STATIOM NUMBERS 



12 14 16 



Figure G. — Comparison of oxygen concentrations in 

 Brownlee Reservoir July 19(52 and July 1963. Xote pro- 

 nounced oxygen block at upper end of reservoir (sta- 

 tions 14 to 18) in 1962. 



p. p.m., or less, and most of the water below 15 m. 

 had 4 p-i^.m. or less. This condition persisted 

 through September Imt was alleviated somewhat 

 in the upper end of the reservoir by Octol)er be- 

 cause of cooler inflow from the Snake and Burnt 

 Rivers. By November, nearly two-thirds of the 

 reservoir water contained 7 to !• p. p.m. dissolved 

 oxygen. 



A small I'emnaut of the hypolimnion remained 

 at the dam in December, but more than nine-tenths 

 of the resen-()ir had completely overturned; 

 oxygen cf)ncentrations ranged from 7 to 1"2 p. p.m. 

 Concentration changes were similar in the Powder 

 River ann. 



Oxygen records indicated tliat location of the 

 turbine intake at 37 m. below normal pool level 

 created sufficient circidation adjacent to the dam 

 to bring some of the oxygenated water from the 

 e})ilimnion down to the hypolinuiion from July 

 through October. Oxygen concentrations in this 



area for tlie same months in 1962 were almost 

 identical. 



An oxygen block or area of oxygen depletion 

 (tig. 6) similar to that described by Fish and 

 Wagner (1950) and Ellis (1942) was present in 

 lute July. 1902; it could be traced progressively 

 through the reservoir in successive months (fig. 5). 

 This block was not observed in 1963, although 

 some evidence suggested that it was beginning to 

 form. Shortly thei'eafter, the incipient block dis- 

 integrated. 



Another major difference in the graphs of oxy- 

 gen concenti-ations is that concentrations in Sep- 

 tember 1962 were considerably lower in the epi- 

 limnial waters than they were dui'ing the same 

 month in 1963. Very possibly the oxygen block, 

 higher air t^emiaeratures, and lower inflow from 

 the Snake River all contributed to the lower epi- 

 limnial concentrations of oxygen in September 

 1962. 



CONDUCTIVITY, pH, AND OTHER CHEMICAL 

 PROPERTIES 



Total alkalinity, phenolphthalein alkalinity, 

 carbon dioxide, hydrogen-ion concentration, sili- 

 con dioxide, sulphates, turbidity, and conductivity 

 were obtained for the surface, middepth, and bot- 

 tom. Ranges for each year are jd resented ; variation 

 with dejjth, during the year and from one year 

 to the other, is described. 



Alkalinity was generally similar for comparable 

 periods during the 27 months of study. Concen- 

 trations (fig. 7) ranged from 68 to 202 p.p.m. for 

 1962-63 and from 86 to 225 p.p.m. for 1963-64. 

 Concentrations were highest in December, Janu- 

 ary, February, and March ; they were lowest dur- 

 ing May and June and increased through one sum- 

 mer. These concentrations were undoubtedly gov- 

 erned in part by the trend in alkalinity in the 

 Snake River and in other tributaries (table 3). 

 Alkalinity concentrations were fairly uniform 

 during December and January when the reser^ oir 

 was nearly homothennous and oxygen concentra- 

 tions were nearly uniform. Range in concentra- 

 tions was widest during the summer, when the 

 reser\oir was stratified. 



The highest alkalinity occurred in the hyiX)lim- 

 nion during June, July, and August. Precipitation 

 of normal carbonates by aquatic organisms and 



LIMNOLOGY OF BROWNLEE RESERVOIR 



309 



