Physical and chemical characteristics of surface sand in different types of dunes in Qingtu Lake, Gansu, NW China, and their environmental implications

The physical and chemical imprints of surface sediments bear key information of the origination, sedimentation, and weathering of sand. Field sampling and laboratory analysis were conducted to investigate the grain size and geochemical characteristics of surface sediment with various types of sand in the Qingtu Lake, Gansu, NW China. Results show that the surface sediment is dominated by fine sand, taking an average content of 72.08%, followed by very fine sand and a minimal amount of clay. The frequency distribution curve exhibits a unimodal distribution, while the cumulative probability curve shows a three-portion pattern, indicating a relatively stable sediment environment. The predominant constant elements are mainly SiO₂, occupying 76.40% in average and then Al₂O₃ and CaO, for 5.05% and 3.74%, respectively. The trace elements consist mainly of Cr, Mn, Co, Sr, Ba, Ti, Ce, and P, in average concentration of over 100 mg/L. The two-variable chart (Y verse Zr, Y/Zr verse Rb/Zr) and the A-CNK-FM graph demonstrate that the Badain Jaran Desert and Tengger Desert were key sand sources for the study area. The abrasion and wind erosion in sand transportation are the main factors affecting the distribution of Fe and Mg elements. In addition, lacustrine and alluvial deposits of the Shiyang River also provided a part of the sand source. The ternary diagrams A-CN-K and A-CNK-FM indicate that the study area experienced weaker wind levels during the early phases of de-Na and de-Ca processes. However, in the progress of sand fixation, pedogenesis was enhanced while eluviation was reduced due to the influence of vegetation, which caused semi-fixed and fixed sand with higher Na and Ca contents.