PLANKTON PRODUCTION IN FISH PONDS 
147 
(Table 8.) In C 4 the phenolphthalein alkalinity increased from 24.26 to 26.28 
p. p. m. and the pH from 8.7 to 8.9. The changes in pH are equal to that in C 1, 
but are much less than in C 2 or 3. The change in alkalinity is less here than in 
either of the other three ponds of this series. The change in temperature between 
8 a. m. and 3 p. m. was 5° C. ; namely, from 25° C. to 30° C. 
Dissolved oxygen . — The dissolved oxygen data are shown in Table 3. This table 
shows that in C 1 the dissolved oxygen varied from 4.36 p. p. m. on June 27 to a 
minimum of 3.43 p. p. m. on July 7. On July 30 it reached a maximum of 12.01 
p. p. m. After this date it gradually decreases to 5.53 p. p. m. on August 20. By 
September 19 the dissolved oxygen is up to 10.25 p. p. m. again. The maximum of 
12.21 p. p. m. when the temperature was 21.1° C. is amply accounted for by the 
plankton data Table 6 and is discussed more fully in that connection. The relation- 
ship between dissolved oxygen and temperature is shown in Figure 2. The variations 
in dissolved oxygen are shown in Figure 2. 
In pond C 2 the dissolved oxygen reached a minimum of 2.14 p. p. m. on July 7. 
Then it rose to a maximum of 11.97 p. p. m. on July 30. Ten days later it had 
dropped to 2.59 p. p. m. On September 19 it was up to 8.18 p. p. m. The two 
minimal values for dissolved oxygen are associated with decreases in the loss on 
ignition and the volume of net plankton. Figure 2 shows the relationship between 
dissolved oxygen and temperature. The variations in dissolved oxygen are shown 
in Figure 2. 
Table 3 shows that the dissolved oxygen in C 3 behaved somewhat differently 
than it did in C 1 and C 2. In this pond the minimum of 1.66 p. p. m. occurred 
simultaneously with a considerable increase in the net loss on ignition. Also the 
midsummer maximum of 6.91 p. p. m. is correlated with a sharp decline in the net 
loss on ignition. In C 1 and C 2 the reverse of this is true. The maximum for the 
season occurred on September 19 and amounted to 9.67 p. p. m. Figure 3 shows 
the variations in dissolved oxygen. 
In C 4 the dissolved oxygen, as shown in Table 3, amounted to 6.29 p. p.m. on 
June 27. This figure is much higher than the corresponding figure for the other 
ponds of this series. The minimum of 3.53 p. p. m. is likewise higher than the mini- 
mum for C 1, C 2, and C 3. Both the season’s minimum and the midsummer maxi- 
mum are correlated with a decrease in the amount of organic matter. The amount 
of dissolved oxygen in C 1 and C 4 parallel each other fairly closely and are on the 
average somewhat higher than those in C 2 and C 3. The lower values for dissolved 
oxygen in C 2 and C 3 as compared with those in C 1 and C 4 are correlated with 
higher values for the average amount of organic matter. The variation in the dis- 
solved oxygen in C 3 is shown in Figure 5. 
Chlorides . — Table 3 shows that the amounts of chloride in solution in the water 
of C 1, C 2, and C 4 are comparable. The same is also true of their variations. In 
C 1 it ranges from 2.5p. p.m. to 4. 5 p. p. m. and the average for nine determinations 
is 2.94 p. p. m. In C 2 and C 4 it ranges from 2.0 p. p. m. to 3.5 p. p. m., but the 
average of nine determinations for C 2 is 2.7 p. p. m., while the average for an equal 
number of determinations in C 4 is 3.11 p. p. m. ; that is, the unfertilized pond had 
on the average more chloride in solution than a pond fertilized with either super- 
phosphate or soybean meal. In C 3 the amount of chloride in solution is much greater 
than that in C 1, C 2, and C 4. It ranges from 16.0 p. p. m. to 21.0 p. p. m. The 
average for nine determinations is 18.2 p. p. m. The higher values for dissolved 
