Calcium Carbonate Accumulation Research Articles

Effect of different aggregates on the properties of carbonated self-pulverized low-calcium clinker mortar

This study investigated the effects of four aggregates - standard sand, manufactured sand, slag, and coal gangue - on the properties of carbonated self-pulverized low-calcium clinker (SPLCC) mortars. The SPLCC, aggregates, and water were mixed in a mass ratio of 1.00:2.50:0.15 and compaction molded, then carbonation cured by 99.99 % CO2 exposure at 0.2 MPa. Tests determined the weight gain, compressive strength, water absorption, and interfacial transition zone (ITZ) microstructure after 1, 4, and 24 h of curing. Results showed the manufactured sand mortar had the highest compressive strength (39.7 MPa) and lowest water absorption (3.50 %) at 24 h, indicating the best macroscopic performance. This was due to the manufactured sand's stone powder content improving SPLCC binding and accelerating calcium carbonate accumulation in the ITZ. Nanoindentation revealed the manufactured sand mortar had the narrowest ITZ width (15 μm). SEM-BSE also showed higher Ca content in its ITZ. The Ca: Si ratio in the ITZ strongly correlated with strength and absorption. Overall, manufactured sand as aggregate can enhance carbonated SPLCC mortar properties, providing potential for precast products.

A closer look at clasts and groundmass: Micromorphological features in sediments with archaeological significance in Obishir and Katta Sai complexes (Central Asia)

The aim of this study is to investigate the relationship between coarse and fine material in sediments at four archaeological sites in Central Asia, which share a common characteristic of coarse clasts dispersed within a silty matrix. By using micromorphology and grain size analysis, the study aims to understand the microscale processes that have affected the geogenic material and, by extension, the potential impact on the archaeological assemblages. The four sites studied are Obishir-1, Obishir-5, Katta Sai 1, and Katta Sai 2, which are located at the toe or along a slope in Kyrgyzstan and Uzbekistan. The study focuses on the micro-features occurring on the surfaces of pebble-sized clasts and identifies four typical features: loamy cappings, loamy coatings, secondary calcium carbonate accumulations, and cracks. The processes related to these features are identified as alteration of the mineral grains, frost action, redeposition, and pedogenetic and anthropogenic processes. The study concludes that the primary contact between the two components has been disrupted in most cases, and suggests that the findings can be used to analyze site formation and post-depositional processes at archaeological sites. Furthermore, analogies with gravel-sized artifacts can be drawn, particularly with regard to secondary calcium carbonate accumulation.

The environmental assessment of soil chemical properties irrigated with treated wastewater under arid ecosystem of Al-Ahsa, Saudi Arabia

PurposeThe present study focused on examining the effect of treated wastewater (TWW) on soil chemical properties. Also, efforts were made to compare the soil chemical properties under TWW irrigation with that under groundwater (GW).Design/methodology/approachDuring the years 2021 and 2022, surface and subsurface soil samples were randomly collected in triplicate by using an auger fortnightly at two depths (20 and 40 cm) from the selected spot areas to represent the different types of irrigation water sources: TWW and GW. Samples of the GW and the TWW were collected for analysis.FindingsThis study examines the impact of TWW on soil characteristics and the surrounding environment. TWW use enhances soil organic matter, nutrient availability and salt redistribution, while reducing calcium carbonate accumulation in the topsoil. However, it negatively affects soil pH, electrical conductivity and sodium adsorption ratio, although remaining within acceptable limits. Generally, irrigating with TWW improves most soil chemical properties compared to GW.Originality/valueIn general, almost all of the soil’s chemical properties were improved by irrigating with TWW rather than GW. Following that, wastewater is used to irrigate the soil. Additionally, the application of gypsum to control the K/Na and Ca/Na ratios should be considered under long-term TWW and GW usage in this study area in order to control the salt accumulation as well as prevent soil conversion to saline-sodic soil in the future. However, more research is needed to thoroughly investigate the long-term effects of using TWW on soil properties as well as heavy metal accumulation in soil.

