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International audience; Weathering phenomena are ubiquitous in urban environments, where it is easy to observe severely degraded old buildings as a result of water penetration. Despite being an important part of any realistic city, this kind of phenomenon has received little attention from the Computer Graphics community compared to stains resulting from biological or flow effects on the building exteriors. In this paper, we present physically-inspired deep weathering effects, where the penetration of humidity (i.e., water particles) and its interaction with a building's internal structural elements result in large, visible degradation effects. Our implementation is based on a particle-based propagation model for humidity propagation, coupled with a spring-based interaction simulation that allows chemical interactions, like the formation of rust, to deform and destroy a building's inner structure. To illustrate our methodology, we show a collection of deep degradation effects applied to urban models involving the creation of rust or of ice within walls.

Microplastics are an emerging and persistent pollutant due to their threat to global ecological systems and human health. Recent studies showed that microplastics have infiltrated the remote Third Pole - the Tibetan Plateau. Here, we summarize the current evidence for microplastic pollution in the different environments (rivers/lakes, sediment, soil, ice/snow and atmosphere) of the Tibetan Plateau. We assess the spatial distribution, source, fate, and potential ecological effects of microplastics in this broad plateau. The integrated results show that microplastics were pervasive in biotic and abiotic components of the Tibetan Plateau, even at the global highest-altitude, Mt. Everest. Although the concentration of microplastics in the Tibetan Plateau was far below that found in the densely populated lowlands, it showed a higher concentration than that in the ocean system. Tourist populations are identified as a substantial source of anthropogenic plastic input rather than local residents due to the rapid development of the tourism industry. In the sparsely inhabited remote area of the Tibetan Plateau, long-range atmospheric transport facilitates allochthonous microplastic diffusion. Robust solar radiation in the Tibetan Plateau might enhanced production of secondary microplastics by weathering (UV-photooxidation) of abandoned plastic waste. A rough estimation showed that the microplastic export flux from melting glaciers was higher than that measured in most of the world's largest rivers, which affects local and downstream areas. Since the Tibetan Plateau is vital for Asian water supply and numerous endangered wildlife, the potential human and ecological risk of microplastics to these fragile ecosystems needs to be fully evaluated within the context of climate-change impacts.

This article presents a comprehensive vision of particularities and constraints of the Paja Formation in the Northern Andes of Colombia, supported by personal, institutional, and academic experiences, including a doctoral thesis in completion (geomorphology and risks research line). Such fine-grained marine rocks cause severe damage in diverse zones, with little spread, and are very unfavorable, especially within the Eastern Cordillera (departments of Santander and Cundinamarca), whose socio-environmental problems motivated a popular legal action in the municipality of Vélez due to the cracking and collapse of houses, damage to roads and landslides in the urban area, as well as flows, subsidence, and high hydrogeochemical dynamism or rare earths, although they also presented spontaneous ignition at the rural area. Understanding how these problems originate and interrelate is the main objective of the work. At the beginning, we include some brief definitions, terms, and key approaches to understand the consolidated geomaterials, location, and background of the problem; then, the results of meso–macro–micro studies, obtained by combining the field techniques and conventional instrumental laboratory analyses (tests on the chemistry of water and soil, description of samples with magnifying glasses, petrography with a polarized light microscope, micromorphology of regoliths–colluvions) of nanoscientists (emphasizing RXD-RXF, SEM, IR-Raman spectroscopy, TOC-TS) are presented. These characterizations and new knowledge must be socially and institutionally appropriated and applied in land use planning and risk management for the sustainability of challenging environments with the stratiforms of Lower Cretaceous rocks and associated Quaternary deposits in populated mountainous areas and contrasting intertropical hydroclimatological regimes, geologically active, so unstable and insecure.

Data on the mineralogy and geochemistry of rare earth elements (REE + Y) in water, suspended matter and stratified sediment cores from different parts of Lake Onego are presented. The study finds that the dissolved REE + Y in the water from different areas of Lake Onego have common features: (1) a maximum in the area of middle rare earth elements (MREE), (2) a distinct negative Ce anomaly and (3) a positive Eu anomaly. Comparison of the average concentration of elements in the stratified core of the bottom sediments and particulate matter (from the filters and sedimentation traps) from different parts of Lake Onego and the distribution of REE + Y do not reveal any significant differences. The trend of the REE + Y distribution for samples from the South Onego completely coincide the REE + Y distribution in siltstones and sandstones of the Russian Platform Scale Composite (RPSC). In the water area of Lake Onego from south to north, a well-defined trend of changes in REE + Y patterns relative to the RPSC is revealed, with depletion by heavy REE + Y and gradual enrichment by light rare earth elements (LREE). Geochemical and mineralogical data confirm our hypothesis of a significant reformatting of the catchment basin of the Onego Ice Lake in the Late Pleistocene. During the formation of the preglacial lake, a significant part of the catchment area was located south of Lake Onego and is mainly represented by Russian Platform sedimentary rocks. Due to the degradation of the Last Glacier from the Lake Onego depression and the nearby territories, the catchment area changed of its southern and south-eastern sections. Today the composition of the modern sedimentary matter entering Lake Onego is determined by mixing clusters from two geochemically contrasting feeding areas: loose sediments formed by the repeatedly re-deposited products of the weathering of the Fennoscandian Shield's crystalline rock massifs, including Phanerozoic sediments; and to a lesser extent the sediments of the sedimentary cover of the Russian Platform, except the bottom sediments of the South Onego, in which Phanerozoic sedimentary formations have completely predominated throughout the lake's development.

This research evaluates the behavior of plaster with a water-repellent additive when submitted to a natural aging process. Casting plaster and silane/siloxane-based water-repellent were used as materials. The water/plaster ratio was set at 0.7 and the contents of 0.2% and 0.4% of water-repellent were used, in relation to the plaster mass. Plaster pastes without water-repellent (reference) and containing mass water-repellent were evaluated at ‘zero’ age and after 30, 60, 90, 120, and 150 days of natural aging. After 150 days of natural aging, it was observed that the mechanical properties of the material (compressive strength and hardness) did not undergo significant variations and remained above the minimum required by a standard. The addition of water-repellent resulted in a considerable reduction in water absorption, demonstrating the water repellency capacity of the material, compared to the reference specimen.

