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2.0 I ' __m_ ------- I - - , I I' I I I I I . I : I I I I I I I : I . : I I : I 1.8 . ----l--!-------r-------r-T---~l' --r-I----j-------l---iL-' :: =-1~~t:==:t:=i~--+-8--- t ~==:j:=~~-r-~- i 1.2 -!--~-----~-------+- - --t-t---+------t.l ~ 1.0 - --1---~---- I ,_-+__ I -- I OB . -t-----I------ T- ~ 0.6 ,-----1---- 0.04 '--1' ---- ------+ f 0.2 ,- I -----t- i 0.0 ..it' ~ -0.2 I j 6' -0.04 -0.6 -OB -1.0 -I I -+---tc I . I . I --L:-f- -i-+--~----- --+---- I I I- I llIOO1 QIIIO\/ ll1lIlO Q'II'N Q1flI!II ONI.R lMPR O'N'IY Q1..IJN ClUJ. lMLIQ ll'JlEIP Q100T - WflJ&7 - WYIi!llClO Figure 4 Comparison of warming at Lees Ferry between 1997 and 2000 Dissolved Oxygen and pH Some quality assurance problems have been experienC,ed with pH and dissolved oxygen measurements. Dissolved oxygen measurements can be inconsistent because of drifting debris collecting on the instruments, restricting circulation of fresh water around the probe, or the sensitivity of the probe to flow velocities. At low velocities, oxygen is consumed near the probe and measurements are artificially depressed. Due to the design of the Hydrolab pH reference junction a drift of approximately 0.20 pH units is experienced over a typical month-long deployment due to leaching of reference electrolyte. Attempts have been made to reduce these problems in the future. Verification and calibration adjustments still need to be made to these data before they can be interpreted. This information will be presented in a subsequent report. In general, recent dissolved oxygen levels below Glen Canyon Dam are between 5 and 6 mg/L. Patterns at Lees Ferry show daily fluctuations in pH and dissolved oxygen that reach a maximum in early summer, corresponding to primary producitivity patterns in the Glen Canyon reach between the dam and Lees Ferry. IOns/OO DRAFT 6