Calcite Weathering Research Articles

A pragmatic approach of hydrochemical and irrigation indices of groundwater quality of district Ballia, U.P. India

ABSTRACT In the groundwater aquifer media, enormous amounts of ions can be found naturally in rocks from the Pleistocene and Holocene ages. There are several reports of metals and ionic contamination in the different blocks of the Ballia district. This article focuses on a thorough investigation of the hydrogeochemical properties and the cause of ionic contamination in the Ballia district's groundwater system. This article discusses the interactions between the numerous cations and anions that are hydro-geologically present as well as several physico-chemical factors. The relationship analysis was conducted utilizing irrigation indices and a Stufzand classification, which was further supported by a Durov and Stiff plot. The Durov plot shows the mineralization of the aquifer by sand and evaporates of geological formation. The Gibbs plot shows that the rock–water interaction, weathering of silicates, evaporates dissolution, carbonate dissolution, and anthropogenic activities. The Stiff plot shows the highest concentration of Mg-rich minerals and Cl due to the weathering of calcite, amphiboles, and anthropogenic activities also proven by the Irrigation indices and Stufzand classification. The high water quality index (WQI) value was discovered to be mostly due to greater EC, total dissolved solids, hardness, nitrate, sulfate, chloride, and magnesium levels in groundwater.

Ions release stages of Cu-Pb-Zn mine tailings waste: A column leaching simulation

Characterizing the leaching behavior and temporal variability of tailings is conducive to managing and preventing ionic toxicity to indigenous communities and environment. For this purpose, this work selected Cu-Pb-Zn tailings waste from Huili County, Sichuan province in China, as a research case, conducting a 60-day column leaching experiment to simulate the leaching behavior of the tailings. The results reveal that the weathering features of tailings, both salt-based ions and potential toxic elements (PTEs), could be subdivided into the rapid dissolution stage and carbonate dissolution stage. Additionally, acid rain can accelerate the weathering of calcite and dolomite, as well as the leaching of PTEs. The weathering of calcite precedes that of dolomite. A bulk release of PTEs occurs in the early stages, ranging approximately between 10.9 % and 33.6 % in the initial seven days, with As and Zn showing notable significance. Therefore, ecological effects of this abnormality necessitate thorough examination, given that the release of PTEs occurs over an extended and prolonged duration. Acid rain can promote ion desorption and weathering of major minerals, thereby facilitating the leaching of salt-based ions and PTEs. This study emphasizes the early rapid release stage of ions pollution from tailings, providing a preliminary understanding of the environmental impacts that may arise from tailings deposition and acidic rain leaching.

Hydrochemical characteristics and water quality assessment of natural water in the South China Mountains: the case in Lianzhou.

South China Mountain Region has a well-developed water system with the most abundant water in China. Untreated natural water is the main source of drinking water for the local people. This study aimed to investigate the hydrochemical characteristics and trace element concentrations of natural water in the mountainous regions of South China. In this study, 116 water samples were collected. Traditional hydrochemical methods, water quality index (WQI), hazard index (HI), and nutrient speciation of trace elements (NSTE) were used for analysis. In general, the hydrochemical type was mainly Ca-HCO3- type. The hydrochemical characteristics were mainly influenced by the weathering of calcite and silicate rocks. Overall total dissolved solids (TDS) were low, indicating mainly soft and very soft water. The water that met the standards for mineral water had an average concentration of 59.69mg/L for Sr (strontium) and an average concentration of 0.46mg/L for H2SiO3 (silicic acid). Although the water quality index (WQI) indicated that 91.3% of the water samples in the study area were of good quality (WQI < 25), 2.58% of the water samples had significant non-carcinogenic risk (HI > 1) due to the high As and Pb concentrations. The water in the study area contributed significantly to human intake of Sr, Cr, and V, accounting for 8.4, 8.3, and 7.7% of the required daily intake for adults, respectively. It is recommended that a comprehensive water quality evaluation system be constructed to ensure that mountain water is managed for development and safe to drink.

