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: or ganic pollution. The effect has been demonstrated by dosing a water body wi th 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 tube s) suspended from a raft in a small lake in North East Scotland. The additi on of organic pollution burden to the lake water produced two effects. The mean DO value was lowered initially, but increased as organic loading was c onsumed. Secondly, the amplitude of the DO cycle increased as organic loadi ng 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 ca n be concluded that dissolved oxygen cycles may be useful as an indicator o f biodegradable organic pollution load. (C) 2000 Elsevier Science Ltd. All rights reserved.