Publications
A submission to the National Pollutant Inventory
Prepared by the Resource Science Division Department of Environment Western Australia
Department of the Environment and Heritage, September 2004
ISBN 1 920947 44 2
The catchment of the Vasse and Wonnerup estuaries has an area of 96,093 hectares and encompasses the catchments of the Ludlow, Abba, Sabina, Vasse and Buayanup Rivers and Locke Swamp. It forms part of the Geographe Bay catchment which has an area of 204,700 hectares. The main population centre in the catchment, the town of Busselton, currently has a population of about 19,000 and is one of the fastest growing regional centres in Western Australia.
The coastal plain portion of the catchment consists of sandy and duplex soils which are often water-logged in winter. Since settlement in the 1840’s an extensive drainage network has been established to enable agricultural land uses and protect the towns of Busselton and Wonnerup from flooding. The Vasse and Wonnerup estuaries also have barrages to limit sea water inflows on high tides and protect the estuarine flats from flooding. The waterways of the catchment are generally in poor condition due to nutrient enrichment from the surrounding land uses and the modified drainage. They suffer from algal blooms, de-oxygenation events and fish kills. Regardless of this, the waterways provide important water bird habitat. The Vasse-Wonnerup wetland which supports tens of thousands of birds was listed as a wetland of ecological importance under the Ramsar convention in 1990.
Aggregated emissions of total nitrogen (TN) and total phosphorus (TP) to the waterways from diffuse and point sources in the catchment are modelled with the Catchment Management Support System (CMSS). These are reported to the National Pollutant Inventory for each land use in specified subcatchments. The total average annual emissions are estimated to be 517 tonnes of TN and 43 tonnes of TP. Point sources account for approximately a half of the phosphorus and one-fifth of the nitrogen emissions, with septic tank and dairy shed effluent being the main contributors. The land uses which have the greatest contributions to diffuse nutrient emissions are dairy pastures and other pastures for sheep and beef cattle.
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