Sediment Source Tracing Research Articles

Using the check dam deposit for an individual event to document the sources and erosional loss of sediment-associated organic carbon from a small catchment on the Chinese Loess Plateau

Information on the sources and fate of organic carbon mobilized by soil erosion is crucial for understanding the impact of erosion on carbon (C) cycling. However, few studies have evaluated this in low-order stream systems. In this study, we adopted a novel approach, that used the sediment deposited behind a check dam constructed at the outlet of the Fengzigou catchment (0.91 km2) on the Chinese Loess Plateau by a single high magnitude storm event, to simplify the field sampling requirements. The total sediment-associated organic carbon (TOC) was fractionated into particulate organic carbon (POC) and mineral associated organic carbon (MOC). These results were combined with those from a sediment source tracing exercise. This made it possible to explore further the source and loss of the sediment-associated organic carbon. The results showed that the inter-gully areas contributed the most eroded TOC (52.3 ± 7.6 %) and, together with the gully walls, represented the main TOC source. The primary contributor of the POC fraction in the deposited sediment was the inter-gully areas (80.5 ± 12.6 %), whereas the gully walls were the main contributor of the MOC fraction (54.9 ± 10.2 %). The total output of sediment produced by the event was 1304 ± 48 t and the equivalent value for sediment-associated TOC was 2.94 ± 0.26 t, of which the POC fraction accounted for 27.6 ± 3.6 % and the MOC fraction 72.4 ± 9.8 %. The TOC lost (0.3 ± 0.02 t) through the mobilization and delivery processes was 10.2 ± 1.2 % of the TOC mobilized by erosion, and the lost carbon was dominated by the POC fraction (86.7 ± 8.8 %). The specific TOC output from the catchment associated with the event documented was 0.3 t km−2. This work demonstrates the potential for erosion-induced carbon redistribution to provide a source for atmospheric CO2 in the study area.

Sediment source tracing in a Brazilian subtropical catchment using diffuse reflectance: Effect of spectral ranges, pre-processing techniques, and multivariate model

ABSTRACT Agriculture intensification in Southern Brazil’s subtropical regions combined with the frequent occurrence of erosive rainfall has rendered the area a global water erosion hotspot. In this scenario, understanding and regulating erosion processes at the river catchment scale is critical for mitigating soil and water resource degradation. Traditional methods for tracing sediment sources are expensive and time-consuming and justify the development of alternative approaches. Therefore, in this study, we employed diffuse reflectance spectroscopy analyses in the ultraviolet-visible (UV-VIS), near-infrared (NIR), and mid-infrared (MIR) ranges, combined with multivariate models and spectral pre-processing techniques to estimate sediment source contributions in a homogeneous subtropical catchment (Conceição River, 804 km²). Soil samples (n = 181) were collected to characterize the four potential sediment sources, including: cropland (n = 78), stream bank (n = 36), unpaved road (n = 40) and pasture (n = 27). Moreover, 44 sediment samples were collected, including suspended sediment (n = 8), fine sediment deposited on the riverbed (n = 15), and suspended sediment samples collected in the water column during storm events (n = 21). Vector machine (SVM) model outperformed the others, with better accuracy and reliability. While UV-VIS spectra proved less effective due to soil homogeneity across the catchment, NIR and MIR spectra provided valuable information for discriminating sediment sources. Furthermore, reducing the number of potential sources (from four to three or two) improved model predictions, especially when distinguishing between surface sources (cropland and pasture) and subsurface sources (unpaved roads and stream banks). The study’s findings shed light on the power of efficient and cost-effective alternative methods for assessing sediment sources, which are vital for promoting effective erosion control and sustainable land management in similar regions.

