Time transformation of fractionation of rare-earth elements in soils under urban load in the humid subtropics of Russia

Abstract

The peculiarities of the fractionation of rare earth elements (REE) were studied in three genetically similar types of soils in the territory of the humid subtropics of Russia. REE contents were determined by inductively coupled plasma mass spectrometry with full acid decomposition of samples. The following soils were studied: burozems formed on mudstones in the Mzymta river valley; burozems transformed to the state of abrozems formed on similar rocks in Sochi; and brown soils on carbonate rocks in the territory of the Utrish Reserve. Burozems formed in natural conditions on mudstones are characterized by REE fractionation with the predominance of their middle subgroup. In urban soils similar in genesis, an increase in the content of elements of the light subgroup is observed. These changes are due to their transformation as a result of urban load. Over the past 100 years, the soils of the city have undergone significant alkalinization, the index of pH in them increased by 2 units. The relationship between REE fractionation and soil acidity is confirmed by the REE distribution curve for the soils of the Utrish Reserve. The latter are distinguished by an even greater predominance of the light REE subgroup, due to the increased alkalinity of soils caused by the formation of soils on carbonate rocks.