HS9.1

EDI
Techniques for quantifying the sources and the dynamics of sediment in river catchments across a range of spatial and temporal scales

Obtaining quantitative information on the spatial pattern of soil redistribution during storms and on the spatial sources supplying sediment to rivers is required to improve our understanding of the processes controlling these transfers and to design effective control measures. It is also crucial to quantify the transfer or the residence times of material transiting rivers along the sediment cascade, and to reconstruct the potential changes in sources that may have occurred at various temporal scales. During the last few decades, several sediment tracing or fingerprinting techniques have contributed to provide this information, in association with other methods (including soil erosion modelling and sediment budgeting). However, their widespread application is limited by several challenges that the community should address as priorities.
We invite specific contributions to this session that address any aspects of the following:
• Developments of innovative field measurement and sediment sampling techniques;
• Soil and sediment tracing techniques for quantifying soil erosion and redistribution;
• Sediment source tracing or fingerprinting studies, using conventional (e.g. elemental/isotopic geochemistry, fallout radionuclides, organic matter) or alternative (e.g. colour, infrared, particle morphometry) approaches;
• Investigations of the current limitations associated with sediment tracing studies (e.g. tracer conservativeness, uncertainty analysis, particle size and organic matter corrections);
• Applications of radioisotope tracers to quantify sediment transit times over a broad range of timescales (from the flood to the century);
• The association of conventional techniques with remote sensing and emerging technologies (e.g. LiDAR);
• Integrated approaches to developing catchment sediment budgets: linking different measurement techniques and/or models to understand sediment delivery processes.

Co-organized by GM3
Convener: Olivier Evrard | Co-conveners: Hugh Smith, Gema Guzmán
Presentations
| Mon, 23 May, 13:20–14:50 (CEST)
 
Room 2.17

Presentations: Mon, 23 May | Room 2.17

Novel approaches and ideas for sediment tracing
13:20–13:26
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EGU22-10576
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ECS
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On-site presentation
Ghulam Abbas, Seifeddine Jomaa, Patrick Fink, Arlena Brosinsky, Karolina Malgorzata Nowak, Steffen Kümmel, and Michael Rode

Soil erosion and associated sediment transport can cause severe water quality and ecosystems health deterioration. The fingerprinting approach has widely been applied for sediment source apportionment using a variety of sediment tracers. This study evaluates the applicability of the Compound Specific Stable Isotope (CSSI) fingerprinting technique of fatty acids to identify crop-specific soil loss and the importance of upland erosion compared to river bank erosion. We tested this new technique with fallout radionuclides, geochemical and spectral tracers in a small agricultural loess soil catchment (Geesgraben, 75 km²) within the lowland Bode river catchment in Central Germany. The CSSI tracer was combined with a linear multivariate mixing model to discriminate soil loss from areas with specific crop types (e.g., C3 vegetation/wheat and C4 vegetation/maize) and identify the share of river bank sediment source on total sediment loss. We compared the CSSI technique with fallout radionuclides, geochemical and spectral fingerprinting properties for tracing subsurface sediment sources. We found that the CSSI fingerprinting technique of fatty acids allowed to decipher surface sediments from wheat and maize fields. The CSSI δ¹³C-fatty acids were also used to disentangle arable and river bank sediment sources. The crop-specific soil loss from wheat and maize was 40% and 11%, respectively. Relative sediment contribution from river banks was up to 49%. The outcomes using the CSSI tracer were consistent and similar to those using fallout radionuclides, geochemical and spectral fingerprinting properties for arable land and river bank sediment sources, which indicated a mean sediment source contribution of 46% from river bank and 54% from surface sources, respectively. Our results showed that the stable isotope composition of fatty acids could discriminate C3 and C4 vegetation sources, and such information is of prime importance for decision making. Furthermore, the relatively high proportion of sediment losses from river banks has clear implications for management measures to reduce sediment losses in these agricultural loess areas. 

Keywords: sediment fingerprinting, CSSI, fatty acids, C3 and C4 vegetation sources, sediment sources.

How to cite: Abbas, G., Jomaa, S., Fink, P., Brosinsky, A., Nowak, K. M., Kümmel, S., and Rode, M.: Exploring novel Compound Specific Stable Isotopes (CSSIs) tracers with conventional fingerprinting properties for sediment source apportionment in an arable lowland catchment in Central Germany, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10576, https://doi.org/10.5194/egusphere-egu22-10576, 2022.

