Sediment Fingerprinting Techniques Research Articles

Quantification of the provenance contribution and sedimentary mixing effect of sediments in the Yellow River Basin, China

Quantifying the source contributions of sediments in large fluvial systems with active wind erosion problems has crucial implications for understanding morphological evolution and ecological progression in the Earth system. Much effort have been focused on characterizing sediments of the Yellow River, but quantitation of the sediment source proportions at the basin-wide scale is lacking. To this end, the research aims to quantitatively elucidate the potential source contributions of sediments in the Yellow River based on geochemical characteristics and sediment fingerprinting technique, in order to identify sedimentary mixing effect and propose sustainable development strategies. In total, samples of four source groups (n = 107) and target floodplain sediments (n = 61) were collected and tested for elemental composition, grain size, magnetic susceptibility, and quartz grain microtextures. The results indicated that the optimal tracer combination was determined as P, Zn, and Ca. The average contributions of the “Tibetan Plateau”, “Sandy deserts-Loess Plateau”, “Loess Plateau”, and “Loess Plateau-Qinling Mountains” source groups to the target sediments were 23.0 %, 21.5 %, 31.6 %, and 23.9 %, respectively. The accuracy of source apportionments was supported by the goodness of fit (GOF) and virtual mixtures tests. Meanwhile, large amounts of debris from surrounding mountains was transported to the Loess Plateau through fluvial processes and ultimately mixed with aeolian deposits, leading to sedimentary mixing effect. To maintain water balance and minimize erosion risk, the drought-resistant perennial planting and moderate grazing were recommended. The findings are instrumental in promoting soil and water conservation and disclosing fluvial and aeolian interaction on a global scale.

Sensitivity of source sediment fingerprinting to tracer selection methods

Abstract. In a context of accelerated soil erosion and sediment supply to water bodies, sediment fingerprinting techniques have received an increasing interest in the last 2 decades. The selection of tracers is a particularly critical step for the subsequent accurate prediction of sediment source contributions. To select tracers, the most conventional approach is the three-step method, although, more recently, the consensus method has also been proposed as an alternative. The outputs of these two approaches were compared in terms of identification of conservative properties, tracer selection, modelled contributions and performance on a single dataset. As for the three-step method, several range test criteria were compared, along with the impact of the discriminant function analysis (DFA). The dataset was composed of tracer properties analysed in soil (three potential sources; n = 56) and sediment core samples (n = 32). Soil and sediment samples were sieved to 63 µm and analysed for organic matter, elemental geochemistry and diffuse visible spectrometry. Virtual mixtures (n = 138) with known source proportions were generated to assess model accuracy of each tracer selection method. The Bayesian un-mixing model MixSIAR was then used to predict source contributions on both virtual mixtures and actual sediments. The different methods tested in the current research can be distributed into three groups according to their sensitivity to the conservative behaviour of properties, which was found to be associated with different predicted source contribution tendencies along the sediment core. The methods selecting the largest number of tracers were associated with a dominant and constant contribution of forests to sediment. In contrast, the methods selecting the lowest number of tracers were associated with a dominant and constant contribution of cropland to sediment. Furthermore, the intermediate selection of tracers led to more balanced contributions of both cropland and forest to sediments. The prediction of the virtual mixtures allowed us to compute several evaluation metrics, which are generally used to support the evaluation of model accuracy for each tracer selection method. However, strong differences or the absence of correspondence were observed between the range of predicted contributions obtained for virtual mixtures and those values obtained for actual sediments. These divergences highlight the fact that evaluation metrics obtained for virtual mixtures may not be directly transferable to models run for actual samples and must be interpreted with caution to avoid over-interpretation or misinterpretation. These divergences may likely be attributed to the occurrence of a not (fully) conservative behaviour of potential tracer properties during erosion, transport and deposition processes, which could not be fully reproduced when generating the virtual mixtures with currently available methods. Future research should develop novel metrics to quantify the conservative behaviour of tracer properties during erosion and transport processes. Furthermore, new methods should be designed to generate virtual mixtures closer to reality and to better evaluate model accuracy. These improvements would contribute to the development of more reliable sediment fingerprinting techniques, which are needed to better support the implementation of effective soil and water conservation measures at the catchment scale.

