Preliminary experiments to assess the effectiveness of magnetite powder as an erosion tracer on the Loess Plateau

Abstract

Soil water erosion monitoring is essential for long-term soil conservation and ecological restoration on the Loess Plateau region of China. Traditional approaches, such as runoff plots and water weirs in a watershed, provide reliable spatially averaged soil erosion data but cannot validate process-based erosion prediction models for dynamic soil erosion evaluation. Erosion tracer techniques are capable of quantitatively determining spatial distribution of soil erosion. Ideal tracers are expected to provide highly contrasting values compared with background ones, and be analyzed efficiently and acquired cost-effectively. In this laboratory study, magnetite powder was selected as an erosion tracer to test. The tracer was implanted into loessial soils from the Loess Plateau using a wet soil-tracer mixing procedure. The effectiveness of magnetite powder as an erosion tracer was evaluated in aspects of basic magnetic features between the tracer and soils, distribution under different soil aggregate sizes, mobility along soil profiles, and detachment of tracer-labeled loessial soils by shallow surface flow along a slope. Results showed that magnetite powder was bound tightly to loessial soil aggregates, with no noticeable vertical mobility under long-term leaching conditions, and almost synchronous detachment with the eroded soils. Furthermore, the tracer is an inexpensive tracer (approximately 0.08 US$·kg−1), which has higher magnetic susceptibility over two or three orders of magnitude than ordinary soils and high sensitivity of analysis (<1% measuring error). It can also provide quick measurement (<15s) with equipment expenditure at relatively low price (approximately 5000 US$). The work demonstrates that magnetite powder as a promising erosion tracer will be great potential on the Loess Plateau region. Effectiveness of the magnetite powder tracer under simulated and natural rainfall conditions in this region still need to be testified in the future studies.