Extreme hydrological regimes of a small urban river: impact on trace element partitioning, enrichment and fluxes.

The input of trace elements from a small urban river (Las River, Toulon, France) located on the northern Mediterranean coast was studied during both base flow and flood events. A 2-year monitoring period of water flow and suspended particulate matter (SPM) showed a typical Mediterranean hydrological regime: a strong increase in water flow and SPM during short flood periods. During the flood event, an up to 2-fold increase in dissolved trace element (DTM) concentrations and particulate trace element content in SPM (PTM) was observed compared to the baseline discharge. The enrichment factor of elements in the SPM ranges from low or moderate for Co, Ni and Cr (1.0-4.7) to extremely high for Cd (157). However, the enrichment factors decrease from base flow to flood, indicating a dilution effect with a large yield of weathering particles with higher particle size. The most significant total trace element loading occurred during flood, ranging from 78% for As and Ni to 91% for Pb, while PTM loading during flood ranged from 35% for As to 77% for Pb. The specific dissolved fluxes during the flood are significantly higher for Pb, Cu and Zn than in the surrounding rivers, indicating specificity in the catchment (lithology). This study shows the importance of monitoring the transport of pollutants through small urban rivers and their potential impact on the coastal region, especially when they enter small and closed bays, as a receiving pool.

Elutriate preparation affects embryo development test with Paracentrotus lividus: An in-depth study on the differences between two protocols and three different sediment/water mixing times.

Coastal areas are under continuous and increasing pressure from different human activities. A mixture of contaminants (e.g. hydrocarbons, pesticides, persistent organic pollutants (POPs), emerging contaminants, and others), originating mainly from populated, industrialised and agricultural areas, can reach the marine environment through different means such as wastewater discharge, soil runoffs, leaching from agriculture, and volatilisation/deposition. In this context, marine sediments have increasingly been considered repositories for a variety of pollutants that can accumulate and be stored for long periods, acting as a secondary source of contaminants during subsequent dredging operation or vessel manoeuvring. Chemical and ecotoxicological analyses of sediments are routinely conducted to evaluate the potential hazard/risk to the environment, either on bulk sediment or elutriate. In general, sediment elutriates are commonly prepared according to ASTM Guide even if alternative protocols are proposed by USACE for the various condition that they have to represent. The goal of the present study was to determine if the toxicological properties of ASTMprepared elutriates are comparable to those obtained from the USACE protocol. Sediment coming from 3 harbours (Olbia, Cagliari, and Toulon), as part of the "Se.D.Ri.Port" Interreg Project, were processed to obtain elutriates according to ASTM Guide and USACE Dredging Elutriate protocol and tested with the sea urchin Paracentrotus lividus embryo development test. Moreover, the significance of different stirring times of water/sediment mixture (1 h, 3 h, and 24 h) was tested with both the ASTM and USACE protocol. In addition to the biological analysis, for each sediment sample, heavy metals concentration, granulometry, and organic matter were determined. Even if for the ports of Toulon and Cagliari, the ASTM and USACE elutriates showed comparable results with P. lividus bioassay, for the port of Olbia the two protocols showed different criticalities. Preliminary results show that for the site Olbia elutriates prepared with the USACE protocol resulted in higher toxicity than elutriates obtained with ASTM (p < 0.001). In conclusion, differences in preparation protocols appear to be significant and can lead to different results in biological testing. To overcome this problem and to obtain more reliable evaluations of risk to the environment, standardisation and regulation must be the next goals in sediment management procedure.

Cd transfers during marine sediment resuspension over short and long-term period: Associated risk for coastal water quality.

Cadmium (Cd) is a highly toxic metal, regularly monitored uniformly for water quality across Europe, but scarcely for sediments. This study was designed to compare the kinetics of Cd remobilization and the amplitude of its transfers with different marine sediments. The results showed a highly reproducible transfer kinetics. Dissolved Cd was strongly and quickly removed from the dissolved phase (from 5 min up to 7 h). Then, the dissolved Cd concentration increased progressively to reach a maximal value after two weeks of mixing. The influence of the resuspension intensity representing light wind-induced resuspension up to dredging operations was observed after 2 weeks. The intensity of the sediment resuspension clearly impacted the amplitude of Cd remobilization, dissolved Cd ranging from a few ngL-1 to few hundreds of ngL-1, exceeding the maximal dissolved Cd concentration accepted by the European Union Water Framework Directive (WFD-2008/105 32/EC).

Integration of spatio-temporal variations of surface metabolomes and epibacterial communities highlights the importance of copper stress as a major factor shaping host-microbiota interactions within a Mediterranean seaweed holobiont.

