Salt Crust Research Articles

Efficient evaporation of seawater desalination by novel double-interface evaporator: Photothermal conversion, water transfer and salt-resistant

Interfacial solar-driven water evaporation emerged as an established eco-friendly method for seawater desalination to combat water scarcity, yet the low water evaporation rate and cost-effectiveness limit the practicable application. Herein, we presented a double-interface evaporator with a bilayer structure (BCCu@FC). The upper layer was constructed using carbonized copper-doped biochar (BCCu), which exhibited broadband sunlight absorption and effective photothermal conversion capability for the localized surface plasmon resonance (LSPR) effect. Meanwhile, the lower layer was constructed by felt fabric (FC), which featured a large spatial network structure, guaranteeing sufficient water transportation. Therefore, BCCu@FC exhibited a high photothermal conversion efficiency of 87.05% with a 1.571 kg m-2 h-1 water evaporation rate under 1 sun illumination. Moreover, BCCu@FC further exhibited high stability and salt resistance, showing no significant salt crust formation after continuous operation for 24 h under 3.5 wt% brine. Especially, BCCu@FC could stably work under 21 wt% brine, and the salt crust re-dissolved within 4 h after the cessation of illumination. This facile and universal strategy was anticipated to pave the way for future designs and fabrication of diverse, more efficient, and cost-effective photothermal conversion devices.

Evaporation of a heated saline marble: Interplay of interfacial and thermal effects

A multistage evaporation of continuously heated liquid marbles, coated with polytetrafluoroethylene colloidal particles was investigated experimentally and theoretically. Liquid marbles initially contained an almost saturated aqueous NaCl solution. Numerical heat transfer calculations and analytical evaluations of initial evaporation showed that the equilibrium marble temperature and saturated salt concentration are reached relatively rapidly compared to the “long” marble evaporation time. This means that a typical long period of marble evaporation is determined by the low permeability of the salt crust formed beneath the marble colloidal shell. A theoretical estimation of the total evaporation time of marble water based on Darcy's law for the porous crust and the marble shell is suggested. A comparison with experimental data allowed obtaining an approximate value of the very low permeability of this bilayer barrier to marble evaporation. The proposed phenomenological model of the saline marble evaporation provides insight into why marble evaporation is so slow.

Episodic sediment accumulation linked to global change in the endorheic Qaidam Basin of the Tibetan Plateau revealed by feldspar luminescence dating

Given its high accumulation rate in sediments, the endorheic basin in arid regions plays a crucial role in reconstructing paleo-environment. However, it would not provide high-resolution climatic records if significant wind-eroded depositional hiatuses were inevitable within a severe wind environment. Unconformable contacts have been found during field survey in the top part of the stratigraphy in the Qaidam Basin, a prototypical endorheic basin in central Asia. To elucidate whether the sediment is continuous, we employed luminescence dating methods of feldspar pIR200IR250 and quartz OSL to date sediments, including lacustrine sediments and salt crusts, from the Qarhan Playa that is the Quaternary depositional center of the Qaidam Basin. Various experiment tests, including preheat plateau, dose recovery, and residual dose, were conducted. The dating results show that the feldspar pIR200IR250 can provide dependable ages with negligible residual doses. The pIR200IR250 dating ages within the last glacial cycle reveal several environmental shifts. A Qarhan paleolake in Marine Isotope Stage (MIS) 5 was demonstrated by the cluster ages of ∼140–80 ka of lacustrine sediments. The salt crust ages of 136 ± 10 ka and 97 ± 6 ka indicate that, before completely disappeared, the paleolake with shallow dish-shape depression had been dried up more than once, illustrating “shallow——dry——shallow” cycles. The playa in the eastern Qaidam Basin evolved mainly in warm periods, such as MIS 5 and MIS 1, supported by the salt crust ages of MIS 5 (136 ± 10 ka and 97 ± 6 ka) and MIS 1 (10 ± 1 ka and 0.6 ± 0.1 ka). Depositional hiatus in the last glacial cycle were identified by unconformable contacts in three sections between the lacustrine strata and their overlying playa strata, with corresponding age gaps of 158 ± 20–97 ± 6 ka, 131 ± 10–10 ± 1 ka, and 84 ± 7–0.6 ± 0.1 ka, respectively. In all the three sections the sediments for the whole of the last glacial period is missing, eroded by wind. This process should have occurred periodically during the glacial-interglacial cycles of the orbital global climatic changes. The results also show that hiatuses are common for endorheic basins on the Earth with age gaps of up to ∼100 ka, suggesting that robust chronology should be established before any climatic correlation due to severe wind erosion leading to episodic sediment accumulation.

