146 
BULLETIN OE THE BUREAU OF FISHERIES 
Table 2 shows that free C0 2 occurred only twice in pond C 2. The remainder 
of the time the water was alkaline to phenolphthalein, that is, a free C0 2 deficiency 
existed. The maximum free C0 2 deficiency amounted to 57.60 p. p. m. and the 
maximum free C0 2 was 7.58 p. p. m. The first occurrence of free C0 2 is associated 
with a rapid decrease in organic matter and the dissolved oxygen, and a very marked 
rise in the ammonia nitrogen. The second occurrence of free C0 2 is marked by a 
less-pronounced decrease in the organic matter and the dissolved oxygen, but there 
is a slight decrease in the ammonia nitrogen. The maximum C0 2 deficiency is accom- 
panied by an increase in the organic matter and the volume of net plankton. The 
variations in free C0 2 are shown in Figure 2. 
According to Table 2, free C0 2 appeared only once in C 3; namely, on August 20 
when 6.06 p. p. m. were found. For the rest of the season, with one exception on 
July 30, when the water was neutral to phenolphthalein, there existed a free C0 2 
deficiency. This C0 2 deficiency was at its height early in the season. The maximum 
of 85.94 p. p. m. occurred on July 7. Although this is associated with a large decrease 
in organic matter, the number of algae that were present (Table 8) indicates that 
photosynthesis was still going on actively. However, Tables 2 and 9 show that the 
maximum alkalinity is not correlated with the maximum number of algae. Later 
in the season the alkalinity was greatly reduced: From July 19 to August 30 it never 
exceeded 30.34 p. p. m. In September, however, the alkalinity increased rapidly 
again so that by September 19 it had reached 65.72 p. p. m. again. This rise in 
alkalinity in September is correlated with a rise in the number of algae per liter of 
water. Figure 3 shows the variations in free C0 2 . 
In pond C 4 as in C 1 free C0 2 was never encountered. Table 2 shows that the 
phenolphthalein alkalinity here varied from a minimum of 8.08 p. p. m. on June 27 
to a maximum of 45.50 p. p. m. on September 19. The minimum and the maximum 
phenolphthalein alkalinities correspond to the minimum and the maximum pH values. 
The minimum alkalinity corresponds also to the maximum for the net loss on ignition. 
The fact that the maximum alkalinity occurs simultaneously with the minimum for 
the net loss on ignition is due to the appearance of some filamentous algae on the 
bottom. These algae would not appear in the samples, yet they use up C0 2 . Figure 
3 shows the variations in free C0 2 . 
Table 2 shows that two sets of determinations of pH and free C0 2 were made on 
August 9. The first sample was taken at 8 a. m. and the second at 3 p. m. This 
was done in order to obtain some idea as to the amount of variations that may occur 
during a relatively short interval of time. This test was carried out on a bright day. 
The table shows that in C 1 the phenolphthalein alkalinity increased from 44.50 p. p. m. 
to 72.80 p. p. m., and the pH rose from 8.9 to 9.1. These changes are correlated with 
the presence of 216,000 colonies of Pleodorina and 748,800 colonies of Pandorina per 
liter of water. (Table 8.) These algae used up more C0 2 for photosynthesis than 
they produced through respiration. Hence the increase in pH and in alkalinity. 
In C 2 the free C0 2 decreased from 7.58 p. p. m. to —23.34 p. p. m. and the pH rose 
from 7.55 to 8.7. These changes in C 2 are likewise correlated with fairly high 
counts for the algae Oocystis and Chroococcus. (Table 8.) In C 3 the changes were: 
Phenolphthalein alkalinity from 5.06 p. p. m. to 13.14 p. p. m. and pH from 8.0 to 
8.7. The changes in alkalinity are smaller in C 3 than in C 1 and C 2, but the 
change in pH is greater than in C 1. These changes in C 3 are correlated with 
fairly high counts for the algae, Scenedesmus, Chroococcus, and Aphanizomenon. 
