PLANKTON PRODUCTION IN FISH PONDS 
159 
June 30: 
Blanket algae (Hydrodictyon) covers about 20 per cent of area. 
Elodea cover about 15 per cent of area. 
Sagittaria cover about 3 per cent of area. 
Cattails (Typha) cover about 1 per cent of area. 
Narrow-leafed Potamogeton present. 
July 23: 
Elodea cover about 10 per cent of area. 
Cattails (Typha) cover about 3 per cent of area. 
Sagittaria cover about 2 per cent of area. 
Blanket algae cover about 5 per cent of area. 
Broad-leafed Potamogeton present. 
August 16: 
Elodea cover about 10 per cent of area. 
Sagittaria cover about 2 per cent of area. 
Blanket algae cover about 8 per cent of area. 
Cattails (Typha) cover about 1 per cent of area. 
LIMNOLOGICAL DATA 
Table 10 shows that the temperature was 17.2° C. on May 9, when the first 
observations were made. On May 19 the temperature had gone down to 13.3° C. 
The maximum temperature of 26.7° C. occurred on June 30 and July 28. 
A study of Table 10 shows that the transparency of the water in D 4 was relatively 
high. Transparency, or the depth at which a 4-inch white disk disappears from 
view varied from 2 to 4 feet. The lower values for transparency were due to silt. 
Table 10 shows that the minimum pH value of 7.6 occurred on August 18 and 
the maximum of 9.7 on July 10. Figure 5 shows that in a measure the higher pH 
values correspond to the higher temperatures. The correlation, however, is not close 
enough to warrant the conclusion that the hydrogen-ion concentration varies inversely 
as the temperature. 
Free C0 2 did not occur in this pond until August 18, when 12.64 p. p. m. of the 
gas were present. This is the maximum of free C0 2 observed in this pond. After 
August 18 free C0 2 was present regularly. From May 9 to August 8 the water 
always showed a free C0 2 deficiency or a phenolphthalein alkalinity. This alkalinity 
ranged from a minimum of 6.08 p. p. m. on May 19 to a maximum of 46.5 p. p. m. 
on June 30. Table 10 shows that the maximum alkalinity corresponds to practically 
the maximum pH value. The variations in C0 2 are shown graphically in Figure 5. 
The dissolved oxygen varied from a minimum of 2.86 p. p. m. on August 18 to a 
maximum of 10.46 p. p. m. on June 9. The low values for dissolved oxygen on August 
8 and 18 are probably due to the decaying of blanket algae. The notes on vegetation 
show that there had been a marked decrease in blanket algae since June 20. Figure 5 
shows the variations in dissolved oxygen. 
The dissolved chlorides ranged from 1.8 to 3.5 p. p. m. There is no correlation 
between the variations in the chlorides and those in the organic matter that points 
toward the soluble chloride as a limiting factor. The variations in chlorides are shown 
in Table 10. 
All nitrogen data are shown in Table 10. This table shows that the ammonia 
nitrogen varied from a minimum of 0.016 p. p. m. on May 29 to a maximum of 0.128 
p. p. m. on June 9. This increase in ammonia nitrogen is associated with a decrease 
in organic matter. The decrease in ammonia nitrogen after June 9 is due to the 
growth of blanket algse. The fact that there were 0.052 p. p. m. of ammonia nitrogen 
