Carbonate Weathering Research Articles

Chemical weathering processes in the Chinese Loess Plateau

Covered by erodible loess and affected by significant seasonal climate variations, chemical weathering in the Chinese Loess Plateau (abbreviated as CLP) has important effects on the hydrochemistry of the Yellow River and the global carbon cycle. However, chemical weathering processes in the CLP are still unclear. Based on 296 river water samples in the CLP in the different seasons, hydrochemistry, weathering processes, and their controlling factors were revealed. River waters in the CLP exhibited slightly alkalinity (pH = 8.4 ± 0.5) with much high total dissolved solids (TDS) values (691 ± 813 mg/L). The water types of river water in the CLP were primarily SO42− − Cl− − Na+, HCO3− − Ca2+ − Mg2+, and SO42− − Cl− − Ca2+ − Mg2+. According to the forward model, evaporite dissolution has the largest contribution (55.1% ± 0.2%) to riverine solutes in the CLP, then followed by carbonate weathering (35.6% ± 0.2%) and silicate weathering (6.5% ± 0.1%). For spatio-temporal variations, the contribution of evaporite dissolution in the CLP decreased from northwest to southeast with higher proportion in the dry season, carbonate weathering increased from northwest to southeast with a higher proportion in the wet season, and silicate weathering showed minor spatio-temporal variations. Ca2+ and Mg2+ were affected by carbonate precipitation and/or incongruent calcite dissolution, and about 50% of samples exhibited cation exchange reactions. The physical erosion rate in the CLP, which was 372 ± 293 t·km−2·yr−1, varied greatly and was greater than those of other worldwide rivers. Chemical weathering rates in the CLP showed an increasing trend southward. During the wet season, high runoff led to the release of evaporite and carbonate from loess, while the interfacial reaction kinetic limited the increase of the silicate weathering rates. The CO2 consumption budget by carbonate weathering (6.1 × 1010 mol/yr) and silicate weathering (1.6 × 1010 mol/yr) in the CLP accounted for 0.29% and 0.08% of the global carbon cycle, respectively. Meanwhile, the weathering proportion by sulfuric acids was relatively high with a CO2 release flux of 6.5 × 109 mol/yr. By compiling the data, we propose that the interfacial reaction kinetic and runoff control CO2 consumption rate by silicate and carbonate weathering, respectively. These results contribute to the understanding of modern weathering processes of loess in the CLP, thus helping to deduce the environmental and climatic evolution of the basin.

Spatio-seasonal patterns and sources of major ions in the Longjiang River catchment, Southern China.

River water quality is closely related to the major ion sources and hydrological conditions. However, there is a limited cognition about the geochemical sources and the seasonal variations of major ions. Thus, in this study, a total of 90 water samples were collected from the Longjiang River and its three tributaries in the dry and wet seasons. The samples were analyzed, including major ion concentrations and physicochemical parameters. Statistical analysis, such as correlation analysis and principal component analysis (PCA), was employed to investigate the spatial and seasonal variations in major ion composition and their respective sources. Our study revealed that the predominant major ions in the studied samples are Ca2+, Mg2+, HCO - 3, and SO2 - 4. Most of ions exhibited notable spatial disparities attributable to variations in geological settings and human activities. Regions characterized by igneous rock outcrops tend to exhibit higher levels of K+ and Na+, while areas with higher population densities in the middle and downstream segments show elevated concentrations of Cl-, NO - 3, SO2 - 4, Na+, and K+. The observed peak SO2 - 4 levels may be attributed to active mining operations. Most parameters displayed higher values in flood season than those in dry season due to dilution effects. Stoichiometric analysis indicated that carbonate weathering inputs contribute to over 85% of the mean total cation concentrations in the water, followed by contributions from silicates, atmospheric deposition, and anthropogenic inputs. On the whole, although the water quality remains non-polluted and is suitable for drinking and irrigation purposes, the enrichment of SO2 - 4 and NO - 3 may contribute to water eutrophication. Caution is warranted during the dry season due to reduced water flow resulting from dam interceptions and limited dilution capacity, potentially leading to elevated pollutant concentrations. Taken together, our results provided a scientific basis for water quality managements of monsoon rivers.