Characteristics and Mechanism of Salt Weathering in Moist Earthen Sites: A Case Study on China’s Jinsha Earthen Site

ABSTRACT This study investigates salt weathering in the indoor, humid environment of China’s Jinsha earthen site. Methods such as digital microscope, scanning electron microscopy (SEM), ion chromatography (IC), energy dispersive spectroscopy (EDS), and laser particle size analysis were employed to collect and analyze samples from four heavily weathered walls. The sampling approach took into account differences in depth and height and prioritized the extraction from various weathering layers to unveil the attributes, causes, and mechanisms of salt weathering. The findings indicate that the Jinsha site’s eastern segment suffered salt-induced damage, such as powdering, salt crusts, and blistering, due to the presence of gypsum and magnesium sulfate. These salts were primarily sourced from groundwater. Groundwater ions ascended to the site’s surface via capillary action, instigating various forms of salt damage. Salt damage severity has a direct link to salt and moisture content. The degradation patterns can be categorized into powder and multi-layered composite deterioration, both seems related to soil particle composition. Powder deterioration tends to occur when the sand content exceeds 40%. This research proposes preservation strategies that focus on managing groundwater and conducting environmental surveillance. These measures are designed to effectively address and mitigate the risks associated with salt damage.

3D change detection for cultural heritage monitoring: Two case studies of underground sculptural reliefs

The preservation of underground cultural heritage is a challenging goal. Difficult acquisition conditions, the need for uniformity of temporal data and the speed at which surfaces change are some of the issues to consider. Also, quantifiable three-dimensional data are often unavailable when assessing changes on sculptural reliefs because traditional records are two-dimensional. In this paper, we present a workflow to easily detect and measure 3D superficial changes in sculptural reliefs using the deviation analysis technique. We compared multitemporal surveys, testing a quantitative, replicable, and verifiable procedure in two case studies: the reliefs of Pakal's Tomb at Palenque, Mexico, and those of the Osimo Caves in Italy. Both are located underground and show similar superficial alterations such as material disaggregation, efflorescence, salt crusts, and biological colonization. The reliefs showed visible and quantifiable changes on the deviation maps. The procedure to detect changes can be implemented with models generated by structured light scanning as well as photogrammetry.

Kalidium cuspidatum colonization changes the structure and function of salt crust microbial communities.

The changes of soil moisture, salinity, and nutrients by halophyte colonization in high-salinity environment profoundly affect the assembly and structure of microbial communities. However, salt marshes in arid region have received little attention. This study was conducted in Lianhuachi Lake, a typical inland salt marsh wetland in China, to determine the physicochemical characteristics of salt crusts in [Kalidium cuspidatum (Ung.-Sternb.) Grub.] colonization areas and bulk soil, respectively, and to analyze the microbial community structure of salt crusts by high-throughput sequencing. Kalidium cuspidatum colonization significantly decreased total salinity, soil water content, and water-soluble ions of salt crusts and increased total carbon, total nitrogen, and total phosphorus content. At the same time, changes in physicochemical properties caused by Kalidium cuspidatum colonization affect the ecological processes of bacterial, fungal, and archaeal community assemblies in salt crusts. In addition, cross-kingdom network analysis showed that Kalidium cuspidatum colonization increased the complexity and stability of microbial networks in salt crust soils. Functional projections further showed that bacterial diversity had a potential driving effect on the nitrogen cycle function of salt crust. Our study further demonstrated the different ecological strategies of microorganisms for halophyte colonization in extreme environments and contributed to the understanding of restoration and management of salt marsh wetlands in arid region.

