Weathering Research Articles

Composite Superhydrophobic Coating with Transparency and Thermal Insulation for Glass Curtain Walls.

In this paper, the preparation of a transparent superhydrophobic composite coating with a thermal insulation function using antimony-doped tin oxide (ATO) nanoparticles is proposed, which has advantages of being mass-producible and low-cost. In short, nanosilica and ATO are used as raw materials for constructing rough structures, and superhydrophobic coatings are obtained by mixing and adding binders after modification of each, which are then applied to the surface of various substrates by spraying to obtain a transparent superhydrophobic coating with a heat-insulating function. The specific role of each nanoparticle is discussed through comparative experiments that illustrate the mechanism by which the two particles construct rough structures. The coating achieves unique thermal insulation properties while possessing excellent superhydrophobicity (WCA of ∼163° and WSA of ∼3°) and high light transmission (∼70%). Heat-shielding experiments have demonstrated that the composite coating effectively reduces the room temperature by approximately 19% for the same irradiation time. The coating achieves a balanced improvement in visible transmittance, thermal insulation, and superhydrophobicity. In addition, the coating's self-cleaning properties, mechanical properties, chemical weathering resistance, high-temperature resistance, and anti-icing properties were verified through various experiments.

Unveiling the release mechanism of potentially toxic elements from Pb/Zn smelter contaminated soils under the coupled effects of freeze–thaw and acidification: Insights from mineralogical analysis

Most Pb/Zn smelter contaminated sites in China are often encountered natural phenomenon known as freeze–thaw (F–T) cycles and acid rain. However, the coupled effects of F–T cycles and acidification on the release behavior of potentially toxic elements (PTEs) from soils remains unclear. A mechanistic study on PTEs release from soils was conducted by revealing the physicochemical weathering characteristics of minerals under F–T cycles combined with acidification. The results from F–T test indicated that among F–T parameters, F–T frequency were the more important factors influencing PTEs release, with the corresponding contribution ranges of 21.20–94.40 %. As pH decreased, the leaching concentrations of As, Cd, Cu, Mn, Pb and Zn did not increase under the same F–T frequency. As F–T frequency increased, the leaching concentrations of these studied PTEs also did not increase under the same pH condition. Microstructure characteristics revealed that the soils were a complex system with multi–mineral aggregates, which had experienced complex physicochemical weathering after F–T combined with acidification treatment. Combined with geochemical modeling results, PTEs release was found to be mainly influenced by the microstructure damage and proton corrosion of minerals, while little affected by their precipitation and dissolution. The mutual coupling relationships of mineral weathering and PTEs release were conducive to the better understanding of the migration behavior of PTEs in contaminated sites under complex environment scenarios. The present study results would provide theoretical instruction and technical support for the longevity evaluation of multi–metal stabilization remediation.

Comprehending Spatial Distribution and Controlling Mechanisms of Groundwater in Topical Coastal Aquifers of Southern China Based on Hydrochemical Evaluations

Groundwater quality and availability in coastal aquifers have become a serious concern in recent times due to increased abstraction for domestic, agricultural and industrial purposes. (1) Background: Zhuhai city is selected as a representative coastal aquifer in Southern China to comprehensively evaluate the hydrochemical characteristics, spatial distribution and controlling mechanisms of groundwater. (2) Methods: A detailed study utilizing statistical analyses, a Piper diagram, Gibbs plots, and ion ratios was conducted on 114 surface water samples and 211 groundwater samples. (3) Results: The findings indicate that the pH of most groundwater is from 6.06 to 6.52, indicating a weakly acidic environment. The pH of surface water ranges from 5.35 to 9.86, with most values being weakly alkaline. The acidity in the groundwater may be related to the acidic atmospheric precipitation, an acidic unsaturated zone, oxidation of sulphide minerals and tidal action. The groundwater chemical types are predominantly mixed, followed by Ca-Mg-HCO3 type. Surface water samples are predominantly Na-Cl-SO4 type. The NO3− concentration in groundwater is relatively high, with a mean value of 17.46 mg/L. The NO2− and NH4+ concentrations in groundwater are relatively low, with mean values of 0.46 mg/L and 7.58 mg/L. (4) Conclusions: The spatial distribution of the principal chemical constituents in the groundwater is related to the landform. The chemical characteristics of groundwater in the study area are mainly controlled by the weathering and dissolution of silicate and sulfate minerals, evaporation, seawater mixing and cation exchange. Nitrate in clastic fissure groundwater, granite fissure groundwater and unconfined pore groundwater primarily originates from atmospheric precipitation, agricultural activities of slope farmland and forest land. Nitrate in confined pore groundwater and karst groundwater primarily originates from domestic sewage and mariculture wastewater. Our findings elucidate the processes characterizing the hydrogeology and surface water interactions in Zhuhai City’s coastal system, which are relevant to other catchments with similar geological characteristics.

