Distribution of trace elements in Holocene loess-paleosol sequence and environmental change in the upper reaches of Jinghe River

Based on field survey, samples of Holocene loess-paleosol sequence were systematically collected at the Zhaojiacun (ZJC) site in the upper reaches of Jinghe River. The contents of Ba, Zn, Cu, Pb, Cr, Rb, Sr, Co, Th and Zr were then determined by X-Ray fluorescence and compared with magnetic susceptibility and particle-size distribution. It is noted that most of the trace elements including Ba, Zn, Cu, Rb, Co, Th and Zr accumulate in paleosol layer (S0) and drop in Malan loess layer (L1). The correlation coefficients of element content with magnetic susceptibility and clay (<0.005 mm) content are positive, while they are negative with coarse silt (0.01~0.05 mm) content. But the trace elements of Pb, Cr and Sr are high in Malan loess, low in paleosol. They have a negative correlation with magnetic susceptibility and clay content, but are positively related with coarse silt content. During Holocene megathermal epoch, the contents of trace elements are higher in paleosol than in loess because of strong pedogenesis, adsorption and complexity. Cr is largely stable, only weakly fluctuating in the entire sequence. Sr content is high in Holocene loess (L0) layer and the topsoil (TS) because of warming and drying climate, strong topsoil alkalescence and weak CaCO3 eluviation. High Pb content in the topsoil is mainly due to human activity such as “three-waste” discharge, mining and smelting of metals, coal and petroleum combustion, and automobil exhaust emission.