Quantifying organic carbon (OC) levels and the processes altering them is key in unlocking soils potential as a mediator of climate change through sequestration of atmospheric CO₂. In areas of high soil erosion increased fluxes of OC across the terrestrial-aquatic interface are likely and understanding these fluxes is crucial in integrating lateral OC fluxes within the carbon cycle. For this study of a small UK catchment, OC mapping and Revised Universal Soil Loss Equation (RUSLE) based erosion modelling provided estimates of proportional soil OC loss coming from each land use. Sediment fingerprinting using n-alkane biomarkers and a Bayesian unmixing model provided a comparison of streambed OC proportions by land use to assess which processes were dominating OC input to streams. Results showed that RUSLE-based soil OC loss proportions exhibited disconnect with sediment fingerprinting OC composition and the river corridor and riparian environment were key zones in regulating terrestrial to aquatic fluxes of OC.

How to cite: Wiltshire, K., Glendell, M., Waine, T., Grabowski, R., Thornton, B., and Meersmans, J.: From field to stream: Tracing streambed organic carbon origins at a catchment scale, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4571, https://doi.org/10.5194/egusphere-egu21-4571, 2021.

To manage effectively excessive sediment inputs to rivers and streams, it is crucial to have detailed and reliable information on key sediment sources. Such evidence is important for implementing targeted measures for improving ecosystem functioning and meeting environmental objectives. Although sediment fingerprinting is increasingly adopted worldwide to provide such evidence, current procedures do not provide detailed information on how sediment sources can change over both short (e.g., events and in between events) and long (e.g., over seasons or years) time scales. These limitations are mainly due to the conventional methods used for target sediment sampling and the high workloads and costs associated with laboratory analyses for tracers, which limit both high-frequency and longer duration sampling campaigns. To address this issue, we propose the use of a submersible spectrophotometer, which measures absorbance in the UV-VIS range in situ and at high frequency (e.g., minutes) to trace suspended sediment sources. In our proof of concept investigation, the approach was first tested in a laboratory setting, using soil samples and artificial mixtures with known proportions of two, three and four soil source samples in an experimental water tank. A total of six soil samples were collected, which were sieved to different fractions to investigate the influence of particle size on the sensor absorbance readings. Both soil samples and artificial mixtures were suspended in the laboratory tank set-up at different concentrations to investigate the effects on: (i) absorbance, and; (ii) un-mixing accuracy. The results showed that absorbance was linearly additive and could be used to predict dominant samples in the artificial mixtures correctly using a Bayesian tracer un-mixing model, largely regardless of particle size and of the concentration inside the experimental tank. This approach is currently being tested in a field experiment in the Attert River Basin (Luxembourg) to investigate if the results found in the laboratory experiments hold under natural field conditions. Our preliminary insights into the use of absorbance for sediment source apportionment in the field will be presented.

How to cite: Lake, N., Martínez-Carreras, N., Shaw, P., and Collins, A.: High-frequency absorbance measurements for sediment source apportionment – laboratory and field assessment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8601, https://doi.org/10.5194/egusphere-egu21-8601, 2021.

Phytoliths are a plant microfossil commonly used as qualitative archive markers in archaeological and paleoecological studies. Their potential uniqueness to the vegetation cover, robustness to weathering, and lack of chemical alteration along the paths make them a potentially suitable tracer for quantitative erosion studies.
In this pilot study, we explore the potential of phytoliths in a sediment fingerprinting study in the Ceguera catchment (28 km2) in NE Spain. The phytolith concentrations and morphologies of four land cover classes (agricultural land, badland, forest, and shrubland) were analyzed, and their contributions to four sediment mixture samples along the river course were modelled. Phytoliths concentrations allowed us to discriminate sources sufficiently, albeit with limited sample size. The performance of the phytoliths as the tracer was tested by reproducing the sources of artificial sediment mixture samples with satisfactory recall ratio. Results identified badlands to be the main contributor, with 84–96% of the sediment load to the sinks, followed by shrublands (median 5%) and agricultural lands (median 2%). Additionally, an intensively used agricultural area in the SW of the catchment was well indicated. These major findings can be reproduced by other conventional erosion studies from this area, indicating that phytoliths are suited to quantifying erosion patterns in mesoscale catchments.

How to cite: Kraushaar, S., Konzett, M., Kiep, J., Siebert, C., and Meister, J.: Suitability of phytoliths as a quantitative process tracer for soil erosion studies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15156, https://doi.org/10.5194/egusphere-egu21-15156, 2021.

The Rapel Basin (ca 14,000 km²), Chile, provides a wide range of ecosystem services from mining activities and water supply from its Central Andean headwaters to mixed agricultural food production and hydropower generation in the Central Valley. The breadth of ecosystem service provision, range of land use and wider anthropogenic pressures makes the Rapel system an ideal natural laboratory in which to evaluate tools to support soil erosion mitigation in the context of enhancing food, water and energy security.

Taking a distributed approach to encompass geological variability plus superimposed land management and natural process variability, replicate tributary sediment samples (n = 10± per tributary, total number of sediment samples= 313) were collected from across the system to characterise sediment inputs from the major potential sediment sources : (a) natural sediment production in steep Andean headwaters driven by (i) glacial retreat and (ii) seasonal snow melt, (b) sediment inputs from major copper mining operations in the Andes, (d) soil erosion on agricultural land in the Central valley basin area and (e) soil erosion on agricultural land in the Coastal Mountain Belt bordering the hydropower reservoir, Lake Rapel. Samples of river bed sediment from two main sub-catchments (north: Cachapoal River, South: Tinguiririca River) were collected at the outlet to the upper Andean catchment, below the central valley agricultural zone and downstream of a major tributary confluence above the reservoir. In addition, 12 surficial sediment samples were collected from the main arm of the reservoir. All materials were analysed for major and minor element geochemistry by Wave-length Dispersive X-Ray Fluorescence (44 elements).