Geoecological evolution of New Zealand’s only inland salt lake

ABSTRACT The Sutton Salt Lake is a rare occurrence of an inland evaporative saline lake on a small landmass with a temperate maritime climate. The lake lies on a bed of impermeable loess silt in a 2 ha depression between tor ridges of Otago Schist in inland east Otago. A rim of salt-tolerant plants (halophytes) occurs around parts of the lake margin. The vegetated lake margin has encroached laterally on to the lake bed by 5–30 m over the past 50 years. Salinity in the lake is dominated by Na and Cl (molar ratio ∼1) that has been concentrated by annual cycles of evaporation and replenishment by rain with marine aerosols. Drying lake margin sediments lose NaCl via rain-driven recycling back into the lake, with the formation of a salt crust that contains Ca, Mg and Na carbonate minerals, gypsum, and remnant halite. The lake and lake sediment chemistry are affected by carbonate dissolution and deposition, and more than 10-fold Ca–Mg carbonate supersaturation in lake waters contributes to elevated water pH (8.9–9.3). Geoecological evolution of the lake margin involves the encroachment of exotic weeds behind active halophytic habitats as dilute surface water lowers salinity.

Observations of Decadal-Scale Brine Geochemical Change at the Bonneville Salt Flats

Over the past century, the Bonneville Salt Flats, which lies on the western edge of the Great Salt Lake watershed, has experienced changing environmental conditions and a unique history of land use, including resource extraction and recreation. The perennial halite salt crust has decreased in thickness since at least 1960. An experimental restoration project to return mined solutes began in 1997, but it has not resulted in anticipated salt crust growth. Here, primary observations of the Bonneville Salt Flats surface and subsurface brine chemistry and water levels collected from 2013 to 2023 are reported. Spatial and temporal patterns in chemistry, focused on density and water stable isotopes, are evaluated and compared with observations across seven periods of research spanning from 1925 to 2023. Declining salinity in the areas to the east of extraction ditches and south of Interstate 80 were observed. Brine extracted for potash production decreased in salinity as extraction rates increased. Between the years 1964 and 1997, the salinity of the shallow aquifer brine located beneath and to the east of the crust experienced a decrease. However, following this period, the salinity stabilized and subsequently increased. Salinity recovery was concurrent with declines in brine extraction and the salt restoration project, with the largest decrease in brine extraction being concurrent with the largest recovery in salinity. The specific impact of the restoration project on the brine salinity increase remains unclear. To the west, the shallow aquifer in the area between the Silver Island Mountains and the salt crust has increased in salinity. This increase is accompanied by a decline in groundwater levels, which enables the underground movement of solutes from east to west, following a salinity gradient away from the saline pan. Over the past 25 years, the alluvial-fan aquifer along the Silver Island Mountains has markedly declined, leading to increasingly more saline and isotopically heavier basinal waters to be extracted for industrial use. This change is concurrent with the onset of the salt restoration project, which relies on alluvial-fan aquifer waters. This compilation of changes in groundwater chemistry provides an important resource for stakeholders working to understand and manage this dynamic and ephemeral evaporite system. It also offers an example of decadal-scale change in a highly managed Great Salt Lake watershed saline system.

Wind Erodibility and Particulate Matter Emissions of Salt‐Affected Soils: The Case of Dry Soils in a Low Humidity Atmosphere

AbstractArid and semiarid ecosystems around the world are often prone to both soil salinization and accelerated soil erosion by wind. Soil salinization, the accumulation of salts in the shallow portions of the soil profile, is known for its ability to decreases soil fertility and inhibit plant growth. However, the effect of salts on soil erodibility by wind and the associated dust emissions in the early stages of soil salinization (low salinity conditions) remains poorly understood. Here we use wind tunnel tests to detect the effects of soil salinity on the threshold velocity for wind erosion and dust production in dry soils with different textures treated with salt‐enriched water at different concentrations. We find that the threshold velocity for wind erosion increases with soil salinity. We explain this finding as the result of salt‐induced (physical) aggregation and soil crust formation, and the increasing strength of surface soil crust with increasing soil salinity, depending on soil texture. Even though saline soils showed resistance to wind erosion in the absence of abraders, the salt crusts were readily ruptured by saltating sand grains resulting in comparable or sometimes even higher particulate matter emissions compared to non‐saline soils. Interestingly, the salinity of the emitted dust is found to be significantly higher (5–10 times more) than that of the parent soil, suggesting that soil salts are preferentially emitted, and airborne dust is enriched of salts.

