Acidification
Acidification of lake water is caused by the input of acid air
pollutants such as acid rain and dry fallout, either directly on the lake
surface or indirectly via inflowing rivers.
Tens of thousands of small lakes in northern and central Europe
and in North America have already become too acid to allow fish to breed there
and, in extreme cases, almost any kinds of animals to survive. At present, the
acidification of lake water is largely confined to rather limited regions such
as Scandinavia, parts of central Europe, the north-eastern United States, and
neighbouring parts of Canada, most probably owing to particular geological
conditions, though acid precipitation itself occurs more widely over the
northern hemisphere.
Fig. 3.3
The relation between the
concentration of suspended solids in lake water and the area of farmland in
corresponding catchment areas (Note: closed and open circles refer,
respectively, to lakes and reservoirs in humid/subhumid regions and those in
arid regions)
However, soil scientists have recently tried to predict how long
it will take for the buffer capacity of the soil to be exhausted by continued
acid precipitation. The predicted value of course depends on soil type, but may
range, e.g. in Japanese soils, from several years to several decades. This is an
alarming prediction, which suggests that the acidification of lake water may
sooner or later become a global
issue.
