Since Horton in 1965, many authors have sought to aggregate different variables characterizing the state of water into a single value called Water Quality Index ( W Q I ). This index is intended to facilitate the operational management of water resources and their allocation for different uses. Detailed and operational description of the main W Q I calculations are here reviewed. The review contains: (1) an historical analysis of the evolution of W Q I calculation methods by looking both at the choice of variables, the methods of weighting and aggregating these variables into a final single value; (2) an illustration of the contradictions observed in the final result when, on the same database, the W Q I is calculated by different methods; (3) the significant progress possible via fuzzy logic to define a W Q I adapted to specific water use.

International audienceNegative self-potential anomalies can be generated at the ground surface by ore bodies and ground water contaminated with organic compounds. These anomalies are connected to the distribution of the redox potential of the ground water. To study the relationship between redox and self-potential anomalies, a controlled sandbox experiment was performed. We used a metallic iron bar inserted in the left-hand side of a thin Plexiglas sandbox filled with a calibrated sand infiltrated by an electrolyte. The self-potential signals were measured at the surface of the tank (at different time lapses) using a pair of non-polarizing electrodes. The self-potential, the redox potential, and the pH were also measured inside the tank on a regular grid at the end of the experiment. The self-potential distribution sampled after six weeks presents a strong negative anomaly in the vicinity of the top part of the iron bar with a peak amplitude of −82 mV. The resulting distributions of the pH, redox, and self-potentials were interpreted in terms of a geobattery model combined with a description of the electrochemical mechanisms and reactions occurring at the surface of the iron bar. The corrosion of iron yields the formation of a resistive crust of fougerite at the surface of the bar. The corrosion modifies both the pH and the redox potential in the vicinity of the iron bar. The distribution of the self-potential is solved with Poisson's equation with a source term given by the divergence of a source current density at the surface of the bar. In turn, this current density is related to the distribution of the redox potential and electrical resistivity in the vicinity of the iron bar. A least-squares inversion method of the self-potential data, using a 2D finite difference simulation of the forward problem, was developed to retrieve the distribution of the redox potential

No abstract

We here review the extraordinary mineralogical properties of green rusts and their naturally occurring form, fougerite, and discuss the pertinence of these properties within the alkaline hydrothermal vent (AHV) hypothesis for life's emergence. We put forward an extended version of the AHV scenario which enhances the conformity between extant life and its earliest progenitor by extensively making use of fougerite's mechanistic and catalytic particularities.

The flow of ground water in a buried permeable paleo‐channel can be observed at the ground surface through its self‐potential signature. We apply this method to delineate the Saint‐Ferréol paleo‐channel of the Rhone River located in Camargue, in the South East of France. Negative potentials, ∼−30 mV (reference taken outside the paleo‐channel), are associated with ground water flow in this major sand‐filled channel (500 m wide). Electrical resistivity is primarily controls by the salinity of the pore water. Electrical resistivity tomography and in situ sampling show the salinity of the water inside the paleo‐channel is ten times smaller by comparison with the pore water of the surrounding sediments. Combining electrical resistivity surveys, self‐potential data, and a minimum of drilling information, a 3‐D reconstruction of the architecture of the paleo‐channel is obtained showing the usefulness of this methodology for geomorphological reconstructions in this type of coastal environment.