Redox reactions are fundamental to life, and local heterogeneities in the soil create gradients in pH, redox and chemical concentrations that support chemical reactions. In situ monitoring of waters can distinguish abiotic and biotic reactions, and the analysis of temporal data makes it possible to establish the kinetics of these reactions. Field data show that the oxidation–reduction potential can vary over a wide range of pe in a few hours, and that fougerite can be a competitor of denitrification. Layered double hydroxides can drive self-organizing reactions, including redox reactions, usable for storage and replication of chemical information.

Fougerite, the natural green rust, first discovered in soils and universally considered as responsible for the bluegreen colour of gleys and an indicator of reducing conditions, has been recently considered as a key mineral for life's emergence in the alkaline hydrothermal vents theory. It inherits all of the reactive properties of layered double hydroxides in its hydrated interlayer but also the specific reactivity of mixed Fe(II)-Fe(III) compounds, including redox reactivity with metals and metalloids. Along with its structural and compositional analogy with metallo-enzymes, all these properties have stimulated research on the possible role of fougerite as a membrane, and a catalytic engine, especially where gradients of pH, redox potential and temperature favour mixing of chemically contrasted reactants, such as at hydrothermal systems. Although the presence of fougerite, however difficult to detect, has never been reported at alkaline hydrothermal systems, we have thermodynamically evaluated whether the environmental conditions met in such modern oceanic systems are compatible with the formation of fougerite. Data on fluids from the Lost City hydrothermal field (30 degrees N, Mid Atlantic ridge, Seyfried et al. (2015)) support the reducing nature of this environment, close to the lower limit of stability of water at 90 degrees C and 80 atm. Calculations show that equilibrium with amakinite, the rare ferrous analogue of brucite, is more likely than equilibrium with brucite. This allows for computing in situ pH values close to 8 and thus mildly alkaline, while pH measured on board on vent fluids at 25 degrees C is higher than 10. This is in favour of the occurrence of ferrous hydroxide deeper in the root of the hydrothermal system where temperature is higher and pH are lower compared to seafloor vents where the fluids discharge. Secondary oxidation of amakinite, thanks to the recurrent circulation of seawater in the hydrothermal conduits, will necessarily lead to fougerite formation. To deepen this question, several lines of investigation are finally proposed, including e.g., the stability of fougerite at elevated temperatures and pressures, its reactivity with key elements for life such as C, N, P, Mo, Ni, S etc. and its potential role for free energy conversion and basic functions of metabolism.

Free Access List of Authors Book Editor(s):Fernand Joly, Fernand JolySearch for more papers by this authorGuilhem Bourrié, Guilhem BourriéSearch for more papers by this author First published: 15 January 2021 https://doi.org/10.1002/9781119808275.contrib AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Mankind and Deserts 2: Water and Salts RelatedInformation

Chapter 4 Salts in Deserts Guilhem Bourrié, Search for more papers by this author Guilhem Bourrié, Search for more papers by this author Book Editor(s):Fernand Joly, Search for more papers by this authorGuilhem Bourrié, Search for more papers by this author First published: 15 January 2021 https://doi.org/10.1002/9781119808275.ch4 AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat Summary Climatic aridity, whether hot or cold, is not a sufficient condition for the formation of salts in deserts. The Great Salt Lake in Utah, the chotts and sabkhas in the northern Maghreb region, the playas of North Mexico and the Uyuni salar in the Bolivian altiplano are all examples of salt deserts. Allogenous rivers, such as the Nile, the Euphrates, the Logona and the Shari have large floods and salts become concentrated and are deposited in the flood plains when the waters retreat. The salts that we find in the deserts can be the result of the dissolution of ancient evaporites, however they are most often the result of the dissolution of continental rocks. Salts are precipitated in reverse order of their solubility: the first to precipitate is calcite CaCO3, followed by gypsum and then anhydrite and halite. Desert populations have used extracted salts from marine and continental evaporites. Mankind and Deserts 2: Water and Salts RelatedInformation

Monique Fort (Pr. Emerite, Universite de Paris, UMR 8586 PRODIG CNRS) Yvette Dewolf nous a quittes le 5 avril 2021. Nee en 1928, elle debuta sa carriere a l’Universite de Caen dans l’equipe d’Andre Journaux, et elle s’investit tres vite au Centre de Geomorphologie ou elle participa, entre autres avec Jean-Pierre Lautridou et Jean-Pierre Coutard, aux experiences sur les milieux periglaciaires et la cryoclastie. Nommee a Paris en 1965, elle co-dirigea, avec F. Durand-Dastes et sous la Direction...

