Mining activities, both industrial and artisanal, play a crucial role in economic development but often come with significant environmental costs, particularly through water contamination. The Hiré region in Ivory Coast is significantly impacted by extensive gold mining and the intensive use of chemicals in ore processing, posing substantial risks to groundwater quality. While industrial mining is subject to regulations, unregulated artisanal mining practices contribute significantly to environmental contamination. This study evaluates the distribution of potentially toxic elements (PTEs) and pollution indices, including the Enrichment Factor (EF), Heavy Metal Pollution Index (HPI), and Heavy Metal Contamination Index (HCI), in groundwater used for drinking purposes. The focus is on metals such as Pb, Hg, Cd, As, Cr, Fe, Al, Zn, Mn, and cyanide contamination.

Results indicate that arsenic, iron, and aluminum concentrations at several sites far exceed international water quality standards, likely due to natural geochemical processes and mining activities. The concentration of potentially toxic elements (PTEs) were generally high, with enrichment factors EF > 1 at the majority of sampled sites. Pollution indices show HPI < 100 and HCI < 50 for over 85% of sampled sites, indicating mild contamination. However, cyanide levels in cyanidation ponds exceeded safe limits by over 5900 times, highlighting critical environmental and health risks.

These findings underscore the importance of monitoring heavy metals, particularly cyanide, in the groundwater of the Hiré zone. Special attention should be given to unregulated artisanal mining and its constant relocation, which can expand the area of contamination. Ultimately, these findings contribute to the development of mitigation strategies and inform policymaking to address water pollution challenges in mining regions globally.

How to cite: Traore Dosso, A., Marc Dufour, R., Kouamé, J. K., and Chèvre, N.: Impact of Mining Activities on Water Contamination by Heavy Metals and Cyanide in the Hiré Region, Ivory Coast, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17362, https://doi.org/10.5194/egusphere-egu25-17362, 2025.

Fluid infiltration plays a crucial role in transporting dissolved elements and may serve as a pathway for nanoparticles from soil surface to the subsurface. Smectite-type nanoparticles, as a key soil mineral component, can act as efficient carriers of cations due to their negative surface charge and large specific surface area. This study aims to understand the dynamics of smectite-type nanoparticles-associated trace metal, focusing on rare earth elements (REEs), from soil to groundwater at two contrasting sites in Thuringia, Germany, namely the Hainich Critical Zone Exploratory (carbonate/siliciclastic bedrock) and Saale-Elster-Sandsteinplatte Observatory (siliciclastic bedrock). Engineered Ni-montmorillonite (Ni-mnt) nanoparticles, synthesized hydrothermally as described by (Reinholdt et al., 2013) were used as tracers.

Nanoparticle migration requires stability against aggregation, influenced by pH, ionic strength, and natural organic matter (NOM). The effect of above-mentioned parameters on stability of Ni-mnt was investigated under controlled conditions in synthetic waters simulating surface-to-subsurface transitions and natural waters from lysimeter and well samples at both sites. Stability was assessed using dynamic light scattering (DLS), while REE adsorption and dissolved organic carbon (DOC) were evaluated with Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Liquid Chromatography – Organic Carbon Detection – Organic Nitrogen Detection (LC-OCD-OND), respectively.

As expected, Ni-mnt stability decreases in Calcium-rich environments and increases in high pH and NOM-rich environments as indicated by the critical coagulation concentration (Ca-CCC). Without NOM, Ca-CCC values of Ni-mnt were in the range of 2.5 mM to 5 mM in the pH range 5 to 8. In contrast, in the presence of NOM, (3.3 mg/L of [DOC]), Ca-CCC values rose to 8 mM at pH 5 and 6, and 15 mM at pH 7 and 8. As revealed by LC-OCD-OND measurements Ni-mnt stabilization is likely due to an association of high molecular weight DOC such as biopolymers and humics.

REEs preferentially adsorb onto organics rather than Ni-mnt under the competitive conditions chosen. Desorption experiments show that light REEs are stronger bond by Ni-mnt (slower reversibility kinetics).

These results highlight the critical role of NOM, particularly biopolymers and humics, in stabilizing clay nanoparticles and influencing REE transport. While NOM reduces aggregation under low to moderate ionic strengths, high ionic strength induces aggregation through cation bridging.