Rare earth elements (REEs) mobilize, fractionate, and are re-distributed during supergene processes, and thus provide a powerful tool with which to quantitatively reconstruct the effects of chemical weathering. Moreover, under certain conditions, the REEs can concentrate to levels in the regolith sufficient to form giant regolith-hosted REE deposits, that are now responsible for much of the World’s production of heavy REEs (HREEs). Understanding the supergene behavior of the REEs is an important first step towards applying the REEs as a geochemical tool and meeting the growing global demand of the REEs. Thermodynamic calculations predict that dissolution of the main REE minerals in REE-rich protoliths, namely synchysite-(Y), gadolinite-(Y), hingganite-(Y), yttrialite-(Y), allanite-(Ce), eudialyte, chevkinite-(Ce), britholite, euxenite and loparite-(Ce), should occur spontaneously during weathering. It therefore follows that a high abundance of these minerals in the protolith implies high mobility of the REEs during weathering and consequently a high potential for the discovery of economic REE resources. Dissolution of apatite is promoted by metamictization or structural distortion and could be also important at low pH. In contrast, some LREE-fluorocarbonate minerals, notably bastnasite-(Ce) and parisite-(Ce), and monazite-(Ce) are likely thermodynamically stable in acidic environments. Thus, they would be preserved in the regolith. Zircon, titanite, aeschynite, fergusonite, and xenotime-(Y) are resistant to acidic dissolution, consistent with their common occurrence as residual minerals. In the cases of the world-class regolith-hosted REE deposits in South China, the groundwater is mildly acidic to circumneutral and carbonate-rich. The REEs are consequently transported dominantly as hydrated cations and carbonate complexes, depending on the pH. The general inheritance of the REE pattern of the regolith groundwater in the clay-sorbed fraction in the regolith indicates that the REEs in regolith are scavenged from the regolith groundwater. Elemental anomalies of specific REEs in the clay-sorbed fraction are very likely caused by an anomalously high REECO3+ fraction in the corresponding regolith groundwater, suggesting a preferential uptake of the REECO3+ complexes by the clay minerals, feasibly by halloysite through intercalation as interlayer complexes. This reaction is expected to be particularly important for the sorption and enrichment of the HREEs in the regolith. Depending on the pH and carbonate concentration of the water, surface complexation on clay minerals or interlayer intercalation particularly in halloysite control the pattern of REE enrichment. Mixing of the regolith groundwater with the alkaline and carbonate-rich aquifer groundwater increases the pH and carbonate concentration and, in turn, affects the ability of the mixed water to transport the HREEs. Interplay of aqueous complexation with the regolith mineralogy significantly affects the REE fractionation and re-distribution during groundwater-regolith interaction.

Statement of problem The climate of tropical Southeast Asia includes high humidity and ultraviolet radiation that reduce the lifespan of silicone prostheses by inducing changes in their mechanical properties and color stability. Studies on the surface roughness (SR) and mechanical properties of different silicone elastomers (SEs) subjected to the natural tropical weather of Southeast Asia are lacking. Purpose The purpose of this in vitro study was to evaluate the SR, tensile strength (TS), and percentage elongation (% E) of different SEs subjected to outdoor weathering in the Malaysian climate. Material and methods Type-II dumbbell-shaped specimens (N-120) (nonweathered=15, weathered=15) were made from 3 room-temperature vulcanized (A-2000, A-2006, and A-103) and 1 heat-temperature vulcanized (M-511) silicone (Factor II). For 6 months, weathered specimens were subjected to outdoor weathering inside a custom exposure rack. Simultaneously, the nonweathered specimens were kept in a dehumidifier. Subsequently, the SR was measured with a profilometer; TS and % E were measured by using a universal testing machine. Two-way ANOVA was used to compare the means of the tested properties of the nonweathered and weathered specimens, and pairwise comparison was carried out between the silicones (α=.05). Results After outdoor weathering, the SR, TS, and % E were adversely affected by weathering in the Malaysian environment. Among the silicone materials, A-2000 showed the least TS changes (2.51 MPa), while A-2006 demonstrated significant changes in percentage elongation after outdoor weathering (266.5%). M-511 exhibited the highest mean value (2.50 μm) for SR changes. In addition, A-103 SE showed statistically significant differences in most pairwise comparisons for all 3 dependent variables. Conclusions Based on the evaluation of mechanical properties, A-103 can be suggested as a suitable silicone for maxillofacial prostheses fabricated for tropical climates. However, A-2000 can be a suitable alternative, although significant changes to surface roughness were detected after outdoor weathering.

The Physico-chemical and mineralogical properties of the Cretaceous shales of Calabar Flank southeastern Nigeria were examined for their Provenance, Paleo-weathering Conditions and Industrial Applications. Twenty samples of shale from Ekekpon and Nkporo Formations were analysed using X-Ray Fluorescence, X-ray diffraction (XRD), scanning electron microscopy (SEM) and geotechnical techniques. Results from the major oxides of elements revealed that the Nkporo Shale is enriched with SiO2 > Al2O3 > LOI > Fe2O3 > SO3 while the Ekepkon shale is also enriched in SiO2 > Al2O3 > LOI > Fe2O3 > CaO > K2O. The XRD revealed kaolinite as the major clay mineral, while other non-clay minerals are quartz, vallerite, mica, nacaphite, sodalite. The SEM shows that the Ekepkon Shale is enriched in calcium. The correlation matrix revealed SiO2 resides more in the quartz phase of the Nkporo Shales, while in the Ekekpon Shale the SiO2 is associated with the clay. The element ratios and discrimination diagrams revealed that the provenance of the shales is of intermediate to mafic igneous rocks and a tectonic setting of continental to oceanic arcs. The presence of kaolinite in the Nkporo Shale with the chemical index of alteration (CIA) values ranging from 83.58 to 96.93, indicated that the shale is derived from intensive chemical weathering in the source area. The low CIA values (37.90–76.96) in Ekenkpon Shale is attributed to CaO and calcium enrichment in the shale and the shale contains high quartz and kaolinite therefore the shale is suggested to have been derived from an intermediate to intense weathering activities in the source area. The geotechnical properties revealed that both shales are suitable for ceramic and refractory industries. The Ekenkpon Shale will be suitable for use as filling material and as raw material in cement industries. However, the shales do not meet the specifications for paper and rubber production due to the high contents of iron oxide, lime, magnesia, potash and soda.

Natural building stones, used as floor cladding stones in outdoor applications in cold regions, are negatively affected by freezing and thawing processes, and this reduces the service life of the stone. The aim of this study is to reveal the change of abrasion resistance of natural stones determined by the wide wheel abrasion test (W-A) with laboratory freeze-thaw (FT) tests. For this purpose, FT tests were applied up to 84 cycles on 23 groups of samples, mainly consisted of carbonate rocks. According to the results, no significant decrease was determined in the dry unit weight (gamma(d)) value, but significant decreases were obtained in open porosity (n) and P-wave velocity (V-P) values. It has been revealed that W-A values are also significantly affected by increasing FT cycles and increased up to about 14%. It was concluded that the increase was evident up to 35 FT cycles, and after this level, the increase continued with a decrease.

The demand for a load distributive compression anchor (LDCA) in construction sites has been increasing, owing to its high bearing capacity and removable steel strands. As an LDCA comprises multiple anchor bodies and unbonded steel strands, the load applied to the strands generates a distributive compressive stress in the grout, preventing high concentration of grout–ground shear stress. Unlike in the conventional anchors, in an LDCA, independent load transfer of each anchor body induces interference effect between adjacent anchor bodies. Therefore, for an efficient design of an LDCA, it is necessary to investigate the load transfer mechanism considering the effect of multiple anchor bodies. In this study, a series of anchor pull-out field tests was conducted for LDCAs consisting of a single anchor body, and double and triple anchor bodies spaced by 1, 2, and 3 m. According to the test results, the LDCA showed a stiffer load–displacement behavior with an increase in the number and spacing of the anchor bodies. The multiple anchor bodies of the LDCA generated an overlapping of the grout axial load and induced its rapid dissipation, increasing the grout–ground shear stress. This interference effect was more clearly observed with a decrease in the anchor body spacing.

