Out of the darkness and into the light : the quest for fluorescence-based soil tracers

Hardy, Robert and Quinton, John (2016) Out of the darkness and into the light : the quest for fluorescence-based soil tracers. PhD thesis, Lancaster University.

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Abstract

This thesis explores the use of fluorescent tracers to monitor the redistribution of soil at high temporal and spatial resolutions. Soil redistribution happens on a second by second basis with individual particles moving millimetres at a time. There are few, if any, existing tracing methods which permit the monitoring of soil movements at temporal and spatial scales that are commensurate with the scales at which these movements happen. This thesis charts the development of new tracing technologies that allow for the movement of soil to be monitored at high spatial and temporal resolution, resolutions which are commensurate with the movement of individual particles. This will allow for deeper insight into how soil moves and has a range of applications for fundamental soil movement studies to applied agricultural investigations. In order to study the movement of clay a novel fluorescent clay tracer was created along with fluorescent imaging techniques which allowed for the movement of this tracer to be captured. The movement of larger soil particles is also important and by using a commercially available fluorescent tracer combined with fluorescent videography it was possible to track the movement of individual soil particles across a soil surface during a simulated rainfall event. The movement of these particles was captured 50 times a second with sub-mm precision. A similar system was then developed for use in the field environment and was demonstrated at field scale by monitoring the redistribution of a tracer across a soil surface as a result of tillage. It was also possible to monitor the vertical redistribution of the tracer within the soil profile by digging soil pits. The methods detailed here show that it is possible to gain much information about the redistribution (i.e. change in location) of soil across a soil surface without the inconvenience, expense and system perturbation that is caused by traditional sampling. Overall these methods demonstrate that it is possible for soil tracing to operate in a data rich environment providing new opportunities to develop, parameterise and evaluate soil movement models.