Mangrove ecosystems are known to play a key role in the global carbon cycle, due to their productivity and their ability for carbon sequestration both in the biomass and in the soil. In the latter, various geochemical processes lead to the production of dissolved organic matter (DOM) that can be exported through tidal pumping and then constitute an important source of organic carbon for adjacent ecosystems. DOM characteristics, and their variabilities, within mangrove soils depend on several factors, including the mangrove species, yet these variations and their origin still need to be precisely constrained. This study examined DOM sources in soils of a carbonate atoll mangrove (Ouvéa, New Caledonia), focusing on two tree species, Rhizophora apiculata and Bruguiera gymnorhiza, at different growth stages. We analysed porewater properties and DOM optical characteristics through spectroscopic and EEM-PARAFAC methods. Our results indicate distinct TOC and DOC concentrations across species, with mature B. gymnorhiza soils showing the highest TOC content (~ 30%) but the lowest DOC content (32 mg L−1). These differences seem not to be directly related to site physicochemical conditions (redox, pH, salinity) but may rather reflect differences in DOM sources and production, notably due to different symbiotic relationships with mycorrhizal fungi, which influence microbial activity and organic matter diagenesis. DOM absorbance patterns also varied significantly between species: Beneath R. apiculata, DOM had higher protein-like and fulvic-like fluorescence, indicating fresher organic matter, while beneath B. gymnorhiza, especially in mature stands, DOM was more humified, suggesting older OM because of a possible long-term accumulation due to the basin-like morphology of this site.

The growing popularity of biofuels has resulted in the generation of large amounts of biofuel ash, which is rich in nutrients. Biofuel ash is an excellent source of raw material in a circular economy. However, often biofuel ash is contaminated with heavy metals. Therefore, it is important to assess and monitor the chemical composition of biofuel ash to best utilize the potential of it. Study represents six years of data on biofuel ash collected from various boilers across Lithuania. It presents the chemical composition of biofuel ash, an environmental risk assessment, and predictive modelling was performed to estimate the doubling time of background concentrations of heavy metals in soil. The study results showed that concentrations of inorganic pollutants in biofuel ash vary significantly from year to year. When assessing the potential use for biofuel ash in agriculture and forestry, it was found that about 30 % of biofuel ash samples had Cd concentrations exceeding the maximum allowable limits for use in agriculture, more than 50 % – forestry. The Cr concentration exceeded in more than 50 % of tested samples for use in agriculture, about in 20 % – forestry. The estimated cumulative potential ecological risk to the environment is very high, which is determined by the high (Cd) or medium (Hg, Cu) risk of individual metals. Also, after evaluating the 6-year results, it was determined that the use of biofuel ash is limited by Cd, Zn since the background level of these metals in the soil would double most likely after 17 and 27 years.

Abstract The Tara Microplastics mission was conducted for 7 months to investigate plastic pollution along nine major rivers in Europe—Thames, Elbe, Rhine, Seine, Loire, Garonne, Ebro, Rhone, and Tiber. An extensive suite of sampling protocols was applied at four to five sites on each river along a salinity gradient from the sea and the outer estuary to downstream and upstream of the first heavily populated city. Biophysicochemical parameters including salinity, temperature, irradiance, particulate matter, large and small microplastics (MPs) concentration and composition, prokaryote and microeukaryote richness, and diversity on MPs and in the surrounding waters were routinely measured onboard the French research vessel Tara or from a semi-rigid boat in shallow waters. In addition, macroplastic and microplastic concentrations and composition were determined on river banks and beaches. Finally, cages containing either pristine pieces of plastics in the form of films or granules, and others containing mussels were immersed at each sampling site, 1 month prior to sampling in order to study the metabolic activity of the plastisphere by meta-OMICS and to run toxicity tests and pollutants analyses. Here, we fully described the holistic set of protocols designed for the Mission Tara Microplastics and promoted standard procedures to achieve its ambitious goals: (1) compare traits of plastic pollution among European rivers, (2) provide a baseline of the state of plastic pollution in the Anthropocene, (3) predict their evolution in the frame of the current European initiatives, (4) shed light on the toxicological effects of plastic on aquatic life, (5) model the transport of microplastics from land towards the sea, and (6) investigate the potential impact of pathogen or invasive species rafting on drifting plastics from the land to the sea through riverine systems.

