Assessing the composition and origin of atmospheric particles is crucial, as their environmental impacts are directly influenced by their physicochemical properties. This study proposes a new selective sequential extraction (SSE) protocol, designed to investigate the reactivity of aerosol particles and to serve as a preparatory step for measuring Sr-Nd-Pb isotopic signatures in dust, three well-recognized tracers of dust sources. Although sequential extraction methods are increasingly used, their performance when applied to complex, real-world aerosol mixtures remain insufficiently constrained. To this end, the SSE procedure was applied to a series of reference materials (rocks, sediments), pure phases (ash, carbonates), and tested on aerosols collected during a dust event. Our results demonstrate that the protocol effectively separates and characterizes each aerosol fraction while preserving the silicate matrix of dust, with overall mass recoveries exceeding 72%. The water-soluble fraction accounts for up to similar to 41% of total particle mass, containing sea salts and highly soluble elements from ash particles. The acid-soluble fraction comprises up to similar to 18% of the mass, including anthropogenic particles, carbonates, and solubilized elements from more refractory ash particles. Such conclusions will be diagnostic for studies focusing on aerosol samples, as they aim to mimic environmentally relevant processes. By quantifying and interpreting elemental release during chemical leaching, this study provides clear insights into aerosol composition and associated element solubility. The second key objective is to assess the robustness of Sr-Nd-Pb isotopic proxies in fingerprinting dust sources. Specifically designed to minimize analytical biases and to establish specific rules for adherence, our protocol consistently preserves the initial Sr-Nd-Pb radiogenic isotopic signatures from sources in the dust record.

The stable isotope ratios of hydrogen (δ2H) and oxygen (δ18O) are useful for studying ecohydrological dynamics in forests. However, most isotope-based eco-hydrological studies are limited to single sites, resulting in a lack of large-scale isotope data for understanding tree water uptake. Here, we provide a first systematic isotope dataset for soil and stem xylem water collected during two pan-European sampling campaigns at 40 beech (Fagus sylvatica), spruce (Picea abies), or mixed beech-spruce forest sites in spring and summer 2023 (https://doi.org/10.16904/envidat.542, Lehmann et al., 2024). The dataset is complemented by additional site-, soil-, and tree-specific metadata. The samples and metadata were collected by different researchers across Europe following a standardized protocol. Soil samples were taken at up to 5 depths (ranging from 0 to 90 cm) and stem xylem samples from the trunks of three beech and/or spruce trees per site. All samples were sent to a single laboratory, where all analytical work was conducted. Water was extracted using cryogenic vacuum distillation and analyzed with an isotope laser spectrometer. Additionally, a subset of the samples was analyzed with an isotope ratio mass spectrometer. Data quality checks revealed a high mean total extraction efficiency, mean water amount (>1 mL), accuracy, and precision. The isotopic signature of soil and stem xylem water varied as a function of the geographic origin and changed from spring to summer across all sites. While δ2H and δ18O were strongly correlated, the soil water data plotted closer to the Global Meteoric Water Line (GMWL) than the stem xylem water. Specifically, the δ2H values of the xylem water were more enriched than those of the soil water, leading to a systematic deviation from the GMWL. Isotopic enrichment of the stem xylem water at mixed forest sites was larger for spruce trees than for beech trees. This dataset is particularly useful for large-scale studies on plant water use, ecohydrological model testing, and isotope mapping across Europe.

