Abstract
Water temperature and dissolved oxygen content were measured vertically in Cultus Lake on 20 occasions and dissolved N 8 times during 1961. The results showed the water in the region of the thermocline became supersaturated markedly as a consequence of warming during the spring and summer. The excess gas was below the extent of surface mixing and was held in solution by the hydrostatic pressure. In mid-July at a depth of 30 ft., O2 was 126% and N 116% of air saturation. By mid-Sept. at a depth of 50 ft., O2 saturation was 94% and N 110% of air saturation. O2 was liberated by photosynthesis in the epilimnion and upper portion of the thermocline, and consumed in the lower part of the thermocline and the upper hypolimhion. Thus N supersaturation could not be diagnosed by measurement of dissolved 02 alone. N supersaturation is discussed in relation to the use of lake water for hatchery culture of fish.

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