Toxicity of sediment-bound pollutants in the Seine estuary, France, using a Eurytemora affinis larval bioassay.

Coastal urbanisation exposes surrounding estuarine environments to urban-related contaminants such as polycyclic aromatic hydrocarbons (PAHs), polychlorobiphenyls (PCBs) and pesticide mixtures. Hydrophobic contaminants can adsorb on estuarine sediments. They can subsequently be released on a massive scale in the aquatic environment due to artificial or natural phenomena (e.g. dredging, tides), thereby threatening living organisms. The contamination of sediment is a significant ecological issue in the Seine estuary, France. However, few relevant methods have been developed to assess sediment toxicity and its ecological impacts in a cost-effective way. In this context, we aimed to assess the toxicity of natural sediments from the Seine estuary on the development of the calanoid copepod Eurytemora affinis using a previously developed larval bioassay. This assay involves direct exposure of nauplii to elutriates of sediments for six days. Sediments were collected along the Seine estuary from six polluted sites and one reference site. Pollutants in this estuary included PAHs, PCBs and OCPs (organochlorine pesticides). Nauplius survival was significantly more affected by exposure to all contaminated sediment elutriates, than by exposure to sediment from Yville-sur-Seine (the reference site), whereas nauplius growth was significantly reduced after exposure to contaminated sediment elutriates from four of the six contaminated sites. We identified two distinct site clusters, one including both the sand-rich and the least polluted sediments (Oissel, Quillebeuf-sur-Seine, Caudebec-en-Caux) and the other including both the clay- and silt-rich, and the most polluted sediments (La Bouille, Poses, Pont de Normandie). As expected, survival was significantly more impacted after exposure to elutriates from the second cluster than from the first. This work enables (i) assessment of the toxicity of natural sediments in the Seine estuary and (ii) validation of the larval bioassay previously developed using sorbed sediment with model molecules.

Flux estimation, temporal trends and source determination of trace metal contamination in a major tributary of the Seine estuary, France.

Anthropogenic impacts on rivers have increased significantly over the past ~150 years, particularly at the beginning of the industrial revolution. Among other signs, this impact is manifested through the addition of trace metals and metalloid elements to rivers. The Eure River watershed in France covers an area of 6017 km2 and is a major tributary of the Seine estuary. It is not exempt from anthropogenic pressures and has been exposed to significant metal discharges over the last 80 years. The average concentrations of metals (i.e., Cr, Co, Ni, Cu, Zn, Ag, Cd, Sb, and Pb), in suspended particulate matter currently transported by the river are high compared to the local geochemical background. Moreover, the lack of correlation between concentration variations and the hydrosedimentary behaviour of the Eure River suggests that the river is currently under anthropogenic pressure. Analysis of sediment cores indicate strong As contamination during the 1940s, Cr, Co, Ni, Cu, Zn, Ag, and Cd contamination during the 1960s and 1970s, and Sb and Pb contamination during the 1990s and 2000s. The enrichment factors calculation suggests that total anthropogenic pressure within the Eure River watershed since the 1940s was comparable or higher than those in many other French watersheds. An estimation of particulate metal flux in 2017 shows that the Eure River watershed contributed to 7, 8, 9, 10 and 16% of total inputs to the Seine estuary in Cr, Cu, Zn, Cd and Pb respectively. Moreover, the estimation of past theoretical flux indicates that during the 1990s the Eure River watershed was the main contributor of particulate Pb to the estuary. The use of Pb isotopes has revealed that this contamination was primarily of industrial origin.

Faecal-indicator bacteria and sedimentary processes in estuarine mudflats (Seine, France).

Over a three-year period, quantification of faecal indicators and the molecular detection of Escherichia coli and Salmonella were monitored in sediments from three contrasting mudflats of the Seine estuary (France). The elevation of the mudflat surface was monitored concurrently using a high-resolution altimeter. During the period of the study, estuarine mudflats were areas of deposition for faecal-indicator bacteria and were mainly controlled by sedimentary processes. In the intertidal freshwater and subtidal mudflats, the highest abundances of faecal-indicator bacteria were counted during a depositional period. Maximum levels were observed in the freshwater mudflats during periods of high flow: thermotolerant coliforms: 3.9 x 10(4) cfu cm(-2), enterococci: 1.2 x 10(4) cfu cm(-2), Clostridium perfringens spores: 9.8 x 10(5) spores cm(-2). Loss of culturability of enteric bacteria in sediment microcosms demonstrated the remediatory capacity of the mudflats, even if they might be a secondary source of bacteria-forming spores to the water column through erosion and resuspension events.

Relationships between hydrosedimentary processes and occurrence of mercury-resistant bacteria (merA) in estuary mudflats (Seine, France).

The Seine estuary (France) is one of the world's macrotidal systems that is most contaminated with heavy metals. To study the mercury-resistant bacterial community in such an environment, we have developed a molecular tool, based on competitive PCR, enabling the quantification of Gram-negative merA gene abundance. The occurrence of the Gram-negative merA gene in relation with the topology (erosion/deposit periods) and the mercury contamination of three contrasted mudflats was investigated through a multidisciplinary approach and compared with a non-anthropized site (Authie, France). The higher abundance of the Gram-negative merA gene in the Seine estuary mudflats indicates a relationship between the degree of anthropization and the abundance of the merA gene in the mudflat sediments. In the Seine mudflats, the maxima of abundance are always located in fresh sediment deposits. Therefore, the abundance is closely related with the hydrosedimentary processes, which thus seem to be determining factors in the occurrence of the Gram-negative merA gene in the surface sediments of the Seine's mudflat.

