Weathering Of Silicate Minerals Research Articles

High levels of fluoride contamination in groundwater of the semi-arid alluvial aquifers, Pakistan: evaluating the recharge sources and geochemical identification via stable isotopes and other major elemental data.

Hydrogeochemical methods were integrated to delineate the geochemical factors controlling fluoride (F-) contamination in groundwater at four sites in the districts of Lahore (Samada) and Kasur (Sari Chimba, Kot Maiga, and Chah Fatehwala) in Panjab province of Pakistan. Hydrochemical data and stoichiometric ratios indicate Na-Cl and Na-HCO3 as the dominant water types with silicate weathering influencing overall hydrogeochemistry of the study area. The groundwater F- concentrations ranged between 0.54 mg/L and 17.5 mg/L, with more than 70% samples having F- concentrations above the World Health Organization (WHO) provisional drinking water guideline (1.5 mg/L). Saturation indices determined that 100% samples were saturated with respect to calcite and 96% samples were undersaturated with respect to fluorite, indicating the influence of calcite precipitation on fluoride enrichment. A positive correlation was observed between fluoride with pH, Na+, and HCO3-, confirming that high fluoride concentrations were the result of weathering of silicate minerals and the exchange of OH- on clay surface under the alkaline pH conditions. The isotopic values of δ18O and δ2H in groundwater ranged from 9.14 to - 5.51‰ and 56.57 to - 39.5‰, respectively. The stable isotope data indicated the meteoric origin of groundwater with some evaporative effect, which is partly influencing groundwater quality such as high pH and salinity, as a result facilitating anion exchange (OH- for F-) on clays surface. The research indicates that the groundwater quality of the study area is not recommendable for drinking due to its high total dissolved solids (TDS) and elevated fluoride concentrations.

Multivariate analysis and geochemical signatures of groundwater in the agricultural dominated taluks of Jalandhar district, Punjab, India

The present study is focused on the agriculturally dominated taluks of Nakodar, Shahkot and Phillaur in Jalandhar district, Punjab. Integrated multivariate technique along with geochemical signatures and vertical depth profiles of major ions were studied to assess the hydrogeochemical characteristics, processes influencing the aquifer chemistry and suitability appraisal for different uses. The analytical results revealed that the groundwater is hard to very hard in nature and their relative abundance of major ions are Na+ > Mg2+ > Ca2+ > K+ and HCO3– > SO42− > CO32– > Cl− > NO3− > F− > PO42− respectively. Elevated levels of NO3− (2 samples) in Phillaur taluk and F− (1 sample in every three taluks) were observed in shallow aquifer of the study area. The overall results of the water quality index show that a major part of the study area possesses good water quality. The taluk wise WQI results depict that certain pockets fall in poor (3 samples in Phillaur, 1 in Shahkot) to very poor (1 sample of Nakodar) water classes. The chemical compositions of the study area were predominantly Ca2+–Mg2+–HCO3– followed by Ca2+–Mg2+–Cl−–SO42−facies. Both Nakodar and Shahkot taluk shows Na+-Mg2+–HCO3– water type, while Phillaur taluk shows Mg2+–HCO3– water type. The water type of the shallow aquifer is complex in nature showing Na+-Mg2+–HCO3– type, further it changed to Na+–HCO3– in the intermediate zone. Interpretation of the geochemical signatures of the groundwater suggested that natural weathering and dissolution of silicate and carbonate minerals and ion exchange process are largely controlling the aquifer chemistry. Principal component analysis (PCA) extracts five principal components (PC's), where PC1, PC2 and PC4 are influenced by mixed factors i.e., lithogenic and anthropogenic inputs. PC3 is exclusively affected by anthropogenic factors like domestic sewage, fertilizer and irrigation return flow respectively and PC5 is mainly controlled by natural factors.

Hydrochemistry and stable isotopes (18O and 2H) characteristics of groundwater in Lokoja and its environs, central Nigeria

