Development of novel lanthanide based particle tracers for rapid monitoring of soil erosion.
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CRUICKSHANK, L. 2016. Development of novel lanthanide based particle tracers for rapid monitoring of soil erosion. Robert Gordon University, PhD thesis.
Soil erosion is a global problem, affecting much of the world’s agricultural land. As the world’s population increases, the pressures placed upon the land resource to provide space for food production, leisure, housing and industrial facilities also increases. Thus it is vital that the land resource is as productive as possible. As soil erosion is the major cause of soil degradation globally, it is vital that methods for accurately monitoring the degree of erosion from a site, and the effectiveness of any remediation attempts are available. Reported here is the development of a novel soil erosion particle tracer, based upon a lanthanide chelate complex doped silica particle. The luminescent lanthanide chelate complexes were comprised of 2-thenoyltrifluoroacetone (TTA) and 2-pyridinol-1-oxide (2PO) coordinated with either trivalent europium or terbium ions. These complexes were then doped into silica sol-gel particles using a core shell technique. This method resulted in the synthesis of two luminescent soil tracers, targeted to two of the key eroded soil fractions; fine silt (63-250 μm) and clay (< 1.2 μm). The behaviour of the tracers was analysed within three different soils obtained from the Glensaugh research station. They retained their luminescence when mixed with soil, and could be detected at concentrations of 10 mg tracer / kg soil using a standard benchtop fluorescence spectrometer (Perkin Elmer LS55B). Scanning electron micrographs indicated that the tracer particles interacted with the soil particles, whilst soil sedimentation experiments demonstrated that the tracer particles had a similar sedimentation pattern to natural soil particles. Soil microbial respiration studies were performed for the tracers and showed that the tracers did not significantly impact the soil microbial population. Studies of the luminescence stability of the tracer in soil over time showed that the tracer could be detected in the soil for one season (approximately 3 months). A prototype rainfall simulator, designed to simulate the kinetic energy of raindrops on the surface of the soil, was developed, and used during a series of rainfall simulation experiments. These simulations were performed at two different rainfall intensities (30 and 90 mm.h-1) and both of these conditions resulted in movement of the tracer particles within the plot. This movement was both horizontal, in overland flow over the plot surface, and vertical, through the plot. The pattern of tracer movement reflected that of the soil mass moved, and as such indicated that the tracers exhibited similar transport behaviour during the erosion simulations performed. These initial simulations demonstrated that the tracers can be detected at low concentrations within the soil using standard laboratory equipment, and that they move with the eroded soil particles during simulated soil erosion experiments. As such, these tracers are excellent candidates for further study in larger scale erosion events.