CO2-rich Groundwater Research Articles

Geochemical Evolution in Historical Time of Thermal Mineral Springs at Campetti Southwest (Veii, Central Italy) through Geoarcheological Investigation

A multidisciplinary study, involving hydrogeological, geochemical, and mineralogical analyses, was conducted to define the evolution of thermal mineral springs in the Sabatini Volcanic District (SVD) (Central Italy) in a historic period. The outcomes were integrated with the archeological findings to improve the knowledge of the evolution of Veii, a settlement established since the Iron Age and later expanded by Etruscans and Romans. During the archeological excavations, water-related buildings were identified, especially at the Campetti Southwest site in the Veii settlement. Votive inscriptions also suggest the presence of buildings linked to sacred waters, even if a clear definition of the source and type of water is missing. In the SVD, some low-flow thermal mineral springs are present as a result of the mixing of thermal and CO2-rich groundwater from the deep carbonate aquifer and the cold, shallow volcanic aquifer. Mineralogical and chemical analyses characterized the travertine and Fe-hydroxide deposits on Roman tanks and walls in Campetti Southwest and in a nearby ancient Roman bath along the Valchetta River. These deposits showed different relative concentrations of sedimentary and volcanic-related elements, testifying a geochemical evolution of the groundwater mixing and the presence of a paleothermal mineral spring in Campetti Southwest.

Estimating annual CO2 emissions and building a leakage scenario in a tectonically quiescent area

Soil CO2 flux (FCO2) was intensively measured in a natural CO2 emission site located in a tectonically quiescent area, with topographic and geophysical investigation, to estimate annual emissions and causes of focused leaks. FCO2 varied between 6.5 and 2155.4 g/m2/d (median 76.1 g/m2/d; n = 67) within a 612 m2 area situated close to a CO2-rich groundwater well. The threshold value for geogenic FCO2 was determined to be 23 g/m2/d using a Q-Q plot. A FCO2 hotspot was delineated where FCO2 exceeded the threshold. Based on linear regression using air pressure and temperature, the annual CO2 emissions from the hotspot in 2019 were approximately 19 tons/y. According to the 2D electrical resistivity distribution, the subsurface around the well was highly weathered, showing low electrical resistivity (<2000 Ω-m) down to a depth of 50 m, whereas the top layer around the hotspot showed a relatively high electrical resistivity (> 500 Ω-m), implying a resistant unsaturated zone. High signal attenuation and discontinuous and dipping reflectors of ground-penetrating radar signals suggested gaseous CO2 transport through preferential pathways in the resistant near-surface. Based on these and previous hydrochemical results, the extremely high FCO2 in the narrow extent can be explained by a leakage scenario in which the frequent usage of CO2-rich water through the well enhances CO2 degassing, while defects in the well casing accelerate the upward movement of CO2 gas, which flows out through a preferential pathway in the resistant unsaturated zone. This study provides insights into focused leakages through faulty wells and near-surface preferential pathways. In addition, the quantification of annual CO2 emissions through point sources is applicable for assessing natural gas emissions produced by hotspots. The non-negligible emission rate in the hotspot (about 92 g/m2/d) emphasizes the need to quantify natural CO2 emissions in tectonically quiescent areas for risk assessments and carbon budgets.

A review on corrosion of cement-based materials in CO2-rich karst groundwater

In karst areas, groundwater has high concentrations of carbon dioxide. It causes decalcification of cement-based materials by reacting with calcium hydroxide and calcium silicate hydrate. Therefore, the corrosion by CO2-rich groundwater has become a significant concern as it may reduce the service life of concrete structure. Based on the chemical reactions, the corrosion can be divided into leaching corrosion, carbonic acid corrosion, and acid corrosion. Calcium carbonate formation and dissolution are critical steps in corrosion process. The loss of calcium from cement results in cracking and spalling of the cement-based materials. The environmental and material factors had a significant effect on the corrosion rate. Based on the study in simulated karst water, adding supplementary cementitious materials or low-calcium alkali-activated materials can improve the corrosion resistance of the cementitious materials.

