Managing Cyanobacteria Blooms in Lake Hume: Abundance Dynamics Across Varying Water Levels

Lake Hume, a critical reservoir within the Murray River system, Australia, has been identified as a potential source of cyanobacteria in downstream rivers during past mega-blooms. This study aims to evaluate the impact of lake-level fluctuations on cyanobacterial abundance at the dam outlets, with the goal of mitigating the risk of cyanobacteria intake from hydropower and irrigation outlets during periods of low dam levels. Utilising a one-dimensional vertical hydrodynamic model (LAKEoneD), the study simulated time series data on water temperature and stratification within Lake Hume. These outputs were then incorporated into a cyanobacteria growth model driven by water temperature, mixing dynamics and light. Despite inherent uncertainties in the models, the simulated cell counts effectively mirrored bloom occurrences. Consequently, a series of simulations across varying water levels in the lake revealed a consistent risk of significant cyanobacteria intake through both the hydropower and irrigation outlets when water levels dropped below specific thresholds. Notably, water levels below 20 m and 10 m posed heightened risks of releases of seed populations of cyanobacteria from the hydropower and irrigation outlets, respectively.