Water-Mediated Conversion of BaTiO3 Nanoparticles into BaCO3 Nanorods in Electrospun Polymer Fibers: Implications for Carbon Capture Applications

Under ambient conditions and in aqueous environments, transformations of nanoparticle-based ferroelectric components can raise important stability issues that are relevant for applications as multilayer capacitors, flexible piezoelectrics, or biomedical devices. We show that X-ray amorphous BaTiO3 nanoparticles that were grown by flame spray pyrolysis and which can be incorporated into electrospun polymer fibers undergo incongruent Ba2+ dissolution in the presence of water. At pH > 5 and in contact with air, corresponding Ba solutes spontaneously convert into crystalline BaCO3 needles to produce characteristic nano- and microstructures. We compared the reactivity of amorphous BaTiO3 nanoparticle powders with those of nanocrystals after annealing-induced crystallization. The stability of aqueous nanoparticle-polymer formulations, which are typically part of nanoparticle encapsulation in polymers and electrospinning, was included in this analysis. Nanoparticle size, crystallinity, surface area, the presence of carbonaceous surface contaminants, and the effect of surface passivation with polymers are addressed to underline the critical role of condensed water during the synthesis, storage, and processing of BaTiO3 nanoparticle-based composites.

[Hydrochemical Characteristics and Control Factors of Pore-water in the Middle and Upper Reaches of Muwen River]

In order to study the hydrochemical characteristics and ion sources of pore water in the middle and upper reaches of the Mouwen River, 29 groups of pore-water samples were collected in the Laiwu Basin. The main ion characteristics and their controlling factors of pore-water in this area were analyzed by using correlation and principal component analysis, Piper trigram, and Gibbs diagram methods. The main material sources of pore water in this area were revealed. The results showed that HCO₃^-, NO₃^-, SO₄^2-, and Ca²⁺ were the main anions and cations in the pore water of the middle and upper reaches of the Mouwen River. With TDS >1000 mg·L^-1 as the standard, the normal water chemistry type was mainly HCO₃·NO₃·SO₄-Ca and HCO₃·SO₄-Ca·Mg, whereas the abnormal water chemistry type was mainly NO₃·Cl-Ca. The chemical evolution of groundwater was mainly influenced by rock weathering, cation alternation adsorption, and human activities. Na⁺+K⁺ mainly came from silicate weathering and dissolution, and HCO₃^-, Ca²⁺, and Mg²⁺ came from calcite weathering and dissolution involving carbonate and sulfuric acid. Alternation adsorption of cations and weathering of silicate rock provided a surplus of Ca²⁺ and Mg²⁺ for pore water. Industrial and mining activities such as domestic sewage mixing, agricultural planting activities, and iron and coal mining changed the chemical composition of pore water, especially NO₃^- exceeding the standard, which has become the main problem of the local groundwater chemical environment.

Chemical Weathering and CO2 Consumption Inferred from Riverine Water Chemistry in the Xi River Drainage, South China

Hydrochemistry and strontium isotope data were analysed in water samples from the Xi River Drainage system to reveal the spatial and seasonal variations in chemical weathering, associated CO2 consumption fluxes, and their control factors. The main ions were Ca2+, Mg2+, and HCO3-, which are characteristic of a drainage system on carbonate-dominated bedrock. The dissolved loads were derived from four major end-member reservoirs: silicate, limestone, dolomite, and atmosphere. The silicate weathering rates (SWRs) increased downstream from 0.03 t/km2/year to 2.37 t/km2/year. The carbonate weathering rates (CWRs) increased from 2.14 t/km2/year in the upper reaches, to 32.65 t/km2/year in the middle reaches, and then decreased to 23.20 t/km2/year in the lower reaches. The SWR values were 281.38 and 113.65 kg/km2/month during the high- and low-water periods, respectively. The CWR values were 2456.72 and 1409.32 kg/km2/month, respectively. The limestone weathering rates were 2042.74 and 1222.38 kg/km2/month, respectively. The dolomite weathering rates were 413.98 and 186.94 kg/km2/month, respectively. Spatial and seasonal variations in chemical weathering were controlled mainly by lithology, vegetation, and climate (temperature, water discharge, and precipitation). The CO2 consumption flux by chemical weathering was estimated at 189.79 × 109 mol/year, with 156.37 × 109 and 33.42 × 109 mol/year for carbonate and silicate weathering, respectively. The CO2 fluxes by chemical weathering are substantially influenced by sulfuric acid in the system. The CO2 flux produced by sulfuric acid weathering was estimated at 30.00 × 109 mol/year in the basin. Therefore, the Xi River Basin is a CO2 sink with a net consumption of CO2 flux of 3.42 × 109 mol/year.