To determine hydrochemical and stable isotope characteristics of groundwater in Lokoja and its environs, 39 samples were collected, analyzed and interpreted. The results of the analyses revealed that pH of the water samples of the area ranged from 5.9 to 8.4 indicating neutral water except few slightly acidic samples. TDS varied between 44 and 1273 mg/L but were generally Ca2+ > Mg2+ > K+ with average values of 48.5 mg/L, 29.4 mg/L, 15.3 mg/L and 13.0 mg/L, respectively; while that of anions are HCO3− > Cl− > SO42− > NO3− with average values of 143.3 mg/L, 59.5 mg/L, 35.8 mg/L and 18.3 mg/L, respectively. Groundwater is generally suitable for drinking purposes as most samples fell within the “excellent water” and “good water” categories, while the quality for irrigation ranged from suitable to unsuitable. Five hydrochemical facies were determined: CaHCO3, mixed CaMgCl, NaCl, CaNaHCO3 and NaHCO3 water types. Several processes such as reverse ion exchange, weathering of silicate minerals and rock–water interactions were main mechanisms controlling ionic constituents of groundwater of the study area. In addition, the results of stable isotopes analyses showed considerable variations, ranging between − 3.9 and − 1.2% with an average of − 2.7% for δ18O and − 23.9% and 11.7% with a mean of 16.9% for δ2H. The plot of δ2H vs δ18O of groundwater system in the study area along global meteoritic water line indicated recent meteoritic recharge. However, all of the samples plotted deviated appreciable from global MWL except a sample from sandstone bedrock that was plotted along the line as defined by this equation: δ D = 8 δ 18O + 10. The deviation was a consequence of kinetic evaporative effect as well as rock–water interaction and carbondioxide exchange effects.

From on high: Geochemistry of alpine springs, Niwot Ridge, Colorado Front Range, USA

AbstractSnowmelt‐fed springs and small (0.5 km2) upland catchments in alpine areas of the western United States contribute significantly to the quantity and inorganic chemistry of water delivered to downstream basins but have not been studied extensively. Mineral weathering, transit time, and hydrologic mixing control the solute chemistry of waters that drain the upland zone of Niwot Ridge, Colorado Front Range, and adjacent areas in the granitic core of the Southern Rocky Mountains. Water in 37 springs sampled in this study flows in generally short steep paths (~0.3 km) through shallow regolith with mean transit times (MTT) of weeks to months, producing solutions dominated by Si, Ca2+, Na+, and HCO3−, locally SO42−. Rock type is a significant control on spring, surface, and shallow groundwater chemistry, and plagioclase (oligoclase) is the major source of dissolved Na+ and Si. Concentrations of Ca2+ exceed stoichiometric predictions of oligoclase weathering by ~3.5×; excess Ca2+ likely represents weathering of aeolian material, vein calcite, or trace minerals. Concentrations of base cations and Si increase slowly with estimated MTT of 0.2 years for Niwot Ridge spring waters, and several years for shallow groundwater sampled by wells. Chemical weathering of silicate minerals is slow with estimated rates of ~2.0 and 0.2 pmol·m−2·s−1 for oligoclase and microcline, respectively; the most mineralized spring waters are saturated only with respect to kaolinite and montmorillonite. More than 50% of the dissolved base cations + Si measured in Boulder Creek at Orodell (~25 km downstream) accumulate before water emerges from alpine springs on Niwot Ridge. Warming global temperatures are shifting more high‐elevation precipitation to rain, potentially changing run‐off patterns, transit time, and solute loads. Acquisition of solutes by alpine waters thus has implications far beyond small upland catchments.

Understanding the hydrogeochemical characteristics of natural water for irrigation use around the hard rock mine in Maddhapara, Northwest Bangladesh

This study assesses the hydrochemical characteristics and water quality for irrigation use around the Hard Rock Mining area. The Hydrochemical analysis shows that there are wide variations of ions (e.g. pH, Sp. EC, turbidity, Fe3+, Na+, Cl−, Cd2+, soluble silica and others) which exceeded the acceptable limit of drinking as well as the irrigation uses. The concentration of SiO2 in the water is very high than the natural limit. It indicates a direct impact of granitic rock extracted from the mine. In fact, such rock contains a large quantity (50.17%–74.7% by weight) of silica. The WQI analysis shows that water samples are slightly marginal to excellent quality water. Where, the surface water samples possess comparatively good quality water than groundwater for irrigation purpose. The scatter graph of (Ca2+ + Mg2+) versus total cations (TZ+) plot suggests that some ions are produced due to the weathering of silicate minerals. The Trilinear diagram exhibits that 77.24% of samples are showing the CaHCO3 type of facies where 85.7% of surface water falls within this category. The Durov diagram illustrates the mixing of ion dissolution with reverse ion exchanging water type. The correlation matrix affirms the relationship, strength, and direction of multivariate data. In particular, the various classification of water such as SAR, Na%, salinity, and TDS values confirmed excellent to permissible use of water for agricultural purpose around the mining area.

