Bedrock Weathering Research Articles

Anatomy of a deep Piedmont critical zone: Evaluating hypotheses on regolith depth controls through comparison of ridge and valley boreholes

AbstractControls on the physical and chemical architecture of the subsurface critical zone are somewhat controversial, with multiple hypotheses proposed to account for variations in the depth of weathering between sites, and with landscape position at a site. In the Piedmont region of the Mid‐Atlantic US weathering of crystalline bedrock has been observed to extend tens of meters below the surface and groundwater in a'bow‐tie’ shape – i.e. weathering extends to lower elevations below ridges than below channels. The chemical and physical structure of a hillslope transect in the Maryland Piedmont was explored with a 45 m borehole in the ridge, as well as shallow bedrock boreholes at the toe of the slope and valley. Chemical weathering fronts were characterized using elemental abundances and mineralogical analysis. The ridge borehole did not extend deeper than the chemically and physically weathered rock. Surface and borehole geophysics and density measurements were used to characterize the weathered rock and saprolite. Na and Ca results suggest that plagioclase feldspar weathering is similar between samples collected from 45 m under the ridge and 2.2 m under the valley bottom. A narrow Fe oxidation garnet weathering front co‐insides with the transition from weathered bedrock to saprolite, suggesting that this reaction may generate initial saprolite porosity. Muscovite weathering co‐occurs with complete depletion of plagioclase a few meters above the Fe oxidation front. These nested weathering fronts in the saprolite appear to follow a subdued version of the surface topography. The location and shape of the nested saprolite weathering fronts may be controlled by the feedback between the transport of reactants and solutes and reaction‐generated porosity, consistent with the conceptual “valve” hypothesis. Differing dominant control mechanisms on deep bedrock weathering and saprolite initiating reactions may explain the thickness and structure of the critical zone at our site.

Hematite U-Pb dating of Snowball Earth meltwater events

The Snowball Earth hypothesis predicts global ice cover; however, previous descriptions of Cryogenian (720-635 Ma) glacial deposits are limited to continental margins and shallow marine basins. The Tavakaiv (Tava) sandstone injectites and ridges in Colorado, USA, preserve a rare terrestrial record of Cryogenian low-latitude glaciation. Injectites, ridges, and chemically weathered crystalline rock display features characteristic of fluidization and pervasive deformation in a subglacial environment due to glacial loading, fluid overpressure, and repeated sand injection during meltwater events. In situ hematite U-Pb geochronology on hematite-quartz veins, which crosscut and are cut by Tava dikes, constrain sand injection at ~690-660 Ma. We attribute early Tava sand injection episodes to basal melting associated with rifting and geothermal heating, and later injections to meltwater generation during ~661 Ma Sturtian deglaciation. A modern analog is provided by the Ross Embayment of Antarctica, where rift-related faults border sediment-filled basins, overpressurized fluids circulate in confined aquifers below ice, and extensive preglacial topography is preserved. Field evidence and geochronology in Colorado further highlight that deep chemical weathering of Proterozoic bedrock and denudation associated with the Great Unconformity predate Cryogenian injection of fluidized sand, consistent with limited glacial erosion.

Scanning Electron Microscopy and Magnetic Characterization of Iron Oxides in Suspended Sediments

<p class="Abstract"><span lang="EN-US">River sediment is the product of a sedimentation process in the river environment that originates from the weathering of bedrock or erosion processes, organic materials, particles, or anthropogenic substances. Previous research shows the magnetic mineral content in the sediments of the Citarum River and its tributaries. Suspended sediment was collected from the Citarum River and its tributaries in West Java, Indonesia, for mineralogical and granulometric analysis. The aim of this research is to distinguish between magnetic mineral sources, a scanning electron microscope equipped with energy dispersive X-ray spectroscopy (SEM-EDX), and rock magnetism. The hysteresis parameter verifies that the XRD measurement results show that the main magnetic minerals in suspended sediments are ferrimagnetic minerals such as magnetite (Fe<sub>3</sub>O<sub>4</sub>). According to the results of the SEM-EDX investigations, the magnetic granules in the Citarum River and its tributaries derive from two distinct sources: pedogenic and anthropogenic. The Citarum River and its tributaries’ magnetic granules are generally octahedral or angular in shape, with broken corners, indicating a pedogenic origin</span></p>