13:26–13:32
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EGU22-2161
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Highlight
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On-site presentation
Amaury Frankl, Olivier Evrard, Fabien Levard, Brice Dupin, Bjorn Tytgat, Erik Cammeraat, Elie Verleyen, and Alexia Stokes

Environmental DNA (eDNA) has recently been considered as a marker that could be used for fingerprinting sediments. Identify sediment sources originating from zones covered with specific plant communities would enhance the sediment fingerprinting method significantly and enable the detailed identification of soil erosion hotspots relative to land use and cover. Here, we explore the relevance of environmental DNA (eDNA) that originates from plant litter and fixes onto fine soil particles as a targeted sediment fingerprinting method. Although research on plant eDNA signatures in soils and sediments is limited, initial results are promising and indicate that eDNA could yield more accurate results than other sediment fingerprints that are sensitive to vegetation. Plant eDNA signatures tend to produce a highly localized signal of sediment sources, mainly reflecting the current vegetation cover of soils. As eDNA is rapidly adsorbed onto fine mineral soil particles such as clay, it is protected against rapid degradation in fluvial environments. Supported by the increasing availability and quality of vegetation maps and eDNA reference libraries, we argue that sediment source fingerprinting using eDNA from plant litter will evolve into a valuable method to identify hotspots of soil erosion and allow stakeholders to prioritize areas where ecological restoration is necessary. We tested our assumptions from a case study in a high mountain environment (catchment of approximately 600 km² in the Central Pyrenees, France) which was recently affected by a severe hydro-climatic event and for which ecological restoration is pertinent.

Keywords:

Pyrenees, river catchments, sedDNA, sediment source fingerprinting, vegetation

How to cite: Frankl, A., Evrard, O., Levard, F., Dupin, B., Tytgat, B., Cammeraat, E., Verleyen, E., and Stokes, A.: The relevance of environmental DNA as a targeted sediment fingerprinting method sensitive to vegetation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2161, https://doi.org/10.5194/egusphere-egu22-2161, 2022.

13:32–13:38
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EGU22-1223
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ECS
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On-site presentation
Ivan Lizaga, William Blake, Samuel Bodé, Olivier Evrard, Borja Latorre, Ana Navas, Kristof Van Oost, and Pascal Boeckx

Soil erosion and the subsequent transport of sediment and pollutants are critical challenges for guaranteeing food security and water quality. Controlling sediment and particle-bound substance export requires the implementation of improved ecological restoration schemes, especially in areas experiencing drastic increases in erosion rates. To this end, we propose the design of an ensemble technique that combines the use of sediment fingerprinting together with radionuclide dating and remote sensing data to fill these critical knowledge gaps.

This project will focus on testing and developing powerful specific land use tracers, such as Compound Specific Stable Isotopes (CSSI) and environmental DNA (eDNA), to improve the land cover discrimination of sediment provenance through the collection and dating of sediment cores in sink areas. This research will be conducted in two contrasting catchments with different land use histories allowing to test the effectiveness of this novel approach: i) the Ésera catchment that flows into the Barasona reservoir (Spain), representative of areas experiencing sediment export decrease due to land abandonment and the subsequent natural revegetation, and ii) the Kihira catchment, Lake Kivu (DR Congo), representative of intensively cultivated areas undergoing an unsustainable and increasing sediment export and nutrient loss. By combining the investigation of these two contrasted catchments and by applying state-of-the-art methods, it will be possible to evaluate the main driving factors of the past and present erosion rates and predict the effects of human management and climate change.

In this first stage of the project, representative sediment samples from different land cover sources will be collected in the Ésera catchment (1.535km2) until its mouth into the Barasona reservoir. Several bulk cores and surface sediments collected in 1995 will be characterised and compared with samples collected in 2013 at the Barasona reservoir. An extra sampling campaign is planned for 2022 to examine the changes that occurred in recent years.  Records of known flood events and reservoir management data will be combined with 137Cs chronology to ascribe the sedimentary record to specific years. Besides, a set of remote sensing and aerial photographs will be analysed to reconstruct the land use variation during the last six decades.

To track the land use apportionment variation during the last decades, geochemistry and radioisotopic activity will be analysed in both source and sediment samples and examined as possible tracers for fingerprinting modelling. The fingerprinting technique will be implemented following state-of-the-art methodologies such as the Consensus and Consistency tracer selection methods.

Thus, by combining the use of remote sensing, novel fingerprinting techniques and radiometric dating, we aim to provide a novel and powerful tool to understand the driving factors of sediment sources (e.g., deforestation, agricultural intensification and abandonment) and associated pollutants, and their variations in space and time in the last decades.

How to cite: Lizaga, I., Blake, W., Bodé, S., Evrard, O., Latorre, B., Navas, A., Van Oost, K., and Boeckx, P.: An integrated sediment export quantification approach for the sustainable management of agroecosystems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1223, https://doi.org/10.5194/egusphere-egu22-1223, 2022.

