Sulfur speciation in drained and restored minerotrophic peatland types of northeastern Germany

Restoring drained peatlands has been practiced to mitigate climate change, regulate water quality, and restore biodiversity. However, no information is available on the long-term impact of drainage and restoration of peatlands on total sulfur (S_t), fractions, and S species. We investigated the long-term drained and restored forested and coastal peatlands and percolation mires using the sequential S fractionation and S K-edge X-ray near-edge absorption structure (XANES) spectroscopy analysis to address this knowledge gap. The S_t concentrations in the drained forested peatland and percolation mire were low by 4 and 1.5 folds compared to their respective restored peatlands at the topsoil horizons. Similarly, the H₂O-S and NaH₂PO₄-S fractions in the drained forested peatland (28 and 18 mg kg^-1) were lower than in the restored forested peatland (165 and 166 mg kg^-1). However, the S fractions were higher in the drained percolation mire (449 and 247 mg kg^-1) than in the restored percolation mire (150 and 41 mg kg^-1). The relative proportion of the residual-S fraction (70-97% of S_t) was equivalent to the relative proportion of organic S species (76-97% of S_t) derived from the XANES analysis. The XANES analysis revealed the reduced organic S (44-62%), organic S with intermediate oxidation states (16-47%), strongly reduced (0-21%) and oxidized inorganic S species (4-12%) of the S_t. The results indicate that long-term restoration conserved S_t, decreased labile S fractions and enriched the strongly reduced inorganic and organic S species.