Hydrogeological origin of the CO2-rich mineral water of Vilajuïga in the Eastern Pyrenees (NE Catalonia, Spain)

The mineral water of Vilajuïga village in Alt Empordà (NE Catalonia, Spain) owes its uniqueness to an emanation of geogenic CO2 that modifies groundwater hydrochemistry to produce a differentiated HCO3–Na- and CO2-rich groundwater among the usual Ca–HCO3 type found in this region. A hydrogeological conceptual model attributes its occurrence to the intersection of two faults: La Valleta and Garriguella-Roses. The former provides a thrust of metamorphic over igneous rocks, formed during the Paleozoic, over a layer of ampelitic shale that, from a hydrogeological perspective, acts as a confining layer. The Garriguella-Roses normal fault, which originated during the Neogene, permits the degassing of geogenic CO2 that is attributed to volcanic activity occurring in the Neogene. Groundwater mixing from the metamorphic and igneous rock units plus the local occurrence of CO2 creates a HCO3–Na water that still holds free-CO2 in solution. Interaction with the gas phase is restricted at the intersection of the two faults. Radiocarbon dating, after correcting for geogenic dead carbon, estimates an age of 8,000 years BP. The low tritium content (0.7 TU) indicates that Vilajuïga water is a mix of “older” groundwater recharged in the metamorphic rocks of the Albera range and “younger” groundwater from the igneous rocks of the Rodes range, over a recharge area of 45 km2 and a maximum elevation of 600 m. Given its origin as rare groundwater in the southern slope of the Eastern Pyrenees, purposeful monitoring is necessary to evaluate the groundwater vulnerability and anticipate impacts from nearby wells and climate-change effects.

Analysis of a travertine system controlled by the transpressional activity of the Alhama de Murcia fault: The Carraclaca site, eastern Betic Cordillera, Spain

Continental carbonates, such as travertines and tufas, formed from CO2-rich groundwater degassing as it emerges at the Earth’s surface, are often associated with major crustal-scale faults. The Carraclaca site, in the Lorca-Totana section of the Alhama de Murcia Fault, Spain, presents a complex geomorphological landscape controlled by active tectonics. The geology here records the interaction between Quaternary alluvial fans, travertines, and a pop-up structure developed in a transpressional section of the fault. The Alhama de Murcia Fault is an 80 km long left-lateral strike-slip fault that is one of the main seismogenic structures in the Iberian Peninsula. In this work, we examined the relation between travertine precipitation in the Carraclaca site and the tectonic activity of this fault zone through morphological and geochemical studies. The δ13C and δ18O isotopic signals indicate that the carbonate deposits are hydrothermal. In addition, the 87Sr/86Sr ratios in the samples suggest subsurface fluid interaction with the Miocene sediments and the Alpujárride basement, located below the alluvial deposits. Tectonic activity in the Alhama de Murcia Fault might generate the opening of deep water circulation in the crust every time a seismic event occurs, giving rise to hydrothermally derived carbonates precipitation. Deep waters rise and reach the surface interacting with meteoric waters, resulting in travertine formation. Therefore, the Carraclaca carbonate deposits study can inform us about the seismogenic cycle of the fault in the Lorca-Totana section.

&amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C, CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; ∕ &amp;lt;sup&amp;gt;3&amp;lt;/sup&amp;gt;He and &amp;lt;sup&amp;gt;3&amp;lt;/sup&amp;gt;He ∕ &amp;lt;sup&amp;gt;4&amp;lt;/sup&amp;gt;He ratios reveal the presence of mantle gas in the CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;-rich groundwaters of the Ardennes massif (Spa, Belgium)

Abstract. Although natural CO2-rich groundwaters of eastern Belgium have been known for centuries, the exact origin of their gas is still unclear. This paper presents the results of a sampling campaign in Belgium (Spa, Stoumont, Malmedy): 30 samples of both carbogaseous and non-carbogaseous groundwaters were analyzed for major elements, CO2 content and carbon isotopic composition. Among them, 13 samples were also analyzed for 3He/4He and 4He/20Ne ratios. The combination of δ13C (between ca. −9 ‰ VPDB1 and −2 ‰ VPDB), CO2/3He ratio (between 1.9×108 and 2.9×109) and 3He/4He (between 0.92 and 2.70 Ra) shows with a high level of confidence that the CO2 in the carbogaseous groundwater of Spa and Bru has a mantle origin. It can likely be attributed to the degassing of mantle from the neighboring Eifel volcanic fields, located at a distance of 100 km eastwards. The identity and nature of the deep-rooted fractures that act as CO2 transport pathways to the surface are still to be clarified, but several major thrust faults exist in the Rhenish Massif and could connect the Eifel volcanic fields with the studied area.

