NO. IO WATER TRANSPARENCY — WILLIAMS, JOHNSON, DYER II 



equivalent of a ioo%jT reading in water was apparently unknown 

 to the data takers, which is not surprising since the instruction book 

 written for the U.S. Navy Hydrophotometer Mk. II specifies a cali- 

 bration setting of ioo percent in air. 



The Secchi Disc readings in general are undoubtedly quite reliable. 

 However, any taken when the sun was low in the sky or in the shade 

 of the boat are probably doubtful. 



In table 2 are given the remainder of the data taken with instru- 

 ments other than the hydrophotometer or Secchi Disc. These data 

 have been tabulated separately, since their meaning is not as well 

 understood as those in table I. 



An attempt was made to deduce some sort of a regular pattern of 

 transparency in the area covered, but no regular pattern appears to 

 exist. This may be due to the fact that all stations were not taken 

 simultaneously (a physical impossibility), although this is not nec- 

 essarily so. Previous experience indicates that local conditions, espe- 

 cially in more shallow coastal regions, almost completely determine 

 transparency conditions at any one point in space and time. Thus the 

 turbidity will vary from one place to another, one depth to another, 

 one time to another with seemingly constant environmental conditions. 

 These data seem to emphasize this seemingly unpredictable nature of 

 transparency in natural waters. 



In general, however, the data do show the following expected 

 changes in transparency : 



1. An increase in transparency with distance from the coast. 



2. A seasonal change in transparency, with the winter months 



seeming to provide the greatest turbidity. 



3. An increased turbidity around heavily industrialized areas. 



These three are, of course, to be expected, as outlined by Williams 

 [35] m a set °f general rules for predicting transparency based on 

 geographical location, weather conditions, proximity of polluting 

 sources, etc. But there are so many variables to be considered simul- 

 taneously that these generalizations are often invalid. 



This information is therefore presented not as a basic scientific 

 study to determine the causes of transparency variations, but rather 

 to present actual conditions existing at particular points in time and 

 space. 