Improving Atmospheric Temperature and Relative Humidity Profiles Retrieval Based on Ground-Based Multichannel Microwave Radiometer and Millimeter-Wave Cloud Radar

Obtaining temperature and humidity profiles with high vertical resolution is essential for describing and predicting atmospheric motion, and, in particular, for understanding the evolution of medium- and small-scale weather processes, making short-range and near-term weather forecasting, and implementing weather modifications (artificial rainfall, artificial rain elimination, etc.). Ground-based microwave radiometers can acquire vertical tropospheric atmospheric data with high temporal and spatial resolution. However, the accuracy of temperature and relative humidity retrieval is still not as accurate as that of radiosonde data, especially in cloudy conditions. Therefore, improving the observation and retrieval accuracy is a major challenge in current research. The focus of this study was to further improve the accuracy of atmospheric temperature and humidity profile retrieval and investigate the specific effects of cloud information (cloud-base height and cloud thickness) on temperature and humidity profile retrieval. The observation data from the ground-based multichannel microwave radiometer (GMR) and the millimeter-wave cloud radar (MWCR) were incorporated into the retrieval process of the atmospheric temperature and relative humidity profiles. The retrieval was performed using the backpropagation neural network (BPNN). The retrieval results were quantified using the mean absolute error (MAE) and root mean square error (RMSE). The statistical results showed that the temperature profiles were less affected by the cloud information compared with the relative humidity profiles. Cloud thickness was the main factor affecting the retrieval of relative humidity profiles, and the retrieval with cloud information was the best retrieval method. Compared with the retrieval profiles without cloud information, the MAE and RMSE values of most of the altitude layers were reduced to different degrees after adding cloud information, and the relative humidity (RH) errors of some altitude layers were reduced by approximately 50%. The maximum reduction in the RMSE and MAE values for the retrieval of temperature profiles with cloud information was about 1.0 °C around 7.75 km, and the maximum reduction in RMSE and MAE values for the relative humidity profiles was about 10%, which was obtained around 2 km.

Enhancement of soil ecological remediation using a hydrogel material constructed by freeze–thaw driving force

Composite polymer materials as soil improvers are developed to enhance soil cohesion and aggregate stability. However, the improved soil still struggles to overcome the reduction in strength caused by day-to-day freeze–thaw (FT) cycle in the plateau area with large temperature difference. In this study, the natural power of FT cycle was used to drive the crosslinking of poly (vinyl alcohol) (PVA) and sodium alginate (SA) to form the interpenetrating networks of PVA-SA hydrogel. Then, this hydrogel was applied to stabilize the soil. The characterizations by FTIR, TGA, SEM and XRD indicated that the PVA-SA hydrogel had a porous, multi-channel and multi-chamber structure. Under the action of FT driving force, a series of studies including physical, chemical, water retention, direct shear, permeability, and aggregate stability were carried out on the soil with hydrogel applied. Compared to the control group, the data indicated that the cohesion of soil is significantly improved to 80 kPa. And the saturated hydraulic conductivity of the soil was reduced to 1/45 of the pre-modification rate, which had a positive impact on the water retention of the soil. What’s more, the results revealed that the PVA-SA hydrogel had effects on the aggregate stability, the submerged soil with added PVA-SA hydrogel still had no sign of disintegration and its mass percentage was greater than 99 % after 70 days. In a word, this composite material can effectively improve the cohesion and aggregate stability of the soil with the help of natural driving forces, which is potential to be used as remediation material for the plant layer in ecological restoration process.