Reference

Reinholdt, M. X., Brendle, J., Tuilier, M. H., Kaliaguine, S., & Ambroise, E. (2013). Hydrothermal Synthesis and Characterization of Ni-Al Montmorillonite-Like Phyllosilicates. Nanomaterials (Basel), 3(1), 48-69. https://doi.org/10.3390/nano3010048

How to cite: Ewouame, R. A., Sieber, S., Merten, D., and Schäfer, T.: Dynamics of Clay Nanoparticle-Associated Trace Metals from Soil to Groundwater: Insights from Contrasting Geological Settings., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13442, https://doi.org/10.5194/egusphere-egu25-13442, 2025.

Nitrogen and water availability are the primary environmental factors limiting crop productivity on a global scale. Nitrogen behaviour in the subsurface is influenced by multiple factors, including continuous wetting, wetting/drying cycles, temperature, system design, and TWW quality, which are often challenging to quantify. This study examined these dynamics using batch adsorption and a laboratory-scale soil aquifer treatment system, simulated in a glass column filled with agricultural soil, to investigate the effects of synthetic ammonium solution under alternating wet and dry cycles. The study focused on ammonium removal and transformation, specifically  ammonium and nitrate, under varying wetting and drying phases. Constant-concentration synthetic wastewater was introduced, allowing analysis of how soil water content, pH, dissolved oxygen, and nitrogen concentrations impacted the geochemical properties of the soil medium. Batch adsorption experiments indicated strong alignment with Freundlich and Temkin isotherm models, suggesting heterogeneous adsorption sites and varying affinities. pH-edge experiments further revealed that ammonium adsorption was greater in alkaline conditions, indicating a pH-dependent mechanism. The column experiment continued for 52 days, studying three scenarios: (1) continuous flow, (2) alternate day wetting and drying, and (3) three days of drying followed by one day of wetting. Under drier conditions, increased ammonium transformation and sorption occur due to the formation of anoxic zones. Therefore, in the third scenario, anoxic conditions are formed, leading to a greater reduction in hydraulic conductivity. This study offers valuable insights and a strong scientific basis for the protection and management of groundwater and soil quality in agricultural areas.  

How to cite: Kumar, A. and Yadav, B.: Investigating Ammoniacal Nitrogen Transport in Subsurface under Alternating Dry-Wet Conditions Using Batch and Column Experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-879, https://doi.org/10.5194/egusphere-egu25-879, 2025.

The research aims to provide a comprehensive understanding of Organic matter (OM) through molecular characterization within the spatial distribution of a freshwater lake system. The sedimentary biomarkers, the n-alkane indices were used for determining OM inputs from terrestrial and aquatic sources of the aquatic system

Shift in OM sources within the lake along with P_aq , ACL and CPI values were analyzed with integration of grain size data for assessment of the origin and processes affecting the preservation of OM.

This approach is crucial in gaining insights how OM is distributed, and preserved, its nutrient cycling, and blend of natural and anthropogenic influences that impact ecological balance.

How to cite: Behera, S., Kumari, A., Jehangir, A., Behera, D., and Ambili, A. and the Soumyashree Behera: Decoding the geochemical mosaic of organic matter in the freshwater lake system of Kashmir Valley through molecular approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-457, https://doi.org/10.5194/egusphere-egu25-457, 2025.

The aim of this study is to develop models for analyzing the dynamics of copper and nickel pollution in small lakes within the influence zone of the Pechenga Nickel Plant (up to 100 km) in the past, present, and future (without emissions).

The research focuses on modeling the dynamics of nickel and copper concentrations in water, soil, and lake sediments caused by atmospheric emissions from the Pechenga Nickel Plant (Kola Peninsula) from 1946 to 2050. The model is built upon heterogeneous data collected during over 30 years of research on pollution effects in the Kola Peninsula. Until recently (2020), the data reflected the state of lakes, rivers, soils, and sediments under significant atmospheric emissions of pollutants. New data, collected in 2023 under drastically reduced emissions, allowed refinement of several parameters and modifications to the model to describe a new phenomenon—the recovery of the region's natural environment.

