ROLE OF CONSTRUCTED WETLANDS IN NUTRIENT STRIPPING

A number of research programs have been established to evaluate potential applications of constructed wetlands in Western Australia. These constructed wetlands are known not only for their nutrient removal capability, but also their role in habitat creation, urban landscaping and water quality and environmental health. They play an important role in the reduction of nutrients, particularly phosphorous, from entering the waterways. This paper reports on the improvement of water quality in the Peel Main Drain before its disposal into the Peel Estuary, Perth, Western Australia. The nitrogen to phosphorous (N:P) ratio was below the critical limit during summer (dry spell) and the system was limited by nitrogen. The concentration of phosphorus was high in summer and low in winter due to increased availability of dissolved oxygen in winter. A wetland was proposed to improve the water quality in the Peel Main Drain using vegetation and substrate. The hydrologic effectiveness was found to be 78% for a detention time of 30 hours. It is expected that the maximum nitrogen removal efficiency of the constructed wetland will be 80% with an estimated efficiency of 40% in the first year and 60-80% in the subsequent years. For phosphorous it is expected that the constructed wetland will be effective in removing filterable reactive phosphorous. Traditional sediment remediation techniques have been found unsuitable for the long term binding of the phosphorous therefore the use of Phoslock TM is recommended.