Wildfires represent an increasing forcing that can strongly affect water quality by enhancing the mobility of trace metals. This effect is expected to be of particular concern in metal-rich environments, such as ultramafic settings. However, it can also be marked in wetlands through the fire-driven formation of Acid Sulfate Soils (ASS). Beyond concerns regarding post-fire trace metal mobility towards freshwater systems in ultramafic wetlands, these considerations raise the question of the geochemical reactions that drive trace metal dynamics in such a context. The present study contributes to addressing this question by characterizing the water chemistry along a flow path extending from a burned doline to a downstream drinking water catchment (DWC) in the ultramafic context of Ile des Pins (New Caledonia). The crystal-chemistry and molecular-level speciation of nickel in the Gleysols of the burned doline were also investigated using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and synchrotron-derived X-ray absorption spectroscopy (XAS). The results obtained revealed exceptionally high post-fire aqueous nickel concentrations at the doline and downstream DWC (i.e., 370 mg/L and 4 mg/L, respectively, compared with the WHO and EU guidelines of 0.07 mg/L and 0.02 mg/L). These high concentrations resulted from the wildfire-induced transformation of the studied Gleysols into ASS through a multi-step scenario involving (1) oxidation of Ni-bearing pyrite [(Ni, Fe)S2) and millerite (NiS) following enhanced O2 diffusion at depth, (2) water acidification upon sulfide minerals oxidation and (3) acidic dissolution of Ni-bearing chrysotile [(Ni, Mg)3Si2O5(OH)4)]. This reaction sequence generated large amounts of dissolved nickel, magnesium and sulfate that further reacted to precipitate Ni-hexahydrite [(NixMg1−x)SO4.6H2O)] upon water evaporation. Owing to its high solubility and major contribution to Ni hosting in the surface horizons of the Gleysols (i.e., 40–50

Manufactured infrastructures of urban areas, including buildings and roads, are contributors of solid particles to the environment due to wear processes and further weathering. Mineral dusts produced by such mechanisms are transported by air or water across urban compartments until they accumulate in surrounding natural and artificial sediment reservoirs, mixing with other minerals of geogenic sedimentary origin. With the expansion of artificialized urban surfaces over time, the contribution of urban-sourced minerals is expected to increase in sediment fluxes, thus taking an increasing importance in biogeochemical cycles. In this study, we postulate that mineral particles emitted from specific man-made materials could be traced in different compartments of urban environments on the basis of their mineralogical signature. Such identified urban mineralogical components could then serve as useful markers to monitor urbanization wear processes and subsequent emprise of urbanization at the regional scale. Here, we have analyzed a collection of urban samples, which comprises urban dusts, road sediment deposits, suspended particulate matter from the Seine and Orge rivers near Paris, and sediments accumulating in stormwater basins along high traffic roads in the Paris region (N118, N104). In almost all of the solid samples studied (n = 34), whose sampling span over a ten-year period, we show by powder X-ray diffraction (XRD) the presence of minerals belonging to the amphibole group, which are necessarily derived from human activities since these minerals do not belong to the Parisian sedimentary basin. Detailed analysis of a mineral pellet embedded in bitumen of road treads sampled in a Paris street by analytical electron microscopies and Rietveld refinement analysis of powder XRD pattern show that a ferro-magnesio-actinolite is a major constituent (17 wt%) of this road material. Further analysis of an amphibole grain in a road dust sample by single crystal X-ray diffraction also points to such FeMg-actinolite of Ca2.15Mg2.44Fe2.56Si8O22(OH)2 composition. Other samples collected in the vicinity of areas subjected to road water runoff also contain amphibole minerals of close crystal-chemical composition to this FeMg-actinolite, likely designating road aggregates as sources of amphiboles in our broad set of samples. A large distribution of sizes was observed for amphibole particles using electron microscopy, from massive (100-10 mu m) to micrometric packages of elongated mineral particles, likely produced by cleavage of massive particles. The presence of micrometric minerals with elongated fiber habit raises questions about public exposure to such urban dusts. This amphibole signature is also detected in samples of river suspended particulate matter from strongly artificialized urban areas, including in a punctual sample collected in the Seine River, which emphasizes the pervasive occurrence of such minerals in this urban environment. Additionally, the presence of amphibole is suggested by X-ray diffraction on a sample taken on a building roof, which calls for a quantitative investigation of amphibole transport pathways, including air transport, in urban areas. Finally, we propose that this amphibole mineralogical pattern could be used as a mineralogical tracer of city wear and urbanization influence on sedimentary fluxes produced by urban materials.