The use of balanced identification techniques enabled the selection of a model of appropriate complexity for the available heterogeneous dataset (over 10 sources), the identification of unknown parameters (both numerical and functional), and the generation of results. The specialized software employed in this study (available at https://github.com/distcomp/SvF) includes examples of various problem-solving scenarios (https://github.com/distcomp/SvF/tree/main/Examples). The programs and corresponding databases used in this work can also be found in the repository.

The developed model matches the complexity of the experimental data and reflects the new reality—a slow recovery of ecosystems under drastically reduced emissions. The obtained forecast is reliable: under the scenario of zero emissions, water concentrations are determined by the release (transition to soluble forms) of Ni and Cu from reserves in the soil and sediments. This process is very slow, resulting in a noticeable reduction in water concentrations on the one hand, but precluding hopes for rapid further improvement on the other. The estimated "half-leaching" period (analogous to "half-life") of these reserves is on the order of several hundred years.

Keywords: atmospheric transport, pollution transformation, nickel, copper, subarctic aquatic and terrestrial ecosystems, mathematical modeling, balanced identification, forecasting

How to cite: Sokolov, A., Gashkina, N., Moiseenko, T., and Sokolov, A.: Emissions Ceased, Problems Persist – The Case of the Copper-Nickel Plant (Kola Peninsula), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20481, https://doi.org/10.5194/egusphere-egu25-20481, 2025.

Artisan small-scale mining (ASM) plays an important role in the global mineral supply but is also a considerable contributor of contamination, due to the unregulated nature of the ASM sector. Artisan mine tailings, often contaminated with trace metals and chemicals used at the extraction process, are typically disposed in the local environment where they enter rivers and spread through sediment transport processes. This unsustainable practice has been largely ignored because ASM mines and processing facilities are tiny compared to their industrial equivalents, despite the fact that ASM collectively accounts for a substantial proportion of global mining output (20% gold, 26% tantalum, 25% tin). Here we examine a small Philippine catchment with extensive ASM activity and use the Caesar-Lisflood numerical model to show that 73% of solid mine tailings (SMT) disposed by pushing them into nearby watercourses during a decade of ASM operation are mobilised becoming a diffuse source of pollution that is difficult to manage. Conversely, when SMT are not disposed into watercourses and instead deposited at the location of ore processing only 26% is mobilised, primarily from areas of high geomorphic connectivity near rivers. 90 years after mine cessation, the amount of diffuse pollution increases further to 80% when SMT have been disposed into rives and only to 30% when SMT have been deposited locally. These results show that the legacy of mine waste dispersal long after ASM has stopped is heavily influenced by the initial decision to dispose or deposit SMT. Our findings underscore that diffuse pollution from the ASM sector must not be overlooked and approaches must be taken to sustainably manage ASM tailings now and in the future.

How to cite: Vasilopoulos, G., Coulthard, T., Gonzalvo, F., Eslava, D., and Williams, R.: The role of geomorphic connectivity on the mobilisation of artisan mine tailings, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13659, https://doi.org/10.5194/egusphere-egu25-13659, 2025.

In Northwestern Europe, sediment transport from agricultural fields to rivers has significant off-site impacts, influenced by connectivity between landscape elements. Sediment connectivity, assessed  using the index of connectivity (IC) developed by Borselli et al. (2008), is shaped by landscape configuration, including features like field boundaries that divide land parcels. Effective management requires understanding these interactions to mitigate soil erosion. IC depends on factors enhancing (upstream area and slope) or impeding (downstream distance and impedance) connectivity, with impedance estimation being particularly challenging to quantify due to vegetation effects. One such effect is the alternation of crops along slopes, a practice known as strip cropping, which is widely recognised in the literature as an effective strategy to reduce connectivity and improve soil conservation. This study proposes refining the IC weighting factor by incorporating parcel connectivity, thereby better reflecting the impact of agricultural landscape fragmentation. We focused on the Dyle sub-catchment in Belgium, where the organisation of agricultural parcels is suboptimal, with 40% of crop sequences along concentrated flow paths  consisting of crops from the same category (e.g., spring crops or winter cereals). We applied the revised IC using high-resolution data (1 m × 1 m) to compare different parcel fragmentation scenarios. Fragmented landscapes yield lower connectivity values, indicating greater sediment disconnection. This is especially pronounced along concentrated flow paths, where up to 49% of the least connected flow paths are disconnected compared to non-fragmented setups. Isoline-based parcel fragmentation emerged as highly effective, promoting larger parcel sizes and better disconnection on concentrated flow paths. These results emphasize the opportunities for improved management of agricultural landscapes in order to reduce sediment connectivity through appropriate land use practices and parcel configurations.

