Salinity is reduced below the evaporation front during soil salinization

7 pages, 5 figures.-- Comunicación presentada en las Novenas Jornadas de Investigación de la Zona No Saturada del Suelo, Barcelona (Spain), 18-20 Noviembre, 2009.[EN] Soil salinzation is a global problem. Salinization is generally caused by salts transported to the soil surface by capillary rising water. Despite its global importance, actual salinization mechanisms are poorly understood (Kampf et al., 2005). We use laboratory experiments and numerical models to show that salt precipitates at the evaporation front, which occurs within a very narrow band. Part of the evaporating water diffuses downwards, where it condensates. This implies that, contrary to widely spread belief, salinization (Xu & Shao, 2002) (i.e. salt precipitation) does not occur below the evaporation front. Instead, the upflowing solution becomes diluted.[ES] La salinización de suelos es un problema global. Generalmente, la salinización es causada por el transporte de sales hacia la superficie por capilaridad y, a pesar de su importancia global, los mecanismos que la controlan aún no están bien descritos (Kampf et al., 2005). En este trabajo, se han llevado a cabo experimentos de laboratorio y simulaciones numéricas que muestran que las sales precipitan en el frente de evaporación, el cual se da en una zona estrecha del suelo y que el flujo de vapor de agua se desplaza, no solo en sentido ascendente, sino también descendente, desde dicho frente de evaporación. El flujo de vapor descendente, condensa, causando la dilución de la solución. Esto implica, que contrariamente a lo creído hasta ahora, la salinización (Xu y Shao, 2002) (la precipitación de sales) no se da por debajo del frente de evaporación.We gratefully acknowledge the financial support received from the EU WATCH project (WATer and global Change) and the Spanish Research Council ATRAPO project.Peer reviewe

Editorial: Modeling-Based Approaches for Water Resources Problems

[No abstract available

Analysis of water vapor adsorption in soils by means of a lysimeter and numerical modeling

Daily temperature oscillations can cause adsorption (and desorption) of atmospheric water vapor by soils. The resulting daily fluctuations in the amount of liquid water in the soil can be measured by high-precision weighing lysimeters. We analyzed the data of a lysimeter in a sandy dune sediment in southern Spain using Codebright, a thermohydraulic numerical model for unsaturated flow that takes into account water, vapor, and heat transport in the soil, as well as soil–atmosphere interactions such as precipitation, evaporation, and solar radiation. The analysis shows that daily temperature oscillations, psychrometrics, and soil water retention can explain the fluctuations of the amount of liquid water in the soil. The retention curve, especially its driest part, is essential for the existence of these fluctuations. The fluctuations could not be reproduced by a model using the van Genuchten retention curve with a constant residual saturation. On the other hand, satisfactory results could be obtained by models using retention curves that at their driest part still show a change of saturation with suction. Moreover, the models suggest within the top few decimeters of the soil a pattern of alternating bands of condensation and evaporation, which follows the daily temperature oscillations that fade out deeper in the soil.We are very grateful to André Peters for providing the AWAT filter and give special thanks to Daniel Jesus Martínez, Fernando Ruiz Bermudo, and Antonio Nicolas Martínez for their excellent technical assistance and support.We are grateful for the support and collaboration of the Biological Station of Doñana, the Biological Reserve of Doñana, and the administration of the Doñana National Park. The contract of Lidia Molano Leno (PEJ-2014-A-68763) was financed by the Ministry of Economy, Industry and Competitiveness of Spain (MINECO) and co-financed by the European Investment Bank (EIB) and the European Social Fund (ESF). Likewise, this work has been financed by the CLIGRO Project (MICINN, CGL2016-77473-C3-1-R) of the Spanish National Plan for Scientific and Technical Research and Innovation. The infrastructure has been co-financed by European Research Funds (SE Scientific Infrastructures and Techniques and Equipment 2013, IGME13-1E-2113).Peer ReviewedPostprint (published version

On the localization of chemical reactions in multicontinuum media

Reactive transport (RT) through heterogeneous media, may cause chemical heterogeneity if water flux is slow through portions of the medium. In such cases, chemical localization (i.e., the occurrence of reactions that would not occur in well mixed media) may develop, which is especially relevant for biochemical reactions occurring in biofilms. The objective of this work is to study the conditions for chemical localization. We represent the impact of heterogeneity by means of the non-local multirate mass transfer (MRMT) model, which views the porous media as consisting of one mobile and many immobile zones. A dimensional analysis of the governing equations shows that the problem is characterized by reaction times and the distribution of residence times in immobile zones, relative to transport time. To analyze the interplay between them, we simulated simple RT problems in multicontinuum media. Results indicate that immobile zones with residence times much smaller than transport can be lumped together with the mobile zone by modifying the reaction rates, which reduces computations. More importantly, reactions driven by species that are not present in the inflowing water but are the result of previous reactions will take place preferentially in immobile zones, whose residence time is comparable to or larger than reaction times. In fact, daughter species may take a long time and distance to build up. That is, daughter species will not be largest near the inflow, where parent species display largest concentrations, but further downstream at isolated (long residence times) immobile zones.The authors acknowledge the financial support of project NITREM (European Union, European Institute of Innovation and Technology, project number 17013, PA2021/EIT/EIT Raw Materials GA2021 EIT RM) and the project RESTORA (Agència Catalana de l'Aigua, ACA210/18/0040). Additional funding was obtained from the Generalitat de Catalunya (2017 SGR1485) and the Spanish Ministry of Science and Innovation (Centre of Excellence Severo-Ochoa, CSIC-IDAEA, CEX2018–000794-S).Peer reviewe

