Geogenic signatures detectable in topsoils of urban and rural domains in the London region, UK, using parent material classified data

Systematic mapping of the chemical environment of urban areas from around the world have shown varying degrees of control of element distributions by the underlying parent material (PM). The purpose of the study reported here is to assess whether geogenic signatures that dominate soil chemistry in rural domains of Eastern England and which are not strongly impacted by human activities, can also be detected in the London urban region. A PM soil chemistry mapping method is used to determine the spatial variation of topsoil chemistry data in London and the surrounding rural areas. Analysis of variance (ANOVA) of the soil data for the London region indicates that 26–33% of the variance of Al, Ce, Cs, Ga, K, La, Mg, Mn, Nb, Nd, Rb, Ti, V and Y is explained by soil PM (surface geology), and a slightly lesser proportion (19–25%) of the variance for Ca, Co, Fe, I, Ni, Sc, Sr and Th. In comparison, soil PM explains only 5% of the variance of Cd. The variance of some other elements appears to be influenced by a mixture of geogenic and anthropogenic controls, including As, Ba, Cr, Cu, Mo, P, Pb, Sb, Se, Sn and Zn for which PM controls 12–16% of the variance. Geogenic soil chemistry patterns observed for the elements strongly influenced by PM in the rural areas surrounding London can be quite clearly followed into and through the London urban area. Spatial patterns of a range of elements primarily controlled by PM have not been destroyed even in a major urban centre with a recorded history dating back over 2000 years and which has been subjected to extensive urban development, destruction and redevelopment especially during the last 200–300 years.