Mechanisms of secondary carbonate precipitation on felsic, intermediate and mafic igneous rocks: a case study for NW Scotland

Silicate weathering is a natural regulator of atmospheric carbon dioxide (CO 2 ), where the majority of carbonate is stored in the oceans. In some instances, carbonates may form via bedrock weathering in terrestrial landscapes, but this is commonly noted in ultramafic rock owing to its desirable mineralogy. In NW Scotland, carbonate minerals surround felsic, intermediate and mafic igneous bedrock. Their abundance suggests that these rocks could potentially be targeted for carbonation, given the absence of other known cation sources nearby. We present geochemical and mineralogical data for bedrock samples and mineralogy and stable carbon and oxygen isotope data for the carbonate samples. Whole-rock geochemistry demonstrates that major abundances of CaO and MgO are present in the bedrock samples and would be sourced from plagioclase and pyroxene, which are target minerals for CO 2 mineralization. The stable carbon and oxygen isotope data demonstrate that there are probably mixed carbon sources (atmospheric and organic), and other environmental factors including temperature, CO 2 degassing or evaporation and nearby waters influence the isotopic composition. Results suggest that rocks traditionally overlooked in CO 2 mineralization studies have the potential to serve as a feedstock for carbonation, given the abundance of secondary carbonates found in NW Scotland.

Characteristics of Effective Fractures in Deep Buried-Hill Basement Gas Reservoirs and Its Effects on Fluids: The Jianbei Slope, Qaidam Basin, China

Summary Buried hills are basement uplifts beneath sediment layers that possess significant exploration potential. Using the Jianbei Slope of the Qaidam Basin in China as a case study, we systematically investigated the types and origins of fractures in deep buried-hill gas reservoirs. In our study, we synthesized various data, including experimental results, production dynamics, and both conventional and special logging with the aim of clarifying the sequence and effectiveness of fracture formation in these gas reservoirs; analyzing the impact of effective fractures on fluid migration, accumulation, and preservation; and proposing a development plan to enhance stable production. Research reveals that since the Late Paleozoic, the region has been influenced by multiple phases of tectonic stress, deep fluid dissolution, and surface weathering leaching. This has resulted in a fracture system dominated by east-west trending deep major faults, with accompanying tectonic fractures, alongside dissolution, diagenetic, and weathering-collapse fractures. Smaller fractures oriented at an angle to the maximum principal stress and fractures with normal stress lower than the compressive strength are conducive to maintaining fracture effectiveness. Fracture widths range from 0.1 μm to 343.36 μm, with effective fractures comprising 63.49% of the total. Based on aperture and permeability, effective fractures are categorized into three levels: Level I fractures (>100 μm) serve as primary migration pathways; Level II fractures (10–100 μm) are well configured with dissolution pores, forming a foundation for favorable reservoir development; and Level III fractures (micron scale) enhance reservoir storage capacity by connecting fractures. The gas-water interface in the reservoir rises rapidly and unevenly. In the I + II + III fracture combination model, fluid exhibits high-conductivity channeling, leading to rapid declines in formation pressure, quick water breakthroughs in single wells, and severe water sealing. Conversely, in the II + III fracture combination model, fluid invasion is characterized by weak-to-strong finger-like intrusion, leading to prolonged stable production. Vertically, the 20-m to 60-m interval above the bedrock weathering crust has a favorable pore-fracture configuration, making it a high-quality reservoir zone in buried hills. In addition, local thick layers of Level II microfractures within the bedrock represent potential exploration targets. Considering the differential distribution of reservoir fractures, the optimal development plan is expected to achieve a recovery rate of 28.35% by 2030.