Physicochemical patterns observed in a groundwater well with CO2 stratification: Learnings from an automated monitoring from South Korean national groundwater monitoring network

Unusual episodic fluctuations of electrical conductivity (EC) were observed twice a year in a national groundwater monitoring network well in South Korea where EC was automatically monitored at a depth of 20 m below ground level (bgl). To address the causes of the observed EC fluctuations, this study examined the depth profile of wellbore water in the 70-meter-deep monitoring well screened between 50 and 70 m bgl and cased down to 50 m bgl. The results of well logging, borehole video recording, and hydrochemical analysis of wellbore water indicated that the CO2-rich groundwater entering through the screened zones below 50 m bgl was physicochemically stratified into three layers with distinct EC that were separated by two transition zones in the well: a bottom layer (70–43 m bgl) with an EC of ∼3900 μS/cm, intermediate layer (35–24 m bgl) of ∼1800 μS/cm, and top layer (16–3 m bgl) of ∼300 μS/cm. The first transition zone at depths of 43–35 m bgl was attributed to CO2 exsolution in the open system and the subsequent physicochemical changes of wellbore water, while the second transition zone at depths of 24–16 m bgl was formed by the precipitation of hydrous ferric oxides with consequent sorption of remaining ions due to a sudden change toward the oxidizing environment. The monitoring probe installed at a depth of 20 m bgl was found to be located within the upper transition zone, which caused EC peaks when the well was purged at a depth of 25 m bgl for well maintenance twice a year. This study shows that automated groundwater monitoring systems may misguide one about the groundwater quality if an unexpected physicochemical variation (such as stratification) occurs in a monitoring well. Therefore, the presence of interface zones caused by abrupt changes in EC must be carefully considered when an automated monitoring well is designed. The screened zone is a suitable location for installing an automated monitoring probe to measure the representative water quality (i.e., EC), in particular, in an aquifer that is under the influence of inputs of low-pH and high-TDS fluids (e.g., CO2-rich groundwater and acid mine drainage).

A hydrogeochemical approach to the characterization of low-enthalpy geothermal systems: the Scordia – Lentini graben (Sicily, Italy)

We describe the geochemical characteristics of groundwater samples collected in 23 water wells located on the northern margin of the Hyblean plateau (East Sicily). This area, mostly made of highly permeable carbonate rocks, is rich in low temperature (T &lt; 50° C) hydrothermal groundwaters, distributed in an active sismogenetic zone, with several ENE-WSW-directed tectonic structures that drove magma to the surface during Upper Pliocene and Pleistocene. The chemical features suggest complex mixing between rainwater, CO2-rich groundwater, steam-heated groundwater and geothermal brines, as highlighted by Principal Component Analysis (PCA). Some parameters, however, indicate widespread pollution of the aquifers from human activities. Stable isotopes analysis confirms the meteoric origin of groundwater and supports the origin of dissolved CO2 mostly from mantle degassing through deep tectonic faults. Geothermometric estimates, mostly based on quartz and Saturation Indexes geothermometers, suggest minimum reservoir temperature between 100 and 120° C.

Geochemical behavior of Mo and W in the CO2-rich mineral waters occurring in the East Elbrus area

Molybdenum and tungsten concentrations in cold CO2-rich mineral groundwaters of east Elbrus area lie in two ranges: 0.01-0.43 ppb and 0.01-410 ppb. The temperature of the water varies from 7.9 to 17.6 °C. Mo concentrations have irregular behaviour with temperature and do not demonstrate a significant correlation with any parameters. Tungsten concentrations are strongly and positively correlated only with As, indicating either common sources or common processes controlling their grades. The highest W concentrations are exclusively associated with Na–HCO3–Cl water types, with a circum-neutral condition (6<pH<7) and lower Eh (-60-+45 mV). The dominant species of Mo and W in mineral waters of eastern Elbrus are molybdate ion (MoO4), and [W7O24]6- polyanion. Based on the risk assessment results, for two potential contaminants (Mo and W), the concentration level of W exceeded the environmental quality standard, which suggests a severe to moderate ecological risk and, therefore, needs to be considered as the priority pollutant for the studied area.

