SPATIAL DISTRIBUTION OF HEAVY METALS RELEASED FROM ASHES AFTER A WILDFIRE

Heavy Metals (HM) in great amounts in soil and water resources can cause coercive effects in the environment and human health. Ash contains high quantities of HM that depend on combusted species, type and part burned and soil characteristics. After a fire, the HM released from ash can lead to a soil solution and water resources contamination. This liberation of HM in solution can be highly variable across the affected area. This work pretends to study the spatial variation of the HM - Aluminium (Al3+), Manganese (Mn2+), Iron (Fe2+) and Zinc (Zn2+) - in a Quercus suber and Pinus pinaster stand affected by a wildfire in Portugal, applying some interpolation methods. The results showed that on average across the plot, Al3+ was the HM released in higher quantities and Zn2+ in lower. The higher variability was observed in Zn2+ and in Fe2+. The interpolation methods assessed showed that polynomial regression (PR) method was the more accurate to predict the distribution of the HM across the plot. Al3+ and Mn2+ showed a rise in their concentration from south towards north section of the plot, and Fe2+ and Zn2+ a decrease from northwest to southeast section of the plot. The liberation of Al3+ and Mn2+ is related with species burning severity, and Fe2+ and Zn2+ with plot topography. The fire evolution across the plot and the consequent rising temperatures can have higher impacts than burned species in HM spatial variability. Over time, with the decreasing ash pH, HM will become more mobile and will be released in soil solution, with potential coercive effects in the environment.