Controls on the stable Mo isotopic composition of inner-continental precipitation

The molybdenum (Mo) isotope budget of the surface environment has been well characterized in recent decades, facilitating accurate mass balance modeling of the ancient redox-driven Mo cycle. One yet unresolved component is the range of possible processes and sources that result in isotopically heavy river waters relative to continental sources. Following a recent hypothesis that isotopically heavy δ98Mo of precipitation may control the final δ98Mo of river water relative to its continental source bedrock, we investigated the δ98Mo composition of 19 snow samples from three locations in Central Europe: the Swiss Alps (“Alpine” samples) from the Hochalpine Forschungsstation Jungfraujoch (HFSJ) in both summer and winter, the Swiss Jura Mountains in winter and the French Vosges Mountains in winter. Stream waters from two snowmelt-fed streams were additionally collected from the Alpine site. Snow sample δ98Mo compositions were highly variable, ranging from −0.03 to +1.93 ‰, with no clear mixing trends indicating complex sources, source pathways, or post-depositional processing. Only the winter snow samples from the high-altitude HFSJ site had δ98Mo values consistently heavier than typical continental crust. The δ98Mo results were coupled with radiogenic Sr isotopic, major ion, and trace element compositions as tracers for three major sources of airborne ion inputs: sea salt, mineral dust, and anthropogenic aerosols. We found that the most likely source of Mo to precipitation in the lower elevation Vosges and Jura Mountains samples was isotopically light soil mineral dust, which reflected the underlying bedrock sources, with a likely additional anthropogenic component. The isotopically heavy winter snow samples at the elevated HFSJ site were attributed to a higher input of carbonate mineral dust from long-distance transport of carbonate-rich Saharan dust, which was overwritten in the summer by an influx of low elevation sources transported upwards during higher vertical thermal mixing. Finally, we concluded that precipitation has a negligible direct effect on the overall Mo content and isotopic composition of inner continental European streams and rivers relative to other sources, such as bedrock weathering. Future time-series studies may augment these conclusions to show possible heterogeneity of precipitation as well as the addition of sample sites closer to marine sources, where a larger flux of isotopically heavy marine aerosols to streams might be expected.

Heavy metal's pollution health risk assessment and source appraisal of groundwater and surface water in Irob catchment, Tigray, Northern Ethiopia

Contamination of water resources by heavy metals causes health problems for humans. This study attempts to investigate the heavy metal contamination levels, health risks and sources of appraisal of groundwater and surface water in the mountain-bounded catchment and low-grade basement rock-dominated area of ​​the Irob, Tigray. Eighteen grab water samples (13 borehole water, 2 spring water and 3 surface water) were collected and analyzed for pH, electrical conductivity, total dissolved solids and heavy metals using standard procedures. The findings were contrasted with those of the standards set by the World Health Organization and the United States Environmental Protection Agency. Integrated techniques, including indexed and statistical methods, were used to determine the contamination levels of metals, risks to human health and sources. The result shows that the pH value, electrical conductivity and total dissolved solids fluctuated between 7.4 and 7.9, 516 and 2410 µs/cm and 396.7 mg/l and 1719 mg/l, respectively. The findings indicate that 94.4% of the water samples had levels of contamination above the critical limit for all three indices: the heavy metal evaluation index (HEI), the degree of contamination (cd) and the heavy metal pollution index. The hazard index of metals for adults and children was greater than 1. 88.9% of the water samples showed a cancer risk value above the recommended value (CR > 1 × 10–4) for Cd and Cr for both adults and children. Multivariate statistical analyses indicate that weathering of bedrocks and partly anthropogenic influences are responsible for the metal contamination. The study concludes that some water samples sources are unfit for human consumption that can pose health risks over time. Therefore, it is recommended to treat contaminated water sources to protect and sustain public health.

Risk assessment and source analysis of trace elements in soils around county landfills in Tibet.

