Weathering Of Silicate Minerals Research Articles

Hydrochemical evolution of groundwater in northwestern part of the Indo-Gangetic Basin, India: A geochemical and isotopic approach

The present study aims to understand the hydrochemical evolution of groundwater in the Ghaggar River Basin, representing a zone of excessive abstraction of groundwater in the northwestern Indo-Gangetic Basin. The study comprises a regional scale and high-resolution sampling of groundwater during pre- and post-monsoon seasons of 2013 and their analyses for major ions, δ18O, δ2H, and 3H. Variation in hydrochemical and isotopic data is found both in spatial and vertical scales. The significant vertical variation of TDS, NO3− and K+ allowed the classification of the aquifer system into two major groups: shallow (depth < 80 m bgl) and deep (depth > 80 m bgl). The depthwise variations of δ18O and δ2H support this categorization of the aquifers. The Ca-HCO3 and Ca-Mg-Na-HCO3 water facies with higher values of 3H in the proximal part of the basin characterize recharge areas under humid conditions. The dominance of Mg-Na-HCO3 and Na-HCO3 facies in shallow and deep aquifers in central part of the basin, illustrate the intermediate to advanced stages of hydrochemical evolution in the system. Dominance of brackish Ca-Mg-Cl-SO4 and Na-Cl-SO4 water types in the discharge areas is due to the prevailing geological conditions and anthropogenic activities. Geochemical modelling supports the reverse cation exchange and mixing during lateral and vertical flows, weathering of silicate minerals, dissolution of crustal salts, and evaporative enrichment are the natural processes governing the evolution of groundwater chemistry along the flowpaths. The developed process-based conceptual model will aid in the formulation of a suitable plan for groundwater resource management in the region.

Sources of major elements and nutrients in the water cycle of an undisturbed river basin – Samothraki Island, Greece

We studied the origin of elements of an undisturbed stream basin during the dry season as derived by atmospheric inputs and lithological processes. Α mass balance model was applied taking into account atmospheric (rain and vapor) inputs and their origin from marine aerosol and dust, as well as the contribution of rock mineral weathering and dissolution of soluble salts. The model results were enhanced using element enrichment factors, element ratios and water stable isotopes. Weathering and dissolution of bedrock and soil minerals contributed the main element portions, besides sodium and sulfate that chiefly derived from wet deposition. Vapor was shown to contribute water to inland waters of the basin. However, rain was the main source of elements compared to vapor, with marine aerosol being the only atmospheric chloride source, contributing also over 60 % of atmospheric sodium and magnesium. Silicate derived from mineral weathering (mainly plagioclase and amorphous silica), while soluble salt dissolution contributed the main portions of the rest of major elements. In headwater springs and streams, element concentrations were more affected by atmospheric inputs and silicate mineral weathering was more intense, contrary to lowland waters that were more affected by soluble salt dissolution. Effective self-purification processes were mirrored in low nutrient levels, despite the significant inputs from wet deposition, with rain being more important contributor than vapor for the majority of nutrient species. Relatively high nitrate concentrations in headwaters were attributed to increased mineralization and nitrification, while the downstream nitrate diminishing was due to prevailing denitrification processes. The ultimate goal of this study is to contribute in establishing stream elements' reference conditions using mass balance modeling approaches.

Hydrogeochemical characteristics and multivariate statistical approach for monitoring groundwater quality scenario in the vicinity of industrial area of western Himalaya, India

ABSTRACT In the present investigation, 50 groundwater samples were collected from Udham Singh Nagar District of Kumaun Himalaya in the pre-monsoon season and 15 physicochemical parameters were analysed using standard procedures. Here, we represent the chemistry of major cations and anions to know the overall water quality and hydrogeochemical characteristics controlling the solute acquisition processes and sources of elements in the study area. The analytical results revealed that in the groundwater samples, Ca2+ and Mg2+ were the dominant cations and was the most dominant anion in the study area. In all the groundwater samples, the content of alkaline earth metals (Ca2++ Mg2+) exceeded the mean content of alkalis (Na+ +K+). In 62% of groundwater samples, the value of weak acid () exceeded the content of strong acid (Cl− + ). Piper diagram, molar ratios and statistical techniques indicated that weathering of carbonate and silicate minerals mostly managed the solute acquisition process with very less involvement of human activities. Most of the groundwater samples were found suitable for potable and domestic purposes except for a few locations nearby SIKDKUL or other industries (the eastern and western part of the study area). Correlation analysis revealed the dependency of WQI values on Fe and Mn content.