Methodological issues and developments associated with sediment tracing
13:38–13:44
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EGU22-4207
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ECS
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Presentation form not yet defined
Niels Lake, Núria Martínez-Carreras, Peter Shaw, and Adrian Collins

Particle size is an important consideration for applications of sediment source fingerprinting. Here, most attention has focused on understanding the relationships between tracer property concentrations (e.g., geochemical, radionuclides and mineral magnetic properties) and particle size, since the fingerprinting approach is founded on the assumption that the properties of source material and target sediment samples are directly comparable. Beyond the careful consideration of particle size controls on tracers, there remains scope to investigate the use of particle size distributions as a tracer, building upon the limited amount of work reported to date. Accordingly, we hypothesize that particle size distributions can be informative of sediment provenance in areas where individual sources exhibit distinct particle size characteristics. To test this hypothesis, laboratory experiments were performed using artificial mixtures consisting of soil samples sieved to the same and different size fractions (<32 µm, 32-63 µm, 63-125 µm). Individual soil samples (i.e., sources) and mixtures were tested in a 40L large experimental water tank, in which a submersible particle size analyser was used to measure particle size distribution. Using the mixtures consisting of soil source samples sieved to different size fractions resulted in un-mixing modelling contributions being close to the known source inputs. Subsequently, a field experiment was conducted with samples collected using a confluence-based sediment fingerprinting approach during several storm runoff events and at low flows. Here, particle size differences between samples collected in an upstream and tributary sampling point (measured using a laboratory-based particle size analyser) were used to estimate suspended sediment contributions from these two spatial units to a downstream target sediment sampling point. The findings from the field experiments show derived estimates were good when discharge and suspended sediment concentrations were high, but less accurate during smaller runoff events and at baseflow.

How to cite: Lake, N., Martínez-Carreras, N., Shaw, P., and Collins, A.: Using differences in particle size distributions to fingerprint suspended sediment sources , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4207, https://doi.org/10.5194/egusphere-egu22-4207, 2022.

13:44–13:50
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EGU22-818
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Presentation form not yet defined
Kazem Nosrati and Peter Fiener

There is a growing interest to understand the sources of sediments in river channels as basis for potential mitigation aiming to reduce soil erosion and sediment delivery in larger catchments. Within the last decades, sediment fingerprinting has been established as a powerful tool to unravel the sources of sediments in larger catchments. However, most sediment fingerprinting techniques are based on time-consuming and costly chemical analysis of sediment samples from river channels and sub- catchments. Recent studies have shown the potential of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) as a rapid, cost-effective, and nondestructive tracers for sediment fingerprinting. The aim of this study is to analyses the sensitivity of DRIFTS based sediment fingerprinting against particle size of sediment tracers and to determine the potential of using multi-size approaches.  We used mid-infrared spectroscopy (MIRS; 4000-600 cm-1) to analyze four size fractions (125-250, 63-125, 63-38, and <38 µm) of 54 sediment samples collected at three different sub-basins spatial sediment sources and 26 target sediment samples collected at the outlet of the main basin of the Andajrood drainage river basin in Iran.  The spectral resolution was averaged over 32 cm-1 intervals to reduce the continues wavelength data to a defined number of spectral bands (n = 104) that is practicable and realistic for a statistical analysis of differences. A one-way ANOVA was used to evaluate the presence of significant contrasts between the content of individual MIRS spectra in the different size fractions. The results showed that MIRS spectra were present and distributed across all size fractions. The results of one-way ANOVA indicated that in sub-basin both, MIRS spectra form spatial sediment sources and target sediment samples, were significantly affected by the particle size fractions. Thus, this confirmed that it was appropriate to identify the dominant particle size fraction in the sediment samples and to confirm that MIRS spectra were present across that fraction rather than a sub-fraction.

How to cite: Nosrati, K. and Fiener, P.: Particle size fraction effects on MIR-DRIFTS: Improving the quantification of sub-basin spatial sediment provenance fingerprinting, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-818, https://doi.org/10.5194/egusphere-egu22-818, 2022.

13:50–13:56
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EGU22-11814
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Virtual presentation
Vladimir Belyaev, Anna Semochkina, Vladimir Van, and Nikolay Lugovoy

Over the last two decades, unmanned aerial vehicles (UAVs) have become widely used in geomorphological investigations at local spatial scales for different purposes. Here we present several examples of the UAV survey application for evaluation of soil redistribution volumes on cultivated hillslopes over a timescale of single to several runoff events. Several cultivated fields with prominent soil erosion and deposition features have been discovered during reconnaissance car trips through several regions of Central European Russia carried out in April-May 2021. The observed features included rill and ephemeral gully networks as well as several types of deposition features such as sheets and fans located within the field, along the field lower boundary and on the adjacent dry valley bottom. Detailed airborne surveys of the detected erosion and deposition zones were carried out using the DJI Phantom 4 Pro quadcopter-type drone with ground control points surveyed by Leica GS 1200 differential GNSS system. Simultaneous control hand measurements of volume of representative sets of erosion and deposition features were carried out within the same areas. Photogrammetric processing of the UAV survey data using the Agisoft Metashape software package allowed producing DEMs and orthorectified images of the surveyed areas with spatial resolution within ±2 cm. Following that, manual and semi-automatic detection of erosion and deposition features were employed and their available parameters (length, width, depth, areas of selected cross-sections, approximate volume for rills and ephemeral gullies; perimeter, area and shape for deposition features) have been measured in the Global Mapper software package. To obtain deposition volumes, the above parameters were combined with hand measurements of the deposited layer thickness. Zones of predominant sediment entrainment, transit, within-slope redeposition, export from the field and deposition in adjacent dry valleys were determined and local sediment budget parameters estimated. Comparison of the results obtained with the spring 2021 meteorological records allowed us to make conclusions on the relative contribution of snowmelt and rainfall-generated runoff into the observed soil and sediment redistribution.