Export fluxes of dissolved inorganic carbon to the northern Indian Ocean from the Indian monsoonal rivers

Abstract. Rivers are an important source of dissolved inorganic carbon (DIC) to the adjacent coastal waters. In order to examine the spatial variability in the distribution and major sources of DIC in the Indian monsoonal rivers and to quantify their export flux to the northern Indian Ocean, 27 major and medium-sized rivers were sampled during the discharge period. Significant spatial variability in concentrations of DIC (3.4–73.6 mg L−1) was observed, and it is attributed to spatial variations in the precipitation pattern, the size of rivers, pollution and lithology of the catchments. The stable isotopic composition of DIC (δ13CDIC) also showed strong spatial variability (−13.0 ‰ to −1.4 ‰) in the Indian monsoonal rivers with relatively depleted δ13CDIC values in rivers of the northwest of India (-11.1±2.3 ‰) and enriched values in the southeast of India (-3.5±2.3 ‰). Results of the linear least-squares regression models of Keeling and Miller–Tan's plots indicated that the chemical weathering of carbonate and silicate minerals by soil CO2 is the major source of DIC in the Indian monsoonal rivers. Spatial variability in the deviation of δ13CDIC from the approximated δ13C of the source may probably be due to dominant autotrophic production in rivers of the southeastern region, whereas heterotrophic decomposition of organic matter largely influences the other Indian monsoonal rivers. It is estimated that the Indian monsoonal rivers annually export ∼10.3 Tg of DIC to the northern Indian Ocean, of which the major fraction (75 %) enters into the Bay of Bengal, and the remaining fraction reaches to the Arabian Sea. This is consistent with the freshwater flux, which is 3 times higher for the Bay of Bengal (∼378 km3 yr−1) than for the Arabian Sea (122 km3 yr−1). Despite discharge from the Indian monsoonal rivers accounting for only 1.3 % of the global freshwater discharge, they disproportionately export 2.5 % of the total DIC exported by the world's major rivers. Despite rivers from the region in the southwest (SW) of India exporting DIC that is an order of magnitude lower (0.3 Tg yr−1) than the rivers from other regions of India, the highest yield of DIC was found in the rivers of the SW region of India. It is attributed to intense precipitation (∼3000 mm), favorable natural vegetation of tropical moist deciduous and tropical wet evergreen and semi-evergreen forests, tropical wet climate, high soil organic carbon, and the dominance of red loamy soils in catchments of the rivers of the SW region.

Dynamic modelling of weathering rates – the benefit over steady-state modelling

Abstract. Weathering rates are of considerable importance in estimating the acidification sensitivity and recovery capacity of soil and are thus important in the assessment of the sustainability of forestry in a time of changing climate and growing demands for forestry products. In this study, we modelled rates of weathering in mineral soil at two forested sites in southern Sweden included in a monitoring network, using two models. The aims were to determine whether the dynamic model ForSAFE gives comparable weathering rates to the steady-state model PROFILE and whether the ForSAFE model provided believable and useful extra information on the response of weathering to changes in acidification load, climate change and land use. The average weathering rates calculated with ForSAFE were very similar to those calculated with PROFILE for the two modelled sites. The differences between the models regarding the weathering of certain soil layers seemed to be due mainly to differences in calculated soil moisture. The weathering rates provided by ForSAFE vary seasonally with temperature and soil moisture, as well as on longer timescales, depending on environmental changes. Long-term variations due to environmental changes can be seen in the ForSAFE results, for example, the weathering of silicate minerals is suppressed under acidified conditions due to elevated aluminium concentration in the soil, whereas the weathering of apatite is accelerated by acidification. The weathering of both silicates and apatite is predicted to be enhanced by increasing temperature during the 21st century. In this part of southern Sweden, yearly precipitation is assumed to be similar to today's level during the next forest rotation, but with more precipitation in winter and spring and less in summer, which leads to somewhat drier soils in summer but still with increased weathering. In parts of Sweden with a bigger projected decrease in soil moisture, weathering might not increase despite increasing temperature. These results show that the dynamic ForSAFE model can be used for weathering rate calculations and that it gives average results comparable to those from the PROFILE model. However, dynamic modelling provides extra information on the variation in weathering rates with time and offers much better possibilities for scenario modelling.

