Pit observations of active layer of tundra wetland near Tiksi, Siberia
Kunio WATANABE and Masaru MIZOGUCHI
Department of Bioresources, Mie-u

1. Introduction

thermistor, which was horizontally inserted into

The permafrost

is overlaid seasonal

the wall with length of 10cm.

The water

thawed layer so-called active layer. Characters

content and density were measured by usingof soil and soil water in the active layer are

undisturbed pedons taken to sampler with

important to consider water cycle in tundra

volume of 100cc.

region. However, there are few places in thewas measured in the filed by falling head

Siberian tundra where sufficient, high-quality

permeability test. A few days past after dug thesoil data exist.

pit, the ground water level was measured fromHere, we report morphology

and properties of soil of the active layer in

The hydraulic conductivity

collected water in the pit.

tundra wetland.
3. Results
2. Observation site and Methods

3.1 General and mother rock

Survey was carried out at tundra wetland
near Tiksi, Russia.

Figure 1 shows soil

observation sites in surveyed area.

In the surveyed area, sedges grew in thesite where ground water level was low or theThere areground was inundated, while mosses grew in the30 observation sites on the 3km line with 100m

site where ground water level was a few

intervals.

centimeters.

Each observation site was given a

number from 1 to 210 as shown in figure.

Gravel spread at the elevation ofhigher than 150 m in stead of the vegetation.

Observation pit with size of 50cm x 50cm

Soil mainly consisted of living plant, peat,

were dug to the frozen ground at each site.

clayey silt that should be weathering material byThen, surface condition, thickness and horizons

freeze-thaw effect and frozen parent materialof the active layer were directly observed.

and the horizon is not so advanced.

surfacecondition

wasrecorded

vegetation in the order of rate.

The

typicalThe horizons

There isalmost unitary mother rock consists of sandy
mudstone in the surveyed area.

The mudstone

were described according to standard techniques

sometime has quartz vein.

Table 1 shows(E. M. Bridges; 1978) but modified for Arctic

mineral component of these materials definedconditions. Using the wall of the pit, profiles

from thin section observations.

of temperature, water content, density, hydraulicconductivity of soil were measured.

The

temperature was measured for several depths by

3.2 Ground water level and vegetation
Table 2 shows elevation, slope, thaw depth,
ground water level, air temperature near groundsurface, ground water temperature, dissolvedof B layer and frozen ground.

oxygen and ground surface condition of soil

horizon tended to have a lot of roots andobserved at each pit.

decomposed organic.

Site 1-10, 20-30, 60-106

The upper

The lower horizon

and 110-210 were made on August 17, 18, 20

generally consisted of clayey silt that weathered

and 22, 1997.

freeze-thaw effect and had gley color and highSlope was measured staff withclinometer put on the pit.

Air temperature,viscosity.

Gravel, which sometimes foundwater temperature and DO of site 1-190 and sitehorizons, became smaller with depth.

200-208 were measured on August 29 andsome layers, for instance Bo layer (dark brown,September 2, 1997, respectively. Soil profileorganic-rich)type is classification from soil water regime andviscosity), is clearly divided.

surface condition (Watanabe et al. 1998).

plant layer thick, active layer was apt to become

Table 3 shows variation of the soil waterconditions for several sites.

andBwg layerAnd(gley, highWhen living

thinner.

Site 197 indicates

Table 5 shows water content, density andwater of T River on cross point of thehydraulic conductivity of each horizon forobservation line.

several observation sites. And, Fig. 2 shows
annual variation of each horizon's temperature at3.3 Horizon and physical properties

same observation pits.

Table 4 shows horizons and the thicknessof soil in the active layer at each site.

Except for gravel richsite, physical property of each site had similar

In thetendency as follows. Water content was high incolumn of horizon, abbreviation "P" indicatesthe surface and the lower horizon while it wasliving plant layer.

low in the upper horizon.

Texture of horizon was

Bulk density wasestimated into four steps: gravelly, sandy, loamy,

low in the surface and the lower horizon, whileandit was high in the upper horizon.

silty.

Boundarycondition

betweenhorizons was estimated into 3 steps: abrupt,clear and gradual.

Air temperature at this moment isshown in table2.

was about the air temperature.

It decreased

with depth and reached 0 degree Celsius atfrozen ground surface.

CONCLUSION
Soil of active layer on tundra wetland wassurveyed.

The temperature in the living plant layer

Morphology and some properties ofthe soil were summarized in Tables.

These soil

characters will be useful for make practicalhydrological model.

Although soil was not

so formed in this area, it was approximately
divided into four horizons: living plant layer,peat or upper horizon of B layer, lower horizon.

conductivity decreased with depth

Soil temperature of each

depth was measured when the observation pit
was made.

HydraulicAcknowledgment
We would like to thank Dr. H. Urano fordefinition of mineral component of rocks