Abiotic and biotic changes of sulphur, iron, and carbon speciation after aeration of wetland soils

摘要

For organic surface and mineral soil horizons of terrestrial and intertidal wetland soils from Germany and Thailand, the kinetics of speciation changes of sulphur, iron, and organic carbon (OC) after aeration was assessed by synchrotron-based K-edge X-ray absorption near-edge spectroscopy (XANES), solid state 13C CPMAS NMR spectroscopy, and wet chemical/GC analyses. The kinetics of speciation change was investigated in a laboratory incubation experiment, in which subsamples were held in contact withambient air for different time periods, ranging from 1 minute to 21 days under controlled boundary conditions. In different experimental variants, abiotic changes were distinguished from biotic changes. The results show that oxygenation of wetland soilsresults in rapid oxidation of reduced inorganic sulphur and iron species (e.g. Fe(II) sulphide) to oxidized species (sulphate, Fe(III)oxides). Under anoxic conditions, labile OC species (O-alkyl-C, e.g. plant-derived sugars such as glucose, arabinose, and xylose) are prevented from microbial degradation. Aeration of these samples resulted in considerable OC losses, microbial degradation of glucose, arabinose, and xylose, and formation of microbial OC compounds (alkyl-C), including the sugars galactose and mannose. Our results suggest rapid, marked losses of labile OC species (terrestrial wetland soil only) and rapid oxidation of reduced S and Fe after aeration of wetland soils due to changes of their hydrological regime.