Hydrograph separation using biogeochemical data is a commonly used method for the vertical decomposition of flow into surface, subsurface and groundwater contributions. However, its application to the spatial decomposition of flow remains limited, despite its potential to identify contributions linked to geological, pedological, and land use characteristics, as well as anthropogenic contaminant sources. In this study, a Bayesian mixing model was applied to the Ratier peri-urban sub-catchment of the OTHU Yzeron observatory. Eight runoff-generating sources were identified and sampled, including different land uses (e.g. forest, grassland, agricultural areas), a colluvium aquifer, and urban point discharges (e.g. sewer system, urban and road surface runoff). A wide range of biogeochemical parameters were analysed including classical (i.e., major chemical compounds, dissolved metals) and innovative tracers (i.e., characteristics of dissolved organic matter, microbial indicators). Streamwater samples collected under contrasting hydro-meteorological conditions revealed distinct source signatures and highly variable contributions, with wastewater dominating under dry weather and rapid surface runoff during summer storms. Using these results, we improved a previously designed perceptual hydrological model of the Ratier and Mercier catchments, at the hillslope scale, which highlighted the potential of spatial tracer-based decomposition in addition to classical vertical hydrological separation. More broadly, this study demonstrates the potential of such mixing model, using classical but also more innovative tracers, to provide insights for validating distributed hydrological models and to anticipate the influence of land use, urbanisation, and climate changes on runoff generation.

Since 2018, in situ caging of Gammarus fossarum has been used by French water agencies at more than 400 river sites. This active biomonitoring tool helps meet the requirements of the Water Framework Directive by analysing priority substances in biota. It is also used to assess the bioavailable chemical contamination level in waterbodies for a wider range of substances. However, the current list of monitored substances, which is partly determined by the analytical capabilities of the service provider's laboratory, needs to be refined to optimise biomonitoring and better reflect environmental contamination. This study proposes a scientific approach for defining a list of "substances of interest" to be monitored in caged gammarids. A total of 1751 candidate substances were classified using a tiered approach based on a decision tree. This approach categorised substances according to their quantification frequency (QF) in biota (Gammarus, other invertebrates and fish) and sediment. The QF data originates from the monitoring programme of the French water agencies using caged gammarids, as well as from an international bibliographic search focusing on contaminants of emerging concern in the aquatic environment (132 studies were used). This approach yielded a list of 235 substances of interest, for which the QF in biota is at least 20

This communication aims at exposing the steps taken by a research lab – in this case INRAE RiverLy – to reduce its carbon footprint. INRAE RiverLy is an interdisciplinary research unit for the functioning of hydrosystems. The environmental transition process originates in 2020 with the creation of the RiverLy Downstream group launched to address the downstream impacts of research practices (see Vidal et al., 2023). The first step taken by the RiverLy Downstream group relates to monitoring the laboratory's carbon footprint and identifying the main emission sources. Yearly carbon accountings carried out since 2019 using the GES1.5 tool (https://apps.labos1point5.org/ges-1point5) show that purchases (equipment, consumables, etc.) account for the majority (>50%) of the lab footprint. They also highlight the impact of changes in individual practices related to business travel, with -63% of travel-related emissions in 2022 compared to 2019. A second step focused on raising awareness through a Climate Day and testing the willingness to change within our research unit through an opinion poll. Results led to writing down a lab charter which was unanimously adopted by the lab council in October 2023. This charter sets a collective 10%/year cut-down trajectory with respect to the 2022 carbon accounting, while affirming the determination to preserve the positive impact of our research on society. A third step now being undertaken by the RiverLy Downstream team is to come up with concrete collective actions to effectively reduce the lab footprint. Participatory workshops are being organised in January and February 2024 to specify agreed actions for the various research activities: long-distance travelling, purchasing scientific and IT equipment, setting up a research project, doing lab and field experiments, performing biological and chemical analyses, performing scientific computations, and organising seminars and conferences. Consolidated and agreed propositions will then be submitted to the lab council for formal acceptation and implementation. The whole process benefits from rich interactions with the INRAE national to regional strategy for reducing its environmental footprint (https://www.inrae.fr/en/corporate-social-responsibility-inrae), and with the French national initiative Labos1point5 which set up a national network of labs in transition (https://apps.labos1point5.org/transition-1point5). Vidal, J.-P., Berni, C., Coquery, M., Devers, A., Gauthier, L., Lauvernet, C., Masson, M., Mimeau, L., and Turlan, M. and the RiverLy Downstream team: How to collectively engage in reducing the carbon footprint of a research lab?, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3462, https://doi.org/10.5194/egusphere-egu23-3462, 2023.