Multivariate approach to assess groundwater resources in the multilayer system of Iullemmeden basin in Dosso Region, Southwestern Niger

The Iullemmeden basin groundwater resources were assessed in the Dosso Region for the groundwater management. Classical and multivariate tools of hydrogeochemistry were thus used to stand out main factors impacting the groundwater mineralization. The multilayer system indicates the occurrence of acidic to basic fresh groundwaters but with an excessive content in some places. Good to excellent drinking groundwaters are largely represented in the system. The categorization of groundwater patterns evolves from (i) mixed types namely Ca/Mg-HCO3, Ca/Mg-Cl, Na-Cl/SO4, Ca-Cl/SO4 and Ca/Mg-Cl/SO4 for the Ct3 particularly; (ii) to chloride types such as NaCl, CaCl and MgCl mostly for Ct1 and Ct2; (iii) and the bicarbonate types precisely Na-HCO3, Ca-HCO3, Mg-HCO3 for Ch. The weathering of silicate minerals and dissolution (carbonate and salts) are the major processes in the multilayer system. The increase of EC and salts (halite and gypsum) in Ct2 could come from the relics of ancient seawater during the last regression. In a lesser extent, fertilizers from agricultural and livestock farming also contribute to the mineralization in the study area. The groundwater assessment of the Iullemmeden sedimentary basin in the Dosso Region stands out the main factors and processes characterizing each aquifer of this system, able to useful for a better groundwater resource management.

Miocene magmatism in Northern Tunisia and its geodynamic implications

The Nefza igneous rocks in Northern Tunisia belong to the Miocene magmatic belt extending from Northern Tunisia to Morocco and consist mainly of Serravallian–Tortonian granodiorite and rhyodacite (~ 14–8 Ma) and Messinian basalts (~ 8–6 Ma). Differences in geochemical composition between units have been interpreted to be the result of geodynamic processes in the upper mantle below the Western Mediterranean area, but their implications for Northern Tunisia are unclear due to limited data. In this contribution, we present an updated geodynamic model for Northern Tunisia based on new petrographic and whole-rock geochemical results from the Nefza magmatic suite from outcrop and OB45 drill core samples. Petrographic observations show that rhyodacites display a microlithic texture with quartz, plagioclase, K-feldspar, biotite, and glass, whilst granodiorite contains plagioclase, quartz and exhibits fine-grained texture with a 2–3 mm crystal size. The Nefza magmatic rocks are overprinted by multiple weathering and alteration processes with loss of ignition (LOI) ranging between 0.88 and more than 5 wt%. The linear relationships between mobile elements (Ca, Na, P, K, Mg, Si), large-ion lithophile elements (LILE), and LOI suggest element mobilisation during alteration. Major and trace element compositions show the Nefza magmatic rocks plot in the rhyolite, dacite, and trachydacite fields for felsic rocks and plot in the basalt and trachybasalt fields for mafic rocks. Granodiorite and rhyodacite rocks exhibit negative Eu anomalies and a LILE enrichment (Rb, Ba, Pb) relative to high-field-strength elements (HFSE: Nb, Ta, Hf, Zr, REE). Mafic rocks enriched in LILE show geochemical characteristics between calc-alkaline and alkaline trends. Comparison with nearby regions suggests that the generation of calc-alkaline magmas resulted from the partial melting of the lithospheric mantle due to slab break-off or tearing in Eastern Algeria. The upward flow of asthenospheric material through the widening tear in the sinking slab leads to partial melting of the mantle and shallowing of the lithosphere–asthenosphere boundary, ultimately leading to the formation of alkaline magma. The Nefza geochemical variations underscore Mediterranean upper mantle heterogeneity, offering crucial insights into Mediterranean geodynamics. More studies are needed to constrain mantle dynamics and the region’s complex geological history.

Research Progress on Effects of Freeze-Thaw Action on Wind Erosion and Dust Resistance of Microbial Cured Bare Soil

Research Progress on Effects of Freeze-Thaw Action on Wind Erosion and Dust Resistance of Microbial Cured Bare Soil

Characterization, formation mechanism, and human health risk assessment of fluoride in shallow groundwater of Suzhou city, East China

ABSTRACT Groundwater is a vital water source for human consumption and irrigation. Understanding its fluoride content and health implications is crucial for water resource management. This study investigated the quaternary aquifer in Suzhou, China, collecting and analyzing 49 groundwater samples. Thermodynamic simulation, multivariate statistical analysis, and health risk assessment models were employed to determine fluoride concentration characteristics, hydrochemical controlling mechanisms, and noncarcinogenic risks. Results revealed an average fluoride concentration of 0.89 mg/L, with 26.5% of samples exceeding the Grade III groundwater quality standard. High-fluoride groundwater (>1 mg/L) exhibited spatial heterogeneity and was predominantly of the Na-Mg-HCO3 hydrochemical type. Multivariate analysis and thermodynamics simulations indicated that water–rock interactions (e.g., silicate mineral weathering and fluorite dissolution) governed groundwater hydrochemistry. Fluoride primarily originated from fluoride-bearing mineral dissolution, while negative cation exchange and precipitation of calcite and dolomite enhanced fluoride enrichment. pH had minimal impact on fluoride concentrations under weakly alkaline conditions. Health risk assessment suggested that fluoride in shallow groundwater posed a higher noncarcinogenic risk to children than adults via ingestion. These findings provide valuable insights for regional groundwater resource management.

