Seasonal Thawing of Soils in the Yana River Valley, Northern Yakutia

Permafrost, Phillips, Springman & Arenson (eds) © 2003 Swets & Zeitlinger, Lisse, ISBN 90 5809 582 7 Seasonal thawing of soils in the Yana River valley, northern Yakutia R.N. Ivanova Melnikov Permafrost Institute, SB RAS, Yakutsk, Russia ABSTRACT: The paper presents the results of investigations on seasonal soil thawing and permafrost conditions in natural meadow landscapes, as well as in areas of agricultural land use. The landscapes of the Yana River valley systems are characterised by continuous permafrost and shallow depths of the active layer. Thaw depths are 0.2–0.4 m below the forest and moss covers. In open sites they range from 0.4 to 1.2 m, depending on soil and meadow type. The mean annual temperature of permafrost is Ϫ5.5 to Ϫ8.0°C. 1 INTRODUCTION Little permafrost research has been conducted in the Yana River valley, north-eastern Russia, owing to the remoteness from research centres and the severe envi- ronment. Data and information on the morphology (distribution, thickness, taliks) and thermal regime of permafrost in the Yana River basin and adjacent areas were first summarised by Nekrasov & Devyatkin (1974). Murzin (1997) studied permafrost conditions in the basin of the Adycha River, a tributary of the Yana. Climatically, the study area is within the Cold Dry Agroclimatic Region (Mozolevskaya 1973). It is not surprising, then, that zones of the cryoarid steppe are present here (Elovskaya et al. 1979). Air temperatures above 0°C occur on 133 days a year. The number of days with temperature above 5°C is 108 and above 10°C is 78. The mean annual precipitation in the region ranges from 170 to 200 mm, of which 83 to 134 mm occur during the summer (Izyumenko 1966–1968). The mean annual air temperature is Ϫ15.4°C with the coldest month’s mean of Ϫ47.7°C and the warmest month’s mean of 15.4°C. Thus the area has a strongly continental climate with severe winters and dry summers. However, the relatively short summers have significant heat gain. Figure 1. Monitoring area. 1 – Weather station; 2 – Moni- 2 MONITORING SITES AND METHODS toring site. 2.1 Monitoring sites Site 1 established to monitor natural landscapes was in the intermontane saddle in the Yansk Upland, 12 km To understand the microclimatic and thermal condi- south-west of Batagai. The mesorelief form is a gently- tions, as well as the ecological state of natural and sloping macrodepression of intermontane-basin type anthropogenic permafrost landscapes in the Yana River with gentle-sloped, flat ridges and wet depressions. area, monitoring observations were conducted by a per- The saddle is at an elevation of 152 m asl and runs from mafrost-climate research group of the Permafrost Insti- north to south for 10 km. It is bordered by mountains tute during the period of 1989 to 1992. The study area 224 m in altitude to the west and a mountain range was located in the vicinity of Batagai, at 67°31ЈN lat- 373 m in altitude to the east. In this area, observation itude, 134°41ЈE longitude, 130 m elevation asl (Fig. 1). plots were established in different types of undisturbed Here the low-water level of the Yana River is 121.1 m. terrain: 1 – hummocky swamp meadow; 2 – cryogenic 479 peat bog with Carex-Calamagrostis vegetation; 3 – Soil moisture contents were determined gravimetri- Carex-Calamagrostis dry meadow; 4 – flood meadow; cally (samples were obtained by hand augering and 5 – water-covered bog with grass vegetation; 6 – swamp oven-dried at 105°C). The gravimetric method is con- meadow with Carex-Eriophorum; 7 – low-centre polyg- sidered to be most accurate in moisture content deter- onal bog; 8 – Carex-Calamagrostis wet meadow. The mination of soil samples and is a reference to check study included measurements of active layer and per- other methods. Sampling frequency for moisture con- mafrost parameters and observations of permafrost- tent determination was once or twice monthly. related features. In addition, microclimate and surface energy balance measurements were made in two of the plots. 