MIB and geosmin compounds are typically associated with blooms of cyanobacteria (blue- green algae), but can also be produced by vegetation, actinobacteria (spore-forming bacteria in water and soils), some species of fungi and myxobacteria. These compounds may then be transferred to the water column with cell membrane breakdown or grazing producers.
The surface water samples are preserved and then, in the laboratory, are first acclimatised to room temperature and homogenised. A sub-sample is then counted in a calibrated counting sedimentation chamber using an inverted microscope (Ütermohl technique). Samples are initially scanned using a magnification of x100 to ensure a random distribution of cells and assess taxon diversity. The entire chamber is then examined in a series of transects using a low magnification (x100/200) in order to count large taxa and colonial or filamentous forms (>150μm long). Smaller or more numerous algae are then counted via a combination of individual random transects (x200) and fields of view (FOV) (x630), with the aim of counting a total of 400 algal units. The cell densities (cells/L) are calculated based on the number of cells counted in each sample and the sample volume.