This study investigates surface water contamination of Ben-Kazza River in Morocco, fed by effluents from an adjacent lagoon-based wastewater treatment plant (WWTP) and seasonally by industrial effluents, and which occasionally serves to irrigate agricultural fields. This study has two purpose: i) to track the main sources of contamination through the evolution of dissolved organic matter (DOM) characteristics along the watercourse, and ii) to characterize the WWTP influents and effluents with a focus on the efficiency of the lagoon treatment. We characterized a total of 495 water samples across the watercourse and from the inlet and outlet of the WWTP, using UV-visible absorption and excitation-emission fluorescence coupled with chemometric analyses. Absorption indicators and fluorescence indices were calculated and compared across sampling points. Results highlight spatial shifts together with temporal changes in DOM. PARAFAC identified components that varied between protein-like, humic-like and anthropogenic-like fluorophores along the river, permitted to trace the anthropogenic components and their sources. The lagoon treatment appeared to better remove fresh organic material than humic material: fluorescence intensity decreased by 68 % for peak T1 and by 22 % for peak C. Maximum fluorescence intensities (Fmax) decreased across all PARAFAC components, leading to more than 55 % reduction of Sigma Fmax.

Socio-ecological research enlists inter- and transdisciplinarity to address complex environmental issues. Yet the "socio-ecological system" concept can be interpreted in many different ways. A characterization of the diverse practices in socio-ecological research could facilitate dialogue between researchers about the possible conceptual and ethical approaches. In this study, we investigated if a detailed analysis of scientific articles would reveal the nature and course of a socio-ecological research network, and the research angle of its members. The example we used was the Rhône River Long-Term Socio-Ecological Research (LTSER) platform in France. We combined a multivariate analysis of a reading grid of publications by Rhône River LTSER researchers and a textual analysis of the scientific narratives. The publications were from a 10-year period and corresponded to those used in a recent international comparative analysis of LTSER platforms. The analysis revealed that the research was dominated by a biophysical approach, with a progressive increase in social aspects. The emergence of a transdisciplinary approach, co-constructed with operational partners, was also shown. The research conducted by the Rhône River LTSER was grounded in the context of managing a river with strong anthropic influences and interests, and the scientific approach aimed to provide knowledge for guiding decisions. Little referencfte was made in the publications to socio-ecological conceptual frameworks. Beyond the example of this LTSER platform, we identified indicators for describing the degree of inter- and transdisciplinarity and the different perceptions of socio-ecological systems. The narrative analysis revealed the angle of the research approach; this method could be used in future studies for a comparison of the diverse approaches of multiple research groups.

Passive samplers accumulate organic contaminants at rates that depend on in-field exposure conditions such as freshwater flow velocity, water temperature and water quality. Time-weighted average concentrations can be determined by using a correction process such as the performance reference compound (PRC) method. This study presented a new approach to predict the accumulation behavior of pesticides in polydimethylsiloxane-coated stir bars under different exposure conditions and assign a specific PRC to each pesticide for quantitative purposes. We used an experimental design with eight simultaneous accumulation kinetics of 13 pesticides and elimination kinetics of three PRC candidates run in a flow-through system to determine the effects of flow velocity, water temperature and dissolved organic matter on the kinetic constants. We identified the parameters that had a significant effect on the accumulation of each pesticide and assigned a PRC candidate to each pesticide. We then used a discriminant function analysis to find the parameters that had a significant effect on accumulation of the 13 pesticides via their physical-chemical properties and to predict through a stochastic approach the parameters for seven other pesticides. This approach provides a better framework for identifying a PRC than conventional methods to determine unbiased concentrations in future monitoring efforts.