3 RESULTS AND DISCUSSION Sites 2 and 3 were established on the first terrace of the Yana River to study agricultural landscapes. Site 2 The severe climate and the presence of permafrost are was situated 7 km north-east of Batagai, at an elevation the dominant factors that determine the state and of 130 m asl. It was a 137 ha tilled field which was appearance of the landscapes in the region. Spatial created by clearing of the north taiga sparse forest in variations in terrain conditions and hence in micro- 1983. After 6–7 years it was abandoned because about climate create a mosaic of soil temperature regimes half of the field was subject to intensive thermokarst. and seasonal thaw depths. Observations were made at two localities: with and The landscapes of the Yana River valley are under- without thaw subsidence. Site 3 was situated 10 km lain by continuous permafrost. The depths of seasonal south-west of Batagai, at an elevation of 135 m asl. This thaw are shallow and range from 0.2 to 0.4 m below the site included two plots established in ploughfields on forest canopy and moss cover and from 0.4 to 1.2 m in the cryoarid steppe. One was an irrigated field and the the open sites, depending on soil and meadow type. The other was a non-irrigated field. ground temperature at this depth ranges from Ϫ5°C to Ϫ8°C (Nekrasov & Devyatkin 1974). 2.2 Methods The depth of seasonal thaw depends on terrain conditions. In the intermontane saddle, for example, the Three methods were used to determine seasonal thaw measured thaw depths were 0.5 to 0.8 m in the wet depths: (1) direct determination, (2) extrapolation, and meadow with a hummocky surface, 1.0 to 1.2 m in the (3) temperature measurement. The first method dry meadow with polygonal microrelief, 0.35 to 0.5 m included probing of the ground with a steel rod, and in the waterlogged bog with grass vegetation, and 0.9 ruler measurements in pits and on cores obtained by to 1.0 m in the Carex-Eriophorum wet meadow where drilling. The extrapolation method used the results of periglacial processes are manifested on the ground routine thaw depth measurements at permanent weather surface by fissured flat-topped, in places hummocky, stations and monitoring sites. With the third method, polygons (Table 1). thaw depths were determined from the position of 0°C. The landscape units which are most widespread in This method provides reliable estimates for medium- the Site 1 area are described below in more detail. textured soils present in the area. For temperature Carex-Calamagrostis meadow. The meadow is measurements in the active layer, thermistor cables degraded by mosses and shrubs. The soil is a shallow of Permafrost Institute design were assembled and Peat Cryogenic Soil (Ivanova 1976). The peat horizon is employed. Temperature measurements were accurate 70 cm deep, very wet, and dark brown. The unit has a to within 0.1°C. Measurements were made once daily typical polygonal microrelief created by an ice-wedge during three summers. Near-surface soil temperatures network. The polygons are rectangular with straight to a depth of 0.2 m were measured by Savinov-type sides and have a size of 15 by 17 m. The meadow sur- thermometers six times daily during three summers. face within the polygons is relatively dry and flat. The Table 1. Depth of seasonal thaw in plots with polygonal microrelief. Depth of seasonal thaw, (m) Below polygon troughs Below polygon Below thaw depressions at Plot centre Dry Water-filled intersection with ice wedge Carex-Calamagrostis meadow 0.50 0.35 0.29 0.40 Flood meadow 0.44 0.36 0.44 – Low-centre polygonal bog 0.55 0.41 0.33 0.35 Carex-Calamagrostis wet meadow 0.48 0.39 0.34 0.35–0.40 480 polygon troughs are 0.2 to 0.4 m deep and 1.1 to 1.3 m annually flooded in the spring and, occasionally in the wide. Ice wedges occur below the troughs from depths summer and autumn. In places, floodwater remains in of 0.4 to 1.5 m. Below 1.5 m is ice-rich silty clay. The the polygon troughs and basins throughout the sum- peat horizon within the polygons is also underlain by mer. The soil is a Peat-Bog Cryogenic Soil. Peat is the ice-rich silty clay. The active layer thickness in this 0.2–0.5, rarely 0.7 m, in thickness, light brown, poorly unit is 0.4 to 0.55 m (curve 1 on Fig. 2). decomposed, and saturated. The permafrost conditions Flood meadow. The vegetation consists of shrubs, are very complicated as evidenced by thermal con- reed grass and sedge. The soil is a Peat-Bog Cryogenic traction cracks and low-centre polygons which meas- Soil with a 40–50 cm thick, poorly decomposed peat ure 17 ϫ 15 m in size and have 0.2 to 0.3 m high rims. horizon. High-centre polygons with a hummocky sur- The polygon troughs are clearly visible on the surface. face are distinct. The polygon troughs are 0.3 to 0.6 m They are 0.15 to 0.4 m deep and 0.3 to 0.5 m wide. The deep and filled with water. The active layer is 0.45 m thickness of the active layer is 0.55 m (curve 3 on thick (curve 2 on Fig.

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