Controls on riverine magnesium isotopic composition: Evidence from mono-lithological catchments

The magnesium isotopic composition (δ26Mg) of river water could provide evidence for continental weathering and the global Mg cycle. However, constraining the lithological and isotope fractionation controls on river δ26Mg is still a challenge. Here, we investigated δ26Mg of various compartments in granitic and basaltic catchments, and δ26Mg of river water in sandstone catchments in the Southeastern Tibetan Plateau. Rivers draining sandstone have the lowest δ26Mg values (−1.86‰ to −1.42‰) due to weathering of carbonate which may exhibit as a matrix, cement morphology, and layers crystallized around silicate. The δ26Mg values of river water in granitic and basaltic catchments are −0.72‰ to −0.54‰ and −0.52‰ to −0.30‰, respectively, lower than the soil and plant in the corresponding catchments. Sequestration of isotopically heavy Mg into clays during silicate weathering is predominant and produces a fractionated source of river water with isotopically light Mg. Such Mg isotope fractionation could be affected by denudation rate which changes mineral residence time in these catchments. The strong correlations between Ca/Mg molar ratio, 1/Mg, and δ26Mg value in rivers draining silicate indicate that Mg re-distribution between secondary clays and solutions is proportional to Mg isotope fractionation, the decrease of riverine Mg from silicate weathering will be accompanied by the decrease of riverine δ26Mg. Based on this, a limited impact of Mg isotope fractionation on river δ26Mg is inferred at the continental scale.

Hydrochemical characterization and assessment of health risks of trace elements in the Huai River Basin of China.

Basin water pollution is a global problem, especially in the densely populated areas. The Huai River Basin (abbreviated as HRB), including the Huai River system and the Yishu River system, is the sixth-largest and most densely populated watershed in China. However, there is a lack of comprehensive studies of river and well water throughout the Huai River basin, including hydrochemistry characterization and assessment of health risks. This study investigated water quality and pollution sources of river and well water in the HRB based on the hydrochemistry analysis and different water quality indices. The water body in the HRB showed weak alkalinity (pH = 8.4 ± 0.7) and had high TDS values (TDS = 339 ± 186mg/L) with water types of HCO3-Ca-Mg and SO4-Cl-Ca-Mg in the Huai River system, and SO4-Cl-Ca-Mg in the Yishu River system. Atmospheric input and evaporation had less impact on hydrochemistry. Evaporite dissolution and carbonate weathering had a greater impact on hydrochemistry. Carbonate precipitation and cation exchange also influenced the dissolved solutes, especially Ca2+ and Na+. Samples had low to medium salinity hazards and sodium absorption ratios and were suitable for irrigation. For drinking purposes, samples were fresh water and have good or excellent according to the Water Quality Index (WQI). Land use types influenced water quality with the worst river water quality from cropland. Combining different assessment indices, the water quality of the Yishu River system performed betterthanthe Huai River system. Absolute principal component analysis-multiple linear regression and the positive matrix factorization models identified the main pollutants as As, Ba, Cr, Ni, and Mn, with natural sources of As, Ba, and Ni and anthropogenic inputs of Cr, and Mn. Although the water quality of the HRB has improved in recent years, high potential risk from As, Cr, Mn, Ba, and Ni should be noted. This study provided vital information for basin hydrochemistry analysis and water quality assessment.

Microbial communities modulate chemical weathering and carbon dioxide cycling in an active orogen in Taiwan

Chemical weathering modulates carbon transfer between the crust, hydrosphere, and atmosphere. The extent to which microbial processes are involved in mineral dissolution remains elusive. Here, we performed geochemical and molecular analyses of river water and other materials collected from a rapidly exhuming catchment in eastern Taiwan. In addition to solute generation driven primarily by pyrite-induced carbonate weathering, highly skewed microbial community compositions with abundant Sulfuricurvum and Thiobacillus members were detected during high-water periods. The yields of these taxa were also correlated with those of sulfate and sediments, suggesting that pyrite oxidation and carbonate dissolution were facilitated by sulfur-respiring microorganisms inhabiting erodible materials at a pace comparable to the supply of sulfur-bearing minerals through rapid exhumation. The net CO2 export regulated by such potentially supply-limited, microbially-mediated mineral weathering greatly surpasses the global average, highlighting active orogens in high-standing islands as important CO2 contributors rendered by tandem biotic and abiotic processes.

