Soil Gleization as Indicated by Redox Potential and Mineral Magnetism and Indirect Sedimentary Evidence in a Catchment in Sw China

Abstract

This paper explores whether redox potentials (Eh) and mineral magnetism could indicate the same spatial variability of soil gleization and whether the inferred pattern could be indirectly supported by sediment characteristics. Fifteen soil profiles were sampled closely around a reservoir built in 1964, at valley floors and on slopes distant from the reservoir in a catchment on Guizhou Plateau, SW China. Eh was measured for these profiles when they were being sampled in the field. A 28 cm-long sediment core was sampled from the reservoir in April 2019. Magnetism measurements and particle-size analysis were made on the soils and sediments, while TOC and TN analysis was performed on the soils and 137Cs activity analysis on the sediments. The Eh values were the lowest for the soils on the flattest and lowest valley floors, intermediate for the soils closely around the reservoir and highest for those on the steepest and highest slopes distant from the reservoir. Thus, reducing conditions were strongest at the valley’s floors, moderate around the reservoir and slightest on the remote slopes. clf, cfd, cARM, IRM300mT, SIRM, cfd%, cARM/SIRM and IRM300mT/SIRM were the lowest for the valley-floor soils, suggesting the most intensive dissolution of ferrimagnets, including their SP and SSD grains, and thus the strongest gleization. These magnetic variables were intermediate for the near-reservoir soils and highest for the remote-slope soils, implying moderate and slightest gleization, respectively. Downward variations in magnetic characteristics, particle size and TOC and C/N in these soil profiles supported such inferences. Magnetism indicated that the valley-floor soils made no contributions to the sediments throughout 1964-2018, even when stronger erosion occurred, as implied by coarser sediment particles. This suggested the most frequent waterlogging, thereby confirming the strongest reducing conditions and gleization on the valley floors, as inferred from the pedological Eh and magnetism.

Keywords: redox potential, mineral magnetism, reducing status, soil gleization, reservoir sediment