A Study of the Eutrophication of North Lake, Western Australia

North Lake is an urban freshwater wetland, and like other wetlands in the Perth metropolitan region, Western Australia, has become nutrient enriched, with the accompanying problems of algal blooms, decay, odour, infestation with midges and aesthetic deterioration. A study of the water quality of the lake was undertaken to quantify the variation of phosphorus, nitrogen and chlorophyll-a, and the sediments store of nutrients and their release with pH. The dominant algae in the lake, Microcystis, was found to be limited in growth by nitrogen because of the high availability of phosphorus (> 0.1 mg/l), and likely by light because of self-shading (chlorophyll-a > 0.3 mg/l). Sediments released a substantial amount of nutrients as pH rose above 8.5. Together with a parallel study of the nutrient budget of the lake, a management strategy has been derived to overcome the problem of nutrient enrichment that could be applied to other wetlands in the metropolitan region.