Mixtures were compared in terms of their source material groups in a series of nested MixSIAR mixing model runs after selection of appropriate tracer groups following established procedures. In the northern tributary to the reservoir, mining effluent dominated the sediment supply in upper reaches (78%) with the reminder from natural landscape denudation plus a small proportion of glacial-derived sediments (5%). The influence of the mine was diluted by significant inputs of sediment from agricultural sources (fruit orchards and grain production) in the central basin (agriculture 53%, mining 25%) but given the scale of the system, mining remained a major contributor to the reservoir sediment column, with high Cu concentrations (ca 450 mg kg^-1) observed in reservoir sediment. In the southern tributary, in the absence of mining, natural erosion upstream was dominated by snow melt processes (70%) compared to glacial melt (30%). In the lower reaches downstream of agricultural land, agricultural inputs dominated (53%) with natural erosion in mountain headwaters still contributing (45% overall). Evaluation of reservoir sediment against main geological, natural and anthropogenic tributary-based classification demonstrated significant inputs of sediment from Coastal Mountain agriculture (41%) where steep hillslopes are being actively converted from natural vegetation to plantations (olives, avocados etc). Moreover, sediment contribution coming from mining activities were still considerable (31%).

Future land-management decisions require quantification of soil erosion  hotspots for targeted mitigation measures. Natural science results are discussed in the context of parallel participatory approaches to developing stakeholder consensus on future actions.

How to cite: Blake, W., Munoz-Arcos, E., Ovando-Fuentealba, L., Kitch, J., Kelly, C., Del Valle, A., and Bravo-Linares, C.: Spatial dynamics of soil erosion impacts on food, water and energy security in a large Andean river basin, Chile, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12370, https://doi.org/10.5194/egusphere-egu21-12370, 2021.

The study site consists of two sub-basins (“Arbolito”, 20.94 km2; and “Horno”, 10.44 km2) divided by the Rolon stream, which in turn flows into the Baygorria hydroelectric dam reservoir (-32.77152 S; -56.84093 W). The "Arbolito" sub-basin consists of natural pasture with extensive cattle from the 19th century to the present day.  Soils are predominantly eutric brunosols and clayey haplic vertisols with slopes > 6% (MGAP, Uruguay). The “Horno” sub-basin consists of intensive agriculture since the mid-1980s, with a history of rice, wheat, oat, soybean and pastureland rotations. At the beginning of the 2000s, direct sowing began in this region of the country. Soils in Horno are predominantly clayey, deep Haplic Vertisols and Typical Eurethric Brunosols, clayey silt, vertically and moderately deep, with slopes ≤ 6 % (MGAP, Uruguay). Both soil types and their formation are associated with basaltic lithologies. A total of 50 surface samples from natural pastures, cropland and channel banks were used as sources to describe the mixture of sediments (fine-bed material) using geochemical elements and the FingerPro mixing model. For the 137Cs technique, a total of 120 surface samples were taken, multi-transect sampling was conducted in both sub-basins, and reference sites were established. Profile Distribution Model (PDM) and Diffusion Model (DM) were used as conversion model for the Arbolito sub-basin, while Mass Balance Model II (MBM II) was used for Horno sub-basin. MODERN model was used in both areas. Sediment fingerprinting results showed that the proportion of sediment sources is divided as follows: cropland (up to 70%), pastures (up to 25%) and channel banks (the remaining 5%). The reference value of 137Cs found was 369.0 bq.m-2 (SD 7.4 bq.m-2) on 01/01/2020 calibration date. The results of the net soil redistribution rates using different conversion models of 137Cs were consistent with each other, and showed erosion in both sub-basins, Arbolito: PDM (-0.72 Mg ha-1 yr-1), DM (-0.29 Mg ha-1 yr-1), MODERN (-0.69 Mg ha-1 yr-1); Horno: MBM II (-0.5 Mg ha-1 yr-1), MODERN (-0.56 Mg ha-1 yr-1). Although the net erosion rate in both sub-basins is similar, the redistribution of soil within each sub-basin is different. While the Arbolito shows on average preserved areas at the top of the slopes (MODERN 1.7 Mg ha-1 yr-1), with high erosion in the middle (MODERN -5.7 Mg ha-1 yr-1) and low erosion in lower areas (MODERN -0.47 Mg ha-1 yr-1); Horno sub-basin shows in average eroded areas at the top of the slopes (MODERN -4.3 Mg ha-1 yr-1) with low sedimentation in the middle (MODERN 0.4 Mg ha-1 yr-1) and high sedimentation in the lower areas (MODERN 2.21 Mg ha-1 yr-1). This would explain a greater redistribution of the soil from the high to the low areas in the Horno sub-basin compared to Arbolito, probably due to the mechanical movement of the soil by agriculture practice. These results may explain a greater export of soils in Horno compared to Arbolito, which agrees with cropland as the most important source of sediments (up to 70%) by fingerprinting techniques.

How to cite: Tassano, M., Sanabria, R., Gonzalez, J., Cabral, P., Tejeda, S., Melgar, E., Zarazua, G., and Cabrera, M.: Evaluation of soil erosion and sediment sources in two contrasting sub-basins, using fingerprinting and 137Cs techniques in Uruguay. Preliminary results., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6466, https://doi.org/10.5194/egusphere-egu21-6466, 2021.

