Organic Matter Dynamics in a Human-Impacted Estuary: Insights from Biomarkers and Excitation-Emission Matrix Fluorescence

International audienc

No-kill in restocking programs: Advances in non lethal detection of fluorochromes in marked juveniles, glass eel case study

International audienceRestocking is one of the alternatives measures that have been widely used as a measure of remediation of ichthyologic biodiversity loss. To assess restocking efficiency, mass-marking provided the discrimination of restocked fish compared to wild fish. The use of fluorochromes recorded in the calcified structures such as otoliths has been used extensively to detect marked fish. However, reading mark on otolith requires the sacrifice of the fish. European eel recruitment collapsed down to 1% of 1980s levels. Within European eel management plan, restocked glass eel are marked with Alizarine Red S (ARS 150 ppm). The aim of our study was to implement a nonlethal ARS mark detection method using modern techniques of microscopy, imaging and fluorimetry. Batches of ARS marked and unmarked glass eels within a restocking protocol were collected before they were translocated. For marked and unmarked glass eels, ARS detection mark was assayed i) on glass eel fins with a binocular microscope, ii) on anesthetized glass eels using a fluorescence reflectance imager and iii) on a piece of caudal glass eel fins using fluorimeter. Among the three alternative methods tested, non-lethal ARS detection using fluorimeter appeared to be most efficient, the easiest method and the cheapest method. Overall, the present results provided a widely applicable, easy and non-lethal method to researchers and managers for detecting endangered marked fish

Caractérisation intégrée de la matière organique dissoute : étude d'empreintes typiques de sources naturelles et anthropiques dans les milieux aquatiques

National audienceLa matière organique dissoute (MOD), constituée d'un mélange complexe de composés chimiques variés, joue un rôle clé au coeur des processus biogéochimiques et dans le fonctionnement des écosystèmes aquatiques. Sa composition et ses propriétés physico-chimiques, combinées aux conditions environnementales du milieu, déterminent son devenir (dégradabilité biotique ou abiotique, distribution dans les différents compartiments du milieu aquatique...) et sa réactivité (consommation d'oxydants, complexation avec des micropolluants et influence sur leur biodisponibilité et donc leur toxicité...). La composition de la MOD dans les milieux aquatiques est fortement liée à son origine. Les sources de MOD dans un bassin versant sont nombreuses : MOD naturelle autochtone ou allochtone issue de différentes occupations de sols ; MOD d'origine anthropique issue de rejet ponctuel (rejet de station d'épuration, déversoirs d'orages...) ou diffus (eaux de ruissellement en zone rurale ou urbaine, débordements ou fuites de réseaux d'assainissement...). Dans ce contexte, l'objectif de nos travaux est d'explorer les empreintes typiques des sources principales de MOD dans les bassins versants soumis à des pressions anthropiques diversifiées. Pour cela, nous avons besoin de développer une nouvelle stratégie de caractérisation intégrée de la MOD (i.e. combinant les informations issues de plusieurs techniques d'analyses) qui soit généralisable à tous les types de MOD et facilement applicable à un grand nombre d'échantillons. Ainsi, depuis 2017, une base de données permet de recenser nos résultats issus d'analyses plus ou moins classiques (carbone organique dissous, demande biologique en oxygène à 5 et 28 jours, spectres UV-vis, fluorescence 3D, HPSEC-UV...) réalisées sur de nombreux échantillons (n=102 en juillet 2019) provenant de rejets et d'eaux de rivière plus ou moins impactées par les activités anthropiques. En parallèle, une approche de caractérisation moléculaire est menée sur ces échantillons par chromatographie liquide couplée à la spectrométrie de masse haute résolution (LC-HRMS). Les premiers résultats obtenus à partir de cette base de données permettent déjà : - de mettre en place un protocole de tri, correction et interprétation des nombreux signaux masse/charge (m/z) générés par LC-HRMS afin de fiabiliser l'étude moléculaires de la MOD ; - de tester de nouveaux descripteurs pour caractériser la MOD par HPSEC-UV (ratios d'aires de domaines de taille, identification de couples poids moléculaire et longueurs d'onde typiques) ou par fluorescence 3D (définition de pics spécifiques avec PARAFAC) ; - d'observer la variabilité de la MOD dans ces échantillons d'origines très variées ; - de mettre en évidence des indicateurs pertinents pour proposer une typologie de la MOD en fonction de ses sources. Cette approche intégrée multi-techniques devrait à terme permettre de caractériser plus finement la composition et les propriétés de la MOD. Elle sera développée plus en profondeur dans un travail de thèse qui commencera fin 2019

