Mobile Forms of Chemical Elements in Soils Formed on the Weathering Products of Igneous Rocks (by the Example of Valaam Island)

Abstract— The type of soil-forming rocks is one of the main factors controlling the geochemical specifics of soil. The behavior of chemical elements in the profiles of two soils, i.e., organo-rzhavozems and rzhavozems (Leptosols), formed on two of the most typical rocks of the Valaam sill (gabbro-diabases and monzonites) has been studied. A water-soluble (colloidal-salt) soil component with a particle size of less than 1000 nm has been extracted from the soil horizons. The samples of soil and its water-soluble (colloidal-salt) component have been analyzed by mass spectrometry with inductively coupled plasma. The comparison of chemical parameters of the water-soluble component and the data of bulk soil analysis permits estimating the ratio of mobile and low mobile forms of chemical elements. The share of water-soluble component in all horizons of the soil profile developed on monzonite is higher than that on gabbro-diabase. Associations of mobile forms of chemical elements have been identified, and the range of chemical elements has been estimated in the soil as a whole and its water-soluble component. Trace elements, especially Sr, Pb, and Ba, are most actively transferred to water-soluble (colloidal-salt) soil component, whereas petrogenic oxides (SiO2, TiO2, Fe2O3, FeO, CaO, MgO, K2O, Na2O, P2O5) are least mobilized to the water extract.