267 



pH 7.50, at Crockett; the hii;liest was pH 8.16, at the Oakhmd Mole, thus giving a 

 range of only 0.66 Sorcnsen unit for the entire bay. 



The average values for each condition at each locality are indicated in the graphs. 

 The variations from hour to hour, as shown in the graphs, are decidedly irregular; 

 hut in a majority of cases the larger \ariations are correlated with the ehl) and How 

 of the tide. This correlation is obvious at Crockett and Dumbarton, and is shown, 

 though in less degree, at the Ferry Building. These three stations border on strong 

 tidal currents of well-marked direction. (_)n the other hand, at the Oakland Mole 

 and at the Fort Scott Mine Dock, Ixith of which localities stand rather in the backwash 

 of the major tidal currents, only a slight degree of correlation between the condition 

 of the water and the ebb and flow of the tide is to be observed. 



A study of the graphs will show that in general the dissolved oxygen and pH 

 values tend to vary together, and that they bear an in\'erse relation to the amount 

 of dissolved hydrogen sulfide. Thus it will be noted that from the first to the last 

 run at all stations there is a general upward trend of the pH values with a corres- 

 ponding upward trend of the amount of dissolved oxygen, and a downward trend 

 of the hydrogen sulfide. This relation is so variable, however, that no one factor 

 can be regarded as a satisfactory index to the others. 



It is to be concluded from this study that the high oxygen content and low 

 hydrogen sulfide content of the waters of San Francisco Bay as a whole present 

 conditions favorable to the growth and reproduction of Teredo and its allies insofar 

 as these factors are concerned, while it is believed further that the narrow range of 

 Sorensen values observed would have little or no effect on so hardy and adaptable a 

 group of organisms. For so large a body of estuarine water, San Francisco Bay presents 

 a surprisingly uniform environment. Salinity and temperature are the most important 

 variables; their effects are discussed elsewhere, in this and the following chapter. The 

 other factors considered appear to play a minor role as regards their effect on the dis- 

 tribution of marine borers, unless it be in the immediate vicinity of sources of con- 

 siderable pollution by sewage or industrial wastes (see below). 



Effects of Sewage Contamination 



It has been claimed that pollution by sewage and industrial wastes may be a 

 factor of some importance in the prevention of damage by marine borers in harbors 

 where such pollution is great. The data set forth above indicate that sewage con- 

 tamination is a factor of little importance in its effect on the condition of the water 

 of San Francsico Bay. In order to throw further light on this point, it was decided 

 to make a special investigation of conditions near the mouth of a sewer, to determine 

 the effect of pollution on the water immediately proximal to the sewer outlet, and 

 the rapidity with which such effect is dissipated with distance. 



The locality selected for this purpose was the Channel Street canal, San Fran- 

 cisco. This canal, about 1200 yards long and 50 yards wide, joins the bay in the 

 so-called "China Basin," near pier 42. The only flow of water is that produced by 

 the rise and fall of the tide. At its upper end the canal receives the discharge of the 

 Channel Street sewer. This sewer is designed primarily for storm water overflows, 

 but is temporarily carrying some human sewage, and has in the past carried a great 

 deal more. 



Water samples were taken at low water slack on August 15, 1923, and at high 

 water slack on the following day, at each of three localities along the canal : one at 

 the upper end, about 100 yards from the mouth of the sewer (station A) ; one near the 

 lower end, about 100 ^'ards from the bay (station B); and one at pier 42, about 50 