Provenance analyses of silted sediments in Shenzhen Bay: Insights based on rare earth elements and stable isotopes

Shenzhen Bay (SZB) in southern China is a typical eutrophic area, with internal pollution from its sediments representing an important nutrient source. However, the transport paths and sources of sediments in SZB remain unclear, making it difficult to analyze the nutritional budget and propose effective sediment management strategies. To address this, we linked a sediment fingerprinting technique to a Bayesian mixing model (MixSIAR) and conducted provenance analyses. We collected particle samples from SZB sediment and surrounding areas, including the Shenzhen River (SZR), Pearl River Estuary (PRE), and the northern South China Sea (SCS). Two groups of natural tracers were measured to trace different phases of sediments: (1) C and N parameters for the fates of the organic phase of sediments, and (2) rare earth element (REE) patterns for the provenance of mineral fragments. The results showed that the concentrations of total organic C and total N were 0.89–1.44 % and 0.05–0.13 %, respectively. MixSIAR suggested that fluvial inputs from SZR and PRE contributed 46.6 % and 30.3 % of organic matter, respectively. The organic matter in the PRE mainly originated from sewage and the upper reaches of the Pearl River. The concentration range of REEs in SZB sediments was 153.12–480.09 mg/kg with clear enrichment for light REE. MixSIAR results showed that the mineral fragments mainly originated from the outer bay (SCS and PRE, which contributed 57.2 % and 32.7 %, respectively). These results indicate that organic pollution follows a different path from the inorganic base, which is mainly related to anthropogenic input from land. This study highlights that complex sediment transport processes and pollution intrusions from the Pearl River are the issues that must be considered for eutrophication restoration in SZB.

Soil erosion and sediment sourcing in the Hyrcanian forests, Northern Iran: an integration approach of the G2loss model and sediment fingerprinting technique

Soil erosion and sediment sourcing in the Hyrcanian forests, Northern Iran: an integration approach of the G2loss model and sediment fingerprinting technique

Fingerprinting sediment sources in two typical watersheds in the dry-hot valleys of Southwest China: The role of gully and orchard land

Identifying the contributions of sediment sources is important for effectively understanding soil erosion processes, adopting appropriate management measures, and optimizing soil conservation strategies. Currently, the sediment fingerprinting technique has gained significant attention worldwide to assess the contributions of sediment sources; however, such studies in the dry-hot valleys of Southwest China, one of the most important sediment sources for several major rivers (e.g., the Yangtze, Mekong, Salween and Yuanjiang River), are largely lacking. In this study, two typical, small watersheds in the dry-hot valley in the Yuanjiang river, which were representative of the landscape, were selected to quantify the relative contributions of potential sediment sources based on the sediment fingerprinting technique. In the orchard-forest watershed, four potential sediment sources, including the slope and level of orchard land, forest, and gully, were identified, while two sources (gully and slope) were identified for the shrub-grass watershed, and the relative contributions of these sources were estimated based on the Bayesian model. The results indicate the following:1) The gully contributed to 55.43% of the total sediment in the shrub-grass watershed, indicating that gully erosion is still significant in the dry-hot valleys, which is in accordance with several previous studies; 2) the ecological restoration in the gully in the orchard-forest watershed has greatly improved the vegetation cover from 2014 to 2021 and substantially reduced the sediment contribution of the gully, indicating that vegetation restoration is an effective ways to reduce sediment yield at the watershed scale; and 3) the orchard land, with an area proportion of<40%, in the orchard-forest watershed contributed to more than 90% of the sediment; this highlights the dominant role of orchard land in sediment yield in the watershed of the dry-hot valley, implying that suitable conservation strategies are necessary to protect soil in the orchard-related watersheds. This study quantitatively evaluated the relative contributions of the main sediment sources in dry-hot valleys, a natural gully, a gully with vegetation restoration, and orchard land, through combined studies. The results of this study could be helpful for deploying appropriate measures to reduce soil erosion and sediment yield in dry-hot valleys.

