156 

 TRANSPARENCY 

 Methods 



The transparency of the water in Santa Monica Bay was 

 measured using both the Secchi disc and a hydrophotometero 

 The Secchi disc, a white metal plate 30 cm in diameters, was 

 lowered at all hydrographic stations as a standard procedure. 

 In 1955 and the early months of 1956 p no partictilar concern 

 was expressed about the traaasparency of the water in the bay, 

 so that no attempt was made to determine any seasonal trends 

 which may fea^e existed „ Although numerous readings had been 

 obtained during the srammer of 1955 p the measurements taken 

 throughout the remainder of 1955 arid 1956 were scattered, and 

 the density of the stations was mot enough to allow the com- 

 pilation of seasonal charts » NeTerthelesSc, determinations of 

 transparency in the bay taken throughout the year were in 

 sufficient numbers to compile a composite chart of the average 

 depth to which a Secchi disc can be seen (Figo 76), In spite 

 of the antiquity of the instruement and method, definite 

 expectable patterns are apparent that show the normal offshore 

 water coMitions as well as the influence of sewage discharge » 



The hydr ©photometer was loaned to the Hancock Foundation 

 by the Uo So Navy Electronics Laboratory » San Diego, It 

 consists of a metal frame holding a light source and a 

 receiving prism^photocello one meter apart „ The light reaching 

 the photocell is transmitted through a waterproof cable to the 

 deck where the electrical impulse is read in micro-ampereso 

 In the first few feet of water light not only came from the 



