Lakes and Watercourses

Aquatic plants in lakes
Introduction
Aquatic plants play an important role in lake metabolism and form an
essential part of the habitat of many organisms. The diversity and
abundance of plants is affected by eutrophication, acidification and other
changes in the environment. Both individual species and entire types of
plant community can therefore serve as indicators of the state of the
ecosystem.
This assessment system uses mainly floating-leaved and submerged
plants. These groups have been chosen because they are well defined and
contain many species giving a good indication of environmental quality.
The assessment of current conditions is based on the number of species
present. When assessing deviation from reference values, use is also made
of indicator ratios, which reflect the normal occurrence of species in
relation to the nutrient status of the water.
The assessment of aquatic plants is confined to lakes. There is no
background data on which to base model criteria for watercourses.
Assessment of current conditions
TABLE 35.
CURRENT CONDITIONS: number of species of submerged and
floating-leaved plants
Class Description Total number of species
1 Very high number of species > 18
2 High number of species 14 – 18
3 Moderate number of species 9 – 14
4 Relatively few species 4 – 9
5 Very few species ≤ 4
The classification can be supplemented by specifying the predominant
type of vegetation: A Isoetid type, B Elodeid type, C Floating-leaved type
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