that concentrations of liig'li carbon dioxide were at 

 the lower depths. 



Concentrations of carbon dioxide were low in 

 the spring and early sunnner, bnt high in the fall. 

 Free carbon dioxide was lacking in January of 

 both years. The range in concentration (p. p.m.) 

 for 1962-63 (July-June) was to 12 for the 

 surface, to 11 for the 30.5- to 45.7-m. layer, and 

 to 19 for the 45.7-m. layer to the bottom. The 

 ranges for 1963-64 were to 19, to 23, and () to 

 43 for the surface, middepth, and bottom. Highest 

 values were at the lower depths. Concentrations 

 were not only far below the lethal levels indicated 

 by Ellis (1937) but usually below the harmful 

 level (39.2 p. p.m.) indicated by McKee and Wolf 

 (1963). 



Hydrogen-ion concentration (pH) in the reser- 

 voir ranged from 7 to 8.9. The high pH of tlie 

 Snake River (table 3) throughout the year ac- 

 counted for the high readings in the reservoir. Tlie 

 readings were highest in surface water where con- 

 centrations of normal carbonate were highest. The 

 range in pH of the surface water in 1963, for ex- 

 ample, was 7.7 to 8.9, but the range at lower 

 depths, 46 m. to bottom, was 7 to 8.3,. Neutral values 

 of 7 were typical near the bottom during August 

 and September, when tlie reservoir was well strati- 

 fied. Decomposition of organic material apparently 



liberated enough carbon dioxide into the hypo- 

 limnion to lower the pH to this level. Concentra- 

 tions were slightly higher on the bottom during 

 these same 2 months in 1962. The pH ranged from 

 7.5 to 8.5 throughout the year in most of the water 

 mass, indicating that Brownlee Reservoir is rela- 

 tively alkaline in comparison with other lakes and 

 reservoirs in the United States. 



Conductivity readings, which were adjusted to 

 20° C., ranged from 253 to 867 micromhos. Values 

 were low in the sjning, progressively higher during 

 the sunnner, and low again in the late fall after the 

 turnover. During stratification, the highest read- 

 ings were usually in the surface layer and the low- 

 est readings in the hypolimnion. This phenomenon 

 is the reverse of what would be expected if con- 

 ductivity fiuctuated with total alkalinity. Con- 

 formity with the expected relation ( when the high- 

 est conductivity readings were in the hypolinuiion) 

 existed only in July and August of 1962 and 1963 

 and only in the lower part of the reservoir. Appar- 

 ently some electrolytic substance, other than those 

 sampled, was reduced at the lower deptlis. Ellis 

 (]94()) found that conductivities paralleled alka- 

 linities and sulfates and thai all three were higher 

 at the lower depths. Although conductivity reached 

 867 micromhos, this figure was still below the level 



APR. 



MAY 



JUNE 



60 



40 

 20 

 •0 



60 : 



40: 

 20, 

 ■0 



60 

 40 

 20 







12 16 20 4 8 12 16 20 

 STATIONS 



5- 

 10- 



uj 0- 



- 5- 



°- IQ. 





 5- 



10- 



JULY 



OCT. 



AUG. 



NOV. 



SEPT 



DEC. 



1 I I I ! I I I I I I I I I ' I I I I 1 r 



4 8 12 16 20 4 8 12 16 20 



STATIONS 



60 

 40 

 20 

 



60 5 



a: 



40 q; 



20 c? 

 ■0 •" 



60 

 40 

 20 

 



Figure 8. — Comparisun iif St-cchi disc readings (solid lines i and .surface silicon dioxide conceutrations (broken lines) 



in Brownlee Reservoir, .January to December 1063, 



LIMNOLOGY OF BROWNLEE RESERVOIR 



315 



