Extensive areas within the permafrost zone

Engineering work can cause disturbance of the geological-geographical environment over large areas and regions and even on the Earth as a whole. The formulation and control of many problems of geocryologi-cal investigations associated with regional environmental disturbance is very topical in the context of harmonious exploitation and problems of environmental management in recent years. The effect on the geocryological environment of such projects as creation of water reservoirs in rivers in the permafrost zone, of urban agglomerations and the intensive development of large areas within oil and gas fields can exceed the possible changes of the geocryological conditions due to the natural changes of climate and evolution of the environment.

Thus air temperature in large northern cities (such as Norilsk, Anadyr, Magadan and others) is 2-3 °C higher in summer and 4-5 °C higher in winter compared to that in the adjacent region. This is associated with direct heat release, albedo changes connected with dust, asphalt, abundance of concrete etc. Under further enlargement of cities, for example, up to the sizes of some Japanese and American centres, their heat loads are correlated with disturbances at the atmospheric scale according to some data. The mean global temperature will not change but the redistribution of heat energy over large areas due to the disturbance of global atmospheric circulation can lead to a change in the geocryological environment.

Atmospheric pollution over the country adjacent to large cities has a great effect on the vegetation cover, which is one of the leading temperature-forming factors. Thus there are data showing that atmospheric emissions of sulphur, nitrogen, sulphur dioxide, nickel and other metals typical, for example, at Norilsk cause formation of concentric belts with different degrees of disturbance of the ecosystem. The zone of complete destruction or significant disturbance of moss-lichen cover and degradation of the tree-shrub community can be 4-10 km in width and up to 1000 km2 in area. The initial stage of vegetation cover disturbance is noted over areas of 40-60 thousand km2. The destruction and change of species composition of vegetation are followed by a change in conditions of snow retention, infiltration and runoff, soil and ground chemical composition over large areas. These inevitably cause changes of mean annual temperature of the ground, of the soil properties and the depth of seasonal thawing and of the cryogenic processes.

Oil and gas production in Western Siberia is also accompanied by important changes of the natural environment. Lowering of reservoir pressure causes ground consolidation and progressive settlement of the ground surface. In one of the fields of the Shainskaya group this settlement has reached 56 cm, while under Western Siberian conditions, ground surface settlement of even 0.5 m causes significant paludification. Consequently it may be suggested that if during the next 10-12 years the reservoir pressure continues to fall the subsidence will reach 1.5 m and the land will be swamped completely. To the south of Sibirskiye Yvaly where the permafrost is associated with peat lands situated 0.7-1 m above the surface of the swamps, the settlement of the ground will lead to complete thawing of the permafrost.

In the early 1980s a project to divert some part of the northern rivers' runoff to southern parts of the country was under discussion. Realization of that project could cause fundamental changes in the geocryological situation over large areas of Western Siberia. One of the variants of that project considered, for instance, taking a water volume of 4-5 km3 from the intake of the lakes of Karelia and diverting it through the Mariynskaya Canal system into the Volga basin. This could cause the water level of the lakes to fall by 2.8-3 m and artificial drainage of more than 60 thousand km2 of ground which are currently swamp. The geocryological consequences of this would be an increase in depth of seasonal freezing and formation of short-term permafrost. Furthermore calculations show that evaporation values could decrease by 0.4km3 year"1 in connection with the reduction of surface of lakes and swamps. As a result mean air temperature as well as ground temperature would rise by 1.6-1.8 °C; climatic continentality would increase. In the southern regions, on the other hand, evaporation would increase through water discharge. This could cause summer air temperature lowering by 2-2.5°C, i.e. the climate would be less continental.

Analysis of this effect of the planned project shows that in the West-Siberian region decrease of runoff in the Ob' river will cause a change of the amount of heat carried by the Ob' river into Obskaya Guba [Ob' bay]. This situation should have an important impact on ice regime of the Ob' estuary and lead to lower summer air temperatures on the adjacent land. Besides, shallowing of the Ob' river and the beds of its tributaries and lowering of the Ob' bay water level will lead to new permafrost in shallow areas and on exposed sand bars. Changes of ice regime and permafrost formation in the Ob' river and estuary bottom will greatly complicate navigation which is of very short duration now and very intricate because of the small depths and numerous shallows.

In the southern regions of Western Siberia where the vast flood plains of the river Ob' and its tributaries are unfrozen, a decrease of the duration of the flooding period will lead to their perennial freezing and the gradual replacement of meadow vegetation, which is widespread here, by mossy swamps. In the zone situated along the Ob' river and its tributaries, the depth of seasonal thawing will increase as a result of drainage and consequently the thermoerosion processes and thermokarst processes will become more active where there is ice-rich ground and wedge ice.

The proposed diversion of some part of the Ob' river runoff to the south included the creation of reservoirs, which can fundamentally change the microclimate and cause thawing of frozen ground over large areas in the vicinity of the southern limit of the permafrost regions.

The examples cited above show that one of the main problems of regional economic planning is to forecast the change of geocryological conditions over large areas. Such forecasts should be based on a comprehensive study of possible regional change of climatic and natural-ecological conditions and is a very complex integrated problem.

Was this article helpful?

0 0

Post a comment