Modelling the oxidation of sulphides in an unsaturated soil

Abstract: Within the framework of a study on the impact of a mine-tailing spill at Aznalrollar, SW Spain, we investigated the oxidation of pyrite and other sulphides by means of two column experiments and reactive transport modelling. The columns were filled with pyritic sludge mixed up with a sandy and a clayey soil, respectively. The columns were located outdoors for 15 months and leached 10 times. Prior to simulating reactive transport, a flow model permitted a detailed escription of the behaviour of the column at a daily time-scale. The most important parameter xtracted was the hydraulic saturation. This parameter controlled the amount of O2 that could diffuse into the soil, which, in its turn, affected the rate of pyrite oxidation. The sandy and clayey columns behaved very differently. In the sandy column, pH dropped due to the oxidation of pyrite. As a result, silicate minerals dissolved, providing Na and/or K that precipitate together with Fe and SO4 as jarosite. The high concentration f Zn in the leachates was consistent with the concentrations predicted from sphalerite oxidation. The low As and Pb concentrations, however, were explained by their coprecipitation in the jarosite. In the clayey column, the dissolution of dolomite kept the pH high, impeding the dissolution of silicate minerals and precipitating amorphous Fe(OH)3 i

Vapor flow control in dune sediments under dry bare soil conditions.

The study presents daily values of inward and outward vapor flux crossing the soil-atmosphere boundary in dependence on meteorological parameters and soil moisture. Measurements of vapor flux, soil moisture and meteorological parameters were evaluated during days without rainfall between 2015 and 2019. Vapor flux data were obtained at 1 min intervals by a precision lysimeter installed in the Doñana National Park, southwest Spain. Meteorological data were measured on-site at 10-min intervals, including temperature, relative humidity, wind velocity and net radiation. After manual and automatic noise elimination of the lysimeter data, time series of a summer and winter period were generated for selected relevant parameters. Furthermore, daily cumulative data of inward and outward vapor flux were calculated for the entire period and analyzed for their control by meteorological parameters and soil moisture. Results show moderate correlations of daily outward vapor flux on the diurnal amplitudes of temperature and humidity whereas daily inward vapor indicates moderate correlations with temperature and soil moisture. A correction coefficient for potential evaporation to estimate actual evaporation was determined based on soil moisture and air temperature.Unidad de Sevilla, Instituto Geológico y Minero de España, EspañaDepartament d'Enginyeria Civil i Ambiental, Universitat Politècnica de Catalunya, EspañaGrupo de Hidrogeología, Universitat Politècnica de Catalunya, EspañaGrupo de Hidrogeología, Consejo Superior de Investigaciones Científicas, Españ

Investigation of geochemical processes during CO2 injection using “push-pull” reactive tracer tests

EGU General Assembly 2011, 3-8 Abril 2011, Viena (Austria)A single well injection-withdrawal, “push-pull”, test is useful to obtain information on a wide variety of physical, biological and chemical aquifer characteristics. This test consists of injecting a solution, either reactive or not, into a well followed by an extraction from the same location. “Push-pull” tracer tests have been used to analyze processes of sorption, advection and dispersion during nonuniform flow, to evaluate longitudinal dispersivity and measure field-scale parameters such dispersion in a stratified aquifer or effective porosity. As regards the reactive “push-pull” tracer tests, from the analysis of the chemical composition of the extracted water it is possible not only to quantify the geochemical reactions occurring in the aquifer, but also to study the changes of the aquifer properties such as porosity and permeability. “Push-pull” test simulations were conducted to design the “push-pull” experiments to be held in Hontomín (north of Spain), a future pilot site for carbon sequestration, with the aim of characterizing the formation before starting the CO2 injection. Using the available geological data geochemical processes such as mineral dissolution/precipitation were modeled to observe their effects on the properties of the aquifer and potentially on the performance of the instrumentation in situ. Since “push-pull” tests have proven to be useful also to assess matrix diffusion of highly fractured rocks, both a single and a double porosity model were used to model the test, in order to simulate the behavior of a high porosity zone (reservoir, where advective processes dominate) and a low porosity region (caprock, mainly diffusive). The results suggest first that a double porosity model provide useful insights on the kinetic properties of geochemical processes, such as mineral dissolution/ precipitation rate, and second that the matrix diffusion effects are appreciable and can be represented well with a multiple porosity model. Furthermore, the simulations indicate that a quite aggressive solution should be used to notice the effects of the injection. Thus an accurate analysis of the geochemical reactions would be useful also to evaluate possible damages on the well structure.Peer reviewe

