Zone Atelier Moselle

Abstract In many ecosystems, detritus is the dominant source of energy and the driver of ecosystem functioning. In particular, in forested headwater streams, allochthonous detritus (e.g. leaf litter, dead wood) constitute the main energy source for detritivores and living primary producers contribute marginally to ecosystem metabolism and energy flows. We hypothesised that a low consumption of benthic diatoms, a high‐quality resource, could be of major importance for the growth of detritivores. In particular, these resources might represent an essential source of polyunsaturated fatty acids ( PUFA s). In a microcosm experiment, three food resources were manipulated: alder ( Alnus glutinosa : Betulaceae) leaf litter, fungal mycelium and a common benthic diatom. They were offered to juveniles of Gammarus fossarum (Crustacea: Amphipoda) as food resources, either alone or in combination, with each resource type being enclosed in agarose pellets. Juveniles were fed for 5 weeks in controlled conditions. Survival, feeding and growth rates were monitored. The fatty acids content of food resources and gammarids were also quantified. Our results showed that detritus alone permits survival, but not the significant growth of detritivores. The presence of diatoms in food resources was necessary to ensure a significantly positive mass growth of detritivores over the 5‐week experiment. More importantly, detritivores that did not receive algae in their food were generally unable to maintain their PUFA levels when compared to juveniles collected in the field. Gut‐content analysis of field‐collected G. fossarum showed that low amounts of benthic algae were always visible, indicating that most individuals fed at least for a small part on benthic algae. These minor, but high quality, food sources might therefore be essential for ensuring the growth and survival of detritivores. Our results clearly highlight the need to consider the functional importance of such minor food sources.

Abstract. Hydromorphodynamic models are powerful tools for predicting the potential mobilization and transport of sediment in river ecosystems. Recent studies have shown that they are able to predict suspended sediment matter concentration in small river systems satisfactorily. However, hydro-sedimentary modelling exercises often neglect suspended sediment properties (e.g. sediment densities and grain-size distribution), which are known to directly control sediment dynamics in the water column during flood events. The main objective of this study is to assess whether a better representation of such properties leads to an improved performance in the model. The modelling approach utilizes a fully coupled hydromorphodynamic model based on TELEMAC-3D (v7p1) and an enhanced version of the sediment transport module SISYPHE (based on v7p1), which allows for a refined sediment representation (i.e. 10-class sediment mixtures instead of 2-class mixtures and distributed sediment density instead of uniform). The proposed developments of the SISYPHE model enable us to evaluate and discuss the added value of sediment representation refinement for improving sediment transport and riverbed evolution predictions. To this end, we used several model set-ups to evaluate the influence of sediment grain-size distribution, sediment density, and suspended sediment concentration at the upstream boundary on model predictions. As a test case, we simulated a flood event in a small-scale river, the Orne river in north-eastern France. Depending on the model set-up, the results show substantial discrepancies in terms of simulated bathymetry evolutions. Moreover, the model based on an enhanced configuration of the sediment grain-size distribution (10 classes of particle sizes) and with distinct densities per class outperforms the standard SISYPHE configuration, with only two sediment grain-size classes, in terms of simulated suspended sediment concentration.

Bretagnolle, V., M. Benoit, M. Bonnefond, V. Breton, J. M. Church, S. Gaba, D. Gilbert, F. Gillet, S. Glatron, C. Guerbois, N. Lamouroux, M. Lebouvier, C. Mazé, J.-M. Mouchel, A. Ouin, O. Pays, C. Piscart, O. Ragueneau, S. Servain, T. Spiegelberger, and H. Fritz. 2019. Action-orientated research and framework: insights from the French long-term social-ecological research network. Ecology and Society 24(3):10. https://doi.org/10.5751/ES-10989-240310

