The contributions of external and internal hydration (OH and H2O) on the shape and strength of hydration related features at 3 and 6 mu m for lunar relevant nominally anhydrous minerals were investigated under vacuum conditions. Understanding the effect of hydration on the reflectance spectra of lunar analog materials in the laboratory can provide insights into remote sensing observations of the lunar surface and the potential for 3 and/or 6 mu m observations to determine the speciation of hydration on the Moon. We demonstrate changes in the shape and strength of the broad 3 mu m absorption feature in olivine and anorthite that is associated with the removal of hydration under changing environmental conditions. The overlapping nature of OH and H2O related absorption features in the similar to 3 mu m region makes it difficult to uniquely determine the speciation of hydration. Despite evidence of H2O loss in the 3 mu m region, we do not observe the fundamental bending mode of H2O at 6 mu m, posing potential challenges for the detection H2O on the lunar surface and throughout our solar system.

The use of various sustainable materials and cement is a frequent and successful strategy for stabilizing problematic soil. The current research discusses the potential use of discarded millet husk ash (MHA) and cement (C) as subgrade ingredients to improve the geotechnical qualities of soil (S). MHA and cement are mixed in different proportions and the engineering characteristics of the stabilized soil are studied. The study involves examining fundamental properties, such as specific gravity and Atterberg's limits, as well as engineering properties, including Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) tests. These evaluations are conducted to assess the feasibility of using the MHA-cement blend as a construction material. Additionally, FTIR & SEM analysis shows the addition of MHA-cement blend effectively couples with the soil. The test findings demonstrate that adding MHA to soil lead to decreased liquid limits and plasticity indices. The maximum dry density (MDD) was observed to decrease when MHA was mixed with soil. When 8% cement was incorporated to the S:MHA (84.5:7.5) combination, the UCS value rose even higher reaching 1600.1 kPa. The S:MHA:C arrangement in the ratio of 84.5:7.5:8 had the greatest California bearing ratio (CBR). Fourier transform infrared spectroscopy (FTIR) elucidated the various types of bond formations present within the soil composite and deeper peaks depicted greater presence of cementitious compounds after curing period. SEM analysis exhibited a greater density of N-A-S-H and C-A-S-H gels in comparison to natural soil samples. The findings suggest that the MHA-cement blend can effectively enhance the geotechnical properties of problematic soils, while addressing issues of agricultural waste management. This research contributes to several Sustainable Development Goals (SDGs), including SDG 9 (Industry, Innovation, and Infrastructure) by promoting innovative construction materials.

The impact of four distinct calcium sources on the microbial solidification of sand in the Kashi Desert, Xinjiang, was investigated. A wind tunnel test over a 60-day period revealed the cracking behavior of four different complex calcium nutrient solutions. By comparing the bearing capacity and the results from dry-wet cycling and freeze-thaw cycle tests, it was concluded that the sample treated with calcium gluconate exhibited superior sand fixation performance, whereas the sample treated with calcium acetate showed weaker sand fixation effects. The microstructure of the treated sand samples was analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Elemental analysis was conducted via energy dispersive spectroscopy (EDS), and functional groups were identified through Fourier transform infrared spectroscopy (FTIR). These experimental findings hold significant implications for soil remediation, pollutant removal in soil, enhancement of soil fertility, and desert soil stabilization.

Sample collection and measurement of soil bulk density (BD) are often labor-intensive and expensive in large regions. Conversely, soil spectra are easy to measure and facilitate BD prediction. However, the literature suggests that the damage to the physical structure of soil during scanning spectra on the ground and/or sieved samples might hinder the capacity of spectral technology to accurately predict BD. In addition, because some soil properties that have high correlations with BD, such as the soil organic matter (SOM), are routinely measured and available in most soil databases, coupling them with soil spectra may improve BD prediction compared to using soil properties or spectra. Therefore, in this study, we propose a novel spectral pedo-transfer function (spectral PTF) that couples the measured visible and near-infrared spectra of soils on intact samples and other soil properties to accurately predict the BD (BD = f (soil spectra, soil properties)), which is different from the traditional PTF that uses only soil properties (BD = f (soil properties)) or spectra alone (BD = f (soil spectra)). In this study, we collected topsoil (0-20 cm) and subsoil (20-40 cm) samples from 586 sites in Northeast China, covering a large area of 1.09 million km(2) characterized by black soils with high SOM contents. Five routinely measured soil properties were selected: SOM, moisture content (MC), Sand, Silt, and Clay, and various spectral PTFs with one, two, and three soil properties were calibrated using the partial least square regression. The cross-validation results show that the traditional PTF can only predict BD for subsoil with an R-2 of 0.51 and an RMSE of 0.11 g center dot cm(-3) when using SOM + MC + Silt or SOM + MC. Compared to subsoil, topsoil and all layers (topsoil + subsoil) had a lower BD prediction accuracy, and a saturation effect was observed for BD values above 1.5 g center dot cm(-3). Unexpectedly, the soil spectra did not provide a higher BD prediction accuracy than traditional PTFs, although the spectra were measured on intact samples. However, adding soil properties to the spectral PTF improved the prediction accuracy and saturation effect for high BD values. The optimal spectral PTF with a single soil property (MC) showed an acceptable BD prediction performance with R-2 >= 0.49, RPD>1.4, and RPIQ>1.7 regardless of whether the sample was topsoil, subsoil, or all layers. Furthermore, the spectral PTF with two or three soil properties yielded a slightly better prediction performance and a more stable prediction among different combinations of soil properties. These results indicate that soil properties and spectra are irreplaceable for BD prediction. Our study demonstrates the potential of spectral PTFs for the accurate prediction of BD and offers insights into the prediction of other soil properties using soil spectra.

