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John Quinton
Lancaster Environment Centre
Lancaster University
NOVEL APPROACHES TO SEDIMENT TRACING
Environment Centre
Environment Centre
ACKNOWLEDGEMENTS
• Jack Poleykett and Rob Hardy
• Alona Armstrong, Mike Coogan, Barbara Maher, Jackie Pates (Lancaster University) and Kevin Black (Partrac Ltd) Debbie Hurst (confocal microscopy), Mike James (image analysis).
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Clay work funded by NERC Grant: NE/J017795/1
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BACKGROUND
• Working on diffuse pollution and erosion for 25 years
• Modelling processes
• Practical mitigation measures
• Our ability to conceptualise processes runs ahead of our ability to measure them
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PARTICLE TRACKING (SEDIMENT TRACING)
• Our aim
• To develop methologies and methods to determine the source-sink relationships (transport pathways), the depositional footprint and rates of sediment transport through the environment.
• How?
• Using natural and artificial sediment that has been ‘tagged’ or ‘marked’ with an identifiable signature. These are called tracers
Images courtesy, Partrac Ltd
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SEDIMENT TRACING
• Why would it be useful to have a sediment tracer?
• Improve the understanding of transport processes
• Evaluate in - field mitigation techniques
• Develop and validate soil erosion and transport models
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Bind to everything
Adding radiation to
environment is
unethical
Density metal ≠ density clay
Not that rare
ICP-MS £15 per sample Density plastic ≠ density clay
Soil is also fluorescent at
similar wavelength
Radionuclides i.e. 137Cs
What's been tried Rare Earths Fluorescent microspheres
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TO TALK ABOUT
• Sediment fingerprinting
• Fallout and cosmogenic radionuclide
• Caffeine or plant molecules
• C14
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• Focus on two tracers
• Commercial dual signature tracer for particles >20 μm
• Development of new fluorescent tracer for particles <20 μm
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• To assess the properties and behaviour of the tracer
• To assess the potential of conducting non-intrusive mapping of the spatial distribution of dual signature tracer particles
COMMERCIAL DUAL SIGNATURE TRACER
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THE TRACER
Photomicrograph
Magnet saturated with tracer
particles
Images courtesy, Partrac Ltd
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LAB EXPERIMENT
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HOW SIMILAR ARE THE SOIL AND TRACER PROPERTIES?
98
%
1.2
%
0.3
%
0.3
%
0.2
%
< 63 125 250 500 1000
Outdoor simulations: particle size distribution ( % ) of the native soil
Particle density ( kg/m3 ± 115 kg/m3 ) - Percentage difference ranged from 3 – 6 %
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HOW DOES THE TRACER BEHAVE? AND,
HOW EFFECTIVELY CAN IT BE TRACKED?
)
Location of the Core
sample
Run-off collection
Tracer deployment
zone
A schematic diagram of the soil box sampling design
25 cm
12.5 cm
Simulated rainfall
Rate - 31 mm h–1
Slope - 10 %
O.3 % Section 1
Section 3
Section 4
Section 5
18 %
0.9 %
0.6 %
0.5 %
Section 2
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• Winton Hill - Sandy loam
• Myerscough – silt loam
• Hazelrigg – Clay loam
HOW MUCH TRACER WAS RECOVERED FROM THE RUN-OFF?
The mean percentage (%) mass recovered from the collected run-off from the three soils following the
deployment of different tracer size fractions.
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A plot of the dry tracer mass (g) recovered from a shallow core Vs the low frequency magnetic
susceptibility of the core captured from the surface.
Can the spatial distribution of the tracer
particles be mapped using magnetic
susceptibility (KLF) ?
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FLUORESCENCE IDENTIFICATION AND PHOTOGRAPHY
Mapping of the spatial distribution of tracer particles following an overland flow event (8 L p/min) using
photography under blue light ( ̴ 395 nm) illumination.
Erosion plot Pre – event Post event
2.75 m
0.5 m
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25 cm
25 cm
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CONCLUSION
‘Dual signature’ tracer provides a particulate tracer that:
• Mimics the particle size and density of the native soil
• Can be effectively deployed, monitored and recovered over
significant temporal and spatial scales
• Enables semi-quantitative spatial mapping of the distribution of
tracer particles and quantitative determination of tracer mass
BUT NO GOOD FOR THE CLAY FRACTION
Environment Centre
• No commercial tracers with same properties
• Some attemps with paraquat and long chain organic molecules but expensive and disruptive
• Use of surrogates e.g. fluorescent microspheres
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To create a fluorescent clay tracer which we could track in real time through a rain storm
AIM
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LABELLING CLAY
+
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THE RESULT
Before After
Average size = 1.9
microns
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LIGHTING IT UP RAINFALL
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ACQUIRING IMAGES
Soil box
DSLR
camera
570 nm
long pass
filter Camera
settings
~6 second
exposure
F-stop 1.8
15M
RAW + JPEG
50mm fixed
focus lens
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0 Seconds 262 Seconds 2252 Seconds
True colour images
from camera
False
colour
images
created
using [r]
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Data processed on a pixel by pixel basis using [r]
Black = Lower
tracer front
Red= Upper
tracer front
HIGH RESOLUTION DATA Bottom of
soil box
Top of
soil box
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Blue = RHS of soil box
Red = LHS of soil box Edges of
soil box
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CONVERSION IN TIME LAPSE FILM
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• Novel tracer
• High tracer/clay similarity
• Cheap and easy to synthesize
• Real time recording of data
• Rapid data processing using [r]
• No need to remove material when sampling
• Quick and cheap
MAJOR ADVANTAGES
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• Non-disruptive quantification of the tracers
• In lab and in field
• Applications to erosion monitoring
• Development of new clay tracers
NEXT STEPS