Air-saturated Water Research Articles

A larval zebrafish model of cardiac physiological recovery following cardiac arrest and myocardial hypoxic damage.

Contemporary cardiac injury models in zebrafish larvae include cryoinjury, laser ablation, pharmacological treatment and cardiac dysfunction mutations. Although effective in damaging cardiomyocytes, these models lack the important element of myocardial hypoxia, which induces critical molecular cascades within cardiac muscle. We have developed a novel, tractable, high throughput in vivo model of hypoxia-induced cardiac damage that can subsequently be used in screening cardioactive drugs and testing recovery therapies. Our potentially more realistic model for studying cardiac arrest and recovery involves larval zebrafish (Danio rerio) acutely exposed to severe hypoxia (PO2=5-7 mmHg). Such exposure induces loss of mobility quickly followed by cardiac arrest occurring within 120 min in 5 days post fertilization (dpf) and within 40 min at 10 dpf. Approximately 90% of 5 dpf larvae survive acute hypoxic exposure, but survival fell to 30% by 10 dpf. Upon return to air-saturated water, only a subset of larvae resumed heartbeat, occurring within 4 min (5 dpf) and 6-8 min (8-10 dpf). Heart rate, stroke volume and cardiac output in control larvae before hypoxic exposure were 188±5 bpm, 0.20±0.001 nL and 35.5±2.2 nL/min (n=35), respectively. After briefly falling to zero upon severe hypoxic exposure, heart rate returned to control values by 24 h of recovery. However, reflecting the severe cardiac damage induced by the hypoxic episode, stroke volume and cardiac output remained depressed by ∼50% from control values at 24 h of recovery, and full restoration of cardiac function ultimately required 72 h post-cardiac arrest. Immunohistological staining showed co-localization of Troponin C (identifying cardiomyocytes) and Capase-3 (identifying cellular apoptosis). As an alternative to models employing mechanical or pharmacological damage to the developing myocardium, the highly reproducible cardiac effects of acute hypoxia-induced cardiac arrest in the larval zebrafish represent an alternative, potentially more realistic model that mimics the cellular and molecular consequences of an infarction for studying cardiac tissue hypoxia injury and recovery of function.

Dissolution behavior of mixed calcium‑cobalt carbonates at 25 °C in contact with different gas phases

The potential immobilization of cobalt in various environments can be achieved through the incorporation of Co into carbonate minerals, forming solid solutions of (Ca1-xCox)CO3. However, the thermodynamic properties of these minerals are not well-understood due to conflicting data from natural observations and experiments. In this work, a series of mixed calcium‑cobalt carbonates were prepared and their interaction with aqueous solution was investigated. Depending on the Co/(Ca + Co) mol ratio (XCo) of the mixed solution, ranging from 0.00 to 1.00, pure calcite, Co-bearing calcite, Co-bearing aragonite, Ca-bearing spherocobaltite and pure spherocobaltite were successively synthesized using a precipitation method. Upon dissolution of the Co-bearing solids (XCo = 0.10–1.00) in N2-degassed water (NW) and air-saturated water (AW), the Co concentration of the aqueous solutions increased gradually to a stable state of 0.017–0.191 and 0.018–0.186 mmol/L after 240–360 d dissolution, respectively. When the dissolution occurred in CO2-saturated water (CW), the Co concentration initially spiked to 0.372–2.258 mmol/L within 6 h ∼ 15 d and then decreased to a stable range of 0.030–0.559 mmol/L after 240–360 d. The Co/(Ca + Co) mol ratio in the aqueous solution (XCo2+,AS) was significantly lower than the Co/(Ca + Co) atomic ratio in the solids (XCo,SS), particularly when dissolved in NW and AW. During these dissolution processes in NW, AW and CW at 25 °C, the average log IAP values at the final stable state were determined as follows: for calcite (CaCO3), the values were −8.25 ± 0.03 in NW, −8.34 ± 0.11 in AW, and −8.10 ± 0.08 in CW; for spherocobaltite (CoCO3), they were −9.24 ± 0.26 in NW, −9.39 ± 0.23 in AW, and −9.38 ± 0.09 in CW. Furthermore, the log IAP values increased from those typical for calcite to −7.89 ± 0.01 ∼ −7.84 ± 0.10 for the solid with XCo,SS = 0.187 as XCo,SS increased, eventually aligning with those typical of spherocobaltite. Lippmann diagrams, constructed using the Guggenheim parameters a0 = 2.30 and a1 = 0.265 for the “subregular” calcite-spherocobaltite solid solutions [(Ca1-xCox)CO3] with a miscibility gap ranging from XCo,SS = 0.251 to 0.858, highlighted the “peritectic” point at XCo2+,AS = 0.0538 on the solutus. This analysis revealed that the solids dissolved non-stoichiometrically in water. Consequently, the Co-poor aqueous solution would reach equilibrium with the Co-rich calcite-structure phase at the solid surface.

