Lakes and Watercourses

Class 3. Clear effects of disturbance. Substantial impact on assemblages
of organisms and their habitat. The bottom fauna deviates moderately
from its normal undisturbed state.
Class 4. Pronounced effects of disturbance. The community deviates
markedly from its undisturbed state.
Class 5. Very great effects of disturbance. Only a few tolerant species
occur.
Reference values specific to a given locality should be used as far as
possible. These may be derived in several ways. They can be estimated
on the basis of historical surveys carried out in the area or they may be
obtained from surveys made in similar but unaffected lakes or watercourses
in the vicinity. If this is not possible, the reference values given in
Table 43 may be used.
TABLE 43.
Reference values for differing habitats and natural geography. Reference values comprise
the 25th percentile (75th percentile for O/C index) in data from lakes and watercourses
included in the 1995 survey of lakes and watercourses, which, as far as possible, are
unaffected. The data used is described in detail in the background report. The boundaries
between the natural geographical regions are shown in Figure 3. The figures given
for the profundal zone of lakes are not specific to regions.
Natural geographical region
Arctic/ Northern Middle Southern Boreo- Nemoral
alpine boreal boreal boreal nemoral
Watercourses
Shannon-Wiener’s diversity index 1.96 2.56 2.34 2.11 1.97 1.89
ASPT-index 5.8 6.2 6.0 5.5 4.7 4.8
Danish fauna index* 5 5 5 5 5 5
Acidity index 6 6 6 6 6 6
Littoral zone of lakes
Shannon’s-Wiener’s diversity index 1.00 1.06 1.46 1.98 2.15 2.01
ASPT-index 4.6 5.0 5.0 5.0 5.1 4.5
Danish fauna index 3 4 4 4 4 4
Acidity index 6 6 6 6 6 6
Profundal zone in lakes
BQI-index 2
O/C-index 8.5
* Reference values for regions 4, 5 and 6 have been adjusted upwards (from 4 to 5) in response to
comments received from consultants, county administrative boards etc working in these regions.
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