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Abstract: Although several studies have used bogs in order to reconstruct paleoclimatic conditions and the historical trends of pollutants, scientific literature is still rather controversial about the role of ombrotrophic bogs as reliable record of past environmental changes. Consequently, understanding whether all vegetational and climatic “information” are effectively preserved in peat deposits during humification becomes an essential aspect to be tested before using bogs as natural archives. The present work focuses on stable isotopic ratios, i.e., 13C/12C (δ13C), 15N/14N (δ15N) and 18O/16O (δ18O), and is based on the assumption that, if bogs are consistent archives of environmental changes, these types of “information” should be recorded also into humic acids (HA), i.e. the fraction of peat more recalcitrant and refractory to degradation. Thus, an 81-cm long peat core, covering the last 2000years, was collected from the Etang de la Gruère bog (Jura Mountains, Switzerland), cut into 3cm slices, and HA were isolated from each age dated layer. Stable isotopic ratios (δ13C, δ15N and δ18O) were then determined in bulk peat and corresponding HA samples. An increase in the humification degree and a decrease of the C/N ratio were observed along the profile. The δ13C of both peat and HA showed a significantly similar trend with depth (p =0.0001), and the same significant correlation was observed for the δ15N (p <0.0001). Also the ratio between δ13C and δ15N closely resembled the C/N ratio observed in the peat and in HA (p <0.0001), thus underlining that the trend of these isotopic ratios is preserved along the studied bog profile. Consequently, our data seem to support both the role of HA as recalcitrant, stable molecules with a long-term residence time, and the potential of ombrotrophic bogs to be used as “archives” of vegetational changes occurring (at least) in the last 2000years. Although a certain relationship (p <0.05) between peat and corresponding HA was found also for δ18O, our data did not allow the solving of the issue of its reliability as paleoenvironmental proxy. [Copyright &y& Elsevier]

Abstract: The process of the transformation of fresh organic matter (OM) into more stable and recalcitrant humic substances is still not completely clear. Understanding how OM humification evolves in northern bog environments is extremely important, especially considering that they represent one of the largest terrestrial carbon pools. Structural changes of OM occurring during the humification process have been generally evaluated by indirect measurements of the degree of humification. Several approaches have been used, often providing contrasting results probably because humification is a complex process that evolves differently according to varying pedoclimatic conditions. In the present work, the authors followed the evolution of peat OM along a 165cm bog profile (covering the mid- to late Holocene) correlating results obtained from both organic petrological and chemical investigation. Data clearly underline a significant agreement between the two perspectives, both showing either a quite immature peat material or the presence of three distinct zones along the profile. In detail, both spectroscopic (i.e., FT-IR and three dimensional fluorescence spectra, humification indexes), and Rock–Eval pyrolysis results (low residual organic carbon content and high hydrogen and oxygen index values) showed the occurrence of a central zone (from 20–30cm to 120cm depth) often characterized by high heterogeneity and a low degree of humification when compared to the upper ∼20 and bottom 40cm sections. [Copyright &y& Elsevier]

Sphagnum peat has been found to efficiently remove heavy metals, oil, detergents, dyes, pesticides and nutrients from contaminated waters since its major constituents, i.e., unesterified polyuronic acids, cellulose, and fulvic and humic acids (HA), show functional groups (e.g., alcohols, aldehydes, carboxylic acids, ketones and phenolic hydroxides) which may adsorb pollutant species. The influence of the extractant on the analytical characteristics of HA is an old but still open topic that should be studied in relation to the nature of the matrix from which they originate. While a number of works have been published on the effects of different reagents on the extraction yields and structural properties of HA from soils, relatively little attention has been devoted to peat HA. In this work, the contents of some major and trace elements (As, Ca, Cr, K, Mn, Sr, and Ti) in five Sphagnum-peat samples and in their corresponding HA fractions isolated using three common extractant solutions, i.e., 0.5M NaOH, 0.1M Na4P2O7, and 0.5M NaOH+0.1M Na4P2O7, where investigated by X-ray fluorescence spectroscopy. In general, Cr, Mn, and Ti concentrations of bulk peat samples were higher than those of the corresponding HA fractions regardless of the extractant used. Arsenic, Ca, K, and Sr concentrations in the HA fractions were affected by the extraction procedure, although at different extents depending on the extractant utilized. In particular, compared to both NaOH and NaOH+Na4P2O7, the Na4P2O7 extractant yielded HA generally richer in As, Ca, K, and Sr, and poorer in Ti. These results may be related to both the nature of each HA fraction and the physical and chemical form of each element supplied to the studied bog via atmospheric deposition. [Copyright &y& Elsevier]