The ecology of the Qinghai‒Tibet Plateau is fragile, and the ecosystems in the region are difficult to remediate once damaged. Currently, landfilling is the mainstay of domestic waste disposal in China, and numerous, widely distributed county landfills exist. trace elements (TEs) in waste are gradually released with waste degradation and cannot be degraded in nature, affecting environmental quality and human health. To reduce the chance bias that exists in studies of individual landfills, we selected 11 representative county landfills in Tibet, total of 76 soil samples were collected, eight TEs (arsenic (As), mercury (Hg), chromium (Cr), copper (Cu), lead (Pb), cadmium (Cd), nickel (Ni), and zinc (Zn)) were determined, and analysed for the current status of pollution, risk to human health, and sources of TEs to explore the impact of the landfills. The results showed that only a few landfills had individual TEs exceeding the risk screening value of the Soil Environmental Quality Risk Control Standard for Soil Contamination (GB 15618-2018) (pH > 7.5). Most of the soils around the landfills had moderate levels of pollution, but some individual landfills had higher levels, mainly due to Cd and Hg concentrations. Source analysis showed that Hg originated mainly from atmospheric transport; the other TEs came mainly from the weathering of soil parent material and bedrock. The potential risk from TEs to human health was low, and the risk to children was greater than the risk to adults. Among the three exposure routes, oral ingestion resulted in the highest carcinogenic risk and noncarcinogenic risk, with a contribution rate of more than 95%. Among the TEs, Ni had the highest carcinogenic risk, followed by Cr and As, and As had the highest noncarcinogenic risk.

Factors influencing seasonal chemistry patterns in Virginia mountain streams

The relative influence of seasonal patterns in hydrological flow and seasonal differences in biological and geochemical activity on stream chemistry patterns is difficult to discern because they covary; temperate systems are characterized by lower mean flow in the summer (i.e. corresponding to deeper flow paths, elevated temperature, and biological activity), and higher mean flow in the winter (i.e. corresponding to shallower flow paths, depressed temperature, and biological dormancy). Using 2018 data, when seasonal stream flow conditions reversed, and two prior conventional water years, the relationship between monthly acid-relevant analyte concentrations and streamflow were compared within and between winter and summer to provide insight into controls on characteristic seasonal chemistry patterns at two mid-Appalachian sites with distinct geology (weatherable mafic and weather resistant siliciclastic). Acid neutralizing capacity (ANC) increased (1) with lower flow, in both seasons and (2) in summer, for all flow conditions. The compounding impacts resulted in a doubling of concentration from typical winter with high flow to summer with low flow at both sites. Base cation patterns tracked ANC at the mafic site, resulting in an ~ 60% increase of from winter with high flow to summer with low flow; distinctions between summer and winter contributed more to the seasonal pattern (72%) than changes in flow. Sulfate increased at the mafic site (1) with higher flow, in both seasons and (2) in winter, for all flow conditions, resulting in an ~ 50% increase from summer with low flow to winter with high flow; distinctions between winter and summer conditions and flow contributed similarly (40–60%) to the typical seasonal chemical pattern. The biogeochemical mechanism driving differences in stream chemistry between summer and winter for the same flow conditions is likely increased rates of natural acidification from elevated soil respiration in summer, resulting in greater bedrock weathering and sulfate adsorption. Findings highlight the significance and consistency of growing vs dormant season variations in temperature and biological activity in driving intra-annual patterns of stream solutes. This data set informs parameterization of hydro-biogeochemical models of stream chemistry in a changing climate at a biologically relevant, seasonal, timescale.

Potentially toxic elements of lake and wetland in Northeastern Qinghai-Tibet Plateau: Distribution, potential sources and risk assessment

The accumulation of toxic elements from sediments poses imminent threats to both the environment and humans. The variation of elements in different sedimentary systems within the same watershed is of significant importance for distinguishing the human activities and adopting relevant management strategies. Based on the surface sediment samples from the Lake Keluke and its wetland, the content and grain size of elements were analyzed. The human health risk indicated in the area the potentially toxic elements (PTEs: Cr, Cu, Zn, Cd and Pb) were at no non-carcinogenic risk to adults or children. Except for Cd, the pollution levels of other PTEs were clean, and potential ecological risk with a low level. However, the pollution of Cd implicated a moderate to heavy pollution intensity and a high ecological risk. According to principal component analysis (PCA), and self-organizing maps (SOM), the main sources of PTEs were of the weathering and leaching of bedrocks; transportation and human agriculture activities. The watershed should reduce pollution caused by human activities and implement efficient agricultural practices.