Induced Polarization as a Proxy for CO2-Rich Groundwater Detection—Evidences from the Ardennes, South-East of Belgium

CO 2 -rich mineral groundwaters are of great economic and touristic interest but their origin and circulation paths in the underground are often poorly understood. A deeper understanding of the system plumbery and the development of non—to minimally—invasive near-surface geophysical methods for the prospection of potential productive areas is therefore of great interest to manage future supply. The objective of this contribution is to assess the ability of the time-domain induced polarization (TDIP) method, combined with the electrical resistivity tomography (ERT) method, to make the distinction between CO 2 -rich groundwater from non-gaseous groundwater. Three combined ERT/TDIP tomographies were performed above known uplift zones in the south-east of Belgium where thousands of CO 2 -rich groundwater springs exist. On all profiles, important contrasts in both electrical resistivity and chargeability distributions were observed in the vicinity of the upflow zone, also reflected in the normalized chargeability sections computed from the measured data. Low resistivity vertical anomalies extending in depth were interpreted as a saturated fracture network enabling the upflow of deep groundwater to the surface. High chargeability anomalies appearing directly close to the CO 2 -rich groundwater springs were inferred to metallic oxides and hydroxides precipitation in the upper part of the aquifer, linked to pressure decrease and changing redox conditions in the up-flowing groundwater approaching the land surface. The combined interpretation of electrical resistivity and induced polarization datasets provides a very promising method for a robust prospection of CO 2 -rich groundwater.

Carbonate-bearing phosphohedyphane–“Hydroxylphosphohedyphane” and cerussite: Supergene products of galena alteration in Permian aplite (Western Carpathians, Slovakia)

ABSTRACT A unique assemblage of hedyphane-group minerals of the apatite supergroup associated with galena, cerussite, and calcite occurs in a Permian aplite dike crosscutting orthogneisses belonging to the pre-Alpine basement of the Veĺký Zelený Potok Valley in the Veporic Unit, Western Carpathians, Central Slovakia. The secondary Ca-Pb phosphates include phosphohedyphane Ca2Pb3(PO4)3Cl and (OH)-dominant “hydroxylphosphohedyphane” Ca2Pb3(PO4)3OH. Detailed EPMA and Raman spectroscopy of the hedyphane-group minerals reveal the presence of Pb, Ca, P, and Cl as major constituents; the systematic presence of (CO3)2– (up to 2.6 wt.% CO2calc; 0.65 apfu C) substituting for (PO4)3– (B-type) is the first reported carbonate-bearing phosphohedyphane in nature. There is also significant localized halogen deficiency (0.38–0.49 apfu Cl+F) which suggests the potential for a new mineral, “hydroxylphosphohedyphane”. The secondary assemblage described herein results from very low-temperature sulfide-carbonate reactions and further near-surface supergene alteration of primary magmatic or metamorphic phosphate minerals (mainly apatite) and hydrothermal galena in the alkaline CO2-rich groundwater.

Groundwater mixing in a heterogeneous multilayer aquifer driven by geogenic CO2 fluxes: Evidence from chemical and isotopic composition of Ferrarelle waters (Riardo Plain, southern Italy)

The successful management of carbon in the Earth's crust is critical for mitigating the increase of anthropogenic CO2 in the atmosphere. Carbon Capture and Storage (CCS) requires an understanding of the behavior of carbon in the crust and the development of robust monitoring techniques to constrain the movement, mechanisms, and pathways for any potential CO2 leakage. Here, we examine an aquifer from the Riardo Plain (Campania Region, southern Italy), which serves as a suitable natural analogue for CO2 migration to the critical zone (i.e., shallow crust and aquifers) and as a case study to evaluate the geochemical processes that occur when CO2-saturated fluids mix with freshwater in shallow aquifers. We investigate the behavior of various geochemical constituents (major and trace elements, δ18O–H2O, δ13C-DIC, and Rn content). Water from this area has a high degree of mineralization (EC 2500–3000 μS/cm), high HCO3- (~2.5 g/L), is saturated with respect to CaCO3, and is enriched in alkali ions (e.g., Na+ + K+). The high degree of mineralization occurs in groundwater that discharges from the basal aquifer of the Roccamonfina volcanic edifice (~6 km NW), with vast CO2 inputs that promote host rock leaching. Superficial volcanic aquifers are recharged by fresh meteoric precipitation when groundwater flows from carbonates at the edge of the plain to aquifers hosted in the southeastern slope of the Roccamonfina volcano. The presence of normal faults in this area permits natural upwelling of CO2-rich groundwater, which locally mixes with shallow freshwater present within the upper volcanic succession. Significant (R > 0.8) linear correlations between conservative elements suggest that groundwater geochemistry is dominated by a mixture of two main endmembers: (i) deep/mineralized waters and (ii) shallow/diluted waters. The intrusion of freshwater to volcanic aquifers induces oxidation, leading to adsorption of select elements (e.g., As and Ba) onto Fe-oxyhydroxide precipitates within these aquifers. Geochemical modeling suggests that CO2 saturation approaches 3 g/L, which agrees with direct measurements of CO2 flux. We conclude that our conceptual geochemical model helps to constrain mixing of CO2 with freshwater and to diagnose the secondary geochemical processes that influence aqueous geochemistry within CO2-influenced groundwater.