Effect of damming on hydrogeochemical characteristics and potential environmental risks in a large reservoir: Insights from different vertical layer sampling

The water environment of large reservoirs is fragility due to effects from hydrological regulation of damming and anthropogenic inputs. As a critical path to quantify the natural chemical weathering and assess environmental risks, solute chemistry of river has been widely focused on. However, the complexed hydrological conditions of large reservoir affect the chemical compositions, and the significance of solute vertical geochemistry as an indicator of chemical weathering and water quality health remains explore. Therefore, the Three Gorges Reservoir (TGR) was selected as a typical study area, which is the world's largest hydropower project and subject to frequent water quality problems. Then, the chemical compositions in stratified water were determined. Ca2+ (52.8 ± 4.3 mg/L) and HCO3− (180.9 ± 8.9 mg/L) were the most abundant ions among cations and anions, respectively. Incremental mean concentration of total major ions followed with the increase of riverine depth and flow direction. An improved inversion model was used to quantify the source contribution, which weathering of dolomite (34%) and calcite (38%) contributed the most to total cations, and the influences of agriculture and sewage discharge were limited. Additional contributions of evaporite and pyrite oxidation were found in analysis of deeper water samples, which also results in 2%–67% difference in estimated CO2 release flux using data from different depth, indicating additional information about sulfuric acid driven weathering was contained. Finally, the water quality of the reservoir was assessed for irrigation and non-carcinogenic risks. Results showed the stratified water of TGR can be used as a good water source of irrigation. However, NO3− (5.1 ± 1.1 mg/L) may have a potential non-carcinogenic risk to children, especially in surface water. To sum up, this study provided an indispensable supplement to the water chemistry archives in the TGR basin, serving as theoretical references for environmental management of large reservoirs.

Hydrogeochemical characterization and quality assessment of groundwater resources in the Upper-Doab region of Uttar Pradesh, India

The present study tries to delineate groundwater zones in the Upper-Doab region of Uttar Pradesh, India based on its suitability for the use of domestic and irrigation purposes considering the physico-chemical parameters of groundwater samples (n ∼ 70) using Weighted Arithmetic Water Quality Index (WAWQI) and Composite Groundwater Quality Index for Irrigation (CGQII) methods, respectively. The Upper-Doab region of Uttar Pradesh is bounded by the mighty rivers of Ganga and Yamuna in the east and west respectively. In the southwest, the region shares the boundary with the national capital of Delhi, which has led to an increase in the growth of urbanization and industrialization in the region. These factors have a visible negative impact on the groundwater scenario of the region. Hydrogeochemical investigation reveals that the ionic dominance in the groundwater samples is in the order of HCO3 &amp;gt; Cl &amp;gt; SO4 &amp;gt; NO3 &amp;gt; F and Na &amp;gt; Mg &amp;gt; Ca &amp;gt; K. Chemical history of groundwater samples using piper-trilinear diagram shows that Ca-Mg-HCO3 and Ca-Na-HCO3 type of groundwater is mostly found in this region. Gibb’s plot reveals that rock-water interaction was dominantly controlling the ionic composition of the groundwater in the unconfined aquifer environment. Further, the bivariate plot of (SO4 + HCO3) vs. (Ca + Mg) reveals that the weathering of calcite and dolomite minerals present in the aquifer environment has largely attributed chemical character to the groundwater of the region. The groundwater zoning concerning its domestic and agricultural use reveals that the groundwater of Meerut, Muzaffarnagar, Baghpat, Ghaziabad, and Gautam Buddha Nagar districts have poorer quality of groundwater due to high electrical conductivity and higher concentration of nitrate which has a higher anthropogenic link. The evaluation of groundwater quality for irrigation using a single index value i.e., CGQII makes this study different from the other hydrochemical investigations under similar hydrogeolocal aquifer conditions in the region. The study suggests that corrective measures like, strict implementation of untreated discharge of industrial effluents to the water or groundwater directly, creating awareness among farmers for lesser use of chemical fertilizers, and regular groundwater monitoring systems for quality analysis must be considered for a sustainable future of the region.