Soil-geochemical assessment of salinization of the territory adjacent to the Kuchuk salt deposit (Altai Krai)

A soil geochemical analysis was conducted to assess the impact of the exploitation of the Lake Kuchuk salt deposit on the salinization of the soils in the adjacent areas. The specific characteristic of the soil forming in the Kulunda steppe is the wide distribution of salinization processes. Solonetzes soils are distributed in the impact zone of the deposit exploitation; therefore, as background soils, we considered also Solonetzes. Background soils are located at a considerable distance (2–10 km) from industrial facilities. The results of the chemical analysis of the soil-water extracts showed that the area of the most intense salinization is concentrated in the eastern and southeastern parts of the depression of the former lake. Nowadays, a salt evaporation pond and an open salt storage, which are the main industrial sources of sodium sulfate dust, occupy the bottom of the lake. The maximum salt content (over 1%) was found in these parts of the basin and is associated with the prevailing wind direction in the study area. With an increase in the hypsometric level of the surfaces and the distance from the open technological sources of dust, as well as on the opposite slope of the basin, there was a sharp (2–3 times) decrease in the salt content. The total salt content in the background soils ranged from 0.3 to 0.6%. The specificity of the chemistry of soil salinization in the impact zone was the dominance of sulfates and sodium in the composition of the soil-water extract, and thenardite, which is a dehydration product of mirabilite, in the composition of salt crust minerals and salt efflorescences. In the background Solonetzes, the participation of soda in the chemical composition became more noticeable, which is a natural halogen geochemical feature of the Kulunda steppe. In the surface salt crusts in the background areas, a greater variety of minerals were noted, among which there were typical minerals of the evaporite association (gypsum, halite, calcite, dolomite, mirabilite) and their rare species (konyaite, wedellit).

Shotgun Metagenomics-Guided Prediction Reveals the Metal Tolerance and Antibiotic Resistance of Microbes in Poly-Extreme Environments in the Danakil Depression, Afar Region.

The occurrence and spread of antibiotic resistance genes (ARGs) in environmental microorganisms, particularly in poly-extremophilic bacteria, remain underexplored and have received limited attention. This study aims to investigate the prevalence of ARGs and metal resistance genes (MRGs) in shotgun metagenome sequences obtained from water and salt crust samples collected from Lake Afdera and the Assale salt plain in the Danakil Depression, northern Ethiopia. Potential ARGs were characterized by the comprehensive antibiotic research database (CARD), while MRGs were identified by using BacMetScan V.1.0. A total of 81 ARGs and 39 MRGs were identified at the sampling sites. We found a copA resistance gene for copper and the β-lactam encoding resistance genes were the most abundant the MRG and ARG in the study area. The abundance of MRGs is positively correlated with mercury (Hg) concentration, highlighting the importance of Hg in the selection of MRGs. Significant correlations also exist between heavy metals, Zn and Cd, and ARGs, which suggests that MRGs and ARGs can be co-selected in the environment contaminated by heavy metals. A network analysis revealed that MRGs formed a complex network with ARGs, primarily associated with β-lactams, aminoglycosides, and tetracyclines. This suggests potential co-selection mechanisms, posing concerns for both public health and ecological balance.

Sedimentary evolution and lake level fluctuations of Urmia Lake (north‐west Iran) over the past 50 000 years; insights from Artemia faecal pellet records

AbstractA 25 m long sediment core from hypersaline Urmia Lake (north‐west Iran) was studied for the Late Quaternary depositional history and palaeoclimate variations using the abundance and compositional characteristics of Artemia faecal pellets. Sediment analysis is supported by scanning electron microscopy – energy dispersive X‐ray spectroscopy, organic and inorganic carbon content measurements, and stable isotopes (δ13C and δ18O) from faecal pellet carbonates. The imprecise chronology of the core back to 50 kyr bp is supported by ten radiocarbon ages from faecal pellets and bulk sediments. The palaeoenvironmental record is subdivided into four periods: (i) During much of Marine Isotope Stage 3, a period of lake level lowering is characterized by a decreasing amount of faecal pellets, and an increasing amount of coated grains, sulphate minerals and reworked shell fragments. (ii) During late Marine Isotope Stage 3 and early Marine Isotope Stage 2 a lake level lowstand and a lake floor exposure is interpreted based on the relatively low abundance of pellets, which are multicoloured and appear together with volcanic lithics and rounded sulphate minerals. (iii) During late Marine Isotope Stage 2 the record is devoid of pellets but dominated by large sulphate crystals suggesting a prolonged low lake level. (iv) During Marine Isotope Stage 1 a relative lake level highstand is rapidly established with sediments that are highly abundant in fresh pellets. The modern lake level lowstand is represented by a salt crust. The δ13C and δ18O records measured from faecal pellet carbonates suggest a link with the precipitation versus evaporation balance in the lake over time. From bottom to top the linear trend towards more negative delta values illustrates the increasing amount of precipitation arriving at the lake from the Late Pleistocene to the Holocene. Two prominent isotope minima during the Late Pleistocene and one prominent minimum in the early Holocene mark relative high lake levels, which can also be linked to Lake Van in Turkey.