Exploring the synergy of enhanced weathering and Bacillus subtilis: A promising strategy for sustainable agriculture.

Climate change is one of the most urgent environmental challenges that humanity faces. In addition to the reduction of greenhouse gas emissions, safe and robust carbon dioxide removal (CDR) technologies that capture atmospheric CO2 and ensure long-term sequestration are required. Among CDR technologies, enhanced silicate weathering (ESW) has been suggested as a promising option. While ESW has been demonstrated to depend strongly on pH, water, and temperature, recent studies suggest that biota may accelerate mineral weathering rates. Bacillus subtilis is a plant growth-promoting rhizobacterium that can facilitate weathering to obtain mineral nutrients. It is a promising agricultural biofertilizer, as it helps plants acquire nutrients and protects them from environmental stresses. Given that croplands are optimal implementation fields for ESW, any synergy between ESW and B. subtilis can hold great potential for further practice. B. subtilis was reported to enhance weathering under laboratory conditions, but there is a lack of data for soil applications. In a soil-mesocosm experiment, we examined the effect of B. subtilis on basalt weathering. B. subtilis-basalt interaction stimulated basalt weathering and increased soil extractable Fe. The combined application displayed higher CDR potential compared to basalt-only application (3.7 vs. 2.3 tons CO2 ha-1) taking solid and liquid cation pools into account. However, the cumulative CO2 efflux decreased by approximately 2 tons CO2 ha-1 with basalt-only treatment, while the combined application did not affect the CO2 efflux. We found limited mobilization of cations to the liquid phase as most were retained in the soil. Additionally, we found substantial mobilization of basalt-originated Mg, Fe, and Al to oxide- and organic-bound soil fractions. We, therefore, conclude that basalt addition showed relatively low inorganic CDR potential but a high capacity for SOM stabilization. The outcomes indicated the importance of weathering rate-GHG emission integration and the high potential of SOM stabilization in ESW studies.

GIS-Based Mapping of the Water Quality and Geochemical Assessment of the Ionic Behavior in the Groundwater Aquifers of Middle Ganga Basin, Patna, India

The study implemented Geographic Information System (GIS) techniques and multivariate hydrogeochemical analysis to evaluate the spatial-temporal and seasonal variation in the groundwater quality of Patna, India. For this purpose, sixty groundwater samples were collected and analyzed for major anions and cations during the pre-monsoon, monsoon, and post-monsoon seasons of 2019-2020. The physicochemical parameters such as pH, EC (Electrical Conductivity), TDS (Total Dissolved Solids), TH (Total Hardness), Ca2+, Mg2+, Na+, K+, HCO3-, Cl-, SO42- were considered to evaluate the water quality index. The result revealed degradation in groundwater quality from pre-monsoon (49.21) to post-monsoon (74.48). EC, TDS, TH, Mg2+, Na+, Ca2+, K+, and HCO3- ions were found accountable for high WQI values at various sampling sites during different seasons. Spatial maps showed that 45 % of the sampling stations exhibited poor quality in all three seasons, where the eastern part of the studied region was revealed to be the most affected area. The application of multivariate statistical methods and hydrogeochemical investigation has clearly defined the dominant role of the weathering process, and reverse ion exchange mechanism in controlling the aquifer’s ionic chemistry. Moreover, poor seepage system, and waste leachate from the surface have been found as the main cause of high levels of Na+, K+, and Cl- in the eastern part of Patna.

