siltflux workshop 1: novel approaches to sediment tracing - john quinton

John Quinton

Lancaster Environment Centre

Lancaster University

NOVEL APPROACHES TO SEDIMENT TRACING

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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

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• 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