Water–Rock Interactions Driving Groundwater Composition in the Pra Basin (Ghana) Identified by Combinatorial Inverse Geochemical Modelling

The crystalline basement aquifer of the Pra Basin in Ghana is essential to the water supply systems of the region. This region is experiencing the ongoing pollution of major river networks from illegal mining activities. Water management is difficult due to the limited knowledge of hydrochemical controls on the groundwater. This study investigates its evolution based on analyses from a previous groundwater sampling campaign and mineralogical investigation of outcrops. The dominant reactions driving the average groundwater composition were identified by means of a combinatorial inverse modelling approach under the hypothesis of local thermodynamical equilibrium. The weathering of silicate minerals, including albite, anorthite, plagioclase, K-feldspar, and chalcedony, explains the observed median groundwater composition in the transition and discharge zones. Additional site-specific hypotheses were needed to match the observed composition of the main recharge area, including equilibration with carbon dioxide, kaolinite, and hematite in the soil and unsaturated zones, respectively, and the degradation of organic matter controlling the sulfate/sulfide content, thus pointing towards kinetic effects during water–rock interactions in this zone. Even though an averaged water composition was used, the inverse models can “bridge” the knowledge gap on the large basin scale to come up with quite distinct “best” mineral assemblages that explain observed field conditions. This study provides a conceptual framework of the hydrogeochemical evolution for managing groundwater resources in the Pra Basin and presents modelling techniques that can be applied to similar regions with comparable levels of heterogeneity in water chemistry and limited knowledge of aquifer mineralogy. The combinatorial inverse model approach offers enhanced flexibility by systematically generating all plausible combinations of mineral assemblages from a given pool of mineral phases, thereby allowing for a comprehensive exploration of the reactions driving the chemical evolution of the groundwater.

Groundwater pollution source identification and health risk assessment in the North Anhui Plain, eastern China: Insights from positive matrix factorization and Monte Carlo simulation

Groundwater contaminants from natural and anthropogenic sources pose a serious threat to the ecological environment and public health. In this study, 30 groundwater samples were collected from shallow wells at a large central water source in the North Anhui Plain, eastern China. Hydrogeochemical methods, positive matrix factorization (PMF) model, and Monte Carlo simulation were used to determine the characteristics, sources, and human health risks of inorganic and organic analytes in groundwater. The groundwater was weakly alkaline with high total hardness and was dominated by HCO3-Mg·Ca, HCO3-Ca·Mg, and HCO3-Ca·Mg·Na hydrochemical facies. The concentration of naphthalene was at a safe level, while the concentrations of F−, NO3− and Mn in 16.7 %, 26.7 % and 40 % of the samples, respectively, exceeded threshold risk-based values based on Chinese groundwater quality standards. Hydrogeochemical methods revealed that water-rock interactions (including weathering of silicate minerals, dissolution of carbonates, and cation exchange), acidity, and runoff conditions control the migration and enrichment of these analytes in groundwater. The PMF model indicated that local geogenic processes, hydrogeochemical evolution, agricultural activities, and petroleum-related industrial sources were the main factors affecting groundwater quality, with contributions of 38.2 %, 33.7 %, 17.8 %, and 10.3 %, respectively. A health risk evaluation model based on Monte Carlo simulation indicated that 77.9 % of children were exposed to a total noncarcinogenic risk above safe thresholds, about 3.4 times higher than the risk to adults. The main contributor to human health risk was F− originating from geogenic processes; thus, F− was identified as a priority for control. This study demonstrates the feasibility and reliability of combining source apportionment techniques and health risk assessment to evaluate groundwater quality.

Constraining the Capacity of Global Croplands to CO2 Drawdown via Mineral Weathering.