[Hydrochemical Composition Characteristics and Control Factors of Xiaohuangni River Basin in the Upper Pearl River]

In order to serve the water resources management of the Xiaohuangni River basin, this study explored the hydrochemical composition characteristics and ion sources of surface water in the basin. Samples of main stream and tributary river water and mine water were systematically collected. By means of a Piper diagram, Gibbs diagram, ion ratio coefficient, and mathematical statistical analysis, we analyzed the hydrochemical composition, spatial distribution characteristics, and main control factors of the Xiaohuangni River and evaluated the solute contribution rates of different sources. The results showed that the pH of the Xiaohuangni River basin ranged between 7.17 to 9.14, with an average of 8.00, which is generally considered weakly alkaline. Additionally, the total dissolved solids ranged between 154 mg·L^-1 to 460 mg·L^-1, with an average of 257.39 mg·L^-1, which was equivalent to that of the main stream of the Xijiang River. The dominant cation was Ca²⁺, accounting for 69% of the total cations; the dominant anions were HCO₃^- and SO₄^2-, accounting for 65% and 30% of the total anions, respectively. The main chemical type of the main stream was HCO₃-Ca. Affected by mining activities, the tributaries transitioned from HCO₃-Ca to HCO₃·SO₄-Ca and HCO₃·SO₄-Ca·Na type. River water solute was mainly controlled by the weathering of carbonate rock and silicate rock, with the participation of sulfuric and carbonic acid. The contribution rate of carbonate weathering to river water solute was 63%, and that of silicate weathering was 16.33%. Meanwhile, human activities contributed markedly to the dissolved solutes of the Xiaohuangni River basin, in which the contribution rate of mining activities was 13.4%, and the contribution rate of agricultural activities and domestic sewage was 4%.

Characteristics of and Influencing Factors of Hydrochemistry and Carbon/Nitrogen Variation in the Huangzhouhe River Basin, a World Natural Heritage Site

In karst areas, the characteristics of water chemistry and carbon and nitrogen are of great significance to basic research. The contents of Ca²⁺, Mg²⁺, K⁺, Na⁺, HCO₃^-, SO₄^2-, NO₃^-, Cl^-, dissolved organic carbon (DOC), and total nitrogen (TN) in water samples from 18 rivers and 14 springs in the Huangzhouhe River Basin were determined. The results showed that the water chemistry type in the Huangzhouhe River Basin is HCO₃-Ca-Mg. The chemical composition is mainly affected by dolomite weathering and also by ion exchange and other human activities. The river and spring DIC remain at the same level in the upper and middle reaches and decrease in the lower reaches. The NO₃-N and TN of river water and TN of spring water increase in the middle reaches, while NO₃-N of spring water decreases in the lower reaches. The DOC in the basin increases with the increase of SO₄^2- and Cl^-, mainly due to the human influence of agricultural and domestic sewage. In the basin, the NO₃-N and TN in spring water are larger, and the DOC in river water is larger, mainly because there are more phytoplankton and human activities in the river water. The carbon and nitrogen in the Huangzhouhe River Basin are mainly HCO₃^- and NO₃^- ions. The evaluation of pH, Cl^-, NO₃-N, SO₄^2-, and TDS shows that the water quality is good and the ecological environment is good.

