Accumulation Of Gypsum Research Articles

Formation of non-evaporitic gypsum in gas hydrate-bearing sediments at Håkon Mosby mud volcano, SW Barents sea

Authigenic minerals such as carbonate and iron sulfide are known features at cold seeps worldwide and form as a result of the anaerobic oxidation of methane in the sulfate-methane transition zone (SMTZ). Recent findings of seep-related non-evaporitic gypsum raise questions regarding its distribution, formation mechanisms, and relationships with the other proxies for confident paleo-seep reconstructions. Here, we report new findings of gypsum in the seep-impacted sediments of the hydrate-bearing Håkon Mosby mud volcano, SW Barents Sea. We combined sediment core logging (XRF, X-Ray) with optical microscopy and scanning electron microscopy - electron dispersive energy to characterize the authigenic mineral fraction of the sediment. Three paleo-SMTZs marked by the co-occurrence of pyrite and gypsum accumulations were found at 7–10 cm, 13–18 cm and 19–21 cm, above the modern one (at ∼50 cm) and match with carbonate-poor and foraminifera-free sediment intervals. Our results indicate that gypsum formation required a descending SMTZ (decreasing methane flux), triggering the oxidation of previously-formed pyrite which supplied extra SO42− to the pore water. Acidic conditions caused by pyrite oxidation would have promoted the dissolution of carbonate particles, thus releasing Ca2+ that is available for gypsum formation. As seen in other studies, the presence of shallow gas hydrates seems to play an important role as a calcium source for gypsum precipitation, via ion exclusion during hydrate formation. HMMV represents an optimal natural laboratory to investigate the interplay between different processes in gypsum biogeochemistry and its potential use as a proxy for methane seeps in modern and ancient settings.

Application of the Industrial Byproduct Gypsum in Building Materials: A Review.

The industrial byproduct gypsum is a general term for byproducts discharged from industrial production with calcium sulfate as the main ingredient. Due to the high number of impurities and production volume, the industrial byproduct gypsum is underutilized, leading to serious environmental problems. At present, only desulfurization gypsum and phosphogypsum have been partially utilized in cementitious materials, cement retarders, etc., while the prospects for the utilization of other byproduct gypsums remain worrying. This paper mainly focuses on the sources and physicochemical properties of various types of gypsum byproducts and summarizes the application scenarios of various gypsums in construction materials. Finally, some suggestions are proposed to solve the problem of the industrial byproduct gypsum. This review is informative for solving the environmental problems caused by gypsum accumulation.

Preparation and Performance Study of Alkali-active Gypsum Mixture System

To improve the mechanical properties and water resistance of gypsum specimens, thus solving the pollution problem due to the accumulation of flue gas desulfurization gypsum (FGD gypsum), etc. The article utilizes flue gas desulfurization gypsum, gypsum citrate, and mineral powder as the main raw materials under a fixed ratio. The Alkali-activation gypsum-based cementitious material (Alkali-activation GM-S95 system) was obtained by modifying it with 0-5% Na(OH) and Ca(OH)2 alkaline admixtures, and the mechanical properties and water resistance of the Alkali-activation GM-S95 system were thoroughly investigated. The structural characteristics of the Alkali-activation GM-S95 system specimens were investigated using XRD, TG, SEM and LF-NMR techniques to explore their interactions. The results showed that the compressive strength of the Alkali-activation GM-S95 system was significantly increased to 26 MPa when 4% Ca(OH)2 was added alone, and the water absorption was decreased to 12.5%.The addition of 4% Ca(OH)2 caused the crystals of gypsum dihydrate to be thicker and denser, and AFT and C-S-H gels were produced, which were attached around the crystals of gypsum dihydrate. The addition of different admixtures can reduce the proportion of large pores and further fill the crystal structure. In summary, the addition of 4% Ca(OH)2 can improve the compressive strength and water resistance of the samples of Alkali-activation GM-S95 system, thus laying a solid foundation for the comprehensive utilization of flue gas desulfurization gypsum.