Terrestrial enhanced weathering of alkaline silicate minerals is a promising climate change mitigation strategy with the potential to limit the global temperature rise. The formation and accumulation of pedogenic carbonate and bicarbonate in soils/subsoils and groundwater offers a large sink for C storage; the amount of soil inorganic carbon (SIC) presently held within soils has been estimated to be 720-950 Gt of C. These values can be augmented by the addition of a variety of calcium and magnesium silicates via enhanced weathering. While the concept of the application of finely milled silicate rocks for faster weathering rates is well established, there has been limited discussion on the role of local climate, natural SIC content (i.e., the SIC innately present in the soil), and soil pH (among other important agronomic factors) on silicate weathering when applied to croplands, especially in view that the aim is to establish terrestrial enhanced weathering as a carbon dioxide removal (CDR) strategy on a global scale. In this work, we emphasized the importance of soil pH and soil temperature on silicate weathering and looked to estimate an upper limit of (i.e., constrain) the global capacity until the year 2100 for enhanced rock weathering (ERW) to draw down CO2 in the form of accumulated pedogenic carbonate or soluble bicarbonate. We assessed the global spatial distribution of cropland soil pH, which serves as a proxy for local innate SIC; annual rate of pluvial (rainfall) precipitation; and soil temperature, and found that the potential CO2 drawdown difference between faster and slower weathering silicates is narrower in Asia, Africa, and South America, while the gap is larger for Europe, North America, and Oceania.

Water-Rock Action Analysis and Quality Evaluation of Shallow Groundwater in Rural Areas: A Case Study of Suzhou City, Northern Anhui, China

Groundwater is the main water source for humans and plays an important role in health and food production. To understand the hydrogeochemical characteristics and quality of shallow groundwater in rural areas of Suzhou, Anhui Province, China, 32 groups of shallow groundwater samples were collected. The results of the study showed that the nature of the groundwater is slightly alkaline. The order of abundance of cations is Ca2+ &gt; K+ + Na+ &gt; Mg2+, whereas that of anions is HCO3− &gt; Cl− &gt; SO42−. The main hydrochemical types are HCO3-Ca, HCO3-Mg, and HCO3-Na. Hydrogen and oxygen isotope abundances indicated that shallow groundwater recharge in the study area is due to precipitation and is affected by evaporation. The ion ratio analysis suggested that the ions in the shallow groundwater originate from the weathering of silicate minerals and the dissolution of carbonate and sulphate minerals, accompanied by different degrees of ion exchange. Water quality evaluation indicated that the water is good and can be used directly as agricultural irrigation water.

First Report on Rhizospheric Silicate Mineral Weathering Bacteria from Indian Himalayas and Their Roles for Plant Growth Promotion of Tomato (Solanum lycopersium L.)

First Report on Rhizospheric Silicate Mineral Weathering Bacteria from Indian Himalayas and Their Roles for Plant Growth Promotion of Tomato (Solanum lycopersium L.)

Assessment of Hydrogeochemical Characteristics and Seawater Intrusion in Coastal Aquifers by Integrating Statistical and Graphical Techniques: Quaternary Aquifer, West Nile Delta, Egypt

The Quaternary aquifer in the western Nile Delta is threatened by seawater intrusion. Few studies have integrated diverse techniques for the assessment of seawater intrusion in this aquifer. The present study aims to determine the geochemical processes and impact of seawater intrusion on this aquifer. To accomplish this investigation, the integration of hydrogeochemical, statistical, multivariate statistical, and graphical tools were implemented on 75 groundwater samples and 5 soil samples. The physicochemical variables were analyzed using hierarchical cluster analysis (HCA), saturation index (SI), ionic ratios, ionic relationships, the seawater intrusion index (SWI) and the correlations among 16 hydrochemical parameters, to identify the influencing processes of groundwater quality in the study area. According to the statistical study, the groundwater is divided into four groups. Those are distributed, from north to south: Group1 (G1), Group2 (G2), Group4 (G4), and Group3 (G3). The samples of G1 and G2 are distinguished by Na–Cl chemical type. While G4 has two main ion associations, HCO3–Ca–Mg and Cl–SO4–Na, G3 is characterized by HCO3–Cl–SO4–Ca–Na type. The processes that affect the chemistry of the groundwater are the seawater intrusion, ion exchange, silicate and Ca-rich mineral weathering, and mineral deposition. G1 and G2 groups are primarily influenced by seawater incursion, evaporation, and the ion exchange mechanism. In addition, the weathering of silicate minerals has a substantial effect on G3 and G4 groups, resulting in the creation of carbonate minerals.