The Role of Bedrock Geochemistry and Climate in Soil Organic Matter Stability in Subtropical Karst Forests of Southwest China

The stability of soil organic matter (SOM) plays a critical role in soil carbon (C) dynamics under global warming. However, the factors influencing SOM stability, particularly the significance of bedrock geochemistry and its hierarchical relationship with climate and soil properties, remain poorly understood. To address this gap, we conducted a study along a large climatic gradient (Δtemperature > 9 °C) in the subtropical karst forests of southwest China, quantifying SOM stability using thermal analysis and investigating the contributions of bedrock geochemistry, climate, and soil properties. Our results showed that SOM stability was positively correlated with mineral-associated organic C (MAOC) rather than particulate organic C. Hierarchical partitioning analysis further demonstrated that bedrock geochemistry was the predominant contributor to SOM stability variance, accounting for 23.7%. Following this, soil minerals contributed to 21.1%–22.6% of the variance, the mean annual temperature to 20.3%, and microbial biomass C to 17.2%. In particular, bedrock geochemistry—specifically the presence of calcium-rich bedrock—was found to enhance SOM stability by promoting the accumulation of exchangeable calcium and calcium carbonate in soils. Additionally, high temperature improved SOM stability by increasing the content and proportion of MAOC and soil pH. These results highlight the fundamental role of bedrock geochemistry in controlling SOM stability and emphasize the importance of considering hierarchical relationships among bedrock–soil–climate interactions for evaluating soil C dynamics.

Calcium storage in Malpighian tubules and the putative use for pupal chamber formation in a wood-feeding insect

Cerambycid beetles form a chamber to spend their pupal stages in various forms according to the species. The red-necked longhorn beetle Aromia bungii (Coleoptera: Cerambycidae), which is an invasive pest that severely damages Rosaceae trees, makes a pupal chamber at the end of a tunnel deep in the xylem. Beetle larvae and the closely related species form a calcareous lid at the entrance of a pupal chamber. Previous studies on the closely related species conducted more than a century ago suggested that Malpighian tubules (MTs) play a vital role in calcium carbonate accumulation. However, the association between this Ca2+ accumulation and pupal chamber lid formation utilizing the possible calcium compounds stored in MTs have not yet been demonstrated. First, we artificially reared A. bungii larvae from eggs in host branches for 100 days and identified the larval developmental status and pupal chamber formation, using X-ray computed tomography. Second, we collected larvae from the branches and observed the internal organs by direct dissection under a microscope. Finally, we analyzed the elemental distribution, particularly calcium, in the larval gut with MTs, using energy dispersive X-ray fluorescence. The results suggest that immature larvae of A. bungii can accumulate Ca2+ in the MTs through wood tunneling and feeding activities. Ca2+ was stored at the proximal regions in two of the six MTs located posteriorly in the body. Additionally, larvae that formed a calcareous lid at the entrance of pupal chambers in the branches did not store Ca2+ in the MTs, suggesting that the larvae of A. bungii used the stored Ca2+ in their MTs for lid formation.

Genesis and Classification of Termite-Mediated Soils along Toposequences in a Semiarid Area of Southeast Ethiopia

Despite the ecosystem functioning they provide, termite pedoturbation along toposequence is overlooked in the genesis of semiarid soils. Therefore, we aimed to describe morphological and physicochemical properties that lead to the classification of termite-mediated soils. In this study, representative pedons, one on each slope class, were described and classified for five different topographical positions, and the soil properties of genetic horizons were compared to those obtained from respective mounds. The result showed that the soils were heavily manipulated by termites except for the pedon at the toe slope. Cambisols were formed on the summit and back slope and resulted from slow pedogenic processes. Luvisols on the toe slope showed redoximorphic features, and gleization and clay synthesis formed the soil, while the upward movement of coarse particles enhanced textural differentiation. Luvisols at the foot of the slope are formed by the partial destruction of iron-bearing minerals accompanied by eluviation-illuviation processes. Accumulation of calcium carbonate following calcification formed Calcisols on the bottom slope. Comparing the mounds and reference pedons, much of the mound’s soil is mined from the subsoil, usually from B horizons. However, their influence on soil properties depended mainly on the topography. Moreover, the morphological and physicochemical properties of the studied pedons exhibited various degrees of variation along topography and clearly showed topographic effects. In conclusion, termites can be a potent mediator of soil genesis across toposequences, and their activities should be considered in the classification and management of semiarid soils. A further retrospective examination of micromorphological evidence is recommended to support this finding.

