International audience | Our study focused on the removal of pollutants from combined sewer overflow (CSO) using aerated vertical flow wetlands (VFW). Over a 7-months period, a pilot was fed with variable inlet concentrations and hydraulic loading rates of 0.5, 1.0, and 1.5 m3.m-2. Two aeration strategies were tested, intermittent aeration and continuous aeration, and their results were compared. Online measurement of NH4-N and NO3-N helps to balance nitrogen oxidation processes during a feeding event. The average removal rates of TSS, COD, dissolved COD (CODs), and NH4-N were always above 74%. Despite continuous aeration had showed higher oxygen concentration, the percentage of untreated NH4-N leaving the filter was similar in both aeration strategies. Additionally, higher NO3-N outflow loads during continuous aeration may be explained by temperature effect. Ongoing tests aim to reach a better comprehension on nitrogen conversion processes.

Green tides occurrence has increased in coral reefs, yet few reference values have been documented to support bloom management in these ecosystems. Here, we took advantage of recent Ulva green tides that occurred in New Caledonia to (i) identify the elements limiting the growth of Ulva spp. during these blooms; and (ii) validate the use of isotopic markers for identifying sources of nutrients that generated blooms. N/P ratios highlighted a stronger limitation of algae by phosphorus than by nitrogen on sites under oceanic influence, while the proportions of N and P were optimal for algal growth at sites where green tides occurred. Macroalgae highly exposed to sewage water was characterized by higher δ15N than macroalgae collected in areas exposed to synthetic inorganic fertilizers. From these results, we established a new set of threshold values for using δ15N in Ulva species as an indicator of nitrogen source type in coral reefs.

The transport of non-indigenous species in ship's ballast water represents a threat to marine biodiversity. This study is the first on marine bioinvasion in Sub-Saharan Africa. The Port of Douala (PoD), located in the Gulf of Guinea, is experiencing increasing maritime traffic, hence the importance of preventing biological invasions. PoD received ballast water from 41 ports and 20 ecoregions during the study period (2018–2021). We used a biological invasion model and showed that ships from the ports of Antwerp, Durban, Dar es Salaam, Pointe-Noire (Southern Gulf of Guinea) and Dakar (Sahelian Upwelling), with their associated ecoregions present a major invasion risk. Treating ballast water from these ships to IMO D-2 standards could reduce their probability of biological invasion by 97.18, 98.43, 98.80, 98.77 and 98.84 %, respectively. Climate change may also mitigate the risk of biological invasion, particularly for ships in the North Sea ecoregion from the port of Antwerp.

The mid-20th century industrial peak caused severe global lead (Pb) marine contamination. Although Europe initiated Pb emission reduction regulations in the 1980s, the short- and long-term impacts remain unclear. This study investigates the evolution of Pb contamination on the French coast through elemental and isotope analysis in oysters and mussels from the French “Mussel Watch” Program. Observations at 114 monitoring stations over four decades have shown decreasing Pb levels in these bivalve mollusks. In 1988, 95 % exceeded the background reference values; this level had dropped to 39 % by 2021. The Pb isotope ratios in bivalves from eight target sites revealed a reduction in bioaccumulated anthropogenic Pb, albeit without complete elimination. The long residence time of legacy Pb combined with inputs from diffuse urban sources likely explains the persistent presence of anthropogenic Pb on the French coast. This study endorses the importance of continuous biomonitoring to evaluate environmental regulations and policies.

The increasing threats to ecosystems and humans from marine plastic pollution require a comprehensive assessment. We present a plastisphere case study from Reunion Island, a remote oceanic island located in the Southwest Indian Ocean, polluted by plastics. We characterized the plastic pollution on the island's coastal waters, described the associated microbiome, explored viable bacterial flora and the presence of antimicrobial resistant (AMR) bacteria. Reunion Island faces plastic pollution with up to 10,000 items/km2 in coastal water. These plastics host microbiomes dominated by Proteobacteria (80 %), including dominant genera such as Psychrobacter, Photobacterium, Pseudoalteromonas and Vibrio. Culturable microbiomes reach 107 CFU/g of microplastics, with dominance of Exiguobacterium and Pseudomonas. Plastics also carry AMR bacteria including β-lactam resistance. Thus, Southwest Indian Ocean islands are facing serious plastic pollution. This pollution requires vigilant monitoring as it harbors a plastisphere including AMR, that threatens pristine ecosystems and potentially human health through the marine food chain.

