Increasing lake water and sediment oxygen levels using slow release peroxide.

The sediment and hypolimnion of many Finnish lakes suffer from anoxia due to increasing nutrient loading. The aim of this research was to develop a method for increasing the oxygen level using granulated calcium peroxide (CaO₂) as a slow oxygen releasing compound. This compound releases oxygen (O₂) in a reaction with water during 5 to 7 months. The method was tested in both laboratory and field conditions. In the field test granulated CaO₂ were then spread manually from a rowing boat over the whole surface of the test pond. The granules sink onto and into the sediment. No mixing was needed. The dissolved oxygen concentration increased significantly during a laboratory experiment with a CaO₂ amendment of 75 g m⁻² and in a pond experiment with a CaO₂ amendment of 50 g m⁻². In the pond experiment, the effect was visible for the entire 40-week experiment. In the laboratory, the abundance of aerobic bacteria increased in the sediment after CaO₂ addition, while the pond experiment gave more mixed results. The organic matter content of the sediment did not change during the experiment in the control pond, but decreased from 18% to 4% in the pond with the CaO₂ amendment. This was possibly due to enhanced microbial activity in the test pond. Although the results show improved oxygen concentrations and effects on the sediment organic matter following CaO₂ amendment, the usability of this method in larger lakes remains to be tested.