Effect of micro and nanobubble size and concentration on membrane fouling: Strategies for energy-saving and ultrafiltration efficiency enhancement

The impact of micro and nanobubbles (MNBs) on preventing membrane fouling in various filtration techniques has been effectively demonstrated. However, there remains a gap in understanding the influence of their size and concentration on membrane fouling. Moreover, the substantial energy demand for MNBs-aided filtration processes hinders the wide adoption of this technology on a global scale. This study controlled MNB size and concentration by optimizing the release pressure of air-saturated water and introducing intermittent operation schemes. At 0.35 MPa, the MNBs averaged 91 μm and 117.9 nm with concentrations of 3.27E+3 and 6.85E+6 particles mL−1. Increasing the pressure to 0.60 MPa reduced the average size to 31 μm and 119.9 nm. Concentrations to 6.43E+5 and 9.40E+6 particles mL−1. Bubbles released at 0.60 MPa reduced TMP from −0.0109 MPa attained with 0.35 MPa bubbles to −0.0052 MPa making a 70 % decrease. Comparing continuous and optimal intermittent release patterns (30 min) revealed marginal differences: normalized transmembrane pressure (4 %), cleaning efficiency (9 %), and rejection efficiency (2.4 %). Our approach enhances membrane filtration efficiency, maintains performance, reduces energy consumption, and advances sustainable filtration technologies encouraging global adoption.

Groundwater and Dissolved Gases Geochemistry in the Pesaro-Urbino Province (Northern Marche, Central Italy) as a Tool for Seismic Surveillance and Sustainability

The Pesaro-Urbino province (PUP) (northern Marche, central Italy) is one of the most seismically active areas in Italy, with the most recent earthquakes (5.2 and 5.5 Mw) having occurred on 9 November 2022 with an epicenter located in the Adriatic Sea. A detailed geochemical and isotopic characterization of 87 groundwaters (and dissolved gases) circulating in the PUP was carried out to (i) unravel the geochemical processes controlling the water circulation, (ii) investigate the interplay between deep originated fluids and shallow aquifers, (iii) evaluate the reliability of specific geochemical parameters as tracers for seismic activity, and (iv) select the most suitable sampling sites to deploy a monitoring network to highlight possible compositional changes related to the regional and local tectonic activity. The geochemical dataset includes waters showing five different hydrochemical compositional facies: (i) calcium bicarbonate with low Total Dissolved Solids (TDS); (ii) calcium bicarbonate with relatively high concentrations of sulfate (>200 mg/L); (iii) sodium bicarbonate with pH > 8.8; (iv) calcium sulfate; (v) sodium chlorine. Two distinct groups of dissolved gases can be recognized: (a) N2-dominated gases with N2/Ar ratios similar to those of Air-Saturated Water (ASW); (b) CO2- and CH4-rich gases associated with high TDS and springs rich in S-bearing reduced species. The isotopic values of δ13C-CO2 and δ13C-CH4 suggest a predominant biogenic origin for both species with a negligible contribution from deep-seated fluids. The Ca-HCO3(SO4), Ca(Na)-SO4(Cl), and Na-HCO3 waters, being likely related to deep hydrological pathways, are the best candidates to be included in the monitoring network in the Pesaro-Urbino province. This will be of paramount importance in addressing the challenge of unravelling fluid geochemical precursors of earthquakes, thus increasing and improving seismic surveillance practices and hazard mitigation.