[Hydrochemical Characteristics and Possible Controls of the Surface Water in Ranwu Lake Basin]

To study the chemistry of surface water and potential control measures in the Ranwu Lake basin, 19 samples were collected from Ranwu Lake in 2019. Conventional hydrochemical techniques and statistical analysis methods (descriptive statistics, the Gibbs figure, ion ratio, Piper triangular diagrams) were applied to better understand the solute geochemistry and surface water hydrochemistry in the Ranwu Lake catchment. Surface water in the Ranwu catchment is slightly alkaline (pH of the samples ranged from 7.54 to 8.48 with an average value of 8.06). The concentrations of total dissolved solids (TDS) in the water range from 59.89 to 96.75 mg ·L^-1 with an average of 79.98 mg ·L^-1, the total dissolved solids of all samples are less than 100 mg ·L^-1 and belong to fresh water. The TDS are dominated by Ca²⁺, Mg²⁺, HCO₃^-, and SO₄^2- in the Ranwu Lake. The ion concentrations in the lake water samples are in the order of Ca²⁺ > Mg²⁺ > Na⁺ > K⁺. The concentrations of Na⁺and K⁺are very low. Ranging from 0.5 to 1.21 mg ·L^-1, with an average value of 0.58 mg ·L^-1, the equivalent concentration of Ca²⁺ accounts for 63.3% to 76.2% of total cations with an average value of 67.2%. The equivalent concentration of Mg²⁺ accounts for 23.4% to 36.2% of total cations with an average value of 31.4%. Ca²⁺ and Mg²⁺ account for 98.5% of total cations. The main anions were HCO₃^- and SO₄^2-. The equivalent concentration of HCO₃^- accounts for 74.31% to 84.29% of total anions with an average value of 78.21%. The equivalent concentration of SO₄^2- accounts for 9.59% to 19.37% of total anions with an average value of 15.34%. HCO₃^- and SO₄^2- together account for 93.55% of total anions on average. All the water samples fall in the water-rock interaction field, which suggests that the weathering of rocks primarily controls the major ion chemistry of groundwater in this area. Solutes are mainly derived from carbonate weathering and silicate weathering. The role of cation exchange in the geochemical process of the lake and the influence of human activities on the lake are found to be weak.

Triple oxygen isotope insight into terrestrial pyrite oxidation

The mass-independent minor oxygen isotope compositions (Δ'¹⁷O) of atmospheric O₂ and [Formula: see text] are primarily regulated by their relative partial pressures, [Formula: see text]/[Formula: see text] Pyrite oxidation during chemical weathering on land consumes [Formula: see text] and generates sulfate that is carried to the ocean by rivers. The Δ'¹⁷O values of marine sulfate deposits have thus been proposed to quantitatively track ancient atmospheric conditions. This proxy assumes direct [Formula: see text] incorporation into terrestrial pyrite oxidation-derived sulfate, but a mechanistic understanding of pyrite oxidation-including oxygen sources-in weathering environments remains elusive. To address this issue, we present sulfate source estimates and Δ'¹⁷O measurements from modern rivers transecting the Annapurna Himalaya, Nepal. Sulfate in high-elevation headwaters is quantitatively sourced by pyrite oxidation, but resulting Δ'¹⁷O values imply no direct tropospheric [Formula: see text] incorporation. Rather, our results necessitate incorporation of oxygen atoms from alternative, ¹⁷O-enriched sources such as reactive oxygen species. Sulfate Δ'¹⁷O decreases significantly when moving into warm, low-elevation tributaries draining the same bedrock lithology. We interpret this to reflect overprinting of the pyrite oxidation-derived Δ'¹⁷O anomaly by microbial sulfate reduction and reoxidation, consistent with previously described major sulfur and oxygen isotope relationships. The geologic application of sulfate Δ'¹⁷O as a proxy for past [Formula: see text]/[Formula: see text] should consider both 1) alternative oxygen sources during pyrite oxidation and 2) secondary overprinting by microbial recycling.