Evaluating CO2 flux and recharge source in geothermal springs, Garhwal Himalaya, India: stable isotope systematics and geochemical proxies.

Evaluation of geogenic carbon fluxes between solid Earth and its atmosphere is essential to understand the global geological carbon cycle. Some of the key geogenic CO2 suppliers are the magmatic mantle and metamorphic degassing from active and quiescent volcanoes, fault zones, geothermal systems and CO2 rich groundwater. Indian Himalayan geothermal field hosts about 340 geothermal springs in natural as well as artesian condition that eject hot waters and volatiles with varied temperature and chemical composition. These sites provide an opportunity to analyse tectonically driven gas emissions and their impact on regional and global climate. Here we adopt a method for direct measurement of Dissolved Inorganic Carbon (DIC ≈ HCO3) concentration in the geothermal springs to estimate geogenic CO2 flux from an active region based on water discharge and area of geothermal system between the tectonic boundaries of the Main Central Thrust (MCT) and Main Boundary Thrust (MBT) of the Garhwal (Northwest) Himalaya. In the study area, geothermal spring water contain high δ13CDIC ratio (- 8.5‰ to + 4.0‰ VPDB), and among the major ions, bicarbonate (HCO3-) varies by an order of magnitude from 1697 to 21,553μEq/L; chloride and sodium vary from 90 to 19,171μEq/L and 436 to 23181μEq/L. The elevated concentration of Cl- and Na+ in geothermal spring waters suggests affinity towards their deeper origin. These geothermal springs cover a large area of nearly 10,000km2 of the Garhwal region showing a significant discharge of CO2 rich water with an estimated carbon dioxide degassing flux of ~7.2 × 106mol/year to the atmosphere. Considering widespread occurrences of geothermal springs in tectonically active areas worldwide, the proposed direct measurement of DIC may be used as a reliable tool to estimate CO2 fluxes in different active orogenic settings within the Earth system. Results of stable isotopes of δ18O (VSMOW) and δD (VSMOW) in these geothermal spring waters follow the Global Meteoric Water Line (GMWL), suggesting affinity of their recharge through the meteoric origin.

Major and trace element geochemistry of CO2-rich groundwater in the volcanic aquifer system of the Eastern Sikhote-Alin (Russia)

The largest CO2-rich mineral water resource in the Sikhote-Alin ridge of Eastern Russia at Gornovodnoe village was studied. The high-pCO2 groundwaters are cold (5.8–10 °C) with pH 5.9–6.5, TDS varied from 1.2 to 2.7 g/l and belong to Ca–Mg (Ca–Na)–HCO3 type. New data on geology, mineralogy, hydrogeology and hydrogeochemistry, in conjunction with isotope data of water and gas phases, have provided a much better understanding of the origin of this distinctive groundwater. It was found that this water is of meteoric origin, but its unusual chemical composition is controlled by interactions of CO2-rich groundwater and the aquifer materials. The dissolved CO2 gas makes the water slightly acidic (at about pH 6.2) which increased the leaching of many trace elements from host volcanic rocks typically considered immobile at these pH values. 3He/4He ratios and δ13C indicate that mantle degassing is important as a source of deep exogenic fluids. The cold CO2-rich groundwater of the Eastern Sikhote-Alin ridge is the result of interactions between fresh groundwater of meteoric origin, mantle gases and the host volcanic rocks. It thus highlights connectivity between deep and shallow fluids along with deep fractures related to ancient terrane boundaries.