The geochemical composition and magnetic susceptibility (MS) of three sections (Weinan, Jingchuan and Jingbian) in the central Chinese Loess Plateau, located along a north-south climate gradient, were analyzed at high resolution in order to reconstruct changes in weathering intensity and hence Asian monsoon evolution during the Holocene. The results show distinct differences in element composition between the loess and paleosol layer, as well as spatial differences which reflect changes in mean annual temperature and annual precipitation along the climatic gradient. The measured major element compositions, combined with the results of previous research, indicate that the provenance of the Holocene loess-paleosol sequences in the central Chinese Loess Plateau was constant over time and space. The degree of chemical weathering in the study area is relatively weak and at an intermediate weathering stage. Based on a magnetic susceptibility age model, the East Asian summer monsoon changes recorded by the loess-paleosol sequences show a distinct two-stage pattern of evolution, with a gradual increase during 13.1–8.5 ka and a gradual decrease thereafter. Comparison of the results with climate records from elsewhere indicates that the East Asian monsoon evolution was mainly controlled by changes in Northern Hemisphere summer insolation and ice sheets.

Water affects the susceptibility of stone to alteration by facilitating physical, chemical and biological weathering. Stone properties determine water transport and retention, but it is also expected that biofilms and extracellular polymeric substances could alter the water-stone relationship. A lot of research on this subject has been carried out on soils, but the effect on stones is understudied. For this reason, three sedimentary building stones, Ernzen, Euville and Savonnieres, each with a different pore size distribution, were biofouled with cyanobacteria. Their relationship with the stone material was investigated by optical and electron microscopy, and the effect of cyanobacterial biofilms on water transport and retention was studied. The results showed that the cyanobacteria primarily colonize the building stones on the outer surface and have a limited effect on the water transport properties. They slightly reduced the capillary coefficient and drying rate of the stones, but enhanced the water content in the stone and increased water vapour sorption. They induced (near) hydrophobic conditions, but had no measurable effect on the gas permeability and water vapour diffusion. Moreover, swelling and shrinkage of the biofilms were observed, which could potentially induce physical weathering. It is expected that these changes could influence other forms of weathering, such as freeze-thaw weathering and salt weathering.

Considerable research has been conducted over the past decade by oil sands mining companies to improve the dewatering and strength properties of fluid fine tailings deposits in an effort to meet the regulatory and closure requirements. Commercially employed dewatering treatment technologies (inline flocculation, thickening, and centrifugation) may not be sufficient to develop the strength for the creation of trafficable landscape without the use of soft soil capping technologies. These treated tailings are continuously deposited creating soft and saturated deep deposits. Seasonal weathering may be an additional promising technology to further dewater the treated tailings and promote the development of shear strength at the surface. This paper presents the effects of seasonal weathering on dewatering and strength that were investigated by performing multiple cycles of freeze–thaw and alternate drying–wetting cycles on two types of treated tailings deposit. The results indicate that multiple cycles of seasonal weathering significantly increased the dewatering and strength properties. However, different parameters such as freezing gradient, number of seasonal cycles, and pore water chemistry play an influential role in changing the magnitude of the strength. The results also suggest that a minimum threshold strength value is required where the effects of rainfall rewetting had a minimal impact on strength reduction (the strength corresponding to the moisture content approaching the plastic limit).

Fungi actively enhance the local dissolution of nutrient-bearing minerals through the combined biomechanical and biochemical actions of their hyphal tips to obtain mineral-bound inorganic nutrients (MINs). However, little is known about the dynamic processes underlying hyphal tip-mineral interactions. Here, we assess the adhesive force between a single hypha of the common fungus Talaromyces flavus and the Fe-bearing silicate lizardite and quartz (as a control), as well as hyphal tip-induced lizardite weathering and hyphal Fe uptake. We showed that T. flavus hyphae formed their maximal adhesive force with lizardite at the growing tips, reaching 6.11 ± 0.69 nN after a contact time of one minute. The adhesive forces of the tip-lizardite interface within two minutes were > 2.65 times stronger than those of the tip-quartz interface. Examination of the hyphal tip-lizardite interface after 18 h indicated the formation of dissolution channels with a depth of 27.7 ± 8.0 nm. Furthermore, the hyphal tips resulted in an altered lizardite up to 46 nm. The thickness of the altered lizardite increased to ∼130 nm after contact with the mature regions of the hyphae for ∼173 min. And the altered lizardite was found to have depleted Fe levels that increased with increasing contact time. The total content of Fe in T. flavus associated with the lizardite surface after 18 h was 52.98 ± 12.20 nmol mg-1, which was 6 times greater than the total amount of Fe in quartz surface-associated T. flavus after 24 h of culture. These results demonstrate that fungi access MINs by the active development of a strong adhesive force with target minerals through their hyphal tips, effectively enabling fungi to flourish in heterogeneous environments and be major geological agents for biogeochemical transformation.

Degraded water quality and environmental impacts caused by weathering of sulfide-bearing mine wastes are a legacy remaining at many historical mine sites. Release and mobilization of toxic metals (e.g., Zn and Cd) in mine drainage are often associated with weathering of primary sulfide minerals and precipitation and dissolution of secondary minerals. This study aims to couple field-scale measurements of physicochemical parameters with μm- and nm-scale mineralogical characterization to investigate sphalerite weathering and controls on Zn and Cd migration in an uncovered mine waste-rock pile. Elevated concentrations of Zn and Cd, potentially harmful to the receiving environment, were detected in waste-rock pore water and seepage. A suite of analytical techniques, including scanning electron microscopy – energy dispersive X-ray spectroscopy (SEM-EDS), scanning transmission electron microscopy (STEM) with EDS, electron microprobe analysis (EMPA), and synchrotron-based micro X-ray fluorescence (μ-XRF) mapping and micro X-ray absorption near edge structure (μ-XANES) spectroscopy were utilized in a high-resolution investigation of elemental- and secondary-mineral associations with sphalerite grains. EMPA and μ-XRF elemental maps and STEM investigations show depletion of Zn, Fe, S, and Cd, local enrichment of Cu, and distinct dissolution pits at the margins of sphalerite grains. Using μ-XANES, the speciation of solid phases containing Zn, Cu, Fe, and S indicates the dominance of primary sphalerite with microscopic inclusions of chalcopyrite, along with sparse occurrence of secondary Cu-bearing sulfides formed during weathering. These results suggest sphalerite oxidation leads to congruent dissolution without formation of distinct secondary-mineral coatings. Sphalerite weathering significantly contributes to elevated aqueous concentrations of Zn and Cd. Field-scale observations and mineralogical investigations indicate common occurrence of Fe-oxyhydroxides in the waste-rock pile. Seepage chemistry and surface complexation modeling results suggest that pH-dependent variations in reactions on the surfaces of the Fe-oxyhydroxides control aqueous concentrations of Zn and Cd, and the Zn/Cd ratio in the seepage. This work highlights the importance of understanding the mechanisms of sulfide-mineral oxidation and subsequent surface precipitation and adsorption, such that appropriate remediation action can be implemented to limit mobilization of metals to sensitive ecosystems.

