Source Ascription Research Articles

Combining sediment fingerprinting and hydro-sedimentary monitoring to assess suspended sediment provenance in a mid-mountainous Mediterranean catchment

Soil erosion and sediment transport are controlled by complex factors promoting variable responses in catchment's erosion rates and sediment yields. To mitigate eventual negative effects derived from altered fluxes, integrated catchment management plans should assess the sediment cascade from upstream erosive processes, sediment mobilization through hillslopes and within the channel, up to downstream sediment yields. This study links hydro-sedimentary dynamics with sediment fingerprinting source ascription in a mid-mountainous Mediterranean catchment during five hydrological years (2013–2018). Soil colour parameters and fallout radionuclides were used as tracers to predict dominant suspended sediment sources using (i) a Bayesian mixing model (MixSIAR) and (ii) an End Member Mixing Analysis (EMMA). MixSIAR suggested that crops were the dominant source in most of the collected samples. EMMA showed similar results, clustering all except one sediment samples close to the crop and channel bank signatures. In addition, a quantitative hysteresis index was calculated and floods were clustered in function of their hydro-sedimentary characteristics. Despite different patterns were associated to each of the four identified clusters (e.g. different sediment loads and maximum suspended sediment concentrations), correlation between sediment origin and hydro-sedimentary variables was not significant due to the little seasonal variation in source type ascription.

Analysis of post-fire suspended sediment sources by using colour parameters

After a wildfire, total or partial removal of vegetal biomass and changes in physicochemical soil properties lead to an increase in overland flow and sediment yield. Eventual damage must be counteracted urgently by identifying erosion hotspots and by implementing post-fire management programmes and sampling campaigns. In this context, the sediment source fingerprinting technique is widely used to determine the origin of suspended sediments in catchments and to evaluate the effectiveness of sediment management programmes. It traditionally relies on the use of physical, biochemical and geochemical properties as tracers. However, measuring these tracers in the laboratory is often expensive and time-consuming. Colour tracers have been shown to greatly reduce time and cost, especially if a normal office scanner is used for measurements. Here we explored whether colour parameters can be used to investigate suspended sediment origin in burned catchments. To this end, sediment and ash were mixed artificially to verify colour linear additivity and ash influence on colour parameters. Colour parameters were then used for source ascription of suspended sediment samples (n = 9) collected during two years after a fire in a small Mediterranean catchment (Mallorca, Spain). In addition, reflectance-derived colour parameters were compared with those obtained using a normal office scanner. The close correlation between most chromatic indexes (obtained using both methods; p < 0.01) suggested that scanning is a good alternative for measuring soil and sediment colour. A Bayesian tracer mixing model (MixSIAR) determined the relative contribution of each source. The type of mixing model enables appropriate representation of natural and sampling uncertainty in tracer data. During the first events, suspended sediment originated mainly in burned surfaces, whereas the contribution of these decreased throughout the study period. Tracing results obtained using colour parameters were compared with calculations using 137Cs and 210Pbex, as recognized tracers to discriminate between surface and subsurface sediment sources after wildfires. Estimated source ascriptions with both methods (i.e. reflectance-derived colour parameters and radionuclides) coincided in predicting the dominant source in 7 of the 9 samples measured. Colour tracers proved useful in discriminating between burned and unburned sources, making them suitable for suspended sediment source ascription and monitoring as part of post-fire management strategies.

COUPLING LITHIC SOURCING WITH LEAST COST PATH ANALYSIS TO MODEL PALEOINDIAN PATHWAYS IN NORTHEASTERN NORTH AMERICA

Projections of Paleoindian range mobility in the late Pleistocene are typically inferred from straight-line distances between toolstone sources and sites where artifacts of these raw materials have been found. Often, however, these sourcing assessments are not based on geologic analysis, raising the issue of correct source ascription. If sites of similar age can be linked to a toolstone source through geologic study, and direct procurement of toolstone can be inferred, geographic information systems (GIS) modeling of travel routes between the source and those sites can reveal route segments of annual rounds and aspects of landscape use. In the Hudson Valley of eastern New York, Paleoindian peoples exploited Normanskill chert outcrops for toolstone during the late Pleistocene. Here, we combine X-ray fluorescence sourcing results that link Normanskill chert artifacts at Paleoindian sites to the West Athens Hill source outcrop in the Hudson Valley with GIS least cost path analysis to model seasonal pathways of late Pleistocene peoples in northeastern North America.