Microplastics provide a persistent substrate that can facilitate microbial transport across ecosystems. Since most marine plastic debris originates from land and reaches the ocean through rivers, the potential dispersal of freshwater bacteria into the sea represents a significant concern. To address this question, we explored the plastisphere on microplastic debris (MPs) and on pristine microplastics (pMPs) as well as the bacteria living in surrounding waters, along the river-sea continuum in nine major European rivers sampled during the 7 months of the Tara Microplastics mission. In both marine and riverine waters, we found a clear niche partitioning among MPs and pMPs plastispheres when compared to the bacteria living in the surrounding waters. Across this large dataset, we found that bacterial community structure varied along the river salinity gradient, with plastisphere communities exhibiting almost complete segregation between freshwater and marine ecosystems. We also described for the first time a virulent human pathogenic bacterium (Shewanella putrefaciens), capable of infecting human intestinal epithelial cells, detected exclusively on MPs in riverine environments. Our findings indicate that salinity is the main driver of plastisphere communities along the river-to-sea continuum, helping to mitigate the risk of pathogens transfer between freshwater and marine systems.

Key learnings from the collective scientific assessment on the effects of plant protection products on biodiversity and ecosystem services

Background. Hydrothermal vent fields are habitats to a diverse array of benthic organisms, including several nematode species, which represent a significant portion of the biodiversity in these environments. Despite their ecological importance, most research on hydrothermal vents has focused on macro-invertebrates. As a result, vent nematode biodiversity remains largely unexplored, especially in peripheral and inactive structures, underscoring the need for further investigation. A sampling program conducted in 2017 and 2018 along a gradient of venting activity led to the collection of a number of Draconematidae species in various habitats. In this paper, we  introduce Dracograllus miguelitus sp. nov., the first species of the genus described at a hydrothermal vent field, sampled from a visually inactive sulphide structure. Methods. The samples were collected at the Lucky Strike vent field, on the Mid-Atlantic Ridge, using the suction sampler of the Remotely Operated Vehicle Victor6000. Specimens were retrieved from an edifice covered by a black layer of manganese oxy-hydroxides, with no local visible hydrothermal activity, at a depth of 1,649 m depth.  Samples were sieved on a 32 µm mesh onboard, sorted and, for nematodes, identified to species level back in the lab. Fluorescent images were obtained using the ApoTome Fluorescence Microscope Module, and 3D observations were possible through the depth change method. Results. We established D. miguelitus sp. nov. as a new species based on the combination of the following characters: four cephalic adhesive tubes (CATs), an elongated loop-shaped amphid with varying branch sizes between males and females, and a circular amphid in juveniles. Additionally, females display a minute setae emerging from the vulvar aperture. In males, the posterior adhesive tubes (PATs) are arranged in four longitudinal rows: two sublateral rows, each containing 10-12 PATs, and two subventral rows, consisting of 10 PATs in each. In females, sublateral and subventral rows with 13 PATs each. So far, D. miguelitus sp. nov. is the first species of the genus to be described from a hydrothermal environment and the deepest one. Beyond the formal description of this new species, we provide ecological and taxonomic backgrounds on Draconematidae at hydrothermal vents, with insights into the genus distribution, biogeography, and nomenclatural issues. Conclusion. This discovery contributes to the knowledge of Draconematidae biodiversity, and highlights the importance to investigate nematode communities at species-level, data that is often missing at vent studies. Additionally, it underscores the significance of preserving inactive hydrothermal habitats, which are threatened by deep-sea mining activities. | Contexte. Les champs hydrothermaux abritent une diversité remarquable d’organismes benthiques, incluant plusieurs espèces de nématodes, qui représentent une part importante de la biodiversité de ces environnements. Malgré leur rôle écologique, la majorité des recherches sur les sources hydrothermales se sont concentrées sur les macro-invertébrés. Par conséquent, la biodiversité des nématodes de ces systèmes reste largement méconnue, en particulier dans les structures périphériques et inactives, soulignant la nécessité d’investigations supplémentaires. Un programme d’échantillonnage mené en 2017 et 2018 le long d’un gradient d’activité hydrothermale a permis la collecte de plusieurs espèces de Draconematidae dans divers habitats. Dans cet article, nous présentons Dracograllus miguelitus sp. nov., la première espèce du genre décrite dans un champ hydrothermal, collectée sur une structure de sulfures visuellement inactive. Méthodes. Les