Welcome To The Lake Database

November 8th, 2009

When one is asked to recall their fondest memory of a lake, the images can vary wildly. Memories of a mirror-like swamp, pink from the light of early morning are conjured. Some envision lunch in a quiet park alongside a manmade lake, ducks meandering about. Still others might envision summertime boating on a wind-swept lake so large that it might be a small ocean. This variation within our memories closely resembles the diverse nature of these bodies of water.

As it turns out, lakes in North America have a life of their own. Their origins have been categorized in 15 different ways by limnologists – scientists who study inland bodies of water. Lakes are sometimes not even lakes – their definition varies wildly, from one hectare to as much as forty hectares. That which we know as a pond, may be a lake by other definitions and vice versa.

Among these 15 categories are graduated levels of ecological support, referred to as a trophic system of classification. The levels define the life of the lake, its nutrient content and, ultimately, what it provides to us on the surface.

The Birth of a Lake

November 7th, 2009

Lakes form from a variety of sources. The formation of a natural lake will often take thousands, if not millions of years and is dependent on powerful forces within nature. The birth of a lake is often the bi-product of significant geological changes in the region. Thus, lakes of similar origin are often clustered in regions of similar geography.

Glaciers are responsible for the single largest lake in North America and the world. Lake Michigan-Huron is referred to as a glacial lake, due to the ice-filled depressions formed by receding glaciers. Although Lake Michigan-Huron are separately named, limnologists refer to these two lakes as one single system, thus technically making them the largest in the world; however, Lake Superior is the largest singly named lake in North America.

These massive glaciations occur throughout North America with the world’s highest concentration of lakes located in northeastern Canada. Massive glaciations in this region stripped the soil from the land and deposited ice in randomly-formed low points. This greatly affected the drainage system in the area, giving the region a uniquely chaotic appearance.

Drainage systems are an important part of the development of one the most common lakes, the Oxbow. Drainage systems in a region define the pattern in which rivers and streams come together. The dendritic or “tree” drainage system is the most common, known for resembling a tree when viewed from above. When sharp curves in the drainage system wear down the far shore, a slow-flowing, bow-shaped bulge can occur in the river. The Reelfoot Lake in West Tennessee formed due to as sudden change of course in the Mississippi River during the New Madrid Earthquake of 1811-1812. The name “Oxbow” is derived from that characteristic shape.

Earthquakes and volcanic eruptions are perhaps the only rapid ways for a lake to form. Lake Superior is actually referred to as a rift lake, since it is located on a fault in the tectonic plates. These lakes are typically deeper than most. Crater lakes are often formed in calderas of inactive or relatively inactive volcanoes. Mount Katmai in Alaska is one of the few true crater lakes in the United States. It is fed by glaciers that surround the lake and sits at an elevation of over 4,200 feet.

In very few instances in North America, a lake is classified as endorheic. These lakes are characterized by having no inflow and no outflow. The most prominent example of such a lake is the Great Salt Lake in Utah. Also called saline, these lakes only gain and lose water through underground sources and evaporation. As a result, endorheic lakes end up with a higher salt ratio than most inland bodies of water.

Man made lakes are often the result of the damming of flowing waterways. These lakes can vary widely depending on the application. Lake Mead is formed by the Hoover dam, and holds over 28.5 million acre feet of water – enough to cover the entire state of Pennsylvania in one-foot deep water. Landscaping projects can produce artificially fed lakes, though these lakes often fail to recycle nutrients, causing their fish populations to die annually.

The Life of a Lake

November 6th, 2009

Lakes are in no way eternal. Their status can fluctuate over thousands of years. Devil’s Lake in the Wisconsin Dells region of Wisconsin began its life as an oxbow lake formed by the flow of the Baraboo River. Glaciations caused a natural moraine, or earthen dam, to block off the body of water, turning it endorheic. Such changes will also modify the lake’s classification in the trophic system.

The trophic system defines the level of nutrients and oxygen. The levels are important, as they are the building blocks for microscopic life forms such as algae and zooplankton. The life forms support smaller fish. Smaller fish, in turn, support populations of larger fish. Larger fish support larger varieties of birds.