How Was the Late Neogene Red Clay Formed in the Ordos Plateau (Northwest China)?

Eolian sediments are extensively distributed across the Earth’s surface, and their formation is intricately linked to climate change, tectonic activity, and topographic features. Consequently, the investigation of eolian sediments bears great geological significance. The northwest region of China is renowned for hosting the most extensive and thickest Late Miocene–Pliocene red clay deposits globally. Nonetheless, scholars have yet to reach a consensus regarding the precise formation processes of these red clays. The identification of the source region of the red clays is crucial for comprehending their formation mechanism. The correlation of zircon U-Pb age spectra is a frequently utilized method for determining the provenance of eolian sediments. In this study, we compared the previously published zircon U-Pb ages (n = 12,918) of the Late Miocene–Pliocene red clays in the Ordos Plateau with those from the potential provenance regions (n = 24,280). The analysis, supported by the tectonic and climatic background of the region, revealed that the Late Miocene–Pliocene red clay in the Ordos Plateau originates predominantly from the Yellow and Wei rivers, with a minor contribution from the weathering of bedrock in the western North China Craton. The transport of these detrital materials by the East Asian winter monsoon is impeded by the presence of the Qinling and Taihang Shan, resulting in their deposition on the flat surface of the Ordos Plateau. This development of red clay is consistent with the proximal accumulation model, illustrating how the hydrosphere, atmosphere, and lithosphere interacted to shape the red clay deposits during the Late Miocene and Pliocene periods in the Ordos Plateau.

Low Mo mobility during the laterization of ultramafic bedrock: Evidence from the East Sulawesi Ophiolite, Indonesia

Mo (isotope) cycling during the chemical weathering of ultramafic bedrock remains poorly quantified, mainly as a result of the analytical challenges caused by low Mo concentration and complex matrix effects in these rock types. Here, we utilize an improved chemical separation protocol that enables the extraction of Mo while reducing Ru and Fe matrix effects. We apply this method to lateritic weathering profiles developed over ultramafic bedrock in a high-intensity tropical weathering regime. The Mo concentrations in the laterite samples are higher (0.022 to 0.58 μg·g−1) than those of the peridotite bedrock (0.006 to 0.021 μg·g−1). The concentration-weighted average δ98Mo of the laterite profiles is −0.05‰ (n = 17), which is slightly higher but very close to the average δ98Mo of the peridotite bedrock (0.17 ± 0.21‰; 2SD; n = 5). Weakly-laterized samples show somewhat low δ98Mo with a minimum of −1.03‰ and Δ98Molaterite-bedrock up to −0.86‰, possibly as a result of preferential adsorption of liberated light Mo onto Fe (oxyhydr)oxides. In contrast, strongly-laterized samples show an overall Mo concentration gain and a slight isotopic shift towards higher bulk δ98Mo, with a maximum δ98Mo of +0.12‰ and Δ98Molaterite-bedrock up to +0.42‰. This likely reflects the re-scavenging of Mo released from weakly-laterized horizons to the ubiquitous Fe (oxyhydr)oxides, with potential superimposition of additional heavy Mo from atmospheric and/or groundwater input. Overall, this suggests a small contribution of dissolved Mo derived from ultramafic bedrock weathering in tropical settings to the aquatic environment.

Investigation of Tunnel Collapse Mechanisms through Numerical Analysis

In this study, tunnel excavations were introduced in two typical ground conditions found in unstable urban areas, and the corresponding tunnel collapse mechanisms were investigated using numerical analysis. The case studies of tunnel collapse in weathered rock and uncemented sandy soil layers revealed that a plastic area extended across the entire tunnel section from the tunnel shoulder to the ground surface. The development of the displacement vector indicated the possibility of a tunnel ceiling depression occurring around the plastic area. The numerical analysis results suggest that tunnel excavation, which accelerates bedrock weathering or induces ground relaxation following groundwater introduction, can lead to the collapse of uncemented sandy soils.