Comparison between two gypsum content determination methods applied to the study of soils in arid regions

With the scarcity, degradation of soils, the growing populations and the need to guarantee their food security, the valorization of gypsum soils widespread in arid and semi-arid regions is becoming a necessity. North African countries have a large part of their land area located in arid regions. It is therefore important to characterize the gypsum content using simple, rapid, economical and, environmentally friendly methods. Several methods have been proposed in the literature (chemical, thermogravimetric, and x-ray techniques). In this work, a comparison between two methods for gypsum determination in soils was undertaken. The first method of Coutinet is chemical and based on the use of BaSO4 for the precipitation of sulfate ions. The second method is Artieda method which is based on measuring the weight difference caused by the loss of crystalline water from gypsum molecules between the temperatures of 70 and 90 °C. To achieve the objective of this work, forty-three soil samples were analyzed. They were taken from two arid regions (Ouargla and Touggourt) located in the northern Sahara (Algeria). The soils contain gypsum accumulations. The results showed that most of the samples are slightly gypsiferous, with 36 and 32 samples for the Coutinet and Artieda methods respectively. A strong positive correlation (R2 = 0.95) exists between the results of the two methods studied. For gypsum contents higher than 2 %, the correlation coefficient is 0.94. However, for samples with contents less than 2 %, the correlation is very weak with R2=0.19. The Artieda method is thus encouraged for the gypsum quantification in soils of arid regions. This method is easy, requiring simple laboratory equipment (mainly a ventilated oven and a precision balance). Chemical methods have the disadvantage of being time-consuming and using expensive chemicals that are dangerous for the environment and human health.

Preparation of calcium carbonate by indirect carbonation desulfurization gypsum with renewable aspartic acid

As an industrial by-product of flue gas desulfurization, flue gas desulfurization gypsum (FGD gypsum), whose main component is CaSO4 · 2H2O, is an ideal raw material for mineralization. The technical problem of indirect mineralization lies in the efficient recycling of leaching agents, while amino acids have the lowest solubility at their isoelectric point, and thus the mixture of amino acids can be separated by adjusting the isoelectric point. Therefore, this paper proposes the use of aspartic acid (ASP) as leaching agent to realize the recycling of leaching agent. The leaching efficiency of Ca2+ was regulated by changing the temperature, liquid-to-solid ratio, ammonia concentration, and the ratio of ASP to the amount of FGD gypsum substance. The results showed that ASP could sufficiently improve the leaching efficiency of Ca2+ from desulfurized gypsum under alkaline conditions provided by ammonia. The leaching concentration of Ca2+ was 7474.92 mg/L at 7% ammonia concentration, temperature of 30 °C, n(ASP): n(FGD gypsum) = 2.5:1, and liquid-solid ratio of 30:1 mL/g, which was 12 times higher compared with the leaching concentration of Ca2+ in pure water of 601.2 mg/L. While improving the leaching efficiency, ASP has lone electron pairs and can form soluble complexes with Ca2+ under alkaline environment, which can convert the crystalline form of the product CaCO3 to sphalerite during the mineralization process, and can regenerate ASP by adding acid to adjust the pH, and the recovery rate can reach 80.72%. This method effectively solves the problem of resource waste caused by the massive accumulation of desulfurization gypsum.

Evolution of soil porosity in loess-palaeosol sequences of the Ebro Valley, NE Iberia

Structure development and porosity evolution are closely related key processes in the formation of soils on loess. In order to better understand changes in soil porosity with time, four loess-palaeosol sequences (LPS) of the Ebro Valley were investigated using micromorphological and multiscalar images of soil thin sections combined with luminescence dating. Scanned and high-resolution mosaic images of thin sections using circular polarized light and backscattered electron scanning images were used to characterize the structural and textural porosity. The results were compared with physical and chemical analyses, and detailed micromorphological descriptions. The main results of our research revealed that 1) the change in loess particle packing, from enaulic to porphyric coarse/fine (c/f) related distribution, is the first process giving cohesion to the loess material and 2) that soil development during stabilization periods is associated with higher bioporosity. Gypsum accumulation is also a relevant process contributing to the increase of packing porosity within channels and chambers in the studied soils. Our results provide new insights into soil formation processes in Mediterranean loess and open new fields of research such as the possibility of using the quantification of bioporosity as an additional palaeoenvironmental marker.

