Three-dimensional modelling of a Microcystis bloom event in the Swan River estuary, Western Australia

In January 2000, there was a record maximum rainfall throughout much of the watershed of the Swan River estuary. Within three weeks of this rainfall event, a large, mono-specific bloom of the cyanobacterium Microcystis aeruginosa had developed in the estuary, with cell counts peaking at over 100,000 cells ml−1. A three-dimensional, coupled hydrodynamic–ecological model, ELCOM-CAEDYM, was applied to the period of development and subsequent decline of the bloom. The model, previously calibrated for more typical years (1995 and 1996) when there was no bloom, accurately reproduced the unusual hydrodynamic conditions in the estuary as well as the approximate magnitude and timing of the M. aeruginosa bloom. The model results supported the hypothesis that salinity and temperature are the primary factors controlling the growth of M. aeruginosa during the period of interest. The simulations described in this study show how the model captures the complex interactions between the physical and biogeochemical environment, and indicate the usefulness of the model as a predictive management tool.