Assessing the quality and the decomposition status of solid phase peat and its porewater dissolved organic matter (DOM) using complementary analytical techniques

Background/Question/Methods

Peatlands sequester one-third of all soil carbon and currently act as major sinks of atmospheric carbon dioxide. The ability to predict or simulate the fate of stored carbon in response to climatic disruption remains hampered by our limited understanding of the controls of carbon turnover in peatlands. Little is known about the chemical processes and decomposition pathways that link solid phase peat and dissolved organic matter (DOM) within its porewaters. In this work we have applied Fourier transform Infra red (FT-IR) and ¹³C NMR spectroscopy to characterize the solid phase peat at varying depths from different sites at the Marcell Experimental Forest (MEF) where the Oak Ridge National Laboratory (ORNL) has begun the Spruce and Peatland Response Under Climatic and Environmental Change (SPRUCE) project. Parallel Factor analyzed Excitation/Emission Matrix fluorescence spectroscopy (PARAFAC-EEMS) and ultrahigh resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) were used to characterize the molecular composition of peat porewaters.

 Results/Conclusions

Analyses of the solid phase and the porewater suggested the presence of three different zones of varying degrees of humification in the peat core with maximum decomposition occurring between 30 and 50 cm. Above 30 cm and below 50 cm, the peat is less well decomposed compared to the samples from 30 to 50 cm. FT-IR and NMR spectra showed variations of molecular composition and chemical structures throughout the three different zones. A general increase in the humification index, defined as the ratio of FT-IR absorbances at 2920, 2850, 1630, and 1515 cm⁻¹ with respect to polysaccharides (1030 cm⁻¹) was observed in the region between 30 and 50 cm. C/N ratios were inversely related to humification; i.e, lower C/N occurred with higher humification index. Analyses of the pore waters were in agreement with the analysis of solid phase peat. FT-ICR MS and PARAFAC EEMS revealed the presence three different zones, where, where intense and continuous transformation processes took place in the transition zone (30-50cm).