In-situ dissolution rates of silicate minerals and associated bacterial communities in the critical zone (Strengbach catchment, France)

Abstract The weathering of silicate minerals in the Critical Zone (CZ) is fundamental for numerous environmental and societal issues. Despite decades of efforts to accurately record biogeochemical variables controlling mineral reactivity in the field and to reproduce them in the laboratory, weathering rate estimates still differ from those observed in natural settings. Here we examine the biogeochemical environment of mineral surfaces exposed to contrasted weathering conditions in various compartments of a temperate CZ (Strengbach observatory, France). A novel approach was developed to probe both in-situ mineral dissolution rates and bacterial diversity associated with mineral surfaces. Labradorite and olivine minerals were either buried in the A and C horizons of a soil profile, directly exposed to meteoric fluids or immersed in stream water. Dissolution rates recorded in the soil profile were up to 2 orders of magnitude slower than those predicted using a numerical weathering model. Samples directly exposed to meteoric fluids exhibited contrasted dissolution rates that could not be explained by simple abiotic weathering, while dissolution rates of samples incubated in stream water were particularly low. In soil profiles, the field-laboratory discrepancy by up to 2 orders of magnitude was attributed to heterogeneity of fluid circulation and local variation of reaction conditions. Mineral substrates changed bacterial communities of the mineralosphere after 9 and 20 months of incubation in the CZ. However, we observed that this effect could be delayed or driven by extrinsic factors. Although mineral probes in soil horizons were enriched in bacterial phylotypes potentially involved in mineral weathering (e.g., Pseudomonas sp., Collimonas sp., Burkholderia sp., Janthinobacterium sp., Leifsonia sp., and Arthrobacter sp.), the relative contribution of biotic weathering could not be quantified in-situ. Altogether, the heterogeneity of in-situ mineral dissolution rates in compartments of the CZ underscores the need to improve spatial characterization of hydrogeochemical properties at the soil profile scale, and to evaluate quantitatively the role of microbial communities in mineral weathering.

The different roles of Aspergillus nidulans carbonic anhydrases in wollastonite weathering accompanied by carbonation

The microbial weathering of silicate minerals is an important part of the elemental biogeochemical cycle on Earth. It can even affect the migration and transformation of carbon, a process in which microbial carbonic anhydrase (CA) plays an important role. However, whether multiple microbial CAs are involved in silicate weathering and carbonation is still poorly understood. In this work, gene deletion, overexpression, and bioinformatics were used to reveal the functional differences that two Aspergillus nidulans CA genes, canA and canB, have in wollastonite weathering. The results show that canA is involved in silicate weathering and can be accompanied by carbonation. However, canB is indispensable for the survival of A. nidulans in present ambient conditions (c. 0.04% CO2, v/v), where it is mainly obligated to cellular respiration and biosynthesis. This study highlights the contribution of microbial CAs to regulating the atmospheric CO2 cycle through silicate mineral bio-weathering. It also presents a potential application of sequestration of CO2 via biochemical weathering.

Redox of Fungal Multicopper Oxidase: A Potential Driving Factor for the Silicate Mineral Weathering

Microbial mineral weathering is ubiquitous in nature, but research related to the direct effect of oxidoreductase (e.g., fungal multicopper oxidase) on silicate mineral weathering is rare. This study uses genetic engineering technologies of heterologous expression and gene overexpression and electrochemical methods to examine the effects of multicopper oxidase (McoA) and its gene (mcoA) of Aspergillus niger in the weathering of K+-bearing silicate minerals (KBS). In the experiment of weathering KBS, the mcoA-overexpressed strain showed higher K+-release ability than the wild-type strain, and the heterologous-expressed McoA demonstrated a direct potential to weather KBS and release K+. The electrochemical results showed that the reduction potential of McoA was 0.302 V, and doubled the current of the KBS-modified electrode, meaning that McoA can enhance the electricity transfer in the experiment of weathering KBS. This study confirmed that McoA of A. niger can directly participate in the weathering of silicate minerals, which promotes electron transport at the instable edge of minerals to accelerate mineral weathering. The study will enable greater understanding of the role of oxidoreductase in the biochemical weathering of silicate minerals and identify a possible way to improve the microbial weathering capacity on minerals by genetic engineering manipulation.