Subaerial physical, chemical and biological weathering processes are significant contributors to mountain landscape development worldwide, and over long time scales. This paper reports on pseudokarst features formed by different subaerial weathering processes on a high-elevation basalt plateau surface in the Maloti–Drakensberg mountains of eastern Lesotho, southern Africa. Different mesoscale landforms identified on this plateau surface include enclosed depressions (containing seasonal pools) that are morphologically similar to karstic solutional features. Such basalt pseudokarst landforms have not been previously described. This study uses field data on depression morphometry, sediments, water chemistry and rock surface hardness to explore the varied subaerial weathering and erosion processes contributing to pseudokarst depression development. Results show that physical, chemical and biological weathering and erosion processes in combination can impact on the basalt land surface in widening and deepening these depressions. An evolutionary model for pseudokarst depression development proposes that different weathering processes in combination within the ‘critical zone’ cause changes in depression morphology, and that there are significant feedbacks between bedrock, weathering, and the development of distinctive micromorphological forms. It is likely that similar pseudokarst landforms from other locations with non-carbonate substrates have been under-reported in the literature.

This work presents the systematic investigation of K contents and stable K isotopic compositions of surface waters, groundwater, wastewaters, suspended particles, bed sediments, and fertilizers in the Upper Mun Rive catchment, northeast Thailand. This area is of particular interest because its abundant potash deposits and intensive agricultural activities and urbanization, therefore this will improve our understanding whether the K isotope is robust enough to resist evaporite dissolution and anthropogenic disturbances on tracing silicate weathering in the highly weathered tropical region. The dissolved loads in surface waters and shallow groundwater display the large variation in δ41Kdiss values from −0.54‰ to +0.09‰ relative to suspended particles (−0.60‰ to −0.41‰), river bed sediments (−0.54‰ to −0.47‰), the upper continental crust (UCC, −0.44 ± 0.05‰), which agrees with the fact that 39K is preferentially retained in weathering products during silicate weathering. The wet and dry seasons difference ranging from −0.05‰ to +0.10‰ δ41K, which is slightly greater than our long-term analytical uncertainty of ±0.06‰. There is likely a limited K input from evaporites dissolution due to weak correlation between δ41Kdiss values and Cl concentrations or Cl/K ratios in the UMR and world rivers, while a major tributary Takhong River is clearly influenced by the contribution of domestic sewage with lower δ41K and higher δ15N values. Based on a mass balance of K budge, the dissolved K in the UMR is mostly (>90%) derived from silicate weathering in the unpolluted area, this is consistent with previous studies of large river basins, and the evaporite dissolution and other non-silicate sources may not strongly influence dissolved K and δ41Kdiss values in rivers, even in evaporite-rich catchment. Therefore, K isotopes cannot be used as lithological tracers in catchments, rather the K isotopic fractionation mainly occurs during silicate weathering, such as the formation of secondary minerals which favor light isotope. Hence, the mechanism of K isotopic fractionation linked to secondary minerals K uptake needs further consideration. Overall, these results clearly show that K isotopes could be an ideal indicator to constrain silicate weathering processes and anthropogenic inputs at catchment scale.

Pliocene-aged carbonaceous rocks of varying thicknesses, alternating with siliciclastic and carbonate rock units, are located on the northern border of the Çameli-Acıpayam basin (in southwestern Turkey), which is filled with thick Neogene sediments. Organic and inorganic geochemical properties of carbonaceous rocks were examined to evaluate their hydrocarbon production potential and paleo-depositional conditions (provenance, paleoclimate, paleosalinity, paleoredox, weathering, heavy metal contents, etc.). Based on organic geochemical analysis, carbonaceous rocks show good to excellent source rock potential and have gas production potential. Organic substances are mostly of allochthonous origin, and their thermal maturity degree is quite low. Carbonaceous rocks have a high amount of inorganic substance (minerals) composed of quartz, clay + mica minerals (mostly illite and a lesser amount of smectite, chlorite, and kaolinite), feldspar, and opaque minerals (pyrite and ilmenite). Although carbonaceous rocks have similar major oxide and trace element concentrations, they show clear differences in terms of Fe2O3, MgO, and some heavy metals (such as Ni, Cr, Co, V, and Sc). The major oxide, trace element concentrations, various element ratios of carbonaceous rocks bear the characteristics of mafic/ultramafic magmatic rocks formed on the active continental margin. In addition, carbonaceous rocks were precipitated in a brackish water environment under oxic conditions. The sediments, which were rapidly stored without recycling in the deposition environment where hot/humid climatic conditions are effective, did not undergo intense decomposition in the source area.

The environmental availability of mineral nutrients plays a role in the adaptation and evolution of soil fungi and fungus-plant symbiotic systems. As nutrient availability is different from soil to soil, it is expected that the most adapted fungi can express multiple genes to promote different mechanisms of mineral attack and of metabolic routes to maximize the use of nutrient resources at the lowest energy cost. Microcosm experiments of Paxillus involutus growing on muscovite, phlogopite and K-exchanged vermiculite as K sources were carried out for 21 days. Gene expression analysis indicated that the level of K-deprivation stress was muscovite > phlogopite >> K-vermiculite. Genes and functions overexpressed in the experiments indicated meaningful metabolic activities including K extraction and transport. SEM-EDS and micro-XRD (∼1.15 mm resolution) analysis of mineral surfaces and chemical analysis of agar and mycelium indicated weathering processes and K uptake in good agreement with gene expression analysis. In many areas, P. involutus caused physical damage to the minerals without any apparent chemical attack, consisting of tracks of different depth, from

Deep atmospheric convection in the Indo-Pacific Warm Pool (IPWP) represents a major source of heat and moisture, thereby affecting the global climate, but its past changes remain debated. Here, we present sub-millennial clay mineralogy and elemental records spanning the last 40 kyr from within the IPWP. From these data, we infer millennial-scale fluctuations in precipitation, with generally lower precipitation during Heinrich Stadials 1-4, corresponding to El Niño-like conditions. Higher precipitation coincided with the warm interstadials, accompanied by La Niña-like conditions. Moreover, our record indicates the lowest precipitation occurred during the late Holocene, supporting the hypothesis of a stronger-than-modern Walker circulation during the Last Glacial Maximum. In combination with other proxy records and TraCE-21 modelling results, we recognize a distinct spatial heterogeneity of precipitation within the IPWP, resulting from the dominant influences of the ENSO-like system and migration of the Intertropical Convergence Zone in the eastern and western IPWP, respectively. Key Points We present sub-millennial clay mineral and elemental records from the Indo-Pacific Warm Pool spanning the last 40 kyr Our records indicate higher precipitation during La Niña-like conditions and lower precipitation during El Niño-like conditions Different patterns and controls on precipitation variability between the eastern and western Indo-Pacific regions are revealed Plain Language Summary Tropical rainfall systems in the Indo-Pacific Warm Pool (IPWP) play a significant role in transferring energy and moisture. However, their millennial-scale variabilities in precipitation during remains poorly understood. Here, we provide sub-millennial sediment mineralogy and elemental reconstructions spanning the last 40,000 years from a sediment core in the IPWP. We infer that variability in precipitation induced by atmospheric convection in the IPWP is the main factor controlling the variability in our data through time. Hence, we interpret our records to reflect sub-millennial fluctuations in precipitation, with lower precipitation during cool stadial periods and higher precipitation during warm interstadials. Such variability corresponds to the changing zonal state of the tropical Pacific atmosphere-ocean system, in a pattern similar to the modern-day. Additionally, our record indicates that precipitation was weaker during the late Holocene than during the Last Glacial Maximum (LGM), suggesting that the Pacific atmospheric zonal circulation was stronger during the LGM than today. Furthermore, a model-data comparison reveals distinct spatial heterogeneity in the precipitation changes, with precipitation in the eastern IPWP (West Pacific) likely controlled mostly by the tropical Pacific atmosphere-ocean system, whereas precipitation in the western IPWP (Indian Ocean) was driven by latitudinal movement of the Intertropical Convergence Zone.

