Limnological features of coastal-plain wetlands on the Gnangara Mound, Perth, Western Australia

Abstract

The Gnangara Mound is an area of elevated sandy soil on the Swan Coastal Plain to the north of Perth. It constitutes a major groundwater resource for metropolitan Perth. Sixteen wetlands on the Mound had total phosphorus concentrations of 12-462µg L^-1, the high values being attributed to agricultural and urban activity. Sediment concentrations of total phosphorus and total nitrogen were 61-954 and 1212-16739 µg g^-1, respectively. Conductivities were 505-10270 µS cm^-1, and pH values were 3.3-9.3. Only one wetland was highly coloured (79.9 8440 m^-1), with an E4/E6 ratio of 4.6. Chlorophyll a concentrations were 0.01-130.8µg L^-1; in wetlands with low gilvin concentrations, Myxophyceae dominated, whereas wetlands with higher gilvin concentrations had large numbers of diatoms and Chlorophyceae. The highly coloured wetland had the lowest chlorophyll a concentration despite high nutrient concentrations, supporting the hypothesis that the consequent reduction in light or other associated factors are important in maintaining low phytoplankton biomass in dystrophic wetlands of the region, particularly those on Bassendean sands.