Investigation of radiogeology and environmental geochemistry of quarry ponds in post-tin mining areas of Phuket Island, southern Thailand

Increasing demand for water supply on Phuket Island for both the local consumption and hotel industry has led to overexploitation of ground- and surface water bodies; hence, it is unremittingly important to monitor the local hydrologic regime. Radiogeological and hydrogeochemical environments are investigated by representative water and surface sediment samples collected from the different quarry ponds located in post-tin mining areas on Phuket Island. The study assessed water quality, analyze the relationship between bedrock weathering and water quality, and identify radiogeological factors and natural radon concentrations, with insights into the local geology of the study areas. The representative quarry ponds of Phuket Island consist of a granite quarry pond (PKW1), a Quaternary sediment quarry pond (PKW2), a granitic-metamorphic quarry pond (PKW3), and the perturbation pond (PKW4), with the formation of a variety of geologic features. All collected water samples show total cation concentrations with Ca2+ > Na+ > K+ > Mg2+ and total anion concentrations with HCO3− > Cl− > NO3− > SO42−. However, Gibbs diagrams suggest that rock–water interactions and precipitation are major factors in geochemical processes controlling the water quality. Radon enrichments in the water samples are involved in the local geological structures and hydrogeological environments, as follows: PKW1 > PKW3 > PKW2 > PKW4. No significant correlation between the radon activity concentrations and major/minor ions is shown. Surface sediment samples are reported, and the activity concentrations of radium-228 and thorium-228 (radioactive decay series of thorium-232) are relatively higher than those of radium-226 (radioactive decay series of uranium-238). Therefore, the activity concentrations of natural radionuclides in the surface sediments could be directly influenced by physical weathering, particularly the depositional environments of granitic bedrock around the quarry ponds. Long-term monitoring is necessary to consider the behavior of quarry ponds, which is related to tourism planning and the overall development of Phuket Island.

Risk assessment and strontium isotopic tracing of potentially toxic metals in creek sediments around a uranium mine, China

The contamination of creek sediments near industrially nuclear dominated site presents significant environmental challenges, particularly in identifying and quantifying potentially toxic metal (loid)s (PTMs). This study aims to measure the extent of contamination and apportion related sources for nine PTMs in alpine creek sediments near a typical uranium tailing dam from China, including strontium (Sr), rubidium (Rb), manganese (Mn), lithium (Li), nickel (Ni), copper (Cu), vanadium (V), cadmium (Cd), zinc (Zn), using multivariate statistical approach and Sr isotopic compositions. The results show varying degrees of contamination in the sediments for some PTMs, i.e., Sr (16.1–39.6 mg/kg), Rb (171–675 mg/kg), Mn (224–2520 mg/kg), Li (11.6–78.8 mg/kg), Cd (0.31–1.38 mg/kg), and Zn (37.1–176 mg/kg). Multivariate statistical analyses indicate that Sr, Rb, Li, and Mn originated from the uranium tailing dam, while Cd and Zn were associated with abandoned agricultural activities, and Ni, Cu, and V were primarily linked to natural bedrock weathering. The Sr isotope fingerprint technique further suggests that 48.22–73.84% of Sr and associated PTMs in the sediments potentially derived from the uranium tailing dam. The combined use of multivariate statistical analysis and Sr isotopic fingerprint technique in alpine creek sediments enables more reliable insights into PTMs-induced pollution scenarios. The findings also offer unique perspectives for understanding and managing aqueous environments impacted by nuclear activities.

Assessment of Elemental Contamination of Selected Major Dams from Osun State, Nigeria by Multivariate and Hazard Index Analyses

