Experimental simulations and regional estimates of mercury emissions from fire-affected Cerrado soils (Central Brazil)

Wildfires are increasingly recognized as drivers of mercury (Hg) mobilization in tropical ecosystems, yet their effects on soil biogeochemistry across Cerrado vegetation formations remain poorly constrained. This study evaluated total mercury (THg) stocks, soil composition, and fire-induced Hg losses in forest, savanna, and grassland soils from the Águas Emendadas Ecological Station (ESECAE), central Brazil. Laboratory heating experiments simulated low (200 °C), intermediate (350 °C), and high (500 °C) fire intensities, combined with elemental and mineralogical characterization and regional emission estimates based on burned area data. Forest soils exhibited significantly higher THg concentrations, organic carbon content, and C/N ratios than savanna and grassland soils, reflecting stronger Hg association with organic matter and reduced ultraviolet radiation exposure. Simulated burning resulted in substantial Hg mobilization, with losses exceeding 70% even at low intensity and reaching near-total depletion at moderate and high temperatures. Mercury emission factors were consistently highest in forest soils (3.85 ± 0.74 g Hg ha−1), compared to savanna (2.47 ± 0.46 g Hg ha−1) and grassland formations (1.2 ± 0.59 g Hg ha−1). Regional scaling indicated that fires mobilized up to 173 kg of Hg in the Federal District (Capital of Brazil) over the last decade. Alterations in organic matter quantity and quality closely paralleled Hg release, highlighting the central role of soil carbon in regulating Hg stability during combustion. While major-element concentrations remained stable, mineralogical transformations were pronounced, indicating secondary controls on Hg retention.