Advances in the determination of humification degree in peat since : Applications in geochemical and paleoenvironmental studies

Abstract

The humification process is one of the least understood and most intriguing aspects of humus chemistry and vital to the global carbon (C) cycle. Peatlands represent the largest terrestrial reservoirs of organic C and support a unique biodiversity, but are also natural archives of climate and environmental changes. In fact, cores from ombrotrophic peatlands are commonly used to reconstruct environmental impacts by human activities during the past decades, centuries and millennia. Understanding the extent to which bogs may serve as reliable archives is of paramount importance in order to ensure that chronological information about natural and human-induced environmental changes are effectively preserved in peat deposits rather than irretrievably affected by humification. Structural changes of the organic matter which constitutes peat are often evaluated by various indirect measures of the degree of humification.Numerous methods and proxies have been proposed and used during the last century, often providing contrasting or inconsistent results. Here we tested multiple physical, chemical, spectroscopic and thermal approaches using peat samples collected from nine bogs on four continents. Despite the different climatic conditions, botanical composition, depth and age of peat formation, we show that the H/C ratio is the simplest, most widely valid and cost-effective humification proxy and should find universal application to multi-proxy geochemical and paleoenvironmental studies. Moreover, we show that three-quarters of the organic C in the studied bogs is in a comparatively undecomposed state, and thus vulnerable to climate changes.

Holocene vegetation history and human impact in the eastern Italian Alps: a multi-proxy study on the Coltrondo peat bog, Comelico Superiore, Italy

“…The ash content is very low throughout the profile (mean ± SD: 3.6 ± 1.8%) down to 239 cm; below this depth, a strong increase occurs, with values up to 97% at 250 cm, where the mineral substrate is reached. Ash content is positively and significantly correlated with both bulk density (R = 0.54, p < 0.01) and Ti concentration (R = 0.92, p < 0.01); this suggests that variations in ash content throughout the profile are mainly the result of changes in the rate of supply of dust particles, rather than differences in the degree of peat mineralization (Zaccone et al 2013(Zaccone et al , 2018.…”

“…The bulk density of the peat ranges between 0.04 and 0.16 g cm −3 (mean ± SD: 0.10 ± 0.03 g cm −3 ) down to 239 cm, without a clear trend and often consisting of poorly decomposed low density peat underlying well decomposed layers (Fig. 3); this is probably the result of environmental conditions in the past that were sometimes more conducive to rapid peat accumulation (Zaccone et al 2018). The basal layers show a significant rise in density in the lowest 10 cm, with values up to 1.41 g cm −3 , due to the increase of inorganic material there.…”

Isotope applications to soil science at the University of Alberta — an historical perspective

“…Numerous experimental approaches and instrumental tools have been proposed and utilized to study peat formation processes. In regard to the specific use of light stable isotopes, researchers in W. Shotyk's group have investigated the value of δ 13 C and δ 15 N measurements as indices of peat humification extent (Zaccone et al 2018).…”

Molecular characterization of ombrotrophic peats by humeomics

“…Such relatively adverse conditions lead to the development of selected microbiological communities, adapted to extreme environments, mostly anaerobic, whose degrading action is relatively slow and may be further influenced by site-specific microclimate [4,5]. In fact, decomposer communities, peat-forming plants, water table fluctuation, pH, oxygen availability and temperature strongly affect the degree of decomposition [6][7][8][9]. Consequently, OM accumulation in peatlands is commonly favored since the rate of OM production is larger than the decomposition rate [10].…”

“…The most common chemical groups usually detected in peats include cellulose, hemicellulose, lignin, protein, cutin and suberin which are mostly derived from plant biopolymers. Therefore, peat is a very heterogeneous and organic C-rich material whose specific molecular composition, as well as its degree of humification, mainly varies according to geographical origin, peat-forming vegetation, and the environmental conditions under which peat was exposed over time but not consistently with age and depth [9].…”