DissolTed oxygen 



A ooraplete series of dissolved oxygen determinations was made 

 at the various stations using the basic Winkler method as described 

 in Ellis, Westfall and Ellis (1946). Table 5 is a complete tabulation 

 of the findings in parts per million of dissolved oxygen at the various 

 stations on the lake. The 'oxygen readings are accompanied by temper- 

 atures because of the comparative importance of the latter in the 

 respiration of aquatic organisms. Oxygen demand, for example, is 

 almost doubled by a rise of 10**C, eind oxygen has twice the supply 

 value at 5° as at 15**C, (Ruttner, 1926). Considering that water 

 containing 5 P. P.M. dissolved oxygen free from pollutants is gener- 

 ally regarded as favorable for fresh water fishes, it can be seen 

 from Table 5 that sufficient oxygen for fish exists in the reser- 

 voir. It is interesting to note that slightly leas oxygen was fovuid 

 in the Spokane River area than at other points. This may possibly 

 be a result of oxidation of raw sewage ajid industrial pollutants 

 which are poured from the City of Spokane sewer system into the 

 river at the present time. No dangerously low oxygen concentrations 

 were found, however. 



Table 6 contains the values in percentages of saturation of 

 oxygen in accordance with temperatures smd normal stirfaoe barometric 

 pressure at an elevation of 1,000 feet. From the Table it can be 

 seen that practically all readings were at or near the saturation 

 point. 



Transparency of the Water 



A secohi disk was used to measure transparency of the lake water. 

 It consisted of a round metallic plate weighted with lead having black 

 and white quadrants painted on its surface; it was lowered by a rope 

 marked at half meter intervals. The depth at which the disk disap- 

 peared from view was recorded, and it was then lifted until it reap- 

 peared. The average of these two readings was listed as the limit of 

 visibility. These Seochi disk readings furnished a useful, rough 

 index for purposes of comparison. 



Table 7 is a summary of transparency readings taken in 1948. 

 Prom them, two phenoiaena are apparent: a gradual diminution of the 

 silt load near the surface at stations successively farther down- 

 stream in the reservoir J and a clarification of the water tlaroughout 

 the reservoir as flows subsided from the record spring runoff in 1948. 



15 