Current travertines precipitation related to artificial CO2 leakages from a natural reservoir (Gañuelas-Mazarrón Tertiary Basin, SE Spain)

In the framework of a natural CO2 reservoir with CO2 leakages as an analogue of a failed CO2 deep geological storage, the current precipitation of travertines and the associated upwelling of CO2-rich saline groundwater were analysed. This natural analogue is located in the Gañuelas-Mazarrón Tertiary Basin (SE Spain). The study comprises of the chemistry of both groundwater and travertines, including stable isotopes, mineralogy and petrography of the travertines, all this performed after a review of the geology of the basin. In this sense, the basin gathers the main features of a safe natural CO2 reservoir in a deep saline aquifer sealed by a thick marl formation. The aquifer was artificially perturbed by the drilling of wells, inducing the travertines precipitation at these water discharge points. Groundwater is saline, slightly acid, oversaturated in aragonite and calcite and with significant concentrations of heavy elements, some of them toxic. From an isotopic viewpoint, the relative constant δ13C-DIC values suggest that carbon is mainly inorganic in origin with minor organic and mantle contributions. Travertines are basically composed of aragonite or calcite, their precipitation being controlled by a sudden CO2 degassing and minor biological activity. Their δ13C signatures indicate that carbon mainly has an inorganic origin, although some contribution of organic carbon must be considered as well. Furthermore, these carbonate deposits did not precipitate in isotopic equilibrium, as determined by δ18O values. Finally, it is suggested that the appearance of travertines along with their carbon isotopic signatures represent efficient tools for detecting CO2 leakages from any CO2 storage site.

Evaluating the geogenic CO2 flux from geothermal areas by analysing quaternary travertine masses. New data from western central Italy and review of previous CO2 flux data

Quantification of carbon fluxes between solid Earth and its atmosphere is necessary to understand the global geological carbon cycle. Some of the main CO2 contributors are metamorphism and magmatic-mantle degassing. CO2 is discharged from active and quiescent volcanoes, fault zones, geothermal systems and CO2 rich groundwater. Here a new method for the estimation of the geogenic flux of CO2 from tectonically active regions, based on the volume, composition and age of travertine deposits, is proposed. The method is applied to the travertine deposits of western Central Italy where travertine deposition is driven by degassing of CO2 charged groundwater.Results show that the study areas are characterized, since Middle Pleistocene, by diffuse CO2 degassing processes with time averaged CO2 fluxes ranging between 1.24 ± 0.12 106 mol y−1 km−2 and 1.38 ± 0.42 106 mol y−1 km−2. These values are of the same order of magnitude of carbon dioxide fluxes measured by different methods in western central Italy and are higher than the global baseline CO2 flux from high heat flow regions.The review of the available 234U/230Th and 14C data shows that the CO2 degassing processes that affects western Central Italy nowadays were already active at least 350 Ka ago, proving that this region is a globally relevant case for the study of Earth degassing.Considering the widespread occurrence of travertine deposits in tectonically active areas worldwide, the proposed approach can be used as a reliable tool to estimate the CO2 flux in different geodynamic settings within system Earth.

Modelling induced bank filtration effects on freshwater ecosystems to ensure sustainable drinking water production

Induced bank filtration (IBF) is a water abstraction technology using different natural infiltration systems for groundwater recharge, such as river banks and lake shores. It is a cost-effective pre-treatment method for drinking water production used in many regions worldwide, predominantly in urban areas. Until now, research concerning IBF has almost exclusively focussed on the purification efficiency and infiltration capacity. Consequently, knowledge about the effects on source water bodies is lacking. Yet, IBF interrupts groundwater seepage and affects processes in the sediment potentially resulting in adverse effects on lake or river water quality. Securing sufficient source water quality, however, is important for a sustainable drinking water production by IBF.In this study, we analysed the effects of five predicted mechanisms of IBF on shallow lake ecosystems using the dynamic model PCLake: declining CO2 and nutrient availability, as well as increasing summer water temperatures, sedimentation rates and oxygen penetration into sediments. Shallow lake ecosystems are abundant worldwide and characterised by the occurrence of alternative stable states with either clear water and macrophyte dominance or turbid, phytoplankton-dominated conditions. Our results show that IBF in most scenarios increased phytoplankton abundance and thus had adverse effects on shallow lake water quality. Threshold levels for critical nutrient loading inducing regime shifts from clear to turbid conditions were up to 80% lower with IBF indicating a decreased resilience to eutrophication. The effects were strongest when IBF interrupted the seepage of CO2 rich groundwater resulting in lower macrophyte growth. IBF could also enhance water quality, but only when interrupting the seepage of groundwater with high nutrient concentrations. Higher summer water temperatures increased the share of cyanobacteria in the phytoplankton community and thus the risk of toxin production. In relative terms, the effects of changing sedimentation rates and oxygen penetration were small. Lake depth and size influenced the effect of IBF on critical nutrient loads, which was strongest in shallower and smaller lakes. Our model results stress the need of a more comprehensive ecosystem perspective including an assessment of IBF effects on threshold levels for regime shifts to prevent high phytoplankton abundance in the source water body and secure a sustainable drinking water supply.

