There are two mechanisms of the impact of the seasonal frozen layer on the redistribution of mobile compounds in soils and landscapes: 1 - the frozen layer as an aquacluder and 2 - the frozen layer as a selective fixer of the mobile soil compounds. Both are described in this paper as follows:

The frozen layer as an aquacluder. The seasonal frozen layer is the water impermeable horizon which closes the infiltrate flow of the surface water. As a result the infiltration is lacks and the surface water is spent on a surface run-off and on the flow in an upper freeze vadoze horizon. The run-off intensity of the mobile soil compounds (water soluble and exchange sorption forms of ions) in the both surface and vadoze flow was calculated. The data of 10-year observation of the mobile compound balance and soil freezing dynamics was used as a base for this calculation. The most contrast impact of the seasonal freeze layer on the mass transfer in the soils and landscapes was described for the soils with high water permeability.

The frozen layer as a selective fixer of the mobile soil compounds. A peak of the permeability, concentration and chemical potentials of the mobile compounds is observed on the boundary between frozen and thaw soil. This boundary is a geochemical barrier. Mobile components are concentrated selectively in a thin thaw layer in proximity to this boundary. The laboratory experiments showed that the high mobility of elements promotes their intensive concentration in this layer and run - off by the vadoze flow. If the elements have low mobility then they are preserved in a frozen layer in the fixed state.

Six types of the geochemical flow structure in landscapes were classified depending on the time and depth of the thawing of seasonal freeze layer.

V. Demidov
Institute of Soil Science and Photosynthesis
Russia Academy of Sciences
Pushchino
Moscow Region, Russia, 142292
Telephone: 7(0967) 732604
E-mail: demidov@issp.serpukhov.su