Wildfire severity: Environmental effects revealed by soil magnetic properties

Abstract

AbstractStrong wildfires pose significant damage to all soil qualities and lead to land degradation. The complex nature and properties of fire‐derived materials require multidisciplinary efforts for their reliable characterization. The main objective of our study was to evaluate the suitability of magnetic properties of fire‐affected soils as proxy parameters for wildfire severity and to relate magnetic signature of burnt soils to carbon and nitrogen contents as influenced by wildfires. We present mineral magnetic investigation of 22 sites with wildfire‐affected soils and 17 nonburnt soils from nearby locations. We employed measurements of magnetic susceptibility and anhysteretic remanence in combination with scanning and transmission electron microscopy observations on magnetic particles from burnt soils and ashes. Bulk soil and vegetation ash analyses of total carbon and nitrogen, organic carbon, and elemental content were carried out as well. We show that pyrogenic magnetic enhancement is restricted to the uppermost 0‐ to 2‐cm soil depth and can be used as a proxy for wildfire severity. Strong wildfires lead to the production of nanometer‐sized superparamagnetic magnetite and/or maghemite particles and smaller amount of single‐domain fraction. These strongly magnetic minerals have typical characteristics of high‐temperature combustion products with spherical shape and diameters between 0.1 and 2 μm. Fire‐affected soils show relative enrichment with phosphorous, manganese, and heavy metals (Cu, Pb, Zn, Ni, Co, and As) calculated with respect to soils from nonburnt nearby localities. Our results demonstrate the potential of environmental magnetic methods as an additional tool for assessment of wildfire severity and the content of main soil nutrients.