Novel sediment source fingerprinting quantifying erosion-induced total nitrogen and total phosphorus outputs from an intensive agricultural catchment, North China

Intensive farming is a primary cause of increased sediment and associated nitrogen (N) and phosphorus (P) loads in surface water systems. Determining their contributing sources, pathways and loads present major challenges in the high-intensity agricultural catchments. Herein, we quantify the sediment sources and magnitude of sediment total N and total P from different sources using a novel application of compound-specific stable isotope (CSSI) and fallout radionuclides (FRNs) of 137Cs and 210Pbex in an intensive agricultural catchment in North China. Sediment sources from surface and sub-surface soils were estimated from FRNs fingerprint and accounted for 62 ± 7% and 38 ± 7% respectively, while surface soil from land uses that originated from hillslope were identified by CSSI fingerprint. Using a novel application of FRNs and CSSI sediment fingerprinting techniques, the dominant sediment source was derived from maize farmland (44 ± 0.1%), followed by channel bank (38 ± 7%). The sedimentation rate (13.55 ± 0.30 t ha−1 yr−1) was quantified by the 137Cs cores (0–60 cm) at the outlet of this catchment. The total N and total P in sediment were both mostly derived from maize farmland and least from channel banks. The channel banks are significant sediment sources but contribute little to the input of sediment N and P for eutrophication. It implies that chemically-applied farmlands are the main hotspots for catchment erosion control and pollution prevention. The novel application of FRNs and CSSI techniques cost-effectively quantified sediment N and P loads from different sources with a single visit to the catchment, enabling rapid assessment for optimizing soil conservation strategies and land management practices. Keywords: Sediment sources, Land use, N and P loads, Compound-specific stable isotope, Fallout radionuclides.

Cosmogenic and Geological Evidence for the Occurrence of a Ma-Long Feedback between Uplift and Denudation, Chur Region, Swiss Alps

We used concentrations of in situ cosmogenic 10Be from riverine sediment to quantify the basin-averaged denudation rates and sediment fluxes in the Plessur Basin, Eastern Swiss Alps, which is a tributary stream to the Alpine Rhine, one of the largest streams in Europe. We complement the cosmogenic dataset with the results of morphometric analyses, geomorphic mapping, and sediment fingerprinting techniques. The results reveal that the Plessur Basin is still adjusting to the landscape perturbation caused by the glacial carving during the Last Glacial Maximum c. 20,000 years ago. This adjustment has been most efficient in the downstream part where the bedrock comprises high erodibility North Penninic flysch and Bündnerschist, whereas glacial landforms are still prominently preserved in the upstream region, comprising low erodibility South Penninic and Austroalpine bedrock. This geomorphic observation is supported by the 10Be based denudation rate and sediment provenance analysis, which indicate a much faster sediment production in the flysch and schist lithologies. Interestingly, the reach of fast denudation has experienced the highest exhumation and rock uplift rates. This suggests that lithologic and glacial conditioning have substantially contributed to the local uplift and denudation as some of the driving forces of a positive feedback system.

Using sediment fingerprinting to identify erosion hotspots in a sub-catchment of Lake Kivu, Rwanda.

Sedimentation of water bodies affects water quality and biotic communities of aquatic ecosystems. Understanding the causes and origin of sediments is crucial for planning watershed management activities and safeguarding aquatic biodiversity and critical ecosystem services. Rwanda, as a hilly country, experiences increased sedimentation due to unsustainable land use practices in upstream catchment areas which negatively affects irrigation, fishing and hydropower generation. We used a sediment fingerprinting technique to determine sources of sedimentation and identifying hotspots of soil erosion in Sebeya River Catchment (area of 357km2), a sub-catchment of Lake Kivu located in Northwest Rwanda. Five soil samples were collected from each of the six geological classes, and 34 suspended sediment samples were taken within key locations of the hydrological network in the catchment. X-Ray Spectrometry was used to determine the geochemical composition of suspended sediments and soil. A multi-step statistical procedure with a Bayesian mixing model was used to determine the contribution of each geologic group and sub-catchment to the suspended sediments in the river. Erosion hotspots were classified based on the underlying land use and their contribution to the suspended sediments. The resulting erosion hotspot map shows that about 70.9% of the Sebeya Catchment area contributes at least 50% of sediment load in the river and currently experiences unsustainable land use and land cover. The erosion hotspots identified and culpable factors should be used to guide best land use practices, prioritizing the areas with high contribution to the river sedimentation in Sebeya Catchment.