Anthropogenic activities linked to various new technologies are increasingly disrupting REEs biogeochemical cycles. A catchment-based perspective is therefore necessary to distinguish between natural (i.e., changes in lithology) and human-related sources of REEs variability. In the present study, REEs patterns, anomalies and fluxes were investigated in the French part of the Moselle River basin (Moselle River itself and some of its headstreams and tributaries). The REEs patterns in the headstream waters were highly variable and mostly related to the complex underlying lithology (granite, sandstone, tuff and graywacke). Along the Moselle River, the presence of positive Gd anomalies and a regular LREEs depletion/HREEs enrichment pattern on sandstone/limestone substrates were the most distinctive features. The Gd anomaly varied from 1.8 to 8.7, with anthropogenic Gd representing 45 to 88% of the total Gd. A linear relationship was obtained between the anthropogenic Gd flux and the cumulative population along the watershed. However, the magnitude of the Gd anomalies was shown to depend on the methodological approach chosen for their calculation. The use of a threshold value to identify the presence of an anthropogenic Gd anomaly may therefore be basin (and lithology) dependent, and care has to be taken in comparing results from different rivers or lithologies. Concentration of anthropogenic Gd in the Moselle River and its tributaries were close to, or above, the value of 20 ng/L reported in literature to elicit adverse biological effects in laboratory cell cultures. The ecotoxicological significance of Gd anomalies deserves further investigation because concentrations of anthropogenic Gd may also vary depending on the methodological approach used for calculating Gd anomalies.

Rare Earth elements (REE) have become essential in strategical sectors such as high- and green-technologies. Their increasing use in human activities worldwide leads to anthropogenic REE releases detectable in all compartments of the environment, transforming REE into emerging contaminants. However, their potential impacts on ecosystems are still poorly understood. In order to have a comprehensive understanding of REE ecotoxicology and to properly assess their environmental risk, we analysed the toxicity of three representative REE (neodymium Nd, gadolinium Gd, and ytterbium Yb). Following recommendations of the European Chemicals Agency, we assessed REE hazard by performing standard ecotoxicological tests on three freshwater species belonging to different trophic levels (algae, crustacean and fish). EC50 were calculated using different modes of expression of REE exposure concentration (based on nominal, measured total and dissolved concentrations) in order to more properly and accurately determine REE toxicity. In order to get closer to environmental conditions, we also tested the toxicity of REE in mixture because all of them occur naturally as such in the environment. Moreover, we added dissolved organic matter (DOM) in the test medium because DOM is ubiquitous and drives REE speciation in freshwater systems. The Results showed that DOM significantly reduced REE bioaccumulation and toxicity, probably by formation of non-bioavailable REE-DOM complexes. The algal species was the most sensitive to REE. Despite slight differences between Nd, Gd and Yb in behaviour and bioaccumulation, the three REE exhibited comparable toxicity and additive effects in mixture to all tested organisms. Thus, we considered REE as a uniform group and, for the first time, we used mixture toxicity values and environmental mixture concentrations to assess the risk of REE in freshwater (instead of considering different REE separately). The results revealed that the risk is currently limited to wastewater treatment plants, and industrial and mining activities, where released quantities of REE can induce severe damage to exposed freshwater organisms. However, the risks are likely more widespread in the future because anthropogenic REE releases are expected to increase.

Correlation of the mass transfer characteristics of microfluidic parallel-plate electrochemical reactors is proposed for the first time. Firstly, the variation in the mass transfer coefficient (km) (1.61–3.94 × 10−5 m s−1) over a wide range of interelectrode distances (delec) from millimetric (3 mm) to micrometric values (100 µm) is reported. Secondly, a drastic slope change in the curve makes it possible to identify the onset of microfluidic behavior in a quantitative way for the first time, i.e. below a 1000 µm gap. Thirdly, a mathematical model is proposed which predicts km for any delec of interest. Fourthly, under laminar flow (7 < Reynolds (Re) < 623) and for temperatures in the range of 10–50 °C (532 < Schmidt (Sc) < 3315), new Sherwood (Sh) correlations are obtained for both microfluidic and millimetric configurations. It is thus feasible to extrapolate km for microfluidic electrochemical reactor scale-up.

