Karst flow processes explored through analysis of long-term unsaturated-zone discharge hydrochemistry: a 10-year study in Rustrel, France

The unsaturated zone of karst aquifers influences the dynamics and the chemistry of water. Because of a lack of direct access, other than via caves, flows in the aquifer matrix and the smallest conduits remain poorly characterized. The few artificial underground structures in the unsaturated karst provide a rare opportunity to study the variety of flow processes. At the low noise underground research laboratory (Laboratoire Souterrain à Bas Bruit, LSBB) in Rustrel (France), 12 variables (temperature, pH, electrical conductivity, alkalinity, major anions and cations, total organic carbon) have been monitored on 12 perennial or temporary flows and leakages over a 10-year period covering contrasting climatic periods. This unique dataset of 1,135 samples has been used to discriminate, identify, and rank the processes associated with the hydrochemical variability of these different types of flows. A principal component analysis and a hierarchical cluster analysis, using mean values and standard deviation of the flow along the principal components, were performed. The results indicate that seasonal variability, mean water residence time, and the depth of acquisition of the chemical characteristics are the main factors of the variability of chemistry at the monitored flow points. Distinguished clusters highlight the great diversity of flows and processes occurring in the fine pathways that may be neighboring the large and structured fractures and conduits. Long-term monitoring with various climatic conditions appears to be a useful tool for assessing this diversity

Solid-state NMR and SAXS studies provide a structural basis for the activation of alphaB-crystallin oligomers.

The small heat shock protein alphaB-crystallin (alphaB) contributes to cellular protection against stress. For decades, high-resolution structural studies on oligomeric alphaB have been confounded by its polydisperse nature. Here, we present a structural basis of oligomer assembly and activation of the chaperone using solid-state NMR and small-angle X-ray scattering (SAXS). The basic building block is a curved dimer, with an angle of approximately 121 degrees between the planes of the beta-sandwich formed by alpha-crystallin domains. The highly conserved IXI motif covers a substrate binding site at pH 7.5. We observe a pH-dependent modulation of the interaction of the IXI motif with beta4 and beta8, consistent with a pH-dependent regulation of the chaperone function. N-terminal region residues Ser59-Trp60-Phe61 are involved in intermolecular interaction with beta3. Intermolecular restraints from NMR and volumetric restraints from SAXS were combined to calculate a model of a 24-subunit alphaB oligomer with tetrahedral symmetry