Organic matter and metal distribution in an ombrothrophic bog profile: mobile versus immobile OM

Vortragender: Prof. Dr. Teodoro M. (Teddy) Miano, Agro-Forestale ed Ambientale, Università degli Studi di Bari
Do. 24.01.2002 (16:15), H6

Peatlands, or organic soils, are water logged deposits of partly decomposed plant debris that contain up to 90% moisture content. Worldwide, such soils cover about 500 million hectares, equal to nearly half the area of Europe, and have a carbon content close to 0.67 billion metric tons. These deposits are known as ³Histosols´ because the term rightly refers to an accumulation of living bodies, mostly plants, and their residues and by-products. Peatlands can be classified from various perspectives, according to the present surface flora, main botanical origin, water source and its mineral and flow properties, degree of decomposition, etc. An ³ombrotrophic´ bog is a bog domed peatland in which the surface peat layers are hydrologically isolated from the influence of local groundwaters and surface waters, and are supplied solely by atmospheric deposition. This type of peatland exhibits a convex morphology, a particularly impoverished flora and an acidic pH. The maintainance of the ombrotrophic status of the peat with increasing depth beneath the surface of the bog can also allow for the reconstruction of the historical climatic changes of the area. The behaviour of metals in environmental systems is governed by their concentrations and by a variety of reactions that include complexation with organic and inorganic ligands, ion exchange, adsorption and desorption processes, precipitation and dissolution of solids, acid/base equilibria. Natural organic matter plays an important role in the biogeochemistry of metals and can be divided into three main classes: (i) substances of known molecular structure and chemical properties; (ii) xenobiotics; and (iii) humic substances. Because of their physico-chemical and biological stability with time and ability to interact with metal ions, the latters are very important in the formation of organo-mineral complexes. An ombrotrophic site represents a great opportunity to better understand interactions between humified organic matter and metals. In this paper a preliminary study on humic acids (HA) isolated from the top layer of an ombrotrophic swiss bog, and their interactions with several metals (Al, B, Ba, Ca, Cd, Co, Cu, Fe, K, Mg, Mn, Ni, Pb, Sr, Zn) is described. A peat core was isolated, frozen and sliced into 3 cm sections. Pore waters expressed from the peat slices were analyzed by fluorescence spectroscopy. Solid peat residues were freeze-dried and analyzed by means of Fourier-transform Infrared (FT-IR) and Electron Spin Resonance (ESR) spectroscopies. In addition, HA were isolated from the solid samples and characterized by means of FT-IR, fluorescence and ESR spectroscopies. Further, the elemental content of the humic fraction has been evaluated in comparison with the main features of the peat bog profile. Results indicate the occurrence of two-three distinct sections in the bog profile, in which different physico-chemical and biological environments determine different decomposition and humification processes of originally similar indigenous organic residues. A sharp transition between sections may be observed at a depth corresponding approximately to the location of the permanent water table. The use of spectroscopic means provides useful information on the transformation and evolution of organic matter in natural systems, and enables one to characterize its status in aerobic versus anaerobic conditions. Metals content confirms the ombrotrophic status existing at Etange de la Gruyère.

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