148 
BULLETIN OF THE BUREAU OF FISHERIES 
POND C-3. 
POND C-4. 
chlorides in C 3 must be due to the tj^pe of fertilizers (shrimp bran) used. The fact 
that the average amount of chloride in C 1 and C 2 is less than that in C 4 prob- 
ably does not mean that the superphosphate and the soybean meal contain no chlo- 
ride, but rather that more chloride was consumed in the production of a relatively 
much larger crop of plankton. The variations in the dissolved chloride in C 1, C 2, 
C 3, and C 4 are shown in Figures 2 and 3, respectively. There is nothing in this 
chloride data that would point toward it 
as a limiting factor. 
Nitrogen . — All the nitrogen data are 
combined in Table 4. The variations in 
the different forms of nitrogen are shown 
for C 1 in Figure 2, forC 2 in Figure 2, for 
C 3 in Figure 3, and for C 4 in Figure 3. 
Nitrate nitrogen . — Table 4 shows that 
nitrate nitrogen in C 1 varied from a mini- 
mum of 0.008 p. p. m. at the beginning of 
the experiment to a maximum of 0.080 
p. p. m. at the end of the experiment. In 
C 2 the minimum nitrate nitrogen of 0.032 
p. p. m. occurred on August 9. The maxi- 
mum of 0.150 p. p. m. was present on Sep- 
tember 19. The minimum for the nitrate 
nitrogen corresponds to the maximum for 
ammonia nitrogen. Since this maximum 
for ammonia nitrogen occurs after a large 
decrease in the organic matter, the assump- 
tion seems warranted that this ammonia 
nitrogen is due rather to the bacterial de- 
composition of the organic matter than to 
the action of denitrifying bacteria. This 
conclusion seems justified also in view of 
the fact that there has not been a corre- 
spondingly large decrease in the nitrate ni- 
trogen. The nitrogen as nitrate in C 3 is at a 
minimum of 0.023 p. p. m. and a max im um 
of 0.120 p. p. m. at the beginning and at 
the end of the experiment, respectively. 
In C 4 this form of nitrogen varied from a 
minimum of 0.009 p. p. m. to a maximum 
of 0.095 p. p. m. The minimum and the 
maximum occur here at the same time as 
the corresponding maxima and minima 
for C 1 and C 3. C 2 and C 3 contain on the average more nitrate nitrogen than 
C 1 and C 4. The average for nine determinations are: C 1, 0.036 p. p. m.; C 2, 
0.059 p. p. m.; C 3, 0.053 p. p. m.; and C 4, 0.035 p. p. m. C 2 and C 4 differ from 
each other only by 0.001 p. p. m. and C 2 and C 3 differ from each other by 0.006 
p. p. m. As in the case of the ammonia nitrogen the ponds fertilized with organic 
fertilizers yield the higher values for nitrogen. 
1928 JUNE JULY 
AUG. 
5E.PT. JUNE JULY 
AUG. 
SEPT. 
Figure 3.— Variations in free carbon dioxide, dissolved oxygen, 
chloride, different forms of nitrogen and phosphorus, and 
organic matter expressed in p. p. m.; pH values and tempera- 
tures in degrees C. for ponds C 3 and C 4 