Weathering of Reactive Mineral Phases in Landslides Acts as a Source of Carbon Dioxide in Mountain Belts

AbstractBedrock landsliding in mountain belts can elevate overall chemical weathering rates through rapid dissolution of exhumed reactive mineral phases in transiently stored deposits. This link between a key process of erosion and the resultant weathering affects the sequestering of carbon dioxide through weathering of silicate minerals and broader links between erosion in active orogens and climate change. Here we address the effect on the carbon cycle of weathering induced by bedrock landsliding in Taiwan and the Western Southern Alps of New Zealand. Using solute chemistry data from samples of seepage from landslide deposits and river discharge from catchments with variable proportions of landsliding, we model the proportion of silicate and carbonate weathering and the balance of sulfuric and carbonic acids that act as weathering agents. We correct for secondary precipitation, geothermal, and cyclic input, to find a closer approximation of the weathering explicitly occurring within landslide deposits. We find highly variable proportions of sulfuric and carbonic acids driving weathering in landslides and stable hillslopes. Despite this variability, the predominance of rapid carbonate weathering within landslides and catchments where mass wasting is prevalent results at best in limited sequestration of carbon dioxide by this process of rapid erosion. In many cases where sulfuric acid is a key weathering agent, a net release of CO2 to the atmosphere occurs. This suggests that a causal link between erosion in mountain belts and climate change through the sequestration of CO2, if it exists, must operate through a process other than chemical weathering driven by landsliding.

Lithium and its isotopes as tracers of groundwater salinization: A study in the southern coastal plain of Laizhou Bay, China

In the southern coastal plain of Laizhou Bay, due to intensive exploitation of groundwater since the early 1970s, the shallow aquifer has been severely influenced by saltwater intrusion, which causes the extraction to shift from shallow to deeper aquifer changing the hydrogeological condition greatly. This study was conducted to investigate the groundwater salinization using hydrochemistry and H, O and Li isotope data. Dissolved Li shows a linear correlation with Cl and Br in seawater, brine and saline groundwater indicating the marine Li source, whereas the enrichment of Li in surface water, brackish and fresh groundwater is impacted by dissolution of silicate minerals. The analyses of hydrochemistry and isotopes (H, O and Li) indicate that brine originated from seawater evaporation, followed by mixing processes and some water-rock interactions; shallow saline groundwater originated from brine diluted with seawater and fresh groundwater; deep saline groundwater originated from seawater intrusion. The negative correlation of δ7Li and Li/Na in surface water, brackish and fresh groundwater is contrary to the general conclusion, indicating the slow weathering of silicate minerals and hydraulic interaction between surface water and shallow groundwater in this area. The analyses of hydrochemistry and isotopes (Li, H and O) can well identify the salinity sources and isotope fractionation in groundwater flow and mixing, especially groundwater with high TDS. As both mixing with saltwater and isotope fractionation can explain the combination of high δ7Li and low TDS in brackish groundwater, isotope fractionation may limit their use in recognizing salinity sources of groundwater with low TDS.

Controls on the solute geochemistry of subglacial discharge from the Russell Glacier, Greenland Ice Sheet determined by radiogenic and stable Sr isotope ratios

We used radiogenic and stable Sr isotope ratios (87Sr/86Sr and δ88/86Sr) to examine controls on solute acquisition in subglacial discharge from the Russell Glacier, a land-terminating lobe of the Greenland Ice Sheet (GrIS) located in western Greenland. The study focused on two melt seasons in 2014 and 2015. Subglacial discharge 87Sr/86Sr ratios are 13,000 ppm higher than those measured for bedload and suspended sediment digests, and are more similar to those of bedload sediment leachates. These results point to the preferential dissolution of minerals with high 87Sr/86Sr ratios. Analyses of mineral separates from bulk rocks demonstrate that biotite, chlorite, hornblende, and K-feldspar have relatively high 87Sr/86Sr ratios. Subglacial discharge δ88/86Sr values are ∼0.10‰ higher than those for bedload and suspended sediment digests. Isotope fractionation during secondary mineral formation and/or adsorption cannot account for the difference between subglacial discharge and bedrock δ88/86Sr values, as suspended and bedload sediment leachates and digests produced similar δ88/86Sr values and are within the range for bulk silicate Earth. Consistent with the interpretation of 87Sr/86Sr ratios, we attribute the difference to the preferential dissolution of minerals with high δ88/86Sr values. Mineral separates display a wide range of δ88/86Sr values (∼0.40‰). Those having high δ88/86Sr values include hornblende and K-feldspar, as well as apatite and titanite. Taken together, the preferential weathering of predominately silicate minerals explains the Sr isotope geochemistry of subglacial discharge.Subglacial discharge from the Russell Glacier feeds the proglacial Akuliarusiarsuup Kuua River (AKR). Along a 32 km transect of the AKR from the GrIS margin toward the coast, riverine 87Sr/86Sr ratios increase from ∼0.722 to ∼0.747 in an approximately step-wise pattern that corresponds to point-source inputs of additional subglacial discharge. Major cation concentrations and 87Sr/86Sr ratios minimally vary along lengths of the transect with no hydrological inputs. This suggests that proglacial chemical weathering is negligible and likely does not contribute significantly to GrIS solute fluxes.In general, this study supports the recent contention that silicate mineral weathering dominates the solute geochemistry of GrIS subglacial discharge in contrast to valley glaciers, which typically show substantial contributions from carbonate and sulfide weathering regardless of primary bedrock composition. Ice sheet subglacial chemical weathering may therefore have a greater impact on long-term atmospheric CO2 drawdown than previously realized.