How to cite: Herpoel, M., Michez, A., and Degré, A.: Field patterns as game changers of the sediment connectivity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17782, https://doi.org/10.5194/egusphere-egu25-17782, 2025.

Suspended sediment and the associated sediment-bound elements play a crucial role in the geomorphic, chemical and ecological status of a river. Representative in situ sampling of these suspended solids has shown to be complex, because the concentrations vary strongly over time and across the river cross-section. This leads to large uncertainties in suspended sediment and element load calculations in rivers.

This contribution summarizes the findings of the URSACHEN project which ran between 2020 and 2024 at the German Federal Institute of Hydrology (BfG). The project analyzed the spatiotemporal variability of suspended sediment and element concentrations in rivers and derived the consequences for representative in situ river monitoring. The project included case studies along the German part of the Rhine at three focus sites (Koblenz, Brohl-Lützing, Emmerich) under different flow conditions (low, middle and high discharge), as well as studies based on existing monitoring data from the river monitoring network of the Federal Waterways and Shipping Administration (WSV) and data from the Global Water Quality Database GEMStat.

In this PICO, we will present a method that allows to determine the required sampling interval for a river segment, in order to determine the annual suspended sediment load with an uncertainty of <20%. Results from a global study highlight the type of river catchments in which higher sampling intervals are required and others where infrequent sampling is sufficient. Furthermore, we will highlight the importance if amalgamated in situ sampling, to reduce the uncertainty introduced by short-term, turbulence-driven temporal variability.

To analyze the spatial variability of suspended solids in the Rhine river cross-section, a new in situ sampling method was developed, which enables the simultaneous in situ sampling of five samples in a depth-gradient. The collected samples were analyzed on suspended sediment concentrations and the concentrations of 67 different chemical elements. The data from the conducted sampling campaigns, as well as the existing data from the WSV monitoring network, show strong lateral and depth gradients in suspended sediment and element concentrations across the river cross-section. Collecting water samples from the water surface and near the riverbank can lead to an underestimation of the annual sediment and element loads of up to 30%.

Overall, the URSACHEN project has significantly improved the understanding of the temporal and spatial variability of suspended sediment and element concentrations in rivers. The project provided important insights and recommendations for in-situ water monitoring and river management worldwide.

How to cite: van Dongen-Köster, R., Arndt, J., Belkouteb, N., Schroeder, H., Slabon, A., Terweh, S., Dietrich, S., Duester, L., and Hoffmann, T.: Temporal and spatial challenges in the in situ monitoring of suspended sediment and element concentrations in rivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18960, https://doi.org/10.5194/egusphere-egu25-18960, 2025.

South America has experienced significant landscape transformations over the last century, with the expansion of agriculture (pasture, cropland, plantations) at the expense of natural ecosystems (forest, grassland).

More specifically, the Rio de la Plata Grasslands composing the Pampa biome, a temperate grassland ecosystem, mainly located in Uruguay and north Argentina, is among the regions with the highest global rates of land-use change, thereby threatening its biodiversity, land and water resources. 

The consequences of agricultural development in this region have been poorly documented since its beginning. 
Retrospective analysis using sediment coring can provide valuable insights into these impacts over extended periods. 
Such a retrospective was successfully conducted by Foucher et al (2023) \cite{foucher_inexorable_2023}. Nevertheless, their sediment core did not reach the reservoir's bottom, limiting the reconstruction of these processes to the post-1990 period.

In this study, we are analysing a sediment core collected in the Rincon del Bonete dam, draining a 39,500 km² catchment, and dated back to 1948. Various analyses were performed along this sedimentary archive in order to date and characterise the sediment properties (gamma spectrometry, high-resolution geochemical content analysis (XRF), pesticides) and their changes with time. 
Statistical analyses of the sediment fluxes enabled the differentiation of distinct phases in the sediment delivery process.

