1.4.1. Environmental Magnetism: Sediment Source Tracing

Sophie C. Sherriff1,2 1 School of the Environment, University of Dundee, Dundee, DD1 4HN, Scotland ([email protected]) 2Johnstown Castle Environment Research Centre, Teagasc, Johnstown Castle, Wexford, Ireland

ABSTRACT: Environmental magnetism is a technique used to analyse the natural characteristics of materials. The mineral magnetic array exhibited by a sample e.g. a single rock-based or composite soil, sediment or core material, are differentiated according to the iron oxide assemblage. Such accumulations of iron oxides principally reflect the parent material characteristics, but also any subsequent environmental processes e.g. erosion, deposition, and biogenic processes. Consequently, environmental magnetism has been utilised in sediment source tracing investigations. Sediment accumulations in impacted locations, i.e. ‘targets’ such as rivers and lakes, are assumed to possess the characteristics of the soils within the contributing catchment area. Mineral magnetic measurements, including magnetic concentration, mineralogical composition and magnetic grain size, can therefore be used as sediment tracers to indicate subtle differences between potential source samples. The contribution of sources to the target is determined using multivariate statistical analysis or un-mixing models. The results of source tracing studies are essential to inform cost-effective management strategies targeted at reducing soil erosion and improving water quality.

KEYWORDS: environmental magnetism, remanence, susceptibility, sediment sources

Introduction magnetic fields, and this enables discrimination between contrasting sources Environmental magnetism utilises the mineral and processes. magnetic behaviour of a material to interpret the environmental processes acting upon it. The principles of environmental magnetism, The magnetic character is dependent upon initially introduced as a research area by the assemblage of minerals within a material. Thompson and Oldfield (1986), were founded Although all materials will respond to magnetic on rock magnetic techniques. Since then, the fields, iron oxides are particularly sensitive. approach has been applied to a variety of The near-universal occurrence of iron oxides applications (Table 1), including: estuarine in the environment e.g. haematite, magnetite and fluvial sediment source tracing and goethite, provides many opportunities to (Caitcheon, 1993; Jenkins et al., 2002); apply the technique. The assemblage of reconstruction of ice extent in glacial magnetic minerals is primarily dependent environments (Walden and Ballantyne, 2002); upon the parent material, specifically rock- climatic reconstruction of loess sequences formation, and any subsequent modification (Heller and Evans, 1995); reconstruction of due to geomorphic processes e.g. paleo-environmental geomorphology (Sun et transportation, deposition and post- al., 2011); classification of soils (Booth et al., depositional processes (Liu et al., 2012). Due 2005); and, pollution studies to identify spatial to the range of electron structures within patterns of vehicle pollution (Maher et al., different oxides, responses from each type will 2008). differ when exposed to externally applied

British Society for Geomorphology Geomorphological Techniques, Chap. 1.4, Sec. 1 (2014) Environmental Magnetism 2 Table 1: Summary of environmental containing iron or iron-based substances, e.g. magnetism studies for multiple applications iron-oxides and iron-sulphides. When exposed to a small magnetic field, the concentration of Application magnetic material termed the magnetic Glacial Nolan et al. (1999), Walden susceptibility (휒) is measured. Characteristics and Ballantyne (2002), of 휒 for different magnetic behaviours are Gurney and White (2005), summarised in Table 2, however, composite Ojala et al. (2011) samples such as soils and sediments will vary Palaeoclimatic Sagnotti et al. (1998), according to the constituent minerals (Hatfield Dearing et al. (2001), and Maher, 2008). Gathorne-Hardy et al. (2009), Bradák et al. (2011) On application of stronger magnetic field, Paleomagnetism Zijderveld et al. (1991), ferromagnetic minerals additionally respond Dupont-Nivet et al. (2002), such that they hold a permanent magnetic Lisé-Pronovost et al. (2009), moment or natural remanent magnetisation. A Sun et al. (2011) sample cannot return to the original pre-field Pollutants Maher et al. (2008), Blundell magnetisation measurement (Dekkers, 1997). et al. (2009), Zhang et al. As field strength increases, remanent (2008a), Wang (2013), magnetisation also increases until it reaches Crosby et al. (2014) ‘saturation’, i.e. the maximum magnetisation Sediment sources Caitcheon (1993), Foster and possible which is known as the Saturation Iso- Walling (1994), Caitcheon thermal Remanent Magnetisation (SIRM). (1998), Jenkins et al. (2002), Once the material reaches the saturation Hounslow and Morton (2004), Blake et al. (2006) magnetisation, an ‘in-field’ hysteresis loop (Figure 1) is established. To remove the Soil Maher (1998), Booth et al. remanence, de-magnetisation must be (2005), Neff et al. (2005), Hannam and Dearing (2008), conducted (Walden, 1999a). The magnetic Lourenço et al. (2014) field required to return a sample to full demagnetisation is defined as the coercivity.

