fertilization. Although Sawyer found in his study of Wisconsin lakes that
0.010 mg/l of phosphate were necessary
to sustain algal blooms, actually no
“magic number” can be applied to all bodies of water. Algae have different
nitrate and phosphate requirements, and the degree of eutrophication de—
pends upon the species of algae in question as well as on the nutrient level.
Some algae can store ve to ten times the amount of phosphorus they need, so
the phosphorus concentration in the water at any one time is a poor
indicator
of potential growth [38]. Experiments have revealed the fallacy in relying on
industry’s suggestion of a 0.010 mg/l critical level for eutrophication. In one
set of experiments, various dilutions of effluent from treatment plants in the
District of Columbia were added to the Potomac River. The level of phos—
phorus collected in the river was 0.037 mg/l. Blue—green algae growth re—
sulted from the addition of sewage eluent in proportion to the amount of
phosphorus in the eiuent sample. These results showed that even in the face
of already high levels of phosphate, the addition of more phosphate compounds further intensied algal growth [39].
Reversing the Process
Nut1‘ient Reduction.
A further question is whether or not man-made eu—
trophication can be reversed. Do eutrophic lakes now contain so much phos—
phate that removal of phosphates from detergents will have no remedial ef—
fect whatsoever? This question has unfortunately been confused by the
conviction on the part of many that, since lakes age, once a particular state is
reached in the lake’s history, reversal is impossible. There is some evidence,
however, that the condition of many lakes may be improved, although they
may not be restored to an original and pristine state. Lake Washington is one
example. Although diversion is a questionable means of stemming water pol—
lution, results do illustrate that eutrophication can be reversed and that the
health of such & lake can be restored. Diversion was also successful in three
Wisconsin lakes—Lake Monona, Lake Waubesa, and Lake Kegonsa. These
are
naturally eutrophic lakes, but sewage efuents intensied their algal
.
blooms. In order to curb this trend in Lake Monona, treatment plants were
built in 1914 and effluents were transferred into Lake Waubesa. By the 19505,
efuents were bypassing all three lakes. The amount of copper sulfate (a her—
bicide) needed to kill algae in Lake Monona has dropped signicantly—from
70,000—80,000 pounds in the 19205 and 19305 to only a few thousand pounds
in 1955. Although farm drainage still causes some eutrophication, nuisance algae have decreased [40].
Would similar diversion tactics help Lake Erie? According to the Inter—
national ]oint Commission’s report on Lake Erie and testimony given at the
,
'
phosphate and detergent hearings, there is some chance of restoring the lake
removal. About 70 percent of the phosphorus reaching Lake
Er1e and Lake Ontario comes from municipal and industrial wastes, and de—
-
tergents are the source
of 50—70 percent of municipal and industrial phosphates.
This means that detergents are responsible for close to half of all phos— .
138
Overfed
0.010 mg/l of phosphate were necessary
to sustain algal blooms, actually no
“magic number” can be applied to all bodies of water. Algae have different
nitrate and phosphate requirements, and the degree of eutrophication de—
pends upon the species of algae in question as well as on the nutrient level.
Some algae can store ve to ten times the amount of phosphorus they need, so
the phosphorus concentration in the water at any one time is a poor
indicator
of potential growth [38]. Experiments have revealed the fallacy in relying on
industry’s suggestion of a 0.010 mg/l critical level for eutrophication. In one
set of experiments, various dilutions of effluent from treatment plants in the
District of Columbia were added to the Potomac River. The level of phos—
phorus collected in the river was 0.037 mg/l. Blue—green algae growth re—
sulted from the addition of sewage eluent in proportion to the amount of
phosphorus in the eiuent sample. These results showed that even in the face
of already high levels of phosphate, the addition of more phosphate compounds further intensied algal growth [39].
Reversing the Process
Nut1‘ient Reduction.
A further question is whether or not man-made eu—
trophication can be reversed. Do eutrophic lakes now contain so much phos—
phate that removal of phosphates from detergents will have no remedial ef—
fect whatsoever? This question has unfortunately been confused by the
conviction on the part of many that, since lakes age, once a particular state is
reached in the lake’s history, reversal is impossible. There is some evidence,
however, that the condition of many lakes may be improved, although they
may not be restored to an original and pristine state. Lake Washington is one
example. Although diversion is a questionable means of stemming water pol—
lution, results do illustrate that eutrophication can be reversed and that the
health of such & lake can be restored. Diversion was also successful in three
Wisconsin lakes—Lake Monona, Lake Waubesa, and Lake Kegonsa. These
are
naturally eutrophic lakes, but sewage efuents intensied their algal
.
blooms. In order to curb this trend in Lake Monona, treatment plants were
built in 1914 and effluents were transferred into Lake Waubesa. By the 19505,
efuents were bypassing all three lakes. The amount of copper sulfate (a her—
bicide) needed to kill algae in Lake Monona has dropped signicantly—from
70,000—80,000 pounds in the 19205 and 19305 to only a few thousand pounds
in 1955. Although farm drainage still causes some eutrophication, nuisance algae have decreased [40].
Would similar diversion tactics help Lake Erie? According to the Inter—
national ]oint Commission’s report on Lake Erie and testimony given at the
,
'
phosphate and detergent hearings, there is some chance of restoring the lake
removal. About 70 percent of the phosphorus reaching Lake
Er1e and Lake Ontario comes from municipal and industrial wastes, and de—
-
tergents are the source
of 50—70 percent of municipal and industrial phosphates.
This means that detergents are responsible for close to half of all phos— .
138
Overfed