Improving the quantification of sediment source contributions using different mathematical models and spectral preprocessing techniques for individual or combined spectra of ultraviolet–visible, near- and middle-infrared spectroscopy

In recent years, several sediment fingerprinting studies have used ultraviolet–visible (UV–Vis), near-infrared (NIR) and middle-infrared (MIR) spectroscopy as a low cost, non-destructive and fast alternative to obtain tracer properties to estimate sediment source contributions. For this purpose, partial last square regression (PLSR) has often been used to build predictive parametric models. However, spectra preprocessing and more robust and non-parametric models such as support vector machines (SVM) has gained little attention in these studies. Accordingly, the objectives of the current research were to evaluate (i) the accuracy of two multivariate methods (PLSR and SVM), (ii) the effect of eight spectra preprocessing techniques, and (iii) the effect of using the information contained in the UV–Vis, NIR and MIR regions considered either separately or in combination on sediment source apportionment. The estimated source contribution was then compared with contributions obtained by the conventional fingerprinting approach based on geochemical tracers. This study was carried out in the Arvorezinha catchment (1.23 km2) located in southern Brazil. Forty soil samples were collected in three main potential source (cropland surface, unpaved roads and stream channels) and twenty-nine suspended sediment samples collected at the catchment outlet during nine rainfall-runoff events were used in this study. Both PLSR and SVM models showed a higher accuracy when calibrated and validated with the spectra submitted to spectral processing when compared to the direct use of the raw spectra. The best model results were obtained with PLSR and SVM mathematical models associated with the spectral preprocessing techniques 1st derivative Savitzky-Golay (SGD1), normalization (NOR) and combining NOR + SGD1 in the UV–Vis + NIR + MIR. The lowest errors were observed when the UV–Vis + NIR + MIR bands were combined due to the gain in information and, consequently, the increase in discriminant power achieved by the models. Despite the good accuracy of the models calibrated and validated with the artificial mixtures, significant errors remain when results of source contributions are compared to those obtained with the conventional sediment fingerprinting technique based on geochemical tracers. Nevertheless, the magnitude of the contributions calculated by the spectroscopy and geochemical approaches remains very similar for all sources, especially when using the SVM-UV–Vis + NIR + MIR model. Therefore, spectroscopy proved to be a fast, cheap and accurate technique, offering an alternative to the conventional geochemical approach for discriminating sediment source contributions in agricultural catchments located in subtropical regions.

Variations in transport of suspended sediment and associated elements induced by rainfall and agricultural cycle in a Mediterranean agroforestry catchment

Soil erosion and fine particle exports are two of the major concerns of soil nutrient loss and water quality decrease nowadays. In Mediterranean mountainous environments, agricultural practices during different cropland stages likely increase sediment supplies and the export of fertilisers and pesticides out into the drainage system. In this study, we attempt to evaluate the soil response to different agricultural practices implemented during the agricultural cycle by monitoring the bare soil cropland area through the use of remote sensing and applying the sediment fingerprinting technique together with the newly consensus-based tracer selection method. To this purpose, 128 source samples were distributed over the four main land use/land covers and geomorphic elements existing in the study area. To analyse the spatio-temporal variability of source contributions, three sampling stations were established along the catchment and collected during two hydrological years. The consensus method was used to show the individual messages of each tracer, revealing non-conservative and dissenting tracers, followed by a discriminant function analysis (DFA) to select the best set of tracers for each mixture. Overall, the unmixing model outputs displayed channel bank and agriculture as the main contributing sources for all the seasonal campaigns. Nevertheless, the agricultural contribution was higher during the periods when the soil surface in croplands had no plant cover protection.Certain elements such as As, Co, Li, Mn, Zn and 238U were above source ranges in the sediment mixtures. The enriched elements showed higher content in the sediment mixtures during sowing and after harvest periods. Besides, an enrichment of phosphorous during both agricultural practices periods points out to agricultural activities as the main cause of sediment and elements export to streams. Thus, in the subcatchment with less bare soil cropland area, the agriculture source contributed with the lowest percentages. Our results support the protection of croplands, especially in periods of vegetation cover absence to prevent the loss of fertile soil and the export of potential pollutants to downstream water bodies.

