The development of dual signature, fluorescent magnetic sediment tracing technology

The erosion, transport and deposition of sediment create environmental problems and social issues worldwide. Due to these ecological, environmental and economic implications for society, the importance of protecting and managing the sediment and soil resource is increasingly recognised through legislation and government policy. These legislative drivers have inspired the development of new and innovative approaches towards applied sediment management research, to develop effective erosion and pollution control strategies and improve the understanding of sediment transport processes to inform management decisions. To implement real change and inspire a holistic view of coastal and catchment management, of which sediment is critical, it is necessary to fully understand how sediments, contaminants and microbes move around the planet and the environmental impact that this constant flux of material has on the wider environment and on specific ecosystems. As sediment and soil are a fundamental resource for humans appropriate management of these resources requires a full understanding of these issues. Crucial to this is the use of direct field techniques, practically able to identify the sediment sources, transport pathways and sink areas of different soil and sediment types. Active sediment tracing is a field technique which uses materials designed to replicate the movement of sediment, whilst remaining identifiable within the native sediment load. Active sediment tracing techniques have been developed over the last century, yet despite extensive study, the ‘perfect’ sediment tracer and field methodology remains elusive. Sediment tracing provides a unique applied sediment and soil research and management tool able to provide information which can be used to protect ecological habitats, inform sediment and soil management, and provide information and quantitative data to improve environmental modelling approaches. The development of a robust tool able to provide direct field information regarding sediment transport dynamics is important as sediment flux and deposited sediments and the associated contaminants and microbes negatively impact the environment and society as a whole. The development of informed management strategies is therefore crucial to maintain the sediment and soil resource for future generations. Sediment tracing methodologies and tracer design has progressed significantly in the last century recovering from significant setbacks (i.e. the environmental ban on the use of irradiated grains) and fluctuations in popularity due to the somewhat resource intensive nature of a sediment tracing study. Recent technological developments have reinvigorated the technique and led to original application and commercial enterprise within the sector. A variety of sediment tracers are now available. Each tracer material has unique benefits and limitations. The search for the ‘perfect’ sediment tracer is ongoing. Here the evaluation and application of a novel dual signature sediment tracer are described. The tracer has two signatures: fluorescence and ferrimagnetism which is considered an advance on previously used mono-signature tracers. The tracer provided unique opportunities to employ a variety of techniques to monitor tracer within, and recover tracer from the environment. These techniques were applied within an informed methodological framework developed to provide consistency of methodological approach within all active sediment tracing studies across disciplines. The framework provides a clear and robust step by step guide to conducting a sediment tracing study. Further it has outlined a range of techniques useful to practitioners with a focus on the practical application of the technique to the field. Field trials were conducted to investigate real world sediment management problems, these being: soil erosion within an agricultural field; sand transport on a beach within a complex anthropogenically affected environment; and, the release of fine material as part of nearshore dredging activities. The soil erosion study showed the tracer had the potential to be applied to trace multiple size classes and different soil types and explored the potential use of both passive and active sampling techniques to determine a soil erosion rate. The results indicated that the dual-signature tracer was an effective tracer of soil and showed strong potential as an applied soil management research tool. The beach face study demonstrated the utility of sediment tracing within the sediment and coastal management arena and again explored the use of passive and active sediment tracing approaches to optimise sediment monitoring and recovery from the field. The field trials successfully delineated the sediment transport pathways on the beach face in a complex environment. The study of the dispersion of fine material in the nearshore coastal zone demonstrated the critical role of tide and current in the near and far field transport of disposed dredged sediment. The spatiotemporal distribution and sedimentation pattern of the discharged particles was mapped over a tidal scale to determine the immediate, near and far field impact of disposed dredge material. The results highlighted the potential for significant redistribution of fine sediment through the nearshore coastal zone, with potentially significant environmental impacts. These three distinct field trials provide highlights the utility of active sediment tracing studies to further our understanding of sediment transport within different environments. These data are useful to manage and mitigate the associated impacts of eroded and transported sediment on the environment. The dual signature tracer was found to be an improvement over previously used, mono-signature tracers. Throughout laboratory testing and field trials the tracer upheld the key fundamental assumptions of an active sediment tracer. The tracer imitated the hydraulic properties of natural sediments, whilst not disrupting the transport system and remaining identifiable within the native sediment load. For each field application a practical, multifaceted, sampling approach was developed which increased the quantity and quality of information garnered from each tracing study: an advance since sediment tracing studies fundamentally comprise an empirical evidence-based approach. Further, the development of an analytical procedure which reduced timescales and associated costs, has improved the benefit-cost ratio of an active sediment tracing study. Continued development of the active tracing methodology can increase and enhance application of these techniques in both conventional and novel contexts. This thesis has provided baseline data for future studies utilising dual-signature tracer within laboratory or field research, or industry based studies.