. The phenomenon of Langmuir circulation can be observed on lakes when wind speeds are between five and sixteen miles per hour (two and seven meters per second). Langmuir circulation is characterized by parallel surface streaks of aggregated matter aligned with the direction of the wind. These windrows of seeds, leaves, and other plant material are the result of wind-produced surface currents that create a series of helical currents in the surface water. In the Great Lakes, large circulation patterns also produce slicks of aggregated material, but they are of greater size and separation than the streaks created by Langmuir circulation. Seiches are another fascinating phenomena of lakes. A steady wind causes water to pile up at the downwind end of the lake. This forces the tilting of the cooler, dense deep water deeper on the downwind end and shallower at the upwind end. The water level will be higher at the downwind end of the lake than at the upwind end. When wind stops, the warm, less dense surface water that piled up sinks until it hits the cooler, dense deep water, then flows horizontally back from where it came. In a thermally stratified lake, the thermocline may teeter back and forth for hours or days before returning to an equilibrium state or horizontal condition. Water moves within lakes even when they are covered with ice in the winter. These winter water currents are the result of heat rising from the lake sediments and from underwater springs.
The selection of plants and animals listed below is not meant to replace field guides but to provide a more detailed sketch of lake ecology. While we interpret the ecological value of particular species or taxa, we could remember that they are things to admire and appreciate.
PLANTS
A lake's plant community provides many environmental services to us, such as absorbing nutrients that reduce water quality, reducing erosion from waves, and providing food and habitat for fish and wildlife. Perhaps as important, the native flora, more than anything else, defines the ecological character of our lakes. The animals we see from our dock or cabin add to the experience of lakeshore living, as well as contributing to the ecological processes of the lake.
Blue-green cyanophyta (bacteria) are primitive plants that have existed on Earth for billions of years. They produce a considerable amount of oxygen through photosynthesis. Blue-greens come in many colors, from red to paint-like greens and violets, and they may exist as single cells, multicell filaments, or large colonies. In productive systems, blue-greens grow rapidly and extensively, creating noxious scum or slick conditions. They reach their highest abundance, often called "blooms," in mid to late summer. These blooms can produce strong odors, and they contain toxins that cause rashes, respiratory distress, and other problems. Wildlife and pets are also highly susceptible to these blooms; the cyanophyta-produced toxins can cause death with very high exposure. Common genera of blue-greens include Microcystis and the filamentous genera Anabaena and Aphanizomenon. Some organisms, such as certain zooplankton species, eat blue-greens; however, their contribution to the lake food web is generally as a source of food for bacteria after they die and settle on the lake bottom.
Algae, like the blue-green cyanophyta, exist as single-or multicelled life forms. Algae can be found in the open water, attached to aquatic plants, and even on the lake bottom if light is sufficient. Algae form the foundation of a lake's food web, as planktonic algae (phytoplankton) are the main food source for microcrustaceans and other small planktonic organisms (zooplankton). In the littoral zone, algae provide food for insects and other organisms, such as tadpoles, salamanders, and fish. Families of algae include green algae, golden-brown algae, and diatoms. There are thousands of species, and the variety of form is quite spectacular, ranging from the beautiful filaments of the green algae Spirogyra and the spherical colonies of Volvox in shallow water, to diatoms with silica cases and petri dish- like structures like the pinnate Aneumastus and the centric Stephanodiscus and Cyclotella.
A large number of algae species can be found in a lake at any given time, with some species reproducing and others in resting stages. Algal communities are very dynamic, fluctuating with light and temperature conditions, availability of nutrients, competition, and grazing by small organisms. If a lake is turbid or not very transparent, most of the algal activity will be near the surface. In other lakes, algae that are adapted to low light and cooler water temperatures may be most productive at greater depths. There is often a seasonal rhythm to algal activity. Winter is a period of low growth due to low light conditions and cold water. In spring, the large diatom algae dominate due to their preference for cool temperatures. Diatom blooms might last a few weeks to a month. Not surprisingly, the availability of silica in the lake water can influence the abundance of the diatom algae. During summer in productive lakes, various green algae proliferate followed by blooms of blue-greens. Diatoms may again become dominant in the fall, with their activity abruptly declining when winter comes.
The annual variability of algae productivity in a lake is often determined by nutrient loading. For most lakes, phosphorus is the limiting nutrient for phytoplankton. In lakes with unaltered and undisturbed watersheds, year-to-year algae seasonal abundance patterns are fairly consistent. In infertile lakes, zooplankton can effectively graze down populations of phytoplankton. Algae reproduce asexually, primarily by cell division or formation of spores. Algae don't live as long as many other plants because they tend to sink to the lake bottom where light is unavailable for survival. Even the algae that have adaptations to reduce sinking rates, such as gas vacuoles within their cells, rely on high rates of reproduction to maintain their lake presence. To estimate the abundance of algae, limnologists measure chlorophyll a pigment concentrations in the upper waters of a lake's pelagic zone. Lakes with average summer water chlorophyll a concentrations less than ten micrograms per liter (or parts per billion) generally have high water transparency and low frequency of nuisance algal blooms in the summer. Lakes that have chlorophyll a concentrations above twenty to thirty micrograms per liter generally have poor water transparency.
(Continues...)
Excerpted from LAKESHORE LIVING by Paul J. Radomski, Kristof Van Assche. Copyright © 2014 Paul J. Radomski and Kristof Van Assche. Excerpted by permission of Michigan State University Press.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