Lithological zoning and stable O and C isotopes distribution in carbonates in the Polish native sulfur deposits: Implications for origin of the ores

The northern marginal part of the Polish Carpathian Foredeep hosts numerous native sulfur deposits associated with the Middle Miocene evaporite horizon. These deposits reveal lithological zoning, wherein both the barren and sulfur-bearing limestone zones are embedded within the gypsum basin area (zone). However, such zoning is incompatible with the bioepigenetic formation model of native sulfur deposits. Hence, their genesis remains enigmatic. Regional variations in stable oxygen and carbon isotope values of the limestones disclosed in the Osiek–Baranów Sandomierski native sulfur deposit are inconsistent with the molecular replacement of solid sulfate by calcium carbonate and native sulfur accumulations that expand from a fault zone into the gypsum basin. Instead, the distribution patterns of stable isotopes and sedimentological data suggest that a very shallow freshwater-dominated sedimentary–diagenetic environment developed in the hypersaline basin’s marginal zone, where the mixing of meteoric and highly saline water, as well as various bacterial processes, were responsible for lithological zoning and native sulfur distribution. The proposed results necessitate a reinterpretation of the epigenetic model of native sulfur ore formation.

Calcium carbonate mineralization is essential for biofilm formation and lung colonization

Biofilms are differentiated microbial communities held together by an extracellular matrix. μCT X-ray revealed structured mineralized areas within biofilms of lung pathogens belonging to two distant phyla – the proteobacteria Pseudomonas aeruginosa and the actinobacteria Mycobacterium abscessus. Furthermore, calcium chelation inhibited the assembly of complex bacterial structures for both organisms with little to no effect on cell growth. The molecular mechanisms promoting calcite scaffold formation were surprisingly conserved between the two pathogens as biofilm development was similarly impaired by genetic and biochemical inhibition of calcium uptake and carbonate accumulation. Moreover, chemical inhibition and mutations targeting mineralization significantly reduced the attachment of P. aeruginosa to the lung, as well as the subsequent damage inflicted by biofilms to lung tissues, and restored their sensitivity to antibiotics.This work offers underexplored druggable targets for antibiotics to combat otherwise untreatable biofilm infections.

Application of improved enzyme induced calcium carbonate precipitation (EICP) technology in surface protection of earthen sites

Tabia is a common building material in ancient China. At present, there are few studies on protective materials for tabia ancient buildings, and the existing protective materials of earthen ruins have many problems. To study protective materials that are compatible with the tabia and have superior performance, sucrose and skimmed milk powder improved enzyme induced calcium carbonate precipitation (EICP) technology was applied to the surface protection of tabia relics. The results indicate that the effect of EICP modified by sucrose is better than that of skimmed milk powder. After being treated with 5% sucrose -EICP material, the surface hardness, salt corrosion resistance, weather resistance and water repellency of tabia samples can be increased by 12.7%, 550%, 300% and 512% respectively. The reason is that sucrose regulates the growth morphology of calcium carbonate crystals and provides nucleation sites for them. Moreover, sucrose has certain viscosity, which promotes the accumulation and cementation of calcium carbonate, and finally forms a dense protective layer on the surface of the tabia. Compared with loose calcium carbonate crystal formed by EICP treatment, the protective effect of sucrose improved EICP is significantly improved. Sucrose modified EICP technology can be used as an effective method for the protection of tabia relics and even ancient buildings.

Experimental analysis of inorganic scale deposition in pipes: Mesoscale flow loop development and case study

To study the scaling process in sub-sea pipelines, a mesoscale experimental loop was developed, it was used to generate inorganic salt deposition in a one-inch diameter pipe. A specially monitored test section was developed, it would be removed and weighed after the experiments to study the scale build-up over time. Changes on the experimental conditions such as flow rate and fluid concentration allowed us to understand how calcium carbonate accumulation affects pipeline surfaces over time. The calcium carbonate concentration of the fluid passing through the pipe was controlled using a turbidity meter. The size of the loop, a novelty on the field, allowed us to generate extensive data on the calcium carbonate scaling process, conduct longer experiments, and visualize smaller changes in temperature or accumulation using non-intrusive infrared (IR) technology. The experiments were conducted using IR images and chemical analyses by Energy dispersion X-ray spectroscopy (EDS) and the results were compared with predictions from analytical models.

