PLANKTON PRODUCTION IN FISH PONDS 
145 
mous decrease in the net loss on ignition. The minimum comes after a slight decrease 
in the net loss on ignition while the latter is on a low level already. The minimum 
pH is correlated also with a decrease in dissolved oxygen and a large increase in 
ammonia nitrogen. With a subsequent rise in the organic matter, a decrease in 
ammonia nitrogen and an increase in dissolved oxygen, the pH goes up again. The 
variations in pH and temperature in C 3 are shown in Figure 3. In C 4 the pH 
ranges from 7.7 to 8.8 in the morning sam- 
ples and from 8.9 to 9.05 in the afternoon 
samples. The minimum and the maximum 
occur here at the beginning and at the 
end of the season, respectively. Figure 3 
shows the variations in these values in C 4. 
On the whole it may be stated that 
with very few exceptions the water in these 
ponds was alkaline with respect to phenol- 
phthalein. Also it may be stated that as 
a general rule the pH maxima correspond 
to the minima for free C0 2 and conversely 
the free C0 2 maxima correspond to the 
minima for pH. This would suggest that 
the acidity or hydrogen-ion concentration 
is controlled by the free C0 2 . 
Free C0 2 . — Table 2 shows that free 
C0 2 was never present in C 1 . In fact there 
existed always aC0 2 deficiency or a phenol- 
phthalein alkalinity. This alkalinity varied 
from a minimum of 10.10 p. p. m. on June 
27 to a maximum of 68.76 p. p. m. on July 
30. From this date on the phenolphthalein 
alkalinity decreases, at first rapidly and 
then more slowly, until by September 19 it 
is down to 11.72 p. p. m. again. The great 
change in the phenolphthalein alkalinity or 
the free C0 2 deficiency from July 19 to Au- 
gust 9 is associated with a rapid rise and 
decline in the net loss on ignition, also by 
an increase in pH. The dissolved oxygen 
m. to 12.21 p. p. m. and decreases again to Fl ^ RE ^‘ations in free carbon dioxide dissolved oxygen 
r r ° chloride, different forms of nitrogen and phosphorus, and 
8.74 p. p. m. An examination of Table 6 organic matter expressed in p. p. m.; pH values and tempera- 
shows that the net plankton increased from ture in degrees c ' for ponds 0 1 and c 2 
0.1 cubic centimeter per 10 liters of water on July 19 to 3.5 cubic centimeters on July 
30, and to a maximum of 9.0 cubic centimeters per 10 liters of water on August 1. On 
August 9 it was down to 3.8 cubic centimeters again. These plankton samples were 
composed almost exclusively of algae. This, of course, would mean a very rapid rate 
of photosynthesis and hence the great free C0 2 deficiency and the large increase in 
dissolved oxygen. The variations in pH and the free C0 2 deficiency or the phenol- 
phthalein alkalinity is shown in Figure 2. 