Magnesium isotope fractionation during microbially enhanced forsterite dissolution

Bacillus subtilis endospore-mediated forsterite dissolution experiments were performed to assess the effects of cell surface reactivity on Mg isotope fractionation during chemical weathering. Endospores present a unique opportunity to study the isolated impact of cell surface reactivity because they exhibit extremely low metabolic activity. In abiotic control assays, ²⁴ Mg was preferentially released into solution during forsterite dissolution, producing an isotopically light liquid phase (δ²⁶ Mg = -0.39 ± 0.06 to -0.26 ± 0.09‰) relative to the initial mineral composition (δ²⁶ Mg = -0.24 ± 0.03‰). The presence of endospores did not have an apparent effect on Mg isotope fractionation associated with the release of Mg from the solid into the aqueous phase. However, the endospore surfaces preferentially adsorbed ²⁴ Mg from the dissolution products, which resulted in relatively heavy aqueous Mg isotope compositions. These aqueous Mg isotope compositions increased proportional to the fraction of dissolved Mg that was adsorbed, with the highest measured δ²⁶ Mg (-0.08 ± 0.07‰) corresponding to the highest degree of adsorption (~76%). The Mg isotope composition of the adsorbed fraction was correspondingly light, at an average δ²⁶ Mg of -0.49‰. Secondary mineral precipitation and Mg adsorption onto secondary minerals had a minimal effect on Mg isotopes at these experimental conditions. Results demonstrate the isolated effects of cell surface reactivity on Mg isotope fractionation separate from other common biological processes, such as metabolism and organic acid production. With further study, Mg isotopes could be used to elucidate the role of the biosphere on Mg cycling in the environment.

Predicting Water Cycle Characteristics from Percolation Theory and Observational Data

The fate of water and water-soluble toxic wastes in the subsurface is of high importance for many scientific and practical applications. Although solute transport is proportional to water flow rates, theoretical and experimental studies show that heavy-tailed (power-law) solute transport distribution can cause chemical transport retardation, prolonging clean-up time-scales greatly. However, no consensus exists as to the physical basis of such transport laws. In percolation theory, the scaling behavior of such transport rarely relates to specific medium characteristics, but strongly to the dimensionality of the connectivity of the flow paths (for example, two- or three-dimensional, as in fractured-porous media or heterogeneous sediments), as well as to the saturation characteristics (i.e., wetting, drying, and entrapped air). In accordance with the proposed relevance of percolation models of solute transport to environmental clean-up, these predictions also prove relevant to transport-limited chemical weathering and soil formation, where the heavy-tailed distributions slow chemical weathering over time. The predictions of percolation theory have been tested in laboratory and field experiments on reactive solute transport, chemical weathering, and soil formation and found accurate. Recently, this theoretical framework has also been applied to the water partitioning at the Earth’s surface between evapotranspiration, ET, and run-off, Q, known as the water balance. A well-known phenomenological model by Budyko addressed the relationship between the ratio of the actual evapotranspiration (ET) and precipitation, ET/P, versus the aridity index, ET₀/P, with P being the precipitation and ET₀ being the potential evapotranspiration. Existing work was able to predict the global fractions of P represented by Q and ET through an optimization of plant productivity, in which downward water fluxes affect soil depth, and upward fluxes plant growth. In the present work, based likewise on the concepts of percolation theory, we extend Budyko’s model, and address the partitioning of run-off Q into its surface and subsurface components, as well as the contribution of interception to ET. Using various published data sources on the magnitudes of interception and information regarding the partitioning of Q, we address the variability in ET resulting from these processes. The global success of this prediction demonstrated here provides additional support for the universal applicability of percolation theory for solute transport as well as guidance in predicting the component of subsurface run-off, important for predicting natural flow rates through contaminated aquifers.