Dams and their environment, interrelate with a degree of complexity that often affects the availability of potable water. In Nigeria, dams are an important source of drinking water in many communities but are vulnerable to contamination from different sources. This study assessed the possible elemental (Cd, Cr, Cu, Fe, Ni, Pb, Mn, and Zn) contamination sources of selected dams in a total of 126 samples comprising 54 surface water, and 72 sediment samples collected from six main dams in Osun State using multivariate analyses like Principal Component Analysis (PCA) and Cluster Analysis (CA). Generally, the average elemental concentration was in the decreasing order of Cr > Ni > Cd > Pb > Cu > Fe > Zn > Mn and Pb > Cr > Ni > Cd > Zn > Mn > Fe > Cu for surface water and sediment samples respectively. Furthermore, statistical analysis showed that the average concentrations of the potentially toxic elements (PTEs) did not differ significantly (p < 0.05) across the sampling sites, indicating similar PTEs profiles. The PCA and CA revealed possible sources of elemental contamination to the dam quality as weathering of bedrocks, uncontrolled farming activities, abandoned equipment, boat fueling, maintenance, and repairs. Although only 13.9% of the hazard quotients (HQ) were higher than one for all the studied heavy metals in surface water, 91.7% of the hazard index (HI) were higher than one. This suggests an unacceptable risk of non-carcinogenic effects from the direct consumption of dam water. Furthermore, the oral target cancer risk, TCRoral in children > adults and > 1 × 10−4 for cancer risk set by USEPA, however, the % contribution of Cr to ∑TCRoral in adults which is > 1 × 10−4 ranged between 98.9 to 99.5%, indicating that Cr is the most dominant carcinogens in the overall cancer risk in adults.

Perspectives from modern hydrology and hydrochemistry on a lacustrine biodiversity hotspot: Ancient Lake Poso, Central Sulawesi, Indonesia

The highly biodiverse Lake Poso, located in Central Sulawesi, Indonesia, can be considered one of the least studied ancient lakes in the world. Here, we present a comprehensive analysis of Lake Poso's hydrology and hydrochemistry, shedding light on factors that may have contributed to the exceptional biodiversity. Riverine and lake water chemical compositions indicated a soft water lake and relative major cation and anion abundances of Ca2+ ≫ Mg2+ > Na+ > K+ and HCO3– ≫ SO42− > Cl−, primarily a result of the high annual precipitation and chemical weathering of calcareous-siliceous metamorphic bedrock. Lake Poso’s nutrient concentrations were low (average DIN/TDP mass ratio of 6.2 and 50.9 for the lake surface water and its tributaries, respectively), indicating that most of the inlets were P-limited and that the lake was likely P-limited as well. Metal pollutants indicated a minor to moderate impact of anthropogenic land use (∼32 % of the catchment area). Water isotopic compositions of the different tributaries clearly delineated rivers draining higher elevation catchments with lower δ2H and δ18O from those draining lower elevation catchments with higher δ2H and δ18O. Surface lake water isotopic compositions indicated detectable evaporation from the lake leading toward more enriched isotope compositions than the integrated source signal. Overall, the findings suggested that Lake Poso remains relatively resilient to anthropogenic land use and related nutrient and pollutant inputs. However, ongoing alterations to its hydrological balance due to significant changes in land use may drive the lake towards higher trophic levels in the future.

Soil phosphorus fractions dynamics along a 22-ka chronosequence of landslides, western Sichuan, China

Landslides significant influence on bedrock weathering, pedogenesis, and ecological succession, thereby playing a pivotal role in driving biogeochemical cycles. Landslide chronosequences have traditionally served as invaluable study systems for investigating vegetation succession and exploring soil development and nutrient dynamics. In this study, we analyzed soil phosphorus fractions across a 22,000-year landslide chronosequence. Our investigation examined the impact of environmental factors on these fractions and elucidated the supply of bioavailable phosphorus. Our findings revealed a decline in the concentration of all phosphorus fractions with soil age. Notably, even at an age exceeding 22,000 years, primary mineral phosphorus constituted 23 % of the total phosphorus pool at the later stages of soil development, while organic phosphorus accounted for a mere 7 %. This discrepancy can be attributed to frequent landslides replenishing phosphorus stocks. These findings indicate that the Walker and Syers model may not adequately anticipate alterations in soil phosphorus fractions under geologically unstable landscapes. Environmental factors had limited impact on primary mineral phosphorus concentrations. Yet, they significantly influenced occluded and nonoccluded phosphorus. Changes in organic phosphorus concentrations cannot be fully explained by the examined environmental factors, as organic phosphorus in the soil primarily originates from plant litter decomposition. The sources of bioavailable phosphorus in the investigated region were elucidated using structural equation modeling. The bioavailable phosphorus in the study area is mainly derived from nonoccluded phosphorus rather than organic phosphorus. This observation can be attributed to the distinct landform conditions, which sustain elevated levels of primary mineral phosphorus during soil development. Consequently, the continuous availability of nonoccluded phosphorus ensures a reliable supply of bioavailable phosphorus. In conclusion, the landslide chronosequence serves as a vital example of long-term ecosystem development under unstable landforms. Its refinement of the Walker and Syers model under unstable landscapes.