The Rincon del Bonete catchment in Uruguay has undergone substantial changes of land-use and farming practices, reflecting the broader challenges of environmental degradation in the Pampa region.
Available data over the region show that forest plantations expanded from less than 1\% of the area in 1985 to over 10\% in 2022. Concurrently, agricultural and pastoral land use increased by over 250\% between 1985 and 2022, while natural grasslands declined from covering 80\% of the basin to just 60\%. 
Results show that these changes have led to four distinct phases in sedimentation recorded in the lake archive: an initial period (1948-1964) of reservoir filling and early basin degradation in the northern Brazilian part of the catchment, characterised by extensive DDT insecticide use; a second period (1964-1985) of conventional tillage agriculture with a mix of agriculture-pasture and the beginning of intensive pesticides use in Uruguay (1970-1980). The third phase (1985-2007) was then characterised by a shift to no-tillage agriculture, afforestation, with a notable expansion of this practice occurring between 1999-2005, and the observation of an associated decrease of sediment delivery. During the final phase (from 2007 onwards), rapid and large agricultural expansion under continuous no-tillage practices and wood harvesting led to a large usage of pesticide and to an increase of sediment delivery despite a second notable phase of afforestation in 2007-2014.

This study highlighted the influence of land use changes and agricultural practices on sediment delivery since WWII, revealing the occurrence of high sedimentation rates during early conventional tillage and the onset of pesticide use, followed by a reduction of these rates during the transition to no-tillage and afforestation, and a marked increase with large-scale agricultural expansion and wood harvesting.

How to cite: Bardelle, A., Gastineau, R., Foucher, A., Guillevic, F., Chaboche, P.-A., Chalar, G., Tassano, M., Sabatier, P., Cottin, N., Cerdan, O., and Evrard, O.: Evolution of the impact of land use changes and agricultural practices on sediment delivery in the Uruguayan Pampa, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11054, https://doi.org/10.5194/egusphere-egu25-11054, 2025.

Assessing sediment transfer and provenance in large river basins is complex due to the variety of processes involved and the variability of their controlling factors. In this study, we attempt to quantify the provenance and transfer of fine sediment in the Rhine basin by adopting a synoptic sampling approach. Following a minor flood event during the end of August and beginning of September 2023, which originated in the alpine part of the Rhine basin, we collected samples of freshly deposited fine sediments along the banks of the main branch of the Rhine River and its four major tributaries (Aare, Neckar, Main, Mosel). These samples were mostly collected from hard surfaces (e.g., bank reinforcements, ferry landings) just above the water line. The samples were analysed for elemental composition using ICP-MS. A principal component analysis was performed on the element concentrations. The first principal component was interpreted as the main factor reflecting the  geogenic variation of the sediment composition. Next, a sediment transfer model that accounts for sediment supply to and sediment retention within the river network was set up. The model inputs include a digital elevation model of the river basin, the interpolated scores of the first  principal component based on element concentrations from the FOREGS geochemical atlas, and RUSLE-based estimates of sediment production. The model was calibrated using the ‘observed’ scores of the first principal component in the High Rhine and impounded section Upper Rhine (section between the Rhine-Aare confluence and Iffezheim).

The model results reveal that spatial variation in sediment supply to the river network is primarily controlled by area-specific event runoff and, to a lesser extent, by long-term sediment production. Furthermore, the model results demonstrate the relative importance of nearby sediment sources over sources further upstream: on average the relative importance of the source declines by 1.1% per kilometre downstream transport. It is likely that both retention of fine sediments in the channel network during transport and entrainment of fine sediments due to bank erosion or channel bed incision are at play and explain this decline. The patterns of deviations of the model predictions from measured sediment composition in the free-flowing section of the Upper Rhine and in the upper part of the Lower Rhine suggests that about 50% of the fine sediments reaching the Rhine delta may be derived from sediment nourishments to mitigate channel bed incision.

How to cite: van der Perk, M., Cox, J., and Middelkoop, H.: Composition of freshly deposited fine sediments during the 2023 summer flood event in the Rhine River basin: implications for sediment transfer and provenance, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12859, https://doi.org/10.5194/egusphere-egu25-12859, 2025.