Hydrogeochemical characterization of groundwater with a focus on Hofmeister ions and water quality status in CKDu endemic and CKDu non‒endemic areas, Sri Lanka

Hydro-geochemistry of drinking water was characterized in chronic kidney disease of unknown etiology (CKDu) endemic areas in Girandurukotte (GK) and Dehiattakandiya (DH) and non-endemic areas in GK, DH, and Sewanagala (SW) in Sri Lanka to comprehend any potential risk factors for CKDu. Groundwater (n = 142) and surface water (n = 08) were sampled during wet and dry seasons and analyzed for major anions, cations and stable isotopes of hydrogen and oxygen (δ2H and δ18O). Besides the typical water quality analysis, the water quality status was determined using the weighted arithmetic water quality index (WQI) and Hofmeister ion exposure levels. The measured average groundwater F− level was higher than the permissible level assigned by regulatory agencies for tropical countries at CKDu locations in GK, DH and non-CKDu locations in DH and SW. Significant differences in the content of total hardness (p = 0.017) and total dissolved solids (p = 0.003) were observed between CKDu and non-CKDu locations whereas the differences were insignificant for F− (p = 0.985) and alkalinity (p = 0.203). Weathering of silicate and carbonate minerals was found to be the main governing factor of groundwater compositions in both CKDu and non-CKDu areas, while recharging of groundwater is mainly determined by the rainfall than the surface water inputs. Higher ionic strength of groundwater in non-CKDu areas suggested that the potential environmental CKDu risk factors might be suppressed from dissolution into groundwater. The WQI calculations revealed that the both CKDu and non-CKDu locations were frequently presented with poor water quality. This study highlights the water quality status of the CKDu and non-CKDu locations and signifies the potential health risks that could arise even in non-CKDu areas due to the consumption of poor quality water. Accordingly, regular monitoring of water quality and assessment of Hofmeister ions exposure from food and beverages are highly warranted.

Quantification of CO2 uptake by enhanced weathering of silicate minerals applied to acidic soils

The application of ground silicate minerals to agricultural soils has been proposed as a method for taking up CO2 by enhancing the weathering rate of these minerals through their exposure to soil acids. Alternatively, glacial rock flour, a finely grained material which is abundantly available without the need for energy-intensive grinding, could be used. However, simple and inexpensive methods for determining the amount of CO2 taken up as a result of weathering of applied minerals are still needed, and the impact of non-carbonic acids on CO2 uptake has yet to be accounted for. Here, we present a protocol for correcting estimates of CO2 uptake due to enhanced mineral weathering to account for weathering by non-carbonic soil acids. We determine that soils with a pH below 6.3 need correction for weathering by other acids than carbonic acid and that, given the impact of non-carbonic acids, soils with a pH below 5.2 may not be ideal candidates for mineral applications aimed at CO2 uptake, depending on the pCO2. We report an estimated CO2 uptake of 728 kg CO2 ha−1 after the application of 50 tons ha−1 of Greenlandic glacial rock flour to an acidic, sandy soil in Denmark over 3 years.

Assessment of Groundwater Quality for Pre- and Post-Monsoon Variations in Molakalmur Taluk, Chitradurga District, Karnataka, India