Source ascription in bed sediments of a Mediterranean temporary stream after the first post-fire flush

First flushes can be crucial to sediment transport in fluvial systems of drylands, as temporary streams are a characteristic feature of Mediterranean basins. After a wildfire, storm flows may enhance runoff delivery to channels, so increasing the first-flush effect. 137Cs and 210Pbex were used as tracers for recognizing the first post-fire flush effect on the source ascription of bed sediments temporarily stored in a Mediterranean temporary stream severely affected by a wildfire. Thirty sediment source samples were collected along one of the tributaries of a catchment (4.8 km2) located in Mallorca during a field campaign some weeks after the wildfire. The sample collection took into account effects of the wildfire and distinguished between soil surface and channel bank. To measure the source contribution temporarily stored with the bed sediment, five sediment samples—deposited during the first storm, occurring 3 months after the wildfire—were collected from the bed of the main channel. The 137Cs and 210Pbex concentrations were measured by gamma spectrometry. Then, a linear mixing model was used to establish the contribution of each source type to the bed sediments along the main stream. First post-fire flush effect was generated by a torrential event with a suspended sediment concentration peak of 33,618 mg L−1, although transmission losses under a very low runoff coefficient (1%) promoted sediment deposition. Significant differences were observed in fallout radionuclide concentrations between burned surface soil and burned channel bank samples (p 0.05). Source ascription in bed sediments upstream shows that 67% was generated from burned hillslopes, reaching 75% in the downstream part, because downstream propagation of the sediment derived from the burned area. Bed sediments were mostly generated on burned surface soils because of the fire’s effect on soil and sediment availability, high-intensity rainfall, and the limited contribution of channel banks, because these are fixed by dry-stone walls. This hydro-sedimentary response indicates an association between these factors driving erosion and sediment delivery, generating effective slope-to-channel sediment connectivity. The integration of the short-term response with the medium- and long-term analysis will allow for the analysis of the evolution of catchment sediment sources in future studies, determining if fire modifies the catchment sensitivity to that specific disturbance.

Magnetic susceptibility as a simple tracer for fluvial sediment source ascription during storm events

Sediment tracing using a single tracer, low frequency magnetic susceptibility (Xlf), was used to apportion suspended sediment to geologically defined source areas and to interpret sediment source changes during flood events in the degraded catchment of the Vuvu River, a headwater tributary of the Mzimbubu River, South Africa. The method was tested as a simple tool for use by catchment managers concerned with controlling erosion. The geology of the 58 km2 catchment comprises two distinct formations: basalt in the upper catchment with a characteristically high magnetic susceptibility and shales with a low magnetic susceptibility in the lower catchment. Application of an unmixing model incorporating a Monte Carlo uncertainty analysis showed that Xlf provided a means to assign the proportion of each geological province contributing to the river's sediment load. Grab water samples were collected at ten-minute intervals during flood events for subsequent analysis of suspended sediment concentration and the magnetic susceptibility of the filtered sediment. Two floods are presented in detail, the first represents a significant event at the start of the wet season (max. discharge 32 m3 s−1); the second was a smaller flood (max discharge 14 m3 s−1) that occurred a month later. Suspended sediment concentrations during the twelve monitored events showed a characteristic decline over the wet season. The main source of suspended sediment was shown to be from the mudstones in the lower catchment, which contributed 86% of the total measured load. The sediment dynamics during the two floods monitored in detail were quite different from each other. In the first the sediment concentration was high (11 g L−1), peaking after the flood peak. The Xlf value increased during the event, indicating that contribution to the sediment load from basalt in the upper catchment increased during the recession limb. In the second, smaller flood the sediment peak (6 g L−1) coincided with the flood peak. Low Xlf values indicated that mudstones in the lower catchment soils dominated the sediment load throughout the entire event. Sediment tracing using a single property (Xlf) was thus used effectively to study changing sediment sources both between and during a flood event in a catchment with strongly contrasting magnetic signatures in different areas. The results support the use of magnetic susceptibility as a simple and cheap tool to determine sediment provenance that can be used to guide catchment restoration in similar environments.

