Total contents and mobile fractions of chemical elements within a soil toposequence in the south-east of the Valdai Hills, Russia

Soil properties were analysed at the MSU (Lomonosov Moscow State University) Faculty of Geography: - pH value was measured in suspension (static conditions) using a pH-meter "Expert-рН" (Russia); - total organic carbon (TOC) content was determined in 120 samples using titrimetric method with phenylanthranilic acid (Reeuwijk, 2002); - the particle-size distribution was analyzed using laser diffraction technique and an ‘Analizeter 22’ equipment (Germany).

Particle-size classes (Russian system): G1 – clay (<1 μm), G2 – very fine silt (5–1), G3 – medium silt (10–5), G4 – сoarse silt (50–10), G5 –fine sand (250–50), G6 – medium sand (500–250). Total content of chemical elements (ChEs) and mobile fractions was measured at the VIMS (N. M. Fedorovskii All-Russia Institute of Mineral Raw Materials) using an Elan-6100 ICP-MS System and an Optima-4300 DV ICP-AES System. The studied fractions of the ChEs: - F1 (exchangeable) was extracted with NH4Ac (ammonium acetate buffer) - F2 (bound within organo-mineral complexes) was extracted with with 1% EDTA (ethylenediaminetetraacetic acid) - F3 (bound with Fe and Mn hydroxides) was extracted with 1M HNO3 - F4 (residual fraction) - the difference between the total content of elements and the content of mobile forms.