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

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 5.5 to 8.0°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 15.4°C with the coldest month’s mean of 47.7°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°31N lat- 373 m in altitude to the east. In this area, observation itude, 134°41E 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 5°C to 8°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 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. 2). Fig. 2). The shallow depths of seasonal thaw are attrib- Bog with low-centre polygons. The vegetation con- uted to the high peat content in seasonally thawing sists of grasses (Calamagrostis langsdorfii, Carex acuta, loams and sandy loams. Perennially frozen loams and Eriophorum vaginatum) and mosses. The site is sandy loams are ice-rich. The total moisture content ranges from 20 to 125%. Carex-Calamagrostis wet meadow. The soil is a Peat- Bog Cryogenic Soil. Peat is 0.4 to 0.45 thick and poorly decomposed. Low-centre polygons are present which favour the development of a moss-grass type of bog. Ice wedges occur from depths of 0.35–0.4 m below the polygon troughs and are 0.9 to 1.2 m wide at the top. The thickness of the active layer is 0.45 to 0.65 m (curve 4 on Fig. 2). Discussed further are the ecological state and seasonal thaw patterns in anthropogenic landscapes (Fig. 3). Site 2. Ploughfields created by clearing of the north taiga forest. The active layer varies in thickness from 0.9–1.0 m in the bottoms of thaw settlements (plot 1 on Fig. 3) to 1.15–1.25 m in the flat areas of plough-fields which are not affected by thaw subsidence (plot 2 on Fig. 3). The North-Taiga Soils are gleyed, exhibit thixotropy and have a low hydraulic conductivity. The underlying permafrost is composed of alluvial loam deposits of the first terrace of the Yana River. Charac- teristic features of the permafrost are low temperature (6 to 8°C), high ice content and an abundance of ice wedges. The total ice content, including wedge ice, varies from 40 to 80% by volume depending on grain- size composition. Owing to these properties of the permafrost the active layer of soils is highly sensitive to human impact. Site 3. Ploughfields in the cryoarid steppe areas of the Yana River valley. The depth of soil thawing is 1.5 to 1.7 m on the south-aspect slopes. Sands occur in places in the active layer with 12–15 percent moisture. Mois- ture content of the loamy soils in the active layer is 18–25% (plots 3 and 4 on Fig. 3). Clearing of the forest vegetation and subsequent Figure 2. Soil thaw dynamics in natural meadow land- ploughing result in the following modifications: scapes, the Yana River valley: (a) 1989; (b) 1990; (c) 1991. Site 1: 1 – Carex-Calamagrostis meadow; 2 – Flood meadow 1. A three- to four-fold increase in thaw depth, from 3 – Low-centre polygonal bog; 4 – Carex-Calamagrostis wet 0.3 to 0.9–1.2 m, and thaw penetration up to 0.5 m meadow. of ice-rich permafrost;

481 2. Development of thaw depressions up to 0.5 m in depth and 0.5 to 2 m in diameter. Shallow depressions with depths of 0.1 to 0.3 m dominate in the study area, comprising about 65% of the total number of thaw depressions. The depressions 0.3 to 0.5 m in depth account for about 30–35%. 3. Agricultural land use may lead to additional water input into the root layer from the thawing permafrost and to further increase in thaw depth.

4 CONCLUSION

In the Yana River valley, seasonal thaw depths are great- est in the dry sites (1.0–1.2 m) and shallowest in the waterlogged bogs (0.3–0.5 m). Agricultural activities cause a three- to four-fold increase in thaw depth.

REFERENCES

Elovskaya, L.G., Petrova, E.I. & Teterina, L.V. 1979. Soils of northern Yakutia (Pochvy severnoi Yakutii) (in Russian). Novosibirsk: Nauka. Ivanova, E.N. 1976. Classification of USSR soils (Klassi- fikatsia pochv SSSR) (in Russian). Moscow: Nauka. Izyumenko, S.A. (ed.). 1966–1968. USSR climate reference. Vol. 24 Yakutskaya ASSR. Parts I–IV (Spravochnik po klimatu SSSR. Vyp. 24 Yakutskaya ASSR) (in Russian). Leningrad: Gidrometeoizdat. Mozolevskaya, A.K. (ed.). 1973. Agroclimatic resources of Yakutskaya ASSR (Agroklimaticheskie resursy Yakut- skoi ASSR) (in Russian). Leningrad: Gidrometeoizdat. Murzin, Y.A. 1997. Fluvial reworking of river coasts in Northern Yakutia. In Egorov, I. & Chernyavsky V. (eds) Regional hygiene, sanitation and epidemiolody Figure 3. Soil thaw dynamics in agricultural landscapes, the (Voprosy regionalnoi gigieny, sanitarii i epidemiologii) Yana River valley: (a) 1989; (b) 1990; (c) 1991. Site 2: plot (in Russian). Yakutsk: Izd-vo “Goskomitet Respubliki 1 – ploughfield created by clearing of the north taiga forest Sakha (Yakutia) po sanepidnadzoru”. on the first terrace of the Yana, unaffected by thaw subsi- Nekrasov, I.A. & Devyatkin, V.N. 1974. Morphology of the dence; plot 2 – ploughfield affected by thaw subsidence. cryolithozone in the Yana Basin and adjoining areas Site 3: plot 3 – irrigated ploughfield in the cryoarid steppe; (Morfologia kriolitozony basseina r. Yany i sopredel- plot 4 – non-irrigated ploughfield in the cryoarid steppe. nykh raionov) (in Russian). Novosibirsk: Nauka.

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