Impact of Urban Lawns on Nutrient Contamination of an Unconfined Aquifer

 

This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.

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Impact of Urban Lawns on Nutrient Contamination of an Unconfined Aquifer

Report no. UWRAA 49

December 1992

Synopsis

Experimental and modelling approaches were developed and used to quantify water and nutrient leaching beneath urban lawns, situated on a Coastal Plain.

Four representative lawns were studied. Over a 210 day period, irrigation was the main source of water during summer, precipitation was the main source during winter. There was a strong seasonality in nitrogen and phosphorus concentrations in water leaching through the soil. Fertilising is conducted almost exclusively over spring and summer. About 50% of input water passed below the root zone, carrying nutrients with it. On many occasions, nitrate concentrations in leachate exceeded the World Health Organisation (WHO)drinking water limit of 10 mg/l. Invariably groundwater concentrations, however, were lower due to dilution and denitrification.

Substantial quantities of nitrogen and phosphorous have been shown to leach below the rootzone and are a threat to many urban wetlands, especially the Swan-Canning river system.

Mechanistic modelling approaches were employed to simulate chloride and nutrient leaching below the root zone. A reasonable comparison between measured and modelled NH4and NO3 values was observed. Measurements and modelling showed that although some PO4 –P passed below the root zone, it will take many years for the phosphate peak to reach the groundwater.

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