[Seasonal Variations in River Water Chemical Weathering and Its Influence Factors in the Malian River Basin]

In order to discern temporal variations, sources, and controlling factors of river water chemistry in the Malian River Basin, time series samples were collected from the Yuluoping hydrological station in 2016. The compositions of major cations and anions were analyzed and a forward model was used to calculate the weathering rates of evaporite, silicate, and carbonate. Results showed that river water was brackish with average total dissolved solids of 1154.0 mg·L^-1, indicating significant differences from other main rivers in China. Na⁺, Ca²⁺, Mg²⁺, and SO₄^2- were the major ions present in water, with mean concentrations of 202.8, 86.0, 78.6, and 431.2 mg·L^-1 respectively. Water chemistry exhibited distinct seasonal variations, with major ions gradually declining during the pre-monsoon period and increasing in the post-monsoon period. An abrupt rise in concentrations of major ions during the ice melting interval was observed, as well as a sharp drop during stormy events. Dissolved loads were mainly derived from chemical weathering, with the contribution ratios of evaporite, silicate, and carbonate being 67.1%, 13.7%, and 19.2% respectively. Chemical processes showed different responses to climate forcing, attributed to variations in mineral content in the watershed and dissolution kinetics. The dominant contribution of evaporite in the monsoon season was due to its rapid dissolution, while silicate weathering increased during the pre-monsoon period, with longer water rock interaction times when water discharge was lower. During the post-monsoon season, carbonate weathering was enhanced due to its high content in loess and due to more CO₂ absorption by rain from soil. The average chemical weathering rates of evaporite, silicate, and carbonate were 30.6, 6.2, and 8.7 kg·(km²·d)^-1, respectively. A strong correlation between evaporite weathering rates and river discharge was evident; a correlation was also observed between carbonate weathering rates and river discharge, indicating that water discharge played a dominant role in chemical weathering, rather than temperature or precipitation.

[Hydrochemical Characteristics and Possible Controls of Groundwater in the Xialatuo Basin Section of the Xianshui River]

In order to study the characteristics of groundwater chemistry and groundwater flow system in the Xianshui River fault zone, samples of precipitation, surface water, groundwater, and hot spring samples in the Xialatuo Basin were collected and tested. Through the test data, the main ions and the sources of recharge were analyzed by means of ionic relations, correlation analysis, Gibbs plot, Piper triangular diagrams, and saturation index. The groundwater recharge sources in the basin were studied using combined hydrogen and oxygen isotope information. Results show that all the water samples in the study area were weakly alkaline. The predominant cations were Ca²⁺, Mg²⁺, and Na⁺. Among these, Ca²⁺ accounted for 2.6%-53.6%, with an average value of 28.84%, Mg²⁺ accounted for 2.7%-57%, with an average value of 40.6%, and Na⁺ accounted for 6.2%-93.1%, with an average value of 28.6%. The anions were mainly HCO₃^-, accounting for 82.4%-98% of the total anions and with an average value of 89.6%. HCO₃^- and Na⁺ accounted for most of the ions with 93.1% and 98%, respectively, in the Zhanggu hot spring. The total dissolved solids (TDS) of the groundwater ranged from 116.11 to 372.75 mg·L^-1, and with an average value of 281.91 mg·L^-1. The hydrogeochemical type of groundwater was HCO₃-Mg·Ca and HCO₃-Ca·Mg. It is controlled by carbonatite dissolution with a circulatory depth range in dozens of meters. The hot springs are controlled by the fault zone and are mainly distributed along the main stem of the Xianshui River fault. Their water is of the HCO₃-Na type. The hydrogeochemical process is controlled by silicate dissolution with a circulatory depth range in thousands of meters.

Hydro-Geochemistry of the River Water in the Jiulongjiang River Basin, Southeast China: Implications of Anthropogenic Inputs and Chemical Weathering

This study focuses on the chemical weathering process under the influence of human activities in the Jiulongjiang River basin, which is the most developed and heavily polluted area in southeast China. The average total dissolved solid (TDS) of the river water is 116.6 mg/L and total cation concentration (TZ+) is 1.5 meq/L. Calcium and HCO3− followed by Na+ and SO42− constitute the main species in river waters. A mass balance based on cations calculation indicated that the silicate weathering (43.3%), carbonate weathering (30.7%), atmospheric (15.6%) and anthropogenic inputs (10.4%) are four reservoirs contributing to the dissolved load. Silicates (SCW) and carbonates (CCW) chemical weathering rates are calculated to be approximately 53.2 ton/km²/a and 15.0 ton/km²/a, respectively. When sulfuric and nitric acid from rainfall affected by human activities are involved in the weathering process, the actual atmospheric CO2 consumption rates are estimated at 3.7 × 10⁵ mol/km²/a for silicate weathering and 2.2 × 10⁵ mol/km²/a for carbonate weathering. An overestimated carbon sink (17.4 Gg C/a) is about 27.0% of the CO2 consumption flux via silicate weathering in the Jiulongjiang River basin, this result shows the strong effects of anthropogenic factors on atmospheric CO2 level and current and future climate change of earth.