The geochemistry of water and gas phases from high pCO2 sparkling springs within the northern Sikhote-Alin ridge region (Russian Far East)

Two types of cold CO2 rich groundwaters are located within the northern part of the Sikhote-Alin ridge: the first type is a Ca–Mg–HCO3 water with low TDS content (≤ 1.7 g/l) and high concentrations of Fe2+, Mn2+, Ba2+, and SiO2, whilst the second type is a Na–HCO3 water with a high TDS content (≈ 14 g/l) and elevated concentrations of Li+, Btot, Sr2+, Br–, and I–. A notable feature of these waters is a predominance of CO2 in the gas phase (up to 99 vol. %) and low contents of other gases (CH4, N2, O2, etc.). The origins of both water types can be identified on the basis of water (δD, δ18O) and gas (δ13C, 3He/4He, 4He/20Ne) isotopic compositions considered in the context of the geology and hydrology of the region.

Geochemical Fingerprinting of Rising Deep Endogenous Gases in an Active Hypogenic Karst System

The hydrothermal caves linked to active faulting can potentially harbour subterranean atmospheres with a distinctive gaseous composition with deep endogenous gases, such as carbon dioxide (CO2) and methane (CH4). In this study, we provide insight into the sourcing, mixing, and biogeochemical processes involved in the dynamic of deep endogenous gas formation in an exceptionally dynamic hypogenic karst system (Vapour Cave, southern Spain) associated with active faulting. The cave environment is characterized by a prevailing combination of rising warm air with large CO2outgassing (&gt;1%) and highly diluted CH4with an endogenous origin. Theδ13CCO2data, which ranges from −4.5 to −7.5‰, point to a mantle-rooted CO2that is likely generated by the thermal decarbonation of underlying marine carbonates, combined with degassing from CO2-rich groundwater. A pooled analysis ofδ13CCO2data from exterior, cave, and soil indicates that the upwelling of geogenic CO2has a clear influence on soil air, which further suggests a potential for the release of CO2along fractured carbonates. CH4molar fractions and theirδD andδ13C values (ranging from −77 to −48‰ and from −52 to −30‰, respectively) suggest that the methane reaching Vapour Cave is the remnant of a larger source of CH4, which was likely generated by microbial reduction of carbonates. This CH4has been affected by a postgenetic microbial oxidation, such that the gas samples have changed in both molecular and isotopic composition after formation and during migration through the cave environment. Yet, in the deepest cave locations (i.e., 30 m below the surface), measured concentration values of deep endogenous CH4are higher than in atmospheric with lighterδ13C values with respect to those found in the local atmosphere, which indicates that Vapour Cave may occasionally act as a net source of CH4to the open atmosphere.

A Natural Analogue Approach for Discriminating Leaks of CO2 Stored Underground Using Groundwater Geochemistry Statistical Methods, South Korea

Carbon capture and storage (CCS) is one of several useful strategies for capturing greenhouse gases to counter global climate change. In CCS, greenhouse gases such as CO2 that are emitted from stacks are isolated in underground geological storage. Natural analogue studies that can provide insights into possible geological CO2 storage sites, can deliver crucial information about the safety and security of geological sequestration, the long-term impact of CO2 storage on the environment, and the field operation and monitoring requirements for geological sequestration. This study adopted a probability density function (PDF) approach for CO2 leakage monitoring by characterizing naturally occurring CO2-rich groundwater as an analogue that can occur around a CO2 storage site due to CO2 dissolving into fresh groundwater. Two quantitative indices, (QItail and QIshift), were estimated from the PDF test and were used to compare CO2-rich and ordinary groundwaters. Key geochemical parameters (pH, electrical conductance, total dissolved solids, HCO3−, Ca2+, Mg2+, and SiO2) in different geological regions of South Korea were determined through a comparison of quantitative indices and the respective distribution patterns of the CO2-rich and ordinary groundwaters.