Aquatic ecosystems are frequently considered as the final receiving environments of anthropogenic pollutants such as pharmaceutical residues or antibiotic resistant bacteria, and as a consequence tend to form reservoirs of antibiotic resistance genes. Considering the global threat posed by the antibiotic resistance, the mechanisms involved in both the formation of such reservoirs and their remobilization are a concern of prime importance. Antibiotic resistance genes are strongly associated with mobile genetic elements that are directly involved in their dissemination. Most mobile genetic element-mediated gene transfers involve replicative mechanisms and, as such, localized gene transfers should participate in the local increase in resistance gene abundance. Additionally, the carriage of conjugative mobile elements encoding cell appendages acting as adhesins has already been demonstrated to increase biofilm-forming capability of bacteria and, therefore, should also contribute to their selective enrichment on surfaces. In the present study, we investigated the occurrence of two families of mobile genetic elements, IncP-1 plasmids and class 1 integrons, in the water column and bank sediments of the Orne River, in France. We show that these mobile elements, especially IncP-1 plasmids, are enriched in the bacteria attached on the suspended matters in the river waters, and that a similar abundance is found in freshly deposited sediments. Using the IncP-1 plasmid pB10 as a model, in vitro experiments demonstrated that local enrichment of plasmid-bearing bacteria on artificial surfaces mainly resulted from an increase in bacterial adhesion properties conferred by the plasmid rather than an improved dissemination frequency of the plasmid between surface-attached bacteria. We propose plasmid-mediated adhesion to particles to be one of the main contributors in the formation of mobile genetic element-reservoirs in sediments, with adhesion to suspended matter working as a selective enrichment process of antibiotic resistant genes and bacteria.

Rare earth elements (REE) are emerging contaminants due to their increased use in diverse applications including cutting-edge and green-technologies. Their environmental concerns and contradicting results concerning their biological effects require an extensive understanding of REE ecotoxicology. Thus, we have studied the fate, bioaccumulation and biological effects of three representative REE, neodymium (Nd), gadolinium (Gd) and ytterbium (Yb), individually and in mixture, using the freshwater bivalve Corbicula fluminea. The organisms were exposed for 96 h at 1 mg L−1 REE in the absence and presence of dissolved organic matter (DOM) reproducing an environmental contamination. Combined analysis of the fate, distribution and effects of REE at tissue and subcellular levels allowed a comprehensive understanding of their behaviour, which would help improving their environmental risk assessment. The bivalves accumulated significant concentrations of Nd, Gd and Yb, which were decreased in the presence of DOM likely due to the formation of REE-DOM complexes that reduced REE bioavailability. The accumulation of Nd, Gd and Yb differed between tissues, with gills > digestive gland ≥ rest of soft tissues > hemolymph. In the gills and in the digestive gland, Nd, Gd and Yb were mostly (>90 %) distributed among metal sensitive organelles, cellular debris and detoxified metal-rich granules. Gadolinium, Yb and especially Nd decreased lysosome size in the digestive gland and disturbed osmo- and iono-regulation of C. fluminea by decreasing Na concentrations in the hemolymph and Ca2+ ATPase activity in the gills. Individual and mixed Nd, Gd and Yb exhibited numerous similarities and some differences in terms of fate, accumulation and biological effects, possibly because they have common abiotic and biotic ligands but different affinities for the latter. In most cases, individual and mixed effects of Nd, Gd, Yb were similar suggesting that additivity approach is suitable for the environmental risk assessment of REE mixtures.