Reactive Transport: A Review of Basic Concepts with Emphasis on Biochemical Processes

Reactive transport (RT) couples bio-geo-chemical reactions and transport. RT is important to understand numerous scientific questions and solve some engineering problems. RT is highly multidisciplinary, which hinders the development of a body of knowledge shared by RT modelers and developers. The goal of this paper is to review the basic conceptual issues shared by all RT problems, so as to facilitate advance along the current frontier: Biochemical reactions. To this end, we review the basic equations to point that chemical systems are controlled by the set of equilibrium reactions, which are easy to model, but whose rate is controlled by mixing. Since mixing is not properly represented by the standard advection-dispersion equation (ADE), we conclude that this equation is poor for RT. This leads us to review alternative transport formulations, and the methods to solve RT problems using both the ADE and alternative equations. Since equilibrium is easy, difficulties arise for kinetic reactions, which is especially true for biochemistry, where numerous frontiers are open (how to represent microbial communities, impact of genomics, effect of biofilms on flow and transport, etc.). We conclude with the basic 10 issues that we consider fundamental for any conceptually sound RT effort.This work is part of grants MEDISTRAES III funded by MCIN/AEI/ PID2019-110212RB-C22 and MCIN/AEI/PID2019-110311RB-C21 and Water JPI project MARadentro (PCI2019-103603), and by the Catalan Water Agency through the project RESTORA (CA210/18/00040). IDAEA-CSIC is a Center of Excellence Severo Ochoa (Grant CEX2018-000794-S funded by MCIN/AEI/ 10.13039/501100011033).Peer reviewe

Reactive transport modelling of a high-pH infiltration test in concrete

A laboratory-scale tracer test was carried out to characterize the transport properties of concrete from the Radioactive Waste Disposal Facility at El Cabril (Spain). A hyperalkaline solution (K-Ca-OH, pH = 13.2) was injected into a concrete sample under a high entry pressure in order to perform the experiment within a reasonable time span, obtaining a decrease of permeability by a factor of 1000. The concentrations of the tracers, major elements (Ca2+, SO4 2−, K+ and Na+) and pH were measured at the outlet of the concrete sample. A reactive transport model was built based on a double porosity conceptual model, which considers diffusion between a mobile zone, where water can flow, and an immobile zone without any advective transport. The numerical model assumed that all reactions took place in the immobile zone. The cement paste consists of C-S-H gel, portlandite, ettringite, calcite and gypsum, together with residual alite and belite. Two different models were compared, one with portlandite in equilibrium (high initial surface area) and another one with portlandite reaction controlled by kinetics (low initial surface area). Overall the results show dissolution of alite, belite, gypsum, quartz, C-S-H gel and ettringite and precipitation of portlandite and calcite. Permeability could have decreased due to mineral precipitation. © 2017 Elsevier LtdThe authors would like to thank Jordi Illa and Salvador Galí (Universitat de Barcelona) for their help in the X-Ray diffraction analysis. We acknowledge financial support of the Spanish Ministry of Economy and Competitivity through the project HEART (CGL2010-18450), a Research Grant from the Technical University of Catalonia (UPC) and ENRESA (Spanish Nuclear Waste Management Company).Peer reviewe

A Multi-Continuum Approach to Large Scale Two-Phase Flow in Heterogeneous Media

Ponencia presentada en la 9th European Fluid Mechanics Conference, celebrada en Roma del 9 al 13 de sepriembre de 2012.Spatial heterogeneities impact on the large scale dynamics of two-phase flow in geological media. Unlike for flow in a homogeneous medium, the saturation front is roughened by spa- tial variability in permeability. The impact on the saturation distribution can be measured by a macroscopic dispersion coefficient. For high permeability contrasts, additional inter- faces can be created behind the saturation front due to fluid trapping in low permeability zones. This type of trapping phenomena are well known from passive solute transport in heterogeneous media and in general leads to non-local dynamic equations for the macro- scopic process description. For two-phase flow, the contrast in typical mass transfer time scales on the macroscopic support scale leads to local non-equilibrium, in the sense that the local saturation state cannot be characterized by a single macroscopic value. We approach the quantification of these phenomena using a multicontinuum approach that represents the heterogeneous medium by a primary mobile continuum, in which flow is viscosity dominated and a suite of secondary continua, in which capillary flow is dominant. The mobile and im- mobile continua are connected by continuity in capillary pressure at the material interfaces. Using homogenization theory, we derive a non-local two-phase flow equation for the satu- ration in the mobile continuum that captures non-equilibrium effect in the macroscale flow dynamics.Peer reviewe