Although sediment yield reflects a catchment’s erosive processes, material transfer from hillslopes to rivers depends on a series of phenomena occurring on variable and continuous range of scales. Physically based, distributed models can be used to evaluate erosion’s spatial variability within a catchment and to identify hotspots. Sediment fingerprinting allows source type discrimination based on sediment and soil properties. The analysis of these dynamic systems could be coupled by addressing hillslope processes with modeling, while fingerprinting enlightens the connection between them and the drainage network. We aimed to evaluate the erosive susceptibility and its spatial distribution in three environmentally fragile paired headwater catchments, nested within Guarda Mor catchment, located in the border of the volcanic plateau in southern Brazil. This catchment is characterized by intense agricultural use, diverse geology, and complex terrain. WATERSED model was used as a dynamic method to evaluate the spatial distribution of hydrologic and erosive fragility during rainfall events. WATERSED was parameterized for modeling surface runoff volume, sediment yield and interrill erosion, based on monitored data from a zero-order no-till catchment and literature data. Modeling results were analyzed for each land use. For fingerprinting, two sediment sampling strategies and source groupings were considered. One considered spatial sources, and the endmembers were the sub catchments, the other considered land use source types within each sub catchment. Deposited bed sediment samples were collected at the outlets of each sub catchment and the main outlet. Soil source samples were collected in crop fields, grasslands, stream channels, forests, and unpaved roads. Crop fields and grasslands compose the source type topsoil. Samples were analyzed by near-infrared spectroscopy. Artificial mixtures were made to calibrate the prediction models. Fifteen Support Vector Machine (SVM) models were built and independently trained. Modeled erosion indicates that the steepest areas and those near the drainage network can be the most susceptible to erosion and runoff. The spatial distribution of runoff-prone areas shows the connectivity from upper segments of these catchments increases with higher magnitude events. In fingerprinting, calibration results’ predictors show good performance by the models, validation results vary from poor to good. SVM models for unpaved roads and forest had the best validation performance. For sourcing tributaries, results and poor validation statistical results indicate the need to use different tracers, and to consider unsampled sources associated to soil and geological differences found downstream from the sub catchment’s outlets. As for the sub catchments, there is a variation among the main sediment sources and a significantly constant contribution from unpaved roads in all of them. Other important sources are topsoil and stream channels, while forests did not show significant contribution. These methodologies were useful in seeking a more holistic process understanding, as physical processes were addressed and later integrated with the resulting sediment yield. Despite the results are modelled, the complementation of their insights indicates that there is a possibility for validating the sediment fingerprinting technique once modelling is validated by monitored and measured data.

How to cite: Dambroz, A., Minella, J., Tiecher, T., Moura-Bueno, J., Bernardi, F., Schneider, F., and Evrard, O.: Erosion modeling and tracing sediment sources at Guarda Mor catchment in southern Brazil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12917, https://doi.org/10.5194/egusphere-egu21-12917, 2021.

The combination of a changing climate and growing population poses a contemporary challenge for the water-food-energy security nexus in mountain regions, especially in glacier-fed catchments such as the Rio Santa in the Peruvian Andes. Soil erosion due to both natural processes and anthropogenic activities can exacerbate this challenge, with increased levels of sediment in river systems endangering crucial river functions, such as crop irrigation, drinking water, and hydroelectricity. Furthermore, sediment can act as a transport pathway for contaminants, in addition to being a source of contamination itself. Previous studies have suggested that soil erosion related to human activity vastly exceeds the rate of natural soil production in many Andean catchments, where research to date has primarily focused on larger eastern catchments. Smaller western catchments, however, are important for many major Andean cities reliant upon upstream water supplies. It is thus, important to identify sediment sources and better understand sediment dynamics to manage the threats to water supply.

Sediment fingerprinting approaches are one technique that can contribute to improved understanding of sediment sources and dynamics and the impact of soil erosion in a catchment, and thus contribute to water resource management at the catchment level. Taking a distributed approach along the Rio Santa, this study aims to improve understanding of natural and anthropogenic contributions to sediment production in this Andean system. Key sediment sources explored are glacial sediment potentially enhanced by retreat, agricultural land, forestry operations, land under natural vegetation, and mining. The distributed approach permits quantification of their dynamics throughout the catchment. All source and mixture samples were analysed using Wavelength Dispersive X-ray Fluorescence (WD XRF) to develop geochemical fingerprints and the MixSIAR mixing model was used to apportion sediment sources. While sediment sampling presents a number of challenges when working in remote, mountainous regions such as the Rio Santa catchment, sediment fingerprinting has the potential to help reduce environmental degradation when used to guide local resource management decisions.

How to cite: Kitch, J., Clason, C., Rangecroft, S., Morera, S., and Blake, W.: Assessing the contribution of natural and anthropogenic processes on sediment dynamics in the Rio Santa (Peru) through sediment fingerprinting, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8487, https://doi.org/10.5194/egusphere-egu21-8487, 2021.

Soil erosion is one of the most serious environmental problems caused by land-use changes in semi-arid regions of central Argentina. Hence, to understand the erosive dynamics in these regions becomes fundamental. 

Sub-catchment Durazno del Medio (6.56 km²) is located 21 km northeast of San Luis City (S 33º 08’ 16” – W 66º 09’ 18”; S 33º 11’ 44” – W 66º 08’ 06”), in the central region of Argentina. The average annual temperature is 17 ºC. Annual rainfall ranges from 600 to 800 mm, with a tendency to increase in the last years. Rainfall varies seasonally, with a dry season from May to October and a rainy season from November to April. This agricultural catchment has been researched to identify critical hot spots of land degradation by applying sediment source fingerprinting techniques. 

In the studied area, exotic tree plantations in protected areas (in a state of youth development), native woodland, roads (dirt and paved), agricultural fields, and channel banks were identified as sources of sediments. Most of the sources were found on quaternary deposits (loessoid deposits), except native forests and some roads, which were found in gneiss and migmatites. The sub-catchment has a drainage network formed by two water courses that converge into the main one. Channel sediments (mixtures) were collected at the end of the main channel.

The energy dispersive X-ray fluorescence (EDXRF) analytical technique and the MixSIAR unmixing model were implemented to estimate the contribution of sediment sources in mixtures. The sources and mixtures (tablets) were analyzed in triplicate using a Si-Li detector SDD (resolution 145 keV, Kalpha Mn) with a X ray tube of 50 W and 50 kV. The tracers were analyzed using a fundamental parameters method. Since the selection of correct fingerprints has been proven to be an essential stage in the analysis, before unmixing the natural sediment samples, two artificial mixtures were made using known quantities of soil collected in the identified sources to test the precision and robustness of the tracers selection procedure. These analyses showed that the use of most of the tracers (25 elements) increases the exactitude of calculated proportions. The first mixture was made using two sources, exotic tree plantation in protected areas (35.6 %) and agricultural fields (64.4 %). The second mixture was created using different proportions of 4 different sources including native woodland (30 %), exotic tree plantation in protected areas (20 %), agricultural fields (5 %) and channel banks (45 %). A low mean absolute error (MAE) of 2 % and 4 %, respectively, was obtained when reconstructing the 2 artificial mixtures. This outcome indicates that the selection process was effective.

