Displays

In intermittent rivers and ephemeral streams (IRES), the hydrological regime is the primary driving force controlling the sediment transfer from the upland to the lowland catchment compartment, ergo the river geomorphology. The general objective of this study is to investigate the processes and the relationships between flow regime and suspended sediment (SS) transport in two IRESs with a different degree of intermittency, the Búger River (Spain) and the Carapelle River (Italy). The specific objectives are to (i) identify the drivers of SS transport, (ii) analyse and quantify the temporal variability of the SS transport in response to the hydrological regime. High-resolution data of streamflow and SS concentration (SSC) were used in this analysis and a set of hydrological indicators were computed to characterize and classify the flow regime.

In the Búger River, the high degree of intermittency and the low runoff coefficient were mainly due to the presence of carbonate lithology in headwaters and the specific SS yield (SSY: 0.5-46 t km^-2 yr^-1) was strongly influenced by the flow regime. In the Carapelle River, the high values of the annual runoff coefficient (14-35%) and SSY (89-745 t km^-2 yr^-1) were related to clay and limestone lithology. Most of the annual SSY was transported during floods. In the Búger River, SSY and maximum SSC (SSCmax) were correlated with the runoff, peak discharge, and antecedent rainfall. In the Carapelle River, SSY and SSCmax were correlated to the amount and intensity of rainfall. The catchment size played an important role in the hysteretic behavior since it had an influence on the spatial rainfall and sediment sources distribution. Búger River showed predominant clockwise loops as SS sources were close to the outlet. In the Carapelle River basin, clockwise and counter-clockwise were generated as the larger agricultural area promoted a huge sediment availability.

Lithology and geological characteristics resulted in the most relevant drivers controlling the hydrological regime and river type classification, meanwhile, rainfall was a less relevant factor. Land use and management practices were also relevant factors in SSY, determining the availability of suspended sediment material. At the event scale, a non-linearity in the rainfall-runoff relationship was found for both catchments, as runoff response can be due to different processes (i.e., saturation or infiltration excess).

This work was supported by the research project CGL2017-88200-R “Functional hydrological and sediment connectivity at Mediterranean catchments: global change scenarios –MEDhyCON2” funded by the Spanish Ministry of Science, Innovation and Universities, the Spanish Agency of Research (AEI), the European Regional Development Funds (ERDF),  the project “Soil Erosion in Apulia: Monitoring, Modelling and Control Strategies” performed within University of Bari and funded by the Apulia Basin Authority and the COST Action CA15113 Science and Management of Intermittent Rivers and Ephemeral Streams (SMIRES).

How to cite: Ricci, G. F., Fortesa, J., García-Comendador, J., Gentile, F., Estrany, J., Sauquet, E., Datry, T., and De Girolamo, A. M.: Hydrological regime and sediment transport in two Mediterranean intermittent rivers and ephemeral streams (IRESs), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4807, https://doi.org/10.5194/egusphere-egu2020-4807, 2020.

In the context of increasing anthropic pressures on river systems, including river regulations, land-use changes, and widespread contamination, sediment deposits can act as critical archives of the hydro-sedimentary processes and of the impact of such pressures on river corridors. Depositional environments and their degree of connectivity with the main channel may, however, influence the nature, chronology, and continuity of sedimentary records. This point is highlighted through a case study in a reach of the Rhône River (Péage-de-Roussillon, France) subjected to strong anthropogenic pressures (river training, by-passing hydropower production, contamination). Sediment cores were retrieved from four distinct depositional environments with different levels of connectivity with the main channel: a floodplain, a semi-active secondary channel, a fully connected secondary channel and a small impoundment. A multi-proxy characterization of the cores was conducted, including grain-size, total organic carbon content, historical and emerging contaminants (metallic elements, various organic pollutants such as polychlorinated biphenyls and brominated flames retardants, etc.), and dating techniques. The analysis of these parameters shows that each environment recorded a different time period comprised between the 19^th century and nowadays and associated with distinct markers of anthropogenic activities: the less the environment is connected, the older the record is. By combining the different cores, successive contamination trends can be reconstructed over time. In particular, a shift from polychlorinated biphenyls (PCBs) to polybrominated diphenyl ethers (PBDEs) as the predominant contaminant can be observed in the 1970s-1980s; such contamination sequence has hardly ever been documented in the literature. The diversity of depositional environments also allows identifying two types of infrastructure-induced legacy sediments deriving from two distinct periods of river engineering in the area. Overall, this work illustrates the spatial variability of sediment records in fluvial environments and the importance of retrieving multiple cores in diversified depositional environments to obtain an accurate and comprehensive archive of river contamination and functioning.

How to cite: Vauclin, S., Mourier, B., Dendievel, A.-M., Noclin, N., Piégay, H., Marchand, P., and Winiarski, T.: Influence of depositional environments on the contamination record of fluvial sediments: a case study from the Rhône River (France), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21755, https://doi.org/10.5194/egusphere-egu2020-21755, 2020.

The reconstruction and modelling of contamination trajectories in rivers is a key concern to investigate spatio-temporal impacts of long-term anthropogenic activities. This issue is highly significant for persistent organic pollutants, such as polychlorinated biphenyls (PCBs), known for their toxicity, their low degradation rates and their hydrophobic properties leading to their accumulation in sediments and biota. Increasingly produced and released worldwide from the 1930s to the 1970-1980s, PCBs were analysed in numerous studies dealing with river sediment quality. However, data syntheses are uncommon at the scale of large hydrosystems, and source-to-estuary approaches along rivers are still needed. Accordingly, we propose an original work integrating PCBs analyses on different solid matrices (sediment cores, bed and flood deposits, suspended particulate matters, and dredged sediments) originating from both research programmes and monitoring. Based on more than 1400 validated analyses, temporal trends of the PCB contamination were reconstructed since 1945 along the four main fluvial corridors in France (Rhône, Seine, Loire and Garonne Rivers). The relationships with socio-environmental factors were also deciphered by integrating hydrological and human spatio-temporal data (cumulative river discharge, population hot spots, urban and industrial surfaces). This work highlighted that the main contaminant trends were driven by regulation, but also by sediment transport and accidental releases (especially since the 1990s). In general, urban and industrial areas were the main contributors to the PCB contamination of rivers: around and downstream of Paris and Rouen (Seine River), Lyon and its “Chemical Valley” (Rhône River), Saint-Etienne and Nantes conurbations (Loire River), and probably downstream of Toulouse and Bordeaux (Garonne River). Relatively high concentrations persisted after the end of the PCB production due to chronic diffuse inputs and accidental releases, particularly on the Rhône River. Moreover, the estimation of specific fluxes revealed that up to 12 µg/m²/yr (i.e. 0.9 t/yr on average) of PCBs were brought by French rivers, especially by the Rhône, Seine and Loire Rivers (ranked in order of importance) to Western European seas since the 1970s.

How to cite: Dendievel, A.-M., Mourier, B., Coynel, A., Evrard, O., Labadie, P., Ayrault, S., Debret, M., Faivre, Q., Gardes, T., Vauclin, S., Budzinski, H., Grosbois, C., Desmet, M., and Winiarski, T.: Assessment of PCB trajectories along French river corridors between 1945 and 2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2205, https://doi.org/10.5194/egusphere-egu2020-2205, 2020.

Hydrophobic pollutants in rivers are transported to varying degrees either in the dissolved or particle-bound phase. For either very turbid rivers or very strongly sorbing compounds, transport dynamics are closely coupled to the cascading sediment movement throught the stream network. Hence, an understanding of sediment storage and mobilisation/movement, including the interaction of suspended and bed sediment phases is the basis for properly discribing contaminant transport.

