because divalent cations have greater electrostatic
The redistribution of solutes depends strongly
attraction to charged surfaces than monovalent
on freezing rate, moisture content, soil texture and
cations. More-soluble soil constituents migrate
time. There are cases, especially in fine-textured
soils, where maximum solute concentrations are
more readily through freezing and frozen soils be-
found in the frozen zone (Ershov et al. 1992). Qiu
cause the less-soluble minerals precipitate; this can
et al. (1988) demonstrated that for single-salt so-
play a major role in horizonation and pedogenesis
lutions in moist sands, solutes migrate toward the
of cold regions soils (Hallet 1978, Zvereva 1982,
unfrozen zone (Fig. 3); on the other hand, in silt
Panin and Kazantsev 1986, Sletten 1988, Richard-
and clay soils, solutes migrate toward the freez-
son et al. 1990).
ing zone. Over several freezethaw seasons, surf-
The transport of solutes between water or snow
icial salt applications may be leached to deeper
and soil during freezethaw processes can play an
soil horizons, effectively moving in the opposite
important role in geochemical cycling in cold re-
direction of water during frost periods (Yong et
gions. Kadlec et al. (1988) found that the freezing
al. 1973a). Baker and Osterkamp (1988) found that
of shallow waters in peatlands drives a consider-
significant salt rejection and brine drainage oc-
able portion of solutes into the topsoil. Ostroumov
curred with downward freezing, but there was
et al. (1992) examined the flux of solutes from soil
none with upward freezing. The amount of salt
into snow under laboratory conditions. The maxi-
rejection increased with decreasing freezing rate.
mum concentrations in snow were found at the
These differential responses are due to the role of
snowsoil boundary. Solutes were transferred to
soil physical properties such as porosity, surface
snow in the same direction as the heat flux. The
flux of ions in snow fell in the order: K > Cl >> Li >
area and hydraulic conductivity in controlling
Ca > Cu >> Cd = Pb. They attributed the greater
both water and solute flows along concentration,
temperature and hydrostatic gradients. The com-
flux of K relative to Cl to greater anion adsorption,
plex interactions possible among soil physical and
relative to cation adsorption, on the surface of ice
chemical properties is a strong incentive for de-
particles. This charge separation phenomenon is
veloping computer simulation models.
identical to the WorkmanReynolds Effect, which
Liquid films exist on soil particles in frozen
is, however, usually thought to be due to absorp-
soils, which provides the dominant route for the
tion of anions into the ice phase.
flow of water and associated solutes in frozen soils
Soil freezethaw processes can play a role in
controlling geochemical cycling at larger scales,
(Murrmann et al. 1968, Hoekstra 1969, Cary and
such as watersheds and geographic regions. Ed-
Mayland 1972, Murrmann 1973, Gray and Grang-
wards et al. (1986) found that freezethaw cycles
er 1986, Hofmann et al. 1990). Murrmann (1973)
have significant effects on the chemical composi-
found surprisingly high diffusion rates for Na ions
in the temperature range of 0 to 15C, which he
tion of streams. Substantial amounts of many ele-
ments that dominate stream chemistry become
attributed to the existence of thin water films.
available upon thawing, especially Al, K and or-
Murrmann (1973) concluded that the temperature
ganic C. They also hypothesized that soil freezing
dependence of ionic diffusion at subzero temper-
might also influence solute chemistry by altering
atures is primarily a function of water film thick-
hydrologic pathways. Everett et al. (1989) conclud-
ness. Even in Antarctic soils, which are
ed that snowmelt was the most important hydro-
continuously frozen and relatively dry, the liquid
logic and geochemical event in a small arctic
films at mineral surfaces are believed to be the
watershed in northern Alaska. Ion concentrations
dominant avenue for the movement of solutes
were highest during the first 15% of the snowmelt
(Ugolini and Anderson 1972, 1973).
event. In all cases ion concentrations in the spring
Because many soil surfaces are charged and the
runoff were four to nine times those of the snow-
solubility of different soil minerals are highly vari-
pack. Potassium was present in surface waters only
able, ionic mobility depends on the specific ions.
during meltoff and for a short time thereafter. Ed-
For example, Ugolini and Anderson (1972, 1973)
found that Cl is more mobile in Antarctic soils
wards et al. (1986) also reported the mobilization
than Na+, presumably because of the attraction
of K during the spring thaw. During winters with
between the negatively charged CEC and the posi-
little or no snowmelt before spring, Johannessen
tively charged Na ion. Czurda and Schababerle
and Henriksen (1978) found that 5080% of the
(1988) found that the monovalent cations Na and
winter pollutant load is released with the first 30%
K were more mobile than the divalent cations Ca
of meltwater. Average solute concentrations were
and Mg in frozen clay columns. This is probably
22.5 times higher than snowpack concentrations.
9
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