Mineral magnetism potentially indicating degrees of soil gleization and their implications for tracing sediment sources: Inferences for a small catchment on Guizhou Plateau, SW China

摘要

Ten soil profiles were sampled from a small catchment and two sediment cores were retrieved from a reservoir built in it on the Guizhou Plateau, SW China. Mineral magnetism measurements, particle size, TOC and TN analysis were performed on the soils and sediments. Cs-137 activity analysis was made for one of the cores. Precipitation data were collected for 1957-2017. Vegetation cover and land-use data were acquired for 11 or 12 years included in this period by interpreting remote-sensing images. Magnetic characteristics of topsoil suggest that soils closely around the reservoir were generally strongly gleyed due to lower-lying positions and more frequent waterlog and those distant to it were less or not gleyed owing to better drainage. Particle-size, TOC and C/N data support this inference. The average of chi(lf) , chi(ARM) and IRM300mT/SIRM is only 41 10(-8) m(3) kg(-1), 144 10(-8) m(3) kg(-1) and 0.84 for the topsoil of the strongly gleyed profiles, while the average is high (95 10(-8) m(3) kg(-1), 380 10(-8) m(3) kg(-1) and 0.92, respectively) for the topsoil of the less- or non-gleyed profiles. With the aid of the other data, the sediment magnetism in comparison of the topsoil's suggests varying contributions of the less- or non-gleyed soils versus strongly gleyed soils to the sediments with changes in precipitation and land use. When rainfall was low and vegetation was sparse, contributions to the sediments from the weakly gleyed and non-gleyed soils farther away from the reservoir were bigger. When rainfall decreased and vegetation was better developed particularly in the fields distant to the reservoir, contributions from the strongly gleyed soils distributed closely around the reservoir would relatively increase while those from the remote and weakly gleyed and non-gleyed soils decrease. These results suggest that gleization may strengthen spatial magnetic variability of catchment soils and help to infer sediment sources.