Pyrogenic organic matter from palaeo-fires during the Holocene: A case study in a sequence of buried soils at the Central Ebro Basin (NE Spain)

Abstract

We studied the fire record and its environmental consequences during the Holocene in the Central Ebro Basin. This region is very sensitive to environmental changes due to its semiarid conditions, lithological features and a continuous human presence during the past 6000 years. The study area is a 6 m buried sequence of polycyclic soils developed approximately 9500 years ago that is exceptionally well preserved and encompasses four sedimentary units. The content and size distribution of macroscopic charcoal fragments were determined throughout the soil sequence and the analysis of the composition of charcoal, litter and sediments via analytical pyrolysis (Py-GC/MS). The high amount of charcoal fragments recovered in most horizons highlights the fire frequencies since the beginning of the Neolithic, most of which were probably of anthropogenic origin. In some soil horizons where charcoal was not found, we detected a distribution pattern of lipid compounds that could be related to biomass burning. On the other hand, the low number of pyrolysates in the charcoal could be attributed to highintensity fires. No clear pattern was found in the composition of pyrolysates related to the age of sediments or vegetation type. The most ancient soil (Unit 1) was the richest in charcoal content and contains a higher proportion of larger fragments (> 4 mm), which is consistent with the burning of a relatively dense vegetation cover. This buried soil has been preserved in situ, probably due to the accumulation of sedimentary materials because of a high-intensity fire. In addition, the pyrogenic C in this soil has some plant markers that could indicate a low degree of transformation. In Units 2-4, both the amount of charcoals and the proportions of macrofragments > 4 mm are lower than those in Unit 1, which coincides with a more open forest and the presence of shrubs and herbs. The preservation of this site is key to continuing with studies that contribute to a better assessment of the consequences of future disturbances, such as landscape transformation and climate change.

Influence of topography on sediment dynamics and soil chemical properties in a Mediterranean forest historically affected by wildfires: NE Iberian Peninsula

“…This is the case of the study carried out by Yulianto et al (2004), in which they collected 12 samples in each profile at 150 cm, showing the validity of this method despite the low number of samples collected in each layer. Other authors have used only one sample from each layer in order to determine changes in sediment dynamics and soil properties, and this is a valid and widely used method as in the case of Armas-Herrera et al (2019).…”

Late Glacial and Holocene buried black soils in Emilia (northern Italy): genetic and paleoenvironmental insights

“…Pedogenetic processes and the resulting soil types are strictly dependent on existing climatic conditions (Schaetzl and Anderson 2005;Clark et al 2012;Walker et al 2012;Meier et al 2014;Mauri et al 2015;Tabor and Myers 2015;Binney et al 2017;Pérez-Lambán et al 2017;Zhou et al 2021). The prominent role played by climate change over time, particularly between the end of the Pleistocene and the early Holocene, in conditioning soil-forming processes through vegetation cover change has been observed in various case studies (Tallón-Armada et al 2014;Malkiewicz et al 2016;Pérez-Lambán et al 2017;Chendev et al 2018;Armas-Herrera et al 2019). In northern Italy, the majority of the sites studied from a paleoenvironmental perspective are hilly and mountain settings, mainly lacustrine environments characterized by continuity of sedimentation (e.g., Vescovi et al 2010;Joannin et al 2013, and references therein).…”

“…These sequences often contain black soils, which, although already described by previous studies in the Po Plain (e.g., Amorosi et al 2014aAmorosi et al , 2017Bruno et al 2020;Marcolla et al 2021), have not been interpreted in terms of paleoenvironmental conditions. Notably, in other European countries (e.g., Spain), black soils have been ascribed to specific climatic conditions, vegetation types, and the occurrence of fires (Tallón-Armada et al 2014;Armas-Herrera et al 2019), and related hypotheses need to be tested in northern Italy.…”

Effects of late-Holocene fires on the carbon sequestration capacity of peatlands in the Sanjiang Plain

“…The accumulation of carbon-containing sediments in soils is the long-term result of an imbalance in the production and decomposition of vegetation biomass [3] . Wildfires, by burning vegetation, not only affect soil carbon content during combustion but also change the previous state of carbon accumulation long after combustion [4] .…”