Do bonfire change soil properties and contaminate soils under different vegetal cover? Case study of an urban park, Vilnius, Lithuania

2018 edition

Marcos Francos

Bonfires are a common practice in urban parks being one of the major pollution in urban soils. Despite this, only few works studied the impact of bonfires on soil properties. The main objective of this study is to analyze the direct impact of bonfires on studied soil properties under different vegetal cover. This work wants to determinate how influence fire on soil properties and if the changes in studied properties can contaminate the soils of this urban area. In this study three different sites were selected and sampled. In each site were sampled ten burned and ten unburned samples. One was under mixed forest of Pinus sylvestris L. and Quercus robur L. (Site 1), one under Aesculus glabra Willd. (Site 2) and last one under mixed forest of Pinus sylvestris L. and Platanus L. (Site 3). We studied several soil properties: Soil Water Repellency (SWR), Aggregate Stability (AS), Soil Organic Matter (SOM) content, Total Nitrogen (TN), Inorganic Carbon (IC), pH, Electrical Conductivity (EC), extractable Calcium (Ca), Magnesium (Mg), Sodium (Na), Potassium (K), Phosphorus (P), Aluminum (Al), Manganese (Mn), Iron (Fe), Zinc (Zn), Copper (Cu), Boron (B), Chrome (Cr), Silicon (Si), Sulfur (S), Carbon/Nitrogen ratio (C/N), Sodium:Potassium index (SPAR), Calcium:Aluminum index (Ca:Al) and Calcium:Magnesium index (Ca:Mg). Results show an increment in burned soils in IC, pH, EC, Ca, Mg, Na, K, P, Zn, Cu, C/N ratio, Ca:Al ratio and Ca:Mg ratio. There are a decrease in SWR, AS, TN, Mn, Fe and SPAR ratio by fire. In soil properties as SOM, Al, Cr and S increase and decrease between burned and unburned soils according to the site; Not changes were recorded in B and Si between burned and unburned soils. It is very important the temperature reached during the pile burn were the same using different wood size waste, the time that remain soil over 200 ┬║C. This time that remain soil burning can produced changes in soil properties. The increase in heavy metals can contributed to a contamination aquifers and water used for domestic uses after first rainfall.