BACKGROUND: Although considered as holobionts, macroalgae and their surface microbiota share intimate interactions that are still poorly understood. Little is known on the effect of environmental parameters on the close relationships between the host and its surface-associated microbiota, and even more in a context of coastal pollutions. Therefore, the main objective of this study was to decipher the impact of local environmental parameters, especially trace metal concentrations, on an algal holobiont dynamics using the Phaeophyta Taonia atomaria as a model. Through a multidisciplinary multi-omics approach combining metabarcoding and untargeted LC-MS-based metabolomics, the epibacterial communities and the surface metabolome of T. atomaria were monitored along a spatio-temporal gradient in the bay of Toulon (Northwestern Mediterranean coast) and its surrounding. Indeed, this geographical area displays a well-described trace metal gradient particularly relevant to investigate the effect of such pollutants on marine organisms. RESULTS: Epibacterial communities of T. atomaria exhibited a high specificity whatever the five environmentally contrasted collecting sites investigated on the NW Mediterranean coast. By integrating metabarcoding and metabolomics analyses, the holobiont dynamics varied as a whole. During the occurrence period of T. atomaria, epibacterial densities and α-diversity increased while the relative proportion of core communities decreased. Pioneer bacterial colonizers constituted a large part of the specific and core taxa, and their decrease might be linked to biofilm maturation through time. Then, the temporal increase of the Roseobacter was proposed to result from the higher temperature conditions, but also the increased production of dimethylsulfoniopropionate (DMSP) at the algal surface which could constitute of the source of carbon and sulfur for the catabolism pathways of these taxa. Finally, as a major result of this study, copper concentration constituted a key factor shaping the holobiont system. Thus, the higher expression of carotenoids suggested an oxidative stress which might result from an adaptation of the algal surface metabolome to high copper levels. In turn, this change in the surface metabolome composition could result in the selection of particular epibacterial taxa. CONCLUSION: We showed that associated epibacterial communities were highly specific to the algal host and that the holobiont dynamics varied as a whole. While temperature increase was confirmed to be one of the main parameters associated to Taonia dynamics, the originality of this study was highlighting copper-stress as a major driver of seaweed-epibacterial interactions. In a context of global change, this study brought new insights on the dynamics of a Mediterranean algal holobiont submitted to heavy anthropic pressures. Video abstract.

Trace Metal Contamination Impacts Predicted Functions More Than Structure of Marine Prokaryotic Biofilm Communities in an Anthropized Coastal Area.

Trace metal (TM) contamination in marine coastal areas is a worldwide threat for aquatic communities. However, little is known about the influence of a multi-chemical contamination on both marine biofilm communities' structure and functioning. To determine how TM contamination potentially impacted microbial biofilms' structure and their functions, polycarbonate (PC) plates were immerged in both surface and bottom of the seawater column, at five sites, along strong TM contamination gradients, in Toulon Bay. The PC plates were incubated during 4 weeks to enable colonization by biofilm-forming microorganisms on artificial surfaces. Biofilms from the PC plates, as well as surrounding seawaters, were collected and analyzed by 16S rRNA amplicon gene sequencing to describe prokaryotic community diversity, structure and functions, and to determine the relationships between bacterioplankton and biofilm communities. Our results showed that prokaryotic biofilm structure was not significantly affected by the measured environmental variables, while the functional profiles of biofilms were significantly impacted by Cu, Mn, Zn, and salinity. Biofilms from the contaminated sites were dominated by tolerant taxa to contaminants and specialized hydrocarbon-degrading microorganisms. Functions related to major xenobiotics biodegradation and metabolism, such as methane metabolism, degradation of aromatic compounds, and benzoate degradation, as well as functions involved in quorum sensing signaling, extracellular polymeric substances (EPS) matrix, and biofilm formation were significantly over-represented in the contaminated site relative to the uncontaminated one. Taken together, our results suggest that biofilms may be able to survive to strong multi-chemical contamination because of the presence of tolerant taxa in biofilms, as well as the functional responses of biofilm communities. Moreover, biofilm communities exhibited significant variations of structure and functional profiles along the seawater column, potentially explained by the contribution of taxa from surrounding sediments. Finally, we found that both structure and functions were significantly distinct between the biofilm and bacterioplankton, highlighting major differences between the both lifestyles, and the divergence of their responses facing to a multi-chemical contamination.

Characterization of the submarine disposal of a Bayer effluent (Gardanne alumina plant, southern France): I. Size distribution, chemical composition and settling rate of particles forming at the outfall.