Leakage of old carbon dioxide from a major river system in the Canadian Arctic.

The Canadian Arctic is warming at an unprecedented rate. Warming-induced permafrost thaw can lead to mobilization of aged carbon from stores in soils and rocks. Tracking the carbon pools supplied to surrounding river networks provides insight on pathways and processes of greenhouse gas release. Here, we investigated the dual-carbon isotopic characteristics of the dissolved inorganic carbon (DIC) pool in the main stem and tributaries of the Mackenzie River system. The radiocarbon (14C) activity of DIC shows export of "old" carbon (2,380 ± 1,040 14C years BP on average) occurred during summer in sampling years. The stable isotope composition of river DIC implicates degassing of aged carbon as CO2 from riverine tributaries during transport to the delta; however, information on potential drivers and fluxes are still lacking. Accounting for stable isotope fractionation during CO2 loss, we show that a large proportion of this aged carbon (60 ± 10%) may have been sourced from biospheric organic carbon oxidation, with other inputs from carbonate weathering pathways and atmospheric exchange. The findings highlight hydrologically connected waters as viable pathways for mobilization of aged carbon pools from Arctic permafrost soils.

Synglacial carbonate records of snowball Earth ocean composition—Evidence from the Nantuo Formation, South China

Abstract The Cryogenian (ca. 717–635 Ma) snowball Earth glaciations ended with the precipitation of “cap” carbonate successions with negative carbon isotope (δ13Ccarb) values, which have been explained by the addition of various 13C-depleted carbon sources in the deglacial process. These arguments assumed that marine dissolved inorganic carbon (DIC) was enriched in 13C in the synglacial ocean. However, this assumption has not yet been tested, because the synglacial ocean chemistry is unknown. In this study, we carried out detailed analyses of the petrology, carbonate carbon (δ13Ccarb) and oxygen (δ18Ocarb) isotopes, organic carbon (δ13Corg) isotopes, major and minor elemental compositions (Ca, Mg, Mn, Fe, Sr), and iron speciation (total Fe, highly reactive Fe, pyrite Fe) of the carbonate layers (also called synglacial carbonate layers) from the Nantuo Formation (ca. 650–635 Ma) on the Yangtze block, South China. Petrographic observations indicated that the synglacial carbonate comprises dolomicrite, mud-crystal powder dolomite, lime dolomite, and dolomitic limestone, supporting an authigenic carbonate origin, and thus, it potentially recorded the ocean chemistry during the Marinoan ice age. The synglacial carbonate is characterized by extreme Mn enrichment, low Fe/Mn ratios, and low δ13Ccarb (−7‰) values. High Mn contents and low Fe/Mn ratios imply marine redox conditions favoring Mn2+ accumulation and Fe2+ oxidation, while low δ13Ccarb values might be attributed to CO2 degassing of submarine volcanoes as well as low primary burial during the glaciation. Since the δ13CDIC value of the synglacial ocean was lower than the δ13Ccarb values of most cap carbonates, we infer the addition of 13C-enriched DIC or removal of 12C during cap carbonate precipitation, such as through carbonate weathering or organic carbon burial. These findings provide new insights into the nature of Cryogenian glaciation, the origin of cap carbonates, and the aftermath of global glaciation.

Geochemical Weathering Variability in High Latitude Watersheds of the Gulf of Alaska

