Above Brownlee (at Weiser ) t.'-'-y/i 

 Below Brownlee 

 Below Oxbow 



APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. 



Figure 20. — Temperature, dissolved oxygen, and alkalinity in the Snake River above Brownlee Reservoir, 



reservoir, and below Oxbow Dam, 1963. 



DEC. 



below the 



Brownlee Reservoir, the Snake River had a rapid 

 increase in temperature from April through Au- 

 gust, whereas Ijelow Brownlee. and Oxbow Dams 

 it showed a definite lag in wannmg. Temperatures 

 were nearly identical at all three stations in Sep- 

 tember. The trend from October through Decem- 

 hev reversed in tlie spring and summer; i.e., 

 intiowing water cooled rapidly, and outflowing 

 water was warmer tlian inflowing water for several 

 months. Outflow at Oxbow Dam was slightly 

 cooler than that from Brownlee Reservoir; never- 

 theless, it remained warmer than the inflowing 

 Snake River water. 



Dissolved oxygen concentrations in the river 

 upstream from Brownlee Reservoir remained rel- 

 atively Iiigh through July 1963, declmed sliarply 

 in August, and gradually increased m September. 

 During the same period dissolved oxygen concen- 

 trations below Brownlee wei-e ntuch lower than 

 those in the inflowing water except during heavy 



spilling discharge in June. Undoubtedly, removal 

 of .subsurface water (through turbine intakes) 

 from oxygen-depleted layers in the reservoir 

 caused the lower concentrations of oxygen below 

 Brownlee Dam. Re^idings fell below 5 p.p.m. from 

 August tlirough October, a condition which ap- 

 proached the critical limit for survival of sal- 

 monids (Ellis, 1944), especially when these levels 

 were accompanied hy water temperatures in ex- 

 cess of 21.1° C. Oxygen concentrations below Ox- 

 bow Dam were somewhat higher; apparently 

 some oxygen was restored in the Oxbow Dam area. 

 Iniprovejnent below Brownlee and Oxbow Dam 

 began in November, 2 months after increases in 

 the river above Brownlee. 



Measurements of total alkalinity indicated a de- 

 lay in trends similar to that of temperature and 

 oxygen. In August, the alkalinity of inflowing 

 water increased shar^Dly, whereas the increase in 

 outflowunff water was trradual. About 4 months 



LIMNOLOGY OF BROWNLEE aBSERVOIR 



331 



