Urban ecosystems are to a certain extent isolated from various other geochemical landscapes. Although occupying relatively small territory (less than 6 % of the Earth’s land surface), urban areas give a shelter for the prevailing part of the humanity. In this regard, environmental assessment of cities, as well as studies of favourable developmental conditions of urban fauna are of paramount importance.

Several primary reasons caused the current ecological problems. First, the natural (wild) fauna of suburbs is gradually included into the growing urban areas that develop the adjoining territories (Burden, 2006; González-García et al., 2009). Secondly, the areas surrounding the city have become widely used by urban residents and biogenic landscapes – steppes, forests etc. – have begun to transform into technogenic areas, mainly agricultural, road and industrial ones. This has caused significant migration of fauna from suburbs to settlements (Garden et al., 2006; Luniak, 2004). This process primarily involves birds and rodents. Third, the number of wild (e.g., squirrels) and domestic animals has increased (Rhodes et al., 2011).

All the appearing fauna has moved to the cities carrying diseases, and got to unusual conditions, which is most important and in most cases has a negative impact. As a result, many illnesses of terrestrial animals and birds have become dangerous to humans.

In accordance with the Law of chemical element behaviour in the biosphere (formulated by V. A. Alekseenko in 1992, 2006, 2017), the content, distribution and even occurrence forms of chemical elements are particularly transformed in residential landscapes as compared with natural ones. For instance, the role of technogenic migration and accumulation, superimposed on natural processes, has significantly increased. Moreover, in the vast majority of cases, the consequences of technogenesis are paramount.

Under the influence of numerous anthropogenic factors, such as electromagnetic, thermal, sound (noise), radioactive, light 16 pollution, the composition of living matter can undergo certain changes. In accordance with the Law of connection between changes within a single landscape (formulated by V. A. Alekseenko in 1992), these changes affect over time the geochemical characteristics of the urban atmosphere, groundwater and ultimately the fauna life quality.

As the chemical elements are transported to residential landscapes both as a result of normal regional natural processes and as a result of technogenesis, geochemical anomalies are often formed in various city zones as compared with the surrounding natural areas. Considering the occurrence conditions of such anomalies, they should be classified as natural-technogenic and polygenic.

Their particular feature is a partial overlay of anomalies made up by various chemical elements. Thus, these anomalies can be considered as multi-component, different from natural analogues. First, urban anomaly (or rather, group of anomalies) presents the pollutants in different forms. Secondly, the pollutants are usually presented by numerous chemical elements (compounds) that do not have common crystal-chemical properties. The extreme irregularity of pollutant abundances should be noticed as a particularity of urban anomalies.

Discussion

Let us first consider several properties of the atmochemical anomalies in the near-ground air of residential landscapes:

1. The composition of atmospheric gases in urban areas is significantly different from that of natural (biogenic) landscapes. In fact, in cities, we are dealing with a large technogenic atmochemical anomaly, made up of various pollutants and which is, from this point of view, polygenic. For example,
an atmochemical anomaly over a megacity, with a population of over a million, various industries and vehicles produce approximately 1,500 tons of hydrocarbons, over 600 tons of nitrogen oxide, 5,000 tons of carbon monoxide, 500 tons of sulphur oxides etc. daily. About 90 tons of various aerosols are
also emitted into the air.

2. This anomaly over large settlements is absolutely inhomogeneous and is divided into smaller ones, differing in composition and contents of gases. Over 30% of aerosols come from vehicles, and nitrogen oxides are derived from fuel combustion. Accordingly, a spatial relationship exists between anomalies and pollutants.

3. Location of certain atmochemical anomalies in cities is not strictly fixed in different districts. These anomalies are mobile, depending on pollutant content, and can even completely disappear with changing weather conditions and hours of enterprise and transport operation.

The urban waters are characterised by the following features:

1. The content of components allows consideration of urban water bodies as major technogenic hydrochemical anomalies;

2. In such aqueous anomalies, the distribution of contaminants, as well as oxidation-reduction and acid-alkaline characteristics are patchy;

3. The contents of priority pollutants are determined by nearby industries and vary depending on seasons and even years. For example, in the centre of a megacity the Ca contents in the groundwater is often 10–20 times higher than the contents in the suburbs, and the element content in summer is 1.5 times higher than in winter.

Vegetation of urban areas is different from a plant cover of landscapes surrounding settlements:

1. Urban plants represent a geobotanical anomaly compared to a vegetation cover of suburbs. It differs in species composition of plants; the rate of branch growth, chlorosis, necrosis, stag-headedness, die-away of small tree branches; drying and withering.

2. The contents of numerous chemical elements in urban vegetation differ significantly from their contents outside the settlements. This allows consideration of a city as a large multicomponent biogeochemical anomaly.

3. Development of biogeochemical and geobo- 17 tanical changes in the vegetation of urban areas is mosaic.

4. The specificity of occurrence of urban biogeochemical and geobotanical anomalies, in conjunction with leaf-litter removal, results in the unique biological cycle of chemical elements, typical only for residential landscapes. This, in turn, makes specific conditions of migration and accumulation of
chemical elements in the urban soils (Tume et al., 2018).