Erosion processes and sediment source tracing on heterogeneous slopes in the red soil region of southern China

AbstractUnderstanding erosion, sediment sources and the spatial distribution along heterogeneous slopes is essential for soil and water conservation. In this study, soils derived from nodular limestone, mud‐like limestone and limestone breccia (abbreviated as SMTL, SMDL and SLBC, respectively) were utilized to establish artificial homogeneous and heterogeneous slopes. The homogeneous slopes MTL, MDL and LBC represent SMTL‐, SMDL‐ and SLBC‐filled‐ slopes, respectively. The heterogeneous slopes were abbreviated as MTL/MDL, MDL/LBC and LBC/MTL. Rare earth elements (REEs; lanthanide, cerium and ytterbium) were used to tag soils on the upper and lower slope sections to track sediment transport and deposition. The results showed that for homogeneous slopes, the LBC slope was the most severely eroded, followed by the MDL and MTL slopes. For heterogeneous slopes, the order of erosion was LBC/MTL > MTL/MDL > MDL/LBC. Upslope sections contributed a sizable portion of the total sediment yield, ranging from 51% to 79%. Over time, the difference in the sediment contribution between the upslope and downslope regions decreased and reached equilibrium. Runoff rates on heterogeneous slopes demonstrated an inverse function (R2 > 0.75) in contrast to a logarithmic distribution (R2 > 0.87) on homogeneous slopes. Heterogeneous slopes displayed minimal intersegment variation and the absence of a consistent ordering of the magnitude of hydraulic parameters. Conversely, the hydraulic parameters of homogeneous slopes were consistently ordered across the slope sections. For sediment transport, all slopes exhibited suspension‐dominated flow with percentages greater than 89%. However, the particle size distribution of the sediment of heterogeneous slopes exhibited greater diversity and complexity because of the coexistence of distinct soils. These findings underscore the importance of customized strategies for soil and water conservation in environments characterized by diverse soil parent materials.

Soil erosion, sediment sources, connectivity and suspended sediment yields in UK temperate agricultural catchments: Discrepancies and reconciliation of field-based measurements

Robust understanding of the fine-grained sediment cascades of temperate agricultural catchments is essential for supporting targeted management for addressing the widely reported sediment problem. Within the UK, many independent field-based measurements of soil erosion, sediment sources and catchment suspended sediment yields have been published. However, attempts to review and assess the compatibility of these measurements are limited. The data available suggest that landscape scale net soil erosion rates (∼38 t km−2 yr−1 for arable and ∼26 t km−2 yr−1 grassland) are comparable to the typical suspended sediment yield of a UK catchment (∼44 t km2 yr−1). This finding cannot, however, be reconciled easily with current prevailing knowledge that agricultural topsoils dominate sediment contributions to watercourses, and that catchment sediment delivery ratios are typically low. Channel bank erosion rates can be high at landscape scale (27 km−2 yr−1) and account for these discrepancies but would need to be the dominant sediment source in most catchments, which does not agree with a review of sediment sources for the UK made in the recent past. A simple and robust colour-based sediment source tracing method using hydrogen peroxide sample treatment is therefore used in fifteen catchments to investigate their key sediment sources. Only in two of the catchments are eroding arable fields likely to be important sediment sources, supporting the alternative hypothesis that bank erosion is likely to be the dominant source of sediment in many UK catchments. It is concluded that the existing lines of evidence on the individual components of the fine sediment cascade in temperate agricultural catchments in the UK are difficult to reconcile and run the risk of best management interventions being targeted inappropriately. Recommendations for future research to address paucities in measured erosion rates, sediment delivery ratios and suspended sediment yields, validate sediment source fingerprinting results, consider the sources of sediment-associated organic matter, and re-visit soil erosion and sediment cascade model parameterisation are therefore made.

Temporal sediment source tracing during storm events in the black soil region, Northeast China

