Global Land Use Agriculture and Urbanization

One of the main spatial factors of anthropogenic impact on the biosphere is the rapid growth of agricultural lands, with accompanying change in their land use. Human activity to produce food leads to the reduction of areas of habitat for natural organisms and to a sharp increase in the area of marginal ecosystems. Improvement of agricultural technologies and wide application of fertilizers led to a fourfold rise in land productivity and sixfold rise of agricultural yield in the twentieth century. However, this was accomplished by reducing populations of organisms and biodiversity of natural ecosystems (Figure 4). The biomass of agrocenoses never reaches the biomass of forests, while agrocenosis productivity is lower than that of natural ecosystems. Replacement of natural ecosystems by agrocenoses results in an 11.7% loss of the net primary product, while about 27% of NPP is lost in all human-degraded ecosystems.

About 23% of all usable lands in the world are subject to degradation, which leads to a reduction in its productivity. Agricultural technologies also lead to the destruction of a mid-term reservoir of biogenes, that is, soils. Significant amounts of soil are washed away. As a result of desertification, about 3% of NPP is lost, but soil organisms essentially suffer since they perish due to soil erosion and compression by agricultural implements, plowing, and application of fertilizers. For example, administration of nitrogen in the ground amounting to 3 g m~2 a year, with an unchanging amount of other fertilizers, would reduce the population of species by 20-50% (Figure 5).

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Figure 4 Loss of large animal species in Africa (a), North America (b), Australia (c), Madagascar and New Zeeland (d) (The World Environment, 1992).

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Figure 4 Loss of large animal species in Africa (a), North America (b), Australia (c), Madagascar and New Zeeland (d) (The World Environment, 1992).

no3-n

Table 3 Human-disturbed terrestrial ecosystems (not including glaciers and bare lands)

1920

1940 1960 Year

1980

2000

Figure 5 Change in concentration of nitrogen compounds in estuary of the Mississippi River since the beginning of the twentieth century. From Vitousek PM (1994) Beyond global warming: Ecology and global change. Ecology 75(7): 1861-1876.

Cities exert a spatially concentrated impact on the environment. While the world population has grown, since 1976, by 1.7% a year on average, population of cities increased by 4% annually. Accelerated urban growth leads to pollution of water, soil, and the air, making their inhabitants live in an unfavorable ecological and social environment. In addition, urbanization is accompanied by a sharp decrease in resistance of urban area territories to technogenic and technonatural hazards. This raises risks of urban dwellers and requires huge efforts of municipal authorities to maintain viability of urban infrastructure.

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