Evaluation of modelled and measured patterns of dissolved oxygen in a freshwater lake as an indicator of the presence of biodegradable organic pollution

Changes in dissolved oxygen (DO) cycling patterns in natural surface waters have been shown to be useful as a potential indicator of biodegradable organic pollution. The effect has been demonstrated by dosing a water body with 2.5 and 5.0 mg l−1 TOC, added as pot-ale, and monitoring the DO values continuously for 96 h. These loadings were added to water columns (in tubes) suspended from a raft in a small lake in North East Scotland. The addition of organic pollution burden to the lake water produced two effects. The mean DO value was lowered initially, but increased as organic loading was consumed. Secondly, the amplitude of the DO cycle increased as organic loading increased from 2.5 to 5.0 mg l−1 TOC. From the results of a DO dynamic model developed in this project, and from the lake raft experiments, it can be concluded that dissolved oxygen cycles may be useful as an indicator of biodegradable organic pollution load.