This communication aims at testifying how individual commitments of researchers can be combined to engage a whole research lab – in this case INRAE RiverLy – in a carbon transition path. INRAE RiverLy is an interdsciplinary research unit for the management and restoration of river systems and their catchments. In 2020, a group of RiverLy people started questioning the downstream impacts of their research practices. An official internal action called RiverLy Downstream was thus launched to address these issues. A first lab-scale carbon accounting for the year 2019 was performed thanks to the GES 1point5 tool (https://apps.labos1point5.org/ges-1point5). It showed a large contribution of air travel to the total carbon footprint. Further carbon accounting for 2020 and 2021 however highlighted the even larger impact of purchases (equipment, consumables, etc.) thanks to newly implemented features in GES 1point5. An open “climate day” was organized in the lab in September 2022 for (1) raising awareness through a general-public-oriented tool, (2) provide live feedback from other research labs engaged in a carbon transition, and (3) collectively identify propositions of local actions on different themes: purchases, travels, premises, computing, food, and research activities. These propositions fed a lab-wide survey that will help defining a few carbon footprint reduction scenarios based on their social acceptability. These scenarios will then be submitted to the lab board for implementation. The whole process benefited from rich interactions with INRAE national to regional strategy for reducing its environmental footprint (https://www.inrae.fr/en/corporate-social-responsibility-inrae), and with the French national initiative Labos1point5 (https://labos1point5.org/).

Water pathways and water contamination in mixed land-use catchments are complex to understand. Runoff-generating sources can be numerous and water pathways modified by anthropogenic elements. Monitoring surveys considering geochemical and microbial parameters, are often carried out on such catchment, but are often simple in terms of studied parameters. Nonetheless, they can be helpful to identify the specific signatures of the main runoff-generating sources and estimate their contribution to total runoff at the outlet of mixed land-use catchments. Based on a monthly biogeochemical monitoring program conducted between 2017 and 2019 in the Ratier catchment (19.8 km2) near Lyon (France), a step-by-step approach was developed to: (1) identify the main runoff-generating sources using a perceptual model of the Ratier catchment, (2) identify the respective biogeochemical signatures of each source using this biogeochemical dataset and hydro-meteorological indicators and (3) estimate their contribution to the stream total runoff using an End-Member Mixing Analysis method. We identified three main runoff-generating sources outside of rainy periods: a colluvium aquifer, a fractured gneiss aquifer and a saprolite layer. The monitored geochemical datasets were found divided into three groups matching these sources. Contributions of these sources were estimated based on representative tracer concentrations. Microbial parameters showed a homogeneous agricultural and anthropogenic contamination among the catchment surface water, but also deeper into the fractured gneiss groundwater. This approach showed the potential of using simple monitoring datasets to identify runoff-generating sources and estimate their contribution to total runoff. A biogeochemical dataset was used to identify three main runoff-generating sources matching the geological diversity of a peri-urban catchment. Parameters Li, Zn and Al were chosen as representative tracers of these sources to estimate their contribution to total runoff. The Human-specific HF183 and ruminant-specific rum-2-bac bacterial markers were used as tracers of respective anthropogenic and agricultural contribution to streamwater.image

