Table 12. --Average carbon dioxide values in the summer of 1929 



free carbon dioxide at all depths throughout the whole 

 lake. By the time our first determinations were made 

 in June, this carbon dioxide had already been removed 

 by the phytoplankton. The analyses show no free car- 

 bon dioxide in the surface waters during the period 

 from June to September and a marked decrease in 

 free carbon dioxide at the bottom with advance of the 

 season. The photosynthetic action of the phyto- 

 plankton must be tremendous to bring about such 

 changes, especially since the processes which release 

 carbon dioxide are also proceeding with perhaps more 

 than usual speed at this same time of year. The 

 Deep Hole is probably the only spot in the lake which 

 is characterized by free carbon dioxide the year 

 round, but even this may be neutralized by the au- 

 tumnal overturn. 



Entirely too little is known about the production 

 and utilization of organic materials in aquatic en- 

 vironments. In a large lake like Erie it is the rela- 

 tively shallow area which reacts to changing cli- 

 matic conditions in larger measure than the deep 

 zone. This is the region in which greater photosyn- 

 thetic activity proceeds. During the warm and light 

 summer period practically the whole lake yields to a 

 pulse of photosynthesis whose pace is greater than op- 

 posing processes of carbohydrate fermentation and 

 protein decomposition. The result must mean a sea- 



sonal increase in synthesized organic stuffs existing 

 in the original manufacturing organisms, the plants; 

 in the consumers, the animals; and in solution in the 

 water. How nearly the distribution of organic matter 

 in Lake Erie approaches that reported for the Wiscon- 

 sin Lakes by Birge and Juday (1926) remains to be 

 shown. How much exists in the plankton? How much 

 in solution? How much is left over and above the 

 annual turnover? 



Methyl -Orange Alkalinity 



The methyl -orange alkalinity of Lake Erie waters 

 did not fluctuate appreciably during the period of 

 observations. 



The total alkalinity (expressed as p. p. m. of 

 calcium carbonate) in the summer of 1929 ran con- 

 sistently lower at the surface than at the bottom, as 

 shown by the mean of all the determinations made 

 each month. This difference was, however, only a 

 fractional part per million. In June the mean sur- 

 face alkalinity was 0. 7 p. p. m. lower, and in Sep- 

 tember 0. 2 p. p. m. lower than the mean bottom al- 

 kalinity. 



There also was an apparent small seasonal var- 

 iation in total alkalinity. In June the mean surface 



84 