Noble gas characteristics of microbial gas in the Qaidam Basin, China: Implications for helium enrichment processes

Helium is a critical, strategic and nonrenewable resource with limited reserves and unstable supplies. However, the helium sources and migration processes in petroliferous basins remain unclear. The Qaidam Basin features multiple reservoir layers, multiple genetic types of natural gas, and varying helium concentrations, providing an ideal natural laboratory for understanding the helium enrichment processes. Here, we present the original noble gas isotopic compositions and major gas components of 11 microbial gas samples from three gas layers in the Sebei No.1 gas field, eastern Qaidam Basin, China. The helium isotopic ratios range from 0.007 to 0.057 Ra, reflecting a predominantly crustal source. The Quaternary Sebei microbial gas features much lower helium concentration (0.0003–0.001%), 21Ne/22Ne ratio (0.031–0.034), and 40Ar/36Ar ratio (292–380) than thermogenic natural gases in the Qaidam Basin. The middle gas layer (II) of the Sebei gas field features higher 21Ne/22Ne and 40Ar/36Ar ratios than the top and bottom gas layers, displaying positive correlations with higher 4He groundwater concentrations before degassing, as calculated from 4He/20Ne ratios and 20Ne concentrations in air-saturated water. However, the correlations between the 4He contents in natural gas and the 21Ne/22Ne and 40Ar/36Ar ratios are unclear, suggesting that 4He dissolves into the groundwater system before degassing into a gas reservoir and that the variations in the 4He concentration in the gas phase are caused by the different levels of hydrocarbon dilution. Quantitative calculations of helium production revealed an external helium flux from the crustal basement except for the in-situ production from sedimentary strata even in this broadly-defined self-generating and self-preserving natural gas system. The helium resources in the Qaidam Basin are mainly distributed in tectonically active zones with uplifted pre-Jurassic basement rocks (providing sufficient helium sources), ancient groundwater systems (accumulating more helium) and suitable hydrocarbon production (acting as a carrier gas but diluting helium as slightly as possible).

Efficient injection of gas tracers into rivers: A tool to study Surface water–Groundwater interactions

Surface water (SW) - groundwater (GW) interactions exhibit complex spatial and temporal patterns often studied using tracers. However, most natural and artificial tracers have limitations in studying SW–GW interactions, particularly if no significant contrasts in concentrations between SW and GW exist or can be maintained for long durations. In such context, (noble) gases have emerged as promising alternatives to add to the available tracer methods, especially with the recent development of portable mass spectrometers, which enable continuous monitoring of dissolved gas concentrations directly in the field. However, long-duration gas injection into river water presents logistical challenges. To overcome this limitation, we present an efficient and robust diffusion-injection apparatus for labeling large amounts of river water. Our setup allows fine, real-time control of the gas injection rate, and is suitable for extended injection durations and different gas species. To illustrate the effectiveness of our approach, we present a case study where helium (He) is used as an artificial tracer to study river water infiltration into an alluvial aquifer. Our injection of He as a tracer increased the dissolved He concentration of the river water by one order of magnitude compared to air-saturated water concentration for 35 days. This experiment yields valuable information on travel times from the river to a pumping well and on the mixing ratios between freshly infiltrated river water and regional groundwater.

Kinetics of Direct Reaction of Vanadate, Chromate, and Permanganate with Graphene Nanoplatelets for Use in Water Purification.

Oxometalates of vanadium(V), chromium(VI), and manganese(VII) have negative impacts on water resources due to their toxicity. To remove them, the kinetics of 0.04 mM oxometalates in natural and synthetic water were studied using graphene nanoplatelets (GNP). The GNP were dispersible in water and formed aggregates >15 µm that could be easily separated. Within 30 min, the GNP were covered with ~0.4 mg/g vanadium and ~1.0 mg/g chromium as Cr(OH)3. The reaction of 0.04 mM permanganate with 50 mg of GNP resulted in a coverage of 10 mg/g in 5 min, while the maximum value was 300 mg/g manganese as Mn2O3/MnO. TEM showed a random metal distribution on the surfaces; no clusters or nanoparticles were detected. The rate of disappearance in aerated water followed a pseudo second-order adsorption kinetics (PSO) for V(V), a pseudo second-order reaction for Cr(VI), and a pseudo first-order reaction for Mn(VII). For Cr(VI) and Mn(VII), the rate constants were found to depend on the GNP mass. Oxygen sorption occurred with PSO kinetics as a parallel slow process upon contact of GNP with air-saturated water. For thermally regenerated GNP, the rate constant decreased for V(V) but increased for Cr(VI), while no effect was observed for Mn(VII). GNP capacity was enhanced through regeneration for V(V) and Cr(VI); no effect was observed for Mn(VII). The reactions are well-suited for use in water purification processes and the reaction products, GNP, decorated with single metal atoms, are of great interest for the construction of sensors, electronic devices, and for application in single-atom catalysis (SAC).

Tolerance threshold of a pelagic species in China to total dissolved gas supersaturation: from the perspective of survival characteristics and swimming ability.