Objectives: To ascertain whether the groundwater in Molakalmur Taluk is suitable for human consumption and it is anticipated that the study will assist regulators and policymakers in taking the proper actions to provide the study area’s population with safe domestic water. The study’s overall goal is to examine the suitability of groundwater for domestic purposes in accordance to WHO and BIS standards. Methods: The current study was carried out to analyze the water quality and spatial distribution of physicochemical parameters of groundwater in study area. A total of 92 groundwater samples were collected in the study region for study during both pre- and post-monsoon monsoon period, ArcGIS 10.1 was used to create a spatial distribution map based on a geographic information system. The concentrations of various ions like Ca+2, K+1, Cl-1, Mg+2, HCO3 -1, Na+1, CO3 -2, and SO4 -2 were evaluated as per BIS 3025 (2014) and compared with BIS and WHO standards for drinking purpose. Findings: The Gibbs diagram shows that the two main elements that affect the chemical composition of groundwater are evaporation and rock-water interaction. Weathering of silicate minerals and carbonate minerals are the principal sources of carbonate and bicarbonates. Roughly 68% and 58% of the samples exceeded the permissible level of 500 mg/l for TDS. According to the interpretation of Piper’s trilinear diagram, the majority of the water samples fell into the categories of mixed CaMgHCO3, MgHCO3, and CaCl2 types, in that order of dominance. The plot shows that alkaline earths correspond to 75% of the samples. Novelty: The major ion chemistry of the groundwater in Molakalmur Taluk has never been studied, and there is no perennial river in the research area. The current investigation makes an effort to investigate if water is suitable for domestic purpose. The study’s conclusions will help with the gathering of vital information on the condition of the groundwater in Molakalmur Taluk. The study’s conclusions may also beuseful to groundwater managers and city planners in their efforts to restore and enhance groundwater quality. Keywords: Groundwater; Physicochemical Parameters; Gibbs Diagram; Pre-Monsoon; Post-Monsoon Water Quality; Geographic Information System; Pipers Chart

Elevated physical weathering exceeds chemical weathering of clays during the Paleocene-Eocene Thermal Maximum in the continental Bighorn Basin (Wyoming, USA)

The Paleocene-Eocene Thermal Maximum (PETM) global warming event at ∼56 million years before present changed catchment weathering and erosion. Increased chemical weathering of silicate minerals is thought to be an important process removing CO2 from the atmosphere. However, changes in clay mineralogy can often be explained by enhanced erosion of catchment laterites during the event. Here, we investigate chemical and physical weathering and erosive flux changes through the PETM interval in the Bighorn Basin, Wyoming, a Laramide foreland basin, in a proximal continental-interior alluvial setting. These show an increase of detrital smectite with a lag time of 20-kyr after the main onset the PETM. The smectite increase continued for at least 50-kyr after the event. In-situ, post-depositional pedogenic clay mineral formation is similar between pre-PETM and PETM soil profiles, despite large macroscopic differences between soils that formed before and during the event. Drier, hotter summers during the PETM probably caused decreased vegetation cover that, in concert with more frequent and heavier rainstorms, intensified the erosion of smectite-rich Cretaceous bentonites on the margins of the catchment, which exceeded changes in chemical weathering within the catchment. The lagged response in reaching full PETM clay mineral values can be explained by the time required for upstream sediment to reach the catchment basin floodplain. The prolonged nature of smectite enhancement after the PETM event may again relate to signal propagation times that are now even longer due to lower fluvial recycling rates. Our results indicate that chemical weathering changes were probably superceded by enhanced physical weathering and clay-mineral transport from basin margins at this continental-interior study site.

Groundwater chemistry and health hazard risk valuation of fluoride and nitrate enhanced groundwater from a semi-urban region of South India.