Selecting Color-based Tracers and Classifying Sediment Sources in the Assessment of Sediment Dynamics Using Sediment Source Fingerprinting.

The use of sediment color as a fingerprint property to determine sediment sources is an emerging technique that can provide a rapid and inexpensive means of investigating sediment sources. The present study aims to test the feasibility of color fingerprint properties to apportion sediment sources within the South Tobacco Creek Watershed (74 km) in Manitoba, Canada. Suspended sediment from 2009 to 2011 at six monitoring stations and potential source samples along the main stem of the creek were collected. Reflectance spectra of sediments and source materials were quantified using a diffuse reflectance spectrometry, and 16 color coefficients were derived from several color space models. Canonical discriminant analysis was used to reclassify and downsize sediment source groups. After the linear additive test and stepwise discriminant function analysis, four color coefficients were chosen to fit the Stable Isotope Analysis in R model. Consistent with the conventional fingerprinting approach, the color fingerprint results demonstrated a switch in the dominant sediment source between the headwaters and the outlet of the watershed, with the main sources being topsoil in the upper reaches, whereas outcrop shale and stream bank materials dominated in the lower reaches. The color fingerprinting approach can be integrated with conventional fingerprints (e.g., geochemical and fallout radionuclide properties) to improve source discrimination, which is a key component for source ascription modeling. We concluded that the use of color fingerprints is a promising, cost-effective technique for sediment source fingerprinting.

Combining visible-based-color parameters and geochemical tracers to improve sediment source discrimination and apportionment

Parameter selection in fingerprinting studies are often time-consuming and costly because successful fingerprint properties are generally highly site-specific. Recently, spectroscopy has been applied to trace sediment origin as a rapid, less expensive, non-destructive and straightforward alternative. We show in this study the first attempt to combine both geochemical tracers and color parameters derived from the visible (VIS) spectrum in a single estimate of sediment source contribution. Moreover, we compared the discrimination power and source apportionment using VIS-based-color parameters and using the whole ultra-violet–visible (UV–VIS) spectrum in partial last square regression (PLSR) models. This study was carried out in a small (1.19km2) rural catchment from southern Brazil. The sediment sources evaluated were crop fields, unpaved roads, and stream channels. Color parameters were only able to discriminate unpaved roads from the other sources, disabling its use to fingerprint sediment sources itself. Nonetheless, there was a great improvement in source discrimination combining geochemical tracers and color parameters. Unlike VIS-based-color parameters, the distances between sediment sources were always significantly different using the whole UV–VIS-spectrum. It indicates a loss of information and, consequently, loss of discriminating power when using VIS-based-color parameters instead of the whole UV–VIS spectrum. Overall, there was good agreement in source ascription obtained with geochemical tracers alone, geochemical tracers coupled with color parameters, and UV–VIS-PLSR models, and all of them indicate clearly that the main sediment source was the crop fields, corresponding to 57±14, 48±13, and 62±18%, respectively. Prediction errors for UV–VIS-PLSR models (6.6±1.1%) were very similar to those generated in a mixed linear model using geochemical tracers alone (6.4±3.6%), but the combination of color parameters and geochemical tracers decreases the prediction error (5.4±2.0%). Therefore, the use of VIS-based-color parameters combined to geochemical tracers can be a rapid and inexpensive way to improve source discrimination and precision of sediment source apportionment.

