November/December 1970
By the Mother Earth News editors
Nearly everyone is aware of the smog we breathe, the oil fouling our beaches and the mountain of "one-way" containers filling the canyons, all the major ecological problems. As desert residents, however, we have less contact with a problem which has reached gigantic proportions in the lakes and rivers of the East and the Midwest—eutrophication. Many lakes are dead or dying, and they are being killed by our "cleaner than clean" clothes, dishes and homes. California, for its scarcity of lakes, is not immune.
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In 1965, detergent manufacturers began producing "bio-degradable" products. This changeover eliminated a major pollution eyesore—detergent foam on rivers, but biodegradability is not enough. We must now be concerned with the effects of the elements into which the new biodegradable detergents decompose.
EUTROPHICATION
When the growth of aquatic plants is overstimulated they seasonally die and rot, using up the oxygen dissolved in the water. Game fish die of oxygen deficiency and are for a time replaced by scavengers. As the plant growth cycle periodically repeats, the lake loses all aesthetic value. Finally the water itself is displaced by the accumulating vegetation and its decay products. The lake first becomes a bog; later dry land. This process occurs naturally as lakes mature, age and die. It has been estimated, however, that the eutrophication which has occurred in the past few decades because of man's pollution would require thousands of years under "natural" conditions.
The availability of plant nutrients controls the rate of algal growth and directly affects the rate of eutrophication. A plant might require 33 units of carbon, ten units of nitrogen and one unit of phosphorus to attain one-unit of growth. If there were 66 units of carbon, and 20 units of nitrogen available, it still could not grow until it found a second unit of phosphorus. Nitrogen is, in general, not the critical growth-limiting nutrient, since blue-green algae can fix nitrogen from the air (air is 80 per cent nitrogen). Upon death and decay, they may supply enough nitrogen for growth of other kinds of algae. Thus phosphorus, which is not widely available in nature, is the most critical nutrient.
Phosphorus enters the water from many sources; land runoff, soil erosion, waste from animals and plant decay and municipal sewage. The relative contributions of phosphorus from these sources will vary with the watershed. Even if the main source of nutrient phosphorous in rural areas is agricultural runoff, on the average human waste contributes 1.4 pounds per person per year and detergents contribute from 1.5 to 2 pounds of phosphorus per person per year to surface waters. It has been estimated that from 50 to 75 per cent of the phosphorus in lakes and rivers is from detergents. The elimination of this source would bring about an immediate and massive decrease in the rate of eutrophication.
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