(1,000) set by Ellis (1944) as the upper limit of 

 conditions favorable to fish life. 



The rano-e in sulfate concentrations for July 106'2 

 to June 1964 was 2 to fi9 p.p.m. The value through- 

 out the reservoir was 1 5 to 50 i>.p.m. during most of 

 tlie year, wliicli is considered the optimum range 

 for aquatic life (McKee and Wolf, 1963). Sulfate 

 concentrations were highest in the sui-face waters 

 and lowest in the deeper waters during most of the 

 year. Tliis distribution may account in part for the 

 lower conducti\ities at tlie lower depths mentioned 

 earlier. 



Secchi disc readings and silicon dioxide concen- 

 trations for 1963 are sliown in figure 8: the read- 

 ings were typically low when silicon dioxide con- 

 centrations were high. Turbidity showed an annual 

 cycle comparable to that of total alkalinity and was 

 greatest in Febiiiary (Secchi disc 0.3-0.6 m.) dur- 

 ing drawdown, when silt deposited in the upper 

 reservoir was recirculated l\v the turbulent river 

 inflow. Turbidity continued high throughout the 

 spring and ea.rly summer and then gradually 

 decreased tlirough the fall. The highest Secchi disc 

 readings (lowest tnrl)idity) were in October at 

 stations 4 and 6 (7.1 and 7.6 m.) . The Snake Eiver 

 above Brownlee Resen^oir remained turbid 

 throughout the year; the maximimi reading in the 

 river was 0.6 m. Hence, the uppermost portion of 

 tlie reservoir was always rather turbid. 



Several autliors liave analyzed the relation 

 between turl)idity and plankton production and, 

 lience, witli fish production. Tlieir conclusions vary 

 depending on the characterifstics of the water mass 

 studied and on their interpretation of available 

 data. For example, Van Oosten (1948) found no 

 correlation, whereas Langlois (1941) indicated a 

 Iiigh correlation. The large phytoplankton blooms 

 on tlie surface of Brownlee Reservoir throughout 

 the sunnner indicated that liigh turbidity did not 

 seriously hinder primary production near the 

 surface. 



DIURNAL OBSERVATIONS OF LIMNOLOGICAL 

 CONDITIONS AND CONDITIONS AT TRAP SITES 



Four diurnal studies were carried out from June 

 1962 to June 1964 to measure fluctuations under 

 unusual conditions during mortalities at a finger- 

 ling trap sit©, or to determine diurnal fluctuations 

 at the end of winter or in late summer. Studies 



were made September 5 and 6, 1962, July 17 and 

 18, August 19 and 20, 1963, and May 12 and 13, 

 1964. The studies in the early spring (May 1964) 

 and late summer (September 1962) showed that 

 diurnal variations in temperature and water chem- 

 istry were minor. Temperatni-es in the reservoir 

 in September and May did not change more than 

 1.1° C. Maximum change in oxygen concentration 

 was 1.3 p.p.m. in September and 3 p.p.m. in May. 

 Changes in concentrations of other factors were 

 similarly minor. 



The diurnal observation at a floating fish trap 

 at station 18 was done to determine if water tem- 

 perature and chemisti-y contributed to the high 

 mortality of young salmon captured on July 17, 

 1963. Samples were taken at 1500 hours on July 18 

 and every 3 hours over the ensuing 24-hour period 

 at the trap and at a point 30 m. outward from it. 

 Tlie samples at the two sites did not difl'er sig- 

 nificantly. Water temperatures ranged from 22.1° 

 to 23° C. at the 6-m. level and from 22.3° to 23.3° 

 0. at the surface. Diurnal variation was 1.1° to 

 1.65° C. at the surface; the temperature was high- 

 est in the early afternoon. Dissolved oxygen con- 

 centrations ranged from 3.2 p.p.m. to 2 p.p.m. on 

 the surface and from 2.1 p.p.m. to 1.6 p.p.m. at the 

 6-m. level. No cyclic trend in oxygen concentra- 

 tions appeared. The high temperatures and the 

 low dissoh'ed oxygen concentrations apparently 

 were major factors in the high mortality of cap- 

 tured fish. Concentrations of pH, carbon dioxide, 

 and sulfates were suitable for survival of fish 

 (Ellis, 1937, 1944) ; diunial fluctuations were 

 lacking. 



A day-night study also was done in the Powder 

 River arm of Brownlee Reservoir on August 19 

 and 20, 1963. The purpose was to detennine the 

 extent of diurnal variation in water chemistry 

 and temperature in an area of high concentrations 

 of algae. A series of samples was taken from the 

 surface to the bottom at stations PR4 (PR4 lo- 

 cated midway between PR3 and PR5) and PR5, 

 in a relatively shallow pond at the head of the 

 arm, and at station PR3, at midarm. Surface 

 water tem])eratures varied 2.3° C. through the 

 day-niglit cycle, ranging from 20.5° to 22.8° C. 

 Diurnal fluctuation in dissolved oxygen concen- 

 trations at the three stations was high ; maximum 

 variation at the surface was at PR4, where the 

 range was 6.8 to 14 p.p.m. Concentrations were 



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U.S. FISH AND WILDLIFE SERVICE 