Mineral magnetism provides great utility for techniques such as source tracing studies. Identification of sources of fluvial sediment is crucial to inform targeted and cost-effective soil and water quality mitigation programmes. Characteristics of sediments collected from a catchment outlet, e.g. lake or river, are compared to the soils within the contributing catchment area and the source provenance un- mixed. By determining the principal sources, these areas may be targeted for management. This chapter summarises the principles of magnetic behaviour and application of the technique to fluvial source tracing.

Mineral magnetism Three main types of magnetic behaviour exist; diamagnetism, paramagnetism and ferromagnetism (Smith, 1999). Diamagnetic minerals include those lacking in iron such as calcite, quartz and halite (Booth et al., 2005), Figure 1: Theoretical remanence acquisition organic substances and water (Maher et al., and hysteresis of a ferrimagnetic mineral 2009). Paramagnetic minerals, for example denoting key susceptibility and iso-thermal olivine, biotite and pyrite may contain iron in remanence terminology. (From Maher et al., their structures (Dearing, 1999). 2009). Ferromagnetic behaviour occurs in minerals

British Society for Geomorphology Geomorphological Techniques, Chap. 1.4, Sec. 1 (2014) 3 Sophie C. Sherriff

Table 2: Response of magnetic mineral sub-classes to susceptibility and remanence measurements. (Summarised from Dearing, 1999; and Smith, 1999).

Susceptibility Remanence (10-6 m3 kg-1) Diamagnetism Weak negative magnetisation No remanence (<0) Paramagnetism Weak positive magnetisation No remanence (0.01-1) Canted anti-ferromagnetism Moderate positive magnetisation Low fields: little or no remanent (magnetically hard) (0.27-1.19) magnetisation High fields: 300 mT required to obtain response Ferrimagnetism Strong positive magnetisation Remanent magnetisation (magnetically soft) (50-1116) exhibited at lower applied fields e.g. <100 mT Ferromagnetism Very strong positive Abundance limited in natural magnetisation samples (68850-276000)

The character of remanence acquisition in a Sediment source tracing is a ferromagnetic material alters according to the geomorphological technique to determine the mineralogy and the domain arrangement provenance of sediments within a catchment. within it. In general, magnetically ‘softer’ The method has been applied on a series of minerals known as ferrimagnets (e.g. scales, from catchments less than 15km2 magnetite) exhibit a large proportion of the (Gruszowski et al., 2003) to those greater than SIRM in lower applied fields. Magnetically 100,000 km2 (Maher et al., 2009). Sediment ‘harder’ materials known as canted anti- sources are determined according to their ferromagnets (e.g. haematite) require much particulate characteristics, therefore the range higher applied fields to achieve a substantial of parameters or ‘tracers’ measured by remanent response (Table 2). As such, mineral magnetics provides a suitable multiple fields of measurement are technique for source tracing. investigated to determine the mineralogical composition. A number of assumptions underlie sediment tracing techniques and must be considered: Magnetic domains or grain size additionally (1) a tracer must distinguish at least two affects remanence measurements. Five grain sources; (2) a tracer is transported with size classes are defined (from the finest): sediment and not altered by selective erosion; super-paramagnetic, viscous magnetism, (3) source properties are stable over time; stable single domain, pseudo-single domain, and, (4) no post-depositional tracer and multi-domain (Smith, 1999). For a single modification (Foster and Lees, 2000). mineral larger, multi-domain grains will respond to remanence measurements Desktop study differently to smaller, single domain grains which are more resistant to external current Source tracing programmes require sub- (Peters and Dekkers, 2003; Maher and division of a contributing catchment area into Thompson, 2009). Anhysteretic remanent definable and contrasting source areas. The magnetisation (ARM) is used to detect ultra- specific research hypothesis will dominate fine magnetic mineral grains (Banerjee et al., source area definition, e.g. to target sub- 1981) and has been utilised in multiple catchment basins, erosion processes or using investigations. a pilot study to determine appropriate source areas. In order to effectively sub-divide, it is Application of technique essential to understand the sources and generation of magnetic minerals in the Tracing sediment sources environment.