Micromorphological features of medieval cultural layers formed in different environmental backgrounds

This research compares results of micromorphological case studies conducted on four early medieval archaeological sites with differentiated spatialization of human impacts and a varied craft production located in different background environments: humid climate, subzone of mixed forests, floodplain of the Dnieper River (Gnezdovo site); semi-humid climate, subzone of forest-steppe, Middle Volga region (Muromsky Gorodok and Malaya Ryazan’ sites); arid climate, cold desert of the Aral region, ancient delta-alluvial plain of the Syr-Darya River (Dzhankent site). Micromorphological studies of habitation deposits revealed clear geographical and geochemical regularities in the occurrence of geogenic (soil, sedimentary and post-sedimentary) features. Intrasoil migration and accumulation of clay and coarser silicate material in textural pedofeatures were described in cultural layers of sites located in forest and the forest-steppe zones. An anthropogenic input of phosphates provokes simultaneous migration and illuvial accumulation of phosphates and clay. In the habitation deposits in steppe landscapes with calcareous lithology, the key background soil process is redistribution and intrasoil accumulation of calcium carbonates. In the alluvial desert landscape, major soil processes are accumulation of gypsum and readily soluble salts. All layers are or were affected by at least some seasonal over-moisturizing that resulted in a variety of redoximorphic features depending on their palaeo- and/or contemporary water regime. The high variety of anthropogenic processes and corresponding microfeatures was grouped as follows: (1) input, output, turbation, compaction; (2) neoformation and migration; (3) pyrogenic processes (products); technological processes (products). The set of anthropogenic features records past human impact in the locality. The higher the variety of anthropogenic features and their general abundance is, the more intensive and variable the human impact which had occurred in the past. At the same time, the occurrence of certain anthropogenic features may indicate not only human-related processes of their formation (or input), but also a contemporary soil environment. This environment can be favorable, or, in the opposite, deteriorative for earlier formed anthropogenic features.

Mechanical Properties and Coagulation Characteristics of Flue Gas Desulfurization Gypsum-Based Polymer Materials.

To resolve problems caused by the accumulation of flue gas desulfurization gypsum (FGDG) in the environment, a polymer material was prepared using FGDG, granulated blast furnace slag (GBFS), fly ash (FA), and solid sodium silicate (SSS). The compressive strength of these polymer specimens cured for 3, 28, and 60 d was regularly measured, and their condensation behavior was analyzed. Both the formation behavior of mineral crystals and microstructure characteristics were analyzed further using X-ray diffraction and scanning electron microscopy. The compressive strength of pure FGDG polymer specimen (whose strength is generated by particle condensation crystallization) is insufficient and the condensation is slow. The addition of appropriate amounts of GBFS, FA, and SSS can continuously and considerably improve the compressive strength and shorten the setting time. The optimal proportions of FGDG, GBFS, and FA are 50%, 20%, and 30%, respectively, with the SSS addition amount of 20 g. The incorporation of GBFS, FA, and SSS can promote the polymerization of calcium, silicon, and aluminum in FGDG to form silicate and aluminosilicate minerals. Their formation is the main reason for the increased compressive strength and accelerated coagulation.

Synthesis of high-length calcium sulfate whisker, an ideal substitute of the plant-based pulp fiber for papermaking

ABSTRACT As a byproduct of the industrial synthesis of phosphoric acid, there was a large quantity of phosphor gypsum (PG) accumulation, which needs enormous storage space and endangers the environment. The preparation of calcium sulfate whisker (CSW) from waste PG could solve the large amounts of PG accumulation and substitute the plant-based pulp fiber, reducing the pollution of wastewater in paper and pulp industries. In this work, the CSW, which length could reach 230 μm, was fabricated from the PG in a glycerol–water solution. It could be found that the glycerol–water volume ratio of 4:6 was the best ratio that could reduce the water activity and accelerate the phase transition from calcium sulfate dihydrate (CSD) to CSW. Meanwhile, the CSW, after calcination, could prepare the anhydrous calcium sulfate whisker (ACSW) with low solubility in water; when the ACSW substitution rate reached 50%, the property of the complex paper could still satisfy the standard of mechanical and optical for offset book paper.

