150 



determining the salinities and in choosing a value for the 

 salinity of normal shelf water. 



Extent of the Sewage Field 



Figures 74 and 75 are typical representations of the 

 sewage field, as shown by surface salinities » On both charts 

 limits are defined by a salinity of 34,40 o/oo, representing 

 a dilution of one part sewage to 332 parts of normal shelf 

 water. On June 20 and Aragust 10 j, 19 55, the sewage field was 

 better defined by salinity than by temperature. On June 20, 

 the field was restricted to an area extending between Playa 

 del Rey and Manhattan Beach and approximately 2y miles from 

 shore. On August 10, the effects of a northerly flow are 

 evident, with the field occupying an area between Santa Monica 

 and Manhattan Beach and 3|- miles from shore. Minimum sali- 

 nities were encountered at the outfall, and were less than 

 approximately 32»60 o/oo and 32.90 o/oo, respectively. 



Nutrients 



On January 13, 1956, and on subsequent cruises the central 

 and northern parts of the bay were not covered, but on that 

 date and at a point about 1^ miles off Palos Verdes Point the 

 concentrations of silicate-silicon and phosphate-phosphorus 

 were approximately half that present on August 16 and 17, 1955, 

 and they showed a slight increase with depth. Nitrate-nitrogen 

 at this time could not be detected in the surface water, but 

 it did occur at deeper levels (2.0 jig-=a*/L). Only a trace of 

 ammonia was found in the surface water, and oxygen was near 

 saturation. 