Lateritic profiles are natural archives recording the weathering history in the tropics over million-year time-scales. This study combines oxygen, hydrogen, and silicon isotope data with mineralogical, geochronological, and geochemical analyses of lateritic secondary mineral assemblages to constrain the environmental and climatic conditions prevailing in the central Amazon Basin during the Cenozoic. The studied lateritic profile was developed over the sedimentary succession of the Alter do Chao Formation in Manaus, Brazil. Three distinct weathering episodes were identified, each constrained by (U-Th)/He and EPR ages. Dated to the Oligocene, the earliest (Oligocene) and long-lasting (duration >10 Ma) weathering episode involves the formation of well-ordered kaolinites through in situ chemical weathering of parent minerals under well-drained conditions, indicative of a tropical climate with restricted seasonality. The second episode, occurring in the mid-Miocene (similar to 16 +/- 3 Ma), involves the formation of a ferruginous duricrust. Most probably resulting from lateral iron migration and precipitation at the oxidizing front of an oscillating water table, the duricrust developed in a context of rising sea levels. The third episode, during the Upper Miocene (similar to 10 Ma), led to the replacement of the kaolinite initially precipitated at the top of the profile by lower-crystallinity kaolinite formed at faster kinetics. This episode coincides with the final phase of the Andean uplift and the onset of the transcontinental Amazon River, reflecting enhanced water drainage under a "monsoon-type" climate.

Artificial reservoirs significantly alter the natural transport of suspended particulate matter (SPM) from rivers to oceans, thereby reshaping the global carbon cycle through changes in particulate organic carbon (POC) dynamics over decadal to millennial timescales. Here, we investigate dam-induced perturbation of POC composition, transport, and fate within the Changjiang (CJ) River basin in response to the operation of cascade mega-reservoirs (CMRs) along the Jinshajiang (JSJ) in the upper CJ. The CMRs have introduced new perturbations to SPM and POC delivery, compounding the effects of the Three Gorges Dam (TGD). We analyzed elemental, stable, and radiogenic isotopic compositions of POC, as well as the inorganic chemistry of SPM collected from both the upper and lower CJ. Since the construction of CMRs, POC sequestration in artificial reservoirs reaches approximately 6.6 megatons carbon per year (MtC yr-1), 3.8 MtC yr-1 of which being POC of biospheric origin (POCbio). Notably, the flux of POC trapped in the TGD declined from 1.6 to 0.4 MtC yr-1, while CMRs sequestered 0.7 MtC yr-1. This shift highlights the relocation of POC burial sites from the TGD and estuary to upstream reservoirs. The rapid burial of terrestrial POC in large mountainous river reservoirs is expected to enhance POC preservation by minimizing mineralization caused by prolonged transport to estuaries. The significant reduction in sediment load and the increased proportion of POCbio due to reservoir retention have substantially altered the composition and flux of exported POC, impacting downstream and estuarine carbon cycles.

In the context of global warming, wildfires are expected to increase in both frequency and intensity in the forthcoming decades. Among the environmental and ecological wildfires -induced impacts, the risk of freshwater pollution by soilborne trace metals deserves a more extensive and accurate assessment because of its potential threat to human health. This study aims to contribute to this evaluation by investigating the influence of laboratory soil heating on chromium solid speciation (including redox state) and mobility in Ferralsols, Cambisols, Vertisols and Regosols holding varying amounts of this trace metal in New Caledonia (South Pacific). A first result is that soil heating from 400 degrees C induces a partial Cr(III) oxidation to Cr(VI) in all the studied soils, confirming recent findings and extending them to a wider range of soil types. A second result is that the rate of heatinduced Cr(III) oxidation to Cr(VI) appears to depend on chromium speciation. This latter parameter might thus represent the primary driver of chromium reactivity in burned soils. Finally, a third result is the confirmation that most of the Cr(VI) formed in the heated soils is highly mobile. Heat -induced Cr(III) oxidation to Cr(VI) in burned soils thus represents a significant risk towards freshwater quality. At the local scale, this risk might concern a large range of drinking water catchments since the soils investigated in this study encompass a wide portion of the pedological diversity in New Caledonia. At a broader scale, considering the wide occurrence of Crbearing pedological settings worldwide, the potential threats to freshwater systems resulting from the occurrence of highly toxic Cr(VI) in burned soils should be considered as a global emerging risk towards water quality that requires further assessment.

