The eutrophication of our ponds and lakes

As summer draws to a close each year, many of us are appalled by the state of many of our ponds and lakes. In the spring and early summer, the impoundments were basically clear and inviting; but as the season progressed, they became more and more congested with blooms of filamentous algae. A dense growth developed until the pond was covered by a thick mat that frequently smelled to high heaven. In the few open areas, the water was pea–soup green due to the presence of suspended unicellular algae. And each year, the degradation process starts earlier, becomes more intense and lasts longer.

Ecologists term this process eutrophication (pronounced, you-tro-fi-ka-tion), which means “well fed” in Latin. Eutrophication is a natural phenomenon that occurs gradually in the evolutionary ecology of any impoundment of water due to a buildup of organic nutrients. Unfortunately, when human actions add large additional quantities of fertilizer nutrients containing phosphorus and nitrogen compounds to the impoundment, the process of eutrophiation is greatly accelerated.

A pond or lake in which the water is clear and aesthetically pleasing for swimming, fishing, and boating is said to be oligotrophic (“little fed”). Though such an impoundment may be nutrient poor, it will support a productive ecosystem that includes various species of snails, clams, crayfish, insects, fish, and a variety of other organisms. The food chains supporting these forms of life are based on bottom-rooted plants that provide an abundant supply of oxygen through the process of photosynthesis. Over an extended period of time, nutrients build up as a result of the death and decomposition of the plants and animals; and the pond gradually becomes more and more eutrophic, and algal growth accelerates.

The dissolved oxygen content of the water is gradually reduced to the point where fish and the other aquatic species cannot survive. But, if the process of eutrophication is not speeded up by man’s endeavors, this natural cycle is gradual and slow. After an extended period of time, a shallow body of water will pass through the eutrophitic stages and eventually become a bog. Additional organic matter will build up in the bog, and over many years, the bog will be transformed into dry land.

Human activities, especially those associated with agriculture and sewage disposal practices, are primarily responsible for the highly eutrophic condition of most of our ponds and lakes. In the more than six years I have lived in the Gingerwood section of Loves Park, I have watched the rapid eutrophication of two small, lovely ponds within the area. The homeowner’s association sees to it that all of the yards are heavily fertilized at least twice a year with compounds rich in nitrogen and phosphorus. Each year, the grass is greener, but so are the ponds. Needless to say, all of Gingerwood and the surrounding area drain into the ponds. When will we ever learn?

There are two general approaches to combating human-induced eutrophication. One is “band-aid” method of attacking the algae with chemical or physical means. The chemical quick fix is expensive and effective for only a short period of time, and extreme care must be taken when using toxic aquatic herbicides.

The second method is to control the input of nutrients, especially those rich in nitrogen and phosphorus that are at the root of the problem. This method offers the best long-term approach to the problem. Sources of pollution such as effluent from sewage treatment facilities and septic fields must be pinpointed and eliminated. Non-point sources of nutrients such as runoff and leaching from urban, suburban, and agricultural areas must not be overlooked.

Controlling the input of nutrients into our waters will not be an easy or inexpensive task. However, most of us who enjoy the natural beauty of a clear and pristine pond or lake and the abundance of species they support believe the end results are worth the effort.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

From the Aug. 30-Sept. 5, 2006, issue

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