British Society for Geomorphology Geomorphological Techniques, Chap. 1.4, Sec. 1 (2014) Environmental Magnetism 4 Naturally, the variety of abundance and of the natural mineral magnetic signal. Non- characteristics of magnetic materials occurs metallic equipment must be used where due to the combined effect of parent materials possible, and where unavoidable, potentially and secondary processes. The formation of contaminated particles in contact with a crystals in igneous rocks is dependent on the metallic surface must be removed. Relevant speed of magma cooling, subsequently site specific information such as, in the case determining the exact components of metallic of soils, the sampled horizon, which may compounds. In metamorphic and sedimentary explain primary or secondary mineral forming rocks however, the materials available for processes, should be recorded in order to aid formation, in addition to the nature and later interpretation. Where surface intensity of formation, will determine the measurements are made with a field-sensor, magnetic character (Liu et al., 2012). high vegetation cover and soil moisture may Consequently, contrasting catchment geology cause fluctuations in results due to the will create a primary magnetic ‘imprint’. addition of diamagnetic materials. Source areas must be adequately sampled in order to fully determine the characteristics of each Field assessment area. Where intra- and inter- unit variability In some cases, parent signatures are overlap, the definitive capabilities of the final sufficient to distinguish between soil types or result are compromised (Lees, 1999). lithologies (Booth et al., 2005; Hatfield and Maher, 2008). However, a range of secondary Target sample collection for un-mixing is processes may affect the consistency of the dependent on the depositional environment. magnetic signature (e.g. ex-situ material Suspended sediments, river-bed, lake, delivery), bio-mineralisation, in-situ estuarine and sea-shelf deposits have all authigenesis, and anthropogenic additions been collected in source provenance studies (Thompson et al., 1980; Hilton et al., 1986; (Collins et al., 1998; Jenkins et al., 2002; Dekkers, 1997). Collins and Walling, 2007; Maher et al., 2009).

Bio-mineralisation, for example, occurs in Signature modification may also occur in the topsoils which enhance the fine ferrimagnetic post-depositional environment due to the concentration in water-logged soils or those bacterial formation of magnetite. Jelinowska et frequently exposed to wetting and drying al. (1997) discovered that bacteria in anoxic cycles (Maher and Taylor, 1988; Fassbinder lake sediments reduced iron-oxides such that et al., 1990). Burning of vegetation for the magnetic domains were irreversibly vegetation control or by wildfire increases the altered. Maher et al. (2009) used acid fine magnetic component in topsoils due to dissolution to remove secondary magnetic extreme soil temperature (Blake et al., 2006). material to expose particles within host grains Such secondary signatures modify the of target samples, i.e. the primary magnetic primary, parent material signature, providing signature for source tracing. Measurements either an opportunity to define a source performed on treated and un-treated samples according to such characteristics, or adding were found to be distinctly different, complication to source interpretations. supporting the concept that the impact of Additionally, small quantities of strong secondary magnetic processes is significant. magnetic material may overpower the signal of weaker minerals, in some cases this will Post-collection, samples must be made air- make the technique unsuitable for the tight and refrigerated to prevent biological particular study (Lees, 1999). It is therefore activity altering the mineral magnetic essential to complete a visual field composition. Depending on ambient assessment and a preliminary magnetic temperature during field sampling, it may be susceptibility study of the monitoring area, to sensible to store samples in a cool box to determine which areas may be dominated by prevent temperature related modifications of secondary magnetic processes (Lees, 1999). the magnetic signature.

Sample collection Sample preparation Collection of source samples must be Samples can be processed as a composite carefully conducted to prevent contamination sample or core. Where samples need to be

