Geochemical mapping the urban and industrial legacy of Sisak, Croatia, using discriminant function analysis of topsoil chemical data

Modelling of topsoil geochemical data using discriminant function analysis, along with a set of corresponding geochemical maps, portray a legacy of environmental contamination in the city of Sisak. Based on centred log-ratio (clr) transformed compositional data from topsoil samples collected on Kupa-Odra and Sava River floodplain sediments and loess, underlying the Sisak urban area, and regrouped according to their land use characteristics (urban, industrial and agricultural areas), a few element clusters emerged accounting for discrimination between the defined groups. The most prominent feature of the lithological model, as suggested by the first discriminant function, is the carbonate group (Mg, Ca, Sr) versus anthropogenic sourced elements/transition metals (e.g., Sn, Zn, Ba, Mn, Pb, U, Ag, Cr, V) dichotomy separating soil developed on floodplain sediments of Sava and Kupa-Odra Rivers from those evolved on loess. The major attribute of the land use model, according to the main discriminant function, is differentiation between urban/industrial and rural (agricultural) samples based on contrast provided by the carbonate component and other anthropogenic sourced element clusters (predominantly alkaline and concentrated over the loess substrate), in contrast to fertiliser trace and transition element clusters (predominantly acid and disseminated over Kupa-Odra and Sava River floodplain sediments). In both cases, the second discriminant function provides additional information on the secondary level, i.e., in the lithology model the Kupa-Odra sediment group is distinguished from other lithological groupings owing to its predominantly transition element signature. In the land use model, urban soil samples are separated from industrial ones based on the characteristic Na-Sr-Ca-pH(KCl) element association (urban waste) against a typical 'industrial' element signature (Zn-Cd-Mn-Pb-Mo).