Geophysical investigations of the Siljan impact structure

Abstract

An attempt is made to relate variations in the chemical composition of Swedish fresh waters (mainly analyzed by Lohammar, 1938) to topographical, geochemical, and biological factors. The following are among the more general conclusions: 1.(1) In Uppland lake waters, and certain of those in Dalarna, total salt concentration is clearly related to altitude.2.(2) There are distinct differences in ionic proportions between richer and poorer lake waters in both Dalarna and Uppland. In Dalarna the preponderance of moraine or Dalălven river sediments appears to be the important factor. In Uppland the high proportions of Cl, Na, and Mg in the waters of the lowest and richest lakes bear witness to the marine submergence of the district at the end of the glacial period.3.(3) A comparison of Dalarna drainage and seepage lakes reveals that the waters of the latter are proportionally very rich in K but low in Ca. It is suggested that this may be due to a lesser degree of biotic influence on the waters reaching the seepage lakes.4.(4) Dalarna seepage lakes exhibit low SO4 levels in their waters, which may be connected with a slow rate of water transfer through them.5.(5) The cations of bog waters are dominated by Na, those of fen waters by Ca. This illustrates the relative importance of atmospheric precipitation in the former, and mineral soil leaching in the latter.6.(6) The frequency distributions of dissolved plus particulate minor constituents in fresh waters may be far from normal, low values predominating. Medians are therefore desirable in place of averages.7.(7) Fe is most abundant in the more dilute waters, especially in Norrland. Mn is higher in the richer waters within each district, except in the Siljan area of limestone, where the lowest median occurs. Both elements tend to be highest (in respect of surface waters) in the shallower lakes.8.(8) P is lowest in the Siljan limestone lakes, and highest in the Dalarna seepage lakes.9.(9) N is lowest in the most dilute waters, Norrland being particularly low, and higher in the richer waters within each district (except in the Siljan area).10.(10) Sr, which like the major constituents is highly correlated with total ion concentration, forms a slightly larger part of the total ions in the more dilute waters, especially in Norrland.