Geochemistry of elements and parent materials of non-alluvial soils from Tokai and Okinawa districts, Japan

Abstract

We have studied the geochemical behavior of multi elements during weathering and formation of soil to reveal the origin of non-alluvial soils collected in the Tokai and Okinawa districts. Some constituents such as total organic carbon, total sulfur, Sb, Bi, Pb, Cd, Sn, and Hg are often enriched in the uppermost soil layers. Their enrichments are not explained by simply chemical weathering process and pollution. Certain plants enrich in heavy metals, suggesting that biological accumulation plays an important role for the chemical composition of soils. If the long-range transported aeolian dust is the main source of studied soils, the soil samples would have the homogeneous chemical composition. However, the chemical composition of soil is similar to those of igneous rocks, sedimentary rocks and sediments, which are exposed to the each sampling localities. The aeolian dust does not particularly contribute to the soil formation. The reworked clastic materials, sea salts, plant and aeolian dust are in short supply to explain the accumulation rate of soil layers. Analytical results of water-extracted elements from the powdered rocks and sediments show that all elements are removed as dissolved and suspended forms during soil forming process. The inconsistency of accumulation rate of soil layers and supply rate of source materials is probably due to the removal of surface materials.