Suspened sediments from the Ammer River in southwestern Germany show a gradual decrease of polycyclic aromatic hydrocarbons (PAH) loadings in a downstream direction, reflecting urban sources in the headwaters. The decrease of PAH loading is, however, only weak which we attribute to only moderate inputs of more or less clean sediments along the river profile, capable of diluting the contaminant signal. The bed sediments of the river comprise a large fraction of grain sizes < 250 µm and constitute an important storage compartment for hydrophobic contaminants. Transformation or leaching into the water phase may reduce the stored amounts. Furthermore, the particle-bound mobility of the stored contaminants clearly depends on the distribution among grain size fractions. We have, therefore, also sampled the bed sediments < 250 µm along the river profile and separated into four grain size fractions (< 19 µm, 19-54 µm, 54-100 µm, 100-250 µm) using vacuum filtration and fine stainless steel meshes. The fractions have been analyzed for urban pollutants of different origins (PAH, heavy metals and the musk fragrance galaxolide) and particulate organic carbon (POC) content. First results show that POC is enriched in the 19-54 µm fraction and that metal contents are neither correlated with POC nor with grain size. This contradicts the common assumption that compounds typically sorbing to surfaces acumulate in the finest fractions due to the large specific surface area. Final results for PAH and galaxolide concentrations as a function of POC contents and particle sizes will also be presented (analysis still pending). At least for PAH a strong affinity to organic carbon is anticipated, while not much is known to date about the sorption and storage behaviour of galoxolide.

The results will give further insights into the environmental behaviour of the investigated compound groups. Comparison with data from suspended sediment sampling will enhance our understanding of mobile and immobile phase interactions and, hence, the transport dynamics of these sediment-associated pollutants.

How to cite: Schwientek, M., Renner, D., Glaser, C., Rügner, H., and Grathwohl, P.: Mobility and storage of hydrophobic urban pollutants in an agricultural river in southwestern Germany (Ammer River), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11331, https://doi.org/10.5194/egusphere-egu2020-11331, 2020.

Wastewaters are highly contaminated waters by anthropogenic compounds. To limit the propagation of these contaminants in water bodies and allow safe reuse of this resource, sewage treatment plants were developed. For the last few decades, many studies evidenced the partial cleaning efficiency of these systems. Many compounds, such as pharmaceuticals, are therefore designated as emerging contaminants. Most of the studies investigated sewage treatment plants releasing rates, but spatial and temporal behaviours of pharmaceuticals in natural environments received less attention. In this study, 27 pharmaceuticals were investigated into both water, bed-load sediments and suspended particles from a small tributary of the Loire River: a peri-urban stream named Egoutier (Loiret, France). The catchment area of the Egoutier is characterized by an upstream/downstream anthropogenic gradient and the presence of two sewage stations whose effluents are released in the watercourse: one coming from the Central Army Pharmacy, a second one draining a psychiatric hospital and a last one defining a bad connection of the pluvial piping system. Only 13 pharmaceuticals were found in our samples. Cationic compounds, such as doxepin, metoprolol, atenolol, codeine and trimethoprim, were mostly adsorbed on mineral phases, except tramadol appearing mostly associated with organic matter, like the anionic and neutral compounds, such as sulfamethoxazole, ibuprofen, diclofenac, acetaminophen, diazepam, carbamazepine and oxazepine. High spatial and temporal variabilities were observed. Bed-load geochemistry fluctuations appear linked to the sedimentary dynamic from both suspended particles and organic matter. In the suspended particles fraction, pharmaceuticals contents seem to be driven by grain-size distribution. Variations in pharmaceutical inputs and low half-life of some molecules also have an influence on both particulate fractions contents.  In this way, some compounds highly biodegradable, such as acetaminophen, are accumulated near to their emission zones, while other molecules highly transported in suspended particles, for example diazepam, are transported over the stream and mostly accumulated in bed-load sediments during dry periods. On the contrary, compounds adsorb on coarser particles, such as trimethoprim, have higher propagation distances during humid periods. Some molecules could be used as sourcing markers. Indeed, codeine is for example exclusively released by the psychiatric hospital. In the same way, sulfamethoxazole, ibuprofen, tramadol and codeine are specifically emitted from the Central Army Pharmacy and the psychiatric hospital. This study improve the understanding of pharmaceuticals adsorption, dispersion and accumulation in receiving environments. Moreover, it allow better distinction between domestic consumption releases and hospital and/or pharmacy facilities impacts.

How to cite: Ledieu, L., Simonneau, A., Cerdan, O., Fougère, L., Destandau, E., Thiebault, T., and Laggoun, F.: Roles of the particulate phases in pharmaceuticals spatio-temporal dynamics in a peri-urban stream, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20122, https://doi.org/10.5194/egusphere-egu2020-20122, 2020.

Viticulture, which plays a major role in the economy of several EU countries, is highly dependent of pesticides. In the São Lourenço experimental catchment, located in an important wine-growing region in Portugal, vineyards are the dominant land cover. Previous studies in this catchment showed the presence of different pesticide residues in surface water and erosion rates in vineyards of up to 30 Mg ha^-1 y^-1. However, information on the presence of pesticide residues in topsoils and water-eroded sediments are lacking, not just in this catchment but in general. To address these knowledge gaps, we conducted two soil sampling campaigns (fall 2015, fall 2016) and a field runoff-erosion experiment (winter 2015). We sampled 3 vineyards in the first campaign and 9 in the second, both covering different soil types (humic cambisols, calcic cambisols and chromic luvisols). Soil samples were collected within and between the vine rows, at the top, middle and bottom of the slope, and at two soil depths (0-2 and 15 cm). The runoff-erosion experiment involved 9 plots of ~12 m²; pesticide residues were monitored in topsoil and eroded sediments at six occasions after important rainfall events (>50 mm). 47 prioritized pesticide residues were analysed in 162 soil and 108 sediment samples. The levels of residues in soil were compared with their predicted environmental concentrations (PECs), calculated according to European Food Safety Authority (EFSA) pesticide application recommendations and to local farmers records. All soil samples contained pesticide residues, dimethomorph, glyphosate and its metabolite AMPA being the most frequent detected compounds. Measured levels of the different residues in soil occasionally exceeded predictions. Pesticide levels seemed related to slope position, generally being higher at the bottom than at the top or middle of the slopes, but not to the position within or between vine rows. Soil depth played a noticeable role in pesticide levels, with 80% lower concentrations of glyphosate and tebuconazole at 15 cm than 0-2 cm depth. For dieldrin (the only long-banned pesticide detected), the concentration was higher at 15 than 0-2 cm depth. Sediments had fewer compounds than soils, but the frequencies with which they were detected were similarly high. Pesticide levels were significantly higher in sediments than soils, especially in the case of the finest sediments (<0.04 mm). Dimethomorph and pyrimethanil were the most common compounds in the eroded sediments, but glyphosate and AMPA had the highest concentrations. Pesticide export varied between compounds but never exceeded 3% of the content at 0-2 cm depth. Pesticide export strongly depended on erosion rates, which, in turn, differed between soil types. Overall, our results reinforced the notions that: (i) intensive pesticide use turns soils into pesticide sinks and (ii) soil erosion leads to lateral transport of pesticides and their further accumulation in deposition zones at slope bottoms, with subsequent risks for nearby aquatic systems. It therefore seems increasingly urgent to establish and implement monitoring programs for pesticide residues in soil, in order to enable pesticide post-registration control and comprehensive risk assessments.

How to cite: Silva, V., Gonzalez-Pelayo, O., Abrantes, N., Keizer, J. J., Mol, H., Ritsema, C., and Geissen, V.: Pesticide residues in vineyard soils and water-eroded sediments – predictions versus observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10656, https://doi.org/10.5194/egusphere-egu2020-10656, 2020.