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

In order to study the hydrochemical characteristics and ion sources of pore water in the middle and upper reaches of the Mouwen River, 29 groups of pore-water samples were collected in the Laiwu Basin. The main ion characteristics and their controlling factors of pore-water in this area were analyzed by using correlation and principal component analysis, Piper trigram, and Gibbs diagram methods. The main material sources of pore water in this area were revealed. The results showed that HCO3-, NO3-, SO42-, and Ca2+ were the main anions and cations in the pore water of the middle and upper reaches of the Mouwen River. With TDS >1000 mg·L-1 as the standard, the normal water chemistry type was mainly HCO3·NO3·SO4-Ca and HCO3·SO4-Ca·Mg, whereas the abnormal water chemistry type was mainly NO3·Cl-Ca. The chemical evolution of groundwater was mainly influenced by rock weathering, cation alternation adsorption, and human activities. Na++K+ mainly came from silicate weathering and dissolution, and HCO3-, Ca2+, and Mg2+ came from calcite weathering and dissolution involving carbonate and sulfuric acid. Alternation adsorption of cations and weathering of silicate rock provided a surplus of Ca2+ and Mg2+ for pore water. Industrial and mining activities such as domestic sewage mixing, agricultural planting activities, and iron and coal mining changed the chemical composition of pore water, especially NO3- exceeding the standard, which has become the main problem of the local groundwater chemical environment.

Surrogate modelling-assisted comparison of reactor schemes for carbon dioxide removal by enhanced weathering of minerals using seawater

Reactor-based enhanced weathering of minerals represents one of the options for CO2 removal from the atmosphere to control the concentration of greenhouse gases for stabilising the climate. Earlier studies have modelled two reactor types, namely trickle-bed reactor and packed bubble column. However, their CO2 removal potential has not been compared. Building on the previous studies, this work further develops the mechanistic reactor models to enable them to consistently describe continuous weathering of minerals using seawater. Addressing the computational demands of the mechanistic models, a surrogate modelling-based optimisation procedure is developed to allow each reactor type to be rigorously optimised for minimising two competing objectives, namely energy consumption and space requirement. This has allowed the Pareto fronts of the two reactor types to be produced and compared. When applied to calcite weathering which is predominantly controlled by gas–liquid mass transfer, the packed-bubble column has been shown to consistently outperform the trickle-bed reactor, thanks to its superior mass transfer performance. However, when considering the weathering of forsterite, packed-bubble column performance is significantly worsened compared to calcite weathering, primarily because its low dissolution rate shifts the controlling mechanism of the process from gas/liquid mass transfer to solid dissolution. These results provide new insights to inform the future evaluation of reactor-based enhanced weathering schemes in terms of reactor design selection and the implication of mineral types.

Seasonal Differences in the Hydrochemical Characteristics of Karst Wetlands and the Associated Mechanisms in Huixian, China

The present study aimed to identify the seasonal changes in the hydrochemical characteristics of the Huixian karst wetland and the underlying mechanism. Conventional ions and isotopes of 130 groundwater samples collected during the wet and dry seasons were analyzed. The hydrochemical characteristics of groundwater in the Huixian karst wetland were clarified using mathematical statistics and hydrochemical methods, including Durov diagrams, ionic ratios, Gibbs diagrams, and H and O isotopes. The hydrochemical evolution and sources of major ions in the Huixian karst wetland were also investigated. The results showed that cations and anions in groundwater in the study area were dominated by Ca2+ and HCO3−, respectively, sourced mainly from calcite weathering. The ions of some groundwater samples were regulated by weathering of dolomite, dolomitic limestone, and pyrite, resulting in relatively high concentrations of Mg2+ and SO42−. K+, Na+, SO42−, NO3−, and Cl− in groundwater originated from precipitation, Na+ and Cl− originated from domestic sewage, K+ was related to the application of potassium fertilizer in agriculture, and NO3− mainly originated from chemical fertilizer. Groundwater ions were primarily controlled by rock weathering, followed by evaporative concentration. The sources of major ions were dependent on the dissolution and precipitation of carbonate rock, as well as the chemical weathering of silicate rock and evaporite. Samples from the various water sources were scattered on both sides of the local meteoric water line (δD = 3.13δ18O − 13.9), which indicated isotopic composition was affected by evaporation and precipitation.

