Introduction

Microtopography has a significant effect on arctic soiltemperature (Miller, 1982; Nelson et al., 1988; Young etal., 1997). Consequently, different positions on themicrotopography are associated with differences invegetation cover (Webber, 1978; Shaver et al., 1996),snow cover and soil moisture regime (Hinkel et al.,1996), all of which have a direct effect on soil tempera-ture. Among other things, soil temperature controls var-ious soil ecological processes in arctic regions, particu-larly in the topsoil (Chapin et al., 1992; Nadelhoffer etal., 1991).

The objectives of this study were to characterize thesoil temperature regimes at different depths in troughand mound microsites (Plot B) and to compare thesedata with equivalent data from a near-level portion ofthe study area (Plot A).

Study area

The study area (66¡23' 35" N; 65¡28' 51" W, 15 m a.s.l.)is located about 0.5 km south of the Overlord cabin inAuyuittuq National Park Reserve at the head of

Pangnirtung Fiord on Cumberland Peninsula, BaffinIsland, N.W.T. The surficial material in the study area isvery stony and bouldery colluvium with a thin veneerof eolian sand, and is underlain by continuous per-mafrost. The soil at the study site is a moderately welldrained Regosolic Static Cryosol (Agriculture CanadaExpert Committee on Soil Survey, 1987), or an Orthel inthe U.S. Soil Taxonomy (ICOMPAS, 1996). The vegeta-tion in the area can be described as a dwarf shrub com-munity (after Gray, 1989). At the Pangnirtung meteoro-logical station (15 m a.s.l.) in this vicinity, precipitation(rain/snow) is 395 mm and the mean annual air tem-perature (MAT) is -9.8¡C, with extremes of 26.7¡C inJuly and -43.3¡C in January (Yorke, 1972).

The study area, which is situated on a moderate (15%)southwest-facing slope, was divided into two plots, 40 m apart (Figure 1). Plot A was situated on near-levelterrain and is a long-term soil climate site. Plot B (1 m2)was divided into two microsites characterized bymicrotopography consisting of a mound and an adja-cent trough (Figure 1), which have different biologicalactivities (Mueller and Broll, submitted). The moundmicrosite (referred to as the mound) rises approximate-ly 25 cm above the adjacent trough microsite (referred

Abstract

Soil temperature regimes were studied on a southwest-facing slope at the southern end of Pangnirtung Passon Cumberland Peninsula, Baffin Island, N.W.T., Canada. Soil temperatures at several depths were recordedwith data loggers at two study plots, which are characterized by different microtopography and soil properties.In order to study the relationship of soil temperature to microtopography, one plot was established on near-level ground while the other plot was divided into two microsites, a small mound and an adjacent trough.

The calculated ranges for various soil temperature parameters at the study plots show similar patterns dur-ing the study period. At the plot where the effect of microtopography on soil temperature was studied, differ-ences between soil temperatures were most evident when temperatures approached their extremes. In general,vegetation cover and thickness of the surface organic layer are the major factors affecting soil temperatures and,therefore, depth of the active layer.

Gerald Mueller, et al. 771

SOIL TEMPERATURE REGIMES AND MICROTOPOGRAPHIC CONTRASTS,BAFFIN ISLAND, N.W.T., CANADA

Gerald Mueller1, Gabriele Broll2, Charles Tarnocai3

1. 2. Institute of Landscape Ecology, University of Muenster, Robert-Koch-Stra§e 26, 48149 Muenster, Germany 1. e-mail: muelleg@uni-muenster.de2. e-mail: brollg@uni-muenster.de

3. Agriculture and Agri-Food Canada, Research Branch (ECORC), K.W. Neatby Building, 960 Carling Avenue, Ottawa,Canada, K1A 0C6

e-mail: tarnocaict@em.agr.ca

to as the trough). The vegetation on the trough is domi-nated by Salix arctica, Vaccinium uliginosum, Carex sp.,and a moss layer composed of Polytrichum hyperboreumand Rytidium rugosum, while that on the mound is do-minated by the lichens Alectoria ochroleuca and Cetrariaislandica . The vegetation cover on the trough is 10Ð15 cm high, while that on the mound is 1Ð3 cm high.

