Soil erosion and organic carbon export by wet snow avalanches

Abstract

Abstract. Many mountain belts sustain prolonged snow cover for parts of the year, although enquiries into rates of erosion in these landscapes have focused almost exclusively on the snow-free periods. This raises the question of whether annual snow cover contributes significantly to modulating rates of erosion in high-relief terrain. In this context, the sudden release of snow avalanches is a frequent and potentially relevant process, judging from the physical damage to subalpine forest ecosystems, and the amount of debris contained in avalanche deposits. To quantitatively constrain this visual impression and to expand the sparse literature, we sampled sediment concentrations of n = 28 riverspanning snow-avalanche deposits (snow bridges) in the area around Davos, eastern Swiss Alps, and inferred an ordersof-magnitude variability in specific fine sediment and organic carbon yields (1.8 to 830 t km −2 yr −1 , and 0.04 to 131 t C km −2 yr −1 , respectively). A Monte Carlo simulation demonstrates that, with a minimum of free parameters, such variability is inherent to the geometric scaling used for computing specific yields. Moreover, the widely applied method of linearly extrapolating plot scale sample data may be prone to substantial under-or overestimates. A comparison of our inferred yields with previously published work demonstrates the relevance of wet snow avalanches as prominent agents of soil erosion and transporters of biogeochemical constituents to mountain rivers. Given that a number of snow bridges persisted below the insulating debris cover well into the summer months, snow-avalanche deposits also contribute to regulating in-channel sediment and organic debris storage on seasonal timescales. Finally, our results underline the potential shortcomings of neglecting erosional processes in the winter and spring months in mountainous terrain subjected to prominent snow cover.

Digging deeper: A holistic perspective of factors affecting soil organic carbon sequestration in agroecosystems

“…Further, erosion‐induced transport leads to differential removal of SOC fractions. The particulate organic C (POC) is removed preferentially by inter‐rill erosion (Wang et al., ; Wang, Cammeraat, Cerli, & Kalbitz, ), whereas the mineral‐bound organic C (MOC) is relatively protected (see Table ). Worrall, Burt, and Howden () observed that soil erosion is a source of GHGs and has emission factors of 5.5, 4.4, and 0.3 Mg CO 2 eq/year for one Mg of fluvial C, gross C erosion, and gross soil erosion, respectively.…”

A new CT scan methodology to characterize a small aggregation gravel clast contained in a soft sediment matrix

“…Wet avalanches in lacustrine deposits have been identified by Vasskog et al (2011) using grain size analysis to identify layers of poorly sorted grain accumulation associated with gravels resulting in a multi-modal grain size distribution. Such deposits on lake ice would result in drop stones at thaw season (Luckman, 1975), and may contain such deposits on lake ice would result in drop stones at thaw season, and may contain terrestrial organic matter (OM; Irmler et al, 2006;Wilhelm et al, 2013;Korup and Rixen, 2014).…”

Soil erosion in an avalanche release site (Valle d'Aosta: Italy): towards a winter factor for RUSLE in the Alps

“…While the causes and effects of erosion as a soil degradation threat in the world are widely described and investigated (Lal, 2001), soil loss estimation in sloping areas still has some uncertainties, as the methods commonly used are not specifically designed for mountain environments, where climate and relief are extreme (Alewell et al, 2008;Garcia Rodriguez et al, 2012). Recently, the relevance of winter erosion processes, besides the ones taking place in the growing season, has been pointed out.…”

“…Recently, the relevance of winter erosion processes, besides the ones taking place in the growing season, has been pointed out. For example, Ceaglio et al (2012), and more recently Korup et al (2014), proved that snow movements are a significant agent of soil redistribution at mountain sites. Within these snow movements, wet avalanches are well known for their high sediment yields (Gardner, 1983;Ackroyd, 1987;Bell et al, 1990;Jomelli and Bertran, 2001;Heckmann et al, 2005); however, so far regionalization and parameterization of these processes are missing.…”