Lakes and Watercourses

Chlorophyll-a concentrations refer to seasonal means (May –
October) over three years, based on monthly readings taken in the epilimnion
or, if only one sample is taken, surface water (0.5 m). Alternatively,
August readings taken over three years can be used, although
account must then be taken of the relatively high variation from one year
to another, particularly in eutrophic environments (class 4 and 5). The
chlorophyll concentrations represent the intervals on the phytoplankton
scale and the corresponding interval on the total phosphorus scale. The
chlorophyll concentration has been assumed to constitute 0.5 per cent of
plankton volume. Discrepancies in relation to the concentration of total
phosphorus depend on lake depth, among other things.
TABLE 27.
CURRENT CONDITIONS: spring-developing diatoms (mm 3 /l)
Class Description Biomass
1 Very small biomass ≤ 0.05
2 Small biomass 0.05 – 0.5
3 Moderate biomass 0.5 – 2.0
4 Large biomass 2.0 – 4.0
5 Very large biomass > 4.0
TABLE 28.
CURRENT CONDITIONS: water-blooming cyanobacteria (mm 3 /l)
Class Description Biomass
1 Very small biomass ≤ 0.5
2 Small biomass 0.5 – 1.0
3 Moderate biomass 1.0 – 2.5
4 Large biomass 2.5 – 5.0
5 Very large biomass > 5.0
The class boundaries have been set on the basis of the greatest
biomass of diatoms occurring in corresponding classes for total volume
of algae.
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