Концентрация и эмиссия метана и сероводорода в озере Баскунчак, ручье балки Улан-Благ и дегазирующих источниках подземных вод в весенний период

For the first time, the distribution of methane in the brine and bottom sediments of Lake Baskunchak, as well as its tributary, the Ulan-Blag stream, in the beam of which the discharge of ascending degassing groundwater sources takes place, was studied. In addition to CH4, concentrations of total hydrogen sulfide (ΣH2S), Eh and pH values, humidity and density were determined in various horizons (up to 35 cm) of stream sediments. Concentrations of CH4, major ions and pH values were determined in the brine of the lake and stream; experimental measurements of CH4 emission by the chamber method were carried out on one of the debit fields where degassing sources are discharged. Brine mineralization in Lake Baskunchak is 312 g/dm3, which is 2.1 times more than in the Ulan-Blag stream; the water class in the stream and lake is chloride, the sodium group, type II and III, respectively. The fluxes of CH4 into the atmosphere from the surface of the studied degassing source vary in the range of 1.97–2.07 mg/(m2 h). In the brine of degassing sources, a high concentration of CH4 (up to 215 μl/dm3) is recorded, which is 1-2 orders of magnitude higher than in the brine of the lake. Low concentrations of CH4 in the brine of the lake are due to its insignificant flow from bottom sediments into the water due to the presence of a salt crust that prevents gas emission, as well as due to its small concentrations in the upper layers of sediments (0.01 μg/g). Low concentrations of CH4, despite the reducing conditions, are also characteristic of the sediments of the mouth of the Ulan-Blag creek (0.04–0.32 μg/g), which, at high concentrations of ΣH2S in them (0.06–1.32 mg/g), is probably caused by the suppression of methanogenesis in the sediments by sulfate reduction. In general, the distribution of CH4 and ΣH2S along the vertical of deposits is quite synchronous (r = 0.64) and correlates with the distribution of Eh values.

Effects of sodium chloride crystallization on shear characteristics of road base aggregates under unsaturated state

The precipitation and intrusion of sodium chloride into pavement structures is inevitable in coastal regions, which can affect the mechanical properties of the road base courses. To investigate this problem, samples with sodium chloride solution were cured in a thermostatic chamber until they reached the specified states of sodium chloride precipitation within the pores. A critical crystallization degree ( ωc) was discovered by computerized tomography scan, corresponding to the start of the formation of porous salt crust cementing the soil particles. A series of unsaturated large-scale triaxial shear tests were then conducted under various states of salt crystallization. The results showed that in the early stages of crystallization (i.e., ω < ωc), the peak stress and internal friction angle decreased with ω because of the coating and lubricating effects of salt powders, while the apparent cohesion remained constant. When ω > ωc, owing to the increasing adsorption and cementation effects of the salt crust, rapid growth was observed for the peak stress, internal friction angle, and apparent cohesion of the road base aggregates. Considering the influence of salt precipitation, a modified shear strength criterion that can predict the shear strength of the salinized road base aggregates was formulated.

Geochemistry of Sabkhas in Abu Ghraib, Western Baghdad, Iraq

The study aims to detail the chemistry of Sabkha located in Abu-Graib, western Baghdad to know the content of the rare elements distributed. Sabkhas are found in dry areas with significant evaporation rates. The quantity of dissolved salts rises as water evaporates from the shallow basins, eventually causing salt to crystallize. The creation of the distinctive salt pans and crusts on the top is greatly influenced by this process. The trace elements (Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Sn, Ba, Ta, Tl, Pb, Th, U, I, and Br) beside the major oxides were analyzed using XRF technique. There are no clear significant differences in the distribution of the elements between the two Sabkhas in the village of Kadim Alaa’ab and the village of Haj Shiaa. Sabkhas are characterized by limited oxygen supplies in the brine, high temperatures, and precipitation of evaporite minerals including chlorides, sulfates, and sulfides. Halite predominates in the Sabkha sediments due to the association of chloride with Na2O. The CaO is distributed forming calcite, dolomite and gypsum as well as a small amount of clay minerals. The association of trace elements, especially Ni, Rb, Ta, Tl and Br, is mainly concentrated with clay minerals, followed by their concentration in silica, especially Y, Zr and Th. As for halite, it is not associated with trace elements.