A review of sediment fingerprinting for erosion hotspot assessment in southern Africa

ABSTRACT Sediment fingerprinting techniques are increasingly utilized across the globe to identify and quantify sources of sediment in catchments to assist adequate management and rehabilitation strategies. The technique generally includes classifying source groups, sampling sediment sources and sink zones, analysing tracers and applying statistical analyses to discriminate and quantify the contribution from sources. Although sediment fingerprinting has been used in southern African catchments, a contextual review of studies for the region does not exist. An overview is given of the basic methodological steps, including the tracers utilized in southern Africa, the history and main findings of the studies and recommendations for further research. There are many regions in southern Africa where this technique can still be implemented, especially erosion hotspots of Lesotho and Swaziland. Similar to regions elsewhere, the technique has not been standardized due to variability of erosion processes and causal factors in different environments. Several studies state that soil is the dominant erosion factor in South Africa, especially in catchments that consist of duplex and dispersive soils that are highly erodible. It is recommended that a tracer or set of tracers be found for these problem soils. Sediment fingerprinting has the potential to discriminate soils as potential sediment sources.

Testing the sediment fingerprinting technique using the SIAR model with artificial sediment mixtures

The accurate identification of primary sediment sources in a watershed is necessary to implement targeted management practices that will reduce erosion and restore water quality. Sediment fingerprinting is a commonly used tool to accomplish this task. However, the accuracy and precision of different procedures to select tracers for un-mixing sediment sources are still a largely uninvestigated area in relation to sediment fingerprinting. The goal of this research was to validate a sediment fingerprinting methodology by applying it to the Oostanaula Creek watershed in southeast Tennessee, USA. We assessed three method protocols (soil digestion procedure, objective source grouping, and tracer selection) that are utilized for assessing the performance of fingerprinting in terms of apportionment outputs. The major and trace elemental composition of sediment source and suspended sediment were determined by total dissolution and nitric acid extraction followed by analysis with inductively coupled plasma-optical emission spectrometry (ICP-OES). The Kruskal-Wallis (KW) test as well as stepwise discriminant function analysis (DFA) was utilized during tracer selection. The source un-mixing model utilized was a Bayesian mathematical model within Stable Isotope Analysis in R (SIAR). Sediment fingerprinting in the Oostanaula watershed proved to be difficult due to the chemical and mineralogical similarities of the potentially erodible source material. Upon analysis, it was found that the sediment tracers identified as those with low misclassification during cluster analysis would not guarantee a high degree of accuracy during source apportionment. However, there are certain outputs with low errors as compared with the real proportional contributions in artificial mixtures, for example, findings showed that bank erosion is a primary source of suspended sediment in the Oostanaula Creek. Source apportionment from sediment fingerprinting was sensitive to the digestion procedure, objective source groupings, and the tracer selection. Our research provides a quantitative approach for assessing the validity of the sediment fingerprinting technique.

Use of n-alkanes to trace erosion and main sources of sediments in a watershed in southern Brazil

Erosive processes can transport sediments containing nutrients, heavy metals and contaminants of organic and inorganic origin into bodies of water, therefore affecting the local ecosystem and the population that benefits from the water sources. In order to better understand the origin of sediment sources and establish mitigation measures, the use of the sediment fingerprinting technique has been highlighted. Thus, the present work had as objective to apply n-alkanes in order to trace and understand the main sources of organic matter in sediments and associate the results with land and soil occupation. The study area is located in the municipality of Rio Negrinho - Brazil, in the Saci river basin. Soil samples were collected and classified according to their use and occupation, as well as and samples of local vegetation to be used as reference. The distribution of n-alkanes in the sediments was compared with the distribution found in the vegetation and soil. Previously, a distribution pattern of n-alkanes had been identified in all major vegetation used to trace the source of organic matter and hence the soil. The concentrations of total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP) and granulometry were also analyzed in the soil and sediment samples. Indexes between n-alkanes were used and applied to assess the source together with statistical analysis (PCA). In sum, the results showed that the sediments are mainly composed of Pinus taeda reforestation soils, as well as soil from the abandoned roads used to transport the cut trees, while the contribution of autochthonous sediments was found to be minimal. In this way, the fingerprint technique served as an auxiliary tool in order to establish measures for the good management of a river basin, bringing important information about the contributing sources of sediment to water bodies.