Abstract In addition to global warming, aquatic ecosystems are currently facing multiple global changes among which include changes in nitrogen (N) loads. While several studies have investigated both temperature and N impacts on aquatic ecosystems independently, knowledge on their interactive effects remains scarce. In forested headwater streams, decomposition of leaf litter represents the main process ensuring the transfer of nutrients and energy to higher trophic levels, followed by autochthonous primary production, mainly ensured by phototrophic biofilms. The main aim of this study was to disentangle the independent and combined effects of temperature increase and nutrient availability on the relative importance of brown and green processes involved in stream functioning. We hypothesised that water temperature and nutrients would lead to a general increase in leaf‐litter decomposition and primary production, but that the intensity of these effects would be largely modulated by competitive interactions arising between microorganisms as well as by the top‐down control of microorganisms by macro‐invertebrates. Macro‐invertebrates would, in turn, be bottom‐up controlled by microbial resources quality. To test these hypotheses, we conducted a 56‐day experiment in artificial streams containing leaf litter, microbial decomposers and biofilm inoculum, and an assemblage of macro‐invertebrates. Two water inorganic N:phosphorus (P) ratios (33 and 100, molar ratios) and two temperatures (ambient, +2°C) were manipulated, each treatment being replicated three times. Fungal and biofilm growth as well as leaf‐litter decomposition and primary production were quantified. Top‐down impacts of invertebrate primary consumers on brown and green compartments were evaluated using exclosures while bottom‐up control was evaluated through the measurement of resource stoichiometry and fatty acid profiles, as well as quantification of macro‐invertebrate growth and survival. Contrary to expectations, microbial decomposition was not significantly stimulated by nutrient or temperature manipulations, while primary production was only improved under ambient temperature. In the + 2°C treatment with high N:P, greater biofilm biomass was associated with lower fungal development, which indicates competition for nutrients in these conditions. Temperature increased macro‐invertebrate growth and leaf‐litter consumption, but this effect was independent of any improvement of basal resource quality, suggesting that temperature mediated changes in consumer metabolism and activity was the main mechanism involved. Most of our hypotheses that were based on simplified laboratory observations have been rejected in our semi‐controlled mesocosms. Our study suggests that the complexity of biological communities might greatly affect the response of ecosystems to multiple stressors, and that interactions between organisms must be explicitly taken into account when investigating the impacts of global change on ecosystem functioning.

Summary Organisms commonly face multiple stresses in ecosystems, among which are toxic substances that add to natural ecological constraints such as insufficient resource quality. The combined effects of these stressors on species and ecosystems remain poorly investigated. We hypothesised that feeding on high‐quality resources in terms of phosphorus (P) content will improve the physiological state of consumers and thus increase tolerance to episodic metal stress by silver (Ag). We used a detritivorous crustacean from streams, Gammarus fossarum , to test this hypothesis. The experimental design involved two phases. In the first phase, gammarids were fed ad libitum for 15 days to evaluate the effect of food quality on their energetic status. Gammarids were placed in laboratory microcosms and allowed to feed on two leaf species, alder and sycamore, that were colonised by aquatic fungi and experimentally enriched with P. At the end of this feeding period, we determined (i) food consumption, (ii) energetic reserves and (iii) physiological and behavioural states. In the second phase, gammarids previously consuming food of different quality were exposed to dissolved Ag (0, 0.5 and 1 μg L −1 ) for 4 days to investigate the physiological and behavioural responses of the consumers. Elevated P concentrations in leaf litter increased the energetic reserves and locomotor activity of G. fossarum . Gammarids exposed to Ag had a low glycogen content, regardless of the Ag concentration and leaf P concentration, suggesting significant energy allocation to several aspects of organism maintenance (e.g. detoxification or compensatory mechanisms). In most cases, this investment appeared to prevent gammarids from carrying out lipid peroxidation (indicating cell membrane damage), except for those gammarids feeding on leaves with the highest P concentration. Higher energetic storage (measured as glycogen content), related to higher elemental food quality, did not lead to a systematic increase in consumer tolerance to Ag, gammarids being unable to compensate for negative effects of Ag at the concentrations tested.