Controls on riverine calcium isotope ratios during basalt weathering in the Skagafjörður watershed, Iceland

This study examines the Ca isotope (δ44/40Ca) geochemistry of Icelandic rivers with the overall aims of improving the δ44/40Ca tracer, constraining solute sources, and addressing the hypothesis that basalt weathering disproportionately regulates Earth’s long-term climate. We report Ca isotope and elemental data for mainstem rivers, tributary streams, thermal and non-thermal springs, basalt, calcite, soil, vegetation, and sediment collected from the Skagafjörður region in North Iceland. Waters and calcite were further analyzed for their carbon isotope (δ13C) composition, and we conducted experiments to characterize δ44/40Ca values of riverine colloids, the clay-size fraction (<2 µm) of soil, and exchangeable leachates obtained from soil and bedload sediment. The dataset includes analyses of travertine and coexisting water samples collected from a CO2-rich spring (Hvanná river) in South Iceland.Samples show a ∼2‰ range, with groundwater, the ultrafiltered fraction of river water, and hydrothermal calcite producing among the highest δ44/40Ca values and travertine, soil exchangeable Ca, and vegetation the lowest. Riverine δ44/40Ca values are on average ∼0.20‰ higher than those for basalt, which shows minimal isotopic variability. Mainstem glacial-fed rivers entering the Skagafjörður valley from the soil- and vegetation-free highlands have higher δ44/40Ca values than direct-runoff tributaries draining catchments to the north where pedogenesis is more pervasive. Riverine δ44/40Ca values correlate with Sr/Ca and Na/Ca ratios, as well as the saturation index of calcite (SIcal). Riverine δ13C values increase from ∼−8‰ (atmospheric) to ∼−3‰ (calcite) as SIcal values increase from highly-undersaturated to near-equilibrium. One watershed (Svartá river) shows unique trends, where riverine δ44/40Ca values and Sr/Ca ratios do not correlate, and soil exchangeable leachates produced anomalously high amounts of Ca. Clay-size fractions isolated from three horizons composing a brown andosol show slightly lower δ44/40Ca values than bulk basalt, but the values overlap with those for primary minerals. Colloids appear to have lower δ44/40Ca values than truly dissolved Ca. The proxy could be developed as a tracer for colloidal contributions to riverine dissolved loads, especially in soil-mantled catchments where the inputs appear most pronounced. Groundwater δ44/40Ca values correlate with pH, temperature, distance from the coast, and Sr/Ca ratios, all consistent with fractionation control yielding varying degrees of geochemical evolution. The combined riverine patterns largely reflect three-component mixing between basalt weathering, calcite weathering, and hydrothermal water inputs. Subsurface Ca isotope fractionation indirectly impacts riverine δ44/40Ca values by elevating the δ44/40Ca values of groundwater and hydrothermal calcite. This study highlights the significance of hydrothermal water inputs of Ca and HCO3 to Icelandic rivers, which have been previously underappreciated. Mixing calculations suggest that a maximum of ∼20% of the Ca in mainstem rivers derives from surficial basalt weathering. Small tributaries draining the flanks of the valley show the clearest signals of basalt weathering by atmospheric CO2, but these waters have much lower solute concentrations than those employed in previous attempts to estimate basalt weathering rates and parameterize the climate sensitivity of the basalt weathering feedback.