échantillons ont été récoltés sur le site hydrothermal Lucky Strike, situé sur la dorsale médio-atlantique, à l’aide du système d’aspiration du véhicule téléopéré Victor6000. Les spécimens proviennent d’un édifice recouvert d’une couche noire d’oxydes et d’oxyhydroxydes de manganèse, sans activité hydrothermale visible localement, à une profondeur de 1 649 m. Les échantillons ont été tamisés à bord sur une maille de 32 µm, triés, puis les nématodes ont été identifiés au niveau spécifique au laboratoire. Des images fluorescentes ont été obtenues à l’aide du module de microscope à fluorescence ApoTome, et des observations 3D ont été réalisées par la méthode de variation de profondeur. Résultats. D. miguelitus sp. nov. a été définie comme une nouvelle espèce sur la base des caractères suivants : quatre tubes adhésifs céphaliques (CATs), un amphide en boucle allongée avec des branches de tailles différentes chez les mâles et les femelles, et un amphide circulaire chez les juvéniles. Les femelles présentent également une soie minuscule émergeant de l’orifice vulvaire. Chez les mâles, les tubes adhésifs postérieurs (PATs) sont disposés en quatre rangées longitudinales : deux rangées sublatérales, contenant chacune 10 à 12 PATs, et deux rangées subventrales, comportant 10 PATs chacune. Chez les femelles, les rangées sublatérales et subventrales comptent chacune 13 PATs. À ce jour, D. miguelitus sp. nov. est la première espèce du genre décrite dans un environnement hydrothermal, et la plus profonde connue. En plus de la description formelle de cette nouvelle espèce, nous fournissons des éléments écologiques et taxonomiques sur les Draconematidae des sources hydrothermales, ainsi que des données sur la distribution, la biogéographie et des considérations nomenclaturales du genre. Conclusion. Cette découverte enrichit les connaissances sur la biodiversité des Draconematidae et souligne l’importance d’étudier les communautés de nématodes à l’échelle spécifique, un niveau d’information souvent négligé dans les études hydrothermales. Elle met également en évidence l’importance de préserver les habitats hydrothermaux inactifs, menacés par les activités d’exploitation minière en haute mer. | Contexto. Os campos hidrotermais são habitats que abrigam uma grande diversidade de organismos bentônicos, incluindo diversas espécies de nematódeos, que representam uma parte significativa da biodiversidade nesses ambientes. Apesar de sua importância ecológica, a maior parte das pesquisas em fontes hidrotermais tem se concentrado nos macroinvertebrados. Como resultado, a biodiversidade de nematódeos nesses sistemas permanece amplamente inexplorada, especialmente em estruturas periféricas e inativas, destacando a necessidade de investigações adicionais. Um programa de amostragem realizado em 2017 e 2018 ao longo de um gradiente de atividade hidrotermal permitiu a coleta de diversas espécies da família Draconematidae em diferentes habitats. Neste artigo, apresentamos Dracograllus miguelitus sp. nov., a primeira espécie do gênero descrita em um campo hidrotermal, coletada em uma estrutura de sulfetos visualmente inativa. Métodos. As amostras foram coletadas no campo hidrotermal Lucky Strike, localizado na Dorsal Mesoatlântica, utilizando o sistema de sucção do Veículo Operado Remotamente Victor6000. Os espécimes foram obtidos em um edifício coberto por uma camada preta de óxidos e oxi-hidróxidos de manganês, sem atividade hidrotermal visível localmente, a uma profundidade de 1.649 metros. As amostras foram peneiradas a bordo com malha de 32 µm, triadas e, no caso dos nematódeos, identificadas em nível de espécie no laboratório. Imagens fluorescentes foram obtidas com o módulo de microscopia de fluorescência ApoTome, e observações tridimensionais foram realizadas por meio da técnica de variação de profundidade. Resultados. D. miguelitus sp. nov. foi estabelecida como uma nova espécie com base na combinação dos seguintes caracteres: quatro tubos adesivos cefálicos (CATs), um anfídeo em forma de alça alongada com ramificações de tamanhos diferentes entre machos e fêmeas, e um anfídeo circular nos juvenis. As fêmeas apresentam ainda uma ceta diminuta emergindo da abertura vulvar. Nos machos, os tubos adesivos posteriores (PATs) estão dispostos em quatro fileiras longitudinais: duas sublaterais, com 10 a 12 PATs cada, e duas fileiras subventrais, com 10 PATs cada. Nas fêmeas, as fileiras sublaterais e subventrais contêm 13 PATs cada. Até o momento, D. miguelitus sp. nov. é a primeira espécie do gênero descrita em um ambiente hidrotermal, além de ser a mais profunda registrada. Para além da descrição formal da nova espécie, fornecemos informações ecológicas e taxonômicas sobre os Draconematidae em fontes hidrotermais, incluindo dados sobre a distribuição do gênero, sua biogeografia e aspectos nomenclaturais. Conclusão. Esta descoberta contribui para o conhecimento da biodiversidade dos Draconematidae e destaca a importância de investigar comunidades de nematódeos em nível específico, uma informação frequentemente ausente em estudos hidrotermais. Além disso, ressalta a relevância da preservação de habitats hidrotermais inativos, que estão ameaçados por atividades de mineração em águas profundas.