Département Ressources aquatiques et eau potable

Increasing phosphorus (P) fertilizer use efficiency from bio-based waste products (i.e., recycled amendments) requires promoting a larger proportion of bioavailable P in soil for plant uptake. Therefore, this study aimed to elucidate how recycled amendment P solubility and movement vary when interfaced with soils of contrasting characteristics. Microcosms were created with a fine-mesh screen to incubate recycled amendments (iron-precipitated sewage sludge (sewage), sewage sludge ash (ash), and meat and bone meal (MBM)) with four soils. After 14 or 120 days of incubation, microcosms were destructively sampled. Soil was sliced at the millimetre scale (up to 4 mm) from the interface. Soil P solubility was assessed via water-extractable P (P_w) and labile P (P_lab; resin plus bicarbonate P), while a sequential fractionation isolated changes to the recycled amendment P pool composition. Results indicated that multiple factors influenced the distance P travelled from the recycled amendment-soil interface. First, a greater proportion of recycled amendment P_lab ensured movement passed the interface. For example, soluble soil P increased far beyond the MBM interface after 14 days. Second, soil characteristics dictated whether recycled amendment P remained soluble after leaving the interface. For example, ash P_lab increased and promoted greater travel when incubated with the acidic soil (Orthic Podzol). Finally, time unevenly impacted movement. Sewage P pool composition fluctuated before promoting greater soil transport between the 14- and 120-day incubation. Thus, increasing plant root access to recycled amendment P requires a timed approach that accounts for the physicochemical characteristics of both matrices.

Reactivity-related characterization of dissolved organic matter (DOM) is crucial for mitigating undesirable byproduct formation during ozonation. However, the characterization of DOM remains challenging due to its molecular complexity, especially in distinguishing olefin- and phenol-type moieties, primary O₃ reactive sites responsible for generating carbonyl-containing byproducts. Here, we present a novel approach based on stable oxygen isotope analysis of H₂O₂, a common byproduct of ozone reactions, to differentiate between these two moieties. The natural abundance oxygen isotopic signatures of residual H₂O₂ (δ¹⁸O_H2O2) after ozonation with 13 model compounds (6 olefins and 7 phenols) at pH 3 and 7, and their pH-dependency, Δ¹⁸O_H2O2 (δ¹⁸O_H2O2 (pH 7) – δ¹⁸O_H2O2 (pH 3)), enabled the distinction of olefins and phenols. Olefins exhibited near-zero or positive Δ¹⁸O_H2O2 (0.4–9.0‰), whereas phenols showed negative Δ¹⁸O_H2O2 (−14.2 – −1.6‰). These contrasting trends allowed derivation of an empirical correlation linking Δ¹⁸O_H2O2 to olefinic-phenolic fractions in mixtures, resulting in estimation of molar fractions of the two moieties in DOM isolates. This stable-isotope based approach offers unique mechanistic insights into H₂O₂ formation mechanisms for widespread applications in H₂O₂-generating reactions, as well as for synergistic use with existing DOM characterization techniques.

Groundwater faces increasing pressures from climate change, urbanization, land-use change, and emerging contaminants. To assess current challenges, future strategies, and priorities, the international survey "Hydrogeology: Quo vadis…?" gathered responses from the hydrogeology community across four continents. Key concerns included groundwater contamination, impeded recharge and water availability, insufficient regulation of new chemical substances, climate-related extremes, fragmented governance, and limited data accessibility. Strategic priorities focused on strengthening interdisciplinary cooperation, enhancing monitoring and data integration, ensuring sustainable resource allocation, and improving education and public awareness. However, a persistent gap between goal-setting and implementation emerged, driven by weak enforcement, governance and research silos, and resource constraints. To address this gap, seven possible ways forward are outlined: (1) strengthening implementation and enforcement, including improving legislation to protect groundwater; (2) improving cross-level and cross-sector coordination; (3) building networks; (4) investing in education and public engagement; (5) enhancing data integration; (6) tackling emerging challenges proactively; and (7) cultivating political will with long-term resources. The results provide a benchmark for global hydrogeology perspectives and a practical roadmap to advance more effective groundwater governance and protection.

Marine phytoplankton play a key role in biogeochemical selenium (Se) cycling. By transforming inorganic Se into organic species, many of which remain uncharacterized, they influence Se availability for other organisms and may contribute to Se volatilization. Characterizing organic Se species in phytoplankton is challenging and no standard analytical workflow has been established. Here, we used the marine phytoplankton species Gephyrocapsa huxleyi and Effrenium voratum to systematically assess how cultivation (Se concentrations in the medium), cell harvesting, extraction, and chromatographic parameters influence Se speciation measurements quantitatively (extraction yields, column recoveries) and qualitatively (species distribution), when performed by HPLC-ICP-MS/MS. We show that medium Se concentrations and choice of chromatography had the largest effect on measured Se speciation. The two phytoplankton showed marked differences in intracellular Se speciation, likely reflecting a dissimilar selenometabolism. Resolving these speciation differences was only possible with select chromatographies (e.g. anion-exchange but not mixed-mode). Both phytoplankton also showed changes to intracellular Se speciation when grown in Se-enriched media in comparison with near-natural concentrations. The selection of Se concentrations in the medium is therefore crucial for studying Se metabolites, e.g. under environmentally relevant conditions. We recommend extraction–chromatography workflows tailored to specific experimental needs in phytoplankton Se research, providing a framework for future studies to uncover further effects these organisms have on biogeochemical Se cycling.