Industrialization and changes in the landscape have disturbed natural geochemical cycles of carbon and other elements significantly for several centuries. Fossil fuel emissions are the main contributor, along with deforestation and cement production. Projection of future trends in atmospheric CO2 and global carbon flows, under human disturbance, requires understanding of the natural exchanges between atmosphere, marine and terrestrial ecosystems, and geosphere pools. Regulation of the rates of flux in the global carbon cycle occur in enumerable biogeochemical processes, but overall through major feedbacks in the biogeochemical cycle of carbon through weathering, photosynthetic fixation, respiratory metabolism, and the ocean calcium carbonate buffering system. Mathematical computer models have become the means by which the complex, biogeochemical processes of atmosphere, land, and oceans can be represented, quantified, and used to describe the past, present, and future dynamics of the Earth's carbon cycle.

Dissolution and chemical weathering of carbonate rocks have complex effects on their mechanical properties, accelerating their rate of deterioration that can lead to early failure under external stresses. To investigate the effects of acidic solutions on the mechanical properties of inherently low-porosity karstic limestone, compression tests were performed on sound and weathered samples exposed to different corrosive environments and for different durations. The tested samples exhibited a general increase in porosity and decrease in peak strength and Young's modulus for higher acidity and exposure duration. To establish links between these mechanical changes and those at the micro-scale, microstructures and mechanisms of deformation were also studied. As indicators of the sample degradation, the distribution, orientation and intensity of the fractures in the tested samples and their twinning density were used. Based on these parameters, it was found that chemical erosion influences microcrack propagation, orientation, distribution and intensity, due to modification of the competence contrast between the constituents of the rock. These effects significantly influence the semi-brittle behaviour of the samples, including the distribution and intensity of microcracking and crystal plasticity.

Deep-seated relict permafrost was identified in borehole Udryn PIG-1 (north-eastern Poland) at depths from +450 to 357 m. In potential its extant provides an opportunity to expand the known effective realm of grain weathering. Specifically, uncertainty exists as to whether or not glacial-period frost weathering could even occur at such considerable depths, which is well outside an active-layer range (i.e., beyond the currently acknowledged domain of grain weathering). Sand deposits collected at a 410.70–396.75 m depth were subjected to grain-size analysis, then 0.5–0.8 mm quartz-grain surfaces were analysed under stereoscopic and scanning electron microscopy. The obtained results indicate that these relict-permafrost grains were both mechanically and chemically weathered. Mechanical weathering of quartz grains is identified as P- & F-type weathering. The former is associated with an increase in stress generated both by overlying ice-sheet masses and permafrost degradation. Here mechanical weathering was facilitated by the presence of well-sorted sediment, rounded or well-rounded grains, and high porosity. Its effects are microtextures such as breakage blocks and conchoidal fractures. F-type weathering is/was generated by freezing water in various sorts of cavities and cracks. Weathering is directly associated with the presence of permafrost at this depth. Additionally, chemical weathering is recorded on quartz-grain surfaces in the form of a ragged discontinuous coating. It has been proven here that weathering of quartz grains is not just a near-surface phenomenon, but also occurs deep below Earth's surface.

The Fezouata Shale in Morocco is the most diverse Lower Ordovician unit yielding soft-tissue preservation. Iron played a crucial role in the preservation of soft parts in this formation through the damage of bacterial membranes under oxic conditions and the pyritization of soft parts under the activity of bacterial sulphate reduction. However, the origin of Fe in this formation remains largely speculative. Herein, trace and rare earth elements were investigated in drilled-core sediments from the Fezouata Shale. It is shown that a correlation exists between Fe and Al suggesting that most Fe has a detrital source. Elemental concentrations in the Fezouata Shale are most comparable to rivers and are the least similar to loess and sediments deposited near active island arcs. In this sense, continental weathering and its related Fe in river fluxes dictated occurrences of exceptional fossil preservation in the Fezouata Shale.

To investigate the influence mechanism of weathering in the biogas production from coal, the characteristics of three coal samples with different weathering degrees obtained from the Wuhai mining area in Inner Mongolia and from the Xishan and Jincheng mining areas in Shanxi province were analyzed using the following methods: humic acid (HA) extraction, three-dimensional fluorescence spectroscopy, X-ray photoelectron spectroscopy and X-ray diffractometry. The results showed that the HA content in weathered coal increased with an increase in weathering degree. The content of dissolved organic matter in moderately and intensively weathered coals was clearly higher than that in slightly weathered coals. Meanwhile, the C–C and C–H in the aromatic ring was broken under the action of weathering, thus decreasing the aromaticity. Additionally, the weathering process also intensified the disordering of the directional arrangement of the macromolecular structure, causing the crystallinity of the coal to decrease. These conditions facilitated the degradation and utilization of coal by microorganisms and can be helpful to produce more biogas from coal.

The groundwater of Awe-Keana saline fields in central Nigeria was studied to investigate physicochemical processes that influence its groundwater chemistry and quality and hence determine its quality for drinking and irrigation purposes. Twenty groundwater samples were collected from hand-dug wells and boreholes for the purpose of identifying the hydrochemical characteristics and assessing the quality of groundwater of the Awe-Keana saline fields. Principal component analysis was performed to identify the hydrochemical controlling processes while water quality index (WQI) was used to determine the overall quality of the water samples. Multiple regression analysis, however, revealed the parameter(s) that impact the overall water quality the most. The results showed that the chemical compositions of the groundwater of the area is influenced by weathering of hostrocks, salinity and anthropogenic activities. Four hydrochemical facies were deciphered (Ca-Mg-HCO3, Na-K-HCO3, Na-K-Cl-SO4, and Ca-Mg-Cl-SO4) and this revealed the diversity in the chemical controlling processes that yield different facies. Two clusters of water groups were identified from cluster analysis, namely, groundwater characterized with very high salinity, high nitrate contamination and high Ca, Cl, Na, and HCO3 ionic concentrations and groundwater with high Mg, K, and SO4 ionic concentrations. Saturation indices in relation to different minerals showed that precipitation and dissolution processes gave rise to the concentrations of different ions in the groundwater. Water quality assessment showed that about 85 % of the groundwater of the area is unsuitable as drinking water but, generally suitable for irrigation. Multiple regression analysis revealed that NO3 ion among the hydrochemical parameters measured was observed to be the major pollutant in the groundwater of the study area.