British Society for Geomorphology Geomorphological Techniques, Chap. 1.4, Sec. 1 (2014) 5 Sophie C. Sherriff dried: air-drying, freeze-drying, or oven drying Where sample quantity is limited, the sample below 40ºC is advised. Temperatures can be immobilised in cling film and packed exceeding this threshold may modify the using cotton wool. Some instruments cannot natural magnetic assemblage (Walden, accommodate sample lids and tape can be 1999b). Manual grinding is recommended as used to seal the pot. For core based samples, mechanical grinders pose greater risk of cross specific equipment attachments can be used contamination and mineral breakdown. Sink for magnetic susceptibility measurements or samples, particularly those in suspension non-metallic blades used to split cores into require freeze-drying, centrifuging or sub-sections. sedimentation methods to extract particulates for analysis. Where mass specific measurements are intended, each sample must be weighed and Particle size separation should also be recorded. Once the sample pot is filled and considered for target samples. Hatfield and clearly labelled, it is helpful to draw an axis Maher (2008) sub-divided suspended direction on each pot. This will aid Advanced sediment samples into four particle size Remanence Measurements (ARM) and Iso- classes (<2 µm, 2-8 µm, 8-31 µm, 31-63 µm) thermal Remanence (IRM) measurements to determine inconsistencies in magnetic which are made on, or reversed to, a single imprint. The 8-31 µm and 31-63 µm classes axis. were found to be most effective for source tracing, whereas <2 µm and 2-8 µm reflected post-depositional bacterial magnetite Measurement formation. Mineral magnetic measurements must be approached systematically with increasing The majority of magnetic analysis instruments, field strength (Figure 2). Units are generally (such as the MS2 laboratory sensor, pulse reported as volume specific magnetisation, magnetiser, and magnetometer) accept however conversion to mass specific samples in 10 cc sample pots. It should be measurements are beneficial for interpretation ensured that the sample completely fills the of results and comparison with the wider pot to prevent movement of particles during literature. analysis, which may produce spurious results.

Advanced Susceptibility Iso-thermal remanence Anhysteretic Remanence measurements 1. Low field remanence

2. High field e.g. increasing temperature, stability of remanence acquisition

Increasing strength of applied field

Figure 2: Schematic diagram showing order of magnetic measurements and relative field strength

Magnetic susceptibility 10-6 m3 kg-1 are converted, shown by Equation 1: Magnetic susceptibility meters (e.g. MS2/MS3 푀푎푠푠 푠푝푒푐푖푓푖푐 휅 ×10 Bartington Instruments Ltd shown in Figure 3) = (Eq. 1) are used to collect lab- and field- based 푠푢푠푐푒푝푡푖푏푖푙푡푖푦 푆푎푚푝푙푒 푚푎푠푠 susceptibility data. Magnetisation is reported Where the sample mass is in grams. The as volume specific (dimensionless κ), mass laboratory based sensor features both low- (휒 specific susceptibility, 휒 , in SI units of LF-0.465 kHz) and high- ( 휒 HF-4.65 kHz)

British Society for Geomorphology Geomorphological Techniques, Chap. 1.4, Sec. 1 (2014) Environmental Magnetism 6 susceptibility frequencies and two sensitivity Magnetic susceptibility equipment must be categories. The frequency dependent situated in a magnetically stable environment. susceptibility (%휒퐹퐷 ) is a ratio between 휒퐻퐹 Readings are sensitive, therefore, care must and 휒퐿퐹 measurements that reflects the super- be taken to remove metallic or electronic paramagnetic grain size component (Blundell components in the vicinity of the sensor. To et al., 2009) and is calculated by Equation 2: an extent, background interference can be accounted for by ‘zeroing’ the sensor before a χ −χ ( 퐿퐹 퐻퐹) × 100 (Eq.2) sample is measured and taking a subsequent χ퐿퐹 air-measurement to monitor and account for drift (Dearing, 1999).

Figure 3: Bartington MS3 magnetic susceptibility meter with attachments: a) laboratory sensor, b) surface sensor, c) core scanning sensor, d) core logging sensor, e) surface point probe (The images for b-e are taken from www.bartington.com).

Remanence acquisition Where sample weight is in grams and the mass specific magnetisation is reported in Isothermal remanence measurements are units of 10-5 Am2 kg-1. made using two instruments: (1) a magnetiser or electromagnet to apply a magnetic field; Measurement of multiple fields is and, (2) a magnetometer to measure the recommended between zero and SIRM, to intensity of magnetisation (Walden, 1999a). characterise the remanence acquisition curve. The SIRM is commonly defined as 1 Tesla. It The exact number is dependent upon study is sufficient to distinguish mineralogical requirements, access to facilities and time differences between soft and hard materials, (Walden, 1999a). These intermediate fields however, if full saturation of hard minerals is can be performed as forward or backward required, a larger field may be required. fields. Forward fields are repeated at Values are most commonly reported in 10-3 increasing strength from low (~20 mT) through Am-1. Conversion to mass specific medium (~100 mT) to high (~300 mT) denoted measurements uses Equation 3 below: as IRM20mT, IRM100mT and IRM300mT 푀푎푠푠 푠푝푒푐푖푓푖푐 푀푎𝑔푛푒푡𝑖푠푎푡𝑖표푛×1.29 respectively. = (Eq. 3) 푚푎푔푛푒푡푖푠푎푡푖표푛 푆푎푚푝푙푒 푤푒𝑖𝑔ℎ푡

British Society for Geomorphology Geomorphological Techniques, Chap. 1.4, Sec. 1 (2014) 7 Sophie C. Sherriff

Table 3: Summary of common interpretations of mineral magnetic parameters (Summarised from: Blake et al., 2006; Blundell et al., 2009; Booth et al., 2005; Dekkers, 1997; Liu et al., 2012; Maher, 1998; Maher and Taylor, 1988; Walden, 1999a; Walden and Ballantyne, 2002).