On one end of the classification systems sit the eutrophic lakes. Eutrophic lakes contain the nutrients necessary to support algae, phytoplankton and zooplankton. These creatures in turn support a comparable level of small fish. Eutrophic lakes typically have limited visibility. In addition, the additional organic matter settles and slowly decomposes on the bottom of the lake. In the right conditions, this sediment can continue the nutrient cycle or create a deadly gas buildup. Lakes that are more on the eutrophic end are desired by fishermen and outdoorsman.

At the opposite end of the trophic classification is oligotrophic lake. In contrast to the eutrophic, these lakes contain little or no nutrients. This lack of nutrition breeds little organic material, making the water exceptionally clear. Often the watersheds that feed these lakes, if any, are equally rocky and nutrient free. These lakes make for poor fishing, as even the fish that are available are too small or undernourished.

It’s important to note that the trophic classification system is a graduated system of measurement. Limnologists find that lakes are often in transitive states of eutrophism or oligotrophism. It is important to remember that these two classifications are different ends of the spectrum, with eutrophic being the “(e)utopia” of lake ecosystems, as it were.

It is important to understand the role of thermoclines. In deep bodies of water, the varying temperatures will actually cause the water to separate. Cold water sinks to the bottom while warm water sits on the surface. These separations are referred to as thermoclines.

The cold water at the bottom is often devoid of any oxygen, a necessary component to supporting life in a lake ecosystem. Furthermore, the organic matter at the bottom of a deep lake requires oxygen in order to decompose. In a temperate climate, cold temperatures cause the top layer of the thermocline to drop. This temperature drop will cause the lake waters to mix, distributing oxygen and nutrients throughout all layers until they separate again in the summer and fall months.

At extreme depths, even winter cannot cause oxygen-starved water to rise to the surface. An excellent example of this is the recovery of wooden logs at the bottom of Lake Superior by the Superior Lumber Company. In the 1890, heavy logging activities occurred in the then dense forests around Ashland, Wisconsin. During this time, many logs were lost, sunken into Lake Superior. At a depth of 60 feet, the logs found water that was completely without oxygen. Because of this, they survived decomposition for over 100 years.

Variations in the surrounding ecosystems can cause lakes to fluctuate within the trophic classification. A prime example is hypertrophic lakes which have been enriched with nutrients. The nutrient enrichments are often caused by human intervention, such as agricultural runoff, and can cause algal blooms that decrease the dissolved oxygen. This creates a poor environment for humans and fish species.

The Death of a Lake

November 5th, 2009

All lakes ultimately exist through a delicate process of intake and outtake. If these systems become unbalanced – whether naturally or through human intervention – the result is the ultimate disappearance of that lake. This process is not too noticeable in a human timescale, as it happens over generations.

Oxbow lakes forms in river valleys and can be very susceptible to disappearance. Since oxbow lakes are the direct result of the flow of a river, meander rivers and streams can cause the reads and peat to intrude upon the edges of the lake. As these intrusions continue, the systems begin to form a wetland. As the wetland continues to dry, trees will intrude, sealing the fate of that area of the lake.

Irrigation is a prime example of human-initiated lake disappearance. Many lakes are fed by watershed and drainage systems. When these rivers and streams are diverted for agricultural purposes, they can affect lake systems thousands of miles away. Walker Lake in Nevada is an example of such an irrigation effect. The decreased water levels caused by upstream diversion have increased the salinity of the lake. The increased salinity can be toxic to fish and algae populations if it gets too high.

As global warming creeps into every aspect of our lives, researchers are beginning to find a connection between the disappearance of lakes and the thawing permafrost. As the permafrost levels decrease, these predominantly arctic lakes are beginning to drain into the newly thawed soil. In some instances, the rapid thawing also causes ages-old methane bubbles to release from the soil. These significant climate changes affect not only the lake, but the atmosphere and geography of the surrounding areas.

Lakes are an ecosystem of constant fluctuation. Their creation and continued existence rely upon the land surrounding them. Their purpose and existence are as varied as our individual experiences with them. The next time you’re out on a lake, stop to consider the incredible forces that brought these natural wonders to your senses.