Lakes and Watercourses

TABLE 24.
(continued)
Cu Zn Cd Pb Cr Ni Co As V Hg
Lakes (µg/l)
natural, pristine concentr. 0.3 1 0.005 0.05 0.05 0.2 0.03 0.2 0.1 0.001
background, N Sweden 0.3 0.9 0.009 0.11 0.05 0.2 0.03 0.2 0.1 0.002
background, S Sweden 0.5 2.0 0.016 0.24 0.2 0.4 0.06 0.3 0.2 0.004
Sediment (mg/kg ds)
natural, pristine concentr. 15 100 0.3 5 15 10 15 8 20 0.08
background, N Sweden 15 150 0.8 50 15 10 10 20 0.13
background, S Sweden 20 240 1.4 80 15 10 10 20 0.16
Aquatic moss (mg/kg ds)
background, all Sweden 10 100 0.5 5 2 5 5 2 0.07
* There is no data on watercourses unaffected by acidification and the figures for southern Swedish
lakes are therefore used.
contains far more organic matter and that most metals are found in that
fraction of the sediment.
Comments
Classification must be based on samples taken and analyses made in
accordance with the Swedish EPA Environmental Monitoring Handbook
and analyses made in accordance with the Swedish standard. Data
for water and aquatic moss should have been obtained over at least three
years, whereas that for sediment and fish can derive from single years.
Concentrations in running water should have been monitored once a
month, those in lakes four times a year. It may be necessary to take
samples more frequently in minor watercourses and lakes with shorter
retention times. If assessments are made on the basis of more limited
data, this should be stated.
Classification should be based on the arithmetical mean. However,
account should be taken of the fact that biological effects may occur
when the concentrations given under Assessment of current conditions
are exceeded for about a month or more. If individual analyses indicate
that this may have occurred, the water sample programme should be
expanded and/or a biological sampling programme initiated to determine
whether damage is occurring.
48