- مبلغ: ۸۶,۰۰۰ تومان
- مبلغ: ۹۱,۰۰۰ تومان
Systematic mapping of the chemical environment of urban areas from around the world has demonstrated the strong impact of urbanisation on topsoil geochemical distributions originally controlled by the underlying parent material (PM). The variance of some elements including As, Ba, Ca, Cr, Cu, Mo, P, Pb, Sb, Se, Sn and Zn in urban domains appears to be impacted by a mixture of geogenic and anthropogenic controls. This study evaluates how soil chemistry has been influenced by different eras of urbanisation within London and other UK urban areas using (a) the pre-1940 Dudley Stamp First Land Utilisation Survey data and (b) the modern urban domain principally defined by the aggregate classes of the 2007 Land Cover Map. In the London area, calcium, and possibly a substantial proportion of Cu, Pb, Sn and Zn enrichment observed in soils impacted by pre-1940 urbanisation relative to soils impacted only by post-1940 urbanisation, may be partly related to the destruction of buildings during the period 1940–1941 rather than from the disposal or aerial dispersion of coal ash from domestic fires. Some Pb, Cu, Sb, Sb, Sn and Zn contamination appears to be caused by road traffic (leaded petrol and brake dust). The relationships between pre- and post-1940 urbanised areas in London also characterise most of 20 other urban centres in England and Wales for which BGS holds soil chemistry data.
Surface soil samples from currently built-up areas within the London GLA that were also built up in the pre-1940 have Ca, Cu, Ge, P, Pb, Sb, Sn and Zn median concentrations that are 1.2–1.75 times higher than in areas that have been built up (urbanised) since 1940. Ca, Cu, Pb, Sb, Sn and Zn are 2.2–3.2 times higher in areas built-up pre-1940 compared with areas that have never been built up in the GLA, and 2.1 to 5.2 times higher than in areas not built up outside the GLA but within the London Region. In all cases, Pb exhibits the highest enrichment ratios followed by Sn and Sb.
Enrichment (contamination) ratios suggest that an event or process that impacted the pre-1940 urban domain has caused soils to be enriched in Ca and to a lesser extent P, as well as some metals and metalloids. One possibility is that widespread destruction of buildings across large sectors of the London urban domain, especially during the period 1940–41, when more than 1 million houses were destroyed or severely damaged by strategic bombing, may have resulted in Cabearing cement and lime dust being incorporated into top soils. Similarly elevated Pb in the pre-1940 urban areas may be partly derived from leaded paint and lead pipes. Construction of new buildings using cement and concrete will also result in enhancement of Ca in the soil. The bomb density is spatially and statistically correlated with the soil Pb and Ca, but the correlation is not very strong. However, a progressive increase in Ca with proximity to bomb sites in the pre-1940 domain suggests that contamination related to destruction of buildings may be a significant factor, especially as Ca does not increase with proximity to bomb sites in the post-1940 domain. The variation of Ca, Pb and Zn medians in relation to distance from bomb sites is remarkably similar to the variation of the centred log-ratio (clr) medians for these elements.