The Global Distribution of Water and Hydroxyl on the Moon as Seen by the Moon Mineralogy Mapper (M3)

The Moon Mineralogy Mapper (M3) on the Chandrayaan-1 spacecraft provided nearly global 0.5–3 μm imaging-spectroscopy data at 140 m pixel–1 in 85 spectral bands. Targeted locations were imaged at 70 m pixel–1 and higher spectral resolution. These data enable a detailed look at the mineralogy, hydroxyl, and water signatures exposed on the lunar surface. We find evidence for multiple processes, including probable solar wind implantation, excavation of hydroxyl-poor and water-poor material in cratering events, excavation of hydroxyl and water-rich materials from depth and global trends with rock type and latitude. Some water-rich areas display sharp boundaries with water-poor rocks but have a diffuse halo of hydroxyl surrounding the water-rich rocks indicating a weathering process of destruction of water, probably due to a regolith gardening process. Mapping for specific mineralogy shows evidence for absorptions near 2.2 μm, probably associated with smectites, and near 1.9 μm due to water. Lunar swirls are confirmed to be OH-poor, but we also find evidence that swirls are water-poor based on a weak 1.9 μm water band. Some swirls show enhanced pyroxene absorption. “Diurnal” signatures are found with stable minerals. Pyroxene is shown to exhibit strong band depth changes with the diurnal cycle, which directly tracks the solar incidence angle and is consistent with changing composition and/or grain size with depth. Mapping of M3 data for the presence of iron oxides (e.g., hematite and goethite) is found to be a false signature in the M3 data due to scattered light in the instrument.

Surface weathering process of earthen heritage under dry-wet cycles: A case study of Suoyang City, China

Dry-wet cycle is a key factor in surface weathering of earthen heritage, which remains insufficiently explained. It involves the interaction of humidity, stress, and damage. Using the RFPA (realistic failure process analysis) numerical method, this study reproduced the processes of humidity diffusion, deformation, stress, and damage evolution under dry-wet cycles in the soil site of Suoyang City, China. The numerical results indicate that the drying phase following rainfall has the most significant deteriorative impact on the earthen heritage. The evaporation of surface moisture during this phase causes volume shrinkage, which in turn generates tensile stress and leads to the formation of numerous desiccation cracks. Desiccation cracks provide channels for moisture diffusion, which further exacerbates generation of the cracks, leading to a mutual promotion between the two phenomena. Furthermore, during the wetting phase, the model elements undergo hygroscopic expansion, resulting in a slight increase in strain and displacement. Previously formed cracks may exhibit temporary narrowing or closure, but will revert during the subsequent drying phase. Ultimately, the overall displacement increases with the number of dry-wet cycles. The findings provide a theoretical foundation for protection against surface weathering and other damage in earthen heritage in arid regions.

The Impact of Induced Industrial and Urban Toxic Elements on Sediment Quality

Abstract: The increasing population has subjected rivers and streams to high levels of both industrial and domestic pollution. Significant environmental challenges have been brought about by their effects, particularly with regard to biota, ecosystem processes, soil quality, and groundwater pollution. This study examined the effects of human activity by applying pollution index models to evaluate the input of toxic elements in river sediments. Prior to sediment quality analysis, the total amount of arsenic (As), lead (Pb), cadmium (Cd), mercury (Hg), thorium (Th), and uranium (U) was determined in the concentration range of 1.09–10.0 mg/kg, 8.53–475 mg/kg, 0.12–0.16 mg/kg, 4.85–77.5 mg/kg, 3.14–5.9 mg/kg and 0.93–2.86 mg/kg, respectively. The enrichment factor, contamination factor, pollution load index, and geo-accumulation index revealed alarmingly high levels of Pb and Hg contamination at some sampling points, which are related to possible human input, ranging from severe enrichment to considerable contamination. The low ranges of pollution indices of some toxic elements suggest enrichment through the natural weathering process and atmospheric deposition. The Pearson correlation coefficient revealed a significant correlation between Pb-Fe and As-Fe, suggesting the possibility of acid mine contamination. Continual monitoring of river sediment is essential to minimize the impact of toxic elements to sustain sediment health and quality.

Migration of dissolution front in a fracture network − Implications for weathering of fractured bedrock systems and boulder formation

Fracture networks contribute to the differential weathering of fractured bedrock at multiple scales. The influence of competing fracture networks is discussed in light of hydrogeochemical conditions to predict the dissolution pattern resulting from spheroidal weathering. The investigation of the dimensionless Péclet (Pe) and Damköhler (Da) numbers on a simple case of a dual-scale fracture network and its application to three fracture network weathering reveals the influence of fluid flow and reaction rate conditions on the dissolution patterns.The conceptual model was numerically validated and compared with observations on lateritic nickel deposits in New Caledonia. A fracture network will contribute to boulder development if the associated fluid flow regime reaches a Pe threshold of around 10. On the other hand, predominant diffusion will inhibit the fracture set in favour of a higher permeability fracture network. The Da drives, for its part, the width of the dissolution halo. Owing to the dependency of the fluid flow regime on the fracture network characteristics, scaling laws were established to estimate the size of the boulders at different scales by predicting the fracture contribution as a function of their Pe.