Once the tracers were properly selected, the natural sediment samples were analyzed. Hence, for the catchment mixture, the main sources of sediments were exotic tree plantation in protected areas (96.7 %) and roads (1.8 %). The application of the fingerprint technique highlighted that forests are one of the largest contributors of sediment, followed by dirt roads.

How to cite: Garcias, Y., Torres Astorga, R., Borgatello, G., Tejeda-Vega, S., de los Santos-Villalobos, S., and Velasco, H.: Geochemical fingerprints for tracing sediments in the sub-catchment Durazno del Medio, Argentina , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7811, https://doi.org/10.5194/egusphere-egu21-7811, 2021.

The Nechako River Basin (NRB) in central British Columbia is a large (52,000 km²), regulated basin that supports populations of sockeye and chinook salmon and the endangered Nechako white sturgeon. These important species are experiencing population declines and one potential cause of this decline is excess sediment, which can clog their spawning habitat and reduce juvenile success. This excess sediment is likely the product of a combination of factors, the most visible being the significant land cover changes that have occurred in the basin, which includes pressure from forestry and agriculture, the Mountain Pine Beetle epidemic, and large-scale wildfires in 2018. Focusing specifically on the impact of the 2018 wildfires on sediment transport from upland burned areas to adjacent waterways, this research aimed to determine the spatial and temporal contamination of tributaries and the mainstem of the Nechako River with polycyclic aromatic hydrocarbons (PAHs), which are produced during the combustion of organic matter and have been identified as toxic to aquatic organisms and to humans. Additionally, this study intended to determine if burned areas were a more significant contributor of sediment than unburned areas and better understand the utility of PAHs as a potential tracer. Source soil samples were collected in 2018 and 2020 from burned and unburned sites, and suspended sediment samples were collected throughout the ice-free period from 2018-2020 in three tributaries and three mainstem sites. All samples were analysed for PAHs, magnetic susceptibility, colour, and particle size. Results from the fall 2018 source samples show a significant difference in PAH concentrations between unburned and burned soils, and while concentrations of PAHs in source soils in 2020 were lower than in 2018, they were still elevated compared to unburned soils. Sediment samples showed that concentrations of total PAHs are higher in the mainstem sites than in the tributaries, with the greatest concentrations consistently found at the most downstream site on the mainstem of the Nechako River. Concentrations across sites were highest in samples taken during the spring snowmelt period in 2019, have decreased throughout the rest of the sampling period (2019-2020), and are well below sediment quality guidelines for total PAHs. In addition to determining the spatial and temporal extent of PAH contamination, this study also aims to use PAHs along with colour and measurements of magnetic susceptibility to trace sediments associated with the 2018 wildfires. The high cost of PAH analysis limits the number of samples that can be analysed and thus, these additional tracers will allow for the use of models such as MixSIAR that improve with a more robust number of samples. As large-scale megafires continue to burn across the globe, understanding their potential to contribute PAHs to local waterbodies and potentially be used as a tracer is as prescient as ever.

How to cite: Kieta, K., Owens, P., and Petticrew, E.: Using polycyclic aromatic hydrocarbons to determine post-wildfire contamination and sediment sources in a large watershed in central British Columbia, Canada, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10491, https://doi.org/10.5194/egusphere-egu21-10491, 2021.

In the Sahel, climate variability and high population growth have led to changes in surface conditions that resulted in increased runoff coefficients and discharge in the major Sahelian rivers. The mid reaches of the Niger river have experienced significant increases in the Red flood, or local flood, that occurs during the rainy season between June and September, relative to Black flood, or Guinean flood that arrives in Niamey from December onwards.
The objective of this work was to characterize suspended particulate matter (SPM) during the Red and Black floods in the Niamey area and analyse their spatio-temporal dynamics. Two approaches are used : the first one consists of regular in-situ measurements of SPM concentration and in their physical and mineral characterization by electron microscopy; the second is based on monitoring water color by both in-situ and satellite (Sentinel 2) radiometric measurements.
SPM are characterized by very fine particles (with a major mode around 0.1-0.2 micrometers) mainly composed by kaolinites (iron oxides are also observed during the Red flood). This, combined with the very high levels of SPM concentration reached during the rainy season, results in very high values of reflectance in the visible end infrared bands. Radiometric measurements in the nir band by both the in-situ SKYE sensor and the Sentinel2 sensor are found to be significantly correlated to in-situ SPM, allowing efficient monitoring of SPM concentration in time and space.
SPM-discharge curves, reveal a complex relationship : SPM increases very rapidly at the beginning of the rainy season when soils are washed out after the long dry period, reaching a peak before the first discharge peak (Red flood). SPM continues to decrease during the second discharge peak (Black flood) from December to February, providing a distinct and unique signature. Analysis of satellite data allowed identifying the main sources of SPM and to quantify the significant contribution of the right bank river tributaries to sediments in the middle Niger river bassin. This contribution may further increase in the context of global changes (climate and anthropogenic) with important consequences on sediment transport but also on water quality and bacterial concentration which are strongly influenced by high SPM.

How to cite: Boubacar Moussa, M., Abdourhamane Touré, A., Lartiges, B., Rochelle Newall, E., Kergoat, L., Robert, E., Gosset, M., Alkali Tanimoun, B., and Grippa, M.: Hydrological variability and suspended particulate matter in the middle river Niger bassin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2210, https://doi.org/10.5194/egusphere-egu21-2210, 2021.

The FDNPP-derived ¹³⁷Cs triggers significant concern due to its potential health risk and on-going environmental pollution. Approximately 27% of ¹³⁷Cs are deposited in the terrestrial environment, and most of them remain in catchment until now. This severe radioactive contamination situation has driven government-led decontamination efforts to be implemented since 2012. Earlier studies reveal the influence of decontamination on local soil erosion, thereby changing the fluvial sediment supply and ¹³⁷Cs concentration. However, the dynamic transport process of suspended sediments (SS) and particulate ¹³⁷Cs remains unknown and the resulting variation of particulate ¹³⁷Cs fluxes into the ocean hasn’t been totally evaluated because of the unavailable decontamination relevant materials and long-term monitoring data. Moreover, the shortcomings in the present SS load estimation method limited the possibility for further qualifying the impact of anthropogenic perturbation on SS load and their relative contribution by anthropogenic perturbations.