For evaluating the resistance performance of cement-stabilized soils in cold regions, the variation of the strength of the cemented sand-gravel (CSG) mixture concerning the hydration process should be explored. This paper aims to study the effect of freeze-thaw (F-T) cycles on the strength and microstructure of a CSG mixture with 10% cement that is subjected to 12 cycles of freezing at a temperature of -23 degrees C for 24 h and then melted at room temperature of 24 degrees C for the next 24 h. The uniaxial compressive strength (UCS), California bearing ratio (CBR), and weight volume loss of the samples were measured after individual F-T cycles. Furthermore, the change in the microstructure of the CSG mixture in various F-T cycles was explored. The results showed a considerable reduction in the UCS up to Cycle 3, then a slight increase for Cycles 3-6, and finally a gradual decrease for further cycles. However, the CBR and weight loss slightly fluctuated up to Cycle 6, and then gradually decreased for subsequent cycles. The majority of compounds of hydrated cement were damaged in the first three cycles. In the following cycles, between Cycles 3 and 6, the portlandite compound was dissolved and recrystallized within the microvoids. Depending on the environmental conditions, carbonation may be generated from the hydrated cement fraction, which fills the microvoids and improves the strength and structure of the mixture. During further cycles after the sixth cycle, the mechanical action of the ice lenses coupled with the disintegration of the hydrate compounds imposed many new microvoids and cracks with considerable length and width, which intensified the strength reduction of the moisture and weakened the adhesion between grains. Since cement is widely used in pavement and dam engineering for stabilizing soils, the durability of cemented soils is of prime concern. This study may help improve the durability and resistance of cemented soils in cold climates. The F-T action not only influences the macrostructure of cement-stabilized soils by imposing a wide crack and ice lens but also induces a considerable change in the complexes existing in the hydrated cement paste of the mixture. Three patterns govern the change of the mixture microstructure in various F-T cycles that correspond to the observed trend in strength. The mentioned trend for the microstructure change and, consequently, the strength variation of the CSG mixture are associated with many factors such as pH, cement content, CO2 content, moisture content within the mixture, and relative humidity within the environment. Accordingly, the pattern of microstructural changes in the CSG mixture after the middle F-T cycles may vary depending on environmental conditions.

Spectral variations due to the removal of surface adsorbed H2O at 3 and 6 mu m in reflectance spectra on lunar soils and relevant minerals (olivine, pyroxene, and plagioclase) have been assessed. This study characterizes variations in hydration features as a function of lunar relevant surface temperatures, to further understand current (i. e., M-3, HRI-IR, VIMS) and future (i.e., Lunar Trailblazer) observations of diurnal changes in surface hydration. Additionally, we explore the utility of using the 6 mu m H2O feature to discern the speciation of surface hydration at 3 mu m. We perform controlled temperature measurements (25-200 C-degrees) in a Linkam THMS600 Environmental Stage fixed to a Bruker LUMOS Microscope Fourier Transform IR (mu FTIR) spectrometer. We observe clear and systematic changes in the strength of the 3 mu m H2O/OH feature associated with the thermal removal of adsorbed H2O, in addition to changes in the overall shape and band position of the feature in both the terrestrial and lunar samples. The strength of the 3 mu m feature for the compositionally distinct and relatively brighter Apollo highland soil (62231) is stronger and more symmetric than the 3 mu m feature observed for the darker mare soil (10084). While several silicate related absorption features are identified near 6 mu m, neither a distinguishable hydration feature nor any changes in reflectance that could be attributed to the presence or a change in the amount of surface adsorbed H2O were observed at 6 mu m.

