Lakes and Watercourses

TABLE 37.
Reference values for number of species and indicator ratios for submerged
and floating-leaved plants in lakes of various sizes and
location
Northern Sweden*
Southern Sweden
Lake area km 2 No. of species Indicator ratio No. of species Indicator ratio
< 60 m above sea level
< 0.1 3 – 5 5.5 4 – 12 7.4
0.1 – 1 9 – 14 6.5 11 – 16 8.1
1 – 10 10 – 18 6.3 15 – 23 8.0
≥ 10 17 – 21 6.5 17 – 25 8.0
60 – 199 m above sea level
< 0.1 ** ** 5 – 11 6.9
0.1 – 1 5 – 13 6.3 10 – 17 7.0
1 – 10 10 – 16 5.8 17 – 25 6.5
≥ 10 13 – 20 6.3 > 17 6.6
> 200 m above sea level
< 0.1 ** ** ** **
0,1 – 1 4 – 11 6.3 8 – 16 7.2
1 – 10 8 – 15 6.2 15 – 25 6.2
≥ 10 13 – 17 5.9 ** **
* North of the Dalälven River ** Reference values are not provided due to
lack of data.
Comments
A survey to determine the number of species and indicator ratio in an
entire lake requires the use of methods providing information on the
vegetation of the whole lake. Studies should be made in high summer or
late summer. The forthcoming description of methods in the Swedish
EPA Environmental Monitoring Handbook should be used. For the time
being, instructions issued in the form of ”Standards for Biological
Surveys” (in Swedish only, Swedish EPA 1987) can be used.
Available data on the occurrence of aquatic plants in watercourses is
inadequate as a basis for assessment. Systematic surveys are needed
before work can progress.
Studies of contemporary vegetation that cover large or representative
areas of the country are also lacking. Here, too, therefore, the data has
great limitations, although it can be supplemented using regional surveys
to determine reference values. These surveys can also provide data for a
future revision of the Environmental Quality Criteria.
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