Contrasting effects of siderophores pyoverdine and desferrioxamine B on the mobility of iron, aluminum, and copper in Cu-contaminated soils

International audienceSiderophores are biogenic metallophores that can play significant roles in the dynamics of a range of metals, including Cu, in the soil. Understanding the impact of siderophores on the mobility and the availability of metals in soil is required to optimize the efficiency of soil remediation processes such as phytoextraction. This study compared the ability of siderophores desferrioxamine B (DFOB) and pyoverdine (Pvd) to mobilize metals in a series of Cu-contaminated soils, and investigated the extent their metal mobilization efficiency changed over time and with the level of Cu contamination of the soil. Siderophores were supplied (or not) to Cu-contaminated soils and metal mobility was assessed through their total concentration in 0.005 M CaCl2 extract. DFOB selectively mobilized Fe and Al while Pvd also mobilized Cu and Ni, Co, V and As but to a lesser degree. The 1:1 relationship between DFOB in the CaCl2 extract and Fe + Al mobilized from the solid phase suggests that DFOB mobilized metals by ligand-controlled dissolution. The accumulation of Cu in soil enhanced the adsorption of DFOB and Pvd at the surface of soil constituents and the mobilization of Fe to the detriment of Al by the two siderophores. The metal mobilization efficiency of DFOB and to a lesser extent of Pvd decreased over 22 days. According to N-15-Pvd analyses, Pvd degradation at least partly contributed to the progressive reduction in the metal mobilization efficiency of Pvd. The processes behind these results and the relevance of these results for manipulating the availability of Cu (and Fe) in soil are discussed

Antagonistic impacts of benthic bioturbator species: Interconnected effects on sedimentary properties, biogeochemical variables, and microbial dynamics

International audienceMacrofaunal species inhabiting intertidal mudflats and performing intense bioturbation are considered as ecosystem engineers, since they profoundly influence their physical, chemical, and biological environments. Nowadays, to complete our knowledge on the effect of bioturbation processes on the surrounding environment, interdisciplinary approach is essential to unravel their complex intertwined effects on intertidal mudflats. In this study, the effects of bioturbators on sediment properties, biogeochemical variables, and microbial dynamics (microphytobenthos, bacteria and archaea) were investigated. To this end, manipulation experiments were carried out in an intertidal mudflat of the Seine Estuary (France) by revamped the abundance of the two dominant bioturbators, Scrobicularia plana and Hediste diversicolor, in winter and late summer. Results showed that the presence of H. diversicolor in winter had a significant effect, with a significant increase in bed level accretion and microbial nitrate reduction rates. In contrast, the presence of S. plana showed no significant impact on sediment properties, most likely due to a reduced bioturbating activity at low temperature. In summer, both ecosystem engineers strongly influenced their surrounding environment but with opposite effects. The intense reworking of the sediment surface by S. plana limited microbial growth and enhanced erosion processes. Conversely, the presence of H. diversicolor favoured sediment accretion and enhanced microbial growth. Overall, this interdisciplinary study confirms the importance of these two ecosystem engineers in temperate estuarine mudflats by highlighting their simultaneous and intertwined effects on the sedimentary, physicochemical, and biological features. This confirms the importance of actively considering ecosystem engineers when restoring the natural habitats of tidal flats to cope with the different vulnerability risks related to global warming (sandification of estuarine sediments, disappearance of productive mudflats, sea level rise, vulnerability to storms and erosion)