Knowledge of the occurrence of water in the solar system provides key information concerning the formation and evolution of the solar system and lifeforms. In recent years, multiple remote-sensing observations have suggested the existence of water ice in permanently shadowed regions on some inner solar system bodies; however, the exact amount of water ice is highly uncertain. To test the performance of ice detection equipment for future lunar polar exploration missions, we constructed an apparatus to produce minute amounts of water ice (0.1-2 wt%) on lunar regolith analog minerals and measured their near-infrared spectra. The relationship between the strength of water absorption and the water content was quantified using the absorption at 1.5 mu m in the reflectance spectra. The results show that the detectability of water ice attached to mineral grains depends on the mineral species. Laboratory reflectance spectra were compared to Hapke model spectra, and the observed spectral feature similarities indicate that the Hapke model can be effectively used when the ice is mixed in the form of spherical grains.

Soil microbial communities in the Arctic play a critical role in regulating the global carbon (C) cycle. Vast amounts of C are stored in northern high latitude soils, and rising temperatures in the Arctic threaten to thaw permafrost, making relatively inaccessible C sources more available for mineralization by soil microbes. Few studies have characterized how microbial community structure responds to thawing permafrost in the context of varying soil chemistries associated with contrasting tundra landscapes. We subjected active layer and permafrost soils from upland and lowland tundra sites on the North Slope of Alaska to a soil-warming incubation experiment and compared soil bacterial community profiles (obtained by 16S rRNA amplicon sequencing) before and after incubation. The influence of soil composition (characterized by mid-infrared [MIR] spectroscopy) on bacterial community structure and class abundance was analyzed using redundancy and correlation analyses. We found increased abundances of Alphaproteobacteria, Gammaproteobacteria, and Bacteroidetes [Sphingobacteriia] post incubation, particularly in permafrost soils. The categorical descriptors site and soil layer had the most explanatory power in our predictive models of bacterial community structure, highlighting the close relationship between soil bacteria and the soil environment. Specific soil chemical attributes characterizing the soil environments that were found to be the best predictors included MIR spectral bands associated with inorganic C, silicates, amide II (C=N stretch), and carboxylics (C-O stretch), and MIR peak ratios representing C substrate quality. Overall, these results further characterize soil bacterial community shifts that may occur as frozen environments with limited access to C sources, as is found in undisturbed permafrost, transition to warmer and more C-available environments, as is predicted in thawing permafrost due to climate change.

Water ice may be allowed to accumulate in permanently shaded regions on airless bodies in the inner solar system such as Mercury, the Moon, and Ceres [Watson K, et al. (1961) J Geophys Res 66: 3033-3045]. Unlike Mercury and Ceres, direct evidence for water ice exposed at the lunar surface has remained elusive. We utilize indirect lighting in regions of permanent shadow to report the detection of diagnostic near-infrared absorption features of water ice in reflectance spectra acquired by the Moon Mineralogy Mapper [M (3)] instrument. Several thousand M (3) pixels (similar to 280 x 280 m) with signatures of water ice at the optical surface (depth of less than a few millimeters) are identified within 20 degrees latitude of both poles, including locations where independent measurements have suggested that water ice may be present. Most ice locations detected in M (3) data also exhibit lunar orbiter laser altimeter reflectance values and Lyman Alpha Mapping Project instrument UV ratio values consistent with the presence of water ice and also exhibit annual maximum temperatures below 110 K. However, only similar to 3.5% of cold traps exhibit ice exposures. Spectral modeling shows that some ice-bearing pixels may contain similar to 30 wt % ice that is intimately mixed with dry regolith. The patchy distribution and low abundance of lunar surface-exposed water ice might be associated with the true polar wander and impact gardening. The observation of spectral features of H2O confirms that water ice is trapped and accumulates in permanently shadowed regions of the Moon, and in some locations, it is exposed at the modern optical surface.

Water and/or hydroxyl detected remotely on the lunar surface originates from several sources: (i) comets and other exogenous debris; (ii) solar-wind implantation; (iii) the lunar interior. While each of these sources is interesting in its own right, distinguishing among them is critical for testing hypotheses for the origin and evolution of the Moon and our Solar System. Existing spacecraft observations are not of high enough spectral resolution to uniquely characterize the bonding energies of the hydroxyl molecules that have been detected. Nevertheless, the spatial distribution and associations of H, OH-or H2O with specific lunar lithologies provide some insight into the origin of lunar hydrous materials. The global distribution of OH-/H2O as detected using infrared spectroscopic measurements from orbit is here examined, with particular focus on regional geological features that exhibit OH-/H2O absorption band strengths that differ from their immediate surroundings. This article is part of the themed issue 'The origin, history and role of water in the evolution of the inner Solar System'.