Urban biogeochemical provinces

One of the most usable approaches to distinguishing urban areas from other populated ones is the formal approach of population number. This approach is in wide usage in many countries, for example, in Denmark, where the area with a compact population of more than 250 people is considered as a town. However the functional approach, taking into account the labor types of the local population is also applied. For instance, in Russia the urban status requires that 75% of the local population should be employed in non-agricultural labor activity and the number of people should not be less than 12 thousand. 

Nevertheless, a common approach is absent in spite of UN recommendations to consider as a city any area with compact population more than 20 thousand. Sometimes city status has historical roots and this is often found in Europe. For example, Vereya city was a large and important place during the historical development of Russia, however at present its role has been lost and its population has decreased up to a few thousand but still maintains city status. 

Urbanization is the most important global process. At present the World s urban population is about 3 billion or very close to 50% of all global inhabitants. During 

The main reasons for urban population growth are related (a) local migrations from rural areas as well as from other countries, and (b) urban population growth due to higher birth rates in comparison to mortality (Golubev, 1999). 

Both retrospective and prospective planning are also impressive (Table 1). 

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These peculiarities of urban area development led to the technogenic biogeochemical provinces, i.e., the areas with local increase of pollutants in different components of urban ecosystems such as soils, grounds, surface and ground waters, plants, atmosphere. These pollutants create ecological risk to human and ecosystem health by their accumulation in the biogeochemical food webs (food stuffs and water). 

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