Evaluation of groundwater chemistry and its related health hazard risk for humans is a prerequisite remedial measure. The semi-urban region in southern India was selected to measure the groundwater quality to know the human health risk valuation for different age groups of adults and children through oral intake and skin contact with elevated concentrations of fluoride ([Formula: see text]) and nitrate ([Formula: see text]) groundwater. Groundwater samples were collected from the semi-urban region for pre- and post-rainfall periods and resolute its major ion chemistry. The pH values showed the water is alkaline to neutral in nature. Total dissolved solid (TDS) ranged from 201 to 3612mg/l and 154 to 3457mg/l. However, [Formula: see text] concentration ranges from 0.28 to 5.48mg/l and 0.21 to 4.43mg/l; and NO3- ranges from 0.09 to 897.28mg/l and 0.0 to 606.10mg/l elevating the drinking water standards of [Formula: see text] in 32% and 38% samples and for [Formula: see text] about 62% and 38% during pre- and post-rainfall seasons, respectively. The fluoride-bearing minerals are the main sources of elevated concentrations of [Formula: see text] and excessive use of chemical fertilizers as the chief source of NO3- concentration in the aquifer regime. Water quality index (WQI) ranged from 18.3 to 233 and 12.97 to 219.14; 20% and 22% showed poor water quality for pre- and post-rainfall seasons with WQI ≥ 200. Piper plot suggests that 46% and 51% of samples signify carbonate water type ([Formula: see text]), and 32% and 28% of groundwater samples show ([Formula: see text]) type water for pre- and post-rainfall seasons respectively. Gibbs' plot suggests the dominance of water-rock interaction in the aquifer system. Further, the principal component analysis (PCA) revealed three and four components which explain 74.85% and 79.30% of the variance in pre- and post-rainfall seasons with positive loading of EC, TDS, Ca2+, Na+, Mg2+, K+, [Formula: see text], Cl-, and [Formula: see text] due to mineral weathering and water-rock interactions altering the chemistry for an elevated concentration of [Formula: see text] and [Formula: see text] in groundwater. Cluster analyses of chemical variables observed four clusters with a linkage distance of 5 to 25 with a linkage between different variables displaying predominant ion exchange, weathering of silicate and fluoride-rich minerals, salinization of the water, and a high value of [Formula: see text] concentration, resulting from fertilizers. The hazard quotient (HQ) through ingestion (HQing) and dermal (HQder) pathways of F- and NO3- was observed higher than its acceptable limit of 1.0 for different age groups indicating the non-carcinogenic effect on human health. Effective strategic measures like defluoridation, denitrification, safe drinking water supply, sanitary facilities, and rainwater harvesting structures are to be implemented in the area for improvement of human health conditions and also bring awareness to the local community about the health hazard effects of using high concentrated [Formula: see text] and [Formula: see text] water for daily uses.

What we talk about when we talk about the long-term carbon cycle.

The terrestrial biota is a crucial part of the long-term carbon cycle via the deposition of biomass as coal and other sedimentary organic matter and the impact of plants, fungi, and microbial life on the weathering of silicate minerals. Understanding these processes and their changes through time requires both geochemical modeling of the system as well as expertise in the living and fossil biotas and their ecological interactions, but details of these components are often lost in translation between disciplines. Here, we highlight misconceptions of the long-term carbon cycle that most frequently infiltrate the literature and hamper progress: mass balance requirements, the nature and duration of perturbations, opposing timescale constraints on biological and geological processes, and the role of models.

Hydrogeochemical processes regulating the enrichment and migration of As and B from the river sediments in the Singe Tsangpo River Bain, Western Tibetan plateau

Although the enrichment of arsenic (As) and boron (B) has been extensively observed in the major river basin within the Tibetan Plateau, little is known about the hydrogeochemical processes regulating the enrichment and mobility of As and B within river sediments. The present study conducted geochemical investigations of river sediments along the river flow path of the Singe Tsangpo River (STR) basin, and examined the mobility of As and B within river sediments under various environmental conditions through incubation experiments. The results suggested that the weathering of Cs-bearing silicate minerals could be a potential origin for As in the river sediments, which was evidenced by the corresponding variations between Cs and As (R = 0.60, P < 0.01). In contrast, carbonate weathering has contributed to the B enrichment, supported by the correlation between CaO and B concentrations (R = 0.60, P < 0.01). The incubation experiments showed intense mobilizations of As and B (∼12 mg/kg) under varying environmental conditions, where the increases in HCO3− concentration and temperature could enhance both As and B mobilization. Additionally, the As mobilization was enhanced by the anaerobic and alkaline conditions. These scenarios are relevant to the hydrogeochemical processes that regulate the As and B enrichment in both river water and groundwater from the STR basin, including the redox fluctuations that resulted from flood and draught cycling and the variations in the water/sediment particle ratios. The present study thus provided new insights into the hydrogeochemical control on the enrichment and mobility of As and B in the river sediments from the STR basin, which is also applicable in other riverine systems under similar conditions.

Nutrient-doped synthetic silicates for enhanced weathering, remineralization and fertilization on agricultural lands of global cold regions- A perspective on the research ahead.