Storage and weathering of landslide debris in the eastern San Gabriel Mountains, California, USA: Implications for mountain solute flux

AbstractThe weathering of silicate minerals in mountain landscapes provides a critical source of chemical solutes in the global biogeochemical cycles that sustain life on Earth. Observations from across Earth's surface indicate that the greatest flux of chemical solute is derived from rapidly eroding landscapes, where landsliding often limits the development of a continuous soil cover. In this study, we evaluate how weathering of landslide debris deposits may supplement the chemical solute flux from rapidly eroding, bedrock‐dominated landscapes. We present new measurements of depositional surface and soil morphology, soil geochemistry, and luminescence‐based depositional ages from debris stored in Cow Canyon, a tributary to the East Fork of the San Gabriel River in the eastern San Gabriel Mountains of California. Cow Canyon deposits include locally derived debris emplaced by dry colluvial and debris flow processes. Deposits have planar, low‐angle, sloping surfaces with soils exhibiting a greater degree of weathering than nearby soils formed on bedrock. A ~33–40 ka depositional age of Cow Canyon deposits exceeds the estimated recurrence time for the largest landslides in the San Gabriel Mountains, suggesting the stored landslide debris may be a persistent source of chemical solute in this landscape. To quantitatively explore the significance of landslide debris on the landscape solute flux, we predict the flux of chemical solute from bedrock and debris soils using a generic, time‐dependent model of soil mineral weathering. Our modeling illustrates that debris soils may be a primary source of chemical solute for a narrow range of conditions delimited by the initial landslide debris porosity and the comparative soil age. Broadly, we conclude that while landslide debris may be an important local reservoir of chemical solute, it is unlikely to dominate the long‐term solute flux from rapidly eroding, bedrock‐dominated landscapes. © 2018 John Wiley & Sons, Ltd.

Quantifying anthropogenic contributions to century-scale groundwater salinity changes, San Joaquin Valley, California, USA

Total dissolved solids (TDS) concentrations in groundwater tapped for beneficial uses (drinking water, irrigation, freshwater industrial) have increased on average by about 100 mg/L over the last 100 years in the San Joaquin Valley, California (SJV). During this period land use in the SJV changed from natural vegetation and dryland agriculture to dominantly irrigated agriculture with growing urban areas. Century-scale salinity trends were evaluated by comparing TDS concentrations and major ion compositions of groundwater from wells sampled in 1910 (Historic) to data from wells sampled in 1993–2015 (Modern). TDS concentrations in subregions of the SJV, the southern (SSJV), western (WSJV), northeastern (NESJV), and southeastern (SESJV) were calculated using a cell-declustering method. TDS concentrations increased in all regions, with the greatest increases found in the SSJV and SESJV. Evaluation of the Modern data from the NESJV and SESJV found higher TDS concentrations in recently recharged (post-1950) groundwater from shallow (<50 m) wells surrounded predominantly by agricultural land uses, while premodern (pre-1950) groundwater from deeper wells, and recently recharged groundwater from wells surrounded by mainly urban, natural, and mixed land uses had lower TDS concentrations, approaching the TDS concentrations in the Historic groundwater. For the NESJV and SESJV, inverse geochemical modeling with PHREEQC indicated that weathering of primary silicate minerals accounted for the majority of the increase in TDS concentrations, contributing more than nitrate from fertilizers and sulfate from soil amendments combined. Bicarbonate showed the greatest increase among major ions, resulting from enhanced silicate weathering due to recharge of irrigation water enriched in CO2 during the growing season. The results of this study demonstrate that large anthropogenic changes to the hydrologic regime, like massive development of irrigated agriculture in semi-arid areas like the SJV, can cause large changes in groundwater quality on a regional scale.

