Mineralization of Organic Matter in Santa Monica Bay 649 



pleths are equivalent to semicircles, and that they represent hori- 

 zontal concentrations in one-half of a right circular cone whose 

 apex is located over the outfall at a depth of 10 m. Continuity 

 requirements for dilutions of 20, 100, and 300 parts sea water 

 per part effluent at 0, 4, and 24 hours, respectively, and of ex- 

 trapolated values to 48 hours, permit computation of the total 

 PO4-P within the mass for observed concentrations. This calcu- 

 lated value is then corrected by subtracting the background 15- 

 20 /'g/L and compared with quantities which represent the 

 PO4-P discharged with the effluent through various time intervals. 

 Figure 3 shows the results of these computations where the dif- 

 ference between the total excess amount in the water and the 

 increment furnished by the outfall reaches a maximum of 3,500 

 kg PO4-P after about one day; this difference may be ascribed 

 to mineralization. The differences indicated after about one and 

 one-half days are of doubtful significance because dilution has 

 brought the concentrations to within the normal variation. 



DISCUSSION 



Profiles of nutrient concentrations within 3 km of the outfall 

 imply mineralization of organic nitrogen and phosphorus at rates 

 of 1,000 and 300 kg/day, respectively, on the bottom, and 2 and 

 0.6 kg/day, respectively, in the effluent field. Thus, about 5 per 

 cent of the available material is regenerated in the sediments 

 while about 0.1 per cent is regenerated in the water. Although 

 there are several uncertainties implicit in the analysis, the greater 

 efficiency of mineralization within the sediment is apparent. 



Increases in the standing crop of microplankton have been 

 observed (7, 12); these vary from about 20 per cent during most 

 of the year to some 300 per cent during the spring and fall blooms. 

 Dinoflagellates appear to be the most responsive to the nutrients 

 in the discharge. The nitrogen and phosphorus content of the 

 standing crop of microplankton have been computed by means 

 of the conversion factors given by Sverdrup et al ( 14, p. 929) ; the 

 resulting values were less than normal background variations of 

 the inorganic nutrients. The effects of normal and increased pro- 

 ductivity and of the mineralization of plankton detritus have 

 accordingly been neglected. 