This study aims to assess the water quality of the Mahananda River in Bangladesh and its suitability for drinking and agricultural uses. For water quality determination, 15 samples were collected from different sites of the Mahananda River to calculate Water Quality Index (WQI) and Entropy Water Quality Index (EWQI). Result shows that among different Hydrochemical parameters, carbonate and bicarbonate concentrations crossed the maximum limit in all the samples, while fluoride concentration exceeding in Sample-15 with the highest value found in Baroghoria area. From WQI result, water quality for the Baroghoria area was found unsuitable for drinking with WQI − 309.22, whereas another two samples of Mollikpur and Namo Neemgachi fall under ‘poor’ category with WQI of 184.49 and 198.99, respectively. EWQI reveals medium to excellent water quality. Result from different irrigation indices (Na%, sodium adsorption ratio (SAR), residual sodium carbonate (RSC), magnesium hazard (MH), total hardness, Kelly ratio (KR), and permeability index (PI) values) showed their suitability for irrigation. Principal component analysis (PCA) explained a total of 89.71% of variances in the dataset. Significant positive association within EC–Na, EC–sulfate, Ca–TH, nitrate–sulfate, etc., were reported indicating prominence in terms of both geogenic as well as anthropogenic processes such as silicate weathering and the release of untreated sewerage, respectively, which governs the water quality evolution in the study area. Cluster analysis (CA) classifies all water samples in five different clusters based on five different characteristics. Mahananda River water is found safe for both drinking and agricultural purposes, except for few samples near the dense human settlement areas. Result from this study is useful for decision makers to design management plans for the river water quality, environmental pollution and human well-being.

Aptian to Campanian sediments from the Western offshore to Central Orange Basin were studied by integrating molecular geochemistry, inorganic and isotopic studies to recognize their geochemical characteristics via the reconstruction of the Orange basin’s paleoweathering, paleosalinity, paleovegetation, paleoclimate, and tectonic records. Molecular analyses of both aliphatic and aromatic compounds reveal an input dominantly from a marine source. The source rocks accumulated in a reduced, anoxic, saline water column. Based on various biomarker proxies and vitrinite reflectance data, some samples are thermally mature to produce petroleum, while others are not. According to the V/Ni ratio, samples from the Orange Basin in South Africa are mainly anoxic, with only a few samples ranging from suboxic to anoxic. This is congruent with biomarker and isotope analyses that further indicate the presence of marine-derived source rocks with some terrestrial remains generating hydrocarbons. The investigated sediments are made up of intermediate igneous rocks that have undergone moderate chemical weathering. Geochemical figures on tectonic setting discriminant function diagrams revealed a continental rift of passive margin settings. As a result, the extrapolated crustal processes are directly analogous to the genesis and evolution of the Orange Basin, demonstrating Gondwana’s breaking up and the opening of the Atlantic Ocean Margin.

There are abundant vanadium ores in the Cambrian strata in southern Shaanxi, China. Many years of mining activities and surface leaching have polluted the surface water to a certain extent, but the researches on the water quality characteristics and pollution degree are relatively weak. This contribution was organized to investigate the surface water quality by general parameters, including TDS, Eh, pH, DO, TOC, COD, and EC, in the vanadium ore belt (Yinhua River basin). Major ions were determined to detect the water type and natural chemical weathering, while trace elements were used to illustrate their geochemical characteristics and ecological risk assessment of heavy metals. The study found that the surface water was weakly alkaline and mainly dominated from normal to pool grade. The particle size with 1000–10,000 nm of suspended particles was the main carrier of organic matter. The concentration of HCO3− and SO42− in the anions and Ca2+ and Mg2+ ions in the cations were relatively high, and the water type was Ca-Mg-HCO3-SO4 type. Rock weathering had a great influence on surface water, and the weathering products were mainly silicate and carbonate. Compared with the Type river, the contents of V elements showed an obvious positive anomaly, which may be affected by mining activities of vanadium ore and the annual leaching of the tailings pond. As and Cd in the surface water was polluted seriously. The integrated pollution index suggested that the surface water pollution was serious, and the main stream was more serious with the increasing tailings ponds.

The Moon has experienced an intense bombardment history since its formation1. Fragments of the impactor can remain on the lunar surface2–4 and can provide evidence of the evolution of the impactor composition and impact population in the Earth–Moon system3–5. However, the retained impactor fragments previously identified in the Apollo samples have been well mixed into bulk lunar regolith due to the subsequent impact gardening, and their properties cannot be easily isolated3,6,7. Here we report observations of a two-metre-sized crater that formed less than one million years ago obtained by the Yutu-2 rover of Chang’e-4. Hyperspectral images in the visible and near-infrared range (0.45–0.945 μm) with a spatial resolution less than 1 mm per pixel highlight the presence of glassy material with high concentration (47%) of carbonaceous chondrites. We identify this material as remnants of the original impactor that was not entirely vaporized by the impact. Although carbonaceous chondrite fragments have been found in Apollo samples8,9, no carbonaceous chondrite remnant had been directly observed on the lunar surface by remote sensing exploration. We suggest that carbonaceous chondrite-like bodies may still provide one of the sources of water to the present Moon. The Chang’e-4 rover observed a small crater formed less than one million years ago, finding glassy materials with spectral characteristics similar to those of carbonaceous chondrites that are identified as remnants of the original impactor that have not yet been affected by weathering processes.

Within the eolian Lower Jurassic Navajo Sandstone, exposed in the Coyote Buttes area of Vermilion Cliffs National Monument in Arizona, a site (informally known as the “Dinosaur Dance Floor”) is reinterpreted as an enigmatic, modified (possibly pedogenic) eolian surface that was exposed and further modified and accentuated by modern weathering and erosion. The resultant surface is covered with small, shallow potholes or weathering pits, with no direct evidence of dinosaur activity.

Detailed investigation on hydrogeochemistry of hard rock terrains is important to identify the major geochemical processes and the source of ionic constituents in groundwater. The present study is carried out to understand the hydrogeochemistry of groundwater resources and the major hydrogeochemical processes, controlling the concentration of major ions in groundwater in the Kallada River Basin (KRB), South India. About 166 groundwater samples were collected from KRB during pre- and post-monsoon of 2016 for hydrogeochemical analysis. Most of the groundwater samples in KRB were within permissible limits of drinking water quality. The dominant groundwater types during pre-monsoon were Ca2+-Mg2+-Cl− which was changed to Na+-Cl− during post-monsoon. This is supported by the inverse relationship of depth of wells and change in EC during pre- and post-monsoon periods. Rock-water interaction processes such as reverse ion exchange and silicate weathering are major geochemical processes responsible for the hydrogeochemical signatures of KRB. The shallower wells (< 10 m) show strongest relation with the water types Na+-HCO3− and Ca2+-Mg2+-Cl− which have been changed to Na+-Cl− and Ca2+-Mg2+-HCO3− during post-monsoon. However, in deeper wells, Na+-Cl− is the dominant type of water during both seasons. The hierarchical cluster analysis displays different hydrogeochemical associations representing diverse physicochemical parameters both spatially and temporally. This study could shed light on diverse hydrogeochemical processes which are responsible for the hydrogeochemistry in KRB. Major hydrogeochemical processes in the Kallada River Basi

Microbially induced calcite precipitation method is gaining attention as an environmentally friendly method for enhancing the strength and liquefaction resistance of sands as compared to conventional techniques, which are carbon-intensive and cement-based. However, the durability and effect of weathering on liquefaction resistance of biocemented sand are not yet fully explored. Thus, the present study was aimed at investigating the durability of biocemented sand by subjecting the biotreated sand to different weathering conditions, i.e., variable time periods of aging (1.5, 3, 4.5, and 6 months), cyclic freeze–thaw (5, 10, 15, and 20 cycles) actions, and wet–dry (5, 10, 15, and 20) cycles. The biocemented sand biotreated using Bacillus (B.) Sphaericus was tested for ultrasonic pulse velocity (UPV) and unconfined compressive strength to assess durability under different tested conditions. The amount of calcite precipitation was determined, and microstructural changes were also observed through SEM and EDX methods. The liquefaction resistance of biocemented sand was investigated using UPV results and dynamic cyclic simple shear test results. Overall, the results showed up to 2.8 times increase in strength after 6 months of aging, and significant strength with liquefaction resistance was maintained even after 20 freeze–thaw and wetting–drying cycles.

