Sediment oxygen demand (SOD) was measured in two shallow, interconnected lakes in southern Oregon, Upper Klamath Lake and Agency Lake, in spring and late summer of 1999. Upper Klamath Lake contains populations of two endangered fishes, the shortnose sucker and the Lost River sucker, and low dissolved oxygen concentrations in summer are thought to be one factor affecting sucker populations.
The distribution of SOD20 values (measured sediment oxygen demand values corrected to 20o C [degrees Celsius]) had a median value of 1.6 g/m2/day (grams per square meter per day) in the spring and 1.7 g/m2/day in the late summer. These values were well within the range of values in the literature for sites with similar sediment characteristics: primarily silty with at least a moderate amount of organic content.
Little variation in SOD was observed--the interquartile range in values was 0.4 g/m2/day in the spring and 0.7 g/m2/day in the late summer. A significant exception was apparent in Ball Bay, where SOD in the late summer was greater than 10.2 g/m2/day. In the absence of primary production, an SOD of this magnitude could deplete the water column of oxygen in a few days. This measurement provided evidence that localized areas of very high SOD occur episodically in the bays, perhaps associated with large algal mats being trapped by the lake circulation patterns.
A statistical test for a spring to late summer difference in the median values of SOD confirmed that SOD in the late summer (median value 1.7 g/m2/day) was significantly higher than in the spring (median value 1.2 g/m2/day). The difference was primarily due to seasonal changes in temperature, however; when SOD values were corrected to 20o C, there was no seasonal difference in the median values.
There was no correlation between SOD20 and the sediment characteristics measured in this study: percent fines, organic carbon, and residue lost on ignition.