There is now a dire demand for negative emissions technologies (which sequester CO2 from the atmosphere) that can be rapidly deployed, are scalable, and are demonstrably safe and effective. Enhanced weathering of silicate minerals has demonstrated a significant potential for CO2 capture and sequestration by the formation of pedogenic carbonates in soils, subsoils, and sediments. This technique has also been shown to deliver fruitful results in terms of improving soil health, and in turn plant health, through remineralization. The silicate minerals that possess the highest weathering rates (e.g., wollastonite), are relatively rare in nature, whereas the abundant ones (e.g., anorthite and forsterite) have a slower pace of weathering, especially in colder and drier climates such as found in the extensive agricultural lands of Western Canada and the Western United States. Herein, we offer a perspective on the opportunities for computational studies targeting atomic-scale interaction of CO2 with silicates and synthesis of fast-weathering silicates (such as larnite and bredigite), whose composition can be tuned to also support soil fertilization and remineralization, and whose production must be integrated with green and carbon-neutral technologies to ensure net-negative life cycle emissions.

Impacts of dissolved phosphorus and soil-mineral-fluid interactions on CO2 removal through enhanced weathering of wollastonite in soils

The weathering of silicate minerals removes carbon dioxide (CO2) from the atmosphere over geologic timescales and is also investigated as an engineered strategy to mitigate climate change on decadal timescales. “Enhanced rock weathering” (ERW) is a carbon dioxide removal strategy that involves spreading of pulverized, highly reactive silicate rock at the Earth's surface such as within agricultural and natural soils. The rate and efficacy of ERW in agricultural soils to remove CO2 is difficult to quantify owing to the complex geochemical environment including biological-mineral-fluid-atmosphere interactions and human interventions that occur. Column experiments containing wollastonite [CaSiO3] and soils were conducted to investigate the geochemical processes that remove CO2 during ERW, and to determine the potential impact of P-bearing fertilizers on CO2 removal. Columns containing wollastonite, soil, or 8:1 soil-wollastonite mixtures were irrigated with de-ionized water or a 1 × 10−4 M K3PO4 solution. Analysis of column effluent concentrations indicated that P was rapidly removed from solution and retained within the columns, with little difference in weathering rate between columns irrigated with water and those receiving the K3PO4 solution. Bulk wollastonite weathering rates were significantly enhanced in the presence of soils compared to columns with wollastonite alone. Cation concentrations in effluent from columns with soil-wollastonite mixtures were strongly impacted by adsorption to soil surfaces, complicating efforts to estimate CO2 capture. Based on wollastonite weathering rates estimated by Si release, a maximum of 255 kg CO2 t−1 amendment yr−1 was captured in the soil-wollastonite mixture columns. The majority of CO2 stored in the soil-bearing columns was most likely soil-generated rather than removed directly from the atmosphere. The results of this study indicate that adsorption to soils may limit the ability of P to enhance wollastonite weathering, that silicate weathering behaviour within soils differs substantially from that of pure mineral phases, and that CO2 budgets must be carefully constrained to assess the source of stored CO2. Moreover, leachate concentrations of cations and HCO3− may not serve as accurate indicators of the extent of silicate weathering, at least over the short term, due to the numerous processes that control their concentrations in soils, such as sorption to soil components.

Mineralogical, magnetic and geochemical data constrain the pathways and extent of weathering of mineralized sedimentary rocks

