”
i
much of the other nutrients can be used. If only half a unit of phosphorus 1sr
present in the water for every
ten units of nitrogen and 106 of carbon, only
half the nitrogen and carbon will be used by the algae or other aquatic plants
The presence of large amounts of carbon and nitrogen in the water and the
_
absence of phosphorus would indicate that phosphorus was the factor limitingf
plant growth. If sewage effluents rich in phosphorus were added to this
an increase in plant productivity could result.
To understand the limiting factor concept in relation to the three critical
nutrients, consider the following hypothetical analogy. To purchase a pack—_
age of cigarettes from a coin—operated dispenser, presume you
must insert r
into three appropriately sized slots a nickel, a dime, and a quarter. If you are
missing one coim even the humble nickel, the other two are useless. You can—
not operate the machine even though you may have three dimes and two f—
quarters. Similarly, if phosphorus, for example, is missing in a body of water,
au aquatic plant cannot
utilize any of the nitrogen and carbon present, even
if the latter elements exist in abundance. The two nutrients generally consid—'
ered by scientists to be the most frequent limiting factors in the aquatic
ronmentïàre the nitrates and the phosphates. Phosphates, in particular, are
garded by some scienüsts as the major limiting factor because their levels are _
so low in nature in relation to plant needs _[22].
A number of studies have been conducted in an effort to determine the
sources of nitrogen and phosphorus and the relative amounts of each which
can be assigned to natural sources as compared with agricultural, industrial,
or domestic
Mendota in Madison, Wisconsin, was the site of
one extensive survey. There,36 percent of the phosphorus was from municipal and industrial waste; 17 percent from urban runoff, which included lawn
fertilizers, automobile exhausts, precipitation, and chemicals used in street
deicing; 42 percent from rural nmoff from croplands, woodlands, pastures,
manure, and drainage from silos and barns; two percent from precipitation;
and two percent from ground (subshrface) water. Ten percent of the nitrogen
entering the lake Was from municipal and industrial waste; six percent from
_
urban runo; 11 percent from rural runoff; 20 percent from precipitation; 52
percent from ground water;
percent from nitrogen xation; and some
fraction of the nitrogen from several sources Was attributable to con—
tamination from nitrate fertilizers. Small but undetermined amounts of both
phosphorus and nitrogenwere also attributed to marsh drainage. From these
Ï
estimates the authors of
this study concluded that 50 percent of the nitrogen
and 90 percent Of thé phosphorus in Lake Mendota was associated with
wastes from human activities, added irit_entionally or mütentionay to the |
lake [23l— OIY 12 percent Of the nitrogeÏn,and 56 percent of the phosphorus %
entering Lake Washington in Seattle
was from sewage effluent [24].
Different studies reect some variations in the proportion of nitrogen and
phosphorus assigned to their respective-sÇŒCes. Variations would be ex—
.
pected according to the degree and
and industry, the
of the city, and the type of waste treaüneutu1 ÎhC΀SË area,
only
1 34
Overfed
.
,
…
m=rm
‘°
*iîï‘ … ill l‘…… “ ““'MÏ”i
” '\l lil … Î’Îl'w
'
i
much of the other nutrients can be used. If only half a unit of phosphorus 1sr
present in the water for every
ten units of nitrogen and 106 of carbon, only
half the nitrogen and carbon will be used by the algae or other aquatic plants
The presence of large amounts of carbon and nitrogen in the water and the
_
absence of phosphorus would indicate that phosphorus was the factor limitingf
plant growth. If sewage effluents rich in phosphorus were added to this
an increase in plant productivity could result.
To understand the limiting factor concept in relation to the three critical
nutrients, consider the following hypothetical analogy. To purchase a pack—_
age of cigarettes from a coin—operated dispenser, presume you
must insert r
into three appropriately sized slots a nickel, a dime, and a quarter. If you are
missing one coim even the humble nickel, the other two are useless. You can—
not operate the machine even though you may have three dimes and two f—
quarters. Similarly, if phosphorus, for example, is missing in a body of water,
au aquatic plant cannot
utilize any of the nitrogen and carbon present, even
if the latter elements exist in abundance. The two nutrients generally consid—'
ered by scientists to be the most frequent limiting factors in the aquatic
ronmentïàre the nitrates and the phosphates. Phosphates, in particular, are
garded by some scienüsts as the major limiting factor because their levels are _
so low in nature in relation to plant needs _[22].
A number of studies have been conducted in an effort to determine the
sources of nitrogen and phosphorus and the relative amounts of each which
can be assigned to natural sources as compared with agricultural, industrial,
or domestic
Mendota in Madison, Wisconsin, was the site of
one extensive survey. There,36 percent of the phosphorus was from municipal and industrial waste; 17 percent from urban runoff, which included lawn
fertilizers, automobile exhausts, precipitation, and chemicals used in street
deicing; 42 percent from rural nmoff from croplands, woodlands, pastures,
manure, and drainage from silos and barns; two percent from precipitation;
and two percent from ground (subshrface) water. Ten percent of the nitrogen
entering the lake Was from municipal and industrial waste; six percent from
_
urban runo; 11 percent from rural runoff; 20 percent from precipitation; 52
percent from ground water;
percent from nitrogen xation; and some
fraction of the nitrogen from several sources Was attributable to con—
tamination from nitrate fertilizers. Small but undetermined amounts of both
phosphorus and nitrogenwere also attributed to marsh drainage. From these
Ï
estimates the authors of
this study concluded that 50 percent of the nitrogen
and 90 percent Of thé phosphorus in Lake Mendota was associated with
wastes from human activities, added irit_entionally or mütentionay to the |
lake [23l— OIY 12 percent Of the nitrogeÏn,and 56 percent of the phosphorus %
entering Lake Washington in Seattle
was from sewage effluent [24].
Different studies reect some variations in the proportion of nitrogen and
phosphorus assigned to their respective-sÇŒCes. Variations would be ex—
.
pected according to the degree and
and industry, the
of the city, and the type of waste treaüneutu1 ÎhC΀SË area,
only
1 34
Overfed
.
,
…
m=rm
‘°
*iîï‘ … ill l‘…… “ ““'MÏ”i
” '\l lil … Î’Îl'w
'