Abstract Because of the first observations in the 1900s of the oligotrophic and eutrophic states of lakes, researchers have been interested in the process that makes lakes become turbid because of high phytoplankton biomass. Definitions of eutrophication have multiplied and diversified since the mid‐20th century, more than for any other ecological process. Reasons for the high number of definitions might be that the former ones did not sufficiently describe their causes and/or consequences. Global change is bringing eutrophication more into the spotlight than ever, highlighting the need to find consensus on a common definition, or at least to explain and clarify why there are different meanings of the term eutrophication. To find common patterns, we analyzed 138 definitions that were classified by a multiple correspondence factor analysis (MCA) into three groups. The first group contains the most generic scientific definitions but many of these limit the causes to increased nutrient availability. A single definition takes into account all causes but would require additional work to clarify the process itself. Nutrient pollution, which is by far the primary cause of eutrophication in the Anthropocene, has generated a second group of environmental definitions that often specify the primary producers involved. Those definitions often mention the iconic consequences of nutrient pollution, such as increased algal biomass, anoxia/hypoxia and reduced biodiversity. The third group contains operational definitions, focusing on the consequences of nutrient pollution, for ecosystem services and therefore associated with ecosystem management issues. This group contains definitions related to regulations, mainly US laws and European directives. These numerous definitions, directly derived from the problem of nutrient pollution, have enlarged the landscape of definitions, and reflect the need to warn, legislate and implement a solution to remedy it. Satisfying this demand should not be confused with scientific research on eutrophication and must be based on communicating knowledge to as many people as possible using the simplest possible vocabulary. We propose that operational definitions (groups 2 and 3) should name the process “nutrient pollution,” making it possible to refine (scientific) definitions of eutrophication and to expand on other challenges such as climate warming, overfishing, and other nonnutrient‐related chemical pollutions.

Ecological stoichiometry seeks to understand the ecological consequences of elemental imbalances between consumers and their resources. Therein, the well‐accepted growth rate hypothesis (GRH) states that organisms exhibiting rapid growth have higher phosphorus (P) demand – and thus lower C:P and N:P ratios – than slow growing ones, due to a higher allocation to P‐rich rRNA. However, GRH has rarely been extended to other biological traits than growth, especially at the community level. In this study, we investigated whether macroinvertebrate stoichiometric traits (e.g. C:P and N:P ratios) can be linked to their development traits, and whether these stoichiometric traits are related to macroinvertebrate community assemblage under different nutrient conditions. We allocated more than 400 European taxa to different groups, defined using available information about three development‐related traits: ‘life span', ‘voltinism' and ‘number of reproductive cycles per individual'. We sampled 18 invertebrate taxa in six streams exhibiting different levels of nutrient concentration and measured their stoichiometric traits. Further, we quantified invertebrate taxon abundances in these streams during an annual survey. Based on these data, we tested whether community composition regarding the developmental groups differs, depending on nutrient concentration. We found significant differences in the proportions of the developmental groups along a gradient of water N:P, in relation to their stoichiometric traits. Taxa with low C:P and N:P ratios were generally associated with faster development groups, and these taxa tended to occur at higher proportions in streams exhibiting low dissolved N:P ratios. In contrast, communities from P‐poor, high dissolved N:P streams, were dominated by slowly developing taxa with high N:P ratios. Our results highlight that extending the GRH to species development rate might give some insights about the mechanisms by which nutrient concentrations in ecosystems influence consumers' community composition.

Polyculture offers an alternative to monoculture in recirculated aquaculture systems (RAS). Nevertheless, RAS polyculture can potentially result in beneficial as well as detrimental consequences. This places a premium on assessing consequences of a particular polyculture prior to its implementation in farming production. In fish aquaculture, most of previous assessments of polyculture consequences have been carried out through multi-trait approach by analysing independently species traits related to a single biological function. Yet, polyculture can impact many biological functions and the overall consequences are the result of multiple interactions from different functions. Therefore, an integrative analysis is required to synthesise the polyculture consequences at the multi-trait levels. Here we propose a multi-trait evaluation framework (i.e. considering traits related to multiple functions), for the polyculture consequence assessment. We analyse this framework through multivariate analysis prior integrating results for each trait. As test case, we used pikeperch (Sander lucioperca), reared in monoculture and in polyculture with European perch (Perca fluviatilis), common carp (Cyprinus carpio) and black-bass (Micropterus salmoides). Our results revealed the importance of applying multi-trait framework to obtain a reliable assessment of fish polycultures. The divergence that might occur in the expression of some traits in the same polyculture has been highlighted to support this argument. Through the integration method, it was possible to find the suitable combination(s) of fish and to exclude the unsuitable ones. For future researches, we suggest to support the multi-trait assessment by weighting the traits involved in the multivariate analysis.

