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Shasta |
Topic |
Dissolved Oxygen: Shasta Nocturnal/Diurnal Changes |
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Caption: Shasta River dissolved oxygen (D.O.) levels fall to critically low levels (<5 mg/l) only during several hours in the early morning (5 = 5 A.M. on chart). Dissolved oxygen levels of less than 5 are stressful for salmonids and those less than 4 may be lethal. Once algae and other aquatic plants begin to photosynthesize, D.O. levels rise. Note that D.O. starts to drop in evening hours after 6 P.M. (18 on chart). Gwynne (1994) suggests that something in addition to nocturnal respiration of plants is leading to severely depressed dissolved oxygen levels, such as decomposition in sediment along the stream bottom. If water quality tests are conducted very long after sunrise, dissolved oxygen problems are unlikely to be detected. Click on the Info Links tab for more information.
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