Lake Neusiedl is the largest endorheic lake in Central Europe, straddling the Austrian–Hungarian border. The lake has an area of 315 km², 52% of which is covered by a reed belt representing the second largest contiguous reed population in Europe. The lake's drainage basin has an area of about 1,120 km² and is strongly impacted by intensive agricultural production and urban settlements, especially in the catchment of the main inflow River Wulka. On average, the lake's surface lies 115.45 m above the Adriatic Sea and the lake is no more than 1.8 m deep. Due to its chemical composition Lake Neusield can be characterized as soda lake with typical pH values of 9.0-9.3 in the open lake.

In this contribution, we present results from investigations on selected PAH (Benzo(a)pyrene, Fluoranthene) and PFAS (PFOS and PFOA) in the lake with specific focus on sediment associated transport and legacy processes. We apply a holistic approach, by combining emission modelling, targeted monitoring, adsorption and mobilization experiments as well as a lake’s mass balance. We describe the current state of contamination of River Wulka and the lake, we identify the main emission pathways into both river and lake and we shed light on the complex environmental behavior within the coupled system lake - reed belt.

While PFOA and PFOS emissions into the river are dominated by effluents from waste water treatment plants, atmospheric deposition on the lake surface adds a significant contribution to the contamination of the lake. On the contrary, agricultural erosion is the dominant pathway of the contamination of river and lake for Benzo(a)pyrene, Fluoranthene. Our results show that the reed belt at the entrance of River Wulka to the lake acts as a significant sink for these substances due to suspended solid sedimentation.

Persistent chemicals entering the lake may undergo different fates. They may concentrate in water, because in this peculiar lake evaporation exceeds precipitation. They may also be stored in the sediments of the reed belt, from where they might be later re-mobilized. The fate of Benzo(a)pyrene and Fluoranthene is clearly dominated by the latter processes. While these processes cannot be neglected for PFOS and PFOA as well, PFOA shows a strong enrichment in the lake water. The behavior of PFOS is even more complex. Though highly persistent, its removal from the lake water cannot be explained by suspended solid associated transport to and sedimentation in the reed belt. It is removed from the lake water through degradation or conversion to metabolites to a significant extent as well.

How to cite: Zessner, M., Zoboli, O., Reif, D., Kittlaus, S., Krampe, J., and Wolfram, G.: Origin and behavior of contamination of Lake Neusiedl with PAH and PFAS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8895, https://doi.org/10.5194/egusphere-egu2020-8895, 2020.

Vegetation-restored hillslope surfaces not only reduce erosion but they also remove sediment from upslope silt-laden inflow. To investigate the sediment trapping effect of grassland, this study conducted a series of crossed sediment trapping experiments that examined various factors, such as slope (5°–20°), sediment concentration (40–160 g L⁻¹), and unit flow rate (7.5–45.0 L min⁻¹ m⁻¹). The duration of each experiment was longer than required to reach the stable state of sediment trapping, so we measured and verified the individual sediment trapping capacity (R_m) by experiments. The results showed that gentler slopes generated higher instantaneous sediment trapping efficiency (ISTE) and greater R_m. As the sediment concentration of the silt-laden inflow increased, the impact of slope on R_m increased. Higher sediment concentration led to lower ISTE but greater R_m. Similar to the effect of sediment concentration, a larger unit flow rate led to lower ISTE and greater R_m. Thus, it is evident that interaction among these factors affects sediment trapping process. The experiments revealed the greatest sediment trapping effect of grass strips was concentrated mainly in the first 2-m width, and that 90% of sediment deposition occurred within half the time needed to reach the stable state. Slope and flow rate were found to have an effect on sediment trapping in each section of grass strips, whereas the effect of sediment concentration was concentrated primarily in the first 5-m width. Standard regression coefficients of a comprehensive regression analysis showed that the intensities of the influencing factors on R_m were as follows: slope (0.736) > grassland width (0.498) > unit flow rate (0.398) > sediment concentration (0.240). It was established that slope is the strongest influencing factor, and that sediment concentration and unit flow rate mainly affect R_m by changing the rate of sediment delivery. These results will help expand the theoretical basis regarding the effects of vegetation restoration on watersheds in soil erosion research.

How to cite: Luo, M., Pan, C., and Liu, C.: Experimental Study on the Impact of Slope and Silt-laden inflow Conditions on Vegetation Sediment Trapping Process, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5373, https://doi.org/10.5194/egusphere-egu2020-5373, 2020.

Due to the increasing global need for wood, forest management and especially tree harvesting have become increasingly challenging for the sustainability of forest ecosystems. Indeed, the natural dynamics of solid exports in rivers can be strongly disturbed by anthropogenic activities including forestry. The impact of forest management on erosion flux can be due to tree logging but also to forest roads, skid trails, stream crossings required for silvicultural operations.

The impact of forestry on solid exports in mountainous environment has been studied in a small granitic watershed (0.8 Km²) located in the Vosges massif. Between July and August 2014, the Strengbach catchment (Observatoire Hydro-Géochimique de l’Environnement) was concerned by clear-cutting on some plots located near the main stream. This small extended forestry operation (2.3% of the catchment) involved the logging of trees and the implementation of skid trail network including poorly designed stream crossings. The bedload flux was estimated since April 2009. The suspended sediment (SS) flux was evaluated on the basis of stream water samples collected every 16 hours and during high-flow events since December 2012.

Before the forestry operation, the mean bedload flux was 2.5 T/yr±8% for a mean outlet runoff of 730 mm/yr, although the SS flux was 7.7 T/yr±10% for an outlet runoff of 950 mm/yr.

The forestry operation occurring in 2014 has involved a significant and quasi-immediate impact on the SS concentration and flux. As an illustration, the mean SS concentration of the stream was 129 mg/L (outside high-flow periods) the fortnight after the forestry operation beginning, whereas it was only 6.2 mg/L just before. In addition, the forestry operation led to approximately 5 to 6 times larger SS flux than that expected for the July-August 2014 period. The impact on annual SS flux was significant during two hydrological years, with an increase of +100% and +50% for 2014 and 2015, respectively.  This relatively high disturbance is mainly due to the implementation of non-improved stream crossings and skid trails, responsible for the introduction of a huge amount of fine soil particles into the stream. At the opposite, no clear influence of the forestry operation on the bedload export could be observed in 2014 whereas it was 2 times higher than that expected the following year. This delay of the tree harvesting impact on coarse sediment export can be explained by the trapping of bedload upstream of the logs constituting stream crossings during the forestry operation. After the logs removal, the trapped sediments needed several flood events to reach outlet, explaining the delay. Overall, a post-logging recovery time of approximately 10 months can be assumed for the solid exports following the forestry operation.

How to cite: Cotel, S., Viville, D., and Pierret, M.-C.: Partial forest harvesting effects on erosion flux in a headwater catchment (Strengbach catchment, France), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15828, https://doi.org/10.5194/egusphere-egu2020-15828, 2020.

A common issue with large scale erosion modelling is that local processes are often unaccounted for, either because they haven’t been included in the model conceptually, or because they are undetected yet. On the other hand, significant deviations from such a general soil erosion model to the measurements can reveal those local processes. We compared the average yearly sediment amounts of a network of turbidity measurement stations in the catchment of the alpine River Inn to the results of the large scale erosion model RUSLE2015 (Panagos et. al.) for long term yearly erosion amounts and found a significant underestimation of sediment loads in three sub catchments. An important source of sediments in alpine rivers comes from glaciers, which explains the high loads in one of the stations, but two of the three high sediment load sub catchments are too low to have substantial valley glaciers. But another potential source of glacial sediment exists in the form of permafrost soils and in this case a specific permafrost form: rock glaciers. Rock glaciers in particular have been spotted in those two high sediment load catchments, but since they are hard to detect from remote sensing due to the surface being covered with rocks, the existence or the exact spatial extent is often unknown. But with rising temperatures in the Alps, the areas in which permafrost rock glaciers can exist decreases every year and the depth of the seasonal melting layer increases.

