Isotope analysis of pyrolysis products from Sphagnum peat and dissolved organic matter from bog water

Elemental analyses (H, N, C, O, S), bulk isotope analyses (C-13, N-15) and C-13 content of pyrolysis products from Sphagnum moss, underlying peat from a bog and the bog water (Hohlohsee, Black Forest, Germany) were performed to identify humification processes in the early diagenesis of peat formatio n and to determine the origin of dissolved organic matter (DOM) in the bog lake. Atomic ratios of bulk elemental analysis suggest a compositional shif t from carbohydrate dominated structures to phenolic polymers. Observed var iations of bulk delta(15)N and total nitrogen are likely due to microbial p roduction. Combining isotopic and structural information using a coupled Py -GC/MS-IRMS system provides further information on the peat formation, e.g. biogeochemical processes of (1) biological degradation of source material, (2) selective preservation of individual compounds, and (3) formation of m icrobial biomass (e.g. trophic level effect). In particular, the stable iso tope data helped to identify microbial processes as a source for carbohydra te pyrolysis products in deeper horizons. The comparison of pyrolysis produ cts from peat and DOM from the bog lake indicates different sources. From t he isotope ratios of pyrolysates it is suggested that DOM is formed in situ by microbial production and not simply dissolved from the peat profile. Th e uptake of C-13 depleted carbon, e.g. respired CO2, CO2 from the oxidation of methane or acetic acid is proposed as an important factor in the format ion of dissolved organic matter. (C) 2000 Elsevier Science Ltd. All rights reserved.