Tracing sediment sources in a subtropical rural catchment of southern Brazil by using geochemical tracers and near-infrared spectroscopy

Conventional fingerprinting methods based on geochemical composition still require a time-consuming and critical preliminary sample preparation. Thus, fingerprinting characteristics that can be measured in a rapid and cheap way requiring a minimal sample preparation, such as spectroscopy methods, can be a good choice for this purpose. The present study aimed to evaluate the sediment sources contribution in a rural catchment by using conventional method based on geochemical composition and an alternative method based on near-infrared diffuse reflectance (NIR) spectroscopy. This study was carried out in a rural catchment with an area of 1.19km2 located in southern Brazil. The sediment sources evaluated were crop fields, unpaved roads and stream channels. Twenty nine suspended sediment samples were collected from nine significant storm runoff events between October 2009 and July 2011. NIR spectra of the sources and the suspended sediment samples were very similar. Nevertheless, the alternative method used to trace suspended sediment based on NIR spectroscopy was sensitive enough to detect differences in mineralogical composition of the sources materials, which were confirmed by X-ray diffraction analyses. Both conventional and alternative methods were able to discriminate the sediment sources and, despite the lack of correlation between the two methods, provided very close source ascription. The differences in the final results obtained by conventional and alternative methods are due to the nature of the variables used in each case, which are not mandatorily correlated. Efforts should be taken to try to combine both geochemical composition and near-infrared spectroscopy information on a single estimative of the sediment sources contribution in order to provide results with an even higher accuracy.

CHANGING SEDIMENT YIELD AND SEDIMENT DYNAMICS IN THE KAROO UPLANDS, SOUTH AFRICA; POST‐EUROPEAN IMPACTS

ABSTRACTWe provide an overview of published results and a significant body of new data from an ongoing research programme designed to reconstruct sediment yields and sources in small (&lt;60 km2) catchments in the Eastern Cape, South Africa over the last 150 years. Our analysis of four catchments has determined that sediment yield increased significantly in the latter half of the 20th century but that the exact timing of these increases was different in each of the four catchments. In two high altitude locations, sediment yield increases were not associated with a significant change in sediment source although, in one case, areas of former cultivation appear to have made a slightly greater contribution since the 1960s. In a third catchment, increases in sediment yield appear to have been driven by the development of badlands and by an increase in connectivity between the badlands and the main channel network in the 1960s. In the fourth catchment, increased connectivity between the main catchment and dam occurred as a result of the construction of a causeway to carry a main road and by the construction of culverts beneath the road. Occasional changes in sediment source have also been identified in the sedimentary record, but these were not linked directly to road construction. Research to date shows the complexity of sediment delivery in these semi‐arid catchment systems and emphasises the need to combine sediment yield with source ascription to better understand the dynamics of these systems. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Why Does the Plague of Darkness Last for Three Days? Source Ascription and Literary Motif in Exodus 10:21-23, 27

Abstract This article addresses the question of source ascription for the plague of darkness in Exod 10:21-23, 27. It argues that attention to the specific content of this episode, and especially its indication of a three-day duration for the darkness, ties it to Exod 6:9-12, Moses’s initial interaction with the Israelites in the pentateuchal Priestly source (P). Beyond style or form, the darkness plague plays an essential role in the Priestly plot and for this reason may be confidently assigned to P.

Apportioning catchment scale sediment sources using a modified composite fingerprinting technique incorporating property weightings and prior information

Sediment fingerprinting techniques provide a means of assembling valuable reliable information on the principal sources of sediment problems at catchment scale. However, there is a need to refine existing approaches to take account of a variety of sources of uncertainty and to incorporate prior information. To address this need, a modified mass balance model incorporating a Monte Carlo approach for representing the uncertainty surrounding source and sediment sampling, as well as weightings to take account of the within-source variability and discriminatory power of individual tracer properties and prior information on bank erosion, was used to apportion recent sediment sources in sub-catchments of the Somerset Levels, south west UK. Sensitivity tests confirmed that the precision of source apportionment was improved by incorporating the weightings and prior information into the mixing model. Estimates of the overall mean contributions from individual source types, bounded by 95% confidence limits, were assessed to be 42 ± 2% (pasture topsoils), 22 ± 2% (cultivated topsoils), 22 ± 1% (channel banks/subsurface sources), 12 ± 2% (damaged road verges) and 2 ± 1% (STWs). Respective estimates of net sediment delivery to watercourses, provided by integrating the source ascription results with estimated sediment yield ranges and sub-catchment or land use areas, ranged between 33–829 kg ha − 1 yr − 1 , 30–1995 kg ha − 1 yr − 1 , 2–315 kg ha − 1 yr − 1 , 0–217 kg ha − 1 yr − 1 , and 0–28 kg ha − 1 yr − 1 . Sediment fingerprinting should always include uncertainty analysis but on the understanding that the latter will be conditional on the assumptions used.