Water Resources Sustainability of Ulaanbaatar City, Mongolia

Ulaanbaatar (UB), the capital of Mongolia, is one of the fastest-growing cities in the developing world. Due to increasing demand driven by rapid population and industrial growth, sustainable water resource management is required. Therefore, we investigated sustainability in UB from the perspective of water quality. During five sampling campaigns, we collected 135 water samples (58 from bedrock wells, 44 from shallow wells tapped into the alluvial aquifer, 24 from rivers, and 9 from springs). The hydrochemistry of the water samples was controlled by two major processes: NO3 contamination, and silicate and carbonate mineral weathering. The groundwater samples could be classified into three groups based on their NO3 levels and spatial distribution. Group 1 had natural background NO3 levels (median: 1.7 mg/L) and silicate weathering–dominant water–rock interactions and was distributed in the alluvial aquifer along the floodplain. Group 2 was dominated by carbonate weathering processes, had a maximum NO3 concentration of 47.4 mg/L, and was distributed between the riverbank and upslope area; overall, it reflected ongoing contamination. Group 3 was distributed in the upslope Ger districts and showed significant NO3 contamination (range: 64.0–305.4 mg/L) due to dense and poor living conditions. The stable isotope signatures indicated that the city’s major water supply from riverbank filtration (i.e., Group 1 wells) mixed dynamically with the river; therefore, it showed no sign of NO3 contamination. However, the isotope values and bedrock groundwater quality of wells in Groups 2 and 3 implied that they were closely connected, with the same water source, and showed a strong potential for expanding NO3 contamination toward Group 1 wells. To support sustainable development in UB, the implementation of appropriate institutional measures to protect and preserve water resources, with systematic spatio-temporal monitoring and a focus on Ger districts, is crucial.

Variations of trace elements under hydrological conditions in the Min River, Eastern Tibetan Plateau

In order to better understand the relative importance of hydrologic variation and anthropogenic disturbance and their complex interactions within the trace elemental geochemical cycle, water samples were collected monthly over 1 year in the Min River, eastern Tibetan Plateau, and analyzed for trace element composition. The dissolved trace elements exhibited different relationships with increasing discharge compared with major elements. The elements analyzed can be divided into three groups according to their behavior in response to changing discharge: (1) elements that showed weak positive correlation with discharge, e.g. Cu, V, and Ba; (2) elements that exhibited weak negative correlation with discharge, including Rb, Sr, Pb, Sb, Zn, Cr, Cd, and U; and (3) elements that displayed no significant correlation with variation in discharge, e.g. Ti, Fe, Co, Ni, and As. Cu was strongly affected by anthropogenic activities and flushed into the river with increasing discharge. Ba has a strong solubility in the terrestrial environment, dissolved quickly, and was released into the river. The positive relationship between V concentration and discharge may be attributed to secondary reactions, such as precipitation and adsorption on oxides and aluminosilicate clays. Conservative behavior had an impact on the geochemical behavior of Sr and Rb across hydrologic variation. Pb, Zn, Sb, Cd, and Cr underwent a mild dilution effect connected with anthropogenic activities. The chemostatic behavior of U was regulated by carbonate dissolution and biological uptake. In addition, higher temperatures enhanced biotic activities, affecting the concentrations of Fe and Ni. The relationship between power law slopes and coefficient of variation for discharge and solute concentration suggests that concentrations of trace elements vary significantly with increasing discharge compared with major elements. Silicate mineral weathering had less effect on the fluvial solutes with increasing discharge. Mining activity may exert an additional control on concentration–discharge dynamics of anthropogenic trace elements.

Groundwater dynamics in a hydrologically-modified alpine watershed from an ancient managed recharge system (Sierra Nevada National Park, Southern Spain): Insights from hydrogeochemical and isotopic information