Sediment fingerprinting technology is widely used to differentiate sediment sources. However, despite its long-recognized benefits, there it has been seldom applied to assess the variability of sediment sources during storm events. In this study, sediment fingerprinting is used for four storm events to determine the dynamic changes in sediment sources throughout them in the black soil region in Northeast China. Three potential sediment sources—cultivated land, unpaved roads, and gullies—were effectively differentiated using four geochemical tracers (As, Be, Cs, and Cu), with an accuracy of 100%. The relative sediment contribution from each source was determined using linear and Bayesian mixing models. The mean absolute fit (MAF) values of the linear mixing model (MAFmean = 0.976–0.949) were higher than those of the Bayesian mixing model (MAFmean = 0.921–0.992), indicating that the first performed better. Cultivated land was the primary source of the sediment load, accounting for 59.03% of it (load-weighted mean = 68.29%), followed by the gullies (37.15%, load-weighted mean = 28.09%), and unpaved roads (3.90%, load-weighted mean = 3.69%) for the four storm events. In addition, a high variability in sediment source contribution was observed during the storm events. Cultivated land was the dominant sediment source during storm events with higher sediment concentrations (logarithmic function, r2 = 0.878, p < 0.01), discharge (linear function, r2 = 0.452, p < 0.05), and sediment flux (logarithmic function, r2 = 0.857, p < 0.01), whereas the reverse was observed for gullies. Contrastingly, the contribution of sediment from unpaved roads remained relatively stable during rainfall events. This provides a potential means to assess dynamic changes in sediment contributions from different erosion units. Moreover, it provides data support for exploring soil erosion mechanisms and effective erosion control in the black soil region in Northeast China.

Refining fine sediment source identification through integration of spatial modelling, concentration monitoring and source tracing: A case study in the Great Barrier Reef catchments

Excess fine sediment delivery is a major contributor to the declining health of the Great Barrier Reef and identifying the dominant source areas of fine sediment has been critical to prioritising erosion remediation programs. The Bowen River catchment within the Burdekin Basin has been recognised as a major contributor and hence received considerable research investment over the last two decades. This study adopts a novel approach to integrate three independently derived sediment budgets produced from a catchment scale sediment budget model (Dynamic SedNet), targeted tributary water quality monitoring and geochemical sediment source tracing to refine and map the sediment source zones within the Bowen catchment. A four year study of water quality monitoring combined with modelled discharge estimates and geochemical source tracing both identified that the Little Bowen River and Rosella Creek were the largest sources of sediment in the Bowen River catchment. Both data sets contradicted initial synoptic sediment budget model predictions due to inadequate representation of hillslope and gully erosion. Recent improvements in model inputs have resulted in predictions that are consistent with the field data and are of finer resolution within the identified source areas. Priorities for further investigation of erosion processes are also revealed. Examining the benefits and limitations of each method indicates that these are complimentary methods which can effectively be used as multiple lines of evidence. An integrated dataset such as this provides a higher level of certainty in the prediction of fine sediment sources than a single line of evidence dataset or model. The use of high quality, integrated datasets to inform catchment management prioritisation will provide greater confidence for decision makers when investing in catchment management.

Sediment source tracing during flood events in the Huangfu River basin in the northern Loess Plateau, China

Identifying critical soil erosion areas and sediment sources are essential for sediment control and water resources management in the watershed, especially in the severely eroded northern Loess Plateau, China. In this study, we collected suspended sediment samples at the hydrological stations to identify the sediment source dynamics during flood events in a highly erodible basin, the Huangfu River basin in the Northern Loess Plateau. A total of 6 flood events were sampled during 2016 and 2018 for investigation, the flow discharge was featured by a rapid rising limb and a slow falling limb. Compared with the sediment sources, the silt fraction in the suspended sediments was enriched and the sand fraction in the suspended sediment was depleted. The dominant particle grain size of suspended sediments was coarse sand (56.89%), higher than silt (41.81%) and clay (1.3%). The sediment sources were estimated using the FingerPro unmixing model based on the conservativeness index (CI) and consensus ranking (CR) methods. The results of the unmixing model reveal that the bare land was the predominant source of suspended sediments, ranging from 40% to 57%, which was much higher than farmland (27 ∼ 31%) and grassland (16 ∼ 25%). Our findings imply that the bare land (weathered sandstone area) is the critical region for soil loss control in the Huangfu River basin. A combination of vegetation restoration measures and engineering measures are proposed to improve the sustainable development of ecological environment in the basin.

