Understanding long-term degradation of black carbon: combining PY-GC/MS and THM-TMAH to develop molecular degradation proxies

Abstract

The molecular composition of organic matter (OM) in peat and soil supplies information on its sources (plants, charcoal, microbes) and on the extent of decay. Therefore, the molecular composition of soil OM is often used as a proxy for past environmental conditions, or to obtain information on the rate of carbon sequestration that is a crucial element in the global carbon cycle. Characterisation of soil OM by pyrolysis gas chromatography/mass spectrometry (PYGCMS) provides detailed information on its molecular composition. My work aims to use this molecular signature to develop chemical parameters for i) a palaeo-environmental interpretation of Brazilian peats and soils, and ii) the stability of soil OM by studying the interaction between environmental factors and soil OM chemistry. The results obtained until now showed a relatively large contribution from black carbon (BC) in both peat and soil records. The fate of BC in soils is an important aspect in the actual discussion of global change. The importance of the study area (Serra do Espinhaço Meridional, MG) in terms of climate dynamics, the age of the peatlands in the study area (Pleistocene), and the vicinity of the BC-rich mineral soils, requires a more detailed interpretation of the long-term fate of BC in the natural environment. Unequivocal evidence for decomposition of BC needs to be established by the presence of functional groups (lost during PYGCMS), which can be done by methylation with tetramethylammonium hydroxide (TMAH). An external stay at the Technical Univeristy of Dresden (Germany) under supervision of Prof. Karsten Kalbitz will allow me to i) analyse peat and soil samples with TMAH, and ii) introduce this method in the laboratory in Piracicaba upon my return. (AU)