Lake Tips: Valuable Resources

Think of a Lake You Visit
Freshwater lakes are valuable resources ranging in size from less than an acre to more than 30,000 acres. No matter the size of a lake, each of these landscape features has its own unique qualities and values. A small pond on a farm may be considered a significant resource to some, while a large reservoir supplying drinking water will directly affect hundreds of thousands of lives.

Lakes are significant to plants, wildlife and people. Lakes are critical because they provide habitat for fish spawning and growth. Plants that grow in and around lakes provide a source of food for many animals and nesting sites for birds. These plants also act as natural filters for nutrients and sediments, and stabilize the lake shore to prevent erosion.

Lakes also have economic, recreational and aesthetic value. Lakes provide flood protection, as well as water for drinking, irrigating agricultural crops, navigation, and the power to generate electricity. The quality that lakes add to everyday life is immeasurable. What other experience could be as peaceful as an early morning spent on a high mountain lake, or as joyful as a family gathering in the summer on a lake shore? Preserving and protecting lakes NOW is paramount for future generations to use and enjoy the lakes.

The Lake/Watershed Link
If we want to do our best to be effective stewards of our lake resources, a basic understanding of the lake and its relationship to the landscape around it is important. A lake and its watershed, or the area of land that drains into the lake, can be thought of as a connected system with interacting physical, chemical and biological components. A lake is the lowest point in the watershed and, like the drain of a bathtub, all the water from the surrounding landscape ends up in the lake. This water, called runoff, carries minerals, nutrients, chemicals, sediment and other potential pollutants to the lake.

Because of the close connection between the lake and its watershed, the lake will be affected by the natural characteristics of the watershed and the human activities taking place there. Climate, soil, geography, the relative size of the lake compared to its watershed, the slope of the land, and how the land is used are all factors that will affect the quality of the lake.

For example, let’s say you could identify the following characteristics of your watershed: several growing plants and grasses that provide vegetative covering for the land, a large lake with a comparatively small landscape (large lake-to-watershed ratio), soils that don’t erode easily, gentle sloping land, and light rainfall. You might expect to find a higher quality lake in such a watershed. It would be higher quality compared to one that has a small lake surrounded by land that is stripped of trees and shrubs with highly erodible soils, steep slopes and heavy rainfall. However, things usually are not so obvious in the real world. Each lake and its watershed includes many variables that interact to either pollute or protect the quality of the lake.

The Lake Ecosystem
The lake ecosystem, or the interactions of all living and nonliving components in the lake, is determined not only by the watershed characteristics but also by key processes that take place in the lake. The amount of water that flows in and out of the lake, the size and shape of the lake basin, and the amount of time it takes to completely renew the water in the lake (hydraulic residence time) will all influence the lake ecosystem. Seasonal temperature variations or wind action can cause some lakes to "turnover", or mix from top to bottom, churning up nutrients that may have settled to the lake bottom.

These processes, in addition to the lake and watershed relationship, will determine how much plant and animal life a lake will support. The biological productivity of a lake is referred to as the lake’s trophic condition or trophic status.

The trophic condition can range from least productive (oligatrophic) to moderately productive (eutrophic). Even without human input to a lake watershed, lakes will "age" naturally by becoming more productive–a process known as eutrophication. Human activity can speed up the aging process of a lake by tens or even hundreds of years. This human-induced, accelerated eutrophication is known as cultural eutrophication.

Threats to Lakes
Many of the day-to-day activities of humans promote eutrophication and other types of lake pollution. According to the 1992 National Water Quality Inventory, published by the U.S. Environmental Protection Agency, the primary source of pollution to lakes comes from agricultural operations, including the plant nutrients phosphorus and nitrogen, and organic matter from animal wastes. Other major pollution sources to lakes are runoff from urban areas, storm sewers, sewage treatment plants and runoff from construction sites and roadways. In some areas of the United States, acid rain and drainage from mining sites are major threats to lakes. In addition to the rather large-scale sources of pollution, the cumulative impacts of many smaller-scale activities can be equally detrimental to a lake’s quality. Leaking septic tanks, oil and grease from cars and boats, home use of phosphorus detergents and misuse of lawn fertilizers and chemicals can all contribute to lake pollution.

What are the effects of pollutants from these sources? An overabundance of nutrients can cause algal blooms and excessive aquatic plant growth, and eventually can deplete oxygen supplies in lakes, causing fish kills. Organic wastes also can cause a lack of oxygen needed by fish for survival. Sediment loads from land erosion can fill in lakes and destroy habitats for plants and animals, as well as clog fish gills and smother fish eggs. Organic chemicals and metals such as mercury can contaminate fish and shellfish, making them unacceptable for humans to eat.

Copyright © 2005 North Dakota Department of Health

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