162 
BULLETIN OF THE BUREAU OF FISHERIES 
The pH in this pond varied from a maximum of 8.2 to a minimum of 7.5. This 
minimum value was obtained 6 times in 14 determinations. Figure 5 shows these 
variations in pH. 
Table 14 shows that free C0 2 was always present and varied from a minimum of 
2.02 p. p. m. on May 19 to a maximum of 12.64 p. p. m. on August 8 and 18. The 
higher values for free C0 2 correspond, as a rule, to the lower pH values. (Table 10.) 
The variations are shown graphically in Figure 5. 
The dissolved oxygen ranges from a maximum of 8.14 p. p. m. on July 10 to a 
minimum of 3.33 p. p. m. on August 8. This minimum for dissolved oxygen occurred 
on the same date as one of the maxima for free C0 2 . The variations in the dissolved 
oxygen are shown in Figure 5. 
Dissolved chloride was always present. Table 10 shows that it varied from 2.0 
to 3.5 p. p. m. There is nothing in Table 10 that points toward chlorides as a limiting 
factor. 
The data on nitrogen determinations are given in Table 10. The ammonia 
nitrogen reached a maximum of 0.080 p. p. m. on May 29. The minimum of 0.016 
p. p. m. was reached on July 20. The nitrate nitrogen was at its highest point on 
May 9, when the first determination was made. At that time 0.120 p. p. m. was 
present. It decreased gradually until on June 30 only 0.025 p. p. m. was found. On 
July 10 it was up to 0.055 p. p. m. again. The minimum of 0.015 p. p. m. occurred 
on August 18. Figure 5 shows that at times the ammonia and the nitrate nitrogen 
increase or decrease simultaneously; at other times they vary in opposite direction. 
Nitrite nitrogen occurred only once; namely, on May 19, when 0.002 p. p. m. of this 
form of nitrogen were present. The organic nitrogen ranged from a minimum of 
0.360 p. p. m. on September 9 to a maximum of 0.920 p. p. m. on August 8. Since 
most of the nitrogen present is in the form of organic nitrogen, the values for total 
nitrogen follow the values for organic nitrogen rather closely. The minimum for 
total nitrogen was 0.411 p. p. m., the maximum was 0.972 p. p. m.; and they occurred 
on the same dates, respectively, as the minimum and the maximum for organic 
nitrogen. The variations in the different forms of nitrogen are shown in Figure 8. 
Table 10 shows that the dissolved phosphorus varied from none at all on May 9 
to as much as 0.032 p. p. m. on September 19. The absence of soluble phosphorus on 
May 9 is correlated with the maximum amount of organic matter. The high values 
of 0.028 p. p. m. on July 7 and of 0.032 p. p. m. on September 19 are associated with a 
decrease in the organic matter and the organic phosphorus. (Fig. 5.) It may, 
therefore, be assumed that this soluble phosphorus had been derived from the organic 
phosphorus. The small amount of dissolved phosphorus present from May 29 to 
July 10, in spite of the small amount of organic matter, is perhaps due to the rapid 
growth of cattails. The notes on vegetation show that on June 30 the area estimated 
to be covered by cattails amounted to 85 per cent of the entire pond area. Organic 
phosphorus was always present in considerable quantities. It ranged from a mini- 
mum of 0.013 milligram per liter to a maximum of 0.095 milligram per liter of water. 
The organic matter ranged from a minimum of 0.57 milligram per liter to a 
maximum of 4.24 milligrams per liter of water. The relationship of the organic 
matter to the soluble phosphorus has been discussed above. 
The data presented here would seem to suggest that, at times, the dissolved 
phosphorus may have been a limiting factor that determined the productivity of the 
surface waters of this pond. 
