The use of artificial oxygenation to reduce nutrient availability in the Canning River, Western Australia

Artificial oxygenation has been used for two summer periods to improve the water quality of the Canning River in Perth, Western Australia. The project is part of the Swan Canning Cleanup Program, which aims to reduce the freq uency and severity of nuisance and toxic algal blooms in the Swan-Canning e stuary. The trials have proved that oxygenation has increased the dissolved oxygen concentrations in the water column, particularly in the bottom wate rs where dissolved oxygen concentrations are frequently below a critical le vel of three milligrams per litre. Oxygenation has had a positive impact on nutrient concentrations in the water column and nitrogen cycling processes . Reductions in nutrient concentrations were highlighted by drops in ammoni um and total phosphorus concentrations of 97% and 64% following the recomme ncement of oxygenation after a plant shutdown. Results of a microbiological study combined with the data analysis indicate that the number of nitrifyi ng microbes have increased due to oxygenation. However, comparisons between oxygenated and control areas were inconclusive about the ability of the ox ygenation plant to reduce total nitrogen and phosphorus levels. This could be explained by factors such as spatial variability, water flow during the trials and measurement limitations in the monitoring program. Future work w ill concentrate on assessing the impact of the oxygenation plant on nutrien t concentrations.