Abstrakt:
This study compares the concentration of calcium, magnesium, sodium and potassium in 251 lakes located in the northeast part of Poland in the 1960s and 1990s. It has been proved that the pace of increase in cation concentration was diversified, both in the case of particular lakes and physico-geographical regions. The fastest rise in cation concentration occurred in the lakes located in intensively agricultural regions. Specific attention has been drawn to wider ranges of cation occurrence and changes in the ratio of calcium to magnesium. The main causes leading to the change in cation concentration include lake pollution with sewage and washing chemical compounds out of artificial manures.
