Suspended sediments in fluvial systems originate from a myriad of diffuse and point sources, with the relative contribution from each source varying over time and space. The process of sediment fingerprinting focuses on developing methods that enable discrete sediment sources to be identified from a composite sample of suspended material. This review identifies existing methodological steps for sediment fingerprinting including fluvial and source sampling, and critically compares biogeochemical and physical tracers used in fingerprinting studies. Implications of applying different mixing models to the same source data are explored using data from 41 catchments across Europe, Africa, Australia, Asia, and North and South America. The application of seven commonly used mixing models to two case studies from the US (North Fork Broad River watershed) and France (Bléone watershed) with local and global (genetic algorithm) optimization methods identified all outputs remained in the acceptable range of error defined by the original authors. We propose future sediment fingerprinting studies use models that combine the best explanatory parameters provided by the modified Collins (using correction factors) and Hughes (relying on iterations involving all data, and not only their mean values) models with optimization using genetic algorithms to best predict the relative contribution of sediment sources to fluvial systems.
Purpose Identifying of the sources, stores and pathways of sediments in a catchment is essential to accurately target management actions designed to reduce sediment delivery to receiving waters. Fingerprinting the source of sediment using geochemical properties has increasingly been accepted as an accurate approach for quantifying the contribution of different sources to river sediment discharge. In this study, we seek to examine the effect of particle size and location of the sources on their contribution to suspended sediments. Materials and methods Geochemical tracers (n=41) were employed to calculate proportional contributions of sediment to Emu Creek, a predominantly pastoral catchment (911 km 2 ) in south-eastern Queensland, Australia. The study focused on two high flow events (10-and 6-year return periods) and some lower flow events which occurred during the 18 months from October 2011 to March 2013. Source contributions were determined at eight spatially distributed sites in major tributaries and along the main channel of Emu Creek. Source determination at the in-stream sites was done using end member samples (based on the underlying rock type) collected upstream of the site of interest, thus indicating how different sources dominate at different locations downstream. To examine whether different size fractions shared similar provenances, three size fractions of both source and suspended samples including fine silt and clay (<10 μm), silt (10-63 μm) and fine sand (63-212 μm) were analysed. Results and discussionThe source apportionment results using the distribution mixing model indicate that particle size and location of sources within a catchment are major factors that affect the measured contribution of sources to suspended sediments. The closer a suspended sediment sampling site is to a potential source, the more likely it is that source of sediment will dominate the material being sampled. Conclusions For all size fractions, proximal sources of sediment make a higher contribution to suspended sediments than distal sources. This indicates that management actions should be focused on the more proximal sources to the point of interest/impact. Although proximal soil sources were major contributor of sediments in all three size fractions, the percentage of contribution greatly vary in different size fractions, emphasising the need to trace the size fraction which is causing the downstream problems.
The jet erosion test (JET) is a widely applied method for deriving the erodibility of cohesive soils and sediments. There are suggestions in the literature that further examination of the method widely used to interpret the results of these erosion tests is warranted. This paper presents an alternative approach for such interpretation based on the principle of energy conservation. This new approach recognizes that evaluation of erodibility using the jet tester should involve the mass of soil eroded, so determination of this eroded mass (or else scour volume and bulk density) is required. The theory partitions jet kinetic energy flux into that involved in eroding soil, the remainder being dissipated in a variety of mechanisms. The energy required to erode soil is defined as the product of the eroded mass and a resistance parameter which is the energy required to entrain unit mass of soil, denoted J (in J/kg), whose magnitude is sought. An effective component rate of jet energy consumption is defined which depends on depth of scour penetration by the jet, but not on soil type, or the uniformity of the soil type being investigated. Application of the theory depends on experimentally determining the spatial form of jet energy consumption displayed in erosion of a uniform body of soil, an approach of general application. The theory then allows determination of the soil resistance parameter J as a function of depth of scour penetration into any soil profile, thus evaluating such profile variation in erodibility as may exist. This parameter J has been used with the same meaning in soil and gully erosion studies for the last 25 years. Application of this approach will appear in a companion publication as part 2. Copyright © 2017 John Wiley & Sons, Ltd.
This paper reports the results of jet tester experiments on soil samples of uniform properties which allow quantitative application of the new theory proposed in part 1 of these publications. This theory explores the possibly that a more adequate indicator of soil erodibility may be obtained by using the mass (and so volume) of soil eroded by the jet and the depth of scour penetration, rather than by using penetration depth alone, as assumed in the commonly‐used data interpretation method. It is shown that scour geometry can be well described using a generalized form of the Gaussian function, defined by its standard deviation and maximum depth. Using a published expression for jet kinetic energy flux, the new theory divides this flux into that used to erode soil, and the remainder which is dissipated in a variety of ways. Jet experiments on a specially‐prepared uniform soil sample are reported which provide the key to determining the spatial variability in the profile resistance to erosion offered by field soils. This resistance is expressed in the work required to erode unit mass of soil, denoted as J (in J/kg). The paper also gives results obtained on the profile variation in J for jet tests carried out at riverine sites on the upper Brisbane River, Queensland, Australia. As expected in most natural soil profiles, the results show an increase in J with depth in the profile. The soil resistance (J) is compared to the traditional interpretation of soil erodibility, (kd). The graphical comparison of these two indicators illustrates the inverse type of relationship between them which is expected from their respective definitions, but this relationship is associated with significant scatter. Possible reasons for this scatter are given, together with comments on jet tester experience in a wide variety of soil types. Copyright © 2017 John Wiley & Sons, Ltd.
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