We propose the hypothesis that the high sediment loads in those sub catchments are caused by increasingly deeper melting of permafrost rock glaciers. This process releases fine materials which have been trapped frozen since the glacial period and are now being eroded and transported to the alpine streams. To get an estimation of potential erodible material from rock glacier melting in the respective sub catchments, we developed a model to simulate the heat diffusion from the air into the frozen ground, while accommodating for the change in specific thermal capacity. The model (developed in Python) takes air temperature time series data as input and can be configured for varying ground stratification setups with different thermal diffusivity values depending on the ground properties.

From the simulated melting depth of an average square meter of rock glacier we extrapolate the mass of melted material to the potential permafrost erosion material available in the River Inn sub catchments. We show that this source of sediments can be significant and needs to be factored in should an erosion model be used to calculate sediment input into the rivers. But, with the estimation of sediment load from permafrost origins narrowed down, improving a large-scale erosion model like the RUSLE2015 for this alpine mountain region by accounting for local processes like this one is possible. 

How to cite: Reid, L., Scherer, U., and Zehe, E.: Seasonal melting simulation of permafrost rock glaciers and their potential contribution to sediment loads in Alpine catchments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17504, https://doi.org/10.5194/egusphere-egu2020-17504, 2020.

The mechanism of sediment transport is mainly governed by surface water flow within the river basins. Excessive sediment transport plays an important role in reducing the carrying capacity of channel networks, storage capacity of reservoirs/dams. An important task for most of the hydrologists is to determine the reliable stream flow estimate which causes majority of the sediment transport within river basins/stream channels. The transport effectiveness of a stream flow event of a particular magnitude in carrying a sediment load is defined as the product of the effect of that event (i.e. sediment transport rate corresponding to the stream flow event) and the frequency with which the event occurs. This approach is famously known as magnitude frequency analysis (MFA). MFA provides a mathematical framework to determine various discharge indices such as effective discharge, fraction-load discharge and functional-equivalent discharge. These indices provide information on long-term transport of sediments through river networks and are linked to the exponent of sediment rating curve (which is correlated to the size of sediments, bed armouring and river morphology). Effective discharge index represents that single discharge which carries the most amounts of sediments, whereas fraction-load discharge and functional-equivalent discharge indices deal with mean sediment load which considers the contribution of entire probability distribution of discharge. There is a dearth of attempts to study these discharge indices for Indian catchments. In the present study, lognormal distribution and Gamma distribution -based MFA approaches are used to estimate discharge indices for Cauvery River basin, India. Effectiveness of the approaches was assessed based on their ability to predict discharge indices for 12 catchments in the river basin. Results indicate that Gamma distribution-based approach provides reliable estimates of fraction-load discharge and functional-equivalent discharge. The fraction-load discharges were computed for the catchments by considering various fractions of sediment loads ranging from 10% to 90%. Plots of cumulative sediment yield were prepared for both approaches and compared with empirical cumulative sediment yield. It was observed that the Gamma distribution-based MFA approach tends to provide close match with the empirical yield.

How to cite: Chavan, S. and Maheshwari, S.: Assessment of sediment transfer based on discharge indices for Cauvery River basin, India , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8108, https://doi.org/10.5194/egusphere-egu2020-8108, 2020.

Water quality modelling is very often constrained beforehand by the performance of discharge modelling. When the model is set up at global scale, this discharge performance usually greatly varies in space and can therefore be a limiting factor in many regions around the globe. Besides discharge performances, the quality of the observations themselves can also be highly heterogeneous in space and among datasets. Modeller then has to find a compromise between being restrictive on the quality of his dataset or having a good spatio-temporal representativeness of the various hydrological conditions at global scale. This often relies on subjective thresholds.

This work proposed a more objective calibration strategy that aims to consider both aspects explicitly: observation quality and model performance on discharge. It leads to the construction of two scores that are assigned to each water quality station quantifying their reliability for model calibration and evaluation. The average of those two scores is then used as a weight in the objective function to emphasise the training on the most reliable stations.

The strategy is implemented for sediment modelling using the WW-HYPE model (Arheimer et al., 2019) at global scale. The score on discharge simulation performance is based on the regionalisation of the Nash-Sutcliffe Efficiency that is spatially interpolated at every sediment monitoring stations using inverse Ghosh distance weighting (de Lavenne et al., 2016). The score on the observation quality is based on the location of the station with respect to the catchment outlet and on the amount of data. A multi-objective calibration is performed to optimise parameters on two global databases, one on long terms sediment loads (730 stations) and one on sediment concentrations time series (1440 stations). The sensitivity of the model to this calibration strategy is analysed according to model performances and model outputs, such as sediment loads at global scale, in order to discuss the importance of considering this heterogeneity of the reliability of monitoring stations.

References

Arheimer, B., Pimentel, R., Isberg, K., Crochemore, L., Andersson, J. C. M., Hasan, A., and Pineda, L. (2019), Global catchment modelling using World-Wide HYPE (WWH), open data and stepwise parameter estimation, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2019-111.

de Lavenne, A., J. O. Skøien, C. Cudennec, F. Curie, and F. Moatar (2016), Transferring measured discharge time series: Large-scale comparison of Top-kriging to geomorphology-based inverse modeling, Water Resour. Res., 52, 5555–5576, doi:10.1002/2016WR018716.

How to cite: de Lavenne, A., Bartosova, A., Strömqvist, J., and Arheimer, B.: Accounting for discharge simulation performances and observation quality for modelling sediment at global scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17066, https://doi.org/10.5194/egusphere-egu2020-17066, 2020.

Lake eutrophication is a key point in water environmental problems in the world. Spatiotemporal variations of nutrients and chlorophyll-a and eutrophication index in Poyang Lake, the largest freshwater lake in China, are analyzed in this paper basing on field observation data at 17 sampling points from 2011 to 2016. The results show that nutrient concentrations have obvious seasonality characteristics and present bigger values in the low water period than the high water period. The peak value of chlorophyll-a concentration appears in July and October respectively. As a whole, the eutrophication index in the low water period is higher than the high water period, and the maximum value is found in October which mainly due to the high chlorophyll-a concentration. Poyang Lake is at light eutrophication level from 2011 to 2012, and mesotrophic from 2013 to 2016. From the perspective of space, nutrient concentrations in the southern part of the lake is higher than the northern part in general, and chlorophyll-a and eutrophication index show the similar law. This paper makes a quantitative analysis for spatial and temporal variations of eutrophication which benefit the water management especially water pollution control in Poyang Lake

How to cite: huang, A.: Spatial and Temporal Variations of Eutrophication in Poyang Lake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21521, https://doi.org/10.5194/egusphere-egu2020-21521, 2020.

The Caspian Sea is the largest inland water body on the Earth and a unique object for analysis. It is of great importance for the socioeconomic development of bordering countries. Unique fish resources and oil and gas fields are projected to provide a significant source of food and economic prosperity to the Caspian region, as well as energy to many parts of the world. National and transnational oil and gas corporations are involved in the utilization of the commercially attractive Caspian natural resources. The Caspian Sea has been influenced by climate change and anthropogenic disturbance during recent decades, yet the scientific understanding of this water body remains poor. Climatic variability of water circulation in the Caspian Sea remains unclear. Traditionally, currents in the Caspian Sea have been investigated by numerical methods. Instrumental observations of the currents in the Caspian Sea are mostly carried out in the shelf zone. Available data cover very short periods and reflect variability only in synoptic and higher frequency of the sea dynamics. In this work, water velocity data based on SeaHorse equipment is under consideration. Three stations were in northern Caspian, area adjacent to Jayik (Ural) River delta. In both cases, the instruments were deployed in 2016 and 2017 at the point 46.782N, 51.384E, depth about 3 m. In this work, we will present the preliminary results of our study of the field observations we gathered in these points. We also present the analysis of the potential drivers for the spatial and temporal patterns of the measured currents velocity.

