Potentially toxic cyanobacterial blooms are becoming common in the freshwater wetlands on the Swan Coastal Plain, Western Australia. During summer the dominant bloom-causing species belong to the genera Microcystis and Anabaena and to a lesser extent Aphanizomenon and Nodularia. Although toxic cyanobacteria have been recorded in the Swan-Canning and Peel-Harvey estuaries in Western Australia, very little is known about the blooms in the surrounding freshwater lakes. In this study, a total of 32 natural bloom samples representing 13 lakes were analyzed by HPLC for microcystin (MC)-LR, -RR, and -YR. Twenty-eight samples proved to be toxic. The highest total microcystin concentration ranged from 1645 to 8428.6 microg L(-1), and the lowest concentrations were less than 10 microg L(-1) with some below the detection limit (< 0.05 microg L(-1)). MC-LR (100%) was the predominant microcystin, followed by MC-YR (71.4%) and MC-RR (60.7%). The presence of a Nodularia spumigena bloom in the freshwater Lake Yangebup was associated with the detection of nodularins (1664 microg L(-1)). This is the first study to demonstrate the presence of microcystins and nodularins in urban lakes on the Swan Coastal Plain, Western Australia.

Abstract:Annual data sets, from 1980-81 and 1994-95, provide evidence that inter-annual differences in the seasonal succession of phytoplankton in the Swan River Estuary can be attributed to rainfall and salt-wedge movement. The distribution and succession of phytoplankton are influenced by seasonal variation of rainfall and its subsequent effect on the spatial distribution of salinity. The longer duration of rainfall in 1980-81 compared with 1994-95 effectively restricted the movement of the salt-water wedge, thereby delaying the progression of marine phytoplankton into the estuary. There was little difference in the phytoplankton composition and biomass in the lower estuary, while the upper estuary appeared to have more blooms of dinoflagellates in the summer and autumn of 1994-95 compared with 1980-81.The intensity and duration of rainfall appeared to affect the availability of soluble nutrients. Although there was no significant difference in phytoplankton biomass between the two periods, it was likely that the high phytoplankton biomass in the upper estuary in 1994-95 was due to availability of more soluble nutrients from internal recycling processes at the sediment/water interface.

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The association of diatom assemblages to salinity was studied in 95 lakes and streams ranging from freshwater to hypersaline in the south-west of Western Australia. The relationship between environmental variables and species composition was explored using canonical correspondence analysis (CCA) and partial CCA. Salinity was shown to account for a significant and independent amount of variation in the diatom data, enabling a transfer function to be developed based on the final dataset, which consisted of 89 sites and 150 diatom taxa. The most successful model was derived using tolerancedownweighted weighted averaging. Summary statistics showed that the transfer function performed very well with a high coefficient of determination and low prediction errors that remained high after the crossvalidation method of jackknifing (r apparent 2 = 0.97 and r jackknifed 2 = 0.89). This suggests that salinity can be accurately predicted using relative abundances of diatoms, and the model can now be applied to paleolimnological reconstructions. However, the transfer function also provides the basis for use in future biomonitoring studies to detect increases in salinity for lakes and streams most at risk, as well as to evaluate the success of remediation measures implemented to secondary salinised systems.

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