Silt-sized sediments and gypsum on surface formations in the Ebro valley. A disambiguation of the term gypsiferous silts

Since the 60’s, many authors have reported the presence of common silt-sized materials in the Ebro valley, on surface formations and positions that have given rise to several interpretations, sometimes contradictory. According to the references, three main terms are used (gypsiferous silts, loess and flour-like gypsum) applied to silts and fine sands with gypsum accumulations. The two first terms are applied to materials with carbonate contents up to 40-50%, coarse silty to fine sandy textures, and located in different positions. Loess normally appears as thick outcrops on slopes leeward from the main wind direction, with a limited pedogenesis consisting of a partial carbonate mobilisation and gypsum contents between 0 and 30%. The third (gypsum-rich) type has a variable spatial distribution, appearing between limestone layers, along footslopes, outcropping as metric surface formations, or as generalized karstified subsurface accumulations. Their composition is almost 100% silt- to fine sand size lenticular gypsum. While some authors claim for an aeolian origin to all these materials, only part of them (loess) has a clear aeolian origin, while flour-like gypsum derives from on-site weathering of gyprock or by precipitation of calcium- and sulfate saturated watertables as it is reported to occur in many other arid regions; and the rest (gypsiferous silts sensu stricto) are mainly colluvial-alluvial. This distinction is necessary since they differ in their geotechnical behaviour and properties relevant for agricultural land uses, therefore they should be taken into account when carrying out geological mappings or soil surveys in this and similar arid regions.

Silt-sized sediments and gypsum on surface formations in the Ebro valley. A disambiguation of the term gypsiferous silts

Since the 60’s, many authors have reported the presence of common silt-sized materials in the Ebro valley, on surface formations and positions that have given rise to several interpretations, sometimes contradictory. According to the references, three main terms are used (gypsiferous silts, loess and flour-like gypsum) applied to silts and fine sands with gypsum accumulations. The two first terms are applied to materials with carbonate contents up to 40-50%, coarse silty to fine sandy textures, and located in different positions. Loess normally appears as thick outcrops on slopes leeward from the main wind direction, with a limited pedogenesis consisting of a partial carbonate mobilisation and gypsum contents between 0 and 30%. The third (gypsum-rich) type has a variable spatial distribution, appearing between limestone layers, along footslopes, outcropping as metric surface formations, or as generalized karstified subsurface accumulations. Their composition is almost 100% silt- to fine sand size lenticular gypsum. While some authors claim for an aeolian origin to all these materials, only part of them (loess) has a clear aeolian origin, while flour-like gypsum derives from on-site weathering of gyprock or by precipitation of calcium- and sulfate saturated watertables as it is reported to occur in many other arid regions; and the rest (gypsiferous silts sensu stricto) are mainly colluvial-alluvial. This distinction is necessary since they differ in their geotechnical behaviour and properties relevant for agricultural land uses, therefore they should be taken into account when carrying out geological mappings or soil surveys in this and similar arid regions.

Micromorphological features of soils of semidesertic solonetzic complexes under different herbaceous communities with the participation of fodder plant Kochia prostrata (Caspian lowland)

The aim of the study was to research the relationship of chemical and micromorphological properties of soils with the growth ofKochia prostrata. The objects of study were the soils on natural pastures of the North-Western part of the Caspian lowland. It was laid 4 soil pits (soils – light solonetz, solonetzic chestnut) with the maximum penetration depth of the main mass of roots of the studied plants.K. prostratais a very plastic forage species that can grow on soils with a wide range of morphological properties, different salt content and their chemical composition. It is revealed that on the background of almost the same content of humus and high content of exchangeable magnesium micromorphological features represent the different degree of manifestation of primary pedogenic processes – humus accumulation, leaching of soluble salts, gypsum accumulation, carbonate enrichment, solonetzization. Despite the different content of exchangeable sodium, in all soils there are fresh clay or humus-clay illuvial coatings, indicating the manifestation of the modern eluvial-illuvial redistribution of fine matter (lessivage or illimerization).

Red gypsum utilization and acidic wastewater treatment based on metal self-enrichment process.

The massive accumulation of red gypsum has brought great harm to human and environment. In order to achieve low-cost and high-benefit resource utilization of red gypsum, a method of metal self-enrichment during the cycle and transformation of red gypsum was proposed. The carbon dioxide and ammonia water react with red gypsum to manufacture ammonium sulfate and solid phase products. And solid phase products neutralize pickling wastewater to produce metal-enriched red gypsum for the next cycle. After the cycle, solid phase product with one circulation (containing 39.45% Fe and 7.37% Ca) and two circulation (containing 45.79% Fe, 4.75% Ca) could be obtained, which can be used as the proportioning of metallurgical sinter. The self-enrichment process not only realizes the comprehensive utilization of red gypsum, but also solves the treatment of acidic wastewater.

