Changes of S, P and C Speciation during Initial Soil Formation in Forefields of Receding Glaciers As Assessed By XANES Spectroscopy.

The global retreat of glaciers during recent decades provides an excellent opportunity to investigate pedogenetical processes in initial soils, including the speciation of important bioelements, as e.g. S, P, and C. Modern analytical techniques, namely synchrotron-based X-ray Absorption Near Edge Structure (XANES) spectroscopy allow a direct speciation rather than the traditional operationally-defined fractionation of these elements. We analyzed soil soil chronosequences on moraines with different mineralogy in glacier forefields all over the world (Switzerland, Iceland, China, New Zealand, Canada) for their changes in S, P, and C speciation during initial pedogenesis and vegetation succession from barren rock to either grassland or forest. All studied soils were characterized by a rapid loss of lithogenic sulfide-S and apatite-P, and an accumulation of organic S and P as well as sulfate and phosphate bound to pedogenic sesquioxides. However, the rate, magnitude, and type of S, P, and C speciation change showed significant variance among the studied chronosequences, with the key factors being the type of morainal parent material (granite, andesite, basalt, limestone) and vegetation succession (forest, grassland).