Effects of Deep Circulation on CaCO3 Dissolution and Accumulation in the Southwestern Atlantic Ocean

AbstractDeep oceanic circulation regulates seafloor calcium carbonate (CaCO3) accumulation by transporting atmospheric carbon dioxide (CO2) to depth and then transferring it, with respired CO2, along the global ocean conveyor belt. This creates the shallowing trend of CaCO3 preservation from the Atlantic to the Pacific Oceans. The thermohaline flow can be, however, complex on a basin‐wide scale; here, we use a state‐of‐the‐art data compilation and a carbonate accumulation/dissolution model to explain the CaCO3 distribution within the basins of the Southwestern Atlantic Ocean. Our results demonstrate that different currents foster systematically dissimilar CaCO3 preservation within these connected ocean basins. The more undersaturated, faster moving, northward‐flowing Antarctic bottom water readily dissolves more CaCO3 than the southward‐flowing North Atlantic deep water. We are able to predict quantitatively these observations, based on benthic carbonate chemistry and mass‐transfer rates. Our model and CaCO3 records in such basins have the potential to provide new understanding about deep‐ocean circulation of the past.

Marmara Denizi’nde iki demersal balık türünün bakalyaro Merluccius merluccius (Linnaeus, 1758) ve tekir (Mullus surmuletus, Linnaeus, 1758)’in otolit kimyası ve otolit morfolojisi üzerine ön çalışma

Otoliths are calcium carbonate (CaCO3) accumulations. Under the influence of different ecosystems morphological and chemical composition change. In this study, economically important two demersal fish species; European hake Merluccius merluccius (Linnaeus, 1758) and Stripet red mullet (Mullus surmuletus Linnaeus, 1758) was examined. Otoliths (Sagitta) belonging to these two species have been studied both chemically and morphologicall. Morphometric measurements of otoliths (length, mm; width, mm; area, mm2; perimeter, mm) in the sagittal of each species was made by the Leica M125 tri-ocular microscope. In the chemical analysis of otoliths, strontium (Sr), magnesium (Mg) and calcium (Ca) trace element amounts, the ratios of Sr and Mg trace elements to Ca element (Sr/Ca and Mg/Ca) were determined. For the micro-chemical analysis of otoliths ICP-MS was used. The highest magnesium (24.92±9.57 mmol/mol) and strontium (26.17±1.81 mmol/mol) element values were found in the otolith of red mullet. The difference between strontium (Sr) and magnesium (Mg) amounts for two fish species was found to be significant (P<0.05). In addition to it was found that the difference between them in the amount of calcium is significant (P<0.001). The shape indexes of otoliths are significantly different between the two fish species. Especially in terms of roundness (RD) and aspect ratio (AR) (P<0.001). The results of this study provide information about the habitats of two economic importance demersal fish species. Since such studies can give information about the habitat areas of fish species, they are important for tracking stocks, migration routes and sustainable fisheries.

Middle to Late Eocene Changes of the Ocean Carbonate Cycle

AbstractSedimentary records show that calcium carbonate (CaCO3) preservation fluctuated during the Eocene. These fluctuations are well documented for the equatorial Pacific. However, data from other basins are sparse. In this study, we report new middle and late Eocene bulk calcium carbonate percentages and accumulation rates from the northwestern Pacific (Ocean Drilling Program—ODP—Site 884) and the Atlantic (ODP Sites 1053, 1090, and 1263) Oceans; in addition, we calculate CaCO3 accumulation rates for sites with published percentage bulk CaCO3 to expand geographic and paleobathymetric coverage. Using these data, we investigate the response of the carbonate cycle to environmental changes (e.g., temperatures, primary productivity, weathering, and ocean circulation) at the beginning of the greenhouse‐icehouse transition (∼43–34 Ma). Our results show that in the middle to late Eocene CaCO3 accumulation rates were highly variable at different paleodepths and ocean basins suggesting that the evolution of carbonate accumulation rates over the Eocene was influenced by different processes in different locations. In particular, our data emphasize the role of surface CaCO3 production and ocean ventilation in driving changes in CaCO3 preservation and burial at the seafloor. Our study also highlights the need for a better understanding of the processes regulating CaCO3 surface production today in order to correctly interpret geological records.

