304 EMERY, ORR, RITTENBERG 



Phosphorus, unHke nitrogen, is brought to the ocean only by rivers. 

 The best value available for the concentration of phosphate-phosphorus 

 in river water is probably that computed by Hutchinson (1952) from 

 Clarke's data, 0.07 mg/L. For the 27.2 x 10^^ L (Clarke, 1924, p. 63)^ 

 of river water annually reaching the ocean, this concentration corresponds 

 to an annual contribution of phosphate-phosphorus of 1.9 x 10'' tons. 

 To this should be added the phosphate contained in dissolved organic 

 matter. Assuming that the dissolved organic matter of rivers and the 

 ocean have the same phosphorus to nitrogen ratio, the phosphorus con- 

 tributed in dissolved organic matter of rivers is 0.3 x 10*^ tons annually. 

 The total, 2.2 x 10^ tons, is about 0.2% of the annual use and it is evi- 

 dent that, like nitrogen, most of the needed phosphorus must be regen- 

 erated and re-used. In addition to its dissolved form, much of the phos- 

 phorus contributed to the ocean is in the form of mineral grains and 

 of ions adsorbed on solids (Carritt and Goodgal, 1954). Analyses of 

 phosphorus in river-borne sediments are not abundant, but the average 

 for fine-grained Colorado River sediments trapped in Lake Mead is 

 0.074% (Gould, 1953, p. 178) and for the Mississippi River delta 

 0.079% (Clarke, 1924, p. 509). The total annual tonnage of suspended 

 matter contributed to the ocean by rivers is 16 x 10^ tons, as computed 

 from Conway's ( 1942) average for suspended matter in rivers, 0.6 gm/L. 

 From Twenhofel's (1932) ratio of dissolved to suspended load for 

 eastern United States rivers the tonnage is 5 x 10^, and from Kuenen's 

 (1950, p. 233) estimate of 12 km^ per year it is 24 x 10^. Using the 

 middle value (neglecting deposition on deltas), with the average per- 

 centage of phosphorus in river suspended sediment, the annual contribu- 

 tion of phosphorus is 12 x 10^ tons. The total dissolved and inorganic 

 suspended phosphorus contributed by rivers is 14 x 10^ tons. 



The phosphorus content of pelagic sediments averages about 0.072% 

 on the basis of 87 samples from the North Atlantic (Correns, 1939) and 

 25 from the Pacific Ocean (Revelle, 1944). For 52 near-shore terri- 

 genous muds Clarke (1924, p. 518) gave an average value of 0.092% 

 phosphorus, nearly the same as the average of 0.094% for three basin 

 cores off southern California. Areas of phosphorite, a rich authigenic 

 phosphorus deposit, may be neglected in view of their small extent. Con- 

 sidering the area and rate of deposition of the sediments in the same way 

 as was done for nitrogen, we find that a total of 13 x 10^ tons of phos- 



^Wiist (Sverdrup, Johnson, and Fleming, 1942, p. 120) estimated runoff at 

 37 X 10^5 L. If his value ■were used our estimate of nutrients carried by rivers 

 would be increased 37%. 