[Major Ionic Features and Possible Controls in the Groundwater in the Hamatong River Basin]

In order to study the major ion chemistry and controls of groundwater, 59 groundwater samples were collected and their major ions measured in the Hamatong River Basin. The hydrogeochemical characteristics of groundwater in this basin were analyzed by means of mathematical statistics, Piper triangular diagrams, Gibbs figures, and ionic relations, and the water chemical evolution and ion sources of the Hamatong River Basin were determined. The results showed that Ca²⁺ was the main cation in the groundwater, accounting for 22.1% to 72.4% of the total cations, with an average value of 48.7%. HCO₃^- was the main anion, accounting for 35.3% to 97.5% of the total anions, and with an average value of 80%. Total dissolved solids concentration ranged from 93.3 mg·L^-1 to 521.1 mg·L^-1 with a median value of 219.1 mg·L^-1. The hydrochemical types of groundwater are HCO₃-Ca, HCO₃-Ca·Mg, and HCO₃-Ca·Na. Chemical weathering rates of carbonates and silicates were estimated, and the chemical composition of groundwater samples located in the middle of Gibbs model indicated that the major chemical process of groundwater was controlled by rock weathering. Silicate weathering is believed to significantly contribute to dissolved solute compositions, and carbonate weathering played an important role as the source of dissolved ions.

[Major Ionic Features and Their Possible Controls in the Water of the Niyang River Basin]

In order to study the hydrochemical characteristics and their possible controls for the chemical composition of the water from the Niyang River Basin, 30 samples were collected from wells, springs, and the river in 2014 and major ion concentrations were measured. Descriptive statistics, the Gibbs figure, an ion ratio, and Piper triangular diagrams were used to investigate the hydrochemical characteristics, influencing factors, and hydrochemical evolution of the water in the basin. The results showed that the major cations in this water were Ca²⁺ and Mg²⁺, accounting for more than 84% of cations and the main anions were HCO₃^- and SO₄^2-, accounting for more than 97% of anions The hydrochemical typology of the water is HCO₃·SO₄(SO₄·HCO₃)-Ca·Mg (Mg·Ca). The total dissolved solids (TDS) in the water ranges from 79.11 to 290.48 mg·L^-1 with an average of 165.21 mg·L^-1. The chemical composition of water samples is located to the left of the Gibbs model, which indicates that the chemical process of Niyang River Basin are controlled by rock weathering. According to the principal component analysis and correlation analysis, the hydrochemical composition is controlled by silicate weathering, however, carbonate weathering also plays an important role.

Continental igneous rock composition: A major control of past global chemical weathering

The composition of igneous rocks in the continental crust has changed throughout Earth's history. However, the impact of these compositional variations on chemical weathering, and by extension on seawater and atmosphere evolution, is largely unknown. We use the strontium isotope ratio in seawater [(87Sr/86Sr)seawater] as a proxy for chemical weathering, and we test the sensitivity of (87Sr/86Sr)seawater variations to the strontium isotopic composition (87Sr/86Sr) in igneous rocks generated through time. We demonstrate that the 87Sr/86Sr ratio in igneous rocks is correlated to the epsilon hafnium (εHf) of their hosted zircon grains, and we use the detrital zircon record to reconstruct the evolution of the 87Sr/86Sr ratio in zircon-bearing igneous rocks. The reconstructed 87Sr/86Sr variations in igneous rocks are strongly correlated with the (87Sr/86Sr)seawater variations over the last 1000 million years, suggesting a direct control of the isotopic composition of silicic magmatism on (87Sr/86Sr)seawater variations. The correlation decreases during several time periods, likely reflecting changes in the chemical weathering rate associated with paleogeographic, climatic, or tectonic events. We argue that for most of the last 1000 million years, the (87Sr/86Sr)seawater variations are responding to changes in the isotopic composition of silicic magmatism rather than to changes in the global chemical weathering rate. We conclude that the (87Sr/86Sr)seawater variations are of limited utility to reconstruct changes in the global chemical weathering rate in deep times.

