A review on anthropogenic soils from a worldwide perspective

This review focuses on what are referred to as "anthropogenic soils" (AS). It investigates and clarifies their descriptions, definitions, and classifications in terms of the following: (i) historical temporal trends in AS research worldwide, (ii) geographic distribution at various scales, (iii) dominant research themes, (iv) main site features, and (v) dominant anthropogenic processes. To assess the current status of AS research from an international perspective, an inventory of published studies on AS and related grey literature was prepared and compiled in an annotated bibliography, supported by an electronic database and coupled with a geographic information system. From an initial raw collection of over 3000 issues, 925 references published in the last 70 years (1945-2014) were considered a "representative population" of research focused on AS proper. Analysis of this source of information reveals that AS research is becoming increasingly consolidated. Indeed, it now represents an innovative field among soil sciences, expanding its conceptual scope and scientific production. AS research is spread over 64 different countries, mainly in Europe and North America. The USA is the most investigated country, with AS studies becoming extremely popular from 1965 to 1974 and increasing considerably thereafter. In all other countries, AS investigations only became very popular in the decade 1995-2004. On a worldwide scale, the most investigated urban areas (UA) are Berlin, Moscow, and New York City, while several important metropolises have been partially or entirely neglected. Interestingly, the review shows that although humans are able to significantly alter, transform, manipulate, and damage soil, with an incredible number of negative effects, the transformation of "natural" soils into AS may also have unexpected benefits. It is hypothesized that AS research will become increasingly popular within the international scientific community over the next decades, with particular reference to those characterizing UA (such as Technosols). Finally, it is scientifically recognized worldwide how much AS can deviate from natural soils (in terms of physicochemical features, pedogenic processes, matter and energy fluxes). Therefore, we suggest definitively highlighting such differences, defining those parts of the pedosphere characterized by AS cover as the "anthropedosphere".