Archaeal type IV pili stabilize Haloferax volcanii biofilms in flow

Multicellular communities of contiguous cells attached to solid surfaces called biofilms represent a common microbial strategy to improve resilience in adverse environments.1,2,3 While bacterial biofilms have been under intense investigation, whether archaeal biofilms follow similar assembly rules remains unknown.4,5Haloferax volcanii is an extremely halophilic euryarchaeon that commonly colonizes salt crust surfaces. H.volcanii produces long and thin appendages called type IV pili (T4Ps). These play a role in surface attachment and biofilm formation in both archaea and bacteria. In this study, we employed biophysical experiments to identify the function of T4Ps in H.volcanii biofilm morphogenesis. H.volcanii expresses not one but six types of major pilin subunits that are predicted to compose T4Ps. Non-invasive imaging of T4Ps in live cells using interferometric scattering (iSCAT) microscopy reveals that piliation varies across mutants expressing single major pilin isoforms. T4Ps are necessary to secure attachment of single cells to surfaces, and the adhesive strength of pilin mutants correlates with their level of piliation. In flow, H.volcanii forms clonal biofilms that extend in three dimensions. Notably, the expression of PilA2, a single pilin isoform, is sufficient to maintain levels of piliation, surface attachment, and biofilm formation that are indistinguishable from the wild type. Furthermore, we discovered that fluid flow stabilizes biofilm integrity; as in the absence of flow, biofilms tend to lose cohesion and disperse in a density-dependent manner. Overall, our results demonstrate that T4P-surface and possibly T4P-T4P interactions promote biofilm formation and integrity and that flow is a key factor regulating archaeal biofilm formation.

Brine geochemical changes and salt crust evolution of Lake Urmia in Iran

Gradual desiccation of Lake Urmia (LU) in the northwest of Iran has led to catastrophic water loss by 2022 promoting the salt crust (SC) deposition on the lake bed. Therefore, this study aimed to investigate 1) the effect of water level on the brine composition, 2) the effect of gradual lake desiccation on SC formation, mineralogy and stratification and 3) the SC formation and mineral precipitation in a lab-scale experiment. In 2019, brine and SC samples were collected in July and October, and analyzed for the prevailing ions and minerals. For the simulation experiment, brine samples were added in two vessels and the change in pH, ionic composition and SC evolution were investigated. The wet season brine type changed from Mg-Na-Cl to Na-Mg-Cl and remained unchanged throughout the dry season. In vessels, Mg2+ and Na+ became dominant ions in the surface and subsurface layers respectively, while Cl- remained roughly unchanged; and minerals gradually precipitated from the margins to the center of the vessels based on their solubility. Similar to the lake SCs, in the simulation vessels, halite dominated the SCs and bischofite (MgCl2·6H2O) was detected in most of the vessels’ layers. The formation of oldhamite (CaS) in both in the vessels and the lake SC indicated the prevalence of low oxygen conditions. In the simulation vessel, Calciolangbeinite (K2CaSO4(H2O)4) was one of the first minerals to form along with halite, while Starkeyite (MgSO4·(H2O)4) and Kieserite (MgSO4·(H2O)) were the latest minerals to precipitate. The absence of magnesium sulfate minerals under natural conditions in both newly formed SCs in 2019 and those dated back to 2005, suggested that if the lake level continues to drop, magnesium sulfate minerals will be the final product of the brine. The existence of a dark silicate layer within SC stratification helped to investigate the evaporate deposition at the early stages of SC formation and after the catastrophic shrink. Based in the precipitation of a new layer on top of the submerged SC samples during 2019, a sedimentation rate between 10 and 30 mm/y is calculated with NaCl and CaS as major precipitants.