Episode of intense chemical weathering during the termination of the 635 Ma Marinoan glaciation

Cryogenian (∼720-635 Ma) global glaciations (the snowball Earth) represent the most extreme ice ages in Earth's history. The termination of these snowball Earth glaciations is marked by the global precipitation of cap carbonates, which are interpreted to have been driven by intense chemical weathering on continents. However, direct geochemical evidence for the intense chemical weathering in the aftermath of snowball glaciations is lacking. Here, we report Mg isotopic data from the terminal Cryogenian or Marinoan-age Nantuo Formation and the overlying cap carbonate of the basal Doushantuo Formation in South China. A positive excursion of extremely high δ²⁶Mg values (+0.56 to +0.95)-indicative of an episode of intense chemical weathering-occurs in the top Nantuo Formation, whereas the siliciclastic component of the overlying Doushantuo cap carbonate has significantly lower δ²⁶Mg values (<+0.40), suggesting moderate to low intensity of chemical weathering during cap carbonate deposition. These observations suggest that cap carbonate deposition postdates the climax of chemical weathering, probably because of the suppression of carbonate precipitation in an acidified ocean when atmospheric CO₂ concentration was high. Cap carbonate deposition did not occur until chemical weathering had consumed substantial amounts of atmospheric CO₂ and accumulated high levels of oceanic alkalinity. Our finding confirms intense chemical weathering at the onset of deglaciation but indicates that the maximum weathering predated cap carbonate deposition.

[Rock Weathering Characteristics and the Atmospheric Carbon Sink in the Chemical Weathering Processes of Qingshuijiang River Basin]

Carbon sink produced during rock weathering is critical to global carbon cycles. In this work, the major ion chemistry and ion sources of Qingshuijiang River Basin were investigated. The principal component analysis, mass balance approach and deduction method were applied for estimating the weathering rate and atmospheric CO₂ consumption via the chemical weathering of rocks. The results demonstrated that the chemical weathering of carbonate and silicate rocks within the drainage basin was the main source of the dissolved chemical substances in the Qingshuijiang River Basin, prior to carbonate rock weathering. Some 58.28% of the total dissolved chemical substances were derived from the chemical weathering of carbonate rock, 17.38% from the dissolution of silicate rock, and 17.74% from atmospheric CO₂ contribution rates. The chemical weathering rate of this catchment was estimated to be 109.97t·(km²·a)^-1, which was comparable to Wujiang River Basin, but higher than the average of global rivers. Furthermore, the atmospheric CO₂ consumption rate was estimated to be 7.25×10⁵ mol·(km²·a)^-1. The CO₂ flux consumed by the rock chemical processes within this catchment was 12.45×10⁹ mol·a^-1, of which about 63.13%(7.86×10⁹ mol·a^-1) was resulted from carbonate weathering and 36.87%(4.59×10⁹ mol·a^-1) from silicate weathering. The CO₂ consumed by rock chemical weathering in the Qingshuijiang River reduced the atmospheric CO₂ level and constituted a significant part of the global carbon budget. Correlation and spatial distribution analysis of SO₄^2-, F^-, NO₃^- showed that anthropogenic activities contributed remarkably to dissolved solutes and associated CO₂ consumption worldwide, and anthropogenic inputs probably contributed some 4.87% to the dissolved solutes in the Qingshuijiang River.