Methods

The air and soil climate station was installed at Plot A(Figure 1) to monitor the general temperature regime ofthe area. Because of the stoniness of the colluvium, thesensors could not be installed in an auger hole.Therefore, it was necessary to dig a small-diameter pitat this location to facilitate the installation of the instru-mentation. The pit was carefully back-filled withunfrozen soil material. Instrumentation at this stationconsisted of a Brancker eight-channel XL-800 data log-ger (precision +0.1¡C) connected to thermistors thatrecorded the temperatures every six hours from July 1,1995 to July 15, 1996 at depths of 2.5, 5.0, 10.0, 20.0, 50.0,100.0 and 120.0 cm from the soil surface. Air tempera-ture was measured at screen height by a thermistorplaced in a Campbell radiation shield. The soil profilewas described and sampled, and the soil was analyzedby the methods described in Sheldrick (1984).

Instrumentation was installed at Plot B (Figure 1) tomonitor the soil temperature regimes of the mound andthe trough. At these microsites, temperatures at the 2.5and 5.0 cm depths were recorded every 70 minutesfrom July 1, 1995 to July 15, 1996 by sensors (5 mmdiameter, 80 mm long) attached to DT3 data loggersmanufactured by Elpro Buchs AG of Switzerland (preci-sion +0.1¡C). These sensors were inserted in the soil soas to cause no noticeable disturbance. The topsoil atsimilar, adjacent microsites was sampled and analyzedby standard methods: particle-size distribution wasdetermined by the pipette method, bulk density wasmeasured with defined metal cylinders (volume

50 cm3) and carbon was measured using a CARLOERBA NA 1500 elemental analyzer.

Results

Soil properties of plots A and B are given in Table 1.The topsoils of the two plots have similar particle sizedistributions. In addition, the Ah horizon of Plot A andthe Ah horizons of the mound on Plot B have similarcarbon contents, but the carbon content of the Ah1 hori-zon of the trough on Plot B is nearly three times higher.The bulk density of this Ah1 horizon, however, is justone-third that of the corresponding horizon in themound.

The mean, maximum, and minimum air temperaturesat Plot A are shown in Figure 2, and soil temperatureparameters are given in Table 2. In general, the soil tem-peratures track the air temperatures at both plots. Airtemperatures at Plot A and soil temperatures at Plot A(Figure 2) and Plot B (Figure 3) can be divided intothree distinct periods. In the first period, from July 1,1995 to late September 1995, the mean daily air and soiltemperatures were above 0¡C, with a maximum airtemperature of 18.7¡C (July) and a minimum air tem-perature of -5.3¡C. By the end of September, however,the mean daily air temperature and soil temperatures atall measured depths had dropped below 0¡C. The se-cond period, from late September 1995 to late May1996, was characterized by mean air temperaturesbelow 0¡C with the coldest month being December(minimum -38.3¡C). All soil temperatures also remainedbelow 0¡C until late May, when the soil began to warm

The 7th International Permafrost Conference772

Figure 1. Location of the study area and site characteristics of Plot A (near-level terrain) and Plot B (mound and trough) near Pangnirtung Fiord,Baffin Island, N.W.T., Canada.

Table 1. Properties of the soils at Plot A and Plot B[SL = sandy loam; LS = loamy sand.]

rapidly from the surface downward. In the third pe-riod, from late May 1996 to July 15, 1996, the mean airtemperature again rose, reaching 8¡C in June.

The mean annual soil temperatures (MAST) at the 2.5and 5.0 cm depths of the trough on Plot B were appro-ximately 1¡C higher than those for either the mound orPlot A, with the MAST values for Plot A being coolest(Table 2 and Figure 4). Similar differences were found inthe mean winter soil temperatures (MWST), with Plot Abeing approximately 1¡C colder than the mound and3¡C colder than the trough at comparable depths. Thereverse situation was noted in the summer, howe-ver,when the mean summer soil temperatures (MSST) forPlot A were approximately 2¡C warmer than compara-ble temperatures for the mound and 3.5¡ to 4¡C warmerthan those for the trough.

Only small differences were found in the numbers ofdays with thaw (DWT) and days with frost (DWF) atcomparable depths on Plot A and the two microsites onPlot B. An interesting result, however, is that, while PlotA and the trough had a greater number of DWT and asmaller number of DWF at 2.5 cm than 5.0 cm, thereverse was found for the mound. The thaw degreedays (TDD) and freezing degree days (FDD) values forPlot A, however, were much greater at both depths thancomparable values for Plot B, while values for themound were greater at both depths than values for thetrough.