Autotrophic biofilms are complex and fundamental biological compartments of many aquatic ecosystems. In particular, these biofilms represent a major resource for many invertebrate consumers and the first ecological barrier against toxic metals. To date, very few studies have investigated the indirect effects of stressors on upper trophic levels through alterations of the quality of biofilms for their consumers. In a laboratory study, we investigated the single and combined effects of phosphorus (P) availability and silver, a re-emerging contaminant, on the elemental (Carbon (C) : Nitrogen (N) : P ratios) and biochemical (fatty acid profiles) compositions of a diatom-dominated biofilm initially collected in a shallow lake. We hypothesized that 1) P and silver, through the replacement of diatoms by more tolerant primary producer species, reduce the biochemical quality of biofilms for their consumers while 2) P enhances biofilm elemental quality and 3) silver contamination of biofilm has negative effects on consumers life history traits. The quality of biofilms for consumers was assessed for a common crustacean species, Gammarus fossarum, by measuring organisms’ survival and growth rates during a 42-days feeding experiment. Results mainly showed that species replacement induced by both stressors affected biofilm fatty acid compositions, and that P immobilization permitted to achieve low C:P biofilms, whatever the level of silver contamination. Gammarids growth and survival rates were not significantly impacted by the ingestion of silver-contaminated resource. On the contrary, we found a significant positive relationship between the biofilm P-content and gammarids growth. This study underlines the large indirect consequences stressors could play on the quality of microbial biomass for consumers, and, in turn, on the whole food web.

The effect of the lockdown imposed to limit the spread of SARS-CoV-2 in France between March 14 and May 11, 2020 on the wastewater characteristics of two large urban areas (with between 250,000 and 300,000 inhabitants) was studied. The number of outward and inward daily commuters was extracted from national census databases related to the population and their commuting habits. For urban area A, with the larger number of daily inward commuters (110,000, compared to 53,000 for B), lockdown was observed to have an effect on the monthly load averages of chemical oxygen demand, biochemical oxygen demand, total Kjeldahl nitrogen, total suspended solids and total phosphorus, all of which decreased (confidence level of 95%). This decrease, which varied between 20% and 40% and reached 45% for COD, can be related to the cessation of catering and activities such as hairdressing, which generate large amounts of graywater. The ammonium loads, due to the use of toilets before leaving for work and after returning from work, remained constant. In the case of urban area B, lockdown had no noticeable effect. More data would be necessary in the long term to analyze the effect of changes in the balance between ammonia and carbon sources on the operation of wastewater treatment plants.