Application of ANFIS in Decision-Making on the Smart Control Early Warning System for Tornadoes

A tornado is one weather process that arises due to atmospheric instability. A tornado is a strong wind, but not all strong winds are tornadoes. Tornadoes have a short time frequency but can result in no minor disaster because they can blow objects away and uproot trees. Due to the consequences, an early warning system is needed as an anticipation for the community in the affected areas so that it can help the community by warning early on of the occurrence of a tornado. The ANFIS (Adaptive Neuro Fuzzy Inference System) method is used to forecast the event of a tornado, and the parameters used are wind speed, ambient temperature, and ambient humidity. This study will compare the ANFIS method using hybrid and backpropagation algorithms. Using the backpropagation algorithm, an error of 0.42385 was produced during training and testing, and an average error of 136.54 was obtained. When using the hybrid algorithm, the error during training is 2.0781 x 10-5, and the average error during testing is 0.015%.Keywords — ANFIS ; Anemometer; DHT22; Early Warning System; Tornado.

Recent advancement in microplastic removal process from wastewater - A critical review

Microplastics, small sized plastic particles having size <5 mm are formed through primary process including production of beauty products, microbeads and microfibres as well as secondary process including mechanical weathering, friction, aberration and fragmentation of large plastics. The major sources of microplastics are land-based and ocean-based sources. Microplastic pollution is a serious concern due to the persistent, low biodegradability and bio-accumulative behaviour. Microplastics can bioaccumulate in the food chain and can cause ecological and human health risk. Hence, it is important to remove from the aquatic ecosystems. Microplastics are removed from aquatic systems and wastewater through a series of processes such as physical, chemical and biological treatments. In the present articles, >250 articles are reviewed to collect the information regarding the various physical, chemical and biological methods for the removal of microplastics. Also, the probable control strategies to combat with plastic pollution were assessed. It was concluded that recent water treatment methods are efficient in removing microplastic pollution. The efficiencies to remove microplastic from the water ranged between 74 %-99.2 %, 65 %-99.20 % and 77 %-100 % for physical, chemical and biological treatment methods, respectively. Among the three treatment methods, physical methods especially the filtration of water from biochar is the most efficient way (efficiency up to 100 %) to remove microplastics. It was also concluded that creating public awareness, promoting reusing, recycling and reducing, and application of bioplastics can control the production of microplastics from plastic wastes. This review will be useful to add current knowledge regarding the abatement of microplastic pollution, and finding novel solution to control microplastics. This review will also help the policymakers to implement most effective and cost-efficient method to remove microplastics, and to find out new methods to reduce, reuse and recycle plastic wastes.

Characterization and Making Techniques of Calcareous Construction Materials for Phaya Thon Zu Temple in Bagan Historical Area, Myanmar.

The calcareous materials used in constructing the Phaya Thon Zu temple at the Bagan historical sites in Myanmar are mortars, plasters, and stuccos. Among them, the mortars and plasters are a mixture of original and new materials used for recent conservation treatments. In this study, the making techniques were examined through analysis of calcareous materials by production period. All calcareous materials have a mineral composition similar to soil, except calcite. Stuccos have the most refined aggregates, homogeneous particle size, and the highest lime and organic contents. They were designed to improve ease of carving and weathering resistance, considering the unique characteristics of the stuccos. Because all calcareous materials were mixed with soil, the origin of the clay materials was analyzed. It was concluded that the mortars were produced by mixing clay and sandy soil, and the original mortars showed characteristics similar to soil. It is highly possible that sandy soil from around the Htillominlo temple was used to produce new plasters, and it is estimated that a mixture of clay soil was used for the original plasters and stuccos. A clear provenance interpretation of the original and raw materials used for each construction and the mixing ratio of clay materials need to be discussed through experiments, along with the estimated provenance area of the raw calcareous materials.