Soil salinization processes in small-lake Ballestera wetland ecosystem (La Lantejuela, Seville, Spain)

Salinization processes in soils with thermo-mediterranean-semiarid conditions within a confined environment (basin closed) are studied in Natural Reserve Ballestera small-lake ecosystems (Seville, Spain). Methodologically it is carried out a geopedological catena integrated by five drilling-profiles with depths between 0.20 and 1.50 m. A total of 21 pedo-sedimentary samples have been characterized through pH, electric conductivity, carbonates contents, magnetic susceptibility and texture determinations. The results show the presence of two different phases in the geopedological evolution of the ecosystem: one of them is previous to the geomorphological constitution of the existing wetland, characterized by carbonates and salts lateral lixiviation processes (vertisolization-tirsification processes determinant of a special black color in the soil), and the second one, later and current, distinguishing processes of salt accumulation (saline brines) and surface crust formations (saltcrete) of halite and gypsum with high value of electric conductivity (salinization and hydromorphic processes).

El registro paleoambiental del Pleistoceno tardío al presente en la Laguna de Lobos, Buenos Aires, Argentina

Se caracterizó el medio físico del ambiente, la fisiografía, régimen hidrológico y la historia geológica de la cubeta lagunar. La geología superficial está representada por seis unidades litoestratigráficas y dos pedoestratigráficas, que abarcan del Pleistoceno temprano al tardío y del Holoceno medio al presente. La más antigua, la Formación Ensenada, constituye el sustrato regional, sobre el cual se ubican cuatro unidades eólicas, las Formaciones Buenos Aires, La Postrera I, III y IV, los Geosuelos Sin Nombre y Puesto Berrondo y el Aluvio reciente. Los sedimentos colmatantes fueron obtenidos mediante perforaciones, reconociéndose siete unidades litoestratigráficas (cinco subácueas y dos subaéreas). Las subácueas corresponden a la Formación Luján, Miembros La Chumbiada, Lobos, Río Salado y Monte (Pleistoceno tardío al Holoceno tardío) y al Aluvio reciente. Los depósitos subaéreos a las Formaciones La Postrera I y IV del Pleistoceno tardío y Holoceno tardío-tardío, respectivamente. La excavación de la cubeta se inició en la etapa seca del ?Bonaerense?, la posterior alternancia climática: seco-húmedo facilitó la evolución. Las etapas secas se caracterizaron por deflación, generación de cubetas, sabkhas o lagos salados, precipitación de sales y acumulación de depósitos eólicos. En las húmedas predominó la sedimentación y la pedogénesis. De esta manera, el conjunto de depósitos posteriores a la Formación Ensenada está representado por cinco episodios de clima seco, que abarcan del Glacial Temprano a la Pequeña Edad de Hielo y cinco húmedos, cuyas acumulaciones límnicas conforman los cuatro miembros de la Formación Luján, el aluvio actual y los suelos sincrónicos S4, S1 y S0.

Architecture and sedimentary evolution of the southwestern Gissar carbonate platform (Uzbekistan) during the Middle‒Late Jurassic