Spatio-temporal patterns in obsidian consumption in the Southern Nasca Region, Peru

Geochemical data from 426 obsidian artifacts collected from a range of sites in the Southern Nasca Region (SNR), Peru highlight spatial and diachronic patterns in obsidian consumption. We compare source ascription data against different models of obsidian acquisition, and find that, for the most part, people adhered to a simple economic model where the most proximate source was exclusively used. Slight departures from this model during the Archaic, Early Nasca, and Tiza periods suggest obsidian was in some cases acquired through alternative means. For the Archaic period we attribute this to higher degrees of mobility where obsidian acquisition was embedded within other activities. For the Early Nasca and Tiza periods we attribute this to the development of alternative exchange relations within the south-central Peruvian region. We also examine differences in obsidian acquisition across SNR river valleys and by elevation, with greater source diversity occurring in the central valleys and at lower elevations.

The identification of sediment sources in a small urban watershed in southern Brazil: An application of sediment fingerprinting

Soil particles eroded from the land surface and transported into rivers by runoff are considered one of the main components of non‐point source pollution in urban watersheds. These particles also serve as a vector for a wide variety of both organic and inorganic constituents. As a result, the identification of sediment sources in an urban watershed is necessary not only to understand erosion dynamics, but also to help implement more effective measures to control and/or remediate non‐point source pollution. The present study employs sediment ‘fingerprinting’ to determine the main sediment sources in a small residential urban watershed (0.83 km2) on the outskirts of Porto Alegre in southern Brazil. Based on an evaluation spanning 12 rainfall events, the results show that paved and unpaved roads and the stream channel itself contribute, on average, 46%, 23%, and 31%, respectively, to the suspended sediment flux in the watershed. Furthermore, the source contributions varied both between events and over the course of a single event. This appears to imply that source contributions, at least to some extent, depend on local precipitation patterns. The results from this study indicate that the level of uncertainty in source ascription tends to decline with increasing numbers of tracers; hence, successful sediment fingerprinting and source ascription in complex hydrologic environments, such as urban watersheds, may require the use of a large number of chemical and/or physical tracers.

Particulate organic carbon sources and delivery to river channels in the Somerset Levels ECSFDI priority catchment, southwest UK

Soil erosion and sediment delivery represent an important transport pathway for particulate organic carbon (POC) in fluvial systems. Catchment management strategies designed to protect soil resources therefore require reliable information on the significance of key sediment sources for POC transfers. Within this context, a composite fingerprinting procedure, incorporating uncertainty and prior understanding of catchment processes, was used to investigate the significance of eroding pasture or cultivated topsoils, damaged road verges, channel banks/subsurface sources and point source discharges as POC sources and the associated net delivery to river channels across the Somerset Levels, southwest UK. Overall mean relative contributions of POC from the five individual sediment sources were estimated at 41 ± 2% (pasture topsoils), 18 ± 1% (STWs), 15 ± 2% (cultivated topsoils), 14 ± 1% (damaged road verges) and 12 ±2% (channel banks/subsurface sources). Respective estimates of net sediment‐associated POC delivery to watercourses, provided by integrating sediment source ascription 50th percentiles bounded by 95% confidence limits, organic carbon content, sediment yield ranges and sub‐catchment or land use areas, ranged between 2.4–48.5 kg ha−1 yr−1, 0–16.5 kg ha−1 yr−1, 1.7–119.2 kg ha−1 yr−1, 0–13.8 kg ha−1 yr−1 and 0–7.4 kg ha−1 yr−1.