Reef accumulation is decoupled from recent degradation in the central and southern Red Sea

Reefs are biogenic structures that result in three-dimensional accumulations of calcium carbonate. Over geological timescales, a positive balance between the production and accumulation of calcium carbonate versus erosional and off-reef transport processes maintains positive net accretion on reefs. Yet, how ecological processes occurring over decadal timescales translate to the accumulation of geological structures is poorly understood, in part due to a lack of studies with detailed time-constrained chronologies of reef accretion over decades to centuries. Here, we combined ecological surveys of living reefs with palaeoecological reconstructions and high-precision radiometric (U-Th) age-dating of fossil reefs represented in both reef sediment cores and surficial dead in situ corals, to reconstruct the history of community composition and carbonate accumulation across the central and southern Saudi Arabian Red Sea throughout the late Holocene. We found that reefs were primarily comprised of thermally tolerant massive Porites colonies, creating a consolidated coral framework, with unconsolidated branching coral rubble accumulating among massive corals on shallow (5–8 m depth) exposed (windward), and gently sloping reef slopes. These unconsolidated reef rubble fields were formed primarily from ex situ Acropora and Pocillopora coral fragments, infilled post deposition within a sedimentary matrix. Bayesian age-depth models revealed a process of punctuated deposition of post-mortem coral fragments transported from adjacent reef environments. That a large portion of Saudi Arabian Red Sea reef slopes is driven by allochthonous deposition (transportation) has important implications for modeling carbonate budgets and reef growth. In addition, a multi-decadal lag exists between the time of death for branching in situ coral and incorporation into the unconsolidated reef rubble. This indicates that recent climate related degradation in the 21st century has not had an immediately negative effect on reef building processes affecting a large portion of the reef area in the Saudi Arabian Red Sea.

Exploring the Presence of Five Rare Earth Elements in Vineyard Soils on Different Lithologies: Campo de Calatrava, Spain

The aim of the work described here was to understand the pedogeochemical signature of five rare earth elements (REEs; Ce, Nd, La, Y, and Sc) in vineyard soils in Campo de Calatrava (a unique territory with calcareous, volcanic and metamorphic rocks). The mean contents in surface horizons of Ce, Nd, La, Y, and Sc were 65.7, 32.0, 35.5, 18.8, and 13.9 mg·kg–1, respectively. In subsurface horizons the contents were Ce 62.8, Nd 31.1, La 35.7, Y 17.9, and Sc 14.4 mg·kg–1. The results show that mean contents of REEs in the area under investigation are in the order Ce > Nd > La > Y > Sc. Ce has a very high range, with a value close to 150 mg·kg–1. On the other hand, concentrations of Ce, Nd, Y, and Sc are higher in soils on volcanic material than in soils on nonvolcanic material, while only La values are lower in soils on volcanic rocks. The distributional maps of REEs in surface and subsurface horizons suggest that parent material and pedogenesis such as argillization and calcium carbonate accumulation are more important factors than the use of REE-based fertilizers, except in certain exceptional cases (consistent with a possible specific human impact after continuous fertilization).