Hydrogeochemical characterization, multi-exposure deterministic and probabilistic health hazard evaluation in groundwater in parts of Northern India

This work attempts to identify the latent factors controlling the hydrogeochemistry and assess the groundwater quality and associated health risks in the intermontane valley of Nalagarh in the sub-Himalayan zone in northern India. Analytical results of 64 groundwater samples, 32 each collected during pre monsoon and post monsoon seasons show contrasting results for their major chemical constituents. During pre monsoon period, only 3% of the samples exceed their permissible limits for pH, EC, TH and Mg2+, while during post monsoon period, different parameters, such as TH, Mg2+ and K+, exceed their limits by 9, 16, and 3%, respectively. Gibbs and Piper diagrams reveal that groundwater chemistry is mainly controlled by water-sediment (alluvial) interaction. Geochemical signatures and saturation index (SI) further indicate that the weathering and dissolution of silicate, calcite and dolomite minerals mainly contributed to dominance of Ca2+, Mg2+ and HCO3 - ions in the aquifers. Monte Carlo simulation ascertains non-carcinogenic health risks due to NO3 − and F− in different sub-population groups. Deterministic and probabilistic estimates of these parameters via ingestion and dermal routes confirm their percentage hazard toxicity in the order infants (58.38; 39.62%) >children (15.62; 15.85%) >teens (6.25; 2.73%) >adults (6.25; 1.90%) for pre monsoon. The hazard toxicity for deterministic study implies only on infants (9.38%), whereas, the probabilistic simulation extracted the health risk on infants (6.57%), and children (0.58%) during post monsoon. Minor populations with their lower body weights are more vulnerable to groundwater pollution due to greater consumption of liquid diet. Therefore, treated groundwater is strongly recommended to mitigate health morbidities linked with the non-cancerous risks.

Potential of enhanced weathering of calcite in packed bubble columns with seawater for carbon dioxide removal

Enhanced weathering of minerals is one option being considered for removing CO2 from the atmosphere to help combat climate change. In this work, we consider the weathering of calcite with seawater in a reactor using air enriched with CO2. A mathematical model of the packed bubble column reactor was constructed with the key mass transfer and chemical reaction components validated with experimental data. The modelling results for a continuous process reveal the performance in terms of the specific energy consumption and the CO2 capture rate, which are affected by parameters including particle size, superficial velocities of gas and liquid, reactor bed height and feed CO2 concentration. The major energy requirements are for pumping liquid and compressing gas, and for CO2 enrichment; energy needed for supplying solid particles (mining operations, transport and comminution) was found to be comparatively minor. A trade-off was possible between ground area requirement (determined by CO2 capture rate) and energy requirement. To capture 1 tonne of CO2 at the reactor, optimal designs were predicted to consume 2.1–2.3 GJ of electricity and occupy 1.8–5.2 m2 year of space, depending on the feed CO2 concentration. These would increase to 5.7–8.2 GJ and 7.1–13.1 m2 year per tonne of CO2 captured, after allowing for degassing of the weathering product in the ocean. This increased energy intensity is still within the range of the CO2 removal options previously reported, while the space requirement quantification provides essential information for future feasibility assessment of this scheme.

Characterization of arsenic contaminated groundwater from central Bangladesh: Irrigation feasibility and preliminary health risks assessment

To observe the current hydro-geo-chemical condition of shallow aquifers and the response from anthropogenic activities as well as to study the arsenic contents and affiliated health risks, groundwater samples from different parts of north-central Bangladesh (Tangail) were studied. In doing so, analytical parameters, including pH, total dissolved solids, electrical conductivity, dissolved oxygen, NO3−, HCO3−, Cl−, SO42-, Na, K, Ca, Mg, Fe, Cr, Mn, Ni, As, Cu, Cd, Zn, and Pb abundances were utilized. Aquifer hydrochemistry presents mainly Ca-Mg-HCO3 type water, while in some cases appreciable amount of Na+ and Cl− proclaim their presences in the formation of groundwater mineralogy. Therefore, there was significant impact from irrigation return flow to affect the groundwater hydrochemistry of this region. Source rock-water interactions in the form of dolomite and calcite weathering is the chief natural agent to provide minerals in the groundwater. The waters in the aquifer seem to be comparatively young with mostly being unsaturated in terms of carbonate minerals and having the scope of reverse ion exchange. Among the trace elements of this study average values of As, Mn, Fe, and Cd were above the guideline values, where As is the dominant contaminant in deteriorating the water quality. In terms of irrigation water indices, groundwater of the studied site is mostly suitable for agricultural usages. Although, magnesium hazard ratio and total hardness values can exert potential threats. However, As level in the studied groundwater possesses potential health hazardous for both non-carcinogenic and carcinogenic risks where children are more vulnerable than adults. The outcome this study invokes regular monitoring of groundwater quality, especially for As contamination to save the public-health.

