Iron Oxides as Tools to Assess Water Erosion Processes

The study of erosive processes is essential to maintain agricultural sustainability, but it is often affected by the limitations and costs of conventional methodologies used. This situation is common worldwide, which has resulted in an increasing interest in developing sediment tracers. Here we provide a general review of diverse sediment tracing approaches and some of the advantages and limitations of using iron oxides for tagging soil particles. The scientific literature provided information on the use of sediment tracers of diverse types in water erosion studies (Figure 1). The great diversity suggests that none of them fulfill all of the requirements as an ideal tracer (Zhang et al., 2001). Iron oxides (magnetite, hematite and goethite) are solid pigments used for construction, and can be easily purchased at low cost. Guzmán et al. (2010) evaluated the suitability of tagging soil with magnetite in soils of different textural classes. They observed a slight increase in susceptibility in the smaller aggregates (< 63 μm), that was also correlated with higher clay contents. Guzmán et al. (2015) observed a decreasing tracer distribution with depth of the tagged soil profile. Both features have to be calibrated and considered when this technique is used in a specific experiment (e.g. Guzman et al., 2013, 2015). The potential of using magnetite as a tracer was also evaluated through simulated rainfall trials, obtaining a precision of approximately 0.5 kg m for sediment loss. This suggests its suitability for evaluating relatively large cumulative soil losses or in combination with other techniques. In a field experiment, Guzmán et al. (2013) applied magnetite at the plot scale to estimate soil losses and sediment sources in a rain-fed intensively-managed olive orchard, distinguishing erosion rates among tree rows (tr), inter tree rows (itr), and rills (r), (Figure 2). In a ridged system, origins of sediment and soil