Effects of post-fire soil stabilisation techniques on trace elements lost by erosion

Abstract

The effect of two post-fire stabilisation techniques (Seeding and Mulching) on trace element (Al, B, Co, Cu, Fe, Mn, Mo and Zn) losses with eroded sediments was evaluated over a 13-month period following an experimental fire in a steep shrubland of a temperate-humid region (north-west Spain). With time, concentration of extractable Mn, Zn and Cu in sediments decreased, Fe tended to increase and Al, Co, B and Mo varied without a clear trend. Most sediments and trace element losses occurred during the first 3 months post-fire. Compared with the available elements in ash + burned topsoil, the fraction lost with sediments was highest for Mo (10–16%), intermediate for Mn (4%) and Zn (3%) and low for the rest (0.4–1.2%). Although minor effects of stabilisation techniques on element concentrations were found, accumulated mass losses of trace elements decreased 6–12 times in Mulching because of its 10-fold lower soil erosion rate; no significant changes were found in Seeding. Sediment nutrient losses are probably more important than those published for smoke, leaching or volatilisation. Our results suggest that the Zn and Cu enrichment in sediments from the first erosion events increase the risk of downslope water and soil contamination. In conclusion, soil stabilisation techniques are useful to prevent post-fire ecosystem damage.