Strong and weak acids in surface waters of southern Norway and southwestern Scotland

Abstract

As part of our studies of acidification of rivers and lakes, we have measured pH, strong and weak acids as well as concentrations of major ions in lake-water samples collected regionally in southern Norway and in samples from small lakes and creeks in the New Galloway area, Scotland. Both sets of samples show a similar relationship between strong acid and H +-concentration calculated from the pH of the sample. If pH is higher than about 5.5, the strong acid concentration becomes negative, corresponding to the presence of bicarbonate or other bases. In the pH-range from 4.8 to 5.5 the strong acid concentration is usually positive, but less than the H +-concentration, indicating contributions from weak acids, which may have existed as bases before excess inputs of strong acids started. The variance in weak acid concentrations in lakes in southern Norway and in southwestern Scotland is largely explained by the concentrations of organic carbon and aluminium. Because of increased leaching of aluminium from the soil in areas where deposition of acid components from the atmosphere has increased, an increase in weak acid concentrations has probably also occurred.