NMR Investigation of Water in Salt Crusts: Insights from Experiments and Molecular Simulations

The evaporation of water from bare soil is often accompanied by the formation of a layer of crystallized salt, a process that must be understood in order to address the issue of soil salinization. Here, we use nuclear magnetic relaxation dispersion measurements to better understand the dynamic properties of water within two types of salt crusts: sodium chloride (NaCl) and sodium sulfate (Na2SO4). Our experimental results display a stronger dispersion of the relaxation time T1 with frequency for the case of sodium sulfate as compared to sodium chloride salt crusts. To gain insight into these results, we perform molecular dynamics simulations of salt solutions confined within slit nanopores made of either NaCl or Na2SO4. We find a strong dependence of the value of the relaxation time T1 on pore size and salt concentration. Our simulations reveal the complex interplay between the adsorption of ions at the solid surface, the structure of water near the interface, and the dispersion of T1 at low frequency, which we attribute to adsorption-desorption events.

Random Forest Modeling of Soil Properties in Saline Semi-Arid Areas

The problem of salinization/spreading of saline soils is becoming more urgent in many regions of the world, especially in context of climate change. The monitoring of salt-affected soils’ properties is a necessary procedure in land management and irrigation planning and is aimed to obtain high crop harvest and reduce degradation processes. In this work, a machine learning method was applied for modeling of the spatial distribution of topsoil (0–20 cm) properties—in particular: soil organic carbon (SOC), pH, and salt content (dry residue). A random forest (RF) machine learning approach was used in combination with environmental variables to predict soil properties in a semi-arid area (Trans-Ural steppe zone). Soil, salinity, and texture maps; topography attributes; and remote sensing data (RSD) were used as predictors. The coefficient of determination (R2) and the root mean square error (RMSE) were used to estimate the performance of the RF model. The cross-validation result showed that the RF model achieved an R2 of 0.59 and an RMSE of 0.68 for SOM; 0.36 and 0.65, respectively, for soil pH; and 0.78 and 1.21, respectively for dry residue prediction. The SOC content ranged from 0.8 to 2.8%, with an average value of 1.9%; soil pH ranged from 5.9 to 8.4, with an average of 7.2; dry residue varied greatly from 0.04 to 16.8%, with an average value of 1.3%. A variable importance analysis indicated that remote sensing variables (salinity indices and NDVI) were dominant in the spatial prediction of soil parameters. The importance of RSD for evaluating saline soils and their properties is explained by their absorption characteristics/reflectivity in the visible and near-infrared spectra. Solonchak soils are distinguished by a salt crust on the land surface and, as a result, reduced SOC contents and vegetation biomass. However, the change in saline and non-saline soils over a short distance with mosaic structure of soil cover requires high-resolution RSD or aerial images obtained from unmanned aerial vehicle/drones for successful digital mapping of soil parameters. The presented results provide an effective method to estimate soil properties in saline landscapes for further land management/reclamation planning of degraded soils in arid and semi-arid regions.

The identification, approaches to cleaning and removal of a lead-rich salt crust from the surface of an 18th century oil painting

A thin, grey surface layer was noticed after removing the varnish of an eighteenth century Dutch oil painting, by an unknown artist titled Vision of Saint Lutgard of Tongeren. This layer masked the paint layer almost entirely, casting a greyish veil that greatly influenced the painting’s appearance, colour, and saturation. Using scanning electron microscopy coupled with elemental analysis (SEM–EDX), this layer was identified as a lead-rich salt crust. The crust was a distinct layer on top of the paint layer, closely following the topography of the layer underneath but not embedded in it. The article discusses the possible theories behind the formation of this lead-rich salt crust by characterizing the painting’s material, past treatments, and environmental history. Furthermore, the article reports the decision-making process behind the removal of the crust, focusing specifically on the ethical and technical challenges of the cleaning treatment. Tests with different cleaning agents targeting separate components of the crust to remove it and different application techniques are described. The chelating agent Ethylenediaminetetraacetic acid (EDTA) was found to be the most effective in the removal of the crust and was chosen for its removal. The pH of the EDTA cleaning solution and its application had to be modified according to the colour of the paint the crust lay upon. Visual observations and analytical assessments using optical microscopy and SEM after cleaning indicate a successful reduction of the crust resulting in a significant improvement in the painting’s appearance.