Soils constitute the major reservoir of mercury (Hg) in terrestrial ecosystems, whose stability may be threatened
by wildfires. This research attempts to look at the effect of prescribed fire on the presence of Hg in a shrubland
ecosystem from NE Portugal, delving into its relationship with soil aggregate size and the molecular composition
of soil organic matter (SOM). During the prescribed fire, on average 347 mg Hg ha 1 were lost from the burnt
aboveground biomass of shrubs and 263 mg Hg ha 1 from the combustion of the soil organic horizon. Overall,
Hg concentration and pools in the mineral soil did not show significant changes due to burning, which highlights
their role as long-term Hg reservoirs. The higher Hg concentrations found in smaller aggregates (<0.2 mm)
compared to coarser ones (0.5–2 mm) are favored by the higher degree of organic matter decomposition (low C/
N ratio), rather than by greater total organic C contents. The Hg-enriched finest fraction of soil (<0.2 mm) could
be more prone to be mobilized by erosion, whose potential arrival to water bodies increases the environmental
concern for the Hg present in fire-affected soils. The SOM quality (molecular composition) and the main organic
families, analyzed by Fourier-transform infrared spectroscopy in combination with multivariate statistical
This work was supported by the Interreg V-A Spain-Portugal program
(POCTEP) 2014–2020 (Project 0701_TERRAMATER_1_E) funded by the European Regional Development Fund (FEDER), the EROFIRE
project (PCIF/RPG/0079/2018) funded by FCT, Portugal and the
InMerForEcos project (PID 2021-125114OB-I00) funded by Ministerio
de Ciencia e Innovaciónn and Agencia Estatal de Investigaciónn (MCIN/
AEI) and FEDER. M. Méndez-López was supported by the predoctoral
grant FPU (FPU17/05484) funded by the Ministerio de Educaciónn y
Formación Profesional. N.T. Jiménez-Morillo was supported by a
“Ramón y Cajal” contract (RYC2021-031253-I) funded by MCIN/AEI/10
.13039/501100011033 and the European Union “NextGenerationEU”/
PRTR”. The financial support of the Consellería de Cultura, Educación e
Universidade (Xunta de Galicia) through the contract ED431C2021/46-
GRC granted to the research group BV1 of the University of Vigo is also
recognized. Open-access funding for this research has been provided by
the University of Vigo/CISUG.
