sition of the spring crop of phytoplankton. The diatoms were very abundant 

 in early June but declined in late June and reached the low point for the 

 season on July 1. (Fig. 13). The dead cells would, of course, take a con- 

 siderable amount of oxj'-gen from the water during the process of decay. Recov- 

 ery was rapid, for on July 8 the water was 92 per cent saturated, but there 

 was little change observed on the two following dates. There were few phyto- 

 plankton organisms at this time, hence little photosynthetic activity. Unfrr- 

 tunately no samples were taken in early September. In late Septmeber, when 

 algae were again abundant, the water was 99 per cent saturated, but on Octo- 

 ber lU the algae were declining at Station 37A and oxygen was reduced to 91 

 percent of saturation. On every date but one when samples were taken near 

 the bottom, the bottom water held less oxygen than the surface. The greatest 

 observed difference was 0.7 part per million and it is doubtful whether deple- 

 tion ever reached a point vdiere it would be dangerous to organisms living at 

 the bottom. 



An excess of free carbon dioxide was found at the surface on only one 

 occasion. May 2 3, -Jhen there was an excess of 0.8 part per million. In June 

 there was a deficiency of the gas as a resiiLt of removal of part of the half- 

 bound carbon dioxide by algae. This deficiency was removed by July 1, at which 

 time the oxygen was at its lowest point. On the next two dates the curves for 

 carbon dioxide and oxygen are not in complete agreement. When the oxygen 

 increased between July 1 and 8 there w^s no corresponding change in the car- 

 bon dioxide. In late July the carbon dioxide deficit reached 2.3 parts per 

 million but the oxygen content remained almost unchanged. The single sample 

 taken in August showed only a slight deficit. It was somewhat greater in late 

 September, when the phytoplankton was abundant, but on October ll; the water 

 was neutral to phenolphthalein. The differences observed between surface and 

 bottom samples were not of great magnitude. On August 12 the bottom water 

 held an excess of 1.5 parts per million when the surface water hai a deficit 

 of 0.5 part per million; and on June 19 there was a difference of 1.5 parts 

 per million between the two depths. On the remaining dates little or no dif- 

 ference was found. 



The curve of pH values shows close relationship to the curve of free 

 carbon dioxide; only in the sample taken in August was there failure to 

 respond to a change in carbon dioxide. Exact agreement should not be expected 

 because other factors than free carbon dioxide (particularly carbonates) affect 

 pH. The pH ranged from 7.8 to 8.1. On three occasions when surface and bot- 

 tom samples were taken, they were the same; on three other occasions the sur- 

 face was pH 6.1 and the bottom pH 7.9; once the surface was pH 8.1 and the 

 bottom pH 8.0. 



Methyl orange alkalinity ranged from 89 to 98 parts per million. The 

 highest values were observed during July and the lowest in October. The 

 greatest difference between surface and bottom samr^les was 5 parts per mil- 

 lion, on July 25. In this case the larger amount was at the surface; in 

 other cases where there was a difference, the large amount was at the bottom. 



66 