Investigating contemporary and historical sediment inputs to Slapton Higher Ley: an analysis of the robustness of source ascription methods when applied to lake sediment data

AbstractThis paper reports the results of a quantitative source analysis of the contemporary and historical sediments delivered to Slapton Higher Ley (Devon, UK). Contemporary suspended and bedload sediment inputs to the Higher Ley were apportioned successfully using R‐ and Q‐mode analysis and an unmixing model. Pasture topsoil was responsible for 80% of the suspended sediment load during stormflow, but only 50% under baseflow conditions. Channel bank material dominated bedload (70–80%).Dating by 137Cs of three cores from the Higher Ley indicates that rapid sedimentation has occurred since the 1950s and that pasture topsoil has been the dominant source of sediment deposited in the Higher Ley since the early 1980s. Both the unmixing model and R‐ and Q‐mode analysis support this interpretation. However, the robustness and validity of applying such source ascription techniques to the sediment cores of the Higher Ley is debatable, as chemical and mineral magnetic signatures in the cores are ‘diluted’ in comparison with sediment sources from the Slapton catchment. Particles‐size effects, selective transport and post‐depositional physical and chemical processes are examined as possible causes of this dilution effect. Post‐depositional alteration of the sediment was identified as the most probable explanation, but further analysis of the process was not possible within the scope of this study. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Determining the sources of atmospheric particles in Shanghai, China, from magnetic and geochemical properties

The study describes an investigation into the sources of atmospheric particles collected at 11 sites across Shanghai, China, during one week in November 1998. Source ascription is based on mineral magnetic and geochemical properties, and a chemical mass balance (CMB) model. The CMB model shows that the main contributions to total suspended particles (TSPs) are products of coal combustion, with lesser contributions from construction sites, vehicle emissions, windblown soil and steel-making furnaces. The spatial variability of concentration-dependent magnetic parameters and heavy metal concentrations support the findings from the CMB model. In general, the variability of magnetic quotient parameters is lower than for concentration parameters. This suggests that there are relatively constant proportions of low coercivity ‘magnetite’ and high coercivity ‘haematite’ mineral phases in dust samples at all sites, with a dominance of superparamagnetic (SP) and multidomain (MD)+pseudo-single domain (PSD) ‘magnetite’ grains. MD+PSD grains are produced to a large extent by fossil-fuel combustion emissions, particularly from the main iron and steel manufacturing and power generation industrial complex. Linear multiple regression analyses show that some non-destructive and rapid magnetic measurements may be used to estimate the concentrations of common heavy metals in TSPs.

Problems of core correlation, sediment source ascription and yield estimation in Ponsonby Tarn, West Cumbria, UK

A suite of 27 short cores, 10 of which have been used for magnetic measurements and four for radiometric dating, provides a framework for reconstructing the processes, patterns and rates of sedimentation in Ponsonby Tarn, a small artificial impoundment created towards the end of the 19th century, close to the Sellafield nuclear reprocessing plant in NW England. Spatial and temporal changes in sedimentation are reconstructed and evidence presented for non-synchroneity in magnetic property changes from core to core in the upper part of the sequence, as a result of sorting and selective deposition at different distances from the inflow to the Tarn. Magnetic measurements alone are therefore not a secure basis upon which to quantify sediment yield for defined time intervals at this site. The chronology, established mainly from 210Pb and 134Cs analyses, allows estimates of mean sediment yield per annum for four periods: prior to AD 1940, 1940–1964, 1964–1986 and 1986–1991. The rates of sediment accumulation have increased in recent times, especially since 1964, with evidence for input from both magnetically enhanced soils and gleyed alluvial and/or podsolized subsoil sources. Pre-1940 mean annual deposition within the present area of the lake is calculated as 19·5 t a−1 and for the period since 1986 (the period of maximum sedimentation rates), as 111·3 t a−1. These represent yields of 7·0 t km−2 a−1 and 39·8 t km−2 a−1, respectively, for the catchment as a whole. Rock magnetic evidence, based on measurements of both bulk samples and the finest particle size separates, suggests that bacterial magnetite, formed within the lake, contributes to the magnetic properties of the sediments, thus modifying the signatures relating to allochthonous sediment input. Copyright © 1999 John Wiley & Sons, Ltd.

