Mineralization of Organic Matter in Santa Monica Bay 643 



where Nt = number of survivors after t hours, No = initial popu- 

 lation, T-90 = time in hours for 90 per eent reduction in popula- 

 tion, and T-90m, T-90d, and T-90. = times for 90 per eent reduc- 

 tions due to mortality ( 17.8 hr. ) , dilution ( 20 hours ) , and sedi- 

 mentation (21 hours), respectively. 



The daily discharge contained about 20,000 kg ammonia 

 nitrogen, 200 kg nitrate nitrogen, 22,000 kg organic nitrogen, 

 8,500 kg phosphate phosphorus, and 5,500 kg organic phosphorus. 

 Sedimentation of organic material and mineral nutrients is de- 

 pendent upon their distribution between the suspended and dis- 

 solved fractions, and may be assumed to be related to the reduc- 

 tion in surface coliforms due to sedimentation (4). On this basis, 

 it is computed that 20,000 kg organic nitrogen, 5,000 kg organic 

 phosphorus, and 460 kg P04-phosphorus settled to the bottom 

 during the first day after discharge. 



The present study is a further evaluation of the fate of the 

 effluent in the receiving waters and is directed towards the time 

 and space variations of nitrogen and phosphorus. 



DATA AND CALCULATIONS 



Figures 1 and 2 summarize ol)ser\'ations of tlie effluent field 

 along the 15 m contour between the outfall and 3 km downstream 

 made January 13, 1956, on VELERO IV Cruise 235 (11). The 

 dilutions are based upon chlorinities and define an effluent field 

 floating within the upper 10 meters. The lower limit of this field 

 corresponds with high Oj and low NO3-N values and with dis- 

 continuities in NHs-N and PO4-P concentrations. Water tem- 

 peratures varied from 13.3 to 14.0 C at the surface and from 

 11.9 to 12.3 C at the bottom. A northerly current of about 15 

 cm/sec is estimated from surface dilution and surface coliform 

 concentrations. 



The total inorganic-N, assuming that nitrite is negligible, 

 and PO4-P within the upper 10 meters were markedly less than 