In accordance with the Law of development of ecological-geochemical changes within a single landscape, atmochemical, hydrochemical, biogeochemical anomalies within a single urban area, make up a city-wide lithochemical (soil) anomaly. In partnership with academician N.P. Laverov a special research methodology was designed, analysis methods (often for reliability, duplicating one another) were chosen and the leading laboratories were determined.

All these issues were considered in detail in peer-reviewed monographs and articles (Alekseenko, Alekseenko, 2013, 2014a, 2014b). We only note that the geochemical characteristics of soils of over 300 cities in Europe, Asia, Africa, Australia and America were studied; a number uniformly selected samples in several settlements reached several thousands, but mainly ranged from 30 to 100.

All the work on establishing abundances of the chemical elements in urban soils took some 20 years. The obtained data were compared with abundances in the Earth’s soils (Table 1), characterising the geochemical patterns of the soils of the late XX – early XXI centuries. It is clear that over time abundances of certain elements will change, especially being influenced by changing technologies implemented by urban enterprises.

Biogenic migration and the presence of living organisms largely determine the characteristics of the ecological-geochemical state of the environment and are the leading features of the classification of geochemical landscapes, including urban ones. People make up the significant zoomass in cities. They determine the leading technogenic migration; constitute an important part of the biological cycle; take part in the direct extermination and the emergence of new types of urban fauna.

With this circumstances, residential landscapes were divided into groups depending on the number of inhabitants (Alekseenko, Alekseenko, 2013, 2014b). Average contents of the chemical elements in the soils of such groups are given in Table 2.

Conclusions 

Even a cursory analysis of the information obtained allows to draw the following general conclusions:

1. Urban soils inherited the extreme unevenness of distribution of chemical elements and the connection of their contents with atomic mass from the natural Earth’s soils, which led to the predominance of light and even-numbered elements.

2. Contemporary soil geochemical patterns are primarily formed under the technogenic impact. The concentrations of B, Ba, Ca, Cl, Hg, Li, P, Pb, Sr and Zn are elevated due to this impact. These chemical elements have a paramount influence on all living organisms in cities, including the wild and domestic fauna.

3. Such elements which concentrations exceed the levels of the Earth’s soils Ag (5.3 times), As (9.4), Bi, Mo (2.2), Sn (2.7), W and Yb (1.5) may affect the life quality of urban organisms.

4. In the soils of certain settlement groups, divided by the number of residents, average contents of chemical elements differ significantly. Megacities with over a million of inhabitants, the highest number of elements with high average concentration was found (Pb, Zn, Ag, As, Cu, Mn, Co, Ni,
Ti and Sn). The smallest number of chemical elements with the heightened average content is typical for soils of small towns, villages, hamlets and farms. This must be taken into account when considering the existence comfort of organisms.

5. The established abundances of the elements in urban soils are their geochemical (ecological
and geochemical) characteristic, which reflects the simultaneous combined impact of technogenic and natural processes. With the development of science and technology, the abundances may gradually change. The rate of such changes is merely predictable.

References
Alekseenko V., Alekseenko A. (2014a) The abundances of chemical elements in urban soils. Journal of Geochemical Exploration, 147 (B): 245–249.
Alekseenko V.A., Alekseenko A.V. (2013) Chemical elements in geochemical systems. The abundances in urban soils. Publ. House of South. Fed. Univ., Rostov-on-Don. 388 pp.
Alekseenko V.A., Alekseenko A.V. (2014b) Chemical elements in urban soils. Logos, Moscow. 312 pp.
Burden D. (2006). 22 benefits of urban street trees. Retrieved from http://www.walkable.org/download/22_benefits.pdf
Garden J., McAlpine C., Peterson A., Jones D., Possingham H. (2006) Review of the ecology of Australian urban fauna: A focus on spatially-explicit processes. Austral Ecology, 31, 126-148.
González-García A., Belliure J., Gómez-Sal A., Dávila P. (2009). The role of urban greenspaces in fauna conservation: The case of the iguana Ctenosaura similis in the ‘patios’ of León city, Nicaragua. Biodiversity Conservation, 18, 1909–1920.
Luniak M. (2004) Synurbization – adaptation of animal wildlife to urban development. Proceedings4th International Urban Wildlife Symposium, 50–55.
Rhodes J.R., Ng C.F., de Villiers D.L., Preece H.J., McAlpine C.A., Possingham H.P. (2011). Using integrated population modelling to quantify the implications of multiple threatening processes for a rapidly declining population. Biological Conservation, 144, 1081–1088.
Tume P., Gonzalez E., King R.W., Monsalve. V, Roca N., Bech J. (2018) Spatial distribution of potentially harmful elements in urban soils, city of Talcahuano, Chile. Journal of Geochemical Exploration, 184, B, 333–344.

Article published at the Catalan Academy of Veterinary Sciences‘s annual magazine, 2018 edition.