Abstract Sedimentological investigations have been carried out in the southwestern part of the Gissar Range (Uzbekistan) in order to document the stratigraphic evolution of a vast Middle–Upper Jurassic carbonate platform developed on the northern margin of the Amu Darya Basin. Two major sequences are distinguished, based on their contrasting facies pattern, platform configuration and carbon isotope signature: (1) a Callovian Sequence and (2) an Upper Jurassic Sequence, potentially Oxfordian to Kimmeridgian in age. A carbonate ramp with a double proximal-distal polarity developed during the Callovian Sequence. Oo-bioclastic grainstones were produced in two permanently agitated shallow water areas developing to the north and to the south. Patch and pinnacle reefs mainly built up close to the storm-wave base, passing distally to pellet- and foraminiferal-oncoid-rich mid-to outer-ramp deposits. The top of the Callovian Sequence is a regional discontinuity that could have formed by subaerial exposure of the platform. This probable hiatus could record a major climatic change associated to the Middle‒Late Jurassic transition. The Upper Jurassic Sequence consists of metre-thick alternations of pellet/algal-pack- to grainstones, microbial oncoid floatstones, ooid grainstones, and mudstones, which have likely accumulated in a vast lagoon protected by a large-scale barrier reef observed south of the study area. Gypsum and anhydrite content gradually increased towards the top of the Upper Jurassic Sequence, ending up with a thick chicken-wire gypsum accumulation recording the progradation of a large-scale sabkha over the lagoon. This phenomenon is related to a progressive aridification and restriction of the Amu Darya Basin that could have begun during the Middle/Late Oxfordian and reached its climax during the Tithonian with massive halite deposition. Comparable events occurred in Jurassic platforms located along the Tethyan margins, pointing to regional and global controls on sedimentation.

Geochemistry of soils derived from selected sedimentary parent rocks in Kopet Dagh, North East Iran

Geochemical composition of soils from arid regions is greatly affected by parent materials. In order to investigate the effects of parent materials and pedogenic processes on elemental distribution in some selected soils formed on sedimentary parent rocks in Kopet Dagh area, six representative pedons were characterized by geochemical, micromorphological and clay mineralogical studies. Multivariate statistical analyses were used to interpret geochemical data. In this regard, principal component analysis (PCA) was employed to investigate relationships among elements and cluster analysis was also performed to group soil samples on the basis of geochemical affinity. Calcitic features, gypsum accumulations and pedoturbation were found the most common pedogenic features in the studied soils.The different concentration of elements in soils and parent materials were ascribed to different abundances of major mineral constituents i.e. calcite, gypsum, quartz and montmorillonite. Weathering characterization of soils by geochemical indexes showed that variations of Ba/Sr, Rb/Sr, Ca/Zr and ICV (index of compositional variability) within soil profiles are affected mainly by dissolution and redistribution of calcite and/or gypsum.Based on PCA of Ln-transformed data for elements and selected soil properties, four main types of inter-element relationships could be recognized. These types of relationships which are attributed with host minerals of elements are: the trace elements that tend to be adsorbed on clays or substituted for Al, Fe and K in clay minerals or iron oxides (type 1), highly immobile elements comprising rare earth elements (REEs), Ta, Nb and Th (type 2), elements that can incorporate in silicate minerals lattice including Mg, Na, Zr and Hf (type 3) and finally type 4 with Ca and Sr that reside in calcite and gypsum.The variation of mineralogical composition and as a consequence elemental distributions within soil profiles are influenced by parent materials and pedogenic processes. The abundance and distribution of elements which are in association with each other in types 1, 2 and 3 were mainly controlled by parent materials. In contrast, Ca and Sr were not only affected by parent materials but also by dynamics of calcite and gypsum in soil profiles showing calcification and/or gypsification.By applying cluster analysis on the basis of major and trace elements geochemistry, the soil types are well discriminated and their clustering is influenced by contents of CaCO3, gypsum, clay and Fe2O3.In general, these results support the important influence of parent material on soil geochemistry in arid areas. Additionally, calcification and gypsification, as prevailing pedogenic processes in these areas, can effectively affect elemental distribution within soils.

Monitoring of micromorphological changes in a virgin Solonetz under regional changes in hydrology and climate (Northern Caspian Lowland, Russia)

Over the past 40 years, a clear trend towards an increasing humidity and a rising groundwater table has been observed in the south-eastern semidesert part of European Russia. According to the published data, two clear periods of climate are distinguished: 1950s-1970s and 1970s-2000s. The thin sections of a Solonetz sampled in different periods of time (1950s, 1960s, 1970s, 1982, 2002 and 2013) at the Dzhanybek research station were studied micromorphologically to observe how these natural changes influenced soil pedofeatures. A comparison of thin sections showed no significant changes in soil properties between 1950s and 1982, when the hydrological (ground water table) and climatic parameters remained relatively stable. However, between 1982 and 2013, due to a significant increase in climatic moisture and rising groundwater, the following changes in soil microfeatures took place: the activation of humus accumulation and biogenic structuring, the eluviation of the silty clay-humus matter, the development of solodic features, gleyization of the soil mass, and the accumulation of opaque black organic grains about 2-3 µm formed in the topsoil due to the long stagnation during the springtime after snow melting. The water table rise leads to the consequent rise of the upper boundary of the accumulation of gypsum and carbonates.

