160 
BULLETIN OF THE BUREAU OF FISHERIES 
on June 30 is due to the addition of fertilizer. Nitrate nitrogen ranged from a 
maximum of 0.120 p. p. m. on May 9 to a minimum of 0.010 p. p. m. on August 29. 
On September 29 the nitrate nitrogen was up to 0.047 p. p. m. again. Nitrite 
nitrogen was present only once; namely, on September 29, when 0.002 p. p. m. was 
present. The organic nitrogen ranged from a minimum of 0.602 p. p. m. on May 
19 to a maximum of 1.60 p. p. m. on August 18. This maximum value for organic 
nitrogen is probably due to the decomposition of blanket algae. It occurs simul- 
taneously with the minimum for dissolved oxygen and the maximum for free C0 2 . 
Total nitrogen ranges from a minimum of 0.704 to 1.65 p. p. m. The variations in 
the different forms of nitrogen are shown in Figure 5. 
Table 10 shows that on May 9, when the first observation was made, no dis- 
solved phosphorus was present. After that date dissolved phosphorus was always 
present, although on June 9 it was down to a trace. After June 9 it was always 
present in considerable quantities. This is due, no doubt, to the addition of fertilizer 
at regular intervals. The organic phosphorus varied from a minimum of 0.005 
milligram on June 20 to a maximum of 0.257 milligram on July 10. The variations 
in the soluble and the organic phosphorus are shown in Figure 5. 
The organic matter or the net loss on ignition is rather uniform throughout the 
summer and is uniformly low. The minimum of 1.39 milligrams per liter occurred 
on June 9. This occurs simultaneously with the maximum for ammonia nitrogen. 
The maximum of 3.83 milligrams per liter occurred on May 9, when the soluble 
phosphorus was exhausted. On the whole, the relationship between the dissolved 
phosphorus and the organic matter is not very clear in this case. This is probably 
due to the fact that the pond was fertilized at short intervals and to the abundant 
growth of blanket algae and rooted vegetation such as cattails and Elodea. 
PLANKTON 
Net 'plankton . — Table 10 shows that the volume of net plankton varied from a 
minimum of 0.05 cubic centimeter per 10 liters of water to a maximum of 0.45 
cubic centimeter. The average for 15 determinations was 0.18 cubic centimeter 
per 10 liters. The animals in the net plankton have been enumerated. The 
results are here given very briefly. Cyclops was always present in appreciable 
numbers. The maximum of 177.0 individuals per liter occurred on June 9. 
Diaptomus occurred for the first time on August 29. It was present in all 
September samples. The maximum of 15 per liter occurred on September 29. 
Nauplii were always present. They reached their maximum development in the 
latter part of May and during June. The maximum of 1,245 nauplii per liter was 
found on June 9. Of the Cladocera occurring in the net plankton, Bosmina was 
the most common. It was present in all samples except in two of the May samples. 
Bosmina was most abundant during the last few days in June and during July. It 
was still fairly abundant during the greater part of August. A maximum of 975 
Bosmina per liter was found on July 20. Ceriodaphuia was present in all samples 
except one after June 20. The maximum of 95.2 per liter occurred on August 29. 
Chydorus occurred regularly from May 9 to June 9. After that it occurred only 
twice and then in small numbers. The maximum of 37.8 per liter was found on 
May 29. Daphnia was present in small numbers from May 29 to June 20, and 
again on July 20, the maximum number being 9.0 per liter. Scapholeberis occurred 
once in small numbers. Moina occurred twice in very small numbers. Among the 
