What is eutrophication?
Eutrophication is, in the simplest terms, too much of a good thing. It occurs when too many nutrients are deposited into a body of water, throwing off the established balance of production and consumption of organic matter. Eutrophication can take place in ponds, lakes, rivers, and oceans. At first, the overload of nutrients in the body of water encourages plant growth. However, soon this excess of organic material uses up most of the available oxygen in the water, taking it away from the other plants and animals. These other organisms can no longer survive with such depleted oxygen levels and die off, creating what is referred to sometimes as a "dead zone", devoid of life.
Below is a table of the different trophic states, or levels of organic matter in relation to available oxygen, that a body of water traverses on its way to becoming a "dead zone".
Oligotrophic Clear waters with little organic matter or sediment and minimum biological activity.
Mesotrophic Waters with more nutrients, and therefore, more biological productivity.
Eutrophic Waters extremely rich in nutrients, with high biological productivity. Some species may be choked out.
Hypereutrophic Murky, highly productive waters, closest to the wetland status. Many clearwater species cannot survive.
Dystrophic Low in nutrients, highly colored with dissolved humic organic material. (Not necessarily a part of the natural trophic progression.)
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What causes eutrophication?
Eutrophication of bodies of water is a naturally occurring phenomenon. However, the process has been aggravated by the human population. Such man-made eutrophication is caused by excessive discharge of nutrients, especially phosphorous (P) in the form PO4, nitrogen (N) in the form NO3, and silicate. Pictured is a diagram of how nutrients, such as phosphorous, in runoff lead to plant and animal die offs.
In this diagram, phosphorous in the surface runoff fertilizes small floating aquatic plants. As these aquatic plants proliferate, sunlight penetration is reduced. Submerged aquatic vegetation can no longer survive, and as they die and decompose, oxygen levels in the water are also depleted. Eventually, animals die too, due to lack of oxygen.
Some probable causes of this excessive nutrient runoff include sewage treatment plant leakage, septic tank leakage, urban runoff, agricultural runoff, channel dredging, and loss of wetlands.
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What are the effects of eutrophication?
As mentioned earlier, the initial effect of eutrophication- increased productivity- is deceptively good. However, the first indications of eutrophication's ill effects are such visual changes as muddled and discolored water, coupled with a noxious odor. This change in water clarity is a result of the primary effect of eutrophication, which is algal blooms. To the left is an example of such an algal bloom. For more examples of...