Dark production of hydroxyl radicals by aeration of anoxic lake water

•Hydroxyl radicals are generated in the dark by aeration of anoxic lake water.•The process could take place during lake overturn.•Dark OH generation was compared with photochemical processes.•The process could be important in deep lakes subject to summer stratification.

Lake circulation is an important phenomenon that ensures oxygenation of the water column. Here we report that aeration of anoxic hypolimnion water causes production of highly reactive hydroxyl radicals (OH), which are also produced photochemically in the epilimnion. Model calculations suggest that the dark process of OH generation can be comparable with photochemical reactions in some lake environments, provided that the hypolimnion is a significant fraction of the whole lake volume. In these cases, lake overturn could significantly contribute to the yearly OH budget of the lake water and might cause significant degradation of some pollutants, for which the reaction with OH is an important removal process from surface waters.

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