Assembly process and source tracking of microbial communities in sediments of Dongting Lake

Sediment source tracing can accurately provide a theoretical basis for controlling soil erosion effectively, by identifying the most serious types of land use. Traditional sediment tracing methods are based on physical, chemical, biological, and composite fingerprinting, which have not included microbes. As high-throughput sequencing becomes more prevalent, microorganisms can provide more information than what we think. Thus, whether the microorganism can also be used as a special fingerprint factor for sediment source identification during soil erosion, we have tested it by using microbial source tracking tool FEAST to quantify the microbe contribution from five types of eroded land (including dryland, urban, paddy field, forest and grassland) to the depositional areas (Niubitan) in the Yuanjiang basin. The source microbial community in the erosive area was heterogeneous, and assembly process analysis further demonstrated that the source tracking results could reach higher accuracy. The results of FEAST showed that dryland (35.50%), urban (17.21%), paddy field (8.14%), and forest (1.07%) were the major contributors to Niubitan. Our results follow the general soil erosion rules and prove its validity. Taken together, a new perspective is provided by these results for tracing sediment sources in erosion-sedimentary systems.

Tracing the dominant sources of sediment flowing towards Lake Victoria using geochemical tracers and a Bayesian mixing model

PurposeLake Victoria has been increasingly silting over the past decades, impacting water quality and loss of biodiversity. Sediment control strategies require information on the relative and absolute contributions of sediment from different sources. However, to date, there is no continuous monitoring of sediment flux or water quality in any of the tributaries, prohibiting an assessment of the scale of the problem. The aim of this study was to trace the dominant sources of riverine sediment using geochemical fingerprinting, thereby generating a knowledge base for improving land management and reducing sediment yields in Simiyu River catchment, one of the main contributing rivers to Lake Victoria.Materials and methodsGeochemical tracer concentrations were analyzed in transported sediment from the main river and two tributaries (riverbed sediments) and from soils in five dominant land use types (agricultural land, bush land, forest land, channel banks, and main river banks). Dominant sources to the Simiyu main river sediment were attributed using the Bayesian MixSIAR model.Results and discussionThe mixing model outputs showed that the Simiyu tributary was the dominant source of sediment to the Simiyu main river with 63.2%, while the Duma tributary accounted for 36.8%. Cultivated land was shown to be the main land use source of riverine sediment, accounting for 80.0% and 86.4% in Simiyu and Duma sub-tributaries, respectively, followed by channel banks with 9.0% in both sub-tributaries. Direct unmixing of the Simiyu main river sediment to the land use sources yielded 64.7% contribution of cultivated land and 26.5% of channel banks.ConclusionThe demonstrated application of sediment source tracing provides an important pathway for quantifying the dominant sources of sediment in the rivers flowing towards Lake Victoria. Eroded soil from agricultural areas is the biggest contributor to transported sediment in the Simiyu River. This information is vital for the design of catchment wide management plans that should focus on reducing soil erosion and sediment delivery from farming areas to the river networks, ultimately supporting both food security and water quality in the Lake Victoria Basin.

Sediment source determination for a series of connected check dams in an agricultural catchment in the Chinese Mollisol region

The composite fingerprinting approach is valuable in sediment source identification at different temporal and spatial scales. However, few studies have estimated watershed sediment source connections and transport impacted by multiple check dams. This is due to the complexity of particle sorting under flood discharge practices. Here, we attempt to identify sediment sources with three connected check dams in an agricultural Mollisol catchment in Northeast China based on optimal fingerprints screened from different size fractions (i.e., <10, <63, and <1000 μm). The results showed consistent sediment contributions based on fine particle size ranges (i.e., <10 and <63 μm) but an inconsistent contribution based on a coarse particle size range (i.e., <1000 μm), regardless of the particle size or the organic corrections applied. Sediment deposited in check dams No. 1 and No. 2 was mainly from hillslopes (cropland) (>66.7 %), while sediment in check dam No. 3 was from its adjacent upstream check dam (i.e., No. 2; >60.5 %) based on optimal fingerprints screened from <10 and <63 μm particle size ranges. However, when fingerprints were screened from a coarse particle size (<1000 μm), sediment in all three check dams was mainly from gully slopes (>79.0 %), regardless of the specific surface area (SSA) of particles or the soil organic carbon (SOC) correction factors used in the model except for SOC correction for check dam No. 2. Conversely, sediment was mainly derived from hillslopes when fingerprint values were corrected using SSA and SOC, except that no optimal fingerprints were selected. This indicated the feasibility of sediment source discrimination based on the composite fingerprinting approach for sediment source identification in catchments with a series of connected check dams under the condition that particle fractions impacted by check dams are relatively weak. However, optimal fingerprints screened from a relatively wide range of coarse particles caused divergent results regardless of the particle size or the organic correction factors used in model estimation or in fingerprint values. Further studies are necessary to explore the reliability of the composite fingerprinting approach for sediment source tracing under a series of connected check dams, where coarse sediment is selectively deposited and fine sediment is massively discharged under flood discharge practices.