Deep regolith weathering controls δ30Si composition of groundwater under contrasting landuse in tropical watersheds

Land use changes are known to alter terrestrial silicon cycling and the export of dissolved silicon from soil to fluvial systems, but the impact of such changes on groundwater systems remain unclear. In order to identify the processes responsible for groundwater geochemistry and to assess the impact of agricultural processes, we examined multiple isotopic tracers (δ30Si, oxygen (δ18O) and hydrogen (δ2H) isotopes) in groundwater, soil porewater and surface water from two contrasted watersheds having the same gneissic lithology, one forested (Mule Hole) and one intensely cultivated (Berambadi) in the Kabini basin in South India. In the cultivated watershed, groundwater exhibits high Cl− and NO3− concentrations indicative of fertilizer inputs and solute enrichment from evapotranspiration due to multiple groundwater pumping/recharge cycles. The DSi concentration in groundwater is significantly higher in the cultivated watershed (980 ± 313 μM) than in the forested one (711 ± 154 μM), indicating more intense evapotranspiration due to irrigation cycles. The groundwater δ30Si values ranged from 0.6 ‰ to 3.4 ‰ and exhibit no significant differences between cultivated (1.2 ± 0.5 ‰) and forested (1.0 ± 0.2 ‰) watersheds, indicating limited impact of land use and land cover. Groundwater also shows no significant seasonal differences in DSi and δ30Si within watersheds, indicating a buffer to seasonal recharge during wet season. The δ30Si of a majority of groundwater samples fits a steady-state open flow through system, with an isotopic fractionation factor (30ε) between precipitating phase and groundwater ranging from −1.0 ‰ and − 2.0 ‰, consistent with precipitation of kaolinite-type clays, dominant in the study area. The steady-state flow through system in groundwater can be interpreted as a continuous DSi input from mineral weathering reactions with a dynamic equilibrium between Si supply and precipitation of secondary phases. We also observe, in both watersheds, similar DSi and δ30Si values in local surface water that includes small streams and a river (406 ± 194 μM, 1.6 ± 0.3 ‰) and in soil porewater (514 ± 119 μM, 1.6 ± 0.2 ‰). Compared to soil porewater, groundwater exhibits significantly lower δ30Si signatures and higher DSi, reflecting the contribution of an isotopically light silicon source, resulting from water-rock interaction during percolation through the unsaturated zone. We assign this steady input of DSi to the weathering of primary silicate minerals in the regolith, such as Na-plagioclase, biotite and chlorite, with formation of kaolinite and smectites type clays. A simple isotopic mass balance suggests that deep regolith weathering can contribute to almost half of the DSi in groundwater. We conclude that silicon cycling in soil porewaters, and surface waters are directly impacted by land use, while the isotopic composition of groundwater remains unaffected. Our results indicate that Si isotopic signatures of weathering, adsorption, and plant uptake occurring in the shallow soil and saprolite horizons are partly overprinted and homogenized by the regolith weathering in the deep critical zone, irrespective of land use and seasonality.

The degree of soil arsenic background enrichment by carbonate weathering is mainly controlled by climate in large spatial scale

Spatial distribution of soil arsenic (As) is heterogeneous. Making clear the dominant factor(s) controlling its spatial variation contributes to the differentiation of its natural background from anthropogenic pollution. Recent studies have found that the “high background” of soil heavy metals may be induced by the process of carbonate weathering. However, the extent, process, and factors that controls the degree of this enrichment, is still unclear, especially in large spatial scales. In this study, this problem is to be revealed by a compilation and spatial data mining of soil geochemical data for Australia, North America, Europe, and China with a collection and chemical analysis of bedrock and soil profiles in a typical region. The results indicated that the process of carbonate weathering strengthened the As enrichment in the soil; therefore, the carbonate rock underlaid regions could be distinguished from those of other bedrocks in the soil As maps. In the southwest region of China, an area larger than 12,000 km2 exceeding the intervention value of 100 mg/kg could be produced according to the national standard. Iron minerals play an important role for this enrichment as they serve as carriers for As during the stages of both carbonate leaching and the decomposition of silicate minerals. Geodetector results indicated a significant dependence on climate for the degree of enrichment, and both higher temperature and precipitation were necessary, which caused a decreasing trend of soil As on carbonate region from the warm and humid south to the cold and dry north in China. The dependence of soil As concentration on the mean average precipitation (MAP) and mean average temperature (MAT) was formulated using the data of the wider geographical regions across the world, and a theoretically predicted map has been produced to show the extent caused by this causation.