Parameter Description Examples

Concentration Magnetic susceptibility Concentration of magnetic material a,b,c,d,e,f Mass specific 휒 SIRM Concentration of remanence holding material a,b,c,d,e,f (ferromagnetic grains) Mass specific SIRM

Domain state Frequency dependent Proportion of super-paramagnetic magnetite a,b,d,f susceptibility %휒퐹퐷 Susceptibility of anhysteretic Ultra-fine magnetite particles near to the super- a,b,c,f remanence 휒퐴푅푀 paramagnetic/single domain boundary

휒퐴푅푀/푆퐼푅푀 Relative grain size of magnetite, high values suggest b,e,f superparamagnetic grains whereas low values indicate coarser multi domain minerals

휒퐴푅푀/휒퐿퐹 Stable single domain ferromagnetic grains- super b,f paramagnetic and fine viscous grains can affect parameter

Mineralogical composition Forward IRM fields Abundance of minerals capable of remanence b,c,f

Mass specific (IRMXmT) acquisition at the denoted field Low fields (<100 mT) magnetically ‘soft’ material High fields (>300 mT) magnetically ‘hard’ material IRM ratios (%) Percentage of SIRM acquired at the specified field. e Forward field/SIRM Large values at low fields indicate ‘soft’ minerals. Increases at higher fields indicated ‘hard’ minerals. Hard IRM (HIRM) Mass specific indication of hard magnetic minerals d

SIRM-IRM300mT Backfield ratios Demagnetisation of remanence, magnetically ‘soft’ a,d minerals demagnetise at low backfield fields, ‘hard’ minerals demagnetise at higher applied backfields S-ratio Ratio of saturated to non-saturated minerals at - b,d,f

IRM-100mT/SIRM 100mT. Range of values -1 to +1; values close to -1 are dominated by ‘soft’ minerals, higher values reflect an increasing ‘hard’ component.

SIRM/휒퐿퐹 Proportion of ferromagnetic material in a sample, b lower ratio suggests a greater proportion of diamagnetic and paramagnetic minerals

* Examples of application in source tracing studies: a. Russell et al. (2001); b. Jenkins et al. (2002); c. Hatfield and Maher (2008); d. Zhang et al. (2008b); e. Maher et al. (2009); f. Blake et al. (2006)

British Society for Geomorphology Geomorphological Techniques, Chap. 1.4, Sec. 1 (2014) Environmental Magnetism 8 Conversely, backfield remanent magnetism Case study can be investigated by initially imparting a forward saturating field to obtain the SIRM, Mineral magnetic source tracing was carried 2 and subsequent applications of fields in the out in a small (10 km ) intensively agricultural opposite direction, i.e. 180º of the primary axis fluvial catchment in Ireland. Potential source (Walden, 1999a). areas were selected due to their agricultural or non-agricultural significance, consequently Anhysteretic remanence uses a de- seven sources were sampled; field topsoils, magnetiser, with ARM attachment to impart field subsoils, on-farm tracks, road verges, the measurement and a magnetometer to channel banks, sub-surface drains outlets, determine the magnetisation intensity and open field drains. Channel bank, field (Walden, 1999a). Equation 3 is similarly used drain, track, drain outlet and road verge to determine the mass specific ARM (10-5 Am2 samples were taken using a plastic trowel to kg-1) and when normalised by the biasing field collect a surface scrape. Field topsoils used strength (A/m), is termed the anhysteretic an auger to consistently sample the top 5 cm 3 of soil and a second screw corer to sample at susceptibility (휒퐴푅푀) reported in m /kg. 40 cm for subsoil samples. Target samples The suite of parameters described can be were collected at the catchment outlet using measured quickly with little sample time integrated suspended sediment samplers preparation. The parameters measured, and (TISS) (Phillips et al., 2000), which were ratios between them, are used to interpret the emptied and re-installed at 6-12 week characteristics of each sample (Table 3). intervals.

