Concentrations of RareEarth Elements in Soils of the PriokskoTerrasnyi State Biospheric Reserve

The concentrations of rareearth elements were studied in the profiles of soddy podburs and mucky-humus gley soils. The soil horizons differed significantly in the contents of Corg (0-26%), the phys� ical clay (<0.01 mm) fraction (3-31%), the acidity (pH 4 to 5.5), and the presence/absence of Al-Fehumus accumulations. The most significant relationship was observed between the concentrations of rareearth ele� ments and the physical clay content, particularly for Nd: x(Nd, mg/kg) = 7 + 1.6y (fraction <0.01 mm, %). Weak biogenic accumulations in the upper horizons were observed for Nd, Ce, and Dy; Nd, Pr, and La accu� mulated in the Al-Fehumus illuvial horizon. The concentrations of rareearth elements in the studied soils formed the following sequence (mg/kg): Nd (20-101)—Ce (10-44)—La, Sm, Gd, Dy, Yb (3-20)—Pr (1- 4)—Ho (0.1-0.4)—Tm, Lu, and Tl (0.0). A clear trend was observed to higher contents of evennumbered elements as compared with oddnumbered elements, excluding La.