AbstractHigh latitude regions across the globe are undergoing severe modifications due to changing climate. A high latitude region of concern is the Gulf of Alaska (GoA), where these changes in hydroclimate undoubtedly affect the hydrogeochemistry of freshwater discharging to the nearshore ecosystems of the region. To fill the knowledge gap of our understanding of freshwater stream geochemistry with the GoA, we compile stream water chemistry data from 162 stream sites across the region. With an inverse model, we estimate fractional contributions to solute fluxes from weathering of silicate, carbonate, and sulfide minerals, and precipitation. We assess weathering rates across the region and compare them against global river yields. The median fractional contribution of carbonate weathering to total weathering products is 78% across all stream sites; however, there are several streams where silicate weathering is a dominant source of solutes. Weathering by sulfuric acid is elevated in glacierized watersheds. Finally, cation weathering rates are lower in GoA streams compared to the world's largest rivers; however, weathering rates are similar when compared to a global dataset of glacier fed streams. We suggest that hydrologic changes driven by glacier ice loss and increased precipitation will alter river water quality and chemical weathering regimes such that silicate weathering may become a more important source of solutes and sulfide oxidation may decrease. This contribution provides a platform to build from for future investigations into changes to stream water chemistry in the region and other high latitude watersheds.

The Sustained Response of Dissolved Inorganic Carbon to Urban Constructed Wetland in the Fenhe River, China: A Case Study

Sustained wetland utilization has been effective in purifying urban riverine pollutants and promoting sustainable development. However, its effect on water CO2 system remains unclear in semi-arid areas. In this study, seasonal monitoring of the carbonate system was performed at two compared stations, i.e., in constructed wetland (Xiangyun station) and its upstream (Lancun station) in a semi-arid river (the Fenhe River) in China. As indicated by the result of the sustained monthly observation from May 2020 to May 2021, riverine dissolved inorganic carbon (DIC) and partial pressure of CO2 (pCO2) reached 30.9–46.7 mg L−1 and 524–1050 μatm in Lancun station, respectively, whereas the above-described values declined significantly in Xiangyun station with the values of 24.1–39.1 mg L−1 for DIC and 188–873 μatm for pCO2. Compared with the Lancun station where the carbonate system was primarily controlled by natural factors (e.g., carbonate weathering and temperature), significant aquatic photosynthesis and calcification precipitation due to constructed wetland triggered the decrease in DIC and pCO2 and dominated their temporal variation in Xiangyun station. Thus, the large CO2 reduction arising from constructed wetlands may create vital paths for CO2 neutralization and sustainable conservation in urban rivers in arid and semi-arid areas in the future.

Effects of rainfall on the karst-related carbon cycle due to carbonate rock weathering induced by H2SO4 and/or HNO3

To determine the mechanism underlying the effect of rainfall on the karst-related carbon cycle while controlled by that of H2SO4 and/or HNO3, high-resolution monitoring was conducted in Lanhuagou Spring, which is a typical epikarst spring in southwest China. During the monitoring period, the signals from major elements and stable isotopes showed that the CO2 generated by H2SO4 and/or HNO3 entirely escaped from the water. Therefore, the CO2 consumption induced by H2CO3 and CO2 emission induced by H2SO4 and/or HNO3 jointly affected the karst-related carbon cycle. The CO2 consumption induced by H2CO3 dropped following rainfall events and recovered gradually thereafter, which was only affected by the retention time of infiltrating water (dilution effect of rainfall). However, the CO2 emission induced by H2SO4 and/or HNO3 had showed a downward trend from the first rainfall event (R1) to the end of monitoring. The effects of rainfall on CO2 emission induced by H2SO4 and/or HNO3 were related to both the dilution effect and the removal of H2SO4 and/or HNO3. Although the average CO2 consumption induced by H2CO3 dropped from 2.8 mmol/L before rainfall to 2.21 mmol/L thereafter (decreased by 21.07 %), the average CO2 emission induced by H2SO4 and/or HNO3 dropped from 1.29 to 0.49 mmol/L (decreased by 62.02 %); the range of CO2 emission induced by H2SO4 and/or HNO3 decline (0.8 mmol/L) was larger than that of CO2 consumption induced by H2CO3 (0.59 mmol/L), resulting in higher net CO2 consumption (CO2 consumption induced by H2CO3 minus CO2 emission induced by H2SO4 and/or HNO3) after rainfall than before rainfall in the monitoring period. Therefore, in the model used to predict karst-related carbon flux caused by global climate change, it is necessary to consider the impact of rainfall on CO2 emission induced by H2SO4 and/or HNO3. Importantly, the net CO2 consumption rather than CO2 consumption induced by H2CO3, as well as runoff should be considered as two multipliers when carbonate weathering is interfered by H2SO4 and/or HNO3.