The oxidative weathering of sulfidic rock can profoundly impact watersheds through the resulting export of acidity and metals. Weathering leaves a record of mineral transformation, particularly involving minor redox-sensitive phases, that can inform the development of conceptual and quantitative models. In sulfidic sedimentary rocks, however, variations in depositional history, diagenesis and mineralization can change or overprint the distributions of these trace minerals, complicating the interpretation of weathering signatures. Here we show that a combination of bulk mineralogical and geochemical techniques, micrometer-resolution X-ray fluorescence microprobe analysis and rock magnetic measurements, applied to drill core samples and single weathered fractures, can provide data that enable the development of a geochemically consistent weathering model.This work focused on one watershed in the Upper Colorado River Basin sitting within the Mesaverde Formation, a sedimentary sandstone bedrock with disseminated sulfide minerals, including pyrite and sphalerite, that were introduced during diagenesis and subsequent magmatic-hydrothermal mineralization. Combined analytical methods revealed the pathways of iron (Fe), carbonate and silicate mineral weathering and showed how pH controls element retention or release from the actively weathering fractured sandstone. Drill core logging, whole rock X-ray diffraction, and geochemical measurements document the progression from unweathered rock at depth to weathered rock at the surface. X-ray microprobe analyses of a 1-cm size weathering profile along a fracture surface are consistent with the mobilization of Fe(II) and Fe(III) into acidic pore water from the dissolution of primary pyrite, Fe-sphalerite, chlorite, and minor siderite and pyrrhotite. These reactions are followed by the precipitation of secondary minerals such as of goethite and jarosite, a Fe-(oxyhydr)oxide and hydrous Fe(III) sulfate, respectively. Microscale analyses also helped explain the weathering reactions responsible for the mineralogical transformations observed in the top and most weathered section of the drill core. For example, dissolution of feldspar and chlorite neutralizes the acidity generated by Fe and sulfide mineral oxidation, oversaturating the solution in both Fe-oxides. The combination of X-ray spectromicroscopy and magnetic measurements show that the Fe(III) product is goethite, mainly present either as a coatings on fracture surfaces in the actively weathering region of the core or more homogeneously contained within the unconsolidated regolith at the top of the core. Low-temperature magnetic data reveal the presence of ferromagnetic Fe-sulfide pyrrhotite that, although it occurs at trace concentrations, could provide a qualitative proxy for unweathered sulfide minerals because the loss of pyrrhotite is associated with the onset of oxidative weathering. Pyrrhotite loss and goethite formation are detectable through room-temperature magnetic coercivity changes, suggesting that rock magnetic measurements can determine weathering intensity in rock samples at many scales. This work contributes evidence that the weathering of sulfidic sedimentary rocks follows a geochemical pattern in which the abundance of sulfide minerals controls the generation of acidity and dissolved elements, and the pH-dependent mobility of these elements controls their export to the ground- and surface-water.

Behavior of Li, S and Sr isotopes in the subterranean estuary and seafloor pockmarks of the Hanko submarine groundwater discharge site in Finland, northern Baltic Sea

The impact of submarine groundwater discharge (SGD) on coastal sea biogeochemistry and water quality has been demonstrated in many recent studies. However, the isotopic behavior of terrestrially-derived solutes in the groundwater-seawater mixing zone of coastal aquifers (the subterranean estuary, STE) has been less studied, although solutes such as Li, S and Sr are commonly used as tracers of weathering and biogeochemical processes taking place in aquifers and in coastal sea sediments. This study investigated the behavior of 87Sr/86Sr, δ7Li and δ34S in the STE and three seafloor pockmarks with different degrees of groundwater influence, as constrained based on δ2H and δ18O, at the Hanko SGD site in Finland, in the northern Baltic Sea. These data were supplemented by groundwater and seawater measurements. 87Sr/86Sr showed non-conservative behavior with values elevated up to 0.0167 units above that expected for the conservative mixing in the STE and in the most groundwater-dominated pockmark (up to 100% groundwater), but the deviation was masked by much stronger seawater contributions in the other pockmarks. δ7Li values were shifted down to −1.75‰ below that expected for conservative mixing in the STE and in groundwater-influenced pockmark porewaters, whereas δ7Li was elevated up to 1.53‰ in the porewater of organic-rich mud in a pockmark where groundwater influence had ceased. δ34S deviated between −16.78‰ and 10.51‰ from the conservative mixing in the STE and porewaters of groundwater-influenced pockmarks, while δ34S was elevated up to 16.85‰ in the porewater of the pockmark with no groundwater influence. In the STE, the isotopic fractionation of Sr and Li was explained by chemical weathering of silicate minerals and clay minerals, respectively, whereas δ34S was fractionated by complex interactions of microbial sulfate reduction and sulfide reoxidation. In the pockmark porewater with no groundwater influence, δ7Li and δ34S isotopes were enriched in the heavier isotopes as a consequence of early-diagenetic mineral formation in the organic-rich muds. The measured 87Sr/86Sr and δ7Li were higher than the previously estimated isotopic compositions of their groundwater-derived fluxes to the oceans, and partly higher than the global riverine values. The heterogeneity in the seafloor biogeochemical environment, caused by the focusing of SGD in pockmarks, resulted in strongly variable δ34S of groundwater-derived S flux to the coastal ocean at a spatial scale of a few hundreds of meters.