A possibly prominent role for Green Rust minerals in life's emergence is inferred from a comparison of their structural, mechano-dynamic and electrochemical properties and of the layout of bioenergetic, i.e. free energy converting processes in extant organisms. From fundamental thermodynamic considerations, the conversion of environmental free energy into the decrease of entropy that defines life is an indispensable ingredient for life to emerge. A specific scenario for life's emergence mediated by Green Rust minerals in the framework of the alkaline hydrothermal vent hypothesis is proposed.

Facing global changes and the challenge of food security, scientists are being questioned by decision-makers and stakeholders on the sustainability of agrosystems.The main difficulty in dealing with this question is to obtain enough data over long periods of time.Monitoring slow drifts and weak noises is needed to forecast tipping points that can jeopardize the present steady state.High-resolution datations by radiocarbon coupled with detailed palynological determinations in sediments, historical archives on yields and crop quality, and high-frequency field in situ measurements give information on climatic changes from multi-secular to seasonal and hourly time scales.In the long term, climatic forcing dominates agriculture performance, at that time only organic agriculture, with oscillations between prosperity and misery driven by climate and intermediated by civilization flourishing and collapsing; in the medium term, in modern agriculture, irrigation provides a provisional buffering effect on yield and crop quality despite present warming; in the short term, either under non-fertilized forested ecosystem or intensive rice cropping, the same patterns are evidenced and point to the importance of soil microflora shifting from aerobiosis to anaerobiosis.In all cases, geochemistry offers appropriate tools to decipher the climate-soil-agriculture complex interplay.

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 ( WQI). 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 WQI calculations are here reviewed. The review contains: ( 1) an historical analysis of the evolution ofWQI 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 WQI is calculated by different methods; ( 3) the significant progress possible via fuzzy logic to define a WQI adapted to specific water use.

As there exists extended solid solutions between ferrous and magnesian silicates, experiments were conducted to check if ferrous and magnesian hydroxides can co-precipitate in a solid solution. Results show that no solid solution forms and instead Fe(II) and Mg(II) hydroxides precipitate separately with the same solubilities as pure components. However, in fougerite, F(III), Fe(II) and Mg(II) coexist in a brucitic type hydroxide, with an extended solid solution. This implies that fougerite formation results from Fe(III) precipitation, Fe(III) being surrounded by divalent Fe(II) and Mg(II) to comply with the exclusion rule: Fe(III) ions cannot be direct neighbours. Consequently, Fe(III) - Fe(II) - Mg(II) smectites cannot form by oxidation of a ferrous - magnesian brucitic layer, but by silication of fougerite. The impossibility of formation of a solid solution between Fe(II) hydroxide and Mg(II) hydroxide, while their electric charge and ionic radii are identical can be explained by the differences of electronegativities of the elements. Fe(II) and Mg(II) can dimerize separately in aqueous solution, but an heterodimer cannot form.

Mass transfer between aquifers, vadose zone, including soils and waters may occur at equilibrium or out of equilibrium. Irrigating with low-quality waters can result in soil salinization and/or degradation of soil structure. Checking minerals/solutions equilibria from the chemical composition of solutions implies computing activities and Saturation Indexes (SI) of minerals. In semi-arid-to-arid areas, evaporation concentrates solutions and waters evolve in different geochemical pathways, mainly saline neutral path and alkaline path, separated by bifurcations. Strong non ideality of electrolyte solutions makes it difficult to compute accurately activities and SI. The objective of this paper is to compare Pitzer’s model and Specific Interaction Theory (SIT), both now incorporated in Phreeqc 3.0. Samples can be assigned to the saline neutral path with dominance of sulfate which is the majority and with dominance of chloride as the minority. Data were twofold: (i) groundwaters were sampled in an irrigated plain, in Lower Chéliff valley (Algeria), and analyzed, they cover the range from low to medium ionic strength; (ii) data from a saline system (Chott El Jerid, Tunisia) were taken from the literature to cover the range from medium to very high ionic strength, including brines. Data were processed with both models to check equilibria. Results opposing classical assumptions are obtained: (i) calcite does not form at equilibrium and requires a specific oversaturation (\(\text {SI} \simeq 1.4\)), then relaxes to equilibrium. This is a general result that can be extended to many situations, where calcite forms, including sedimentation; (ii) gypsum, which is more soluble, forms at equilibrium; accordingly, the assumption of equilibrium at low temperature, i.e., in Earth’s surface conditions, holds for gypsum, but not for calcite; (iii) Pitzer’s model gives better results than SIT for calcite and gypsum, but SIT model gives better results for halite, while it is generally admitted that Pitzer’s model is better for \(I> {3}{\hbox { m}}\).

