Purpose: Intact lake sediments reflect the development of terrestrial ecosystems. This development can be understood by decoding mineral and geochemical information of sedimentary archives. Therefore, we characterized a Holocene lake sediment core and revealed bulk to micro-scale variations via a combination of geochemical techniques and statistical methods.Methods: A 2.3 m sediment core was collected from Hotagen, a lake in west-central Sweden; a sediment sample was collected every 5 cm. A part of each sediment sample was kept untreated (named bulk) and another part was size-fractionated into < 4, 4–16, 16–64, and > 64 µm subsamples. Characterization was then made with respect to grain size distribution (GSD), physico-chemical parameters, geochemical properties, organic composition, and mineralogy. The sediments were investigated at bulk, micro-, and elemental scales using powder X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy (SEM–EDX).Results: The deepest sediment was identified as glacial till dating back to the Late Pleistocene. The bulk sediments showed a clear distinction between 0–195 cm (unit 1, U1) and 200–225 cm (unit 2, U2) depths. Quartz and feldspar minerals decreased and organic matter and clay minerals increased from the till towards the lower limit of U1. The development in the sedimentary properties marked the transformation of the terrestrial ecosystem from glacier-covered land to vegetated areas. This development was also well reflected by the appearance of X-ray amorphous materials and the formation of distinct organo-mineral aggregates; chlorite was the predominant clay mineral in these aggregates. The geochemical variation between U2 and U1 sediments was further established by resolving the DRIFT spectral components through multivariate curve resolution alternating least square (MCR-ALS). The U1 sediments settled over a period of ~ 7500 years and showed comparable mineral, geochemical, and organic composition. However, the size-fractionated sediments, mainly < 4 µm, showed diverse mineral and geochemical composition. Indeed, these sediments were distinct by containing relatively higher amounts of X-ray amorphous materials and clay minerals, the latter had variable Na, Mg, and K contents.Conclusion: The combined use of geochemical and statistical approaches used in this study followed the mineral and geochemical development of sediments that had settled during the Late Pleistocene and Early Holocene Epochs. Finally, the U2 sediments marked the terrestrial ecosystem development that occurred during the late glaciation, deglaciation, and post-glaciation periods.Graphical

Submerged sediment cores were collected upstream of a dam in the Orne River, northeastern France. This dam was built in the context of steelmaking to constitute a water reservoir for blast furnace cooling and wet cleaning of furnace smokes. The dam also enhanced sediment deposition in the upstream zone. This study was performed to unravel the contamination status of sediments and to evidence possible contribution sources. The sediment layers were analyzed for water content, grain size, chemical composition, crystalline phases at a bulk scale and poorly crystalline and amorphous phases at a sub-micrometer scale. Visual aspect, texture, color, and chemical and mineralogical analyses showed that the settled sediments were mainly composed of fine black matter, certainly comprising steelmaking by-products. Those materials were highly enriched with Fe, Zn, Pb and other trace metals, except for a relatively thin layer of surficial sediments that had settled more recently. Bulk mineralogy revealed crystalline iron minerals, such as magnetite, goethite, wuestite and pyrite, in the deep layers of the sediment cores. Furthermore, microscopic investigations evidenced the presence of ferrospheres, goethite nanoparticles and newly formed Fe-aluminosilicates; all originating from the former steelmaking facilities. The variation of iron mineralogy, combined with specific chemical profiles and other sediment features, demonstrate the different contributions that constitute the sediment deposit. Furthermore, chemical and mineralogical features of goethite and Fe-aluminosilicates could be used as a fingerprint for such contaminated sediments.