How to cite: Rezvov, V., Zavialov, P., and Krinitskiy, M.: Velocity fields in Northern Caspian near Jayik (Ural) river delta, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20431, https://doi.org/10.5194/egusphere-egu2020-20431, 2020.

In Norway, eutrophication is a major problem for freshwater quality, mainly due to excess phosphorus (P) inputs from agricultural areas. Hence, vegetated buffer zones along water bodies have been used for decades to reduce soil and phosphorus losses from agricultural land to waterbodies. In Norway, buffer zones with grass production are the most popular since these are eligible for subsidies.

The efficiency of grass-covered buffer zones has previously been studied in areas with relatively steep slopes and high risk of surface runoff and erosion. However, more field-based knowledge is needed on the retention efficiency of grassed buffer zones in areas with gentle slopes. In addition, other functions of these zones such as reduced bank erosion, biodiversity, and food production, need to be explored. The latter is important since only 3% of Norway’s area is under cultivation.

Herein, we present the results of three years of monitoring and rainfall simulation experiments carried out along the Hobølelva River in SE Norway. Our aim was to investigate different functions of buffer zones, including the retention of nutrients and particles and the protection against bank erosion in buffer zones with different vegetation cover (grass, shrubs and trees). Results to be presented include comparisons of 1) retention of nutrients and soil practices as observed during a series of rainfall simulation experiments in the field, 2) soil and hydrogeology characteristics (texture, porosity, hydraulic conductivity, infiltration capacity etc.), and 3) stream bank hydrogeological monitoring and stability estimation under different vegetation.

How to cite: Krzeminska, D., Buseth Blankenberg, A.-G., Nemes, A., Boe, F., and Skarbovik, E.: Retention of sediments and nutrients in buffer zones with different riparian vegetation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11401, https://doi.org/10.5194/egusphere-egu2020-11401, 2020.

Small-sized reservoirs have less capacity for the retention of sediment but are widely distributed in regulated basins. Therefore, small reservoirs collectively impart an important anthropogenic signature to the global sediment-flux, increasing the mean sediment retention when compared with estimates of mean sediment retention of large reservoirs.

A geochemical study of sediment-associated metal and phosphorus from a small-sized riverine reservoir, located in a mountainous rural region (Vila Real in NE Portugal), was conducted to evaluate the effectiveness of the reservoir as traps for these elements. The contents of metals and P were determined, as well as their spatial distribution pattern and their potential availability by using a four-step sequential extraction procedure for metals and the Chang and Jackson fractionation for P.

The metal contents in sediments were in the ranges of (µg/g): Cr (22-122); Cu (31-83); Ni (5-71); Pb (49-160); Zn (207-334). All the geochemical phases studied were important in the retention of the metals; within the most labile fractions, the reducible fraction was the most significant. The studied elements can be classed by potential relative mobility: Zn > Pb > Cu > Cr, Ni. The partition of elements contents through the geochemical phases and the balance between contents associated with the most mobile fractions and with the residual fraction suggest an important contribution from lithology to the total contents of Cr and Ni, and a significant contribution of anthropogenic activities to the contents of Cu, Pb, and Zn in the sediments from the reservoir. The analysis of the results on the geochemical partitioning of metals revealed to be important when the Sediment Quality Guidelines (SQGs) are considered. Phosphorus showed contents ranging between 1518-2454 µg/g; most samples revealed the predominance of the Fe-P fraction.

In general, the sediments of the reservoir showed maximum values of contents of metals above the Threshold Effect Level (TEL, µg/g: Cr-37.3; Cu-35.7; Ni-18; Pb-35; Zn-123). Chromium, Ni, Pb and Zn showed total contents exceeding the values of Probable Effect Level (PEL, µg/g: Cr-90; Cu-197; Ni-36; Pb-91.3; Zn-315). Chromium and Ni showed higher values than the reference ones, but these can be considered relatively unavailable since they are associated with the residual phase. The potentially available and/or total amounts of metals and P in sediments were relatively high, indicating that the quality of bottom sediments accumulated in this small-sized reservoir should be considered in management policies.

How to cite: Reis, A. and Roboredo, M.: Metal and phosphorus in bottom sediment of a small-sized reservoir in a rural mountainous catchment (NE Portugal): accumulation and geochemical mobility, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18179, https://doi.org/10.5194/egusphere-egu2020-18179, 2020.

The majority of rivers worldwide are contaminated by various trace metal elements (TME) from different anthropogenic origins. Even if anthropogenic impacts are sometimes very old (e.g. Roman era), many studies agree that these impacts have been much more significant since 150 years and the beginning of industrial revolution. Anthropogenic inputs in particulate form, TME being adsorbed on Suspended Particulate Matter (SPM), from various sources can be transported through the watershed depending on hydraulic conditions, which can be lead to storage of these SPM in depositional zones (e.g. reservoirs behind dams, flood plains, ponds). These stored sediments, defined as legacy sediments, are considered as testimonies of past anthropogenic activities and reflect the trajectory of the studied watershed.

In major European watersheds Pb levels generally exhibit a similar temporal trends (with high concentrations during the 1940-1970s). The temporal trends of Pb in the Eure River Watershed (Normandie, France), the main tributary of the Seine Estuary, was reconstructed from sediment cores sampled in ponds located downstream of the watershed. Pb concentrations variations along the sediment cores were not correlated with grain size and Total Organic Carbon (TOC) variations. Unlike the major European watersheds, the Eure River, showed stable levels until the 1990-2000s, when Pb concentrations have increased significantly and reached a maximum of 859 mg kg^-1. Despite a decrease in concentrations during the 2010s, Pb contents for recent sediments deposits showed concentrations significantly higher (> 200 mg kg^-1) than the local geochemical background, estimated at 10.6 mg kg^-1.

Lead concentrations on SPM collected monthly with a Time-Integrated Mass-flux Sediments Samplers (TIMS Sampler) in 2017-2018 also showed high concentrations, whose monthly variations were not correlated with the hydro-sedimentary behaviour of the river resulting of non-natural inputs. 

The current particular Pb fluxes estimated for the year 2017 would be the equivalent of 16 % of the total Pb inputs to the Seine Estuary. Theoretical past Pb fluxes have been estimated annually from the Pb concentrations in sediment cores. These estimations showed that during the 1990s, Pb fluxes represented more than 50 % of the total Pb inputs to the estuary and therefore the Eure River watershed was the main Pb contributor to the estuary.

Lead isotopes ratios confirmed the existence of an additional anthropogenic source, whose signature were more significant during the 1990-2000s. Three-isotope diagram (²⁰⁸Pb/²⁰⁶Pb vs ²⁰⁶Pb/²⁰⁷Pb) showed that the main source of Pb releases presented an industrial signature. The Pb additional releases have thus been linked with a cathode-ray tubes factory which started operating in 1956 and whose the production has been increased from 1990 to 2000s. The end of industrial activity in the late 2000s did not allow to a return to low concentrations, as evidenced by Pb concentrations in recent sediment deposits and SPM, and this likely related to Pb contaminated soils surroundings this factory and Pb contaminated sediments stored in the riverbanks and channel, which fed the river in Pb during erosion processes.

How to cite: Gardes, T., Debret, M., Copard, Y., Coynel, A., Fournier, M., Deloffre, J., Revillon, S., Develle, A.-L., Sabatier, P., Marcotte, S., and Portet-Koltalo, F.: Temporal trends reconstruction, current and past fluxes estimation and source identification of an industrial lead (Pb) contamination , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-531, https://doi.org/10.5194/egusphere-egu2020-531, 2020.