Total dissolved gas (TDG) supersaturation downstream of dams can occur in the Yangtze River basin and is known to cause stress and even death in fish. Consequently, it is important to establish tolerance thresholds of endemic fish to protect local aquatic resources. We conducted experiments to assess survival characteristics and swimming ability of bighead carp, an important commercial fish dwelling in the Yangtze River, to evaluate its tolerance threshold to TDG supersaturation. The typical external symptoms of gas bubble trauma (GBT) were observed and the time when the fish lost equilibrium and died were recorded. The results showed that the mortality occurred when TDG level exceeded 125%, with obvious symptoms such as exophthalmos and bubbles on the head. The interval between loss of equilibrium and mortality decreased with an increase in TDG level. Neither exposure time nor TDG level significantly affected the critical swimming speed (Ucrit) of fish exposed to non-lethal exposure (110%, 120% and 125% TDG) over a 7day period. Significant reductions in Ucrit were found under 130% and 135% TDG conditions when the exposure lasted 52.0h and 42.9h, respectively. The Ucrit also significantly decreased after exposure of 1.6h under 140% TDG condition. Moreover, after exposure to 140% TDG for 39.2h, 135% TDG for 56.5h and 130% TDG for 95.9h, bighead carp were transferred into air saturated water to recover for 24h or 48h; however, swimming performance remained impaired. The results of this study indicate that 125% TDG was the highest TDG level where limited mortality was observed and the swimming ability was not impaired, showing that 125% TDG can be set as the tolerance threshold of this species to guide the operation of dams in the Yangtze River Basin.

Facile synthesis of solar active charcoal passivated Ag3PO4 and their two-channel mechanisms for H2O2 formation in aerated water

This work presents the use of activated charcoal passivated-Ag3PO4 (CAgP) and bare Ag3PO4(AgP) nanoparticles (NPs) as effective photocatalysts for the generation of hydrogen peroxide (H2O2) in air-saturated water containing either formic acid (FA) or silver nitrate (AgNO3). The synthesized CAgP and pristine AgP were characterized using various state-of-the-art optical and electron microscopy techniques. The CAgP composites showed remarkable photocatalyzed H2O2 formation compared to bare AgP NPs. The CAgP photocatalyzed-assisted H2O2 formation from O2-saturated water under sunlight was achieved via two-channel mechanisms. First, in the presence of FA as a hole scavenger, enhanced H2O2 formation was facilitated by the decomposition of FA to produce proton (H+), followed by a spontaneous reduction of dissolved molecular oxygen by the valence band electrons. The second pathway involves the formation of H2O2 in the absence of electrons (using AgNO3 as an electron scavenger) which occurs via the oxidation of H2O by photo-induced holes to generate hydroxyl radicals (•HO) and the combination of •HO radicals to produce H2O2. The most notable feature of CAgP composite as a photocatalyst is the ease of H2O2 formation in O2/H2O and O2/H2O/FA system, as well as the ability to reuse the recovered CAgP catalyst for a few reaction cycles without losing substantial catalytic activity or mass.

Enhanced arsenic(III) sequestration via sulfidated zero-valent iron in aerobic conditions: Adsorption and oxidation coupling processes

Sulfidated zero-valent iron (S-ZVI) has shown significant potential for the removal of arsenic(III). However, little attention has been paid to the mechanism of As(III) sequestration enhancement and how the phase transformation for S-ZVI strengthens this process in aerobic conditions. In this work, sulfidated ZVI was created by ball-milling (S-ZVIbm) and liquid-mixing (S-ZVIlm) of ZVI with elemental sulfur(S0) to investigate the performance and mechanisms of As(III) sequestration in air-saturated water. Sulfidation was found to significantly enhance the As(III) removal rate constant, which was 2.8 ∼ 6.7 times (S-ZVIbm) and 3.1 ∼ 17.1 times (S-ZVIlm) higher than that without sulfidation. FeS was identified as the predominant sulfur species in the S-ZVI samples using S K-edge XANES spectra. The enhanced electron transfer and ZVI corrosion after sulfidation were verified via electrochemical tests. XANES and Mössbauer spectra suggested that lepidocrocite(γ-FeOOH) was the predominant corrosion product generated on the ZVI surface with the presence of oxygen, and DFT calculations further confirmed the improved performance of γ-FeOOH for As(III) sequestration. Besides, As(III) oxidation occurred dominantly on the heterogeneous surface rather than in solution, and the As(III) sequestration pathway of adsorption followed by oxidation was proposed. This study provides new insight into the enhanced As(III) sequestration by S-ZVI in aerobic conditions.

