36 



REDFIELD, KETCHUM AND RICHARDS 



[CHAP. 2 



organic matter completely, enabling the total phosphorus to be measured in 

 ionic form. The difference yields the phosphorus present in organic combina- 

 tion. This fraction may be divided further by filtration into a portion present 

 as particulate matter, including living microorganisms and debris, and a 

 portion representing the phosphorus present in combination with dissolved 

 organic molecules. 



The total phosphorus content of a sample of sea-water may thus be separated 

 into several fractions according to the following scheme : 



Total phosphorus (P<) 



Inorganic phosphorus (PO4P) 



Phosphorus of oxidative origin 

 Preformed phosphorus 



Organic phosphorus 



Dissolved organic phosphorus 

 Particulate organic phosphorus 



Analysis after oxidation 

 Direct analysis 

 P^ = A.O.U./276 

 Pj, = PO 4 P-P 0a; 



p*-po 4 p 



Separated by filtration 



The phosphorus of oxidative origin is merely the apparent oxygen utilization 

 expressed as its equivalent in regenerated phosphorus. This notation is ad- 

 vantageous in reducing all aspects of the phosphorus cycle to common terms. 

 The methods for the determination of phosphate concentration in sea-water 

 are not precise, being subject to errors as large as 10%. Consequently, estimates 

 of the fractions are only approximate and frequently require statistical 

 treatment. 



In the process of regeneration, dissolved organic phosphorus represents an 

 intermediate product in the liberation of phosphorus of oxidative origin from 

 the particulate phosphorus of living cells and their debris. In Fig. 5 the distribu- 

 tion of phosphorus among these fractions at various depths and seasons at a 



FEBRUARY 



0-60 

 60- 120 

 120- 180 

 180-240 



MAY 



NOVEMBER 



PARTICULATE ORGANIC 



PREFORMED 



_l 1 I L 



1.0 

 mg aloms/m 3 



Fig. 5. Seasonal distribution of phosphorus fractions in Gulf of Maine. (From data of 

 Redfield, Smith and Ketchum, 1937.) 