Source samples were returned to the Statistical analysis laboratory and dried at <40ºC in plastic trays. Analysis methods vary from bi-plot and Once dried, samples were sieved to 125 µm multivariate techniques such as cluster, factor to replicate the particle size distribution of and principal components analysis to TISS samples. TISS samples were determine source area grouping (Booth et al., refrigerated for a minimum of three days to 2005; Hatfield and Maher, 2008). allow sedimentation of particles. Water was Contributions from source areas are siphoned without disturbing the deposited frequently determined using un-mixing models sediment. The remaining sediment and water (Collins et al., 1998; Franks and Rowan, mixture were dried at <40 ºC and manually 2000). Lees (1999) summarises statistical ground using a mortar and pestle once dry. techniques in source tracing exercises.

Figure 4: Principal components analysis of soil and sediment samples for source area ascription of the case study: a) score plot, and b) loading plot.

British Society for Geomorphology Geomorphological Techniques, Chap. 1.4, Sec. 1 (2014) 9 Sophie C. Sherriff All samples were weighed and packed into Earth Surface Processes and Landforms 31: plastic 10 cc pots either full of the sample, or 249-264. where quantities were low, immobilised in Blundell A, Dearing JA, Boyle JF, Hannam JA. cling film and cotton wool. Samples were 2009. Controlling factors for the spatial analysed for 휒 , 휒 휒 , SIRM, bIRM40mT, 퐿퐹 퐻퐹, 퐴푅푀 variability of soil magnetic susceptibility across bIRM100mT, and bIRM300mT. The parameters England and Wales. Earth Science Reviews 휒퐿퐹 , %휒퐹퐷 , 휒퐴푅푀, SIRM, SIRM/ 휒퐿퐹 , 95: 158-188. SIRM/ 휒퐴푅푀 , 휒퐴푅푀 / 휒퐿퐹 , bIRM40mT, bIRM300mT, S-ratio and HIRM were Booth CA, Fullen MA, Walden J, Smith JP, calculated and used for statistical analysis. Hallett MD, Harris J, Holland K. 2005. Magnetic Properties of Agricultural Topsoils of Multivariate analysis showed that the seven the Isle of Man: Their Characterization and source areas could not be satisfactorily Classification by Factor Analysis. distinguish and therefore three parent groups Communications in Soil Science and Plant were identified; fields (topsoil, subsoil and Analysis 36: 1241-1262. sub-surface drains), roads (road verges and Bradák B, Thamó-Bozsó E, Kovács J, Márton tracks) and channel (channel banks and open E, Csillag G, Horváth E. 2011. Characteristics drains). Multiple discriminant analysis showed of Pleistocene climate cycles identified in 96.3% discrimination capability with all eleven Cérna Valley loess–paleosol section tracers (SPSS v18). Principal components (Vértesacsa, Hungary). Quaternary analysis performed on JMP 9.0 showed that International 234: 86-97. the three parent source groups are well defined, and the loading diagram showing the Caitcheon GG. 1993. Sediment source tracing arrangement of parameters to produce the using environmental magnetism: A new score plot (Figure 4a). Target sink values approach with examples from Australia. were enclosed within the spatial limits of the Hydrological Processes 7: 349-358. source areas, indicating that post-depositional Caitcheon GG. 1998. The significance of or transportation effects were not apparent, or various sediment magnetic mineral fractions significant enough to affect sample for tracing sediment sources in Killimicat composition. We can therefore conclude that Creek. Catena 32: 131-142. suspended sediments are predominantly comprised of material from field and channel Collins AL, Walling DE. 2007. Sources of fine bank sources. sediment recovered from the channel bed of lowland groundwater-fed catchments in the UK. Geomorphology 88: 120-138. Acknowledgements Collins AL, Walling DE, Leeks GJL. 1998. Use This chapter was completed whilst funded by of composite fingerprints to determine the the Walsh Fellowship Programme, Teagasc. provenance of the contemporary suspended The author acknowledges the Walsh Fellow sediment load transported by rivers. Earth Overseas Travel Award for funding, and Dr Surface Processes and Landforms 23: 31-52. John Walden for hosting a placement at the Crosby CJ, Booth CA, Appasamy D, Fullen Environmental Magnetism Laboratory at the MA, Farr K. 2014. Mineral magnetic University of St Andrews. The author would measurements as a pollution proxy for canal also like to thank two anonymous reviewers sediments (Birmingham Canal Navigation whose comments helped to improve the Main Line) Environmental Technology (United article. Kingdom) 35: 432-445.

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