The study is supported by the Russian Science Foundation (Project No. 19-77-10061).

How to cite: Belyaev, V., Semochkina, A., Van, V., and Lugovoy, N.: The use of UAV for event-based evaluation of soil redistribution on cultivated hillslopes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11814, https://doi.org/10.5194/egusphere-egu22-11814, 2022.

Applications and original case studies of sediment tracing
13:56–14:02
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EGU22-10742
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On-site presentation
Yuichi Onda, Motosuke Kinoshita, Hiroaki Kato, Takashi Gomi, and Chen-Wei Chiu

While thinning practices are essential for forest maintenance and management, it has been suggested that the amount of sediment discharge from forests to rivers increases with the practices.  In Karasawayama, Tochigi Prefecture, Japan, different types of thinning were carried out in 2011-12, and continuous observation of water and sediment runoff before and after thinning has been carried out. So far, through connectivity analysis, Lopez-Vincente (2017) estimated that work roads can be a major runoff pathway for sediment produced by thinning practices. On the other hand, radionuclides are known to be effective in estimating the source of sediment production. In this catchment, 8kBq/m2 of Cs-137 and Cs-134 were newly deposited due to the Fukushima Daiichi Nuclear Power Plant accident during the observation period. Therefore, the purpose of this study was to estimate the source of fine sediment production from the slope scale to the watershed scale before and after thinning, utilizing Cs-134 of Fukushima origin and changing the end-members of the source sediment production in each year for more detailed source estimation. In addition, by using Pb-210ex, Cs-137, and Cs-134 at the same time, we can distinguish the production sources more clearly. In the field, SS samplers and turbidimeters were installed in the river to observe the amount and concentration of sediment, and soil erosion plots were set up in the forest and along the work road to collect sediment and measure the radioisotope concentration with Ge semiconductor detectors.

As a result of the analysis, the amount of sediment in the watershed where row thinning was conducted increased rapidly in the year of thinning and one year later. On the other hand, in the watershed where point thinning was conducted, there was no significant increase in sediment discharge. In the production source estimation, we were able to clearly distinguish between work roads and river banks by using Cs-134/Cs-137 as the horizontal axis and Cs-134/Pb-210ex as the vertical axis. The tracer analysis showed that the contribution of sediment production from the working road increased during the thinning period in the row-thinning catchment, but no such trend was observed in the point-thinning catchment.

How to cite: Onda, Y., Kinoshita, M., Kato, H., Gomi, T., and Chiu, C.-W.: Estimation of fine sediment transport processes by forest management using Pb-210ex, Cs-137 and Cs-134, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10742, https://doi.org/10.5194/egusphere-egu22-10742, 2022.

14:02–14:08
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EGU22-6057
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ECS
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On-site presentation
Jessica Kitch, Caroline Clason, Sally Rangecroft, Sergio Morera, Shirley Contreras, and Will Blake

The water-food-energy security nexus faces significant challenges from both climate change and growing populations, particularly in glacier-fed mountainous catchments. Sediment generation is driven by both natural and anthropogenic factors, exacerbating the pressures on the nexus; with increased erosion contributing to sedimentation of river systems that in turn endangers crucial river functions, such as drinking water availability, crop irrigation and hydroelectricity. Identifying sediment sources is of great importance to enable better understanding of sediment dynamics and thus, inform our management of water resources. Here we focus on the glaciated Rio Santa catchment in the Peruvian Andes, an important river for agriculture, energy, and domestic water supply.  