Modern and past mercury (Hg) fluxes in the oceanic water column and abyssal sediments are poorly quantified. Here, we investigated the particulate transfer of Hg in the water column of the ultra-oligotrophic Ionian Sea (Eastern Mediterranean) with sediment traps during a one-year period, and its accumulation in the deep central abyssal plain using sediment cores comprising the last 10 ka. The Hg concentrations in the particles collected in the sediment traps varied from 112 to 401 ng g(-1) and enabled quantifying annual Hg fluxes of 2.0, 2.5, and 2.5 mu g m(- 2) a(-1), for traps deployed at 250, 1440, and 2820 m deep, respectively. Hg collected in the upper trap originates from atmospheric deposition, including Saharan dust, which is scavenged by the biological pump. Higher Hg fluxes found at mid-depth and near-bottom than in the upper water layer are attributed to lateral advection under the mixed layer of Hg-rich resuspended sediments from the Adriatic continental margin. In the abyssal sediment, Hg concentrations range from 15 to 134 ng g(-1) with the highest levels in the Sapropel S1. Methylmercury concentrations varied from 0.06 to 0.24 ng g(-1) following the distribution of total Hg, with evidence of its specific accumulation at the oxidized front of the sapropel. We estimated that <1.8% of the total Hg in the sedimentary column was diagenetically reallocated. The reconstruction of historical Hg accumulation rates (HgAR) during the Holocene shows low pre-anthropogenic values (similar to 0.3 mu g m(2)a(- 1) before 4 ka BP), increasing up to similar to 0.9 mu g m(2)a(- 1) during the late Iron Age and the Roman period (1.5-2.5 ka BP), and up to 2.9 mu g m(2)a(- 1) during the Industrial Era. During the Sapropel S1 period (similar to 6-10 ka BP), HgARs rose to 6.4 mu g m(- 2) a(-1) likely due to the intensity of the Hg removal by the biological pump, the organic matter preservation, along with high inputs of Hg-rich terrigenous matter and a possible restricted recycling in the atmosphere. Hg accumulation in the Ionian Sea deep sediment is found similar to 3-fold lower than those in the western Mediterranean abyssal plain.

Mass spectrometry in multiple reaction monitoring (MRM) mode is a powerful technique that can provide highly selective, multiplexed, and reproducible quantification of peptides derived from proteins. Ideal for the application of molecular bio-markers in biomonitoring surveys, MRM tools have been recently developed to quantify sets of pre-selected biomarkers in freshwater sentinel species. Still limited to the validation and application phase of biomarkers, dynamic MRM (dMRM) acquisition mode has increased the multiplexing capacity of mass spectrometers, expanding opportunities to explore pro-teome modulations in sentinel species. This study evaluated the feasibility to propose dMRM tools for investigating senti-nel species proteomes at the organ level and demonstrated its potential for screening contaminant effects and discovering new protein biomarkers. As a proof of concept, a dMRM assay was developed to comprehensively capture the functional proteome of the caeca of Gammarus fossarum, a freshwater crustacean, commonly used as a sentinel species in environmen-tal biomonitoring. The assay was then used to assess the effects of sub-lethal concentrations of cadmium, silver, and zinc on gammarid caeca. Results showed dose-response and specific metal effects on caecal proteomes, with a slight effect of zinc compared to the two non-essential metals. Functional analyses indicated that cadmium affected proteins involved in car-bohydrate metabolism, digestive and immune processes, while silver affected proteins related to oxidative stress response, chaperonin complexes and fatty acid metabolism. Based on these metal-specific signatures, several proteins modulated in a dose-dependent manner were proposed as candidate biomarkers for tracking the level of these metals in freshwater eco-systems. Overall, this study highlights the potential of dMRM to decipher the specific modulations of proteome expression induced by contaminant exposure and pinpoints specific response signatures, offering new perspectives for the de novo identification and development of biomarkers in sentinel species.

For more than half a century, chemical contamination has progressively spread to all the large river basins. Large river outlets integrate multiple anthropogenic pressures in watersheds, making them the largest source of sediment‐bound contaminants to continental shelf areas. However, comparing particulate micropollutant contaminations between the large river basins is a challenging task, especially due to the scarcity of long‐term river monitoring programs. Here we address this issue, with a focus on legacy particulate micropollutants (polychlorobiphenyls [PCBi], polycyclic aromatic hydrocarbons [PAHs] and trace metal elements [TME]) yields. For this purpose, we employed a bottom‐up multiscale approach to chemical contamination in river basins that takes micropollutant yields measured in the Rhône River sub‐basins (France) as a benchmark of other large river basins. Data on the Rhône River basin came from a unique 10‐year‐long monitoring program within the Rhône Sediment Observatory (OSR), and were compared to data gathered on 18 major worldwide river outlets. The Rhône River basin is far cleaner now than a few decades ago, likely due to environmental regulations. At a wider spatial scale, our results depict an overall contamination gradient splitting the most heavily contaminated river basins, located in developing and industrializing low‐to‐middle‐income countries, from the least contaminated rivers located in developed high‐income countries. We argue that chemical contamination levels of large river basins depend on their stage of economic development.