Significant floral changes across the Permian-Triassic and Triassic-Jurassic transitions induced by widespread wildfires

Wildfires are a major source of perturbations to the Earth’s system and have important implications for understanding long-term interactions between the global environment, climate, and organisms. In this study, current evidence for global warming, wildfires, and floral changes across the Permian-Triassic (P-T) and Triassic-Jurassic (T-J) transitions were reviewed, and their relationships were discussed. Available evidence suggests that global plant community turnover and the decline in plant diversity across the P-T and T-J boundaries were primarily driven by widespread wildfires. The Siberian Large Igneous Province and Central Atlantic Magmatic Province released large amounts of isotopically light CO2 into the atmospheric system, contributing to global warming and increased lightning activity. This ultimately led to an increase in the frequency and destructiveness of wildfires, which have significantly contributed to the deterioration of terrestrial ecosystems, the turnover of plant communities, and the decline in plant diversity. Furthermore, frequent wildfires also constitute an important link between land and ocean/lake crises. Large amounts of organic matter particles and nutrients from the weathering of bedrock after wildfires are transported to marine/lake systems through runoff, contributing to the eutrophication of surface water and the disappearance of aerobic organisms, as well as hindering the recovery of aquatic ecosystems. These wildfire feedback mechanisms provide an important reference point for environmental and climatic changes in the context of current global warming. Therefore, the interplay between global warming, wildfires, and biological changes and their feedback mechanisms needs to be fully considered when assessing current and future risks to the Earth’s surface systems.

Tracing the source and transport of Hg during pedogenesis in strongly weathered tropical soil using Hg isotopes

Soil is one of the largest reservoirs and re-emission sources of mercury (Hg) on Earth’s surface. The accumulation and remobilization of Hg during pedogenesis affect how Hg is transported from terrestrial to aquatic environment and biota, but these processes are poorly understood. Here we present Hg concentration and isotope ratios of soil and bedrock samples from a latosol profile formed through intense weathering of Cenozoic basalts in Zhanjiang, Guangdong Province, China, to trace the sources, transport and transformation processes of Hg during pedogenesis, and to gain insights on the potential impact of tropical soils on global Hg cycling. The entire soil profile shows negative δ202Hg (−2.97‰ ± 0.08‰ to −2.54‰ ± 0.08‰) and negative Δ199Hg (−0.68‰ ± 0.04‰ to −0.43‰ ± 0.04‰), with a gradual downward positive shift of Δ199Hg below 35 cm. An isotopic mixing model based on Δ199Hg suggests a dominant Hg input from atmospheric Hg (HgAtm) and limited contribution (<36%) of geogenic Hg (HgGeo) from the bedrock. The strongly negative Δ199Hg throughout the latosol profile suggests that HgAtm was likely subject to substantial photoreduction on soil surface and migrated downward after incorporation into soils. Moreover, there is a distinct positive shift of δ202Hg alongside a rapid decrease of HgGeo from the bedrock to the weakly weathered basalt, indicating a substantial loss of HgGeo with the preferential release of lighter isotopes during the initial weathering, likely due to the dissolution of primary minerals. In addition, the δ202Hg shows a negative correlation with soil pH at some horizons, attributable to the isotopic fractionation during Hg(II) speciation change in soil solution and the selective complexation/adsorption of different Hg(II) species onto mineral surfaces, which are affected by surface charge properties and thus soil pH. Overall, our results provide direct evidence for the accumulation and downward migration of HgAtm in tropical soils during pedogenesis, as well as the loss of HgGeo during the weathering of bedrock, which may serve as an underappreciated source of Hg in tropical regions and have a potential impact on the Hg isotope signatures in aquatic environments.