Stable and low-threshold photon upconversion in nondegassed water by organic crystals.

Photon upconversion (UC) is a technology that converts lower-energy photons (longer wavelength light) into higher-energy photons (shorter wavelength light), the opposite of fluorescence. Thus, UC is expected to open a vast domain of photonic applications that are not otherwise possible. Recently, UC by triplet-triplet annihilation (TTA) between organic molecules has been studied because of its applicability to low-intensity light, although the majority of such studies have focused on liquid samples in the form of organic solvent solutions. To broaden the range of applications, solid-state UC materials have been an active area of research. We recently developed air-stable, high-performance molecular UC crystals that utilize a stable solid-solution phase of bicomponent organic crystals. This article begins with a brief overview of previous challenges in developing and improving solid-state TTA-UC materials. Then, we briefly review and explain the concept as well as advantages of our molecular solid-solution UC crystals. We applied these organic crystals for the first time to a water environment. We observed blue UC emission upon photoexcitation at 542nm (green-yellow light) and then measured the excitation intensity dependence as well as the temporal stability of the UC emission in air-saturated water. In nondegassed water, these organic crystals were stable, functioned with a low excitation threshold intensity of a few milliwatts per square centimeter, and exhibited high photo-irradiation durability at least over 40h; indicating that the developed organic crystals are also viable for aqueous conditions. Therefore, the organic crystals presented in this report are expected to extend the domain of UC-based photonic applications in practical water systems including in vivo diagnostic, clinical, and therapeutic applications.

Dissolution and solubility of Pb-substituted calcite, Ca-substituted cerussite and their mixtures at 25 °C

A series of Pb-substituted calcite, Ca-substituted cerussite and their mixtures with the bulk solid Pb/(Ca + Pb) atom fractions (XPbCO3) of 0.00–1.00 were synthesized and their dissolution in water for one year was experimentally studied at 25 °C. During dissolution of the solids (XPbCO3 = 0.01–0.90) in the N2-degassed water and the air-saturated water, the aqueous Pb concentrations increased rapidly to 0.136–2.095 μmol/L in 1 h and 0.140–3.431 μmol/L in 1–6 h, which were followed by a slight decrease-increase fluctuation to a steady state of 0.235–0.961 μmol/L and 0.177–0.483 μmol/L after 300–360 d, respectively. During dissolution in the CO2-saturated water, the aqueous Pb concentrations increased quickly up to the peak value of 1.351–89.107 μmol/L in <12 h, and subsequently declined slowly to a steady state of 0.194–0.515 μmol/L after 300–360 d. The aqueous Pb/(Ca + Pb) molar ratios (XPb2+,aq) declined with time and were considerably lower than the solid XPbCO3. During dissolution in the N2-degassed water, the air-saturated water and the CO2-saturated water, the mean values of log IAP at the steady state (≈log Ksp) were calculated to be −8.55 ± 0.16 ∼ −8.54 ± 0.11, −8.35 ± 0.21 ∼ −8.35 ± 0.17 and − 8.34 ± 0.07 ∼ −8.31 ± 0.13 for calcite [CaCO3]; −13.07 ± 0.53 ∼ −12.97 ± 0.52, −13.23 ± 0.34 ∼ −13.11 ± 0.20 and − 13.56 ± 0.36 ∼ −13.29 ± 0.26 for cerussite [PbCO3], respectively. In terms of the bulk composition, the calcite-type crystals and the cerussite-type crystals, the log IAP values of the solids at the steady state declined almost linearly with the increasing XPbCO3. The highest XPbCO3 value in the calcite-type crystals and the lowest XPbCO3 value in the cerussite-type crystals were measured to be 0.226 and 0.648, respectively. Thereout, the Guggenheim parameters were estimated to be a0 = 0.405 and a1 = −1.49 for the calcite side, and a0 = 1.77 and a1 = −0.474 for the cerussite side of the calcite-cerussite solid solutions. In the Lippmann diagrams constructed for the Calcite–PbCO3 (R3¯c) system, the Aragonite–Cerussite (Pmcn) system and the Calcite–Cerussite system with the estimated Guggenheim coefficients, the solids dissolved non-stoichiometrically and moved gradually up to the quasi-equilibrium curve for the solids with lower XPbCO3, and then along this curve from right to left, approached and crossed the solutus curve and the saturation curve for calcite, and sequentially moved up along the quasi-equilibrium curve for the solids with higher XPbCO3. Finally, the considerably Pb-poor water was simultaneously in equilibrium with both the Pb-richer cerussite-type crystals and the Pb-poorer calcite-type crystals. The result can provide a deeper insight into the environmental and geochemical cycle of lead.

