A classification of tropical and subtropical Australian estuaries

The ability to use large databases to classify estuaries on the basis of any number of characteristics may be valuable in planning a national system of estuarine reserves in Australia which will conserve the range of variability within and between regions. A recently completed inventory of Australian estuaries and marine embayments has provided quantitative data on a large number of estuaries from which comparisons are made with existing classifications based on qualitative descriptions. Area measurements are analysed for mangroves, salt marsh/clay pan, seagrass, intertidal flats and open water from 571 tropical and subtropical estuaries north from Carnarvon on the west coast around to Coffs Harbour on the east. The relative proportions of mangroves and salt marsh within estuaries show strong relationships with average annual rainfall although there are no consistent trends in the absolute area of each wetland type. The estuaries are classified into three distinct groups on the basis of rainfall and the dominant wetland type. Greater tide range coincides with a greater area per estuary of all wetland types. As with rainfall, the estuaries fall into three categories of wetland proportions.