Using halogens (Cl, Br, I) to understand the hydrogeochemical evolution of drought-derived saline porewater beneath a prairie wetland

Numerous closed-basin prairie wetlands throughout the Prairie Pothole Region (PPR) of North America maintain moderate surface pond salinities (total dissolved solids [TDS] from 1 to 10gL−1) under semiarid climate by accumulation of gypsum and saline lenses of sulfate-rich porewater (TDS>10gL−1) in wetland sediments during droughts. In order to understand the hydrogeochemical origin and composition of these saline porewaters, we made a detailed geochemical survey of Cl−, SO42−, Br, and I in the porewater, pondwater, and upland groundwater of a typical closed-basin prairie wetland (P1 in the Cottonwood Lake study area, North Dakota). Concentrations of Cl− ranged up to 5.9mM in the saline porewaters, and was strongly correlated with SO42− and Br (Pearson's r>0.7, p<0.05; concentrations ranging up to 131mM and 39μM, respectively) due to the conservative effects of surface water evaporation. In contrast, total dissolved I was not significantly correlated with Cl− (Pearson's r=0.18, p=0.273) and was concentrated in porewaters located above the saline lenses with a peak concentration of 4.1μM beneath the center of the wetland— the highest value for dissolved I ever measured in a terrestrial aquatic system and an order of magnitude above that of seawater. We hypothesize that chromatographic separation between more mobile anions (Cl−, SO42−, Br−) and I occurs during droughts when wetland ponds dry and sedimentary iodide (I−) oxidizes to its less-mobile form, iodate (IO3−). Understanding the origin and geochemical composition of porewater salinity that develops beneath prairie wetlands during drought can help to fingerprint sources of salinity to wetland ponds during wet climate and elucidate halogen systematics in saline and organic-rich subsurface environments associated with hydrocarbon generation.

Soil variability in La Violada Irrigation District (Spain): I Delineating soil units for irrigation

The knowledge of the soil variability is essential for its hydrologic characterization, for irrigation management and planning and especially for water movement modeling. Nevertheless, the scarcity of soil information in Spain precludes its use in irrigation management and, particularly, in the on-going irrigation modernization process. The Violada Irrigation District (VID) comprises 5234ha and is located in a semi-arid gypsum-rich region in northeast Spain. VID has been under flood irrigation since the mid-20th Century and has been modernized recently to sprinkler irrigation. Since the early 1980s water balances in VID have been based on average soil properties and bulk irrigation data. The current irrigation system provides detailed irrigation data at plot level, thus allowing for performing distributed balances (in hydrologic homogenous zones) that require detailed or semi-detailed soil information in the form of a soil map. The objective of this two-part study is to define homogeneous zones in relation to hydrological properties relevant for irrigation management, first defining the soil variability within the VID and then analyzing the soils hydrologic and salinity features (in a companion paper). The specific objectives of this paper were (i) to draw the VID semi-detailed soil map; (ii) to explain the variability of soil properties; and (iii) to map the main soil characteristics related to irrigation management. Thirty four soil pits, located on all the different geomorphological areas, were opened and described. Samples were taken from all the horizons and analyzed for chemical and physical properties. The limits of soil units were drawn with the aid of 32 additional auger holes, the data from 72 pits opened during the irrigation transformation works, and all the previous soil information available. Finally the soils were classified down to family level. The main soil formation processes in VID were carbonation and gypsification. Thirteen soil units were defined, included in five soil subgroups and six particle size families. “Fine” particle sizes were dominant along the gypsum-rich valley bottoms. Coarser textures were found on the heights and showed higher CaCO3 equivalent content and no presence of gypsum accumulations. A priori, the main limitation for irrigation in the valley soils was the limited drainage (due to fine textures and reduced slope) while in the highland soils it might be constrained by their low retention capacity. The high gypsum and carbonate content of the VID soils may prevent the development of infiltration problems. The soil properties map in this work will be the basis for a companion paper delineating the hydrologic properties of the soils, the basis for improved soil water balances.