Eutrophication

Lakes, large and small, are constantly being enriched by organic matter from decomposing plant and animal remains, providing nutrition for algae and larger aquatic plant. This fertilization whether from natural sources or man-made is called eutrophication, from the Greek meaning “well fed”. This condition occurs often in nature and is not necessarily bad, for the organic material means food for fish and other aquatic life. But too much mineral nutrient in the water might be more serous than too little. Many people have seen the reddish or greenish cast of lakes, bays or coastal areas in summer or fall caused by enormous number of algae and other phytoplankton. When the algae and other phytoplankton die, decomposition of the superabundance of organic material makes the oxygen in the water to become suddenly depleted. Water cannot absorb the replacement oxygen fast enough to take care of the needs of the living organisms. They suffocate; also toxins have been sometimes produced. The “red tide” that is frequently seen along the coasts of California, the Gulf of Mexico, and India has been caused by the buildup of microscopic dinflagellates. These have been single-cell swimming organisms that have some of the attributes of both animals and plants. They impart a red or dirty brown coloration to the water and at night create a spectacular display of luminescence in the froth of wave or in the wake of a boat. Their most injurious effect has been the production of a lethal poison called saxitoxin, which accumulates in the bodies of clams and mussels.

In contrast to many of the land areas where the scarcity of water has been the chief limitation to the growth of vegetation, the oceans are affected with a lack of nutrients. It has been the most critical factor, but not the only one, in determining the growth of the small plant and animal life of the sea, called plankton. Most of the open sea has been a biological desert, an essentially barren area which comprises 90 percent of the ocean or nearly three-fourths of the earth’s surface.

Diffusion: The expression eutrophication stands for the enrichment of the nutrient supply in stagnant waters.  It is rather complex concept. In order to be able to understand it, one must be familiar with certain basic principles of the nutrient cycle in the life of lakes. The basis of this regular order has been that by using solar energy aquatic plants synthesize organic matter from water, carbon dioxide and mineral salts.

This has been a primary product which has been transformed and accumulated at a higher level by aquatic invertebrates. The latter have been then consumed by fish.