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.

Depuis 2008, plus de la moitié de la population mondiale vit dans les villes. Ce changement global nous impose de changer de paradigme, la Terre devant être considérée comme un ensemble d’espaces et de ressources limités. Cela nécessite d’avoir une vision systémique intégrée et dynamique des villes et de leur hinterland , dans le but d’assurer les besoins vitaux des populations. La méconnaissance des sols, les pressions foncière et réglementaire et l’organisation de la décision en mode sectoriel et par projet sont les principaux freins à un tel changement. La démarche est inclusive et repose sur la construction d’indicateurs de risques à partir de scénarios partagés par toutes les parties prenantes et qui tiennent compte des ressources en sols, en eau et en production alimentaire, autant d’éléments conditionnant le développement et l’attractivité des territoires. Suite au sommet de Rio de 1992, des initiatives locales et/ou internationales ont été mises en œuvre, signe d’un engagement sur cette voie ; elles ne demandent qu’à être diffusées, partagées et enrichies.

Fougerite (IMA 203-057), from green rust (GR) group, is difficult to quantify due to its reactivity and its small concentration in soils and sediments. Chemical extractions with citrate-bicarbonate (CB) reagent, in kinetic mode, can be used for a pre-diagnosis. Performed by steps (0, 1, 6, 48, 168 and 504 h), the proposed protocol was applied on samples from Gleysol of Fougère’s forest with mineralogical controls by Mössbauer and XRD (X-ray diffraction) after each step of extraction. In less than 6 h, the first fraction extracted is composed of 70% Si, 80% Al, 23% Fe and 80% Mg of total element extractable by CB and is ascribed to the “indefinable mineral mixture Si-Al-Fe” named by Tamm. Between 6 and 168 h, the second fraction extracted is composed of Fe and Mg with a constant mole ratio Fe/Mg equal to 10 and is ascribed to the fougerite-GR phase. Analysis of XRD pattern and of Mössbauer spectra confirms: (i) all the other mineral phases containing Al, Mg, Si were not dissolved by CB after 6 h; (ii) the CB treatment extracts fougerite-GR completely. The residual fraction is composed of components not dissolved by CB extraction. Thus, the selectivity of CB can be used to quantitatively estimate the presence of fougerite-GRs in soils and sediments.

Chapter 1 Physico-chemistry of the Soil–Water System Guilhem Bourrié, Guilhem BourriéSearch for more papers by this author Guilhem Bourrié, Guilhem BourriéSearch for more papers by this author Book Editor(s):Guilhem Bourrié, Guilhem BourriéSearch for more papers by this author First published: 30 November 2018 https://doi.org/10.1002/9781119438045.ch1 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Summary The Earth is at a distance from the Sun that allows water to be stable in the three states: solid, liquid and gas. Water has "abnormal" properties compared to other liquids. The fact that the water molecule is not linear is explained by the nature and occupation of molecular orbitals. Five molecular orbitals result from the linear combination of atomic orbitals (LCAO) of oxygen and hydrogen. Cohesion in liquids is due to the so-called dispersion forces, which quickly decrease according to the intermolecular distance. A recent physical chemistry theory, the density functional theory (DFT), makes it possible to estimate the spatial distribution of the electronic density, from which all the properties of a system can be derived. In a saline clayey soil, the two effects, osmotic and matric, add up. The matric potential can be measured using tensiometers. The osmotic potential can be calculated from the ionic strength. Soils as a Key Component of the Critical Zone 3: Soils and Water Circulation, Volume 3 RelatedInformation