106
E. D. 5. CORNER AND ANTHONY Q. DAVIES
111. THE STOICHIOMETRY OF BIOLOGICALLY INDUCED CHANGES IN
NUTRIENT LEVELS
“ It is a remarkable fact that plant growth should be able to strip
sea water of both nitrate and phosphate, and that in the English
Channel the store of these nutrient salts formed during the autumn and
winter should be used up at about the same time ”, wrote H. W.
Harvey in 1926. The implication, that the concentrations of the two
nutrient salts in the sea were apparently in the ratio in which they were
assimilated by the phytoplankton, was taken up some years later by
Redfield (1934). He showed that there was, in fact, an approximately
linear correlation between the concentrations of nitrogen (as nitrate)
and phosphorus (as phosphate) for sea waters obtained from many
different geographical locations and different depths. The lowest
concentrations werc found in the surface layers, where the nutrients
had been utilized by the plants; and their near proportionality meant
that complete assimilation by the phytoplankton of one of the nutrients
would leave very little of the other unused, in agreement with Harvey’s
observation.
The metabolism of organic matter by animals and bacteria releases
into solution organic forms of nitrogen and phosphorus as excretion
products which are eventually oxidized back to nitrate and phosphate
ions, oxygen being consumed in the process. During photosynthesis, on
the other hand, the nutrient salts are utilized for the synthesis of
organic matter by plants, and oxygen is produced. Redfield (1934)
argued that the relative changes in the concentrations of inorganic
nitrogen and phosphorus in sea water resulting from these biological
changes should be directly related t o the elementary composition of the
plankton. He showed that, while there was a considerable variation
between species, the average nitrogen : phosphorus ratio (by atoms) in
a mixed group of phytoplankton and zooplankton was 18*7:1, this
average being in good agreemcnt with the slope of 20:l given by the
plots of dissolved nitrate-nitrogen against dissolved phosphatephosphorus.
A. The “ assimilation ratio ”, AN : AP
Cooper (1937a) presented data which confirmed that the nitrogen:
phosphorus ratios for sea water and marine plankton lay within close
limits; but pointed out (Cooper 193th) that the technique used for
phosphate analyses up to that time was subject to a salt error. When
corrections were made for this, Redfield’s nitrogen : phosphorus ratio
for sea water was reduced t o about 15:l. Cooper (1938b) further
E. D. 5. CORNER AND ANTHONY Q. DAVIES
111. THE STOICHIOMETRY OF BIOLOGICALLY INDUCED CHANGES IN
NUTRIENT LEVELS
“ It is a remarkable fact that plant growth should be able to strip
sea water of both nitrate and phosphate, and that in the English
Channel the store of these nutrient salts formed during the autumn and
winter should be used up at about the same time ”, wrote H. W.
Harvey in 1926. The implication, that the concentrations of the two
nutrient salts in the sea were apparently in the ratio in which they were
assimilated by the phytoplankton, was taken up some years later by
Redfield (1934). He showed that there was, in fact, an approximately
linear correlation between the concentrations of nitrogen (as nitrate)
and phosphorus (as phosphate) for sea waters obtained from many
different geographical locations and different depths. The lowest
concentrations werc found in the surface layers, where the nutrients
had been utilized by the plants; and their near proportionality meant
that complete assimilation by the phytoplankton of one of the nutrients
would leave very little of the other unused, in agreement with Harvey’s
observation.
The metabolism of organic matter by animals and bacteria releases
into solution organic forms of nitrogen and phosphorus as excretion
products which are eventually oxidized back to nitrate and phosphate
ions, oxygen being consumed in the process. During photosynthesis, on
the other hand, the nutrient salts are utilized for the synthesis of
organic matter by plants, and oxygen is produced. Redfield (1934)
argued that the relative changes in the concentrations of inorganic
nitrogen and phosphorus in sea water resulting from these biological
changes should be directly related t o the elementary composition of the
plankton. He showed that, while there was a considerable variation
between species, the average nitrogen : phosphorus ratio (by atoms) in
a mixed group of phytoplankton and zooplankton was 18*7:1, this
average being in good agreemcnt with the slope of 20:l given by the
plots of dissolved nitrate-nitrogen against dissolved phosphatephosphorus.
A. The “ assimilation ratio ”, AN : AP
Cooper (1937a) presented data which confirmed that the nitrogen:
phosphorus ratios for sea water and marine plankton lay within close
limits; but pointed out (Cooper 193th) that the technique used for
phosphate analyses up to that time was subject to a salt error. When
corrections were made for this, Redfield’s nitrogen : phosphorus ratio
for sea water was reduced t o about 15:l. Cooper (1938b) further