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Geochemical Properties of Plant-Soil-Permafrost Systems on Landslide Slopes, Yamal, Russia

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Geochemical Properties of Plant-Soil-Permafrost Systems on Landslide Slopes, Yamal, Russia Permafrost, Phillips, Springman & Arenson (eds) © 2003 Swets & Zeitlinger, Lisse, ISBN 90 5809 582 7 Geochemical properties of plant-soil-permafrost systems on landslide slopes, Yamal, Russia N.G. Ukraintseva, I.D. Streletskaya, K.A. Ermokhina & S.Yu. Yermakov Lomonosov Moskov State University, Vorobyevy Gory, Moscow, Russia ABSTRACT: Cryogenic landslides on saline marine sediments are widely distributed in a typical tundra subzone of the Yamal Peninsula. Interrelation between the height and productivity of willow tundra, and the activation of cryogenic processes is discussed. It is supposed that high willow canopies are the indicators of ancient landslide activity and may be used for mapping landslide areas. Various procedures are proposed to evaluate the relative age of the landslides. They include study of the vegetation cover succession, of the ash content in each vegetation group, and of the ground water and sediment chemistry on the landslide-affected slopes. It is shown that the landslide process causes the desalinization of the marine sediments and enriches the active layer with salts. This is the important peculiarity of the cryogenic landslides in the region with saline permafrost distribution. 1 INTRODUCTION Superficial cryogenic landslides are widely distributed in a typical tundra subzone of the Yamal Peninsula. They actively change the primary surface of ancient marine plains and terraces. The landslide-affected slopes cover up to 70% of the territory. The cryogenic landslides develop on surfaces consisting of fine- grained marine sediments with a high salinity. The permafrost table serves as a landslide shearing plane, or slide-surface. Outcropping of the frozen salty marine sediments took place due to seasonal sliding of the thawed water-saturated ground over the permafrost table. This process leads to sediment desalinization and enrichment of the active layer with salts. In addition to the mechanical dislocation of the deposits by a landslide, lateral redistribution of elements within the active layer is observed (Dubikov 2002, Lewkowicz – Study site (station “Vaskiny Dachi” ) 1990, Leibman 1995, Romanovskii et al. 1996). – Sites of the observed landslide – Southern boundary of the frozen saline marine deposits (after Dubikov 2002, and Brushkov 1998). 2 STUDY AREA AND METHODS Figure 1. Study area in West Siberia. The research is based on data obtained from the “Vaskiny Dachi” since 1988. This station is located on Phytomass was selected according to the layers: the Yamal Peninsula (from 70°15ЈN, 68°51ЈE to shrubs from a site of 5 ϫ 5 m size, and herb and moss 70°20ЈN, 68°56ЈE) within a typical tundra landscape layers from sites of 0.5 ϫ 0.5 m size. Weight of the (Fig. 1). The monitoring of the landslide includes samples in air-dry state was expressed as g/m2. In the study of the a) vegetation cover succession, b) ash laboratory, semi-quantitative spectral and X-ray–fluo- content of each vegetation group, c) ground water rescent analyses of air-dried and homogenized plants extraction chemistry, d) element composition in soils and soils were carried out with the help of XRF spec- and sediments using water extraction. The field sam- trometers ORTEC-TEFA. The main ions in filtered ples of the vegetation, soil, permafrost, and ground soil water extraction were determined by standard water were obtained at selected points of the cross- chemical methods of soil analysis. Ground water sections traversed landslide-affected slopes (80 samples were collected at selected points to character- points). Detailed leveling of the relief, thawing depth ize water chemical composition. measurement with a dip-stick, and description of the Three large landslide-affected slopes have been vegetation cover were carried out on the cross-section. studied since 1996: I. the “Lake” site, is oriented to 1149 the south, about 1000 m long, and between 22 to 47 m acutiflorum, Ranunculus borealis etc.) with active a.s.l.; II. the “Triangular” site, is oriented to the north, willow restoration, as observed on old shearing planes 350 m long, and between 43 to 53 m a.s.l.; and III. the (B2, see Table 1). The next stage is colonization by the “Cirque” site, is oriented to the north, 700 m long, and high willow/meadow parkland communities (B3). between 23 to 48 m a.s.l. Five or more landslides are On young landslide bodies (C1) low shrubs (willow, noticed on each slope. Some landslides are newly dwarf-birch) are dominating, moss cover degrades, formed and rarely covered with pioneer species. The pioneer vegetation (Calamagrostis sp., Poa alpigena others are covered by light-green meadow