Reduction of nutrient losses with eroded sediments by post-fire soil stabilisation techniques

Abstract

Abstract.After an experimental fire in steep shrubland in a temperate-humid region (north-west Spain), the effects of two post-fire stabilisation treatments (grass seeding and straw mulching) on the chemical properties of eroded sediments, and the amount of nutrients lost with them, were evaluated relative to control burnt soil, over a period of 13 months. Total C and N concentrations, and 8 13 C, indicated that sediments were mainly contributed by charred plant and litter material. The highest concentrations of extractable base cations in the sediments occurred during the first 3 months following fire, especially for Na and K. As treatments had little or no effect on nutrient concentration in sediments, differences in nutrient losses were due to the 10-fold lower sediment production in mulching compared with other treatments. In control and seeding treatments, the accumulated amounts of nutrients lost with sediments were 989-1028 kg ha" 1 (C), 77 kg ha" 1 (N), 1.9-2.4 kg ha" 1 (Ca), 0.9-1.1 kg ha" 1 (Mg), 0.48-0.55 kg ha" 1 (NH|-N), 0.39-0.56 kg ha" 1 (K), 0.19-0.34kgha" 1 (Na) and <0.1 kg ha" 1 (P and NOF-N). These values accounted for 22-25% (total C and N) and 5-12% (NH|-N, Ca, P and Mg) of available nutrients in ash, and 1.0-2.4% of those in ash+topsoil. As nutrient and sediment losses were strongly correlated, the reduction of the latter by mulching application leads to an effective decrease of post-fire nutrient losses.

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

“…All these authors pointed out that such a post-fire increase was a result of the contribution of ash from burned vegetation and the physiochemical breakdown of Mn complexed with organic matter. This is also likely in our case, because Gómez-Rey et al (2013) found that sediments of the present study were mainly constituted by charred plant and litter material. Although Pivello et al (2010) found a negative correlation between pH and Mn in burned soils, we found a positive correlation (r ¼ 0.633; P , 0.001) between pH KCl and extractable Mn.…”

“…Moreover, soil-available Mo in these plots was below the detection limit (Gómez-Rey et al 2013), highlighting the importance of the losses of Mo-enriched sediments. Molybdenum is essential for atmospheric N 2 fixation by legumes (Rosolem and Caires 1998), which play an important role in the recovery of N cycling in burnt ecosystems (Hendricks and Boring 1999).…”

“…In Seeding and Control plots, the Fe eroded with sediments during the first post-fire year was less than 1% of the ash þ burned topsoil Fe pool, but it might represent 30-47% of the extractable Fe in ashes. This could explain the depletion of soil-available Fe in these plots (Gómez-Rey et al 2013) and in surface soils affected by recurrent prescribed fires (Pivello et al 2010;Close et al 2011). Post-fire reduction of available Fe could constitute a fertility problem in soils with low levels of plant-available Fe (García-Marco and González-Prieto 2008).…”

“…Little is known about nutrient losses associated with the eroded material (de Koff et al 2006;Gómez-Rey et al 2013), especially in the case of micro-nutrients.…”

“…seeding and mulching) of soils must be applied as soon as possible after the wildfire to accelerate development of ground and vegetation cover and to reduce surface runoff and prevent soil erosion (Pinaya et al 2000;Robichaud et al 2000;Vega et al 2005;Wagenbrenner et al 2006;Groen and Woods 2008;Robichaud 2009;Fernández et al 2011. Despite its undoubted interest, few studies deal with the effects of fire on soil nutrient losses by erosion (DeBano et al 1998;Gabet et al 2005;Robichaud et al 2006;Spigel and Robichaud 2007) and their reduction by post-fire stabilisation techniques (Thomas et al 2000;Robichaud et al 2006;Gómez-Rey et al 2013).…”