An important distinguish feature of the seasonally frozen soils consists in the combination of nonequilirium heat- and mass-transport processes with cyclic processes of freezing and thawing in the open ecosystem: soil - soil water (dilute salt solution) - atmosphere . For explanation of physical and physico-chemical phenomena occurring in the freezing systems with moving boundary between ice/water phases /1/ we have developed the special molecular model of interface charge separation using the notion of orientational D- and L-defects in structure of ice /2/.We have shown that the growing ice crystal takes from liquid phase excess heavy anions (e.g. Cl-) which retain the excess hydrogen ions(H+) in solid phase; as result the hydrogen index (pH) of the frozen part decreases (after thawing). As one would expect analogous changes occur in natural frozen soils. This gives on our opinion on insight into sharp decrease of pH in lake waters during snow thawing (pH-shock /3/)). Special experiments on model systems ( dilute salt solutions , soil samples) were run to confirm our conclusions on soil samples. The result of our research are /4/ :

• The change of frozen soil acidity depends from initial values of pH and moisture content of soil samples ; the effect is more distinguished on more acid and moist samples.
• Increase of frozen soil acidity have a significant influence on ion exchange and carbonate-calcium equilibrium in frozen soil samples that result in increase of the potential soil acidity and cations movement in frozen soils.

References

1. E. Workman, S. Reynolds, Phys.Rev. 1950, v.78, p.254
2. Yu.V. Gurikov, E.M. Savelieva, N.F. Bondarenko, Russ.J.Phys.Chem.1975, v.49, p.
3. Yu.A. Israel (ed.) Acid Rains, 1983
4. E.M. Savelieva, Influence of water-ice phase transition on hydro-meteorologic processes in system: atmosphere - soil. Dissertation Leningrad (St. Petersburg), 1986

N.F. Bondarenko
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Yu.V. Gurikov
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E.M. Savelieva
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