Alkalinity generation from weathering of accessory calcite and apatite and acid drainage neutralization in an Archean granitoid waste rock

Formation of acid rock drainage is a temporal balance of acid-generating and alkalinity-generating reactions during mineral weathering. Accessory calcite and apatite are commonly present in granitoid rocks, and their weathering can be a source of net alkalinity. To evaluate the acid-consuming capability of the calcite and apatite group minerals in a granitoid waste rock, a humidity cell experiment was conducted with a mix of a high carbonate tonalite and a low carbonate pegmatite representative of the country rock surrounding a kimberlite pipe at the Diavik Diamond Mine in Canada. The alkalinity generated from the tonalite + pegmatite was evaluated through release of Ca and Sr, which indicated a primary alkalinity-generating period during the first 25 weeks of the 80-week experiment. This period represents decomposition of readily available carbonates (infillings) and phosphates (euhedral grains) that release acid-consuming CO3 and PO4 into solution. The total alkalinity—represented by the release of Ca—produced during the first 25 weeks was compared to the total acidity—represented by the release of SO4—produced during the first 25 weeks of a previous humidity cell experiment with an acid-generating (Type III) waste rock from the same site. The easily weathered carbonates and phosphates of the tonalite + pegmatite have the potential to produce sufficient net alkalinity to consume the net acid generated from the early weathering of sulfides in the Type III waste rock. Aqueous extractions performed on post-experiment samples of the tonalite + pegmatite indicate remaining carbonate and phosphate minerals that were not readily available at the experimental ≤6.3 mm size. The heterogeneity of carbonate content and availability in granitic country rock at the mine site are reflective of the variability of accessory calcite in granitoids and indicate a continued need for site-specific determination of alkalinity-generating reactions with the weathering of waste rock.

Intense Chemical Weathering at Glacial Meltwater-Dominated Hailuogou Basin in the Southeastern Tibetan Plateau

Climate warming has caused rapid shrinkage of glaciers in the Tibetan Plateau (TP), but the impact of glacier retreat on the chemical denudation rate remains largely unknown at the temperate glacial basins. The chemical weathering processes were examined at a temperate glacial basin (HLG) in the southeastern TP based on comprehensive data from the supraglacial meltwater, proglacial river water, precipitation and groundwater over two glacier melt seasons in 2008 and 2013. The concentrations of major ions and suspended sediments in river water exhibit a pronounced seasonality and display a close relationship with river discharge, suggesting a strong hydrological control on the chemical and physical weathering processes. Runoff chemistry is dominated by carbonate weathering and sulfide oxidation. HCO3−, Ca2+, and/or SO42− are the dominant ions in meltwater, river water, precipitation and groundwater. For river water, HCO3− and Ca2+ primarily come from calcite weathering, and SO42− is mainly derived from pyrite oxidation. Both solute and sediment fluxes are positively related to river discharge (r = 0.69, p &lt; 0.01 for sediments). The solute flux and yields are 18,095–19,435 t·year−1 and 225–241 t·km−2·year−1, and the sediment load and yields are 126,390 t·year−1 and 1570 t·km−2·year−1, respectively. The solute yields, cationic denudation rate (CDR; 2850–3108 Σ*meq+ m−2·year−1) and chemical weathering intensity (CWI; 616–711 Σ*meq+ m−3·year−1) at HLG are higher than those at most basins irrespective of the lithology, suggesting more intense weathering in the TP in comparison to other glacial basins worldwide.

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.

