Interactions between wind erosion and soil organic carbon

Abstract

Wind erosion is a common soil degradation process in semiarid and arid environments of the world that can affect the C cycle by decreasing soil C stocks. Conversely, soil organic C (SOC) contents can, theoretically, modify the susceptibility of the soil to be eroded by the wind, as it influences the soil aggregation. In this chapter, both the role of SOC as a possible factor of wind erosion and the effect of wind erosion on SOC losses are analyzed. The effect of SOC on soil erodibility has been widely studied. The best index of soil erodibility is the proportion of aggregates smaller than 0.84 mm, the erodible fraction (EF). It has been demonstrated that soil texture is the main factor affecting EF of most studied soils, being the sand and clay fractions the determining variables. These studies also indicated that SOC has a secondary role in determining EF, and only in few cases, CaCO3 amount, rather than soil texture, is the main factor affecting it. The effect of wind erosion on the C cycle has been less investigated. We analyzed here the C accumulation in sediments transported by the wind in two different ways: saltation and suspension. This is because, though both transport processes occur simultaneously during wind erosion events, most of the sediment mass is transported by saltation representing suspension the lowest mass proportion. The sediments transported by saltation have coarse textures (mostly >90 μm in diameter) and are mobilized below 1 m height and at short distances (some meters), while the sediments transported by suspension have finer textures and reach higher heights and longer distances (up to 1000 km). These characteristics make saltation to be more linked with the degradation of the eroded soils, while suspension is a concern on distant ecosystems due to its possible either positive or negative effects, including human health. Because of this, we analyzed here the concentration and enrichment ratios of C in sediments transported by both, saltation and suspension, to analyze their potential effects on, respectively, soil degradation and the C cycle. The main results indicated that the low-dense organic compounds with high C concentrations (C enrichments of up to 5.0), such as plant debris and polysaccharides of microbial origin, were preferentially transported at high heights, while those of high density and lower C concentrations or forming coarse aggregates (C enrichments close to 1.0), such as carboxylic acids, ketones, and aldehydes, were transported at low heights. Tendencies of C distribution in height in different textured soils are also presented.