Eutrophication is an insidious form of water pollution that causes progressive
,
deterioration of water resources on a wide scale. Overenrichment with the
very nutrients that are essential for aquatic life results in an
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plant life that is followed by other drastic changes in the ecology of lake,
stream, or estuary. Although the full extent of eutrophication in the United f
States is nuclear, a 1971 EPA survey provides an indication of the scope:
Questionnaires sent to oicials in all states with instructions to list types
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sources of lake pollution produced information on 425 lakes; in 80 percent
of f
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these,
the major problem was overgrowth of algae or other aquatic vegetation
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or some unspeoied eutrophic condition. In most cases in which the causes
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had been determined, the nutrients were in wastes from municipal sewage [
treatment plants, septic tanks, or urban drainage [l].
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The nature
of eutroplcaon can be illustrated by a series of events in Lake
Waslnngtonpn tl1Ç_northwest coast of the UnitedStates. The lake covers
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promnately 38square miles and has 50 miles cf shoreline, 20 miles of which
are occupled bY the City of Seattle. That city and others began dumping raw
scwage mto the lakein-ielaæ 18008.}Be®use of health hazards in the en%
smng years, primary treatment of all sewage deposited in the lake was r6f
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qu1rcd by
secondary-sewage treatment
,
as well [2]. In 1955, 6.4million gallonsoftreated sewage were pumpedinto
Lake Wæ1mläton
tenPlats [3]. Except for an occasional
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