Peat decomposition records in three pristine ombrotrophic bogs in southern Patagonia

摘要

Ombrotrophic bogs in southern Patagonia have been examined with regard topaleoclimatic and geochemical research questions but knowledge about organicmatter decomposition in these bogs is limited. Therefore, we examined peathumification with depth by Fourier Transformed Infrared (FTIR) measurementsof solid peat, C/N ratio, and δ13C and δ15Nisotope measurements in three bog sites. Peat decomposition generallyincreased with depth but distinct small scale variation occurred, reflectingfluctuations in factors controlling decomposition. C/N ratios varied mostlybetween 40 and 120 and were significantly correlated (R2 > 0.55, p< 0.01) with FTIR-derived humification indices. The degree ofdecomposition was lowest at a site presently dominated by Sphagnum mosses. The peatwas most strongly decomposed at the driest site, where currentlypeat-forming vegetation produced less refractory organic material, possiblydue to fertilizing effects of high sea spray deposition. Decomposition ofpeat was also advanced near ash layers, suggesting a stimulation ofdecomposition by ash deposition. Values of δ13C were 26.5 ± 2‰ in the peat and partly related to decomposition indices, while δ15N in the peat varied around zero and did not consistently relate toany decomposition index. Concentrations of DOM partly related to C/N ratios,partly to FTIR derived indices. They were not conclusively linked to thedecomposition degree of the peat. DOM was enriched in 13C and in15N relative to the solid phase probably due to multiple microbialmodifications and recycling of N in these N-poor environments. In summary,the depth profiles of C/N ratios, δ13C values, and FTIR spectraseemed to reflect changes in environmental conditions affectingdecomposition, such as bog wetness, but were dominated by site specificfactors, and are further influenced by ash deposition and possibly by seaspray input.