Combining sediment source tracing techniques with traditional monitoring: The “Arvorezinha catchment” experience

AbstractTo truly understand the hydrologic and erosive processes that occur at the catchment scale regarding land use and soil management changes, intensive monitoring is required over a long period. Variables such as precipitation, flow rate and suspended sediment concentration are the fundamentals needed to estimate sediment yield (SY). However, in order to shed more light on the effects of soil management changes on SY, traditional hydrologic monitoring techniques can be paired with sediment tracing to identify sediment sources. In addition, mathematical models that predict erosion and SY can also help understand the dynamics of erosion and deposition between the hillslope and stream channel. Given the above, this article provides an overview of almost 20 years of monitoring (2002–2021) in the Arvorezinha experimental catchment (1.23 km2) located on the edge of the Brazilian meridional plateau in southern Brazil, which is subject to extreme erosion due to a combination of factors related to intensive agriculture and steep slopes. The catchment was selected as a study site to evaluate the effects of land‐use changes and soil conservation management on hydrology and SY. The text reviews the history of the study, synthesizes the main results and describes the evolution of the monitoring techniques used while giving special attention to the fingerprinting approach. In addition, the article discusses the importance of catchment‐scale studies for teaching, generating technical‐scientific knowledge and fostering collaboration between national and international research groups.

Tributary contributions to sediment deposited in the Jacuí Delta, Southern Brazil

The Jacuí Delta drains into Lake Guaíba which is the main source of water for more than two million people in South Brazil and has suffered from pollution with heavy metals and phosphorus. The objective of the current research is to demonstrate how the use of sediment source tracing techniques, in combination with sediment flux monitoring, can improve understanding of the sediment source contributions to one of the largest lakes in South America. The sediment flux monitoring results were based on data obtained from 12-years of records of water flow and suspended sediment concentrations. The sediment source fingerprinting approach was based on the use of geochemical tracers. Based on the study, the respective contributions of the tributaries to the sediment in Lake Guaíba were estimated to be as follows: the Jacuí River (median of 54% - interquartile range (IQR) 34–71%), the Caí River (12%, IQR 7–16%), the Sinos River (5%, IQR 1–20%), and the Gravataí River (16%, IQR 10–30%). These results are similar to those derived from the sediment flux monitoring, namely: the Jacuí River (70%), the Caí River (19%), the Gravataí River (4%), and the Sinos River (7%). These results demonstrate that the sediment source fingerprinting approach combined with sediment flux monitoring can provide a useful means of estimating the respective sediment contributions from individual tributaries in large and complex delta systems and may provide a powerful tool to guide water resource management.

Soil erosion and sediment transport in Tanzania: Part I – sediment source tracing in three neighbouring river catchments

AbstractWater bodies in Tanzania are experiencing increased siltation, which is threatening water quality, ecosystem health, and livelihood security in the region. This phenomenon is caused by increasing rates of upstream soil erosion and downstream sediment transport. However, a lack of knowledge on the contributions from different catchment zones, land‐use types, and dominant erosion processes, to the transported sediment is undermining the mitigation of soil degradation at the source of the problem. In this context, complementary sediment source tracing techniques were applied in three Tanzanian river systems to further the understanding of the complex dynamics of soil erosion and sediment transport in the region. Analysis of the geochemical and biochemical fingerprints revealed a highly complex and variable soil system that could be grouped in distinct classes. These soil classes were unmixed against riverine sediment fingerprints using the Bayesian MixSIAR model, yielding proportionate source contributions for each catchment. This sediment source tracing indicated that hillslope erosion on the open rangelands and maize croplands in the mid‐zone contributed over 75% of the transported sediment load in all three river systems during the sampling time‐period. By integrating geochemical and biochemical fingerprints in sediment source tracing techniques, this study demonstrated links between land use, soil erosion and downstream sediment transport in Tanzania. This evidence can guide land managers in designing targeted interventions that safeguard both soil health and water quality.