The Dnipro river is the main catchment in Ukraine. Within its territory the river flow is regulated and  represents a cascade of six reservoirs in direction from upper to down: Kyiv,  Kanevsky, Kremenchug, Kamensky, Dniprovsky, and Kakhovsky.  Reservoirs have a total water mirror area of 6950 km² and a total water volume of 44 km³. These figures make 95% and 91% of the total number of all large reservoirs in Ukraine, respectively. Their location in various natural and climatic zones, the difference in morphometric and hydrodynamic characteristics, hydrobiological, physicochemical, and sedimentation processes, as well as levels of anthropogenic load make them a unique object for studying intra-water processes, including processes of transformation, interphase exchange and accumulation of heavy metals in bottom sediments.

The study presents long-term data on the dynamics of the content and patterns of distribution of heavy metals (Fe, Mn, Cu, Zn, Pb, Ni, Co, Cd) in water, as well as in suspended solids, and bottom sediments of these reservoirs.

The influence of hydrological factors, physicochemical and hydrobiological processes on the nature of the transformation and interphase distribution of the heavy metals in the system “water – suspended substances – bottom sediments” has been shown. The contribution of mineral particles, Fe hydroxides and Mn oxides, and high molecular weight fractions of humic substances (humic and fulvic acids) on sorption processes and the removal of heavy metals from the solution phase were studied.

It has been found that the shift of the equilibrium of the calcium-carbonate system towards the formation of the CaCO₃ solid phase, which is associated with intensive hydrobiological processes in the Kremenchug and Kakhovsky reservoirs, leads to the additional removal of heavy metals from the solution due to deposition.

The study reveals the special aspects of the interphase distribution of heavy metals between the liquid and solid phases, due to the physicochemical conditions of the aquatic environment, as well as the morphometric characteristics of the reservoirs, flow rate, water temperature, duration of the ice cover during winter, and the content of organic substances.

The results of the distribution of heavy metals among various types of bottom sediments and their different particle size fractions are presented.

 It has been shown that a specific feature of the first in the cascade Kyiv Reservoir is the high content of dissolved humic substances, which play an important role in the migration of heavy metals.

The co-existing forms of metals in the solution phase are investigated with the thermodynamic modeling approach. This method was also used to evaluate the flow of metals from pore solutions of bottom sediments into the aquatic environment. Differences in the rate of molecular diffusion of metals from bottom sediments have been shown. They are caused by both the water chemistry and pore solutions, and the concentrations of metals and binding ligands.

The levels of anthropogenic load with heavy metals on the reservoir ecosystems have been evaluated over the past 30 years.

How to cite: Osadchyi, V., Osadcha, N., Nabyvanets, Y., Osypov, V., Kozhemiakin, D., and Kanivets, V.: Distribution of heavy metals in water and bottom sediments in reservoirs of the Dnipro cascade (Ukraine)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9558, https://doi.org/10.5194/egusphere-egu2020-9558, 2020.

To predict the transfer and fate of metal contaminants in river systems, a thorough understanding of the factors controlling metal concentrations is essential. This study examines the variability and covariability of dissolved and particulate metal concentrations in the Rhine River at the Lobith monitoring station in the Netherlands in the period 2009 -2017. The data analysis concentrated on copper and zinc as these metals were not affected by limits of detection. The total copper and zinc concentrations are significantly linearly related to the suspended sediment concentrations. The intercept of this relation represents the mean dissolved metal concentration and the gradient the mean particulate metal concentrations. The thus estimated mean dissolved and particulate concentrations of zinc and copper resemble mean measured concentrations. For both metals, the particulate concentrations are only weakly positively correlated to the dissolved concentrations. This correlation can be attributed to the fact that both the dissolved and the particulate concentrations of copper and zinc are negatively related to river discharge, where the decline of the particulate concentrations in response to increasing discharge is relatively larger than that of the dissolved concentrations. When the particulate metal concentrations are standardised for the diluting effect of discharge, the standardised particulate metal concentrations do not correlate significantly with the dissolved concentrations. This may indicate that the sediment solid/liquid partition coefficients (Kd-values) for the considered metals vary considerably in time, although this hypothesis requires further investigation.

How to cite: van der Perk, M.: The variability and covariability of dissolved and particulate metal concentrations in the Rhine River, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11580, https://doi.org/10.5194/egusphere-egu2020-11580, 2020.

Anthropogenic activities release many types of contaminants, such as trace metals, in the environment. For recent decades, numerous studies investigated their behavior, particularly in the dissolved phase. The transfer of contaminants adsorbed on the particulate phase received less attention although particulate matter also plays a key role in their propagation. One first difficulty is the variability of adsorption and releasing processes driven by both water physico-chemical conditions and contaminants properties. Secondly, there are different compartments in particulate phases, e.g. bed-load sediments and suspended particles, and the proportion of these two worlds is highly variable according to climate conditions (temperature, rainfall) and stream (hydro)geomorphological characteristics. In this context, our study investigates trace metal dynamics (Pb, Zn, Cu) in bed-load sediments and suspended particles from a small tributary of the Loire River, the Egoutier stream (Loiret, France). High spatial and temporal sampling frequency of the two fractions allowed to understand the patterns of trace metals transfer. Trends of trace metals contents observed in the particulate phase correspond to those in the dissolved one, except for Pb, the most insoluble compound. Contaminants concentrations and behaviors are driven both by trace metals order of solubility in bed-load sediments and suspended particles, and by external factors such as meteorological conditions, stream geochemistry and geomorphology. Besides, they are mostly adsorbed on iron and manganese oxides from suspended particles and on organic compounds from the bed-load sediments. Their temporal dynamics are controlled by seasons variabilities, notably rain amounts and humid periods, whereas their spatial distribution essentially reflects stream geomorphology, notably by the presence of a small pond creating a disconnection between the upstream and the downstream part of the watercourse and therefore two different patterns of transfert. Upstream, bed-load sediments contamination presents large fluctuations regulated by anthropogenic releases during dry periods and organic supplies during the humid ones, whereas homogeneous levels were observed downstream. In the suspended particles fraction, upstream higher contents are only correlated to humid periods, where more oxides are transported, while downstream transport is amplified by higher rain amounts.

How to cite: Simonneau, A., Ledieu, L., Cerdan, O., Hatton, M., Laperche, V., Le Forestier, L., and Laggoun, F.: River bed-load sediments and suspended particles: two different worlds for trace metals, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19850, https://doi.org/10.5194/egusphere-egu2020-19850, 2020.

We measured dissolved rare earth elements (REEs) in the water samples from Shihwa Lake (SL), which was assumed to be highly polluted, as well as in the downstream portion of the Han River (HR), which runs through, Seoul, Korea. Among the investigated REEs, only Gadolinium (Gd) was found to be significantly enhanced after REE concentrations were shale-normalized (SN). The calculated Gd anomaly (Gd/Gd* = 3×Gd_SN/(Sm_SN + 2×Tb_SN)) was about 1.5±0.1 (n=16) in SL and 1.6±0.3 in HR (n=26) water relative to other types of natural water such as groundwater, seawater, and river water in uncontaminated areas (Gd/Gd*~1.2, n>400). These significant Gd anomalies seem to be due to the inputs of anthropogenic Gd (Gd_anth), especially by the use of Gd-based contrast agents for magnetic resonance imaging (MRI) tests from a number of hospitals and medical institutes surrounding our study areas. The Gd_anth inventory was estimated to be 190±80 g and 680±360 kg Gd in SL and the HR (watersheds in our study area), respectively. The Gd_anth flux to the Yellow Sea from the HR is estimated to be 530±330 g Gd day^-1. Overall, these results suggest that quantitative evaluation of man-made REEs for associated human risk assessments are needed, because considerable amounts of REEs are now used by modern high-tech industries.

