Lakes and Watercourses

Assessment of current conditions
Acidity can be assessed from alkalinity and pH value or either. Whereas
alkalinity is primarily a measure of sensitivity to acidification, pH value
reflects actual acidity as such. However, pH usually varies much more
over the year than alkalinity. If the assessment is based on a single
sample, alkalinity is thus preferable to pH as a basis for classification of
current conditions.
TABLE 15.
CURRENT CONDITIONS: alkalinity (meq/l)
Class Description Alkalinity
1 Very good buffering capacity > 0.20
2 Good buffering capacity 0.10 – 0.20
3 Poor buffering capacity 0.05 – 0.10
4 Very poor buffering capacity 0.02 – 0.05
5 No or insignificant buffering capacity ≤ 0.02
The boundaries between the classes are related to impact and
response. An alkalinity figure of 0.05 meq/l is the upper limit for swedish
government-subsidised liming.
TABLE 16.
CURRENT CONDITIONS: pH
Class Description pH
1 Almost neutral > 6.8
2 Weakly acidic 6.5 – 6.8
3 Moderately acidic 6.2 – 6.5
4 Acidic 5.6 – 6.2
5 Highly acidic ≤ 5.6
Assessment of deviation from reference values
Estimated alkalinity during the pre-industrial era is used as a reference
value. Deviation from this value is expressed as the ratio between present
alkalinity and the reference value. This ratio can be fairly accurately
converted into a pH difference (the difference between present and pre-
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