Lakes and Watercourses

TABLE 46.
DEVIATION from reference value, lakes. For the time being, calculations should only be
made for lakes below 500 m above sea level. Background data on higher altitude lakes is
too limited for reliable assessment. Calculations are only made for lakes that can be
assumed to contain, or have contained, fish.
Class Description Recorded value/reference value
No. of species 1 Species diversity 1 Biomass 1 Number 1
1 No or insignif. deviation > 0.80 > 1.00 0.65 – 1.50 0.60 – 1.40
2 Slight deviation 0.62 – 0.80 0.83 – 1.00 0.45 – 0.65 or 0.37 – 0.60 or
1.50 – 2.15 1.40 – 2.15
3 Significant deviation 0.42 – 0.62 0.60 – 0.83 0.28 – 0.45 or 0.22 – 0.37 or
2.15 – 2.70 2.15 – 2.80
4 Large deviation 0.32 – 0.42 0.38 – 0.60 0.10 – 0.28 or 0.10 – 0.22 or
2.70 – 3.40 2.80 – 3.50
5 Very large deviation ≤ 0.32 ≤ 0.38 < 0.10 or < 0.10 or
> 3.40 > 3.50
Class Description Recorded value/reference value
Proportion pisc. 1 Proportion Proportion Proportion
cyprinids 1 species and tolerant
stages sensitive species 3
to acidification 2
1 No or insignificant deviation 1.00 1.00 a) < 0.10
2 Slight deviation 0.65 – 1.00 1.00 – 1.28 0.10 – 0.25
3 Significant deviation 0.40 – 0.65 1.28 – 1.67 b) 0.25 – 0.50
4 Large deviation 0.23 – 0.40 1.67 – 1.89 0.50 – 1.00
5 Very large deviation < 0.23 > 1.89 c) 1.00
Class Description Proportion alien species 4 Overall index 5
1 No or insignificant deviation 0 ≤ 1.7
2 Slight deviation 0 – 0.10 1.7 – 2.1
3 Significant deviation 0.10 – 0.20 2.1 – 2.6
4 Large deviation 0.20 – 0.50 2.6 – 3.0
5 Very large deviation > 0.50 > 3.0
1 The deviation is calculated as the ratio between recorded value and the reference value. The reference
value is set with reference to Table 47.
2 a) Presence of spined loach (Cobitis taenia) or crayfish or juvenile roach (Rutilus rutilus), minnow
(Phoxinus phoxinus), burbot (Lota lota), char (Salvelinidae), whitefish (Coregonidae) or vendace
(Coregonus albula).
b) Presence of perch (Perca fluviatilis), trout (Salmo trutta), bullhead (Cottidae), ruffe (Gymnocephalus
cernuus), burbot (Lota lota), grayling (Thymalus thymalus) char, whitefish or vendace (Coregonus albula).
c) Species absent (have disappeared) or only mature/large individual specimens of perch or pike are
present.
3 Calculated as percentage by weight of crucian carp (Carassius carassius) and/or tench (Tinca tinca) out
of the total catch. This parameter is only used in lakes where one of these species has been caught.
4 Calculated as percentage by weight of fish species not native to Sweden out of the total catch.
5 The overall assessment of deviation is obtained by calculating the mean class value for all parameters
included (maximum 9 parameters).
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