Elevated fluoride levels in groundwater in the Himalayan aquifers of upper Indus basin, India: Sources, processes and health risk

Groundwater plays an important role in socio-economics and ecosystem development in mountainous catchments of Himalaya. However, enriched geogenic pollutants in groundwater e.g. Fluoride (F−) and Arsenic (As) in many aquifer systems has deteriorated its suitability for drinking purpose. Although, F− enrichment in other Himalayan basins is well documented but its sources, fate and transport in groundwater of upper reaches of Indus Basin, western Himalaya is still unknown. In the present study, we collected groundwater samples (n = 334) across Upper Indus Basin, (UIB) India to assess the distribution, hydrogeological and geochemical processes controlling the origin, fate and transport of F− in the complex aquifer system. The groundwater is circum-neutral to alkaline with HCO3− -Na+, HCO3−- Ca2+- Na+ and HCO3−- Ca2+- Mg2+ type suggesting the dominance of silicate and carbonate weathering. The results showed that F− enriched groundwater is widespread in the basin with 70% samples having F− above the maximum permissible limit of 1.5 mg/L. High F− groundwater showed distinct hydrochemical evolution attributed to higher pH, HCO3−, Na+, low Ca2+ with Na+/Ca2+ ratio >1 exhibiting F− in groundwater is geogenic, facilitated by the release of Na+ and HCO ions via silicate and carbonate dissolution. F− release in groundwater is also assisted by the incessant dissolution of fluorinated minerals (fluoride) with active exchange between Na+ and Ca+. High HCO3− also facilitates exchange of hydroxides (OH−) and F− on sediment surfaces that contributes to F− enrichment in groundwater through desorption. Geochemical modelling indicated that the precipitation of calcite, dolomite and aragonite is conducive for F− release. F− risk assessment exhibited that people living in UIB are highly vulnerable to the potential risk of dental and skeletal fluorosis. Therefore, it is highly substantial to provide an alternative drinking water source or treat the contaminated water before consumption to mitigate human health hazards.

Hydrochemistry and Irrigation Quality of High-Altitude Lakes: A Case Study of the Ramaroshan Lake Complex, Nepal Himalayas

The Ramaroshan Lake Complex (RLC) in Sudurpaschim Province, Nepal, is a Himalayan lake cluster that holds significant ecological, economic, religious, and esthetic importance. This study aimed to provide a comprehensive characterization of the hydrochemical properties of water within the RLC and assess its suitability for irrigation purposes. A total of 38 water samples were collected from seven different lakes of the complex. The physicochemical parameters and major ions were then analyzed. The water samples from the RLC were alkaline, and based on total hardness, they ranged from soft to moderately hard categories. The presence of major ions included the following: Ca2+ > Na+ > Mg2+ > K+ > Fe3+ > NH4+ and HCO3− > Cl− > SO42− > NO3− > PO43−. The alkaline earth metals (Ca2+ and Mg2+) dominated the alkali metals (Na+ and K+) and weak acids (HCO3−) dominated the strong acids (Cl− and SO42−). The dominant hydrochemical facies of the lake water was a Ca-HCO3 type indicating a calcium carbonate type of lithology. Carbonate rock weathering was the most dominant process in influencing the hydrochemistry of the water. A high ratio of (Ca2++ Mg2+)/Tz+ and a lower ratio of (Na+ + K+)/Tz+ revealed the dominance of Ca2+ and Mg2+ resulting from carbonate weathering, with little contribution from silicate weathering. Different irrigation indices revealed the suitability of the RLC water for irrigation. The insights derived from this study are pivotal in safeguarding water quality and bolstering sustainability efforts. The study also furnishes foundational data crucial to an array of stakeholders including researchers and policymakers and significantly contributes to advancing water management strategies and fostering ecosystem conservation in the Himalayan freshwater lakes, particularly in the face of the overarching challenge posed by global climate change.