Using sediment fingerprinting tools, this study assesses the glacial contribution to in-channel sediment along the Rio Santa, whilst investigating the contribution of anthropogenic factors such as land cover change in the Cordillera Blanca. A distributed approach along the two major sub catchments of the study catchment was taken to investigate natural and anthropogenic contributions to sediment generation for this Andean system. The Rio Santa catchment study focused on the contributions to sediment from the cordilleras, whilst the smaller Ranrahirca sub catchment study focused on land cover contributions to sediment. The distributed approach permitted quantification of source dynamics throughout the catchment and sub-catchment. To develop geochemical fingerprints, all source and mixture samples were analysed using Wavelength Dispersive X-ray Fluorescence (WD XRF). The MixSIAR mixing model was used to apportion sediment sources for both catchment scales. Our results indicate that the non-glacial zone (Cordillera Negra Mountains) was the greater contributor to sediment in the upper Rio Santa, possibly due to mining activities and lithological factors, whilst further downstream the glaciated zone (Cordillera Blanca) became the larger contributor. Sediment monitoring in remote mountainous catchments such as the Rio Santa is not without challenges. Sediment fingerprinting evidence has the potential to fill knowledge gaps and inform local resource management policy.

How to cite: Kitch, J., Clason, C., Rangecroft, S., Morera, S., Contreras, S., and Blake, W.: Evaluating sediment source contributions in a river catchment impacted by glacial melt and land use change, the Rio Santa, Peru, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6057, https://doi.org/10.5194/egusphere-egu22-6057, 2022.

14:08–14:14
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EGU22-4088
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ECS
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On-site presentation
Anthony Foucher, Marcos Tassano, Guillermo Chalar, Mirel Cabrera, Joan Gonzalez, Irène Lefèvre, and Olivier Evrard

Recent agriculture expansion and land cover conversion (post-1985) induced major deleterious environmental effects in South-America in general and in Uruguay in particular, affecting locally the sustainability of soil and water resources. Whilst the environmental consequences of agriculture’s development were largely studied (e.g. monitoring, modeling) in Europe or North America, much less attention was devoted to the intensity of land degradation in South-America and more specifically, on the Pampa Biome. In this study, sediment cores collected in two reservoirs installed along the Rio Negro river (catchments of 23.000 and 39.000 km²) and draining agricultural catchments were used for reconstructing the evolution of sediment dynamics and source contributions in this region during the last several decades. Various chemical and physical analyses were performed for characterizing this accumulated sediment (e.g. fallout radionuclides, organic matter properties (TOC, δ15N, δ13C, C:N), X-ray fluorescence). Results indicate the significant acceleration of sediment accumulation rates (e.g. by 67% on average in the Rincon del Bonete dam between 2003 and 2019) associated with major phases of agricultural expansion (e.g. expansion of soybean and afforestation). Sediment properties show an increase of native vegetation source contributions associated with the conversion of native grassland into cropland. Understanding the causes of past and present acceleration of sediment delivery are of prime importance in order to protect the soil and water resources with the design of adapted management schemes at the catchment scale.

How to cite: Foucher, A., Tassano, M., Chalar, G., Cabrera, M., Gonzalez, J., Lefèvre, I., and Evrard, O.: Reconstruction of land degradation associated with recent agricultural expansion in Uruguay (1982-2019) based on sediment cores analyses , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4088, https://doi.org/10.5194/egusphere-egu22-4088, 2022.

14:14–14:20
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EGU22-3785
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ECS
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On-site presentation
Axel Birkholz, Sabrina Albiez, Adrian Gilli, and Christine Alewell

Lake sediments can be used as great environmental archives, especially when they are varved due to anoxic conditions at the lake bottom. Such an annual resolution of these archives can give unique insights in past environmental and climate settings and changes. Here, we try to track back changes in the erosion dynamics and associated land-use and potentially climate changes at the catchment scale from seasonal to centennial scales at Lake Baldegg, Switzerland.

Land-use changes and agricultural practices become nowadays a key factor of sediment dynamics by modifying the soils erosive risk and the catchment sediment connectivity. And while soil erosion is one of the biggest threats to soil fertility as well as to ecological health of freshwater systems, restoration and management plans of water bodies can only be efficient if the sediment sources and their respective contributions, i.e. the proportion attributable to different land uses and agricultural practices, are identified.

For this we used a compound-specific stable isotope approach (δ13C of long-chain fatty acids (LC-FA)) combined with connectivity modelling to a 130-years old varved lake sediment core from a eutrophic Swiss lake. We were able to discriminate grassland, arable and forest soils using the LC-FAs C26:0 and C28:0. Between 1940 to 1960 forest soils were the main source of the terrestrial sediment origin (80-100%). After 1960 a clear change in sediment origin happened. The contribution of arable and grassland soils to lake sediments were increasing. However quantitative attribution and differentiation between grassland and arable land were difficult due to the linear distribution of the tracers between the sources.

For sediments older than 1940 the isotopic signal could no longer be explained by today’s terrestrial sources. We hypothesized additional sources of the assumed terrestrial long-chain fatty acids like (1) historical peatlands and/or former reed grass areas and (2) in-situ LC-FA production by algae.