Abstract: An ombrotrophic peat core was collected from Etang de la Gruère (Swiss Jura Mountains) and divided into 3 cm slices (n =26). Humic acids (HA) were extracted and the yield of HA was employed as an index of humification. Mercury concentrations were measured in both the peat samples and the corresponding HA. The highest Hg concentrations were found in the top half of the peat core, corresponding to the least humified peats, indicating that the changing rates of atmospheric Hg deposition during the past decades, not the degree of humification, is the single most important factor determining the distribution of this trace element in peat cores. Up to 89% of the total Hg in the peat samples, with an average of ca. 66%, is found in the HA fraction, which explains why the distribution of Hg in peat and the corresponding HA is similar. Because of the physico-chemical and biological stability of HA with time, the preservation of most of the Hg in this fraction suggests that peat cores from ombrotrophic bogs may provide reliable records of the atmospheric Hg deposition. The correlation between Hg and Br in HA isolated from these same peat samples suggests that the two elements may behave similarly during humification. [Copyright &y& Elsevier]

Abstract: Scientific results about the role of peatlands as sink or source of bromine are rather antithetic. Although several attempts have been performed to correlate Br content and peat decomposition/humification, the role of humic acids (HAs) as possible sink of this element has not been previously investigated. Two peat cores (2H and 2T), collected from the ombrotrophic bog Etang de la Gruère (Switzerland), were divided in several slices from which humic acids were successively extracted. Bromine content was determined in both peat and corresponding HAs samples using an Energy-dispersive miniprobe X-ray fluorescence multielement analysis (EMMA-XRF). Data show a greater “affinity” of Br for HAs rather than for corresponding bulk peat samples, especially in the first 24 cm of depth where Br concentration in HAs is 3.5 times higher than the one in peat; in particular, approximately 40% (average value) of the total Br in peat is stably incorporated into HAs molecules. Further, the observed correlation between the Br content in HAs and the Pb enrichment factor in peat, especially in the upper part of both profiles, suggests a possible role of HAs as geochemical sink of Br atmospheric deposition. Consequently, humification processes occurring in peat could promote Br accumulation in HAs, thus reflecting the deposition rate of this trace element. [Copyright &y& Elsevier]

Abstract: A peat core (10×10×81cm) removed from Etang de la Gruère (Switzerland) was divided into 27 slices of 3cm and the peat samples were freeze-dried and milled very finely. Humic acids (HA) were extracted from each slice. Both raw peat and HA were analyzed with respect to ash content, moisture and elemental (C, H, N, and S) analysis. In addition, they were analyzed using Fourier transform infrared spectroscopy (FT-IR) and UV–Vis spectroscopy (E 4/E 6 ratio). Physical and chemical properties of the peat core appear to show different conditions along the profile; in fact, these data could indicate the presence of 3 distinct zones in the bog: (i) an acrotelm, or zone of active decay, which may be oxygenated, depending on the season, (ii) a catotelm, which is always anoxic, and where only a very slow and partial organic matter decomposition is possible, and (iii) a “transitional” layer, in which complex interactions between organic and inorganic compounds most possibly happen. E 4/E 6 trend and FT-IR spectra on purified HA appear to confirm this hypothesis and underline different stages of humification of organic matter along the profile showing a greater degree of aromatic condensation in the deeper horizons than in the surface layer. [Copyright &y& Elsevier]