Integrating multivariate hydrogeochemical analysis with human health risk assessment: An inverse geochemical and statistical modeling approach

Chandigarh, an urban center meticulously planned in India, partially relies on groundwater for its water supply. However, rapid urbanization, geological heterogeneity, and anthropogenic actions have elevated the significance of ensuring water quality. This research employs advanced methodologies including inverse geochemical modeling through PHREEQC, multivariate statistics, and the Nemerow Pollution Index (NPI) to discern the governing factors influencing water quality. Furthermore, a human health risk assessment evaluates the potential non-carcinogenic impacts of NO3− and F− on human health. Results indicate during PRM (pre-monsoon), 90 % of shallow aquifer samples exceed an NPI value of 1.0, denoting water impurities. In POM (post-monsoon), 70 % of both shallow and deep groundwater samples surpass this threshold. Approximately 70 % of PRM deep groundwater samples and 75 % in POM exhibit “hard water” characteristics. Hydrogeochemistry is primarily influenced by rock-water interactions, corroborated by Gibb's diagram and negative values of chloro-alkaline indices (CAI-I and CAI-II) indicating cation exchange reactions. Piper's plot illustrates a prevailing Ca-Mg-HCO3 hydrochemical facies, with oversaturation of calcite, dolomite, aragonite, and fluorite at varying depths. Saturation indices (SI) affirm calcite oversaturation, implying CaCO3 precipitation and CaF2− dissolution. Additionally, 33 % of PRM and 52.4 % of POM shallow groundwater samples indicate carbonate weathering's influence on mineral content. Principal Component Analysis (PCA) and Pearson's correlation demonstrate contributions from irrigation return flows and anthropogenic activities alongside geogenic factors, enriching Na+, SO42−, NO3−, and Cl− concentrations. The combined statistical and geochemical models offer a comprehensive insight into groundwater geochemistry which will help the policy makers and municipality to manage groundwater resources effectively in the area.

Amplified Production and Export of Dissolved Inorganic Carbon During Hot and Wet Subtropical Monsoon

AbstractUnderstanding the origins and processes of riverine dissolved inorganic carbon (DIC) is crucial for predicting the global carbon cycle with projected, more frequent climate extremes yet our knowledge has remained fragmented. Here we ask: How and how much do DIC production and export vary across space (shallow vs. deep, uphill vs. depression) and time (daily, seasonal, and annual)? How do the relative contributions of biogenic (soil respiration) and geogenic (carbonate weathering) sources differ under different temperature and hydrological conditions? We answer these questions using a catchment‐scale reactive transport model constrained by stream flow, stable water isotopes, stream DIC, and carbon isotope data from a headwater karstic catchment in southwest China in a subtropical monsoon climate. Results show climate seasonality regulates the timing of DIC production and export. In hot‐wet seasons, high temperature accelerates soil respiration and carbonate weathering (up to a factor of three) via elevating soil CO2 and carbonate solubility, whereas high discharge enhances export by two orders of magnitude compared to cold‐dry seasons. Carbonate weathering is driven more by soil CO2 than water flow. At the annual scale, 92.9% and 7.1% of DIC was produced in shallow and deep zone, respectively, whereas 64.5% and 35.5% of DIC was exported from shallow and deep zone, respectively. These results highlight the uniqueness of subtropical karst areas as synchronous reactors and transporters of DIC during the hot‐wet monsoon, contrasting the asynchronous production and export in other climate regions. A future hotter and wetter climate with more intensive storms in the region may further intensify DIC production and export, accentuating the potential of subtropical karst regions as global hot spots for carbon cycling.

Brazil Margin Stable Isotope Profiles for the Last Glacial Cycle: Implications for Watermass Geometry and Oceanic Carbon Storage

