SECT. 1J THE INFLUENCE OF ORGANISMS ON THE COMPOSITION OF SEA-WATER 57 



After solving this equation for the value of the diffusion coefficient A at each 

 bounding surface, the information necessary to obtain the value of R charac- 

 teristic of each segment was available. 



As an example of the information obtained by this procedure on the pro- 

 cesses determining the phosphate concentrations at depth, a balance sheet of 

 the average rates of these processes in a layer of water in the euphotic zone 

 during a summer period is given in Table X. The phosphate phosphorus 



Table X 



Balance of Factors Changing the Concentration of Phosphorus in Water of 



Long Island Sound between Depths of 2.5 and 7.5 m, and during Period 



May 21-August 19. (Data from Riley, 1956a.) 



concentration in the water increased during the period from 0.51 to 1.0 mg 

 atom/m 3 or at a mean rate of about 0.5 x 10~ 2 mg atom/m 3 per day in spite of 

 a net loss, due to the excess of photosynthesis over regeneration, at a rate of 

 3.0 x 10 -2 mg atom/m 3 per day. This was possible because of the excess rate at 

 which regenerated phosphorus was returned to the layer by vertical diffusion. 

 Of the phosphate diffusing into the layer from below about three-quarters 

 remained in the layer to effect the balance while one quarter moved on into 

 the layer above. 



The rapid turnover which these exchanges produce is brought out by the 

 consideration that the initial concentration was only 0.51 mg atom, while the 

 biological consumption was 3.0 x 10 -2 mg atom per day. At this rate the phos- 

 phate in the layer would have been completely exhausted in 17 days had it not 

 been renewed by vertical diffusion. 



The result of Riley's estimates of the intensity of biological activity in Long 

 Island Sound at various depths and seasons is presented in Fig. 10. They show 

 that, in the summer period, the absorption of phosphorus by growing plankton 

 exceeds regeneration down to a depth of 12.5 m. Below this depth regeneration 

 is in excess and takes place mainly in the layer immediately above the bottom. 

 In spring the total rate of absorption exceeds regeneration, while in summer 

 this relation is reversed. During the winter the overall biological activity 

 appears to be greatly reduced and absorption exceeds regeneration only in 

 the layer immediately below the surface. 



