The Elution of Ions Through Field and Laboratory Snowpacks

Abstract

It has been recognised for many years that the first fraction of meltwater from a melting snowpack contains a much higher concentration of ions than that of the bulk (or average) snow of which the pack is comprised (Foster 1978, Johannessen and Henriksen 1978). This process leads to the so called “acid flush” in the spring and can have severe ecological effects on lakes and streams (Hagen and Langeland 1973, Leivestad and Muniz 1976, National Research Council of Canada 1981). We have studied elution of ions through a snowpack on Folgefonna near Bergen, Norway, and in the laboratory. In the field we collected meltwater samples at hourly intervals for a period of 4 d at the start of the melt season, and analyzed them for pH, , Cl⁻, Na⁺, Mg²⁺, Ca²⁺ and K⁺. 2 m cores were also collected at the beginning and end of the experiment in order to study bulk changes in snow composition. The meltwaters showed a diurnal cycle with high ionic concentrations around noon, with and levels rising by factors of up to four and six-fold compared to the average concentrations on the first day. Cl⁻ levels peaked much later, after the and levels had decreased, and only reached 2.3 times their lowest concentrations. pH values were strongly correlated with and levels, suggesting that a significant proportion of these anions were in the form of strong acids.The laboratory experiments involved slow melting of snow samples collected in the Cairngorm mountains, Scotland, and also showed that and (and also Mg²⁺ and K⁺) ions were removed from the snow preferentially whilst Na⁺ and Cl⁻ tended to remain longer. The position of H⁺ within the ion elution sequence is unclear due to uncertainties in the absolute determination of pH in the field measurements, but the laboratory experiments confirm the differential rates of elution shown in the Norwegian snowpack and reaffirms its importance in the acidification of streams during spring.