Lakes and Watercourses

TABLE 32.
DEVIATION from reference value, potentially toxin-producing cyanobacteria
Class Description No. of potentially toxic genera/
reference value
1 No or insignificant deviation < 1
3 Significant deviation 1 – 1.5
5 Large to very large deviation ≥ 1.5
TABLE 33.
DEVIATION from reference value, Gonyostomum semen
Class Description Recorded volume/reference value
1 No or insignificant deviation ≤ 1.0
2 Slight deviation 1.0 – 10
3 Significant deviation 10 – 25
4 Large deviation 25 – 50
5 Very large deviation > 50
of 15 µg/l. The reference values have then been based on correlations
with the total biomass of planktonic algae. The biomass in August has
been determined by calculating the relationship with the seasonal mean
from the Environmental Monitoring Programme database. The volume
of diatoms in April/May is based on the maximum figure in the database
for mesotrophic lakes having a nutrient status of 15 µg/l (tot-P). Two
reference lakes form the basis for assessment of forest lakes. Maximum
figures from a number of published studies have been used for mountain
lakes, since the Environmental Monitoring Programme database was
inadequate.
Reference values for potentially toxic genera have been set using the
Environmental Monitoring Programme database. Essentially, the
reference value for Gonyostomum semen is considered to be an absence of
viable communities. The reference value has been set using lakes where
there is an influx of humic water capable of carrying limited quantities of
Gonyostomum, which will temporarily survive in a given habitat.
56