Hydrochemical characterization of groundwater in the Loja Basin (Ecuador)

Study region: Loja Basin, Ecuador.Loja city is mainly supplied by surface water and solely few places in the city make use of groundwater. For sustainable handling and consumption; development of groundwater inventories, determination of physical and chemical characteristics and the analysis of modifying phenomena and contaminating sources that may affect these waters, is vital. Chemical analyzes were performed on groundwater samples from Loja basin and with all these data, through the use of bivariate diagrams (TDS vs Na/(Na + Ca), TDS vs Cl/(Cl + HCO3), Mg/Na vs Ca/Na and HCO3/Na vs Ca/Na), determine the hydrochemical processes that control the composition of groundwater.New hydrological insights for the region: In Loja basin, the rock-water interaction determines; mostly, the composition of groundwater. The predominant ion in most of these waters was HCO3- followed by Cl-. Ions such as sulfate, bicarbonate, calcium and gypsum come from the weathering of calcite, dolomite and gypsum (Ca + Mg vs. HCO3, SO42- = r2 = 0.93). Silicate weathering also generates an input of calcium, magnesium and sodium to groundwater. Local increases in the K+ and NO3− levels of some sampling points cannot be justified by the interaction with the basin's geological materials so these variations may probably be influenced by anthropic factors such as: domestic wastewater contamination, application of fertilizers and garbage accumulation contiguous to the places where the water emerge. Springs were more affected by anthropogenic activity.

Ecohydrologic feedbacks controlling sizes of cypress wetlands in a patterned karst landscape

AbstractMany landforms on Earth are profoundly influenced by biota. In particular, biota play a significant role in creating karst biogeomorphology, through biogenic CO2 accelerating calcite weathering. In this study, we explore the ecohydrologic feedback mechanisms that have created isolated depressional wetlands on exposed limestone bedrock in South Florida – Big Cypress National Preserve –as a case study for karst biogeomorphic processes giving rise to regularly patterned landscapes. Specifically, we are interested in: (1) whether cypress depressions on the landscape have reached (or will reach) equilibrium size; (2) if so, what feedback mechanisms stabilize the size of depressions; and (3) what distal interactions among depressions give rise to the even distribution of depressions in the landscape. We hypothesize three feedback mechanisms controlling the evolution of depressions and build a numerical model to evaluate the relative importance of each mechanism. We show that a soil cover feedback (i.e. a smaller fraction of CO2 reaches the bedrock surface for weathering as soil cover thickens) is the major feedback stabilizing depressions, followed by a biomass feedback (i.e. inhibited biomass growth with deepening standing water and extended inundation period as depressions expand in volume). Strong local positive feedback between the volume of depressions and rate of volume expansion and distal negative feedback between depressions competing for water likely lead to the regular patterning at the landscape scale. The individual depressions, however, are not yet in steady state but would be in ~0.2–0.4 million years. This represents the first study to demonstrate the decoupling of landscape‐scale self‐organization and the self‐organization of its constituent agents. © 2018 John Wiley &amp; Sons, Ltd.

Hydrogeochemical Processes in a Small Eastern Mediterranean Karst Watershed (Nahr Ibrahim, Lebanon)

Watersheds located in semiarid areas such as the eastern Mediterranean are particularly sensitive to the impact of climate change. To gain knowledge on the hydrogeochemical processes occurring in the Nahr Ibrahim watershed, a Critical Zone Observatory in Lebanon, we analyze the isotopic composition of the river water as well as the concentrations of the major ions exported (Ca2+, Mg2+, HCO3−, Na+, Cl−, K+, SO42−). Sampling campaigns were conducted from March 2014 to August 2016 to capture contrasting hydrological conditions. The results indicate that the carbonate lithology of the watershed is the predominant source of Ca2+, Mg2+ and HCO3−, whereas the low contents of Na+, Cl−, K+, SO42− mainly originate from sea spray. Except in the headwaters, the Nahr Ibrahim River is oversaturated with respect to calcite and dolomite. During wet seasons, calcite weathering and dolomite weathering contribute in an equivalent manner to the solute budget, whereas during dry seasons, calcite precipitates in the river. The isotopic composition of the river water reveals little seasonal dependency, the groundwater recharge by snowmelt infiltration leading to spring waters depleted in heavier isotopes during the dry seasons. A carbonate weathering rate of about 176 t/km2/year was determined at the outlet of the Nahr Ibrahim watershed. The calculated values of CO2 partial pressure, on average twice the atmospheric pressure, suggest that the river is a significant source of CO2 to the atmosphere (111 t/year).