Here, combining the GIS and aerial photography, we report government-scheduled decontamination dataset for the Nidda river basin and exhibit the significant difference in their land covers in spatiotemporal scales, revealing the existence of different soil erosivity therein. Through a long-term monitoring campaign spanning decontamination and post-decontamination stages, we systematically explore the dynamic influence of decontamination on SS and particulate ¹³⁷Cs transport. Our results show SS load (normalized by precipitation factor) gradually increased but particulate ¹³⁷Cs concentration dropped sharply with the processing of decontamination, which probably is attributable to the increasing supply of ¹³⁷Cs-depleted eroded soil particulate from decontaminated land. We estimate the range of ¹³⁷Cs fluxes within 122 to 588 GBq·a^-1 in 2013-2018 and find a continuous declination tendency in ¹³⁷Cs load after 2015, suggesting that decontamination restraining fluvial ¹³⁷Cs into the ocean. Based on the normalized difference vegetation index (NDVI), we evaluate the land cover changes in the decontaminated regions and applied them in the universal soil loss equation (ULSE) for estimating the fluvial load of SS during the study period. In comparison with the total SS flux in the study region, about 32%~71% of fluvial SS were thought from decontaminated land, highlighting the important role of decontamination in SS supply.  

Scientifically, our findings not only fill the knowledge gap in the influence of decontamination but also respond to the global concern about yearly variations of ¹³⁷Cs fluxes into the ocean under the influence of decontamination. More importantly, we propose and validate an approach for evaluating the input of SS and particulate ¹³⁷Cs to the ocean, which is extendable to apply in other interested catchment and forest.

How to cite: Feng, B., Onda, Y., Yamanaka, Y., and Taniguchi, K.: Influence of the decontamination work on suspended sediment dynamics and 137Cs migration after the Fukushima nuclear accident, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14891, https://doi.org/10.5194/egusphere-egu21-14891, 2021.

The Fukushima nuclear accident released large quantities of radionuclides into the environment in March 2011 and generated a 3000-km² plume of soils heavily contaminated with Cs-137. Soil erosion in the region mainly takes place during typhoons generally occurring between July and October (Laceby et al., 2016). During these events, rivers draining the main plume may transport large quantities of sediment and radiocesium. Typhoon Hagibis that occurred in October 2019 was the most intense rainfall event affecting the Fukushima region (rainfall range: 77–558 mm) since the nuclear accident in 2011. It led to extensive landsliding and river overflow.

The impact of this event on sediment sources and Cs-137 contamination was quantified through the implementation of sediment fingerprinting using geochemistry and spectrocolorimetry as potential input properties. The signature of potential source material (including cropland prepared for recultivation after decontamination, forests and subsurface material originating from landslides and channel bank collapse; n=57) was compared with that of sediment deposits collected in the Mano and Niida River catchments late in October 2019. Results show that cropland supplied the main source of sediment (average: 54%) along with forests (41%). In contrast, the contribution of subsurface material (5%) was much lower, likely because landslides and channel bank erosion mainly took place after the flood peak (Evrard et al., 2020). However, this material that deposited at the foot of hillslopes after the typhoon may be mobilized and delivered to the river network by subsequent rainfall events.

Overall, this flood did not modify the decreasing trend observed in terms of Cs-137 contamination in sediment transiting these rivers between 2011 and 2019. Concentrations in Cs-137 observed in sediment collected in 2019 were on average 84–93% lower than those measured after the accident in 2011. These results demonstrate the effectiveness of decontamination conducted on agricultural and residential soils in the region (Evrard et al., 2019), although the role of forests – that have not been remediated – as a perennial source of sediment and radiocesium in the region remains to be investigated over the longer term.

References

Evrard, O., Durand, R., Nakao, A., Patrick Laceby, J., Lefèvre, I., Wakiyama, Y., Hayashi, S., Asanuma-Brice, C. and Cerdan, O., 2020. Impact of the 2019 typhoons on sediment source contributions and radiocesium concentrations in rivers draining the Fukushima radioactive plume, Japan. Comptes Rendus Géoscience, 352(3): 199-211.

Evrard, O., Laceby, J.P. and Nakao, A., 2019. Effectiveness of landscape decontamination following the Fukushima nuclear accident: a review. SOIL, 5(2): 333-350.

Laceby, J.P., Chartin, C., Evrard, O., Onda, Y., Garcia-Sanchez, L. and Cerdan, O., 2016. Rainfall erosivity in catchments contaminated with fallout from the Fukushima Daiichi nuclear power plant accident. Hydrology and Earth System Sciences, 20(6): 2467-2482.

How to cite: Evrard, O., Durand, R., Nakao, A., Laceby, J. P., Lefèvre, I., Wakiyama, Y., Hayashi, S., Asanuma-Brice, C., and Cerdan, O.: What were the main sources of sediment and associated radiocesium transported during the heavy 2019 typhoons in rivers draining the main Fukushima radioactive plume, Japan ?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-251, https://doi.org/10.5194/egusphere-egu21-251, 2020.

