The trace element distribution in peat soils affected by natural burning events: A proxy of the original composition and metals mobility assessment

Claudio Natali; Mattia Ferrari; Alessandro Bragagni; Gianluca Bianchini; Gian Marco Salani; Riccardo Avanzinelli; Matthias Ghiotto

doi:10.1016/j.scitotenv.2023.167826

The trace element distribution in peat soils affected by natural burning events: A proxy of the original composition and metals mobility assessment

Sci Total Environ. 2023 Dec 20:905:167826. doi: 10.1016/j.scitotenv.2023.167826. Epub 2023 Oct 13.

Authors

Claudio Natali¹, Mattia Ferrari², Alessandro Bragagni², Gianluca Bianchini³, Gian Marco Salani³, Riccardo Avanzinelli⁴, Matthias Ghiotto²

Affiliations

¹ Department of Earth Sciences, University of Florence, via La Pira 4, 50121 Firenze, Italy; CNR, Institute of Environmental Geology and Geoengineering, Area della Ricerca di Roma 1, strada Provinciale 35d, 9-00010 Montelibretti (RM), Italy. Electronic address: claudio.natali@unifi.it.
² Department of Earth Sciences, University of Florence, via La Pira 4, 50121 Firenze, Italy.
³ Department of Physics and Earth Sciences, University of Ferrara, via Saragat 1, 44121 Ferrara, Italy.
⁴ Department of Earth Sciences, University of Florence, via La Pira 4, 50121 Firenze, Italy; CNR, Institute of Geosciences and Earth Resources, via La Pira, 4, 50121, Firenze, Italy.

PMID: 37839488
DOI: 10.1016/j.scitotenv.2023.167826

Abstract

This work evaluates for the first time the effects on the trace element composition of peat soils affected by natural burning events, a recurrent phenomenon in the reclaimed wetland of the Mezzano Lowland (Padanian plain, NE Italy). The trace element distribution of two neighboring soil profiles, one pristine and one deeply affected by burning events, were compared to identify the original geochemical fingerprint of saltmarsh peat environment. The pre-combustion composition of the fired profile was reconstructed to infer the physico-chemical changes occurred as a consequence of the burning event, with a special attention to the mobility of elements of environmental concern, such as potentially toxic trace metals. The increase in concentration of potentially toxic elements (PTE) was particularly evident in two layers of the fired profile. V, Cr, Cu, Zn, Pb, and As contents progressively increase toward intermediate depths (30-75 cm) together with Th, Sr, Ba, U. On the contrary, Tl, Bi and Cd show a concentration peak in a thin, shallower (14-17 cm depth) horizon. The trace element composition of the unfired profile allowed the identification of specific ratios between immobile elements that can be used as geochemical fingerprint of the soils horizons with different soil organic matter (SOM) content. On the basis of Sr/Rb, Th/U and Ba/Sr it was possible to classify three types of sedimentary deposits characterizing both the unfired and fired profile, as well as to delineate the fire severity trends occurred in the different soil horizons of the fired profile. The distribution of immobile trace element, representative of the organic (U) and mineral (silicate, Th, Ba, REE and non-silicate, Sr) soil fractions with organic matter and bulk density in the non-fired profile, allowed the reconstruction of the original physico-chemical composition of the fired/burned profile and the accurate determination of the relative CO₂ lost during the burning event. Moreover, the distribution of PTE with respect to immobile trace elements, used to estimate the element redistribution and mobility after burning in the fired profile, suggested that elements such as Cr, Ni, Zn, V were mainly immobile, whereas Pb, Mo and in particular Tl and Bi suffered a significant redistribution along the burned profile. Nonetheless, results of the gain/loss calculation for the whole soil profile suggested that no significant entry or leak of these elements occurred, limiting their redistribution inside the investigated soil system.

Keywords: Natural burning; PTE mobility; Saltmarsh peat; Trace element.