Calcium carbonate accumulations in Technosols of Moscow city

Complex phenomena of the precipitation and accumulation of calcium carbonate in urban soils and sediments have been studied. They are linked to the interactions between the lithosphere, the biosphere, and the atmosphere. Calcium and its compounds are among the main elements determining soil’s morphological, physical, and chemical characteristics. This study was aimed at summarizing information about calcium carbonate concentrations in soils and finding evidence for the formation of carbonate micronodules by pedogenetic processes in Urbic Technosols under automorphic conditions. Moscow is located within the southern taiga belt, with a humid temperate climate and a percolative water regime. The city’s technogenic deposits contain significant amounts of carbonates due to inclusions of construction waste and additions of airborne dust. Contemporary humus-accumulative horizons of Urbic Technosols were found to contain carbonate accumulations (rounded or isomorphic nodules). Samples from such horizons were studied using a polarizing microscope (analysis of thin sections) and a scanning electron microscope with an energy-dispersive X-ray analyzer (element mapping to detect carbonate accumulations). Laboratory analyses of main chemical and physical soil properties were performed. The analyzed samples contained both primary (i.e., inherited from parent materials) and secondary (i.e., newly formed in soils) calcium carbonates in various forms. Inclusions of solidified mortar (carbonate building solutions) contained dolomite. Although the studied carbonates underwent recrystallization processes, they remained in soils for a long time. Fibrous Mg silicate films deposited at the surface of recrystallization areas were observed. The formation of carbonate micronodules at depths of 15–40 cm in slightly and moderately calcareous humus horizons was investigated. Newly formed calcite was distinguished by a homogeneous composition, a microsparitic size of crystals, and a compact packing within the groundmass. Newly formed calcite was observed within microzones that were free from carbonate inclusions with dissolution features. The dissolution of primary carbonates in soils under humid climate conditions triggers pedogenetic processes of the carbonate heritage redistribution and the mineral matrix transformation. Recrystallized carbonates are the main forms of secondary carbonate accumulations in automorphic Technosols. The presence of compact carbonate nodules composed of microsparitic calcite within the bulk of silicate material may be indicative of carbonate neoformation as a result of interactions between the dissolved CO2 from root respiration and the soil absorbing complex saturated by Ca from soil solution. This is confirmed by a number of studies on the carbonate isotopic composition in urban soils.

Study on the Changes of Calcium Carbonate and Organic Carbon in the Soil after the Feldspathic Sandstone and Sand Compounding

By analyzing the changes of calcium carbonate and free iron oxide in inorganic cement materials in different proportions of the feldspathic sandstone and sand compounding soil under different tillage years (2a and 9a), the calcium carbonate and free soil in the soil were determined in two years. The average content and relationship of iron oxide. The results show that the average content of calcium carbonate is the highest in the mixed soil of feldspathic sandstone and sand in the ratio of 1:2, the ratio is more favorable for the accumulation of calcium carbonate in 0-30cm soil surface inorganic colloid. The difference of organic carbon content in 0-10cm and 10-20cm soil layers was significant, but it was not significant in 20-30cm soil layers. After the mixture of feldspathic sandstone and sand for 9a, the highest content of organic carbon in each soil layer is the mixture of feldspathic sandstone and sand according to 1:1. From the mixture soil which has been cultivated for 9a, the soil layers of 10-20 cm and 20-30 cm, the content of organic carbon tends to be stable in each proportion. The average organic carbon content was 2.00 g/kg in 2a and 3.37 g/kg in 9a, which increased by 68.50% compared with 2a.

The pedogenic formation of coal balls by CO2 degassing through the rootlets of arborescent lycopsids

Coal balls are calcium carbonate accumulations that permineralized peat in paleotropical Permo-Carboniferous (∼320–250 Ma) mires. The formation of coal balls has been debated for over a century yet a widely applicable model is lacking. Two observations have been particularly challenging to explain: 1) the narrow temporal occurrence of coal balls and 2) their typical elemental (high Mg) and isotopic (low δ18O) composition that paradoxically indicate marine and freshwater origins, respectively. We evaluate a new model in which coal balls formed as CO2 escaped from the peat by diffusion through unusual air-filled spaces in the rootlets of lycopsid trees; critically, these trees were very common in paleotropical mires, and their evolutionary range matches the temporal range of coal balls. The episodic delivery of seawater and marine carbonate sediment to coastal mires is the first step in our model, although other pathways for the delivery of divalent cations are permissible. Subsequent dilution by freshwater and dissolution of these carbonates at the elevated CO2 of the mire subsurface is followed by the transport of CO2 through the rootlet airspaces and into the overlying water and atmosphere, which drives carbonate mineral precipitation in the sediment. We show that dilution by freshwater, because it minimally affects Mg/Ca ratios, can result in relatively low pore water δ18O values while allowing high-Mg calcite formation. This model thus explains the restriction of coal balls to the Permo-Carboniferous and resolves the discrepancy between elemental and isotopic compositions of coal ball carbonate minerals. Furthermore, we show with a 3D reactive transport model that CO2 could escape rapidly enough through the rootlets to fill 25 percent of the peat pore spaces with calcite before substantial burial (top decimeter of peat), explaining the exceptional preservation of coal swamp flora. Therefore, we suggest that coal balls are pedogenic in origin and that the disappearance of these pedogenically permineralized Histosols represents the first documented decrease in soil diversity on a vegetated planet. The rock record may thus provide important context for the modern loss and degradation of soils.

