A regional soil and river sediment geochemical study in Baoshan area, Yunnan province, southwest China

Abstract

This study aims to better understand, at a regional scale, the concentration and distribution of selected chemical elements in surface environments and the influence of natural factors (geological background, geomorphology) and anthropogenic factors (mining activities, land-use, agricultural fertilization) on their distribution in the Baoshan area, Yunnan province, southwest China. Mineral resources (such as copper, lead, zinc, mercury, gold, silver) and carbonate and basalt parent materials in this area often lead to elevated potentially toxic metals (PTMs), which are widely distributed where mining activities have rapidly developed since last 20–30 years. This study makes use of 1574 surface soil data and 425 deep soil data from the National Geochemistry Survey of Land Quality project (NGSLQ), and 1585 archived river sediment data which were collected and analyzed for the Regional Geochemistry-National Reconnaissance program (RGNR). These data, once log-ratio (clr) transformed have been studied by compositional data analysis (CoDA), principle components analysis (PCA) and spatial analysis. In the Baoshan area, the concentration of elements As, B, (Br), Co, Cr, Cu, Hg, (I), Mn, (N), Ni, Sb, (Sc), (Se), V, Fe2O3Total and (COrgonic) are enriched compared to the China Soil Geochemical Baselines program (CGB) and RGNR data sets; while elements Sr and Na2O are depleted compared to CGB and RGNR data sets. Influencing factors on surface soil, deep soil and river sediment composition of the study area are revealed. The distribution of most elements in surface soil, deep soil and river sediment are influenced by natural factors such that: Co, Cr, Cu, Ni, Sc, Ti, V, Fe2O3Total and MgO are controlled by the distribution of basic igneous rocks; Ca, Mg, Sr and pH are controlled by the distribution of carbonate rocks and basic igneous rocks; As, Hg, Sb, (Ag), Cd, Pb and Zn are controlled by mineralization; and other elements normally controlled by the distribution of clastic rocks and acid-intermediate rocks; while the organic matter such as Br, N, (P), S, COrgonic and CTotal in soil data set are controlled by geomorphic (altitude and temperature). Anthropogenic factors are also recognized in the soil data set. For example: high pH values in paddy land and grassland, and low pH values in forested land, garden plot and dry cultivated land; in agricultural area fertilization has caused enrichment of the nutrient elements (COrgonic, CTotal, N, P, etc.,) in surface soil; while in areas of mining, surface soils are contaminated by PTMs (incl. Hg, As, Sb, Cu, Pb, Zn and Cd).