vegetation. subsp. alpigena, Equisetum arvense subsp. boreale, The oldest landslides are overgrown with shrub vege- Polemonium acutiflorum, Ranunculus borealis and tation (Salix glauca dominating). These observations cotton-grass) is restoring. On C2 high willow/meadow suggest that cryogenic landslides are cyclic in time in communities with mosses replace them. Dense willow various parts of the landslide-affected slope. As a canopies covering moss/herbaceous communities domi- result of the process, the slopes represent a landslide nate on ancient landslide bodies (C3). system of various ages with a specific set of morpho- The different stages of landslide vegetation provide logical elements: (A) tops of the hills and convex stable the criteria to estimate the relative age of landslides. slopes (not affected by landslides), or a “background”; Thus, background surfaces, not disturbed by landslides (B) concave cirque-shaped depression (shearing (A3), young shearing planes (B1) and young landslide planes), or denudation zone; and (C) hummocky scarp bodies (C1) can be clearly distinguished by the herba- and terraces (landslide bodies), or accumulation zone. ceous community. Old and ancient landslides are simi- The landslides of three generations are studied: (1) lar in vegetation cover, but differ in height and density the young, formed 10 to 30 years ago; (2) the old, of the shrub layer (Table 1). High willow communities formed up to 300 years ago; and (3) the ancient, (Ͼ50 cm) occupy the most ancient landslide slopes. formed 300 to more than 2,000 years ago. According to the structure of their phytomass, land- The age of some landslides is estimated using slide-affected slopes differ distinctly from background radiocarbon dating of buried organic matter (Leibman surfaces. On background surfaces mosses cover 100%, et al. 2000). In other cases, the serial changes of veg- and willow cover less than 10–15% of the area. On the etation or other methods are used as an indicator of landslide-affected slopes the willow quota increases up landslide age (Table 1). to 50–80%, and less than 40–80% is covered by mosses (Ukraintseva et al. 2000). The above-surface phytomass of ancient landslides is higher than that of the back- 3 RESULTS AND DISCUSSION ground – on average about 1400 g/m2 compared to 850 g/m2 of the background (Fig. 2). Thus, high willow 3.1 Change of vegetation on the canopies are the indicators of an ancient landslide activ- landslide-affected slopes ity and may be base of the landslide areas mapping. Willow shrubs are usually considered as the early 3.2 Desalinization of the marine sediments due to stage of serial changes of vegetation, which colonize landsliding bare surfaces formed due to natural or/and anthro- pogenic processes (McKendrick 1987, Jumponen et al. In study area pleistocene marine sediments are preva- 1998, Matsuda et al. 1988 and Andreev 1970). The lent. The amount of water-soluble salts in the changes predominance of high willow canopies (Salix glauca) on landslide-affected slopes is noticed by Rebristaya et al. (1995), Ukraintseva (1997), Ukraintseva et al. (2000). The dominating communities on hilltops and stable slopes (A3) in the study region are the under- shrub/grass/moss and moss/lichen tundra (Table 1). They are the background for a subzone of typical tun- dra. After 10 to 15 years since the landslide event, bare spots alternate with pioneer herbages, such as Puccinellia sibirica, Poa alpigena subsp. alpigena, Deshampsia sp., Phippsia concinna etc. and forbs Tripleurospermum Hookerii on young surfaces (B1, Herbaceous Moss Mortmasse Table 1). The second stage is colonization by meadow Willow Dwarf-birch sedge/grass communities (Calamagrostis sp., Poa alpigena subsp. colpodea, Carex concolor, Nardosmia Figure 2. Above-surface phytomass of vegetation cover at frigida, Equisetum arvense subsp. boreale, Polemonium landslide-affected slopes and “background” surfaces. 1150 Table 1. The vegetation as an indicator of the morphological elements and the relative age of the landslides. Morphological elements of the landslide affected slopes A3 B1 C1 B2 C2 B3 C3 Index of the study site I II III I II III I II III I II I II I III I III Height above see level, m 47.7 52.7 48.8 30.2 49.5 33.8 25.3 49.0 27.6 26.4 47.6 23.7 42.0 38.8 36.6 35.9 23.6 Slope, degree 0 0 1–25–77–87–10 1–25–88–10 7–83–55 3–53–53–55–72–3 Shrub cover, % 20 5 10 0 0 0 70 50 80 10 20 75 70 20 20 80 80 Shrub height, cm 20 15 30 0 0 0 50 50 100 50 30 130 100 115 150 170 170 Salix glauca 1 1 1 3 3 3 2 2 3 3 2 2 3 3 Betula nana 3 1 2 3 Undershrub-herbs cover, % 60 70 35 15 60 20 40 60 55 80 60 60 55 85 85 70 55 Poa arctica 1 1 1 Vaccinium vitis-idaea subsp. minus 2 3 3 Carex arctisibirica 2 3 2 Calamagrostis groenlandica 2 1 1 Rubus chamaemorus 1 1 Puccinellia sibirica 2 3 3 Tripleurospermum Hookerii 1 1 1 Deshampsia sp.
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