| Abstrakt: |
The aim of this work was to show how to construct maps of anthropogenic contamination of agricultural soils in Czech Republic by risk elements. The geochemical datasets for this work originated from state monitoring utilising acid extractions according to past and present national legislative requirements. The goal was to distinguish contamination from natural variability respecting knowledge in environmental geochemistry and available information sources. Conventional approaches to geochemical maps, such as plotting sampling points where element concentrations exceed Tukey or Carling upper fences (boxplot approach), can be used to visualise only extreme contamination, such as historical ore mining and processing. The challenge starts when weak and/or diffuse contamination is of interest and should be distinguished from natural variability. Geogenic anomalies in Czech Republic are represented by mafic volcanic rocks (Cd, Cu, Zn), metamorphic rocks (As, Zn), felsic intrusive volcanic rocks (Pb, Zn), and variegated rocks showing volcanic components (Cd, Pb, Zn). Lithological anomalies are typical for floodplain sediments of lowland rivers. Each cumulation of concentrations above the Tukey or Carling upper fences within the whole-Czech dataset, i.e. potential contamination hotspot, should be examined in detail to judge possible natural controls. Pleistocene and Holocene sediments, in particular aeolian and fluvial deposits with their specific grain size, represent an important controlling factor in such detailed maps. Element concentration ratios in rational subcompositions, e.g. including Co, Cu, Pb, and Zn, were found useful to separate geogenic and lithogenic anomalies, In this subcomposition, Co is promising reference element for datasets obtained by conventional acid extractions as a surrogate for missing analyses of lithogenic elements. There is no automated way of distinguishing anthropogenic contamination from natural variability for weak contamination, expert opinion is indispensable to distinguish natural and anthropogenic factors. The larger (more heterogeneous) the mapped areas, the more complicated interpretation of their geochemical maps and less reliable identification of anthropogenic contamination. Zooming in and examination of empirical cumulative distribution of element concentrations for the zoomed areas is the most powerful tool in converting geochemical to contamination maps, assuming the zoomed areas are covered by relatively homogeneous soils, with small number of soil-forming bedrock and not much geomorphic heterogeneity. [ABSTRACT FROM AUTHOR] |
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