The conclusion that phosphorus is limiting in Lake Washington under
"natural conditions was reached on the basis of studies of the lake made in var—“
ious years. In 1933, when the lake was relatiVely unpolluted, nitrates were
left over once the phosphates had been used up by the plants, indicating that
phosphates were the limiting factor and that .their addition to the lake could
stimulate algal growth. In 1962, however, the reverse was true: Phosphates
remained once the nitrates had been consumed, reecting the immense input
of phosphates in sewage. By 1968 and 1969, after sewage diversion, nitrates
were again in excess and phosphates were the limiting factor [31]. Phosphoms
is also thought to be the limiting factor in Lake Erie. This opinion is based on
laboratory experiments reportedin the International ]oint Commission report
ofLake Erie [32] in which samples of lake water were supplemented by var—
ying amounts of phosphates and nitrates and the growth of algae was mon—
itored. Lake Minnetonka, a large lake in Minnesota, has been studied exten—
sively and it was found that phosphorus is limiting there in the summer [33].
_
On the other hand, in some cases nitrates may be the limiting factor in
fresh water: nitrogen, like phosphorus fertilizers, is sometimes added to lakes
and sh ponds by sh growers in order to stimulate algal growth and increase
sh populations [34].
Nitrogen may also be the limiting factor in coastal
and estuaries, as
demonstrated in Great South Bay and Moric‘hes Bay on Long Island, New
York. In both bays, large amounts of nitrates and phosphates were released in
.
the effluent from duck farms, resulting in algal-bloomS. 'IÈwo types
ments were conducted to determine which hutrient was the limitingfactor.
Water samples from areas with dense algal growths were analyzed for phos—
phate, nitrate, nitrite, ammonia, and uric acid concentrations.
was found, but, except at the source of the efuent,_…nd nitrogen…waè
suggesting that nitrogen was the limiting factor:Laboratory tests in which
samples of water from the hays were enriched With either nitrogenor phos—
also conducted. Heavygrowths of algaeresulted from the addi—
tion of nitrogen, but not fromthe addition of phosphorus. The results of these
experiments, and the fact that the blue—green algae found in estuaries do not
readily x atmospheric nitrogen, indicated nitrogen was the limiting factor in
coastal waters [35].
_
;… …
.
.
…
……
.“
.In‘dustry’s contention that—carbon dioxide isthe limiting factor can be cor—
rect =onlyif all other nutrients are already in excess. In onestudy, carbon diox—‘*
ide
be therlimiingf’factor for algal growth—in certain lakes in
Georgia [36], but these results cannotbe generalized for other =lakes.Ithas
_
been pointed. out that
mg/l of bicarbonate ions provide
a ready—supply for
fOf ;new‘ carbon dioxide which isa‘then
Since
have inCreased while
car—bon“;d10x1de and bicarbonate
“the same in the last 100
remain the most “likely limitingfactor in}, Lake Erie.’
”
CmtæalNutnentszek After
limiting factor, it is then
_
necessa1yto pmpomtthecritical leyel;ôfätlæt
nutrient which will cause over—_
‘
_
‘
Controversîdl l$sues 137
\… \\\\\\ \\ \\
\
\
\
"
\
\
\
‘
"natural conditions was reached on the basis of studies of the lake made in var—“
ious years. In 1933, when the lake was relatiVely unpolluted, nitrates were
left over once the phosphates had been used up by the plants, indicating that
phosphates were the limiting factor and that .their addition to the lake could
stimulate algal growth. In 1962, however, the reverse was true: Phosphates
remained once the nitrates had been consumed, reecting the immense input
of phosphates in sewage. By 1968 and 1969, after sewage diversion, nitrates
were again in excess and phosphates were the limiting factor [31]. Phosphoms
is also thought to be the limiting factor in Lake Erie. This opinion is based on
laboratory experiments reportedin the International ]oint Commission report
ofLake Erie [32] in which samples of lake water were supplemented by var—
ying amounts of phosphates and nitrates and the growth of algae was mon—
itored. Lake Minnetonka, a large lake in Minnesota, has been studied exten—
sively and it was found that phosphorus is limiting there in the summer [33].
_
On the other hand, in some cases nitrates may be the limiting factor in
fresh water: nitrogen, like phosphorus fertilizers, is sometimes added to lakes
and sh ponds by sh growers in order to stimulate algal growth and increase
sh populations [34].
Nitrogen may also be the limiting factor in coastal
and estuaries, as
demonstrated in Great South Bay and Moric‘hes Bay on Long Island, New
York. In both bays, large amounts of nitrates and phosphates were released in
.
the effluent from duck farms, resulting in algal-bloomS. 'IÈwo types
ments were conducted to determine which hutrient was the limitingfactor.
Water samples from areas with dense algal growths were analyzed for phos—
phate, nitrate, nitrite, ammonia, and uric acid concentrations.
was found, but, except at the source of the efuent,_…nd nitrogen…waè
suggesting that nitrogen was the limiting factor:Laboratory tests in which
samples of water from the hays were enriched With either nitrogenor phos—
also conducted. Heavygrowths of algaeresulted from the addi—
tion of nitrogen, but not fromthe addition of phosphorus. The results of these
experiments, and the fact that the blue—green algae found in estuaries do not
readily x atmospheric nitrogen, indicated nitrogen was the limiting factor in
coastal waters [35].
_
;… …
.
.
…
……
.“
.In‘dustry’s contention that—carbon dioxide isthe limiting factor can be cor—
rect =onlyif all other nutrients are already in excess. In onestudy, carbon diox—‘*
ide
be therlimiingf’factor for algal growth—in certain lakes in
Georgia [36], but these results cannotbe generalized for other =lakes.Ithas
_
been pointed. out that
mg/l of bicarbonate ions provide
a ready—supply for
fOf ;new‘ carbon dioxide which isa‘then
Since
have inCreased while
car—bon“;d10x1de and bicarbonate
“the same in the last 100
remain the most “likely limitingfactor in}, Lake Erie.’
”
CmtæalNutnentszek After
limiting factor, it is then
_
necessa1yto pmpomtthecritical leyel;ôfätlæt
nutrient which will cause over—_
‘
_
‘
Controversîdl l$sues 137
\… \\\\\\ \\ \\
\
\
\
"
\
\
\
‘