Gerald Mueller, et al. 773

Figure 2. Mean daily, maximum and minimum air temperatures and mean daily soil temperatures for all depths at Plot A (July 1995 to July 1996).

Figure 3. Mean daily soil temperatures at the 2.5 and 5.0 cm depths for themound and trough (July 1995 to July 1996).

Discussion

Soil temperatures measured at Plot A showed depth-dependent seasonal fluctuations. Such soil temperaturefluctuations were greatest near the surface, anddecreased with depth. Between June and August, whenincident solar radiation is at or near its annual maxi-mum, mean soil temperatures at the 2.5 to 50 cm depthswere above 0¡C. When the soil was described in July1995, before installation of the instrumentation, the frosttable was found to occur at the 90 cm depth. At least inpart as a result of the disturbance caused by the instal-lation, mean soil temperatures at the 100 and 120 cm depths were also above 0¡C in July and August, 1995.

Air temperatures dropped very rapidly in theautumn, as the duration of daylight and the sun angleboth decreased. As a result, the high, steep-sided moun-tains forming the valley wall provided additional shadeat the study site. The minimum air temperature for thestudy period occurred on December 30, 1995, while soiltemperatures at the 2.5 to 20 cm depths reached theirminimum about 14 days later. This time lag in soil tem-perature is similar to that of soil temperatures mea-

sured in Alaska by Ping (1987) and Hinzman et al.(1991).

The microsites on Plot B likewise showed depth-dependent seasonal variations in soil temperature, butan additional factor, the microtopography, also con-tributed to the variation. The mound, because of its ele-vated position, exhibited more frequent fluctuationswith greater daily and annual amplitudes in soil tem-perature than did the trough, with fluctuations beinggreatest nearer the soil surface.

The mound is characterized by a thin, lichen-dominat-ed vegetation cover, which has a lower albedo than themoss-dominated trough and, therefore, warms morerapidly (Miller, 1982; Rouse, 1984). In addition,although both microsites are characterized by sandysoils, the topsoil on the mound has lower organic mat-ter content than that of the trough, and it is also drier,especially in the summer (Farouki, 1986). This results inhigher summer soil temperatures. On the other hand,the thicker, moss-dominated vegetation cover of thetrough and the higher organic matter content of its top-soil insulate the mineral soil (Tarnocai, 1984; Farouki,1986), leading to lower summer soil temperatures. Inautumn, however, soil temperatures on the mounddrop quickly because this microsite is exposed tostrong, cold winds. Snow cover is thin or nonexistenton the mound in both autumn and winter, and so pro-vides little insulation, but snow cover can be expectedon the trough in autumn. The snow cover in thesedepressions has low conductivity and, therefore, pro-tects the soil against rapid cooling (MacKay andMacKay, 1974; Miller, 1982; Baker et al., 1991). Thereverse occurs in late spring when low soil tempera-tures in the trough result from near-saturation of thetopsoil with snow meltwater, which delays warming ofthe soil.

The 7th International Permafrost Conference774

Table 2. Temperature parameters for all soil depths (Plots A and B) at the study site. [MAST = mean annual soil temperature;MSST = mean summer soil temperature; MWST = mean winter soil temperature; TDD = thaw degree days;

FDD = freezing degree days; DWT = days with thaw; DWF = days with frost]

Figure 4. Deviation of the soil temperatures of the mound and troughmicrosites from the soil temperature at Plot A (zero line = values at Plot A)at two depths. [MAST = mean annual soil temperature; MSST = mean sum-mer soil temperature; MWST = mean winter soil temperature]

Conclusions

The effect of microtopographic contrasts on soil tem-perature is obvious on a southwest-facing slope onBaffin Island, Canada. The two microsites, a smallmound and the adjacent trough, showed different fluc-tuations in soil temperature. Generally, the moundshowed greater daily amplitudes and higher mean soiltemperatures in the summer and lower mean soil tem-peratures in the winter. The existence of these largetemperature differences in close geographic proximityarises largely from the effect of microtopography on theinteraction between vegetation and soil properties.

Acknowledgments

This study was supported by the German ScienceFoundation and by Parks Canada, which also providedtechnical assistance and organization, for which we aregrateful.

Gerald Mueller, et al. 775

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