The spatial distribution of fractions and the total content of 24 chemical elements in soil catenas within a small gully's catchment area in the Trans Urals, Russia

Abstract

Background data for a generalized model of the distribution of 24 chemical elements (Al, As, Ba, Ca, Co, Cr, Cu, Fe, P, K, Mg, Mn, Na, Ni, Pb, Rb, S, Si, Sr, Th, Ti, U, V and Zn) in soil catenas within the forest-steppe zone were obtained as a result of analysing total concentrations and mobile fractions of these elements in Chernozem-Planosol catenas (soil sequences down the slopes) within the catchment area (480 000 m2) of a U-shaped gully in Kurgan Region, Trans Urals, Russia. The data obtained on total organic carbon, particle-size distribution and pH in 51 samples from the soils studied allowed the identification of factors that controlled the vertical and spatial distribution of the chemical elements. Factors affecting chemical element migration were similar in Chernozems on interfluves and slopes, which together significantly differed from Planosols at the bottom of the gully. The chemical elements were ordered according to their mobility levels within Chernozems and Planosols as follows: Ca, Mn and Co > Ni and Pb > Ba, Cu, Na, Sr and Zn > Mg and V > Fe and Al > Cr, K and Rb > Si and Ti. Mobile Ca, Sr and to lesser degrees Ba and Mg were found mostly in the F1 fraction (weakly bound by acid-soluble carbonate compounds), while other chemical elements were more strongly held by the soils, particularly, mobile Mn, Pb, Co, Ni, Cu and Ca which were concentrated within the F2 fraction (bound by humic substances) and mobile Fe, Cr, Mg and Ba which occurred mostly within the F3 fraction (bound by Fe and Mn hydroxides). On the basis of the observed contents and migration factors of the 24 chemical elements, the studied Chernozem-Planosol sequence was defined as a ‘low-contrast translocation catena’.