The novel application of the SediPump® sampling device to capture sufficient sediment mass from low concentration flood plume waters has enabled catchment source tracing of GBR flood plume sediment for the first time. Focused on the single largest exporter of sediment to the GBR, the Burdekin River, three wet season discharge events were sampled from 2017 to 2019 to characterise and trace flood plume suspended sediments using geochemistry, fallout radionuclides and clay mineralogy. Sampling targeted the end-of-river (EoR) flow hydrograph to capture contributing catchment sources, and flood plume samples from both the adjacent turbid primary waters and offshore secondary waters up to 160 km from the EoR. Analysis of EoR and plume sediment major element geochemistry indicates standard geochemical sediment tracing approaches cannot be applied to a large river catchment such as this, or across the catchment-marine continuum, where particle fractionation has occurred both within the catchment and across the salinity gradient from the river mouth. Further, the secondary plume sediments have also been affected by the addition of marine-sourced carbonate and biogenic silica. We show elemental ratios of the rare earth elements (REE) and thorium (Th) can be used as stable tracers across this continuum, and importantly, used to trace Burdekin plume terrigenous sediment transported >100 km’s from the river mouth back to its EoR REE/Th signal, which was unique for each of the three discharge events. These ratios were also used to trace this sediment to a major sub-catchment source. Additional fallout radionuclide ¹³⁷Cs analysis of a sub-set of Burdekin EoR and plume samples also reveal sediment being transported in these GBR flood plumes are almost exclusively derived from sub-surface erosion processes.

How to cite: Bainbridge, Z., Olley, J., Lewis, S., and Stevens, T.: Geochemistry and provenance of sediment plume samples collected from the Burdekin region of the Great Barrier Reef Lagoon, Australia., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13826, https://doi.org/10.5194/egusphere-egu21-13826, 2021.

Sediment fingerprinting is a technique for determining the proportional contributions of sediment from erosion sources delivered to downstream locations. It involves selecting tracers that discriminate sediment sources and determining contributions from those sources using tracers.  These tracers can include geochemical, fallout radionuclides, magnetic properties, and compound specific stable isotope (CSSI) values of plant-derived biotracers that label of soils and sediment.  A range of tracer applications and developments in source un-mixing have been demonstrated in the literature and, while the basis for discriminating sediment sources is reasonably well understood, research has drawn increasing attention to limitations and uncertainties associated with source apportionment. Numerical mixtures provide a way to test model performance using idealized mixtures with known source proportions. Although this approach has been applied previously, it has not been used to test and compare model performance across a range of tracer types with varied source contribution dominance and number of sources.

We used numerical mixtures to examine the ability of two different tracer sets (geochemical and CSSI), each with two tracer selections, to discriminate sources using a common source dataset. Sources were sampled according to erosion process and land cover in the Aroaro catchment (22 km²), New Zealand.  Here we sampled top-soils and sub-soils from pasture (n = 12 sites), harvested pine (12), kanuka scrub (7) and native forest (4) locations. Composite soil samples were collected at 0-2 and 40-50 cm depth increments to represent surface and shallow landslide (subsoil) erosion sources. Stream sediment (11) samples were also collected for initial unmixing.  Here, we focus on using numerical mixtures with geochemical and CSSI tracers for an increasing number of sources (3 to 6) where each individual and pairwise combination of sources were systematically set as the dominant source.  Since mixing models for CSSI tracers produce source contributions based on isotopic proportions (Isotopic%) instead of soil contributions (Soil%), CSSI numerical mixtures were created for Isotopic% and Soil% to assess the impact this correction factor may have on model performance.  In total, over 400 model scenarios were tested.

Numerical mixture testing indicated that the dominant source can have a significant impact on model performance.  If the dominant source is well discriminated, then the model performs well but accuracy declines significantly as discrimination of the dominant source reduces. This occurs more frequently with an increasing number of sources. The geochemical dataset performed well for erosion-based sources while both tracer sets produced larger apportionment errors for land cover sources. CSSI model performance was generally poorer for Soil% than Isotopic%, indicating high sensitivity to the percent soil organic carbon in each source, especially when there are large differences in organic matter between sources.

How to cite: Vale, S., Swales, A., Smith, H., Olsen, G., and Woodward, B.: Evaluating the effects of tracer selection, source dominance and source number on the accuracy and sensitivity of source apportionment using sediment fingerprinting. , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13691, https://doi.org/10.5194/egusphere-egu21-13691, 2021.

Episodic flood events are critical for recharging water balance of floodplain lakes and maintaining their ecological integrity, yet are subject to alteration in frequency and magnitude by natural and anthropogenic processes that operate over a range of spatial and temporal scales. To evaluate roles of potential stressors, paleolimnological reconstructions are used to obtain insights into hydrological variability of dynamic floodplain lakes. However, spatial and temporal integration is often underdeveloped because different paleolimnological measurements must be applied across lakes due to the wide range of energy conditions that impart marked differences in sediment composition. Here, we use a linear discriminant analysis to identify 10 significant elemental concentrations in surveyed sediment from multiple sampling campaigns that distinguish the geochemical fingerprints of three end-member sources in lakes at the Peace-Athabasca Delta (PAD; Canada): the Athabasca River, the Peace River and local catchment runoff. Over 90% of the sediment samples were correctly classified into the original groups after cross-validation due to the distinctiveness of the three end members, which permits development of a robust Bayesian mixing model to discern the relative contributions of sediment from the three sources. We evaluate the mixing model at two adjacent lakes in the Athabasca sector of the PAD and demonstrate its effectiveness to discriminate three known hydrological phases during the past 300 years. Notably, the model infers ~60% of the sediment originated from the Peace River during the largest ice-jam flood event on record (1974), which was unrecognized by other methods. We then applied our model to sediment records from 18 lakes spanning the hydrological gradients across the 6000 km² PAD to further probe the hydrological evolution during the past ~150 years. Results demonstrate decline in frequency of flooding from both the Athabasca and Peace rivers and lake-level drawdown since the early 20^th century and align remarkably well with prior interpretation of conventional paleohydrological records of individual lakes. We advocate our approach provides a universal method that can be applied across the full range of sediment composition to quantify change in source, frequency and magnitude of river floodwaters to lakes and is transferable to other dynamic floodplain landscapes where variation of sediment composition challenges efficacy of other approaches.

How to cite: Kay, M., Swanson, H., Burbank, J., Owca, T., MacDonald, L., Savage, C., Remmer, C., Neary, L., Wiklund, J., Wolfe, B., and Hall, R.: A Bayesian mixing model framework for quantifying temporal and spatial variation in source of sediment to lakes across hydrological gradients of floodplains, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1567, https://doi.org/10.5194/egusphere-egu21-1567, 2021.