It has been established from previous studies that chlorophyll-a surface concentration has been declining in the eastern English Channel. This decline has been attributed to a decrease in nutrient concentrations in the rivers. However, the decrease in river discharge could also be a cause. In our study, rivers outflows and in-situ data have been compared to time series of satellite-derived chlorophyll-a concentrations. Dynamic Linear Model has been used to extract the dynamic and seasonally adjusted trends of several environmental variables. The results showed that, for the 1998–2019 period, chlorophyll-a levels stayed significantly lower than average and satellite images revealed a coast to offshore gradient. Chlorophyll-a concentration of coastal stations appeared to be related to the declining fluxes of phosphate while offshore stations were more related to nitrate-nitrite. Therefore, we can exclude that the climate variability, through river flows alone, has a dominant effect on the decline of chlorophyll-a concentration.

This study addresses the scarcity of evidence on the relationship between benthic communities and coarse-grained sediments in the eastern English Channel. The region's geological history contributes to its predominantly coarse sediment composition. The study employs ternary plots to visualize benthic species' preferences and tolerance for sediment types, revealing their effectiveness. Redundancy Analyses (RDA) and species-level quantile regressions explore the influence of grain size on benthic species distribution. The results indicate a moderate impact of grain size, influenced by hydrodynamics. Estuaries, particularly the Seine Estuary, significantly shape benthic species distribution. Quantile regressions underscore the varied responses of benthic communities along the grain size gradient. The study underscores the importance of considering coarse sediments, offering insights into the complex relationship between benthic communities and sediment characteristics.

Estuaries, vital coastal ecosystems, face growing threats from industrialization. To understand the pace of sedimentary changes and heavy metal pollution at the anthropogenically altered and industrialized Nakdong River Estuary in South Korea, we used sediment coring to reconstruct environmental change. Estuarine dam construction in 1934 shifted the sedimentary system from sand to mud, coinciding with a post-1930s mercury increase due to coal burning. Mercury concentrations in other South Korean regions surged in the 1970s, indicating proximity to emission sources matters. However, most heavy metal levels (Cu, Cd, Zn, Ag) sharply rose in the 1960s and 1970s with regional industrialization. Modern heavy metal concentrations doubled pre-industrial levels, underscoring human activities as the primary driver of Nakdong Estuary environmental changes. This emphasizes the need for a balanced approach to development and environmental preservation.

Conservation of ecosystems is an important tool for climate change mitigation. Seagrasses, mangroves, saltmarshes and other marine ecosystems have particularly high capacities to sequester and store organic carbon (blue carbon), and are being impacted by human activities. Calls have been made to mainstream blue carbon into policies, including carbon markets. Building on the scientific literature and the French voluntary carbon standard, the ‘Label Bas-Carbone’, we develop the first method for the conservation of Posidonia oceanica seagrasses using carbon finance. This methodology assesses the emission reduction potential of projects that reduce physical impacts from boating and anchoring. We show how this methodology was institutionalized thanks to a tiered approach on key parameters including carbon stocks, degradation rates, and decomposition rates. We discuss future needs regarding (i) how to strengthen the robustness of the method, and (ii) the expansion of the method to restoration of seagrasses and to other blue carbon ecosystems.

The St. Lawrence River, one of the world's largest estuaries, drains >25 % of the world's freshwater reserves and is affected by various anthropogenic effluents. Although previous studies reported micro- and nanoplastics contamination in the Estuary and Gulf of St. Lawrence (EGSL), this study provides a first evaluation of macroplastic pollution along the north and south shores of the EGSL. Plastic debris categorization was performed according to the OSPAR protocol completed by polymer identification using Fourier-transform infrared spectroscopy. The EGSL appeared ubiquitously contaminated by plastic debris, dominated by single-use plastics primarily made of polypropylene (28 %), polyethylene (25 %) and polystyrene (17 %). The EGSL shores exhibited a mean contamination level of 0.17 ± 0.11 items/m2 and distance to Montreal significantly influenced the distribution of plastic debris. This study provides an essential baseline for implementing local waste reduction and management actions in the St. Lawrence watershed to reduce plastic pollution.