Problems of core correlation, sediment source ascription and yield estimation in Ponsonby Tarn, West Cumbria, UK

A suite of 27 short cores, 10 of which have been used for magnetic measurements and four for radiometric dating, provides a framework for reconstructing the processes, patterns and rates of sedimentation in Ponsonby Tarn, a small artificial impoundment created towards the end of the 19th century, close to the Sellafield nuclear reprocessing plant in NW England. Spatial and temporal changes in sedimentation are reconstructed and evidence presented for non-synchroneity in magnetic property changes from core to core in the upper part of the sequence, as a result of sorting and selective deposition at different distances from the inflow to the Tarn. Magnetic measurements alone are therefore not a secure basis upon which to quantify sediment yield for defined time intervals at this site. The chronology, established mainly from 210Pb and 134Cs analyses, allows estimates of mean sediment yield per annum for four periods: prior to AD 1940, 1940–1964, 1964–1986 and 1986–1991. The rates of sediment accumulation have increased in recent times, especially since 1964, with evidence for input from both magnetically enhanced soils and gleyed alluvial and/or podsolized subsoil sources. Pre-1940 mean annual deposition within the present area of the lake is calculated as 19·5 t a−1 and for the period since 1986 (the period of maximum sedimentation rates), as 111·3 t a−1. These represent yields of 7·0 t km−2 a−1 and 39·8 t km−2 a−1, respectively, for the catchment as a whole. Rock magnetic evidence, based on measurements of both bulk samples and the finest particle size separates, suggests that bacterial magnetite, formed within the lake, contributes to the magnetic properties of the sediments, thus modifying the signatures relating to allochthonous sediment input. Copyright © 1999 John Wiley & Sons, Ltd.

Fingerprinting suspended sediment sources in the catchment of the River Ouse, Yorkshire, UK

Statistically verified composite fingerprints and a multivariate mixing model have been employed to establish the main sources of the suspended sediment transported through the lower, non-tidal reaches of the River Ouse and one of its main tributaries, the River Wharfe, during the period 1994–1997. In the case of the suspended sediment samples collected from the River Ouse, the load-weighted mean contributions from uncultivated topsoil, cultivated topsoil and channel bank sources were estimated to be c. 25, 38 and 37%, respectively, while for the River Wharfe these sources contributed c. 70, 4 and 23%, respectively (c. 4% was derived from woodland topsoil). Suspended sediment samples collected during higher flows evidenced a greater contribution from channel banks than samples collected during lower flows. Source materials were also differentiated according to the three main geological source areas (Carboniferous, Permian and Triassic, and Jurassic) and their load-weighted mean contributions were estimated to be c. 24, 41 and 35% for the River Ouse and c. 91, 9 and 0% (there are no Jurassic rocks in this catchment) for the River Wharfe, respectively. When suspended sediment samples from tributary streams were used to characterize each geological source area, the equivalent results for the River Ouse were c. 30, 46 and 24%. Considering the three main tributaries that contribute to the River Ouse, the load-weighted mean contributions from the rivers Swale, Ure and Nidd were estimated to be 82, 15 and 3%, respectively. These values have been compared with estimates of the relative magnitude of the annual suspended sediment loads of these three rivers for the years 1995 and 1996 derived from continuous monitoring of discharge and turbidity. Differences between the two sets of results are ascribed to the different periods of record involved and to the timing of suspended sediment sampling relative to the overall storm hydrograph, and thus the degree to which the available samples are representative of the overall suspended sediment flux. Although a number of limitations must be recognized, the fingerprinting approach to source ascription is seen as providing valuable information regarding suspended sediment sources in the study catchments. Copyright © 1999 John Wiley & Sons, Ltd.

Quantitative approach to sediment source identification by using magnetic diagnosis model

A sequential quantitative approach to sediment source ascription is presented based on mineral magnetic measurements. Rhode River catchment (USA) and Isabel Ⅱ reservoir catchment (Spain) were taken as the examples for developing the magnetic diagnosis model. The multi-parameter cluster analysis was used to classify the sediment source with respect to their magnetic properties, multi-variable mixing model to link magnetic measurement of mixtures with their source component proportions, and linear programming to determine the sediment source components. It has been shown by these two experiments that the magnetic diagnosis model is successful for the quantitative sediment source ascription. The results correspond well with the relative environmental change proxy.