Polyculture is a potentially interesting rearing practice for future aquaculture developments. Nevertheless, it may result in beneficial as well as detrimental consequences for fish production. One way to maximize the benefits of polyculture is to combine species with high levels of compatibility and complementarity. This requires the development of a ranking procedure, based on a multi-trait assessment, that highlights the most suitable species combinations for polyculture. Moreover, in order to ensure the relevance of such a procedure, it is important to integrate the socio-economic expectations by assigning relative weights to each trait according to the stakeholder priorities. Here, we proposed a ranking procedure of candidate fish polycultures (i.e., species combinations that could be potentially interesting for aquaculture) based on a multi-trait assessment approach and the stakeholder priorities. This procedure aims at successively (i) weighting evaluation results obtained for each candidate polyculture according to stakeholder priorities; (ii) assessing differentiation between candidate species combinations based on these weighted results; and (iii) ranking differentiated candidate polycultures. We applied our procedure on three test cases of fish polycultures in recirculated aquaculture systems. These test cases each focused on a target species (two on Sander lucioperca and one on Carassius auratus), which were reared in two or three different alternative candidate fish polycultures. For each test case, our procedure aimed at ranking alternative combinations according to their benefits for production and/or welfare of the target species. These benefits were evaluated based on survival rate as well as morphology, behavioral, and physiological traits. Three scenarios of stakeholder priorities were considered for weighting evaluation results: placing a premium on production, welfare, or both for the target species. A comparison of our procedure results between these scenarios showed that the ranking changed for candidate polycultures in two test cases. This highlights the need to carefully consider stakeholder priorities when choosing fish polycultures.

Abstract 1. Forested headwater streams are generally considered to be light‐limited ecosystems where primary production is reduced, and the main source of energy and nutrients is composed of allochthonous detritus. We hypothesised that in these ecosystems, the development of primary producers might also be limited by (1) competition for nutrients with leaf‐litter decomposers (e.g. bacteria and fungi), and (2) leaf‐litter leachates or allelopathic compounds produced by aquatic fungi. 2. To test these hypotheses, a 48‐day mesocosm experiment was performed in 12 artificial streams containing stream water inoculated with epilithic biofilm suspensions collected from a forested headwater stream. Three different treatments were applied: control without leaf litter (C), microbially conditioned leaf litter added at the beginning of the experiment and left to decompose throughout the experiment (L), or leaf litter renewed three times during the experiment (RL). 3. We predicted that (1) the presence of litter, through microbial nutrient immobilisation and allelopathy, would reduce primary production and that (2) this effect would be amplified by litter renewal. We also predicted that nutrient competition would mean that (3) leaf‐litter decomposers will alter primary producer community composition and physiology. These predictions were tested by analysing biofilm development, physiology, stoichiometry, and benthic algal community structure. To distinguish between the effects of nutrient immobilisation and allelopathy, the biofilm responses to leaf‐litter leachates collected after different microbial conditioning durations were also measured in a parallel laboratory experiment. 4. Contrary to our expectations, by day 28, primary producer growth was higher in the mesocosms containing leaf litter (L and RL) despite the rapid decrease in dissolved nutrients when leaf litter was present. After 48 days, the lowest phototrophic biofilm development was observed when leaf litter was renewed (RL), whereas phototrophic biofilm development was similar in the C and L treatments. Biofilm stoichiometry indicated that this effect was most probably related to greater nitrogen limitation in the RL treatment. The presence of leaf litter also affected primary producers' photophysiology, which could be attributed to changes in taxonomic composition and to physiological adjustments of primary producers. 5. Laboratory measurements showed that despite a strong inhibition of primary producer growth by unconditioned leaf‐litter leachates, microbially conditioned leaf litter had either low or no effects on the development of primary producers. 6. These results reveal that leaf‐litter decomposers can have both positive and negative effects on primary producers underlining the need to consider microbial interactions when investigating the functioning of forested headwater streams.

