Quantifying bed‐related suspended load in gravel bed rivers through an analysis of the bedload‐suspended load relationship

International audienceSuspended load transport can strongly impact ecosystems, dam filling and water resources. However, contrary to bedload, the use of physically based predicting equations is very challenging because of the complexity of interactions between suspended load and the river system. Through the analysis of extensive data sets, we investigated extent to which one or several river bed or flow parameters could be used as a proxy for quantifying suspended fluxes in gravel bed rivers. For this purpose, we gathered in the literature nearly 2400 instantaneous field measurements collected in 56 gravel bed rivers. Among all standard dimensionless parameters tested, the strongest correlation was observed between the suspended sediment concentration and the dimensionless bedload rate. An empirical relation between these two parameters was calibrated. Used with a reach average bedload transport formula, the approach allowed to successfully reproduce suspended fluxes measured during major flood events in seven gravel bed alpine rivers, morphodynamically active and distant from hillslope sources. These results are discussed in light of the complexity of the processes potentially influencing suspended load in a mountainous context. The approach proposed in this paper will never replace direct field measurements, which can be considered the only confident method to assess sediment fluxes in alpine streams; however, it can increment existing panel tools that help river managers to estimate even rough but not unrealistic suspended fluxes when measurements are totally absent

Time-dependent uptake, distribution and biotransformation of chromium(VI) in individual and bulk human lung cells: application of synchrotron radiation techniques

The original publication can be found at www.springerlink.comChromium(VI) is a human carcinogen, primarily affecting the respiratory tract probably via active transport into cells, followed by the reduction to Cr(III) with the formation of DNA-damaging intermediates. Distribution of Cr and endogenous elements within A549 human lung adenocarcinoma epithelial cells, following treatment with Cr(VI) (100 μM, 20 min or 4 h) were studied by synchrotron-radiation-induced X-ray emission (SRIXE) of single freeze-dried cells. After the 20-min treatment, Cr was confined to a small area of the cytoplasm and strongly co-localized with S, Cl, K, and Ca. After the 4-h treatment, Cr was distributed throughout the cell, with higher concentrations in the nucleus and the cytoplasmic membrane. This time-dependence corresponded to ~100% or 0% clonogenic survival of the cells following the 20-min or 4-h treatments, respectively, and could potentially be explained by a new cellular protective mechanism. Such processes may also be important in reducing the potential hazards of Cr(III) dietary supplements, for which there is emerging evidence that they exert their anti-diabetic effects via biological oxidation to Cr(VI). The predominance of Cr(III) was confirmed by micro-XANES spectroscopy of intracellular Cr hotspots. X-ray absorption spectroscopy (XANES and EXAFS, using freeze-dried cells after the 0–4-h treatments) was used to gain insight into the chemical structures of Cr(III) complexes formed during the intracellular reduction of Cr(VI). The polynuclear nature of such complexes (probably with a combination of carboxylato and hydroxo bridging groups and O-donor atoms of small peptides or proteins) was established by XAFS data analyses.Hugh H. Harris, Aviva Levina, Carolyn T. Dillon, Irma Mulyani, Barry Lai, Zhonghou Cai and Peter A. La