Sub-continental-scale geochemical mapping; sampling, quality control and data analysis issues

During 1996/97, c. 1500 samples of agricultural soils from ten northern European countries (western Belarus, Estonia, Finland, northern Germany, Latvia, Lithuania, Norway, Poland, northwestern Russia and Sweden) were collected from the A (sub p) and B/C-horizons at 750 sites. The sample sites were evenly spread over a 1 800 000 km (super 2) area, giving an average sample density of one site per 2500 km (super 2) . The <2 mm fractions (Poland: <1 mm) of all samples were analyzed for up to 62 chemical elements following ammonium acetate, aqua regia and HF extractions, and for total element concentrations by X-ray fluorescence spectrometry. Electrical conductivity, pH (water extraction) and loss on ignition (1030 degrees C) were also determined. Each method was applied to all the samples in one laboratory only. The analytical results were evaluated and mapped using exploratory data analysis techniques. Even at this low sample density, regional-scale geochemical patterns emerge for all elements. These patterns show the influence of factors such as geology, agriculture, pollution, topography, marine aerosols and climate, and their relative importance for the observed element concentrations in the soils. Low-density geochemical mapping of agricultural soils is a viable tool to study the geochemical processes that determine the element distribution in soils at a sub-continental scale.