Disentangle the sediment mixing from geochemical proxies and detrital zircon geochronology

Detrital zircon UPb geochronology and geochemical proxies derived from immobile elements and isotopes are commonly applied to trace sediment sources because of their durability and stability in most earth surface processes and environments. However, little is known on whether these different tracers can contain identical or similar provenance signals for sediments of interest. This study presents the UPb ages of detrital zircons from a grain-size fraction of 63–125 μm and elemental and Nd isotopic compositions for bulk sediments from the Mulanxi, a small mountainous river in southeast China. We aim to retrieve provenance signals preserved by different tracers and to test whether they are robust in discriminating the effect of sediment mixing in this tidal-dominated river. Our results show that detrital zircons in the Mulanxi catchments and estuarine have two major age groups at 90–110 Ma and 120–150 Ma. Moreover, the results of probability density plots (PDPs) suggest there is no significant difference in detrital zircon UPb ages between the sediments from non-tidal and tidal reaches. The detrital zircon age distributions in the Mulanxi catchments are significantly different from those in the Changjiang (Yangtze River) catchments and in the inner shelf mud belt of the East China Sea which have distinct multiple age populations. A statistical multidimensional scaling (MDS) analysis suggests there is no a source-to-sink connection between the Changjiang and Mulanxi zircons. On the contrary, the geochemical proxies of Sc/Th, Cr/Th, and Nd isotopes reveal different sediment sources between the non-tidal and tidal reaches of Mulanxi, with the fine tidal-reach sediments having mixed sources from the offshore mud and the Mulanxi River, while the coarse-grained sediments from the non-tidal upstream being completely contributed by the Mulanxi. The contradictory results from these different provenance proxies suggest their implications and limitations for sediment source tracing. Detrital zircon ages can track the ‘inherited’ source signals of zircons and relating coarse fractions in sediments, but they are less sensitive to source changes in fine fractions than the geochemical proxies of Nd isotopes, Sc/Th and Cr/Th ratios. It is therefore essential and a prerequisite to carefully evaluate all possible factors controlling detrital sediment compositions, and to weigh the pros and cons of different tracers for sediment provenance discrimination especially in dynamic Small Mountainous Rivers (SMRs) and continental margins.

The potential for colour to provide a robust alternative to high-cost sediment source fingerprinting: Assessment using eight catchments in England

Excess diffuse fine sediment losses from agriculture are associated with a reduction in the ecological status of lakes and rivers. Agri-environment initiatives aim to help reduce these excessive losses through targeted on-farm advice and capital grants. However, to deliver optimum cost-benefit such initiatives must target the most important sediment sources. Sediment source fingerprinting provides an approach by which sediment provenance data can be generated; however, conventional tracers are expensive and state-of-the-art data processing for source discrimination and apportionment requires significant expertise. In consequence, sediment fingerprinting is not routinely used for catchment management. Against this context, sediment colour measured using an ordinary document scanner is trialled as an inexpensive and accessible tracer in eight catchments classed as high priority for an agri-environment initiative in England. Colour is interpreted using simple scatter bi-plots of source and sediment samples and compared to the results produced by a conventional composite tracer sediment source fingerprinting methodology. It was found that in two study catchments, sediment colour was as effective as conventional sediment fingerprinting. In four catchments, sediment colour provided less source discrimination or minor differences in results but still identified the most important targets for sediment mitigation. In two catchments, colour was un-successful; however, significant challenges were also encountered with more conventional tracers due to specific local conditions. The findings suggest that use of low-cost colour tracers by non-experts has the potential to significantly increase the uptake of sediment source tracing to improve the cost-benefit of agri-environment initiatives combating the degradation of water quality and aquatic ecology by accelerated sediment losses.