The accumulation of heavy metals in plant communities has been investigated in the maritime Antarctica but their sources are not clearly identified yet. Here we measured Pb isotope ratios in the mosses Sanionia uncinata (Hedw.) Loeske, soils and bedrocks on King George Island, South Shetland Islands, West Antarctica in order to elucidate the sources of Pb in the moss samples. The enrichment factor of Pb indicated that the moss samples near the research station and oil tank are highly enriched in Pb which is attributed to either leaded gasoline and/or Patagonian aeolian dust. However, Pb isotope ratios clearly indicated that leaded gasoline is the main source of Pb in the moss within 1 km from the station and that chemical weathering of soil and bedrock controls Pb content in the moss far from the station (over 1 km from the station). This study clearly demonstrated that Pb in plant communities, especially moss Sanionia uncinata (Hedw.) Loeske, on King George Island is mainly originated from a mixture of leaded gasoline and chemical weathering with a little effect of Patagonian aeolian dust.

Heritage structures are under the effect of chemical, physical and biological weathering, and out of these common effects, chemical weathering has a significant impact (as it results in nifty formation and causes fractures in heritage structures). Chemical weathering may include carbonation, oxidation, hydration, hydrolysis, and acidification. Most heritage structures are made up of limestone, which is more susceptible to carbonation. According to the reported literature, commercial practices for the maintenance and repair of these heritage structures use epoxy-based solutions, which may not be best suited as per the various regulations imposed by different government/public authorities. But so far little has been reported on the use of innovative, programmable thermoplastic composites for the maintenance and repair of such structures. This study highlights the effect of chemical treatment (as a stimulus) using a one-way programming of three-dimensional-printed thermoplastic composite-based (polyvinylidene fluoride–6% limestone) functional prototype as a solution for the maintenance and repair of heritage structures (grade III). For one-way programming, three-dimensional-printed substrate is exposed to dimethylformamide, and the changes in morphological and surface properties are noticed. After this, carbonation cycle (with carbonic acid) is performed and the changes in morphological and surface properties are compared to ascertain the stimulus effect for one-way programming (of polyvinylidene fluoride–6% limestone composite). The results of the study outline that the prepared composite may be programmed by controlling the exposure of dimethylformamide and carbonic acid (as a stimulus). Further best settings for preparing feedstock filament (for three-dimensional printing of functional prototypes in case of a selected heritage structure) are 200 °C screw temperature, 0.35 N m torque and an applied load of 8 kg in terms of better mechanical properties and shore D hardness.

This study was conducted to determine the characteristics of claystone at the Sebamban Syncline by carrying out geology—geomechanics and geochemistry approach. The aim of this is to provide the latest information on characteristics of claystone at the Sebamban Syncline. Results of the study showed that the provenance of Warukin claystone was from recycled orogen. This was corroborated by the geochemical data which stated that the claystone was composed by clay-sized quartz minerals. Clay-sized quartz minerals indicate that there has been a long process of transport and weathering of the quartz minerals that have high resistance, until they become clay-sized. The other geochemical data result is the absence of minerals from volcanic rocks that appear at the beginning of the Bowen series, which have fragile property. Mg is the fragile element that was not found and the mineral is an element binding in montmorillonite, so the presence of the montmorillonite in claystone of the Sebamban Syncline was also not found. Geomechanical data result shows that claystone had strength of around 100 kPa with internal friction angle of about 14° and cohesion of about 29 kPa.

Three broad morphological zones can be differentiated; the top pedological soil (Zone I) being 3.60 m thick and comprising brown, soft to stiff, clays. The intermediate saprock (Zone II) is 1.12 m thick and consists of brown, very stiff, sandy silt with many lateritic concretions, whilst the bottom bedrock (Zone III) is an outcrop of vesicular olivine basalt with weathering along joints. Constant volume samples show the saprolite (sub-zone IC) to have dry unit weights of 11.78 to 12.80 kN/m3, whilst the solum (sub-zones IA and IB), and saprock, have values ranging from 10.65 to 11.09, and from 11.35 to 11.50, kN/m3, respectively. Porosities are variable; the saprolite with the lowest values of 52 to 56% and the solum and saprock with values of 57 to 60%. Clay and silt contents increase up the profile with a corresponding decrease in sand and gravel contents. Colloid (

Background and aims: Metallophytes are plants that can tolerate extreme metal concentrations in the soil in which they grow. The Dugald River zinc (Zn)-lead (Pb) gossan in Queensland (Australia) is one of the largest metal deposits in the world with a surface gossan formed after weathering over millions of years. It hosts a range of metallophytes which may have potential to be used in mine site rehabilitation. This study aimed to investigate the soil-plant relationships of metallophytes on the Dugald River gossan. Methods: Plant samples and associated rooting soil samples were collected across the gossan and then analysed for metal concentrations. Soil-plant metal relationships were subsequently explored to characterise the species in relation to metal uptake behaviour. Results: The metallophyte grass, Eriachne mucronata, dominated the gossan, yet there appeared to be no direct relationship between the occurrence of metallophytes and prevailing soil metal concentrations. Using transformation-based redundancy analysis (tb-RDA), two groups of metals, copper (Cu) and Zn-Cadmium (Cd), have been identified to be the primary metals driving species distribution. Crotalaria novae-hollandiae, was able to accumulate high concentrations of each of these metals in its leaves, with up to 16,200 mg Zn kg−1, 545 mg Cu kg−1 and 170 mg Cd kg−1. Conclusions: Soil metal concentrations alone are not suitable indications for metallophyte distribution or composition in a polymetallic environment. Crotalaria novae-hollandiae can tolerate high concentrations of metals and accumulate Zn-Cu-Cd above the respective hyperaccumulation thresholds; the species can be described for the first time as a strong polymetallic indicator-type metallophyte.

We investigated the photoaging of polypropylene (PP) microplastics (MPs) in lake water. The results showed that photoaging of PP MPs was significantly inhibited in lake water compared with ultrapure water after 12 d of ultraviolet (UV) irradiation, and humic acid and fulvic acid, rather than carbonate (CO32-), nitrate (NO3-), or chloride (Cl-) ions, were identified as the primary contributors to the observed inhibition. Mechanisms for the roles of humic acid (Suwannee River humic acid) and fulvic acid (Pony Lake fulvic acid) in reducing the rates of photodegradation showed that humic acid and fulvic acid acted as both reactive oxygen species (ROS) scavengers (e.g., of •OH) (dominant contribution) and optical light filters. As ROS scavengers, humic acid and fulvic acid significantly decreased the capacity for the formation of •OH and O2•- by PP MPs under irradiation. In addition, the chromophores in humic acid and fulvic acid competed for photons with MPs through the light-shielding effect, thereby causing less fragmentation of PP particles and changes in other properties (melting temperature, contact angle, and surface zeta potential). The proposed mechanisms for inhibition by humic acid and fulvic acid will aid our efforts to assess the duration of aging and alterations of MP properties during long-term weathering in natural waters.