How to cite: Kim, I. and Kim, S. H.: Substantial gadolinium enrichments in lake and river near metrocities in Korea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12200, https://doi.org/10.5194/egusphere-egu2020-12200, 2020.

During the last two decades, the use of lithium (Li) has dramatically increased due to the proliferation of mobile electronic devices and the diversification of electric-powered vehicles. While Li can exert a toxic effect on living organisms and human beings, few studies have investigated the impact of anthropogenic inputs on Li content in the environment. Here we report Li concentrations and Li isotope compositions of river, waste and tap water, and industrial products from the metropolitan city of Seoul. Results show that the large increase in population density in Seoul is accompanied by a large enrichment in riverine Li content and that Li isotopes evidence a major release from Li-rich industrial products. Water treatment protocols are also shown to be inefficient for Li. Our study therefore highlights the need for a global Li survey and adequate solutions for minimizing their impact on ecosystems and city dwellers.

How to cite: Ryu, J.-S., Choi, H.-B., Shin, W.-J., and Vigier, N.: Anthropogenic lithium in river and tap water, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1368, https://doi.org/10.5194/egusphere-egu2020-1368, 2020.

The Pietra del Pertusillo fresh-water reservoir is located in the High Agri Valley (Basilicata region, Southern Italy). The present work represents a first comprehensive study about the mineralogy and the geochemistry of fluvial-lacustrine sediments and bedrock lithologies of this fresh-water reservoir catchment area. Lacustrine (15 samples), fluvial-lacustrine (14 samples) and local bedrock sediments (27 samples) have been sampled and mineralogical and geochemical analyses have been performed on the sampled sediments. The mineralogical assemblage is mainly composed of quartz and calcite and minor feldspars, muscovite, illite, chlorite, and interstratified clay minerals. The geochemistry reveals that major oxides are SiO₂, Fe₂O₃, Al₂O₃, and CaO. Attention has been paid to the presence of potentially toxic chemical elements (heavy metals) within the sampled sediments. The heavy metals are mainly enriched in the fine fraction of lacustrine sediments since they are mostly absorbed in the clay fraction (<2 µm).

Geochemistry of fluvial-lacustrine and bedrock sediments revealed that, in some cases, several heavy metal elements like Cr, Co, Ni, Zn, As, Ni and Pb exceed some regulatory limits concerning their distribution in lake sediments. It should be noted that, in Italian legislation, there are no regulations concerning limit concentrations of heavy metals in fluvial and fluvio-lacustrine sediments and therefore, for lacustrine sediments, values related to aquatic environments are taken into account. The considered regulatory are the Canadian ISQG (Interim Freshwater Sediments Quality Guidelines) and the Italian D.M. 367/03 (Regulation on the setting of quality standards in the aquatic environment for dangerous substances).

Furthermore, enrichment factors (EFs) for heavy metals were calculated, assuming Ti as an immobile element, both with respect to UCC (Upper Continental Crust) and local bedrock composition. Local bedrock composition was calculated based on the average composition and weighted on the areal extension of the outcropping bedrock lithologies. Enrichment factors showed that heavy metals like Pb, Zn, and Co, in relation both on UCC and local bedrock, showed values of EFs >2, which corresponds to a moderate enrichment. Other heavy metals, in particular Cu and As, showed EFs >5, which corresponds to a significant enrichment.

This work aims to get a clear picture of the causes which control and influence heavy metals concentration as well as their distribution within sampled sediments. Finally, it would be appropriate to establish worldwide quality standards on all pollutants in different natural environments in order to obtain a homogeneous reference for all countries.

References:

Giocoli, A. , Stabile, T. A.,  Adurno, I.,  Perrone, A., Gallipoli, M. R., Gueguen, E., Norelli, E., Piscitelli, S., 2015. Geological and geophysical characterization of the southeastern side of the High Agri Valley (southern Apennines, Italy), Nat. Hazards Earth Syst. Sci. 15, 315-323.

McLennan, S.M., Taylor, S.R., Hemming, S.R., 2006. Compostion differentiation and evolution of continental crust: constraints from sedimentary rocks and heat flow. In: Brown, M Rushmere T (eds) Evolution and differentiation of continental crust. Cambridge p 377.

Reimann, C., De Caritat, P., 2005. Distinguishing between natural and anthropogenic sources for elements in the environment: regional geochemical surveys versus enrichment factors,  Science of the Total  Environment  337(1-3), 91-107.

How to cite: Buccione, R., Fortunato, E., Paternoster, M., Rizzo, G., Sinisi, R., Summa, V., and Mongelli, G.: Geochemistry and mineralogy of lacustrine and fluvio-lacustrine sediments: The case of the Pietra del Pertusillo fresh-water reservoir (Basilicata region, Southern Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9588, https://doi.org/10.5194/egusphere-egu2020-9588, 2020.

The Kyiv Reservoir and the Desna river are the main sources of drinking water supply for Kyiv, the capital of Ukraine. The impact of surface air temperature on the change of the aquatic system chemistry mentioned above water objects was studied based on long-term regular observations (1995–2018).

The findings are based on the analysis of daily air and water temperature, water pH, oxygen and carbon dioxide concentrations, water color index, dissolved organic substances (COD_Mn), Fe, Mn, and phytoplankton abundance (without identifying their species composition).

The winter period. Despite different hydraulic conditions in the Kyiv Reservoir and in the Desna river, the lack of ice cover due to an increase in winter air temperatures (December-February) led to significant improvement of the water oxygen regime in recent years. This fact, as well as the subsequent chain of changes in the water chemistry, contributed to the cheaper drinking water supply.

The ratio of the oxygen content change to the duration of the ice cover, determined by air temperature, was obtained. This allowed us to reconstruct years with observed hypoxia phenomena since 1850. Changes in the water chemistry, triggered by oxygen deficit, were described.

The summer period. The increase in summer air temperature led to a decrease in oxygen concentrations. It had the effect of slowing down the process of N-NH₄⁺ nitrification. Because of the high content of natural organic matters in these water bodies, dangerous hypoxia phenomena were reported in summertime. Such conditions contributed to the restoration of manganese to a mobile Mn²⁺.

All these features created additional difficulties at water treatment plants for supplying drinking water to residents of Kyiv.

In shallow waters, occupying almost half of the Kyiv Reservoir, an increase in water temperature during the summer period led to the intensification of the hydrobiological processes and “water blooming.” This is compounded by the high income of nitrogen and phosphorus from the point and diffuse sources.

The observed decrease in the Dnieper water flow does not allow the active use of releases from the Kyiv Reservoir. The only way to minimize negative consequences in the future is to prevent pollution and eliminate shallow water zones.

This is complicated by the fact that a significant amount of nitrogen compounds enters the Kyiv Reservoir with the water of its main tributary, Pripyat, which basin is highly marshy.

Dredging in the shallow areas will require further research because of the bedding of radionuclides of Chernobyl in the bottom sediments.

How to cite: Osypov, V., Osadchyi, V., Osadcha, N., Ukhan, O., and Mostova, N.: The impact of climate changes on the aquatic system chemistry in the Kyiv Reservoir and the Desna river (Ukraine), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9677, https://doi.org/10.5194/egusphere-egu2020-9677, 2020.