Using reservoir deposits to quantify the source contributions to the sediment yield in the Black Soil Region, Northeast China, based on the fingerprinting technique

Identifying patterns of sediment dynamics is an important aspect of understanding soil erosion processes and developing reasonable management strategies to address environmental problems and assess the ecological functions of soil and water conservation measures. In this study, the sediment fingerprinting technique was applied in order to quantify the relative contributions of sediment to the Hebei catchment in the black soil region of Northeast China, with the aim of determining the response of soil erosion to recent changes in land management. Within an area of approximately 28 km2, three potential sediment sources were identified based on land use types. They included cultivated topsoil, uncultivated topsoil, and gullies. A total of 69 sediment source samples were collected from potential sediment sources from 27 sampling sites for cultivated topsoil, 18 sampling sites for uncultivated topsoil, and 24 sampling sites for gullies. Six uniformly spatially distributed sediment cores were sampled from the Liudui reservoir. The Walling–Collins model was optimized using a genetic algorithm combined with the Latin hypercube sampling procedure. The results indicated that cultivated topsoil and gullies were the primary sediment provenances and that gully erosion is as important as rill and interrill erosion. According to the mean sediment contributions of the six deposited sediment cores, the sediment contribution from cultivated topsoil was 50.6%, ranging from 34.4% to 63.7%, whereas gullies contributed 42.9%, ranging from 30.1% to 57.8%. However, the sediment from uncultivated topsoil (mainly containing forest and grassland) contributed only 6.5%, with a range of 5.0% to 7.8% over the last few decades with a mean absolute fit of 0.95. This indicated that caution is needed in when using only a single core to provide results for a reservoir. Over the 1976–2016 period, rill and interrill erosion showed a general decreasing trend, whereas gully erosion showed an increasing trend. According to the sedimentation depth and time marks based on the 137Cs and D50 peak horizon and decayed vegetation layer in the six sediment cores, sedimentation rates during 1976–1998 and 1999–2016 were 1.6 cm yr−1 (14.4 kg m−2 yr−1) and 0.9 cm yr−1 (7.6 kg m−2 yr−1), respectively. For the entire time series (1976–2016), the sedimentation rate was 1.2 cm yr−1 (10.7 kg m−2 yr−1). A good correlation exists between the distance from the reservoir entrance and sediment contribution/mean annual sedimentation rate (r2 > 0.68, except uncultivated topsoil).

Sources, Sinks, and Subsidies: Terrestrial Carbon Storage in Mid‐latitude Fjords

AbstractFjords are recognized as globally important sites for the burial and long‐term storage of carbon (C) within sediments. The proximity of fjords to the terrestrial environment in combination with their geomorphology and hydrography results in the fjordic sediments being subsidized with organic carbon (OC) from the terrestrial environment. It has been well documented that terrestrial OC (OCterr) is an important component of coastal sediments, yet our understanding of the quantity of OCterr stored in these sediments remains poorly constrained. Utilizing Bayesian isotopic sediment fingerprinting techniques to the surface sediments of Loch Sunart, we estimate that 42.0 ± 10.1% of the OC is terrestrial in origin. Through combining these outputs with sedimentary OC stock estimates, we have calculated that the surface sediments (0–15 cm) hold 0.1 megaton (Mt) OCterr and estimate that the postglacial sediment held within the fjord contains 3.96 Mt OCterr. When these totals are compared to the quantity of OC stored in the adjacent terrestrial environment, it is clear that the fjord's catchment stores a greater amount of OCterr in the form of vegetation and soil. Though when normalized for area the results suggest that the marine sediments are a more effective long‐term store of OCterr than the adjacent terrestrial environment. This striking result highlights the importance of the terrestrial environment as a source of OC to the coastal ocean and that the OCterr subsidy to the marine sediments is a significant mechanism for the long‐term storage of OC in coastal marine sediments.