The submarine discharge of the high pH clarified Bayer effluent of the Gardanne alumina plant (Marseille region, France) leads to the formation of concretions at the outfall 324 m underwater and to a plume of white particles. The bulk chemical composition of the concretions has been determined by SF-ICP-MS. Mg and Al are the major elements measured with concentrations of a few hundred mg g-1. Ca and S are also found at concentrations in the range of mg g-1. Among the measured trace elements there is a specific interest in As and V because of environmental concerns pointed out by regulation authorities. Their concentrations are of tens to thousands µg g-1, respectively. Concentrations of the other elements are in the range of a few ng g-1 to few hundreds µg g-1. In order to constrain the dispersion of particles in the environment and to understand how chemical elements can be scavenged from or released to seawater, the size distribution of particles composing the concretions has been measured by settling rate experiments and, for each size class of particles, their chemical composition has been determined. For example, As and V are mainly associated to particles with mean diameters between 15.6 and 63 µm and settling rates around 96 m d-1. Overall, all the main elements (Mg, Al, Ca, S) composing concretions are associated to this size class of particles which represents 53-60% of the total concretion mass.

Impacts of copper and lead exposure on prokaryotic communities from contaminated contrasted coastal seawaters: the influence of previous metal exposure.

Our understanding of environmental factors controlling prokaryotic community is largely hampered by the large environmental variability across spatial scales (e.g. trace metal contamination, nutrient enrichment and physicochemical variations) and the broad diversity of bacterial pre-exposure to environmental factors. In this article, we investigated the specific influence of copper (Cu) and lead (Pb) on prokaryotic communities from the uncontaminated site, using mesocosm experiments. In addition, we studied how pre-exposure (i.e. life history) affects communities, with reference to previous metal exposure on the response of three prokaryotic communities to similar Cu exposition. This study showed a stronger influence of Cu contamination than Pb contamination on prokaryotic diversity and structure. We identified 12 and 34 bacterial families and genera, respectively, contributing to the significant differences observed in community structure between control and spiked conditions. Taken altogether, our results point toward a combination of direct negative responses to Cu contamination and indirect responses mediated by interaction with phytoplankton. These identified responses were largely conditioned by the previous exposure of community to contaminants.

Long-term monitoring emphasizes impacts of the dredging on dissolved Cu and Pb contamination along with ultraplankton distribution and structure in Toulon Bay (NW Mediterranean Sea, France).

A long-term monitoring during dredging and non-dredging periods was performed. Total and dissolved Cu and Pb concentrations, DGT-labile Pb, ultraphytoplankton abundance and structure were monitored at four sites: dredging site, dumping site (inside/outside of a geotextile bag) and reference site. During the reference period (non-dredging), an increasing contamination in Pb, Cu and a progressive shift from Synechococcus to photosynthetic picoeukaryotes dominance was observed from reference to dumping site. Pb concentrations were significantly higher during dredging period, pointing out sediment resuspension as Pb major source of contamination. Unlike Pb, Cu concentrations were not statistically different during the two periods. Dredging period did not impact on ultraphytoplankton abundance and structure but influence heterotrophic prokaryotes abundance. Sediment resuspension is therefore a major driver of chemical and biological qualities in Toulon Bay. Furthermore, although the geotextile bag reduces particulate transport of the dredged sediment, the transport in the dissolved phase remains a major problem.

Changes in Bacterioplankton Communities Resulting From Direct and Indirect Interactions With Trace Metal Gradients in an Urbanized Marine Coastal Area.

Unraveling the relative importance of both environmental conditions and ecological processes regulating bacterioplankton communities is a central goal in microbial ecology. Marine coastal environments are among the most urbanized areas and as a consequence experience environmental pressures. The highly anthropized Toulon Bay (France) was considered as a model system to investigate shifts in bacterioplankton communities along natural and anthropogenic physicochemical gradients during a 1-month survey. In depth geochemical characterization mainly revealed strong and progressive Cd, Zn, Cu, and Pb contamination gradients between the entrance of the Bay and the north-western anthropized area. On the other hand, low-amplitude natural gradients were observed for other environmental variables. Using 16S rRNA gene sequencing, we observed strong spatial patterns in bacterioplankton taxonomic and predicted function structure along the chemical contamination gradient. Variation partitioning analysis demonstrated that multiple metallic contamination explained the largest part of the spatial biological variations observed, but DOC and salinity were also significant contributors. Network analysis revealed that biotic interactions were far more numerous than direct interactions between microbial groups and environmental variables. This suggests indirect effects of the environment, and especially trace metals, on the community through a few taxonomic groups. These spatial patterns were also partially found for predicted bacterioplankton functions, thus indicating a limited functional redundancy. All these results highlight both potential direct influences of trace metals contamination on coastal bacterioplankton and indirect forcing through biotic interactions and cascading.