The Huanghe (Yellow River), one of the largest turbid river systems in the world, has long been recognized as a major contributor of suspended particulate matter (SPM) to the ocean. However, over the last few decades, the SPM export flux of the Huanghe has decreased over 90 % due to the high management, impacting the global export of particulate organic carbon (POC). To better constrain sources and modes of transport of POC beyond the previously investigated transportation of POC near the channel surface, SPM samples were for the first time collected over a whole channel cross-section in the lower Huanghe. Riverine SPM samples were analyzed for particle size and major element contents, as well as for POC content and dual carbon isotopes (13C and 14C). Clear vertical and lateral heterogeneities of the physical and chemical properties of SPM are observed within the river cross-section. For instance, finer SPM carry more POC in general with higher 14C activity near the surface of the right bank. Notably, we discuss how bank erosion in the alluvial plain is likely to generate lateral heterogeneity in POC composition. The Huanghe POC is millennial-aged (4020 ± 500 radiocarbon years) and dominated by organic carbon (OC) from the biosphere, while the lithospheric fraction is ca. 12 %. The mobilization of aged and refractory OC, including radiocarbon-dead biospheric OC, from deeper soil horizons of the loess–paleosol sequence through erosion in the Chinese Loess Plateau is an important mechanism contributing to fluvial POC in the Huanghe drainage basin. Altogether, anthropogenic activities can drastically change the compositions and transport dynamics of fluvial POC, consequentially altering the feedback of the source-to-sink trajectory of a river system to regional and global carbon cycles.

Abstract. Stable isotope ratios of hydrogen (δ2H) and oxygen (δ18O) are crucial for studying ecohydrological dynamics in forests. However, most studies are confined to single sites, resulting in a lack of large-scale isotope data for understanding tree water uptake. Here, we provide a first systematic isotope dataset of soil and stem xylem water collected during two pan-European sampling campaigns at 40 beech (Fagus sylvatica), spruce (Picea abies), or mixed beech-spruce forest sites in spring and summer 2023 (Lehmann et al., 2024). The dataset is complemented by additional site-, soil-, and tree-specific metadata. The samples and metadata were collected by different researchers across Europe following a standardized protocol. Soil samples were taken at up to 5 depths (ranging from 0 to 90 cm) and stem xylem samples from three beech and/or spruce trees per site. All samples were sent to a single laboratory, where all analytical work was conducted. Water was extracted using cryogenic vacuum distillation and analyzed with an isotope laser spectrometer. Additionally, a subset of the samples was analyzed with an isotope ratio mass spectrometer. Data quality checks revealed a high mean total extraction efficiency, mean absolute water amount (> 1 mL), as well as high analytical accuracy and precision. The water isotopic signature of soil and stem xylem water varied as a function of the geographic origin and changed from spring to summer across all sites. While δ2H and δ18O values were strongly correlated, the soil water data plotted closer to the Global Meteoric Water Line (GMWL) than the stem xylem water. Specifically, the δ2H values of the stem xylem were more enriched than those of the soil water, leading to a systematic deviation from the GMWL. Isotopic enrichment of the stem xylem water was larger for spruce than for beech trees at mixed forest sites. This dataset is particularly useful for large-scale studies on plant water use, ecohydrological model testing, and isotope mapping across Europe.