Since the last presentation at EGU2019 we went back to Lake Baldegg to expand our potential source sample set to explain deviation of source signals from sediments. After consultation of historic maps and reports, we located sites where peatlands and reed grass existed before the 1940s and where reed gras is still growing. There we took plant as well as soil samples and peat/lake sediment cores from a historical pond, which was connected to the lake and where reed grass grows today.

To investigate the potential in-situ production of LC-FAs by algae or other microorganisms in the water column, we did four sampling-trips on the lake between April 2021 and September 2021 to get algae and water samples from different depths and integrating over depth. These samples were filtered over glas fibre filters, extracted and analysed for FAs. In some samples we found LC-FAs in different concentrations. Especially for the algae samples this was surprising. Depending on their isotopic signature we can now differentiate between terrestrial or aquatic production.

The proof of significant aquatic contribution of LC-FAs to lacustrine sediments in Swiss lakes would be an important finding also regarding the common use of assumed terrestrial biomarkers in lake sediments for climate reconstruction.

How to cite: Birkholz, A., Albiez, S., Gilli, A., and Alewell, C.: Aquatic microorganisms or reed grass as potential disturbing factors in varved sediment records when tracing terrestrial input. An example from a eutrophic Swiss lake., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3785, https://doi.org/10.5194/egusphere-egu22-3785, 2022.

14:20–14:26
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EGU22-3395
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ECS
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Presentation form not yet defined
Catherine Wiltshire, Toby Waine, Robert Grabowski, Miriam Glendell, Barry Thornton, Steve Addy, and Jeroen Meersmans

Quantifying land use sources and understanding the dynamics of organic carbon (OC) in river catchments is essential to reduce both on-site and off-site impacts of soil OC erosion. The lake area of Loch Davan, located in Aberdeenshire, Scotland, has been significantly reduced over the last century due to sediment inputs and, in this study, we aimed to identify the primary source(s) and delivery of OC to the loch’s main feeder stream, Logie Burn and its major tributaries.

The relative contribution of different land use sources to organic matter load in waterways can be assessed using sediment fingerprinting (SF) with plant-specific biomarkers such as n-alkanes. However, application of the land use sources based on SF in catchment management is hindered by the following issues: i) broad land use classifications cannot provide accurate OC origins if the same land use exists in multiple locations within a catchment; each with its own susceptibility to erosion and connectivity to the streams, and ii) eroded soil is not the only source of plant-specific biomarkers such as n-alkanes and direct input of leaves or litter to waterways could mask the input from eroded soils.

This inter-disciplinary study aimed to improve upon the SF method by firstly constructing a “Carbon Loss Model” (CLM) to estimate areas of a catchment most likely to provide OC to waterways. We then compared the land use sources of OC estimated using the CLM and SF to improve our insights into both the origin and fate of eroded OC. Secondly, we considered whether soil specific tracers (neutral lipids) of soil microbial or fungal origin, combined with plant specific n-alkanes, could help to reduce the error in SF when discriminating land cover classes, facilitating a more accurate estimation of OC origins by adding a more soil - rather than vegetation - specific fingerprint.

Results show that addition of short-chain neutral lipid fatty acid biomarkers to plant specific n-alkane tracers led to a significant decrease in error when distinguishing between arable, pasture, forest and moorland land uses (error reduction 1.8-9%). Comparison of the land use sources of OC estimated using the CLM and SF identified that areas of estimated high carbon loss were not always the regions contributing most sediment to the streams and that non-erosion processes within the riparian corridor are likely contributing OC to the waterways. This research highlights that to better understand the origin of sediments and OC across the terrestrial-aquatic continuum we must understand both sides of that continuum (the susceptibility of terrestrial OC to erosion and delivery, and the characteristics of OC within the waterways) as well as the role(s) of the riparian area that links the two.

How to cite: Wiltshire, C., Waine, T., Grabowski, R., Glendell, M., Thornton, B., Addy, S., and Meersmans, J.: Assessing the source and delivery of organic carbon at a catchment scale using a combined sediment fingerprinting and carbon loss modelling approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3395, https://doi.org/10.5194/egusphere-egu22-3395, 2022.

14:26–14:32
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EGU22-12555
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ECS
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Presentation form not yet defined
Alice Dambroz, Douglas Utzig, Jean Minella, Ana Londero, Fabio Schneider, Claudia Barros, Davi Koefender, and Olivier Evrard