The origin and transport of water in peri-urban catchments is complex to model as they are affected by multiple anthropogenic modifications of water pathways (surface imperviousness, sewer overflow releases…), especially in a context of fast growing urbanization. The hydrological dynamics are also impacted by natural and agricultural land use patterns. Perceptual models aim at reproducing our understanding of a catchment behaviour and can be useful to illustrate the impact of such spatial contrast and human-induced modifications on a catchment hydrological dynamics. Conservative geochemical and microbiological tracers can be linked to the hydrological processes and water pathways to enhance this understanding and to build-up the hydrological perceptual model of a catchment. From 2017 to 2019, a monthly monitoring of geochemical and microbiological tracers was conducted at the Ratier catchment (19 km²) near Lyon (France). Surface waters were collected and analysed for major chemical parameters (cations, anions, dissolved organic carbon and conductivity), dissolved metals, stable isotopes (2H et 18O), and microbial parameters (total bacterial counts, microbial source tracking DNA datasets, species – specific DNA trackings). Using these datasets, a step-by-step statistical approach was undertaken, and used to build-up the perceptual hydrological model. The main steps were: (1) group correlated biochemical parameters to reduce redundancy in the dataset, (2) compute the main indicators illustrating the hydro-climatologic dynamics during the sampling campaigns (e.g. antecedent index precipitation, average daily flow) based on the hypothesis of a two-component catchment (groundwater and subsurface flow), and (3) perform a principal component analysis to link the biogeochemical dataset to the computed hydro-climatologic indicators and the runoff processes. Results revealed a differentiation of the datasets in two groups matching groundwaters and subsurface waters. Groundwaters showed two geochemical profiles linked to the two main geological formations of the catchment. Subsurface waters showed more variable biogeochemical patterns highly influenced by land use and soil properties. This step-by-step statistical approach led to a better understanding of the dynamics of the water pathways and these insights were then used to build-up the hydrological perceptual model of the catchment. As a next step, such a model should help in the evaluation and improvement of a distributed hydrological model.

Abstract. The Rhône River is amongst the main rivers of Western Europe and the biggest by freshwater discharge and sediment delivery to the Mediterranean Sea. Its catchment is characterized by distinct hydrological regimes that may produce annual sediment deliveries ranging from 1.4 to 18.0 Mt y−1. Furthermore, the course of the Rhône River meets numerous dams, hydro- and nuclear power plants, and agricultural, urban or industrial areas. Thus, suspended particulate matters (SPM) have been involved in the fate of hydrophobic contaminants such as polychlorobiphenyls (PCB), mercury (Hg) and other trace metal elements (TME), and radionuclides for decades. To investigate the concentrations and the fluxes of SPM and associated contaminants, as well as their sources, a monitoring network of 15 stations (three on the Rhône River and 12 on tributaries, from Lake Geneva to the Mediterranean Sea) has been set up in the past decade within the Rhône Sediment Observatory (OSR). A main purpose of this observatory is to assess the long term trend of the main contaminant concentrations and fluxes, and to understand their behavior during extreme events such as floods or dam flushing operations. The dataset presented in this paper contains the concentrations and fluxes of SPM as well as the concentrations and fluxes of several particle bound contaminants of concern (PCB, TME, radionuclides), the particle size distribution and the particulate organic carbon of SPM. Sediment traps or continuous flow centrifuges were used to collect sufficient amount of SPM in order to conduct the measurements. This observatory is on-going since 2011 and the database is regularly updated. All the data are made publicly available in French and English through the BDOH/OSR database at https://doi.org/10.15454/RJCQZ7 (Lepage et al., 2021).