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Physical Geography of Northern Eurasia

Rivers, Lakes, Inland Seas, and Wetlands

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Wetlands

Wetlands (defined in this context as vegetated wetlands) occupy about 2.1 million km2 or 10 per cent of the total territory of Northern Eurasia. The Asiatic part accounts for 1.5 million and the European territory for 0.6 million km2 (Davydov et al., 1973). It is difficult to evaluate how much water is contained in wetlands because such an estimation depends on which ecosystems are included in this category. It is well known that wetlands are very heterogeneous and it is often difficult to distinguish between wetlands and their surrounding areas. The most often quoted figure is 1600 km3 (Babkin, 1987). This includes water stored in bogs and swamps but excludes water stored in peatlands which accounts for a half of the 2.1 million km2 territory. Most of it (1100 km3) occurs in the wetlands of the Asiatic territory. The free water accounts for about 350 km3 of the total (220 km3 in the Asiatic part). The total volume of free water in vegetated wetlands is comparable with the water volume in Lakes Ladoga and Onega.

The most extensive wetlands occur in the tundra and taiga zones (see below). In many regions of the tundra, the proportion of wetlands often exceeds 50 per cent because of the high effective precipitation, permafrost and flat relief. The taiga accommodates about 80 per cent of all peatlands. The thickness of the peat layer here is usually about 4-6 m but locally it may exceed 10 m. Wetlands are particularly widespread in Western Siberia where they cover over 1 million km2. Because wetlands are the basic landscape of the West Siberian lowland, it is often classified as a biome of vegetated wetlands in contrast to the usual division into tundra, forest-tundra, and taiga zones (see below). The level relief with poor drainage and relatively humid summers provides optimal conditions for the development of wetlands which are expanding (Neyshtadt, 1977). Large areas are also occupied by wetlands in the mixed forest zone of the European territory (the areas of Polesye in the Ukraine and Belarus) and in Meshera (just east of Moscow) and in the mixed and deciduous forest zones of the Far East (see below).

The controls, which wetlands exert over the magnitude of annual river runoff, are still subject to discussion. Certain is the fact that following the drainage of wetlands, annual river runoff in the region increases (Novikov and Goncharova, 1978). Further, the dynamics of runoff are determined by the condition of drained lands and if they are occupied by productive ecosystems, runoff can decrease (Shebeko, 1970). Large-scale drainage projects were initiated at the end of the last century but peaked in the 1960s and 1970s. In the European north, 3 per cent of the territory have been subject to drainage works while in Belarus, over 10 per cent and in Baltic countries over 20 per cent of wetlands have been developed. The transformed land supports arable agriculture, hay lands, and pastures (Koronkevich, 1990). Regional economies have largely benefited from the drainage projects although locally, for example in Belarus, such projects have become a source of environmental disturbance.

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