The rapidly expanding utilization of lanthanides (Ln) for the development of new technologies, green energies, and agriculture has raised concerns regarding their impacts on the environment and human health. The absence of characterization of the underlying cellular and molecular mechanisms regarding their toxicity is a caveat in the apprehension of their environmental impacts. We performed genomic phenotyping and molecular physiology analyses of Saccharomyces cerevisiae mutants exposed to La and Yb to uncover genes and pathways affecting Ln resistance and toxicity. Ln responses strongly differed from well-known transition metal and from common responses mediated by oxidative compounds. Shared response pathways to La and Yb exposure were associated to lipid metabolism, ion homeostasis, vesicular trafficking, and endocytosis, which represents a putative way of entry for Ln. Cell wall organization and related signaling pathways allowed for the discrimination of light and heavy Ln. Mutants in cell wall integrity-related proteins (e.g., Kre1p, Kre6p) or in the activation of secretory pathway and cell wall proteins (e.g., Kex2p, Kex1p) were resistant to Yb but sensitive to La. Exposure of WT yeast to the serine protease inhibitor tosyl phenylalanyl chloromethyl ketone mimicked the phenotype of kex2 ∆ under Ln, strengthening these results. Our data also suggest that the relative proportions of chitin and phosphomannan could modulate the proportion of functional groups (phosphates and carboxylates) to which La and Yb could differentially bind. Moreover, we showed that kex2 ∆, kex1 ∆, kre1 ∆, and kre6 ∆ strains were all sensitive to light Ln (La to Eu), while being increasingly resistant to heavier Ln. Finally, shotgun proteomic analyses identified modulated proteins in kex2 ∆ exposed to Ln, among which several plasmalemma ion transporters that were less abundant and that could play a role in Yb uptake. By combining these different approaches, we unraveled that cell wall components not only act in Ln adsorption but are also active signal effectors allowing cells to differentiate light and heavy Ln. This work paves the way for future investigations to the better understanding of Ln toxicity in higher eukaryotes.

Abstract 137 Cs is a long-lived man-made radionuclide introduced in the environment worldwide at the early beginning of the nuclear Era during atmospheric nuclear testing’s followed by the civil use of nuclear energy. Atmospheric fallout deposition of this major artificial radionuclide was reconstructed at the scale of French large river basins since 1945, and trajectories in French nuclearized rivers were established using sediment coring. Our results show that 137 Cs contents in sediments of the studied rivers display a large spatial and temporal variability in response to the various anthropogenic pressures exerted on their catchment. The Loire, Rhone, and Rhine rivers were the most affected by atmospheric fallout from the global deposition from nuclear tests. Rhine and Rhone also received significant fallout from the Chernobyl accident in 1986 and recorded significant 137 Cs concentrations in their sediments over the 1970–1985 period due to the regulatory releases from the nuclear industries. The Meuse River was notably impacted in the early 1970s by industrial releases. In contrast, the Seine River display the lowest 137 Cs concentrations regardless of the period. All the rivers responded similarly over time to atmospheric fallout on their catchment, underlying a rather homogeneous resilience capacity of these river systems to this source of contamination.

In the agricultural regions of Burkina Faso, urban solid waste fertilizers were usually applied. This activity is likely to contaminate the soils and expose populations to serious diseases. This study aims to assess rate of heavy metal (Cd, Cu, Mn, Pb, Zn, Ni, Cr) contamination in both agricultural lixisol and vertisol and to evaluate the removal efficiency of heavy metals using Vetiver grass on different two mixed heavy metal contaminated soils. A pot experiment was conducted to compare the metal accumulation and overall efficiency of metal uptake by different plant parts (roots and shoots) on both tropical soils. After 3 and 6 months growing on laboratory conditions, Vetiver grass plants were harvested and heavy metal concentrations in shoot and root parts determined by Inductively Coupled Plasma - Atomic Emission Spectroscopy. The results indicate that at 3 and 6 moths, the shoot and root concentrations of heavy metals in Vetiver grass harvested in lixisol were higher than vertisol. For different plant parts, all metal concentrations were higher in root than in shoot, except Cu and Pb. At the 3 and 6 months, the BCF values > 1 for Cd, Cu and Zn in both soils showed Vetiver grass as an effective phyto-stabilizer for these metals. However, the TF values > 1 for Cd (lixisol), Mn, Zn Ni and Cr (vertisol) indicated the efficiency of Vetiver for phytoextraction. The results of this study showed that Vetiver is more effective in lixisol, but it can be used for remediation of both studied tropical soils from agricultural region of Burkina Faso. Nevertheless, considering the special limitations of the experimental conditions, further field monitoring is necessary to demonstrate the phytoremediation efficiency of Vetiver in agricultural soils under the climatic conditions of Burkina Faso.