The national atmospheric deposition program

A total number of 1165 stream water and 1172 lake water samples were collected in two different projects in the autumns of 1990 and 1987, respectively. The sampling points in streams were determined to include a drainage area of ca 30 km2. The lakes were selected to represent the lakes in the size range of 0.01–10 km2. The anions have different distributions in the stream and lake water data sets. Stream waters are dominated by HCO3 (median value 200 μeq/l), which comprises over half of the anion sum. Organic anions and sulphates are of the same order of magnitude (ca 70 μeq/l), respectively, followed by chloride (40 μeq/l) and nitrate (ca 30 μeq/l). In lakes, sulphate (85 μeq/l) and organic anion (76 μeq/l) concentrations are higher than those of bicarbonate (64 μeq/l). Chloride concentrations in lakes are comparable to those of the streams (28 μeq/l), but nitrate (1 μeq/l) and fluoride contents (< 1 μeq/l) are very minor. The median concentrations of the main cations appear in the same successive order of magnitude in both stream and lake water data sets: Ca > Mg > Na > K > Al > H. The total amounts of cations (medians) in lake waters and streams are 260 and 450 μeq/l, respectively. The hydrogeochemical maps compiled for this study show elevated concentrations in coastal areas for most of the elements particularly in stream waters, which have a more uniform sampling network grid all over the country. In many cases, the same areal pattern is discernible in lake waters, although there are only a few lakes along the coast as the selection was targeted mainly on the upland areas with a higher lake density. These circumstances result in pronounced differences in the distribution of the concentrations. Small lakes show high individuality even in adjacent hydrological systems reflecting the different hydrographical conditions and soil and bedrock types of their catchments. The larger lakes with extensive catchment areas and higher amounts of dissolved solids have higher buffer capacity than small lakes. Therefore, the chemistry of larger lakes is more compatible with that of streams.