Despite being a basic human right, limited access to clean water is still a major concern in developing countries lacking adequate sanitary infrastructure. A significant proportion of the global population directly depends on surface water resources which are often contaminated with fecal matter. The presence of fecal contamination in waterbodies is often detected using fecal indicator bacteria like Escherichia coli. According to 2016 UNEP report, about one third to one half of Asian rivers are estimated to be severely polluted, with monthly in-stream concentrations of fecal coliform bacteria exceeding 1000 cfu.100 mL^-1. Although various studies on small tropical catchments have improved our understanding of E. coli behavior in a tropical context, little information exists on the underlying mechanisms at large watershed scales during dry and wet seasons. Our study focuses on Mekong River and its main tributaries in Laos, an area that has witnessed rapid changes in land use and deterioration of water quality over the last three decades. We aim (1) to examine the seasonality of E. coli concentrations in stream waters, and (2) to identify the main factors controlling E. coli in-stream concentration, such as land use, hydrometeorology, and suspended sediment concentrations, through field monitoring of a range of catchments across Laos. To this end, we used two different sets of field data monitoring at multiple temporal and spatial scales. First, a total of 18 catchment outlets located between 15°N and 20°N, were sampled twice in 2016, during both dry and rainy seasons, covering a broad range of catchment sizes (240 - 25946 km²), as well as geographical and topographical features. Second, three northern rivers, Nam Ou, Nam Suang, and Mekong River, have been sampled every 10 days since July 2017. Our results shed the light on contamination over the year in all three catchments (100-100000 MPN.100 mL^-1), with higher E. coli concentrations during the rainy season, associated with higher water levels, and higher concentrations of total suspended sediment (TSS) in streams. Partial Least Square (PLS) regression showed a strong positive correlation between E. coli concentrations and the percentage of unstocked forests area. Unstocked forests are exposed to erosion processes resulting in high concentrations of suspended sediment and particle-attached E. coli in-stream concentrations. In contrast, catchments with larger protected and naturally regenerated forest and grassland areas were associated with lower E. coli and TSS concentrations. These analyses highlight the importance of adequate land management in tropical context to reduce soil loss and water quality degradation. Furthermore, our results reveal the importance of improving our understanding of fate and transport of fecal contamination through field monitoring at various spatial and temporal scales, in order to assess the risk to public health, and the impact on ecosystem services, such as contaminant retention.

How to cite: Nakhle, P., Ribolzi, O., Boithias, L., Rattanavong, S., Auda, Y., Sayavong, S., Zimmermann, R., Soulileuth, B., Pando-Bahuon, A., Thammahacksa, C., Rochelle-Newall, E. J., Santini, W., Martinez, J.-M., Gratiot, N., and Pierret, A.: Effects of seasonal hydrology and land use on in-stream Escherichia coli concentration in the lower Mekong basin, Laos, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1362, https://doi.org/10.5194/egusphere-egu2020-1362, 2020.

The River Dee is one of the major river systems in Scotland, renowned for its economically important Atlantic salmon (Salmo salar) population. The Tarland Burn (70 km²), an intensively managed catchment, is a significant source of nutrients and suspended sediments (SS) to the River Dee, causing degradation of its water quality. To trace the SS sources in the Tarland Burn catchment, we used compound-specific isotope analysis (CSIA) fingerprinting technique. The CSIA fingerprinting technique applied in this study involved (i) carbon isotope ratio (δ¹³C) measurements of plant derived long-chain fatty acids (LCFAs) extracted from source soils and from river SS as a mixture signal as input tracer values, and (ii) computation of source proportions in the mixture using an end member mixing model ‘MixSIAR’ which is based on the Bayesian approach.

Source soils were sampled from the land-use types observed in a headwater catchment (10 km²) i.e. arable, temporary grassland under arable rotation, permanent grassland, coniferous forest, heather moorland and riparian zone. SS samples were collected from the headwaters, second order streams, and also from the outlet of the Tarland Burn catchment, representing a nested sampling approach. A comparison of the two common suspended sediment collection techniques to understand the role of sampling technique and associated particle sizes resulted in no substantial difference in the tracer values. SS were sampled once every two months over a period of 14 months between May 2017 and June 2018. δ¹³C values of LCFAs (even homologues between C_22:0 - C_30:0) of the SS (mixture) were within the range of source soils corresponding tracer values, confirming their conservative behaviour during transport.

Quantification of source proportions using mixing model suggested that headwater streams SS originated predominantly from permanent grasslands. They are largely located on steep topography, leading to higher hydrological connectivity and possible increased pressure from livestock. Although plantation forestry and heather moorland are prominent land-uses in the catchment, their contribution as SS sources is marginal. More intensive arable land use in the lowland areas of Tarland catchment was reflected by their high contribution to SS at the downstream locations. More intensive rainfall events during winter likely led to higher sediment fluxes from the normally less connected permanent grasslands at the catchment outlets during high flow.

Our attempt of gathering source soil information from a headwater region of a catchment and upscaling this information to model the source proportions in downstream mixtures integrating the whole catchment was successful, however uncertainties increased for the downstream results

How to cite: Hirave, P., Glendell, M., Birkholz, A., and Alewell, C.: Spatiotemporal variability in sources of suspended sediments from a Scottish river using compound-specific isotope analysis (CSIA): a nested catchment approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9806, https://doi.org/10.5194/egusphere-egu2020-9806, 2020.

Rivers that are hydrologically connected to an agro-ecosystem act as a source or sink of pollutants transported by surface runoff and subsurface water. The Sediment-Water Interface (SWI) of rivers is a critical boundary for river dynamics where hydrological and biogeochemical processes tightly control pesticide dissipation. Transport processes govern pesticide transit time and distribution across the SWI depending on the water flow and hyporheic exchanges. Simultaneously, reactive processes such as sorption and biodegradation are responsible for retardation or actual degradation of pesticides within the porous sediment. However, knowledge on the interplay of these processes at the SWI remain sparse mostly because a physically-based generalized framework to model transport and reactivity at fluid-porous interfaces is still lacking. Here, we combine model development and laboratory experiments to investigate the effects of representative hydrological conditions on pesticide transport at the SWI.

An innovative discrete flow-transport model accounting for sorption was developed to consider the pure fluid layer (via Navier-Stokes model) and the porous medium (via Darcy-Brinkmann model). Advanced and appropriate numerical techniques are implemented to solve the coupled models (Navier-Stokes and Darcy-Brinkmann) without any interface conditions or empirical transfer functions. Conservative (NaCl) and non-conservative (Foron Blue 291 – sorptive) tracer experiments were performed within a 15 cm long and 10 cm deep recirculated river model (3 < equivalent length < 30 km) to characterize pesticide transport at the SWI. Configurations with the contaminant in the sediment (sediment as contaminant source) or contaminations from the overlying water (sediment as a sink) were tested. Simulated tracer concentrations fitted well to measured concentrations over a range of laminar flows representative of low Strahler order rivers (Re < 700, bulk velocities 10 <  U < 100 mm.s^-1). In all flow conditions, the first few mm of sediment constituted the most dynamic layer, which was controlled by advective processes. In contrast, the tracer in deeper sediment layers undergone diffusive transport with lower exchange rates. Sorption was also observed to significantly increase residence time within the sediment and to slow down the progression of the tracer plume into the sediment. The times required to reach the bottom of the river model rose up to 12 times as compared with the non-sorptive tracer, indicating limited hyporheic exchanges with increasing sorption.

To account for biodegradation at the SWI, the model is further extended to include degradation kinetics and stable isotope fractionation of organic micropollutants. Changes of stable isotope ratios of the remaining, non-degraded pool of pollutants over time or across the sediment layer is used as a proxy of in situ biodegradation. Biodegradation is interpreted as a function of oxygen zonation within the sediment. This model is eventually tested against tracer experiments with caffeine, which is used here as a fast degrading anthropogenic micropollutant. Patterns of micropollutant dissipation at the SWI arising from these developments will be further extrapolated at river reaches within an agricultural catchment (Souffel catchment, France). Altogether, this study will help understanding how rivers influence pesticide transport, storage and degradation at the catchment scale.

How to cite: Drouin, G., Fahs, M., Droz, B., Imfeld, G., and Payraudeau, S.: Reactive transport modelling to assess pesticide dissipation at the sediment-water interface, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13884, https://doi.org/10.5194/egusphere-egu2020-13884, 2020.