AbstractVertical profiles of benthic foraminiferal oxygen and carbon isotopes (δ18O and δ13C) imply the volume of southern source water (SSW) in the Atlantic basin expanded during the Last Glacial Maximum. Shoaling of the boundary between SSW and northern source water (NSW) may reduce mixing between the two watermasses, thereby isolating SSW and enhancing its ability to store carbon during glacial intervals. Here we test this hypothesis using profiles of δ18O and δ13C from the Brazil Margin spanning the last glacial cycle (0–150 ka). Shoaling of the SSW‐NSW boundary occurred during Marine Isotope Stage (MIS) 2, 4, and 6, consistent with expansion of SSW and greater carbon sequestration in the abyss. But the watermass boundary also shoaled during MIS 5e, when atmospheric CO2 levels were comparable to MIS 1. Additionally, we find there was little change in watermass structure across the MIS 5e‐d transition, the first major decline in CO2 of the last glacial cycle. Thus, the overall pattern in glacial‐interglacial geometry is inconsistent with watermass mixing acting as a primary control on atmospheric pCO2. We also find that δ13C values for MIS 5e are systematically lower than MIS 1, with the largest difference (∼1‰) occurring in the upper water column. Low δ13C during MIS 5e was most likely due to a long‐term imbalance in weathering and deposition of calcium carbonate or input of 13C‐depleted carbon from a reservoir external to the ocean‐atmosphere system.

Patterns of distribution of eluvia soils in the oil region of Tatarstan

The article is devoted to the study of eluvial deposits in the southeastern part of the Republic of Tatarstan. As a result of river erosion, a highly dissected and rugged terrain has formed here. Its characteristic elements are erosion-denudation watersheds separated by narrow river valleys and terraced slopes. According to the results of the research, it was revealed that the differences in the structure of weathering profiles in carbonate and terrigenous soil massifs are due to the structural and mineralogical features of rocks that were formed at the stage of sedimentation and subsequent diagenesis. In the central part, on the site of the upper plateau, the rocks underwent mainly physical weathering processes, on the site of the middle plateau – chemical weathering processes, on the site of the lower plateau – physical and chemical weathering processes. Such selectivity in the manifestation of hypergenic processes is due to the predominant lithotypes of sedimentary rocks composing the surfaces of the upper, middle and lower plateaus of the studied territory. Based on the conducted research, the zoning of the studied territory was performed and an engineering and geological map was built. The results obtained made it possible to understand the mechanism of weathering of carbonate and terrigenous rocks, as well as to assess the potential change in their physical and mechanical properties during the construction and operation of buildings and structures.

Hydrochemical and Isotopic Characteristics and the Spatiotemporal Differences of Surface Water and Groundwater in the Qaidam Basin, China

In the context of climate change, precipitation and runoff in the arid inland basins of northwest China have undergone significant changes. The Qaidam Basin (QB) is a typical highland arid inland area. Understanding the spatial and temporal variations in surface water and groundwater chemistry and isotopes, as well as their causes, is crucial for future water resource management and ecological protection. Samples of river, lake, and groundwater, as well as others, were collected and tested in five typical watersheds in the summer and winter. The hydrochemistry and isotopic spatiotemporal differences in various water bodies were studied using the significant difference method, water vapor flux models, hydrochemistry, isotopes, and other methods for cause analyses. The results indicate the following: (1) There are differences in hydrochemistry between the southern and northern basins because the southern basin is more influenced by the dissolution of salt rocks and evaporation, whereas the northern basin is mainly affected by carbonate weathering. (2) The enrichment of δD and δ18O in the northern basin gradually increases from west to east, while in the southern basin, it is the opposite. This is because the southern basin receives a larger contribution of water vapor from the mid-latitude westerlies, while the northern basin primarily relies on local evaporation as its water vapor source. (3) Significant differences are observed in the total dissolved solids (TDS) and hydrochemical types of river water and groundwater between the summer and winter due to higher rates of rock weathering and evaporation in the summer. (4) The more pronounced seasonal differences in hydrogen and oxygen stable isotopes in the southern basin are due to higher rates of internal water vapor circulation in the summer. (5) The similarity in characteristics between river water and groundwater is the result of strong exchanges between river water and groundwater from piedmonts to terminals. The spatiotemporal heterogeneity of terminal lakes is attributed to the accumulation of salts and groundwater replenishment from other sources.