A report card and quality indicators for the Seine estuary: from scientific approach to operational tool.

The scientific teams from the interdisciplinary Seine-Aval (SA) research program and the SA's operational pole, GIPSA (Groupement d'Intérêt Public Seine-Aval) have worked together to create a report card designed to help the Estuary Council (Conseil de l'Estuaire) revitalize its original functions: maintaining functional links between the various estuarine ecosystems, comprehending and managing the estuary's natural habitats and biological populations, and monitoring and improving the physical-chemical quality of the estuarine waters. The report card will be able to synthesize the information obtained from several system performance variables and available operational indicators. This approach, intended to guide the estuary managers, is the oeuvre of several scientific teams; it is particularly important in the context of the Water Framework Directive because it facilitates the elaboration of a group of relevant indicators, which can then be used as operational tools. A report card will provide decision-makers (e.g., political authorities; national, regional and local institutions and industries) with the key indicators for evaluating the system and predicting changes in terms of selected objectives, such as the preservation and restoration of the estuary's environmental functionalities. The final objective of the research is to choose among the available indicators to approximate potential ecological risks. Integrating the socio-economical data will perhaps lead to setting risk acceptability thresholds for the different uses of the Seine estuary. In the end, collaboration between the scientists, the managers, and the GIPSA operational pole will be essential to produce a viable report card about the environmental status of the Seine estuary. To illustrate the research now under way, this article presents the results for three actions undertaken, concerning: (i) physical indicators (i.e., an inventory of the estuary first as a whole, and then section by section); (ii) benthic indicators (i.e., seven indices which show a moderate EcoQ for the lower part of the estuary); and (iii) a eutrophication indicator (i.e., an indicator for coastal eutrophication potential (ICEP), which helps to limit the nutrient fluxes (N or P) that exceed the silica flux delivered by the Seine network, based on the Redfield ratios for algal propagation).

Chemical characterization of porewaters in an intertidal mudflat of the Seine estuary: relationship to erosion-deposition cycles.

A seasonal field study was carried out in the Seine estuary to determine the chemistry of sediment porewaters using the 'peeper' technique and changes in the elevation of the mudflats using the 'Altus' technique. This approach allowed us to evaluate the release of nutrients and to link these releases to the sediment hydrodynamics. Our results show that nutrient and organic matter cycling in a Seine estuary mudflat exhibits a seasonal behaviour, which is mainly influenced by variations in hydrodynamics. Sediments, rich organic matter, were input during floods and they were mineralized during summer and autumn, releasing nutrients and dissolved organic carbon into the sediment porewaters. The nutrient release, including ammonium, is mainly linked to the mineralization of organic matter, while the release of phosphate is delayed. The delay could be the result of phosphate association with organic matter and/or its co-precipitation with calcium and iron.

Dating of sediment record at two contrasting sites of the Seine River using radioactivity data and hydrological time series.

Sediment cores were collected at the outlet of the highly anthropogenized catchment of the Seine River at two contrasting sites: a flood plain of the lower Seine River and a quasi-permanently submerged harbour basin (or wet dock) in the upper tidal estuary. Analyses of artificial radionuclides ((137)Cs and plutonium isotopes), coupled with hydrological and bathymetric data, lead to a precise dating of the sediment cores collected at the two sites. (137)Cs signals originating from global fallout (early 1960s) and from the Chernobyl accident (1986) are identified, but at different levels due to the incomplete nature or variable continuity of the records. Anomalous (238)Pu concentrations found at both sites (1-2 Bq kg(-1)) are attributed to unknown industrial releases originating from upstream. Interpolating (137)Cs sediment activities under the assumption of a constant sediment rate, those releases were dated back to 1975 ± 1, thus providing a local but reliable time-marker. Age models have highlighted a very contrasting sediment filling dynamics in these two sites. This study presents the first sediment record of alpha- and gamma-emitting artificial radionuclides obtained at the outlet of the huge catchment area of the River Seine, over a period covering the last 50 years.

Abundance, diversity and activity of sulfate-reducing prokaryotes in heavy metal-contaminated sediment from a salt marsh in the Medway Estuary (UK).

We investigated the diversity and activity of sulfate-reducing prokaryotes (SRP) in a 3.5-m sediment core taken from a heavy metal-contaminated site in the Medway Estuary, UK. The abundance of SRPs was quantified by qPCR of the dissimilatory sulfite reductase gene ß-subunit (dsrB) and taking into account DNA extraction efficiency. This showed that SRPs were abundant throughout the core with maximum values in the top 50 cm of the sediment core making up 22.4% of the total bacterial community and were 13.6% at 250 cm deep. Gene libraries for dsrA (dissimilatory sulfite reductase α-subunit) were constructed from the heavily contaminated (heavy metals) surface sediment (top 20 cm) and from the less contaminated and sulfate-depleted, deeper zone (250 cm). Certain cloned sequences were similar to dsrA found in members of the Syntrophobacteraceae, Desulfobacteraceae and Desulfovibrionaceae as well as a large fraction (60%) of novel sequences that formed a deep branching dsrA lineage. Phylogenetic analysis of metabolically active SRPs was performed by reverse transcription PCR and single strand conformational polymorphism analysis (RT-PCR-SSCP) of dsrA genes derived from extracted sediment RNA. Subsequent comparative sequence analysis of excised SSCP bands revealed a high transcriptional activity of dsrA belonging to Desulfovibrio species in the surface sediment. These results may suggest that members of the Desulfovibrionaceae are more active than other SRP groups in heavy metal-contaminated surface sediments.