No-tillage is an extensively used soil conservation practice in crop fields. Yet, no-tillage is prone to runoff generation, which may lead to downstream concentrated forms of erosion, floods, solute transfer and eutrophication of water bodies. However, infiltration terraces on hillslopes can reduce runoff and erosion. We analyzed nutrient losses, in both dissolved and particulate forms, on terraced and non-terraced agricultural hillslopes under no-tillage in Southern Brazil. Precipitation, runoff, sediment yield and chemical elements’ concentrations were monitored in paired catchments, including a 2.35 ha terraced catchment (TC) and a 2.43 non-terraced catchment (NTC), during rainfall events that occurred from 2017 to 2018. Runoff and suspended sediment samples were manually collected in H-flumes at the outlet of each hillslope, where automatic water level readings were recorded at 5-minute intervals by a limnigraph to estimate runoff discharge. P, K, Ca, Mg, Cu, Zn and N concentrations were analyzed in runoff-water samples and P, K, Ca e Mg in the suspended sediment samples to obtain dissolved and particulate concentrations, respectively, and total nutrient losses. Maximum N concentration in TC’s runoff samples (8.70 mg L-1) were higher than in the NTC (7.41 mg L-1). Ca concentrations were higher in the NTC (average 3.9 mg L-1). Low and similar Mg, Cu, Zn mean concentrations were observed in the catchments. Mean P concentrations were ~0.11 mg L-1 in both catchments but reached higher concentrations in the NTC. Mean (~3 mg L-1) and maximum (8.74 mg L-1) K concentrations were observed the TC. In sediment samples, Ca, Mg, P and K concentrations were higher in the NTC. To compare total dissolved nutrients losses, we chose 13 rainfall-runoff events and 10 events for particulate nutrient losses. Total rainfall for the 13 events was 1020 mm, leading to 110 and 222 mm of runoff in TC and NTC, respectively. Besides higher runoff volume, NTC shows higher losses of all analyzed nutrients in runoff. P losses were of 105 and 352 g ha-1 in TC and NTC, respectively, while K losses were of 2293 and 4604 g ha-1, showing a similar trend. The average increase in Cu losses for NTC was 21 times higher than for TC. Total sediment yield in TC, for the 10 events, was 12 kg ha-1, and 39 kg ha-1 in the NTC. Higher particulate nutrient loss was observed in the NTC outflow. An almost nine-fold increase in particulate P losses was observed in NTC, besides a four-fold increase in Ca, a seven-fold increase in Mg and two-fold K losses. Although higher nutrient concentrations in water were observed in the TC for some samples, overall losses and concentrations were greater in the NTC. This indicates that nutrient flux from agricultural hillslopes is controlled by runoff and that terraces can decrease flow and material connectivity over hillslopes. As soil and water conservation practices are needed to ensure agriculture’s sustainability and to avoid deleterious environmental impacts, measures for runoff mitigation, such as terraces, were shown to effectively control nutrient – and, potentially, other solutes – transfer to water bodies.

How to cite: Dambroz, A., Utzig, D., Minella, J., Londero, A., Schneider, F., Barros, C., Koefender, D., and Evrard, O.: Dissolved and particulate nutrient yields in terraced and non-terraced zero order catchments under no-tillage, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12555, https://doi.org/10.5194/egusphere-egu22-12555, 2022.

14:32–14:38
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EGU22-9912
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ECS
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Virtual presentation
Gabriela Adina Moroșanu, Eugen Traistă, Liliana Zaharia, and Philippe Belleudy

Fine sediments supplied by rivers retain the imprint of the lithological and geochemical characteristics of their zones of origin and sometimes intermediate storage, as well as of the influence of human activities. Advancing the management of watersheds could thus be achieved by taking into account natural and anthropogenic sediment sources, representing the other “half” of the material carried by rivers. In European watersheds, a less common approach to comply with the EU Water Directive is to track sediment sources and pathways within a watershed using the mineralogical and geochemical features of alluvial sediments.  Difficulties arise when quantifying sediment budgets at any spatial or temporal scale especially for watersheds exhibiting complex sediment origins and transfer pathways.

Our study tackles the issues of different fine sediments sources, little-known residence times and the "competition" between natural processes and anthropogenic forcings responsible for sediment suspension delivery, transport, and accumulation. We seek to identify, through a geochemical approach, the relative sources of fine sediment in the Jiu River basin (10,080 km2), a major tributary of the Danube River, located in SW Romania. The study area stands out for its complex morphology and lithology (with in-river sediment footprints attributed to crystalline, limestone, and detrital facies) and its ongoing coal mining. Jiu River is an important alluvial supplier to the Danube River, especially during floods.

The research aims to identify the sub-catchments supplying the most sediments, by analyzing coaly matter from the watershed’s two coal basins, as well as the fine sediment’s heavy minerals and lanthanides content. To meet this objective, alluvial samples were gathered from potential upstream source areas and from an alluvial riverbank deposit, on Jiu river’s lower sector. The coal species (lignite and bituminous coal) and their ratio in the upstream and downstream sediment samples were determined through apparent density differentiation, using solutions of heavy liquids, and by quantifying the volatile matter and ash content. Lanthanum elements and heavy metals samples were analyzed using Rigaku Supermini X-ray Fluorescence Spectrography. Based on their abundance in upstream and downstream samples, the main geochemical indicators (Zr/Si, Ti/Fe, Cu/Fe, Cu/S, Ca/Mg, Na/K, Lanthanides/P ratios), as well as the two coal species, were further correlated with the underlying lithology and hydrological features of the source sub-basins.