The reservoir siltation has been of critical environmental concerns in recent years. The vulnerability and the overdevelopment in the reservoir watershed are the causes of the reservoir sedimentation. While typhoon events happen, in addition to the great amount of sediment volume transported from the upstream to the reservoir region, the density currents may evolve, which will steeply increase turbidity levels for the periods of time. In particular, the Shihmen Reservoir, one of essential hydraulic engineering projects in northern Taiwan, has been exposed to crisis that the sedimentation may fill up in the next few decades. Therefore, in order to maintain the reservoir capacity to an operational extent, modeling the sediment transport patterns in Shihmen Reservoir will utilize the three-dimensional Environmental Fluid Dynamics Code (EFDC) for quantifying sediment concentrations during the typhoon event. Calibration and validation of EFDC are performed by comparing two independent sets of event-based hydrodynamic and sediment concentration data with assistance of the parameter optimization algorithm. Next, the Backward-forward Stochastic Particle Tracking Model (BF-SPTM) is further incorporated into the EFDC hydrodynamic module to check the likelihood of the potential source of sediment particles. Results of simulations are expected to provide a more precise release timing for flow regulation to ensure the effective slag removal for density currents. Additionally, with probable sedimentation sources available for a reservoir, effective land use change and restrictions on overdevelopment of the risk prone areas can be enforced to decrease the sediment yields into the reservoir. It is expected that this incorporation of BF-SPTM into EFDC can be applied to simulate sediment transport in typhoon events, and to provide appropriate reservoir management alternatives.

Keywords: Environmental Fluid Dynamics Code (EFDC), suspended sediment concentration, Backward-forward Stochastic Particle Tracking Model, Probable sedimentation source

How to cite: Liu, W.-J. and Tsai, C. W.: Incorporating Backward-forward Stochastic Particle Tracking Model into the EFDC model for Probable Sedimentation Source identification in Typhoon events, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11346, https://doi.org/10.5194/egusphere-egu21-11346, 2021.

In hydrosedimentological modelling, the lack of high temporal resolution field data is a limiting factor for the assessment of the performance of models. This way, the remote sensing images have been studied to correlate imagery information with suspended sediment concentration (SSC) in the last decades, aiming to complement field data, by improving the SSC information temporal and spatial resolution. Thus, the present work used the Google Earth Engine (GEE), a cloud-based platform, to systematically obtain red band reflectance information from Landsat 5 imagery to support large-scale hydrosedimentological modelling. The test case was to the Rio Grande do Sul state hydrological region in Brazil, a South American region with scarce SSC data. The methodology applied consisted in nine steps using GEE code: (1) river width analysis using remote sensing imagery to localize the virtual gauge stations (VGS) from the intersection between the discretization of hydrosedimentological model and the chosen rivers, (2) TM sensor definition, onboard of Landsat 5 satellite, (3) collection of red reflectance information between 1990 and 2010, based on previous works that presented better correlation between red reflectance and SSC, (4) in each VGS, we created a circle of radius equal to 1000 m, (5) to each image, we removed clouded-pixels, using the Landsat 5 quality bands, (6) we generated a dynamic water mask to each image to ensure that only pixels with water would be used to collected reflectance information, (7) finally, we calculated the mean of red band reflectance inside the intersection of water mask and circle buffer, removing the clouded-pixels, (8) we calculated a filter to remove remnants clouded-pixels and random errors from imagery, (9) we used the MGB-SED model to simulate long-term SSC in the region and we calibrated the model with the GEE data based on a correlation approach. The results found were: (i) 1267 virtual gauge stations, approximately 20 times the number of in situ SSC gauging stations available in the region, (ii) a larger area of data and greater temporal resolution, (iii) improvement in the correlation between model results and red reflectance, when we assess the model with SSC observed data. In conclusion, the work shows the potential of GEE to simply obtain large-scale reflectance data that could be used to improve the calibration processes of large-scale hydrosedimentological modelling.

How to cite: Rossoni, R., Fan, F., and Laipelt, L.: Application of Google Earth Engine (GEE) to obtain calibration data for a large-scale hydrosedimentological model: a test case in South America, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11926, https://doi.org/10.5194/egusphere-egu21-11926, 2021.

Hydro-morphodynamic models are increasingly popular for predicting sedimentation processes in reservoirs. To leverage the accuracy of such models, their boundary conditions have to be defined as precise as possible. While hydrological models provide efficient routines to establish inflow hydrographs at the model boundaries, the determination of the sediment input is challenging and involves large uncertainties. This study identifies prominent parameters that influence the sediment input into a reservoir, and therefore, expected sedimentation rates. For this purpose, erosion and transport processes in the catchment area of the Banja Reservoir (Albania) are analyzed.

The Banja Reservoir is located on the Devoll River in the Southeast of Albania and has a storage capacity of 400 Million m³. The catchment area has a size of 2,900 km² and lies in a mountainous region. The climate is characterized by dry and hot summers and humid winters. There are significant differences in precipitation patterns in the catchment due to topographical conditions and with increasing distance from the coast in the West of the reservoir. Because snowfall is frequent in winter, the runoff regime of the Devoll River and its tributaries is driven by precipitation and snowmelt.

To calculate the sediment input at the inflow boundaries of the reservoir, a comprehensive analysis in combination with hydrological modelling of the catchment is indispensable. This study applies the Revised Universal Soil Loss Equation (RUSLE) model coupled with the SEdiment Delivery Distributed (SEDD) model, as an integrated approach that bridges interdisciplinary expertise in geomorphology and hydrology. Since measured precipitation data neither fulfils minimum requirements in terms of spatio-temporal resolution nor in terms of time series length, the ERA5 reanalysis dataset is used as input data. The coupled model is calibrated with suspended sediment data measured at a monitoring station upstream of the reservoir over a 2–years period. The model enables to approximate the monthly or annual sediment load for any point in the river network. Thus, the sediment load into the reservoir can be assessed for every major tributary, even in areas with limited data availability. In addition, a high spatial resolution (25 m x 25 m) of the model enables the identification of areas that cause particularly high sediment loads.

