Accession Number : ADA295688

Title :   Freeze-Thaw Processes and Soil Chemistry.

Descriptive Note : Special rept.,

Corporate Author : COLD REGIONS RESEARCH AND ENGINEERING LAB HANOVER NH

Personal Author(s) : Marion, Giles M.

PDF Url : ADA295688

Report Date : MAR 1995

Pagination or Media Count : 29

Abstract : This review broadly examines the interactions between freeze-thaw processes and soil chemistry, focusing on (1) the effect of solutes on physical properties such as freezing-point depression, unfrozen water and frost heaving, (2) the effect of freeze-thaw cycles and low temperatures on soil chemistry, and (3) modeling of freeze-thaw processes and chemistry. The presence of solutes causes a freezing-point depression, which increases the amount of unfrozen water in soils. Liquid films on soil particles provide the dominant route for the flow of water and associated solutes in frozen soils. In general, salts reduce the hydraulic conductivity and water flow to the freezing front, which reduces frost heaving. Solute exclusion during freezing leads to supersaturated solutions, which promotes the precipitation of secondary minerals in soils. At the watershed level, ionic concentrations in early melt- waters are often 2-9 times higher than snowpack concentrations. Temperature is the dominant factor controlling decomposition rates, with minimal detectable rates occurring at temperatures as low as -10 deg C; both bacteria and fungi are physiologically active at subzero temperatures. Extracellular enzymes are active in soils at temperatures as low as -20 deg C; this activity is thought to occur in unfrozen water on surfaces of soil particles. Nitrogen mineralization is reported at temperatures as low as 1 deg C and is promoted by freeze-thaw cycles. jg

Descriptors :   *FREEZING, *THAWING, *SOIL CHEMISTRY, TEMPERATURE, LOW TEMPERATURE, WATER FLOW, MODELS, CONDUCTIVITY, LIQUIDS, PHYSICAL PROPERTIES, BACTERIA, SECONDARY, ENZYMES, FILMS, RATES, MELTS, CYCLES, NITROGEN, PRECIPITATION, SOLUTIONS(GENERAL), PARTICLES, SOLUTES, FUNGI, PHYSIOLOGICAL EFFECTS, FROZEN SOILS, WATERSHEDS, HYDRAULICS, SUPERSATURATION, DECOMPOSITION, FROST HEAVE, MINERALIZATION.

Subject Categories : Inorganic Chemistry
      Organic Chemistry
      Physical Chemistry
      Soil Mechanics
      Thermodynamics

Distribution Statement : APPROVED FOR PUBLIC RELEASE