An exploratory study on the use of different composite magnetic and colour fingerprints in aeolian sediment provenance fingerprinting

There is an urgent need for reliable and cost-effective sediment source tracing techniques for apportioning aeolian sediment (sand dune) sources for guiding the selection of best management practices for wind erosion control. Accordingly, the main aim of this study was to quantify the contributions of aeolian sources to sand dune target sediment samples collected in a case study in central Iran using a source fingerprinting procedure based on low-cost fingerprints comprising colour and magnetic tracers. Colour (RGB), magnetic susceptibility (χlf and χhf) and 13 colour and magnetic indices were measured on 54 aeolian sediment source samples and ten aeolian target sediment samples. Three different composite fingerprints for discriminating and apportioning the aeolian sediment sources were selected based on a combination of statistical tests comprising the Kruskal–Wallis H test (KW-H), discriminant function analysis (DFA), principal component & classification analysis (PCCA), and a general classification & regression tree (GC&RT) model. The Modified MixSIR Bayesian un-mixing model was used to apportion aeolian source contributions using the final composite fingerprints. The composite signatures all suggested that the salt flat plain was the dominant (average 63%, and standard deviation, SD, 5.9%) source of the aeolian target sediment samples, whilst agricultural land was second (average 63%, SD 5.6%,) most important. The root mean square difference between the apportionment results based on the three composite fingerprints ranged from 0.2% to 8.3%. Pairwise comparisons of the posterior distributions for the predicted source proportions generated using the three composite signatures showed that eight of 12 pairwise comparisons were not significantly different. Virtual mixture accuracy tests of the fingerprinting models using the three composite signatures suggested errors ranging between 2.2%−20.6% (with a mean of 9.9%), 1.4%−17.0% (mean value 8.3%), and 0.03%−1.0% (mean value 0.8%). The results support the use of low-cost colour and magnetic tracers by investigations into aeolian sediment provenance.

Compound-specific isotope analysis with nested sampling approach detects spatial and temporal variability in the sources of suspended sediments in a Scottish mesoscale catchment

Intensification of land use is a primary cause of increased suspended sediment load in freshwater systems, hence land-use-specific sediment source tracing is necessary to inform sustainable land and water management. Here we tested the application of compound-specific isotope analysis (CSIA) of vegetation biomarkers to fingerprint suspended sediment sources from the mesoscale agricultural Tarland catchment (74 km2) in NE Scotland. Our aim was to test a parsimonious nested sampling approach from a headwater sub-catchment to apportion suspended sediment sources across headwater to catchment-wide scales. Compound-specific carbon isotopic signatures (δ13C) of long-chain fatty acids (LCFAs) from source soils were able to successfully distinguish between forest, heather moorland, permanent grassland, and arable land cover. Permanent grassland was a prominent source of sediment at both headwater and catchment scales, with an annual average contribution of 79% and 56%, respectively, indicating grazing pressure and runoff via preferential pathways. Increased sediment input from arable land at the catchment scale (40%) compared to the headwater sub-catchment (18%) indicated land use intensification in lowland areas. Forest and heather moorland contributed marginally to suspended sediments (~2%), despite covering 43% area of the catchment area. Temporal variability of sediment sources observed over fourteen months (May 2017 – June 2018) showed a higher relative contribution from arable land during summer and autumn and a higher contribution from permanent grassland during winter and spring, likely linked to seasonality of rainfall and agronomic activities.These results demonstrate a successful use of δ13C values of LCFAs to quantify land-use-specific suspended sediment sources. Comparison of two suspended sediment techniques showed usefulness of time-integrated mass samplers for representative and cost-effective sampling. We recommend that future nested sampling designs should include spatially distributed source soil tracer characterization covering the whole catchment area to reduce the uncertainty in sediment source attribution from headwaters to the catchment outlet.