Tracing Sediment Sources in a Subtropical Agricultural Catchment of Southern Brazil Cultivated With Conventional and Conservation Farming Practices

AbstractIn Brazil, agricultural expansion has increased soil erosion and sediment supply to waterways. As elevated sediment loads often degrade freshwater environments, sediment fingerprinting techniques are increasingly used to identify the sources supplying sediment to riverine and lacustrine environments. In this study, the contribution of various soil types to sediment was investigated in the Guaporé catchment (2,032 km2) in southern Brazil. Soil samples (n = 75) were collected to characterise five soil types: Ferralsols (n = 26), Nitisols (n = 13), Acrisols (n = 8), Leptosols (n = 6) and Luvisols (n = 22). Sediment samples (n = 7) were collected in a trap installed at the catchment outlet. Sediment source contributions were modelled according to soil types with elemental geochemistry and 87Sr/86Sr ratios. 87Sr/86Sr ratios, K, Ti, Co, As, Ba and Pb were selected as the optimal suite of properties discriminating between soil types. Sediment samples were modelled to mainly originate from downstream Acrisols [mean 41%, standard deviation (SD) 2%], Leptosols (mean 34%, SD 4%) and Luvisols (mean 17%, SD 4%). In contrast, contributions of upstream Ferralsols (mean 4%, SD 2%) and Nitisols (mean 4%, SD 6%) were low. These results suggest that soils found in lower parts of the catchment, cultivated with conventional agriculture on steep slopes, were the main source of sediment to the river network. In contrast, soils found in upper parts of the catchment, cultivated with soybean under direct sowing, were less eroded or deposited before reaching the sediment sampling location at the outlet. These findings demonstrate that the management of local and degraded soil sources is important for reducing sediment loads. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Biomarkers in sedimentary sequences: Indicators to track sediment sources over decadal timescales

Long-term sedimentary sequence research can reveal how human activities and climate interact to affect catchment vegetation, flooding, soil erosion, and sediment sources. In this study, a biomarker sediment fingerprinting technique based on n-alkanes was used to identify long timescale (decadal) sediment sources in a small agricultural catchment. However, the highly saline carbonate environment and bacterial and algal activities elevated the levels of even-chain n-alkanes in the sediments, leading to an obvious even-over-odd predominance of short and middle components (C15-C26). Therefore, by analyzing three odd, long-chain n-alkanes (C27, C29 and C31) in 27 source samples from cropland, gully, and steep slope areas and one sediment sequence (one cultivated horizon and 47 flood couplets), a composite fingerprinting method and genetic algorithm optimization were applied to find the optimal source contributions to sediments. The biomarker fingerprinting results demonstrated that the primary sediment source is gullies, followed by cropland and steep slope areas. The average median source contributions associated with 47 flood couples collected from sediment core samples ranged from 0±0.1% to 91.9±0.4% with an average of 45.0% for gullies, 0±0.4% to 95.6±1.6% with an average of 38.2% for cropland, and 0±2.1% to 60.7±0.4% with an average of 16.8% for steep slopes. However, because farmers were highly motivated to manage the cropland after the 1980s, over half the sediments were derived from cropland in the 1980s. Biomarkers have significant advantages in the identification of sediments derived from different landscape units (e.g., gully and steep slope areas), and n-alkanes have considerable potential in high-resolution research of environmental change based on soil erosion in the hilly Loess Plateau region.

Spatial distribution of 137Cs in surface soil under different land uses in Chao Phraya watershed: Potential used as sediment source tracing

Sediment fingerprinting techniques involves the discrimination of sediment sources based on differences in source material properties and quantification of the relative contributions from these sources to sediment delivered downstream to the river catchments. Results of the previous study indicated that fallout radionuclides (FRNs); 137Cs and excess 210Pb (210Pbex) are the most suitable radionuclides to be used as sediments sources tracers. This study investigated the spatial distribution of 137Cs in soil under different land uses in Chao Phraya watershed; the most significant watershed in Thailand. Emphasis was placed on discriminating among potential sediment sources including the cultivated (upland crops), pasture field, uncultivated (swamp, forest, and grass field), and channel erosion (stream and river bank). One hundred and twenty four soil samples were collected from all sources and determining for 137Cs. The 137Cs mass activities in pasture areas varied from the limit of detection (LLD) to 1.22±0.05 with the average of 0.64±0.14 Bq kg-1. In cultivated areas the 137Cs mass activities varied from LLD to 1.41±0.04 with the average of 0.38±0.04 Bq kg-1. The 137Cs mass activities were higher in uncultivated areas varied from 0.12±0.03 to 1.73±0.05 with the average of 0.76±0.15 Bq kg-1. The 137Cs mass activities in channel bank varied from LLD to 1.16±0.04 with the average of 0.39±0.05 Bq kg-1.GIS and geospatial interpolations revealed pattern in the spatial concentrations of 137Cs and indicated important differences in its distributions showing the differences behaviour of 137Cs in different land uses.

