PLANKTON I N NITROGEN AND PHOSPHORUS CYCLES
105
D. Inorganic phosphorus
Currently used analytical methods allow the measurement of three
main types of phosphorus in the sea (Strickland and Austin, 1960).
They are (1) dissolved inorganic phosphate; (2) dissolvcd organic
phosphorus; and (3) particulate phosphorus, both inorganic and organic.
However, because of the non-specific nature of the analytical techniques, these divisions are by no mcans clear-cut (e.g. inorganic
phosphate polymers arc included in dissolved organic phosphorus).
The dissolved inorganic phosphate is represented almost cxclusively
by orthophosphate. The apparent dissociatioI1 constants of phosphoric
acid determined by Kcster and Pytkowicz (1967) indicate that in sea
water of salinity 33x0 at 20°C, most of the orthophosphate (87%) would
be present as HPOt- with 12% as PO:- and the rcmainder as H,PO;.
Sillen (1961), using data on the solubility of the various forms of calcium
phosphate, speculated that the orthophosphate in deep sca water, away
from any biological influence, might be in equilibrium with the mineral,
hydroxyapatite, which is present in marine sediments:
Ca,(PO,),OH(s) + 4H+ + 5Ca2+ + 3HPOt- + H,O.
By using ultra-violet irradiation to oxidize the dissolved organic
phosphorus to orthophosphate, Solbrzano and Strickland ( 1968) were
able to show that polyphosphates, which were resistant to the irradiation, were only rarely present at levels above the detection limit of
0.05 pg-atoms P/1 in sea waters obtained off the California coast and
also from the east-central Pacific Ocean. A similar finding has been
reported for English Channel water by Armstrong and Tibbitts
(1968).
E. Organic phosphorus
Although the organic fraction may represent more than 50% of the
total phosphorus in solution, its chemical constitution has yet to be
described. Strickland and Austin (1960) found that dissolved organic
phosphorus concentrations were highest when phytoplankton populations were large, indicating that its release by plankton or formation
during their decomposition was probably its main source. Strickland
and Sol6rzano (1966) found little of the organic phosphorus to be
present as enzyme-hydrolysable phosphate esters and suggested that it
might be nucleic acid material. The fact that substantial quantities of
deoxyribonucleic acid are present in particulate matter in the sea
(Holm-Hansen et al., 1968) lends support to this view.
105
D. Inorganic phosphorus
Currently used analytical methods allow the measurement of three
main types of phosphorus in the sea (Strickland and Austin, 1960).
They are (1) dissolved inorganic phosphate; (2) dissolvcd organic
phosphorus; and (3) particulate phosphorus, both inorganic and organic.
However, because of the non-specific nature of the analytical techniques, these divisions are by no mcans clear-cut (e.g. inorganic
phosphate polymers arc included in dissolved organic phosphorus).
The dissolved inorganic phosphate is represented almost cxclusively
by orthophosphate. The apparent dissociatioI1 constants of phosphoric
acid determined by Kcster and Pytkowicz (1967) indicate that in sea
water of salinity 33x0 at 20°C, most of the orthophosphate (87%) would
be present as HPOt- with 12% as PO:- and the rcmainder as H,PO;.
Sillen (1961), using data on the solubility of the various forms of calcium
phosphate, speculated that the orthophosphate in deep sca water, away
from any biological influence, might be in equilibrium with the mineral,
hydroxyapatite, which is present in marine sediments:
Ca,(PO,),OH(s) + 4H+ + 5Ca2+ + 3HPOt- + H,O.
By using ultra-violet irradiation to oxidize the dissolved organic
phosphorus to orthophosphate, Solbrzano and Strickland ( 1968) were
able to show that polyphosphates, which were resistant to the irradiation, were only rarely present at levels above the detection limit of
0.05 pg-atoms P/1 in sea waters obtained off the California coast and
also from the east-central Pacific Ocean. A similar finding has been
reported for English Channel water by Armstrong and Tibbitts
(1968).
E. Organic phosphorus
Although the organic fraction may represent more than 50% of the
total phosphorus in solution, its chemical constitution has yet to be
described. Strickland and Austin (1960) found that dissolved organic
phosphorus concentrations were highest when phytoplankton populations were large, indicating that its release by plankton or formation
during their decomposition was probably its main source. Strickland
and Sol6rzano (1966) found little of the organic phosphorus to be
present as enzyme-hydrolysable phosphate esters and suggested that it
might be nucleic acid material. The fact that substantial quantities of
deoxyribonucleic acid are present in particulate matter in the sea
(Holm-Hansen et al., 1968) lends support to this view.