Storm event sediment fingerprinting for temporal and spatial sediment source tracing

AbstractSediment fingerprinting has been widely used to distinguish discrete sediment sources; however, application to intra‐storm sediment source variability has received relatively little focus despite the benefit being long recognized. In this investigation, sediment fingerprinting was applied to a 53‐hr storm event sampled hourly to determine sediment source dynamics throughout the event. Sediment sources were differentiated using 16 variables, and source contribution determined using Bayesian and Frequentist mixing models for comparison. Both models provided comparable source predictions for the dominant source estimates and the general temporal pattern. The Frequentist model appeared to exhibit some unreliable values coinciding with low GOF and attributed to inherent model structure. The Bayesian model showed higher uncertainty, likely due to the “process error” utilized associated with single sample mixtures. High variability in sediment source contribution was observed between hourly time steps; however, local smoothing reveals temporal trends during the event. A higher average proportion of mudstone is found in the falling limb (0.544) compared with the rising limb (0.464), and the reverse is observed for mountain range (0.218 vs. 0.283) and unconsolidated (0.073 vs. 0.055). In the initial hours of the storm, mudstone source contribution significantly drops, whereas mountain range and unconsolidated contributions peak. The SSC‐Q clockwise hysteresis indicates proximal sediment sources, suggesting the mudstone sediment is stored channel sediment and easily entrained. This sediment flushes through, coinciding with a drop as the distal mountain range and unconsolidated sources arrive to peak contribution. The wider Manawatū discharge and sediment load then arrive, delivering increasing levels of mudstone throughout the remainder of the event while mountain range sediment diminishes. Spatial representation of the sediment source contribution was derived from distributing sediment source loads to the spatial extent of the source material according to sub‐catchment sediment loads and was weighted according to slope. This provided an effective means to visualize the origin of the sediment and a better spatial interpretation of sediment fingerprinting results, which is typically limited by poor spatial resolution.

Suspended sediment source tracing at the Juksan Weir in the Yeongsan River using composite fingerprints

Since 2008, the Yeongsan River in South Korea has experienced significant environmental changes, such as the dredging of its riverbed and the construction of large weirs. The quantity and quality of the fine sediments that provide adsorptive surfaces for pollutants has an influence on water quality, human health, and aquatic organisms. To determine the dominant contributors and seasonal variation in suspended sediment at the Juksan Weir in the Yeongsan River, reservoir sediments were obtained at monthly intervals using a time-integrated suspended sediment sampler. We applied a fingerprinting procedure combined with a multivariate mixing model to discriminate between different types of land use and to apportion sediment sources. Cropland topsoils, forest topsoils and channel bank materials were selected as end-members, and fallout radionuclides, geochemical elemental concentrations and the magnetic properties of each source material were used as diagnostic tracer properties. According to the mixing model results, channel bank materials were the dominant source of reservoir sediment during the entire monitoring period. In winter, there was a slight increase in the contribution from forest topsoils, which could have been influenced by freeze–thaw processes. Despite the high proportion of agricultural land use in the study catchment and its proximity to the river, there was a small sediment contribution from the cropland topsoils. There were uncertainties resulting from an imperfect classification due to the spatial distributions of forest and cropland and the combination of the mixing model with the fingerprinting procedure. The results provide the basis for developing strategies for sediment control and reservoir management.

Farm dam siltation and sediment source tracing in the Zeerust - Swartruggens area in the North-West of South Africa

Soil erosion and dam siltation are two serious environmental problems facing farmers in South Africa. The study aimed to assess farmers' perceptions on dam siltation and strategies employed to address it, and to assess the potential of sediment source tracing in a farming area in the north-west region of South Africa. Most of the dams in the study area were severely affected by siltation and the most important strategy used to address the problem was regular mechanical removal of the accumulated sediment. In relation to sediment tracing, lead-210 (210Pb) was found to be a more effective tracer than caesium-137 (137Cs) for distinguishing between surface and subsurface sediment sources. On the other hand, magnetic susceptibility offered better distinction of the sediment sources than magnetic remanence. Mass balance modelling indicated that 100% of the sampled sediment dam 1 originated from surface sources. The results reflect the complexity of sediment mobilisation processes influenced by the nature and spatial distribution of rainfall and runoff connectivity in the catchments.