A comparison of geological and statistical approaches to element selection for sediment fingerprinting

PurposeElevated sediment loads reduce reservoir capacity and significantly increase the cost of operating water treatment infrastructure making the management of sediment supply to reservoirs of increasing importance. Sediment fingerprinting techniques can be used to model the relative contributions of different sources of sediment accumulating in reservoirs. The goal of this research is to compare geological and statistical approaches to element selection for sediment fingerprinting modelling.Materials and methodsTime-integrated samplers (n = 45) were used to obtain source samples from four major subcatchments flowing into the Baroon Pocket Reservoir in South East Queensland, Australia. The geochemistry of these potential sources was compared to sediment cores (n = 12) sampled in the reservoir. Elements that provided expected, observed and statistical discrimination between sediment sources were selected for modelling with the geological approach. Two statistical approaches selected elements for modelling with the Kruskal–Wallis H test and discriminatory function analysis (DFA). In particular, two approaches to the DFA were adopted to investigate the importance of element selection on modelling results. A distribution model determined the relative contributions of different sources to sediment sampled in the Baroon Pocket Reservoir.Results and discussionElemental discrimination was expected between one subcatchment (Obi Obi Creek) and the remaining subcatchments (Lexys, Falls and Bridge creeks). Six major elements were expected to provide discrimination. Of these six, only Fe2O3 and SiO2 provided expected, observed and statistical discrimination. Modelling results with this geological approach indicated that 36 % (±9 %) of sediment sampled in the reservoir cores were from mafic-derived sources and 64 % (±9 %) were from felsic-derived sources. The geological and the first statistical approach differed by only 1 % (σ 5 %) for five out of six model groupings with only the Lexys Creek modelling results differing significantly (35 %). The statistical model with expanded elemental selection differed from the geological model by an average of 30 % for all six models.ConclusionsElemental selection for sediment fingerprinting therefore has the potential to impact modelling results. Accordingly, we believe that it is important to incorporate both robust geological and statistical approaches when selecting elements for sediment fingerprinting. For the Baroon Pocket Reservoir, management should focus on reducing the supply of sediments derived from felsic sources in each of the subcatchments.

Sources of fine sediment stored in agricultural lowland streams, Midwest, USA

Agricultural activities can accelerate the offsite transport of productive soil from fields leading to stream water quality degradation. Identification of the nature and relative contribution of different sources to fine-grained sediment (e.g., silts, clays) in streams is important to effectively focus agricultural best management practices in watersheds. Sediment fingerprinting techniques through the use of geochemical tracers are commonly used to differentiate relative contribution from various sources. Research was conducted in lowland streams in the Pleasant Valley watershed in South Central Wisconsin (USA) to identify provenance of fine-grained sediment deposits and evaluate the impact of land use on relative contributions from the following potential sources: cropland, pasture, woodland, and eroding stream banks. Results show that both agriculture (croplands and pastures) and eroding stream banks are primary sources to fine sediment deposits on the stream bed with contributions ranging from 19 to 100% and 0 to 81%, respectively. The increase in area under agricultural land use within a subwatershed results in greater contribution from agriculture (R2=0.846, p=0.0034). Relative contributions from eroding stream banks increased with increasing area under grasslands and woodlands within a subwatershed (R2=0.814, p=0.0055). Subwatersheds with greater mass of fine sediment deposited on the stream bed per unit area should be prioritized for best management practices. The conservation practices should be targeted to stream banks or croplands depending on the dominant source of fine sediment within a subwatershed. Site specific changes in relative contributions from different sources to fine-grained sediment in this watershed highlights the complexities involved in sediment transport dynamics. The nested sampling sites helped determine that sediment dynamics at the subwatershed scale need to be considered for application of targeted conservation techniques.