In many of the alpine watersheds of Sierra Nevada (Southern Spain) exists an ancient network of dug canals that collect, transport and facilitate the recharge the snowmelt in the underlying aquifer during the spring season. This practice, known as careos, in the lower part of the watersheds supply drinking water as spring discharge during the dry season. To study how this managed recharge technique modifies the natural response of these basins this work focuses on characterizing the hydrological behavior of one of the sites, the Berchules watershed. The mechanisms for mineralization of groundwater are based on geochemical processes such as evapo-concentration in the soil layer and silicate mineral weathering due to dissolved CO2 originated from both soil biogenic processes and the atmosphere. Groundwater presents a main hydrogeochemical calcium‑magnesium-bicarbonate type facies, which is associated to groundwater flowing through the upper weathered silicates and quickly drained through springs located in the uplands and in the intermediate altitude catchment zone. Additionally, in the lower part of the basin some springs discharge mineralized groundwater with a sodium–calcium–bicarbonate composition associated to regional groundwater flow. In natural conditions, this hydrogeological system behaves as a sloping aquifer, occurring recharge between 1400 and 2500 m a.s.l. The springs discharge groundwater with an isotopic content and temperature in coherence with the local rainfall isotopic and thermal atmospheric altitudinal lines. Nevertheless, once the careo recharge begins the affected springs reveal the fingerprint of the concentrated recharge system by blurring the fingerprint of both the isotopic and thermal altitudinal dependence in the springs discharge. This validates the previous conceptual model and supports average recharge values of 141 ± 140 mm/yr and total average water resources of 181 ± 111 mm/yr which include a 40% increase in the study period due to the effect of the acequias de careo.

Mineralogy and Geochemistry of Limonite as a Weathering Product of Ilvaite in the Yeshan Iron Deposit, Tongling, China

AbstractLimonite is mainly derived from weathering of Fe sulfide, iron-bearing carbonate, or silicate minerals. The weathering of Fe sulfide or carbonate minerals to yield limonite from the Tongling mineralization cluster has been studied extensively. Knowledge of the mineralogical and geochemical characteristics of the limonite from weathering of Fe-bearing silicate minerals is still incomplete, however. To address this, black limonite containing ilvaite (a silicate mineral) found in Yeshan iron deposit, Tongling, China, was studied using mineralogical and chemical analysis. The mineralogical characteristics indicated that Mn goethite was present as nano-granular (&lt;15 nm) or acicular (50–100 nm long, ~10 nm wide, i.e. high length/width ratio) crystals with low crystallinity. Groutite, ramsdellite, and pyrolusite were identified in the limonite as ~5 nm nanoparticles, and coated on the goethite surface. Amorphous Fe-Mn phases and silica were highly developed in the limonite studied. Ilvaite crystals showed idiomorphic granular morphology and were replaced by Fe-Mn oxides/hydroxides; pyrite was also present as inclusions within the ilvaite and the ilvaite structural formula calculated was Ca1.04(Fe1.57Mn0.31Mg0.04)(Fe1.09Al0.01)[Si1.95O]O(OH). According to the relatively high CuO and ZnO values and the low Al2O3 value in the black limonite, the negative correlations between (Fe2O3+MnO) and (CuO+ZnO+BaO), (Fe2O3+MnO) and Al2O3, high Mn and Si contents, and the characteristics of the textural relationships and compositions between the black limonite and ilvaite, a semi-enclosed environment with acidic to weakly alkaline conditions was deduced; ilvaite was found to be responsible for the formation and enrichment of limonite.

Preliminary assessment of groundwater hydrogeochemistry within Gilan, a northern province of Iran.

In four basins of Gilan province, groundwater samples were collected from 127 piezometric wells to investigate the hydrogeochemistry of groundwater, and additionally its suitability for drinking and irrigation purposes. The average concentrations of major cations and anions follow the order of Ca2+ > Na+ > Mg2+ > K+ and [Formula: see text], respectively. Using Piper diagram delineation, CaMgHCO3 was determined as the main hydrogeochemical facies of groundwater. According to Piper diagrams, Gibbs plots, and ionic ratios, silicate weathering and ion exchange are the major processes regulating the groundwater hydrochemistry. Furthermore, saturation indices (SIs) revealed that carbonate precipitation also plays an important role in aquifers. Among the processes, weathering of silicate minerals seems to be the dominant process. Comparing the analyzed major ions and physicochemical parameters with the WHO guideline values indicates that the potability of most groundwater samples is generally acceptable. Electrical conductivity (EC) and total dissolved solid (TDS) measurements along with sodium percentage (SP), sodium adsorption ratio (SAR), Kelley's index (KI), and residual sodium carbonate (RSC) calculations suggest that groundwater in many areas is suitable for irrigation use. Nonetheless, total hardness (TH) values ranging as high as 650.0mg/l reveal many groundwater samples to be classified as hard and very hard, indicating a requirement for long-term monitoring and further evaluation. The present study shows that the groundwater quality in Lahijan, Astaneh, and to a lesser extent Fouman drainage basins is lower than in Talesh. Therefore, intense monitoring programs towards enhanced water management practices are recommended before poorer quality groundwater is further utilized.