Hydrochemistry and groundwater quality in a semiarid calcareous area: an evaluation of major ion chemistry using a stoichiometric approach.

This study is a wide-ranging evaluation of groundwater within the calcareous semiarid area, Gaziantep in southeast Anatolia, Turkey. The resulting water chemistry data (1) explains the interactions between rock and water, (2) evaluates the quantitative relationships between chemical species (major ions), (3) separates hydrochemical facies, (4) provides information on current water quality for multiple uses, and (5) acts as a benchmark for future research. Relationships between ion concentrations (as meq/L) were analyzed through linear modeling and calculation of coefficients of determination (R2). Stoichiometric calculations were employed to determine the quantitative relationships between ions in groundwater. Calculations between (Ca2++Mg2+) and HCO3- indicated that, even at different concentrations of the total alkaline earth metal ion (M2+), the relative percent remained at 72% for all samples. The majority of Ca2+, Mg2+, and HCO3- ions in groundwater were derived from weathering of calcite, the most common mineral in the local geology. Weathering of dolomite was also important to the contribution of ions in some areas. Ca-HCO3 was found to be the dominant water type for 81% of raw samples; a mixed water type was found in 17% of the samples. The major dissolved components of groundwater are, therefore, Ca(HCO3)2 and, to a lesser degree, Mg(HCO3)2.The sampled groundwater was generally found to meet drinking water quality guidelines for most of the physicochemical quality properties for which standards are available, and with regard to concentrations of Mg2+, Na+, K+, Cl-, SO42-, NO2-, and NH4+. However, NO3-, Ca2+, and HCO3- concentrations in several groundwater samples were in excess of maximum acceptable concentrations (MACs).

Temperature and CO2 dependency of global carbonate weathering fluxes – Implications for future carbonate weathering research

Carbonate weathering and transfer of carbon towards the coastal zone is one of the relevant sinks for atmospheric CO2, controlled by hydrology, ecosystem respiration, river water degassing, and further factors. Specifically, the connection between the soil-rock system to the river systems and instream processes affecting the weathering product fluxes remain under-researched. Based on constraints for soil-rock PCO2, river PCO2, and an identified dependence of river alkalinity on temperature, this work tested which controls should be considered at the global scale to accomplish a more holistic carbonate rock weathering model. Compiled river data suggests that with increasing land temperature, above approximately 11 °C, the amount of instream alkalinity in carbonate catchments decreases due to the temperature effect on the carbonate system, while the converse holds true at lower temperatures. Latter is in accordance with calcite dissolution controlled by soil-rock PCO2 estimates based on ecosystem respiration. In addition, the type of the weathering system (open, semi-closed to closed system with respect to CO2) was identified to be highly relevant for global weathering estimations. Open systems seem to be the most dominant boundary condition of calcite weathering in the soil profile. Tropical areas with thick soil layers, however, cause the carbonate weathering system to shift from open to semi-closed or closed system conditions. The findings support that calcite weathering fluxes in the soil profile are higher than the fluxes to the ocean transported by rivers. Furthermore, an increase in mean land temperature does not necessarily translate into an increase of lateral weathering fluxes because it might have an influence on soil development, discharge, CO2 degassing, soil respiration and calcite dissolution. All these named factors need to be addressed to be able to quantify global carbonate weathering fluxes and to assess the sensitivity of carbonate weathering fluxes on climate variability. Future works should focus on collecting more temporal river chemistry data, mainly in tropical regions, to understand the main mechanism causing the observed decrease of alkalinity concentration with temperature.