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Abstract In the case of environmental samples, the use of a chemometrics-based prediction model is highly challenging because of the difficulty in experimentally creating a well-ranged reference sample set. In this study, we present a methodology using short wave infrared hyperspectral imaging to create a partial least squares regression model on a cored sediment sample. It was applied to a sediment core of the well-known Lake Bourget (Western Alps, France) to develop and validate a model for downcore high resolution LOI550 measurements used as a proxy of the organic matter. In lake and marine sediment, the organic matter content is widely used, for example, to reconstruct carbon flux variations through time. Organic matter analysis through routine analysis methods is time- and material-consuming, as well as not spatially resolved. A new instrument based on hyperspectral imaging allows high spatial and spectral resolutions to be acquired all along a sediment core. In this study, we obtain a model characterized by a 0.95 r prediction, with 0.77 wt% of model uncertainty based on 27 relevant wavelengths. The concentration map shows the variation inside each laminae and flood deposit. LOI550 reference values obtained with the loss on ignition are highly correlated to the inc/coh ratio used as a proxy of the organic matter in X-ray fluorescence with a correlation coefficient of 0.81. This ratio is also correlated with the averaged subsampled hyperspectral prediction with a r of 0.65. Graphical abstract Unlabelled Image Highlights • A chemometrics method based on an internal calibration is proposed for hyperspectral imaging. • Organic matter is predicted by PLSR and applied on a sediment core hyperspectral Image. • Internal calibration was achieved by bootstrapping subsampling of SWIR hyperspectral data. • The correlation of LOI550 predications with XRF inc/coh values validates the proposed method. [ABSTRACT FROM AUTHOR]

Organic matter (OM) sources and transfers are critical questions at the crossroad of ecology, hydrology and paleoenvironmental studies in karst environments. Recently chemical or isotopic characterisations of these organic matters have demonstrated their diversity in karst water and speleothems. However, knowledge of their origin and transfer from soil needs to be improved especially in karst environments where a mosaic of soils occurs. Here we investigate the applicability of the Electron Paramagnetic Resonance (EPR) signature of OM to seek different soil fingerprints in speleothems. The positions and the shapes of semiquinone-type radical’s EPR lines are considered as a robust signature of the organic matter through the different compartment of karst ecosystems. We demonstrate that the combination of EPR lines simulation constitutes a fingerprint that discriminates folic Leptosol developed on limestone outcrops from eutric Cambisols located in the dolines and topographical depressions. We also report the conservation of the thinner OM EPR lines after a water extraction of the organic matter from soils. Finally, OM EPR signatures were detected in two different speleothems sampled near each other: a stalagmite and a subaqueous flowstone. An unexpected two-orders-of-magnitude discrepancy between the free radical concentrations of the subaqueous flowstone and the soils on one hand, and the low free radical concentration of the stalagmite samples on the other, was ascribed to the kinetics of conformational changes in OM occurring during their transfer through karst either in fast or in slow water pathways. A folic Leptosol fingerprint was found in stalagmite and conversely, an eutric Cambisol fingerprint was found in the flowstone sample. This unexpected difference between the EPR signatures of the flowstone sample and stalagmite sample was ascribed to the masking of the Leptosol EPR signature (due to the low concentrations of free radicals) in the case of the flowstone sample and to the fact that the EPR signature of the stalagmite sample clearly shows the Leptosol is the sole source of the OM. Finally, the folic Leptosol fingerprint remains steady over the last four centuries covered by the stalagmite demonstrating that the source of the OM is stable over the growth period strengthening the interest of OM entrapped in speleothem for paleoenvironment studies. [ABSTRACT FROM AUTHOR]

Highlights: [•] We quantify PAH content in a karst steady ecosystem. [•] Mass balance of PAH from atmospheric wet deposit to seepage water was estimated. [•] We demonstrate the role of soil as an accumulator for high molecular weight PAH. [•] Light PAHs in karst water come from atmospheric deposits (dry and wet). [Copyright &y& Elsevier]

Summary: Because of its impact on water quality, organic matter (OM) in karst groundwater has been widely studied. The present article describes a method for monitoring OM in karst aquifers characterized by quick responses to rainfall. This method combines weekly manual sampling and continuous monitoring to provide, qualitative and quantitative information about OM flow. Weekly samples were analyzed for Total Organic Carbon (TOC) content and spectrofluorescence, while continuous monitoring was carried out at the main spring, using a field fluorimeter (310/400–700nm and 280/300–600nm) to quantify chromophoric organic matter (COM). The type and quantity of COM were defined by decomposing Excitation Emission Matrices (EEMs) and by applying a 2D fluorescence decomposition method. Continuous monitoring data showed that the dominant COM was humic-like (HL). We found three types of relationship between HL and discharge and between HL and TOC, showing that caution must be exercised when using field fluorimeter measurements to quantify TOC. Each relationship was characterized by global differences in OM content and by the presence of different percentages of non-chromophoric organic matter. These three relationships are associated with changes in hydrology and microorganism activity during the year. We used these relationships to estimate the annual OM flow (about 15kg/ha/year) and thereby quantify OM flow during the year. Our results show the importance of the non-chromophoric organic matter in such estimation. That work illustrates the need to couple qualitative and quantitative monitoring of OM in karst spring to improve the global comprehension of karst system and of the sources implies in the OM flow. [ABSTRACT FROM AUTHOR]