ABSTRACT
Selecting the optimal abstraction depth to minimise the cyanotoxin risk requires awareness of the depth distribution of other water contaminants – that is, pathogens, dissolved organic carbon, iron and manganese. Observing seasonal patterns of cyanobacterial scum location and/or predicting them from the main wind direction may be useful for planning a drinking-water offtake or the location of a recreational site or beach. Spatial and vertical variability in the concentration of contaminants in lakes and reservoirs is common. The water abstraction depth can also be utilised to release water of poorer quality downstream and optimise the quality of water remaining in the reservoir. The horizontal variation in the distribution of cyanobacterial populations can also be considerable. For controlling cyanotoxin concentrations by sediment passage, operational monitoring of managed aquifer recharge and slow filters can use parameters indicating flow and redox conditions in order to ensure sufficient residence times in the subsurface.
