High precision tracing of soil and sediment movement using fluorescent tracers at hillslope scale

Abstract

Generating high resolution spatial information on the movement of sediment in response to soil erosion remains a major research challenge. In this paper we present a new tracing method that utilises LED (light emitting diode) light to induce fluorescence in a sand-sized tracer, which is then detected using a complementary metal oxide semiconductor (CMOS) sensor in a commercial digital camera, at mm-resolution without the need for removal of soil material. First, we detail two complementary, but independent, methods for quantifying the concentration of tracer from images: particle counting and an intensity based method. We show that both methods can produce highly resolved estimates of particle concentrations under laboratory conditions. Secondly, we demonstrate the power of the method for collecting spatial information on soil redistribution by tillage, with mm precision, over an approximately 50 m hillslope and vertically down the soil profile. Our work demonstrates the potential to collect quantitative time-resolved data about soil movement without disturbing the soil surface which is being studied, and with it the possibility to parameterise or evaluate dynamic distributed soil erosion models or to undertake fundamental research focussed on particle movement that has been impossible to conduct previously.