and the lake waters become richer in nutrients on 
which minute water plants thrive. As the plant 
population on which they feed increases, the 
population of minute water animals and higher 
animals multiplies. 
Increased biological productivity changes both 
the surface and deeper waters. The lake passes 
from the oligotrophic phase eventually into the 
eutrophic phase in which organic and inorganic 
materials fill the basin. Rooted aquatic plants 
become established, gradually converting the area 
to marshland. 
Eutrophication, the aging process, is the process 
of enrichment with nutrients. Accelerated eu- 
trophication of lakes results from the input of 
nutrient materials, largely nitrogen and phos- 
phorus from man’s activities. Natural aging 
proceeds slowly in the geological time scale, 
however, acceleration of the process by human 
activity causes aging that can be observed within a 
generation. 
Accelerated eutrophication is emphasized 
because it is critically impairing the benefits of the 
Great Lakes. It is a very difficult problem re- 
quiring several remedial measures. Problems of 
build-up of dissolved solids and oxygen depletion 
are closely associated with eutrophication. 
Accelerated eutrophication of Lake Erie is 
manifest as follows: 
—Blue-green algae, diatoms, and other algal prolif- 
erations cause noxious odors and appear as 
unsightly scums on the water surface. 
—These algae impart unpleasant tastes to water 
supplies. 
—Dissolved oxygen levels are depressed in ther- 
mally stratified areas. 
—Desirable bottom dwelling, clean water animal 
species are displaced by less desirable species 
tolerant of pollution and low oxygen concen- 
tration. 
—Fish populations change from such highly-prized 
game fish as pike, trout, and whitefish to such 
coarse, less valuable fish as carp, catfish, and 
sheepshead. 
—Objectionable filamentous algae growing in 
shallow waters wash up onto the shores and 
beaches. 
—Unsightly, malodorous masses of algae and other 
pollutants interfere with the recreational use of 
waters and beaches, clog municipal and industrial 
water intakes, and depress property values. 
Nearly all Lake Erie is eutrophic; Lake Ontario 
is nearly eutrophic, and Lake Michigan exhibits 
some symptoms of eutrophy, especially in the 
southwestern part. Isolated evidence of pollution 
has been observed in Lakes Huron and Superior, 
although in general, water quality in these lakes is 
good. 
Increases in the dissolved solids of the Great 
Lakes have been observed over the years since 
routine water quality analyses first were initiated. 
Despite dissolved solids concentrations not having 
impaired water uses seriously, local problems 
influenced by population and industrial growth are 
experienced near points of large waste discharges. 
The dissolved solids problem probably will be 
reduced somewhat through recently adopted State 
water quality standards. Because most bacterial 
contamination can be directly traced to man, it 
can be remedied more easily. 
The accelerated aging of the Great Lakes is not 
the sole cause or symptom of deteriorating water 
quality. However, because other pollution effects 
are intimately linked to this phenomenon, meas- 
ures to prevent accelerated aging and to restore 
water quality help solve other problems. An 
example is lessening oxygen depletion caused by 
the biodegradation of organic wastes. 
Oxygen can be depleted through addition of 
organic substances to a body of water and the 
proliferation of algae. Most organic pollutants can 
be controlled by treatment methods consistent 
with water quality standards. 
B. Causes of Pollution and Accelerated Aging 
To define the necessary action and formulate 
restorative methods, it is essential to understand 
the nature of causative factors. The following 
factors contribute to the accelerated aging of the 
Great Lakes: 
1. Municipal Wastewater 
Municipal sewage is the principal source of 
nutrients, especially phosphorus; 75 per cent of 
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