Relatively little is known about the deep water circulation and the role of deep weathering processes on the Critical Zone (CZ) evolution. In this study, major fractures from four deep boreholes and water collected from these fractures (20–60 m of depth) were studied to improve our understanding of the deep CZ in a granitic headwater watershed (Strengbach watershed, France). Geochemical analysis indicates that chemical composition of deep water (20–60 m) is clearly different than shallow subsurface waters (0–15 m), with higher mean concentrations and a stronger spatial variability across the watershed. Reactive-transport modeling performed with the 1D KIRMAT code (KInetic of Reaction and MAss Transport) highlights the role of minor mineral dissolution (i.e. dolomite) and of longer mean transit time (100–597 yr) along fractures for explaining these differences. The obtained results also shed light on the difference of hydrogeochemical functioning between shallow subsurface system (water sampled from springs and piezometers) and deep system (deep water from borehole fractures). The shallow subsurface system (0–15 m) is characterized by a spatially relatively homogeneous water flow, high mean pore velocities, and water–rock interactions in a porous regolith, while the deep water circulation (20–60 m) behaves much more as independent systems along fractures, with low mean pore velocities, and variable mineralogy and hydrodynamic conditions. A state of chemical equilibrium can also be reached along fractures in the deep CZ for some primary minerals (biotite and K-feldspar), a feature never observed so far in the simulations of shallow subsurface water chemical composition in the Strengbach watershed. Even if the deep water exhibits higher solute concentrations, significantly lower mean pore velocities inferred in the fractured zones imply that the deep water is responsible for a very small part of the total hydrologic and weathering fluxes in the watershed. The limited role of the deep weathering processes (20–60 m) compared to the shallow subsurface processes (0–15 m) suggests an up to bottom control of the CZ evolution at a millennial timescale. Our results also indicate that the majority of fresh water available for water supply at a human timescale originates from shallow subsurface waters, as the deep water circulation is too low for being critical at a timescale relevant for societal needs in this type of geological context.

As rock-derived primary minerals weather to form soil, they create reactive, poorly crystalline minerals that bind and store organic carbon. By implication, the abundance of primary minerals in soil might influence the abundance of poorly crystalline minerals, and hence soil organic carbon storage. However, the link between primary mineral weathering, poorly crystalline minerals, and soil carbon has not been fully tested, particularly at large spatial scales. To close this knowledge gap, we designed a model that links primary mineral weathering rates to the geographic distribution of poorly crystalline minerals across the USA, and then used this model to evaluate the effect of rock weathering on soil organic carbon. We found that poorly crystalline minerals are most abundant and most strongly correlated with organic carbon in geographically limited zones that sustain enhanced weathering rates, where humid climate and abundant primary minerals co-occur. This finding confirms that rock weathering alters soil mineralogy to enhance soil organic carbon storage at continental scales, but also indicates that the influence of active weathering on soil carbon storage is limited by low weathering rates across vast areas.

Rubidium is an active element on Earth, but whether and how its isotopes fractionate during geological processes are not known yet. In this study, we present data showing large variations in δ87Rb in bulk samples and individual mineral species from a granite weathering profile in South China as well as in surrounding stream water. The bulk samples show that the mobility of Rb ( τ R b TiO 2 ) fluctuates dramatically from −42.0% to 259%, and δ87Rb values vary from −0.30 ± 0.13‰ in the unaltered bedrock to 0.04 ± 0.08‰ in the weathered saprolites. Significant isotopic variations exist among individual mineral species. In the parent rock, biotite, chlorite, K-feldspar and plagioclase have the δ87Rb values of −0.42‰, −0.30‰, −0.23‰ and +0.01‰, respectively. In weathered products, major Rb-bearing minerals are K-feldspar, illite and kaolinite. The δ87Rb values of K-feldspar range from −0.23‰ to 0.14‰, which are likely influenced by the secondary clay minerals adhered on the surface. Illite is the intermediate secondary mineral during biotite and K-feldspar decomposition into kaolinite. The δ87Rb values of illite vary from −0.28‰ to −0.10‰. As the final product of chemical weathering in this profile, kaolinite has the heaviest isotopic composition, with calculated δ87Rb values ranging from −0.07‰ to 0.20‰. Chemical weathering drives the δ87Rb values of saprolites to become heavier. Nearby stream water has the average δ87Rb value of −0.22‰, which is slightly heavier than the value of parent rock but lighter than the saprolites at the upper part of the profile. Our results demonstrate significant Rb isotope fractionation at the Earth’s surface and that adsorption and desorption of clay minerals play a crucial role in triggering Rb isotope fractionation.

Physical heterogeneity in the subsurface creates preferential flowpaths that have the potential to impact mineral dissolution rates. Previous studies using numerical simulations have found that physical heterogeneity can reduce the mineral dissolution rate by an order of magnitude relative to homogeneous simulations. These findings indicate that the long-studied difference between laboratory dissolution rates, and field dissolution rates could be the result of processes caused by heterogeneity in the subsurface, specifically variable fluid flowpaths controlling the approach to fluid saturation. In this study, we investigate the behavior of mineral dissolution rates in heterogeneous fractured rock domains through time. Domains containing albite and non-reactive quartz evolve through 1 million years as rainwater percolates through the system and allows for albite dissolution and secondary mineral precipitation. Fracture density and orientation vary in the domains to determine the importance of fracture topology on mineral dissolution rates. In addition, the volumetric flow rate through each domain is systematically varied to determine the impact of changing flow conditions relative to reaction rates. Temporal analysis of the simulation results indicates that domain-averaged dissolution rates decrease with time, similarly to what has been observed in field systems and long-term laboratory experiments. Spatial analysis of the mineral dissolution rates throughout the simulations, indicates that fractures remain reaction limited through most of the simulation, while the matrix is transport limited. Since most of the domain consists of matrix, the domain is transport limited as a whole. However, speciation of the flux-weighted fluid leaving the domain indicates that the fluid is undersaturated with respect to albite, potentially leading to an interpretation that dissolution within the domain is not transport limited. The direct comparison of the spatial distribution of rates and the integrated flux signal appears contradictory, however, this approach reveals that the transport-limited signal that persists through most of the domain is diluted by the higher volume of water that leaves the system through fast-flowing fracture pathways compared to the mass of solutes diffusing out of disconnected portions of the domain. This parsing of the domain into transport-limited regions and kinetic-limited regions, induced by physical heterogeneity, has the potential to further explain the differences between laboratory dissolution rates and field dissolution rates. It is possible that mineral weathering is dominated by transport-limited conditions in many field systems with disconnected fluid pathways where reaction rates are slow due to a buildup of solutes, despite integrated signals in streams indicating far-from equilibrium conditions for dissolution reactions of primary minerals.