Secondary Driver: Timing of Low DO Episodes
Although episodes of low DO concentrations historically have occurred during every month, periods of low DO concentrations most commonly occur from June through November (Jassby and Van Nieuwenhuyse 2004). These months coincide with the months of low precipitation and warmest water temperatures. Warm water temperatures promote decomposition of organic matter and nitrification of ammonia (Jassby and Van Nieuwenhuyse 2004) and decrease the amount of oxygen that can dissolve in water. Additionally, June through August is when chlorophyll a is most abundant (Jassby 2005). See also the physical/chemical model.
Detailed data on DO concentrations in the DWSC from 1984 to 2005 are available in the Data Atlas. A graphic of monthly DO concentrations is provided in "Occurrence of Sensitive Life Stages in the DWSC".