yellow, necessitating the removal of the organic substances responsible.
(Drinking water Will be discussed in detail in the next chapter). When un—
treated water is used for agricultural purposes, toxic substances produced by
blue—green algae may cause the death of cattle and sheep. The growth of
weeds in irrigation canals poses a problem in very arid areas of the United
States, since much water is lost from the canals by evapotmmpimtion (the loss
of water which has passed through a plant and is evaporated at its surface)
[45]. An unexpected cost of eutrophication is the damage to shoreline houses
from hydrogen sulde, the by—product of sulfur bacteria which grow in areas
where oxygen is lacking. This foul—smelling gas reacts with lead—based paint
to form a black precipitate which gradually discolors painted houses.
Preventive Measures?
How to prevent presently unpolluted lakes from becoming eutrophic and to
reduce or reverse the situation in lakes already in advanced stages of eu—
trophication is still a matter of debate. As mentioned previously, proposed so—
lutions range from attacks on the symptoms of the problem to alleviation of
its root causes. One symptomatic solution is to dredge nutrient—rich sediments
and dispose of them elsewhere. In some places, however, nutrients may be as
deep as 10—15 feet below surface sediments, making dredging an imposing
task. Then there is the problem of what to do with the dredging wastes. Often
enough, the answer is to dump the wastes in the ocean, reminiscent of divert—
ing sewage
wastes into Puget Sound. At least two scientic studies have dem—
onstrated that such disposal simply transfers eutrophication and toxicity prob—
lems from one body of water to another [46, 47].
Another method of symptomatic relief is the control of weeds with algi—
cides and herbicides. This is not always a practical answer either. Recently,
for example, the Tennessee Valley Authority (TVA) considered use of the her—
bicide 2,4—D to control watermilfoil, an aquatic weed in Melton Hill Lake—
the only source of drinking water for the city of Oak Ridge, Tennessee, and
one of the city’s recreational centers. Because of the potential danger of this
herbicide, found to cause birth defects in mice and often to persist in the
aquatic environment for over six months, the proposed control program was
abandoned [48].
The other major preventive proposal is to use various techniques to remove phosphates from effluents at municipal treatment plants. Of the tech—
niques available, chemical treatment to precipitate or otherwise reduce the
phosphorus content in waste water is usually regarded as the most practical,
primarily because it is the least expensive. Two serious problems must be con—
sidered, however. First, phosphate—removing technology is applied in con—
junction with either secondary or tertiary waste treatment, most effectively
with the latter. This means that a municipality must rst make the large investment necessary for at least secondary waste treatment, which has already
absorbed large amounts of local and federal funds and Which will require
even larger future investments to bring to completion. Tertiary treatment-—
Preventive Measures?
141
(Drinking water Will be discussed in detail in the next chapter). When un—
treated water is used for agricultural purposes, toxic substances produced by
blue—green algae may cause the death of cattle and sheep. The growth of
weeds in irrigation canals poses a problem in very arid areas of the United
States, since much water is lost from the canals by evapotmmpimtion (the loss
of water which has passed through a plant and is evaporated at its surface)
[45]. An unexpected cost of eutrophication is the damage to shoreline houses
from hydrogen sulde, the by—product of sulfur bacteria which grow in areas
where oxygen is lacking. This foul—smelling gas reacts with lead—based paint
to form a black precipitate which gradually discolors painted houses.
Preventive Measures?
How to prevent presently unpolluted lakes from becoming eutrophic and to
reduce or reverse the situation in lakes already in advanced stages of eu—
trophication is still a matter of debate. As mentioned previously, proposed so—
lutions range from attacks on the symptoms of the problem to alleviation of
its root causes. One symptomatic solution is to dredge nutrient—rich sediments
and dispose of them elsewhere. In some places, however, nutrients may be as
deep as 10—15 feet below surface sediments, making dredging an imposing
task. Then there is the problem of what to do with the dredging wastes. Often
enough, the answer is to dump the wastes in the ocean, reminiscent of divert—
ing sewage
wastes into Puget Sound. At least two scientic studies have dem—
onstrated that such disposal simply transfers eutrophication and toxicity prob—
lems from one body of water to another [46, 47].
Another method of symptomatic relief is the control of weeds with algi—
cides and herbicides. This is not always a practical answer either. Recently,
for example, the Tennessee Valley Authority (TVA) considered use of the her—
bicide 2,4—D to control watermilfoil, an aquatic weed in Melton Hill Lake—
the only source of drinking water for the city of Oak Ridge, Tennessee, and
one of the city’s recreational centers. Because of the potential danger of this
herbicide, found to cause birth defects in mice and often to persist in the
aquatic environment for over six months, the proposed control program was
abandoned [48].
The other major preventive proposal is to use various techniques to remove phosphates from effluents at municipal treatment plants. Of the tech—
niques available, chemical treatment to precipitate or otherwise reduce the
phosphorus content in waste water is usually regarded as the most practical,
primarily because it is the least expensive. Two serious problems must be con—
sidered, however. First, phosphate—removing technology is applied in con—
junction with either secondary or tertiary waste treatment, most effectively
with the latter. This means that a municipality must rst make the large investment necessary for at least secondary waste treatment, which has already
absorbed large amounts of local and federal funds and Which will require
even larger future investments to bring to completion. Tertiary treatment-—
Preventive Measures?
141