Focused recharge enhances soil carbon leakage and carbonate weathering in groundwater: Implications for subsurface carbon sinks

Soil carbon leakage into groundwater is a crucial and natural carbon sink process in the subsurface carbon cycling. However, the primary driving force for soil carbon downward leakage and the following fate of the carbon in groundwater remains elusive. Here, we investigated multi-seasonal hydrodynamics, hydrogeochemistry and environmental isotopes (δ13C, δ2H and δ18O) in groundwater wells in a humid region. Frequent water-table rise (1 ∼ 3 m) and isotopic signature fluctuation after the concentrated rainfall supported evidence for the occurrence of focused groundwater recharge. We found that focused recharge during the shorter and wetter season induced the increase of groundwater DOC (306.5 ± 231 μmol/L) and CO2 (2154 ± 726.6 μmol/L), the dilution of CH4 (1.75 ± 1.2 μmol/L) and DIC (4486 ± 790.8 μmol/L) as well as depleted δ13C signatures (−17‰ ∼ −18‰). These variations jointly elucidated accelerated soil carbon downward leakage and hydrodynamic mixing driven by focused recharge. Saturation index calculation and PHREEQC simulations confirmed that massive groundwater CO2 from soil carbon leakage during focused recharge exerted positive perturbations on carbonate weathering, and ultimately stored in a more stable form by transforming into HCO3−. Carbon isotope analysis further identified carbonate weathering accounted for approximately one third of DIC dynamics compared to biogenic sources. This study highlights that focused recharge has a disproportional contribution to flushing soil-derived carbon into groundwater and activating carbonate weathering in the groundwater, with important implications for temporal variability of non-negligible subsurface carbon sinks in the global carbon budget.

A holistic assessment of groundwater quality for drinking and irrigation purposes

Abstract This study discusses about suitability of groundwater for drinking and irrigation use in Rohtak district of Haryana (India). The entropy water quality index (EWQI), sodium absorption ratio (SAR), permeability index (PI), Sodium percentage (Na%), Kelly ratio (KR), magnesium adsorption ratio (MAR), US salinity, and Gibbs diagram were analyzed. The spatial maps suggest that groundwater quality in central part extending towards southwestern part of area can be categorized as poor. The major ions were reported in the following order: Mg2+ > Ca2+ > Na+ > K+, and Cl− > SO42− > NO3− > HCO3− > F− > CO32− respectively. Moreover, results revealed that most of groundwater exceeded desirable limits for drinking water. The EWQI assessment indicates that 23.4% and 38.4% of groundwater samples have extremely poor quality in pre-monsoon and post-monsoon, respectively. Further other indices shows that various indices exceed their standard limit, and mostly samples are unsuitable for irrigation. The Gibbs diagram and other bivariate plots demonstrate that various ions in groundwater can be attributed to silicate and carbonate weathering, which occur through water -rock interactions and ion exchange phenomena. In addition, the US Salinity diagram verifies that most groundwater samples exhibit significant salinity hazards, particularly concerning high sodium levels.

Water quality of the southern Tibetan Plateau: hydrogeochemical assessment of the Yarlungzangbo River

The Yarlungzangbo River is the largest river system draining the northern slopes of the Himalayan ranges on the southern Tibetan Plateau and has a crucial role in the supply of water downstream. We investigated the chemical composition of the Yarlungzangbo River and its major tributaries (the Nianchu and Lhasa rivers). Water samples ( n = 165) were collected and analysed for major ions and trace elements. Multivariable analyses showed that the geology and climate are the major explanatory variables for the spatiotemporal variations of the water chemistry in this river system. The water chemistry is mainly controlled by carbonate weathering, with Ca 2+ and HCO 3 − as the dominant ions. Another potential ion source affecting the river water chemistry is the discharge from hot springs, which is rich in Na + , Cl − , SO 4 2− and Li, resulting in higher solute concentrations in the source region and upstream, with the total dissolved solids reaching 176.9 mg L −1 . The concentrations of most trace elements are generally low, although elevated concentrations of As (16.6 μ g L −1 ) and Sb (2.08 μ g L −1 ) are found in the headwaters and additions from untreated wastewater are evident. These concentrations exceed the national drinking water standard for China and the World Health Organization drinking water guideline, posing a risk to people living in both the local and surrounding areas. Supplementary material: The basic field records, water chemical compositions and trace elements of the Yarlungzangbo River and its main tributaries, and concentrations of chemicals of health significance as described by the international guideline (WHO) and the China national guideline (GB) for drinking water quality are available at https://doi.org/10.6084/m9.figshare.c.6850720