Boike and Overduin: Seasonal Changes in Hydrology. Energy Balance and Chemistry
301
detection of these heat transport processes, their relative importance for active layer thermal
dynamics is still unknown.
Studies of changes in soil water solute concentrations during freezing provide data for
developing our understanding of the freezing processes and their potential effects on the energy
balance and water chemistry in the boundary layers of the permafrost region.The inputs and
outputs to soil water solutes in a soil profile are outlined in Figure I. As active layer
temperatures drop in late summer, bulk pore water forms an ice matrix, excluding solutes to the
unfrozen water layers surrounding soil particles (a movement from the freezing liquid phase to
the unfrozen), and potentially into unfrozen soil. In addition to the effects of freezing-induced
moisture migration, solute exclusion also leads to solute concentration. The dramatic changes in
depth specific solute concentrations can occur concomitant with freezing has been demonstrated
in laboratory investigations (Ershov et aI., 1992).
The overall objectives of this paper are to present an integrated study of the hydrological and
thermal dynamics of the active layer for one complete freeze-thaw cycle. The results of two
expeditions are evaluated, the first from August to September 1994 and the second from May to
October 1995, carried out in the Levinson-Lessing Lake catchment on the Taymyr Peninsula,
the northernmost continental part of the circumpolar arctic (Figure 2).
Methods and instrumentation
In the summer of 1994, transects were instrumented on 3 slopes in the Levinson-Lessing Lake
catchment (Figure 2) differing in substrate material and slope aspect and inclination (Table I).
During this and subsequent expeditions in 1995, data were collected to calculate the energy and
mass balance of the active layer along the 3 slopes. The data collected included soil volumetric
water content, bulk electrical conductivity and temperature, the thaw depth of frozen ground
and climatic data at two automatic weather stations (Figure 2). Water samples from the saturated
and unsaturated zone, the frozen ground and precipitation were gathered for geochemical
analysis. To trace the effects of the seasonal freeze-thaw cycle on the vertical distribution of
water and solutes, cores of the active layer were taken during late summer and freeze-back and
their soil water was extracted via centrifugation for chemical analysis. Details of the method are
given in Overduin and Young (1997).
Changes in active layer water content and solute concentrations are important in determining
the mode of heat transfer in the active layer, especially during phase change. A direct method
for in situ measurements of solute concentrations over time is unavailable; part of this study
was devoted to exploring the potential of time domain reflectometry (TDR) as a method for
measuring both variables. As a first step, currently applied models were tested for calculation of
the unfrozen volumetric water content (q) and bulk electrical conductivity (Sb) of the active
layer, based on in situ application of TDR. The determination of q was shown to be accurate to
within 0.03 m 3 with current models and does not require soil specific calibration. For
determination of the soil water electrical conductivity sw, a model was developed to calculate
Sw from TDR traces for this permafrost setting to within a factor of 2 of the values obtained via
direct soil water sampling techniques (Boike and Roth, 1997).
Results and discussion
Seasonal hydrological and thermal dynamics a/the active layer
Field experiments carried out for one continuous thaw-freeze cycle gave insight into the thermal
and hydrological dynamics and the dominant heat and mass transfer mechanisms in the active
301
detection of these heat transport processes, their relative importance for active layer thermal
dynamics is still unknown.
Studies of changes in soil water solute concentrations during freezing provide data for
developing our understanding of the freezing processes and their potential effects on the energy
balance and water chemistry in the boundary layers of the permafrost region.The inputs and
outputs to soil water solutes in a soil profile are outlined in Figure I. As active layer
temperatures drop in late summer, bulk pore water forms an ice matrix, excluding solutes to the
unfrozen water layers surrounding soil particles (a movement from the freezing liquid phase to
the unfrozen), and potentially into unfrozen soil. In addition to the effects of freezing-induced
moisture migration, solute exclusion also leads to solute concentration. The dramatic changes in
depth specific solute concentrations can occur concomitant with freezing has been demonstrated
in laboratory investigations (Ershov et aI., 1992).
The overall objectives of this paper are to present an integrated study of the hydrological and
thermal dynamics of the active layer for one complete freeze-thaw cycle. The results of two
expeditions are evaluated, the first from August to September 1994 and the second from May to
October 1995, carried out in the Levinson-Lessing Lake catchment on the Taymyr Peninsula,
the northernmost continental part of the circumpolar arctic (Figure 2).
Methods and instrumentation
In the summer of 1994, transects were instrumented on 3 slopes in the Levinson-Lessing Lake
catchment (Figure 2) differing in substrate material and slope aspect and inclination (Table I).
During this and subsequent expeditions in 1995, data were collected to calculate the energy and
mass balance of the active layer along the 3 slopes. The data collected included soil volumetric
water content, bulk electrical conductivity and temperature, the thaw depth of frozen ground
and climatic data at two automatic weather stations (Figure 2). Water samples from the saturated
and unsaturated zone, the frozen ground and precipitation were gathered for geochemical
analysis. To trace the effects of the seasonal freeze-thaw cycle on the vertical distribution of
water and solutes, cores of the active layer were taken during late summer and freeze-back and
their soil water was extracted via centrifugation for chemical analysis. Details of the method are
given in Overduin and Young (1997).
Changes in active layer water content and solute concentrations are important in determining
the mode of heat transfer in the active layer, especially during phase change. A direct method
for in situ measurements of solute concentrations over time is unavailable; part of this study
was devoted to exploring the potential of time domain reflectometry (TDR) as a method for
measuring both variables. As a first step, currently applied models were tested for calculation of
the unfrozen volumetric water content (q) and bulk electrical conductivity (Sb) of the active
layer, based on in situ application of TDR. The determination of q was shown to be accurate to
within 0.03 m 3 with current models and does not require soil specific calibration. For
determination of the soil water electrical conductivity sw, a model was developed to calculate
Sw from TDR traces for this permafrost setting to within a factor of 2 of the values obtained via
direct soil water sampling techniques (Boike and Roth, 1997).
Results and discussion
Seasonal hydrological and thermal dynamics a/the active layer
Field experiments carried out for one continuous thaw-freeze cycle gave insight into the thermal
and hydrological dynamics and the dominant heat and mass transfer mechanisms in the active