The analysis of the upstream-downstream geochemical relationship was carried out at two spatial scales, to assess the potential upstream alluvial sources in 6 main sub-catchments, and to relate the geochemical composition of the upstream (source areas) samples with that from the downstream alluvial deposit. For the upper sediment layers making up the riverbank alluvial deposit, the information provided by the geochemical indicators was provided, where data was available, with hydrological information on the flood events having generated their accumulation.

As key geochemical indicators for the main areas of sediment production, coal content, heavy metals and lanthanides could improve the control and planning of watershed management and conservation. The results may also provide a holistic understanding of the upstream to downstream coal pollution transfer in watersheds still affected by coal mining.

How to cite: Moroșanu, G. A., Traistă, E., Zaharia, L., and Belleudy, P.: Geochemical “testimonies” of fine sediments’ origins in a lithologically complex and coal mining disturbed Romanian river basin , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9912, https://doi.org/10.5194/egusphere-egu22-9912, 2022.

14:38–14:44
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EGU22-213
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ECS
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Virtual presentation
Jonas Eschenfelder, Alex Lipp, and Gareth Roberts

The concentration of elements in river sediments play a fundamental role in determining the ‘health’ of rivers. They also contain important information about provenance and geomorphic processes (e.g. mixing). For instance, concentrated heavy metals, such as lead, copper and chromium, can identify foci of polluting industry and stressed ecosystems.  Attempts to monitor pollution in river sediments and to generate geological baselines are thwarted by the lack of available measurements of sediment geochemistry in higher-order, downstream, river channels. We address that issue by developing forward and inverse methodologies to predict the composition of river sediments throughout drainage basins from small inventories of geochemical measurements (tens of samples). A case study, centered on the River Clyde near Glasgow, Scotland, shows that conservative downstream mixing generates robust and continuous estimates of element concentrations in river sediments. Predicted geochemistry and independent observations match well for elements that have diverse concentrations in source regions (e.g. magnesium). Anthropogenic enrichment of heavy metals along large rivers, compared to geologic baselines generated by mixing ‘clean’ source regions, correspond to the Glasgow city area and old mining regions. Continuous predictions of river chemistry are used to identify river reaches where heavy metal concentrations exceed toxic threshold levels. 

How to cite: Eschenfelder, J., Lipp, A., and Roberts, G.: Quantifying heavy metal concentrations throughout drainage basins from river sediment mixing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-213, https://doi.org/10.5194/egusphere-egu22-213, 2022.

Conclusions and perspectives
14:44–14:50
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EGU22-858
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On-site presentation
Olivier Evrard, Pedro Batista, Jaume Company, Aymeric Dabrin, Anthony Foucher, Amaury Frankl, Julián García-Comendador, Arnaud Huguet, Niels Lake, Ivan Lizaga, Núria Martínez‑Carreras, Oldrich Navratil, Cécile Pignol, and Virginie Sellier

Sediment fingerprinting or tracing is a technique that allows to quantify source contributions of sediment. A Thematic School was organised in October 2021 to discuss potential options to improve the design and implementation of sediment fingerprinting procedures. The suggestions put forward by the School participants were organised around six complementary topics. First, we suggest a better use of geomorphological information to improve study design. Researchers are invited to scrutinize all the knowledge available on the catchment of interest, and to obtain multiple lines of evidence regarding sediment source contributions. Second, we think that scientific knowledge could be improved with local knowledge and we propose a scale of participation describing different levels of involvement of locals in research. Third, we recommend the use of state-of-the-art sediment tracing protocols to conduct sampling, deal with particle size, examine data before modelling and accounting for the hydro-meteorological context under investigation. Fourth, we promote best practices in modelling, including the importance of running multiple models, selecting appropriate tracers, and reporting on model errors and uncertainty. Fifth, we suggest best practices to share tracing data and samples, which will increase the visibility of the fingerprinting technique in geoscience. Sixth, we suggest that a better organisation of datasets would allow to formulate hypotheses and improve our knowledge about erosion processes in a more unified way. In conclusion, sediment fingerprinting, which is interdisciplinary in nature, should play a major role to meet the current and future challenges associated with global change.

How to cite: Evrard, O., Batista, P., Company, J., Dabrin, A., Foucher, A., Frankl, A., García-Comendador, J., Huguet, A., Lake, N., Lizaga, I., Martínez‑Carreras, N., Navratil, O., Pignol, C., and Sellier, V.: Improving the design and implementation of sediment fingerprinting studies: Summary and outcomes of the TRACING 2021 Scientific School , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-858, https://doi.org/10.5194/egusphere-egu22-858, 2022.