The role of forest trees and their mycorrhizal fungi in carbonate rock weathering and its significance for global carbon cycling

On million-year timescales, carbonate rock weathering exerts no net effect on atmospheric CO2 concentration. However, on timescales of decades-to-centuries, it can contribute to sequestration of anthropogenic CO2 and increase land-ocean alkalinity flux, counteracting ocean acidification. Historical evidence indicates this flux is sensitive to land use change, and recent experimental evidence suggests that trees and their associated soil microbial communities are major drivers of continental mineral weathering. Here, we review key physical and chemical mechanisms by which the symbiotic mycorrhizal fungi of forest tree roots potentially enhance carbonate rock weathering. Evidence from our ongoing field study at the UK's national pinetum confirms increased weathering of carbonate rocks by a wide range of gymnosperm and angiosperm tree species that form arbuscular (AM) or ectomycorrhizal (EM) fungal partnerships. We demonstrate that calcite-containing rock grains under EM tree species weather significantly faster than those under AM trees, an effect linked to greater soil acidification by EM trees. Weathering and corresponding alkalinity export are likely to increase with rising atmospheric CO2 and associated climate change. Our analyses suggest that strategic planting of fast-growing EM angiosperm taxa on calcite- and dolomite-rich terrain might accelerate the transient sink for atmospheric CO2 and slow rates of ocean acidification.

Evaluation of the Impacts of Marine Salts and Asian Dust on the Forested Yakushima Island Ecosystem, a World Natural Heritage Site in Japan

To elucidate the influence of airborne materials on the ecosystem of Japan's Yakushima Island, we determined the elemental compositions and Sr and Nd isotope ratios in streamwater, soils, vegetation, and rocks. Streamwater had high Na and Cl contents, low Ca and HCO(3) contents, and Na/Cl and Mg/Cl ratios close to those of seawater, but it had low pH (5.4 to 7.1), a higher Ca/Cl ratio than seawater, and distinct (87)Sr/(86)Sr ratios that depended on the bedrock type. The proportions of rain-derived cations in streamwater, estimated by assuming that Cl was derived from sea salt aerosols, averaged 81 % for Na, 83 % for Mg, 36 % for K, 32 % for Ca, and 33 % for Sr. The Sr value was comparable to the 28 % estimated by comparing Sr isotope ratios between rain and granite bedrock. The soils are depleted in Ca, Na, P, and Sr compared with the parent materials. At Yotsuse in the northwestern side, plants and the soil pool have (87)Sr/(86)Sr ratios similar to that of rainwater with a high sea salt component. In contrast, the Sr and Nd isotope ratios of soil minerals in the A and B horizons approach those of silicate minerals in northern China's loess soils. The soil Ca and P depletion results largely from chemical weathering of plagioclase and of small amounts of apatite and calcite in granitic rocks. This suggests that Yakushima's ecosystem is affected by large amounts of acidic precipitation with a high sea salt component, which leaches Ca and its proxy (Sr) from bedrock into streams, and by Asian dust-derived apatite, which is an important source of P in base cation-depleted soils.

A framework for predicting global silicate weathering and CO2 drawdown rates over geologic time-scales

Global silicate weathering drives long-time-scale fluctuations in atmospheric CO(2). While tectonics, climate, and rock-type influence silicate weathering, it is unclear how these factors combine to drive global rates. Here, we explore whether local erosion rates, GCM-derived dust fluxes, temperature, and water balance can capture global variation in silicate weathering. Our spatially explicit approach predicts 1.9-4.6 x 10(13) mols of Si weathered globally per year, within a factor of 4-10 of estimates of global silicate fluxes derived from riverine measurements. Similarly, our watershed-based estimates are within a factor of 4-18 (mean of 5.3) of the silica fluxes measured in the world's ten largest rivers. Eighty percent of total global silicate weathering product traveling as dissolved load occurs within a narrow range (0.01-0.5 mm/year) of erosion rates. Assuming each mol of Mg or Ca reacts with 1 mol of CO(2), 1.5-3.3 x 10(8) tons/year of CO(2) is consumed by silicate weathering, consistent with previously published estimates. Approximately 50% of this drawdown occurs in the world's active mountain belts, emphasizing the importance of tectonic regulation of global climate over geologic timescales.