Characterization and Formation of Salt affected Soils in Eastern Rajasthan Upland

Soils of the Bhilwara district are affected with different degree and extent of soluble salts. These soils are distributed in hot semi-arid agro-ecological sub region of Rajasthan. It is located between 25o 01' to 25o 58' N latitude and 74o 01' to 75o28' E longitude at an elevation between 380 and 500 meters above the mean sea level. The physico-chemical analysis of soils revealed the dominant cations such as sodium followed by calcium. Exchangeable sodium percentage was ranged 23.1 to 54.6, 17 to 38.5 and 7.1 to 20.0 in saline, sodic and saline-sodic soils, respectively. The Sodium Adsorption Ratio varied from 2.5 to 16.8, 3.2 to 9.4 and 3.8 to 12.6 in these problematic soils, respectively. Soil reaction was ranged from 7.6 to 8.4, 8.5 to 9.3 and 8.5 to 8.8 whereas electrical conductivity of saturation extract varied from 14.4 to 25.2, 1.0 to 5.6 and 2.4 to 13.6 dSm-1 in saline, sodic and saline-sodic soils, respectively. Area under saline and saline-sodic soils was moderately-well to well drained whereas sodic soils were imperfectly drained. Accumulation of calcium carbonate showed increasing trend with depth of profile in all three soils. Mean values of adjusted sodium adsorption ratio of irrigation water was 43.55, 41.88 and 36.74 for saline, saline-sodic and sodic soils. Use of low quality underground water for irrigation, aggravated the process of formation of the salt affected soils in eastern Rajasthan Uplands.

Pseudo soil in hyper-arid ephemeral stream channel beds: Geo-ecological implications of the fluvio-pedogenic unit (FPU)

The type of stratum in dryland ephemeral channel beds (wadis) determines its hydrological characteristics, which impact vegetation productivity. The objective of this study was to assess some key properties of a cemented, fine-grained bed stratum, previously characterized as a fluvio-pedogenic unit (FPU), as well as those of the overlying non-cohesive gravel bed stratum, known as a fluvially active unit (FAU). While the latter is an outcome of regular fluvial processes of recurring scour and fill, the former is characterized by horizonation, calcium carbonate deposition, oxidation, and accumulation of fine-grained material, defining it more as a soil or pseudo soil than as a sediment. The study was conducted in the hyper-arid southern Negev and Arava Valley of Israel, where the FAU and the underlying FPU were investigated, focusing on geo-ecological functioning. The results revealed considerable differences between the two types of strata. The contents of hygroscopic moisture, total organic carbon, and calcium carbonate were fourfold, 57%, and 36% greater, respectively, in the FPU than these in the FAU. Above all, the fine particle contents, including the clay and silt fractions, were almost eightfold and almost sixfold greater, respectively, for the FPU than those for the FAU, characterizing the former as loamy fine sand and the latter as fine sand. Altogether, these properties determine the stratum's field capacity and permanent wilting point, which were 73% and 50% greater, respectively, in the FPU than those in the FAU. In turn, the last two properties determine the available water capacity, which was almost twofold greater under the FPU than that under the FAU. Considering the (i) FPU's mean thickness of 0.6 m; (ii) FPU's horizonation into A, B, and C horizons; and (iii) a 70–90% decrease in available water capacity between FPU's A and B horizons, as well as between its B and C horizons, then the total available water capacity throughout this stratum's thickness is 20–87% greater under the FPU than that under the FAU. In addition, the FPU's cemented nature seems to provide a safe stratum that remains stable during floods, sustaining the establishment and growth of deep-rooted perennial vegetation. It is concluded that the FUP's properties have positive implications for vegetation growth and survival under the harsh climatic conditions across the region.