The optimized coupled model predicts sediment loads that are in good agreement with sediment loads measured at the monitoring station (Nash-Sutcliffe efficiency: NSE_annual = 0.96; NSE_monthly = 0.81). Consequently, climate reanalysis datasets are a viable alternative in regions with data scarcity. Furthermore, the spatial representation of the results suggests that the sediment load into the reservoir mainly originates from steep and sparsely vegetated or agricultural areas close to the river network. Intensive rainfall additionally fosters erosion, which is why erosion rates are higher in the Western part of the catchment area.

How to cite: Mouris, K., Schwindt, S., Haun, S., Pesci, M. H., Förster, K., Rüther, N., Schwarzwälder, K., and Wieprecht, S.: Climate reanalysis data with global coverage enable sediment load prediction in the absence of systematic field data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8432, https://doi.org/10.5194/egusphere-egu21-8432, 2021.

Dating recent sediment archives (<150 years) constitutes are need for environmental and climatic reconstructions. Radiocaesium (¹³⁷Cs) emitted during thermonuclear bombs testing (~1950 - ~1980) and nuclear accidents (1986 and 2011) was generally used for identifying sediment sources or for establishing sediment core chronology based on discrete time markers. Although this method was widely used during the last several decades, there is a lack of structured and comprehensive worldwide synthesis of radiocaesium fallouts. The current literature overview was based on 573 articles published between 1977 and 2020, reporting the collection of 1351 individual dated sediment cores. This synthesis led to the identification of the worldwide distribution of discrete time markers associated with the thermonuclear bomb testing peak in 1963, the Chernobyl fallout, the Fukushima fallout, as well as the identification of at least 25 events induced by local accidents or nuclear tests (e.g. Sellafield, la Hague accidents, Chinese nuclear tests).

With a growing number of studies focusing on the analysis of recent sediment cores and the increasing interest in sediment fingerprinting techniques, this spatialized synthesis provides a unique worldwide referential for identifying the distribution of the ¹³⁷Cs sources at global scale. It also outlines the main questions that would deserve attention in future research perspectives and the regions where ¹³⁷Cs fallouts investigations should be conducted in priority.

How to cite: Foucher, A., Sabatier, P., Chaboche, P.-A., and Evrard, O.: A review of worldwide sediment core dating research including fallout radiocaesium (137Cs)  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10671, https://doi.org/10.5194/egusphere-egu21-10671, 2021.

High mountain environments are among the most sensitive on Earth. Due to anthropogenic disturbances and climate change, rates of regolith mobilization due to for example landsliding have been accelerating recently. As a result, soils degrade, geohazards occur and flash floods have negative consequences in downstream areas. The restoration of soils in high mountain environments and an improved understanding of nature-based solutions to land degradation is, therefore, urgent. As finding the origin of erosion sources is a first step to improve mitigation strategies and guide the implementation of effective soil restoration measures, we discuss sediment source fingerprinting research in the context of soil restoration in high mountain environments. A literature review was done based on articles that apply sediment source fingerprinting in high mountain environments and additional articles on land use-based markers and soil restoration were used to develop an outlook for future research. The application of sediment provenance studies in high mountains environments has been limited so far. While some studies yield a rough distinction between sediment sources based on environmental radionuclides or elemental geochemistry, they cannot reflect multiple semi-natural vegetation types which are relevant source types that should be discriminated in high mountain environments. Therefore, we explore emerging techniques such as eDNA tracing that could potentially refine the information on the provenance of sediment based on land use and cover sources. Then, we will address the challenging hydro-geomorphic environment of high mountains and the implications for designing properly a sediment tracing study in such a context. We will conclude by presenting an outlook to guide future applications of sediment source fingerprinting in high mountain environments, where geohazards are imminent and soil restoration is urgent.

Key words: alpine, environmental DNA, erosion, landslide, vegetation

How to cite: Frankl, A., Evrard, O., Cammeraat, E., and Stokes, A.: Strengths and limitations of sediment source fingerprinting in high mountain environments and relevance for soil restoration, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-161, https://doi.org/10.5194/egusphere-egu21-161, 2020.

Information on the share of river bank erosion to the total sediment load at catchment scale by using the fingerprinting approach is important to address our knowledge of erosion processes to better target soil erosion control measures. In particular, river bank erosion is affected by many factors such as spatial and temporal variables and is difficult to quantify the relationship of the share of bank erosion to catchment size and upland erosion rate without extensive fieldwork and data analysis. Potential tracers including geochemical, fallout radionuclides, bulk and compound-specific stable isotopes, and magnetic properties have been used, often in combination with sediment source apportionment. In this worldwide review, the global dataset for percent share of river bank and surface erosion using fingerprinting approach was collected to establish the significance of catchment size and other physical controls on river bank erosion. Google Scholar and Web of Science were used to review research articles that included river bank/subsurface as one of the sediment sources in the study areas. This database showed that the UK (n = 84), USA (n = 14) and Brazil (n = 10) had the highest number of catchments, followed by Iran (n = 4), Southern Zambia (n = 1), Australia (n = 1), Spain (n = 1), Mongolia (n = 1) and Burkina Faso (n = 1) ranging in size from 0.31 to 15000 km², predominately agriculture. Based on published studies, there is a clear shift of sediment sources from surface erosion to river bank erosion with increasing catchment size. The results show the wide range of relative contributions of surface and river bank sources to the catchment sediment yield around the globe. There are a number of catchments with river bank contribution exceeding 25% and surface contribution exceeding 90% of total sediment loss. This diversity highlights the many factors that influence river bank erosion. In addition to the wide range, sediment source contribution in the range 1-25% from river bank is generally representative around the World. We recommend that long term monitoring of sediment load and surface and river bank sources at nested sites within a catchment are indispensable. Furthermore, limited information on the share of sources often makes it difficult to target mitigation measures reducing sediment loads at the catchment scale.

Keywords: Sediment load, catchment size, fingerprinting approach, river bank share

How to cite: Abbas, G., Jomaa, S., and Rode, M.: A review on share of river bank erosion to the total sediment load with increasing catchment size, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14536, https://doi.org/10.5194/egusphere-egu21-14536, 2021.