Assessment of austral autumn air–sea CO2 exchange in the Pacific sector of the Southern Ocean and dominant controlling factors

The factors that control the partial pressure of carbon dioxide (pCO2) in the Pacific sector of the Southern Ocean were investigated in April 2018, onboard the icebreaker, ARAON. The mean (± 1σ) of the sea surface pCO2 was estimated to be 431 ± 6 μatm in the north of the Ross Sea (NRS), 403 ± 18 μatm in the Amundsen–Bellingshausen Sea (ABS), and 426 ± 16 μatm in the western Antarctic Peninsula and Weddell Sea (WAP/WS). The controlling factors for pCO2 in the NRS appeared to be meridionally different based on the southern boundary of the Antarctic Circumpolar Current (SB; ~62.5°S in the Ross Sea). The sea surface pCO2 exhibited a strong correlation with salinity and the difference between the O2/Ar (ΔO2/Ar) values of the sample and air-saturated water in the north and south of the SB, respectively. The pCO2 in the ABS and western WAP/WS displayed a strong correlation with salinity. Furthermore, ΔO2/Ar and sea ice formation appear to be the dominant factors that control pCO2 in the Confluence Zone (CZ) and northern parts of WAP/WS. The estimated air–sea CO2 fluxes (positive and negative values indicate the source and sink for atmospheric CO2, respectively) range from 3.1 to 18.8 mmol m−2 d−1 in the NRS, −12.7 to 17.3 mmol m−2 d−1 in the ABS, and −59.4 to 140.8 mmol m−2 d−1 in the WAP/WS. In addition, biology-driven large variations in the air–sea CO2 flux were observed in the CZ. Our results are the most recent observation data acquired in austral autumn in the Southern Ocean.

Evaluating the sources and fate of nitrate in riparian aquifers under agricultural land using in situ-measured noble gases, stable isotopes, and metabolic genes

Riparian zones with their buffering ability and abundant water supply are often subjected to intensive agricultural activities. We investigated a riparian aquifer located near a stream in South Korea that recently experienced sharply decreasing groundwater levels and elevated nitrate (NO3–) concentrations, which were attributed to local agricultural activities. Our goal was to identify the predominant nitrogen sources and NO3– removal processes. Multiple approaches including geochemical and isotopic tracers, land-use analysis, metabolic gene quantification, and inert gas tracers were used to elucidate groundwater and nutrient dynamics in stream-side granitic aquifers. The dual isotopic composition of NO3– identified manure and sewage as the major sources of NO3– contamination. Denitrification was the dominant NO3– removal process in the aquifer, as demonstrated by the negative relationship between δ15N and δ18O values in NO3–and NO3–/Cl–. Denitrification and anammox genes were also observed in microbial communities of the aquifer throughout the study site, suggesting that these processes support effective natural NO3– attenuation in groundwater. A mixing model constructed using a catchment-scale dataset including SiO2 concentrations and δ18O-H2O suggested that mixing with paddy soil water was the major driver of denitrification in the aquifer at the study site, where impervious layers provided anaerobic conditions for natural NO3– attenuation. Denitrification reduced the NO3– flux into the nearby stream by up to 114.4 NO3– kg/ha/y (26 kg N/ha/y). The N2 generated by denitrification did not accumulate in the groundwater, but mostly escaped from groundwater to the atmosphere, as demonstrated by the degassed signature of dissolved inert gases below the air saturated water level. This study identified the predominant NO3– sources and conceptualized N cycling in the heavily developed agricultural riparian aquifer using multiple tracers, demonstrating that NO3– is partially removed through denitrification and possibly anammox while N2 mostly escapes into the atmosphere.

Genesis of the Abunabu antimony deposits in the Tethys Himalayan metallogenic belt: Evidence from He–Ar and S isotopes of stibnite

Introduction: The Abunabu antimony mining area is located between the Indus–Yarlung Tsangpo suture and the southern Tibetan detachment system. Ore deposits in the mining area provide an excellent opportunity to understand the nature and genesis of antimony mineralisation in the Tethys Himalayan metallogenic belt.Methods: In this study, we analysed the He–Ar and S isotopic compositions of stibnite-hosted fluid inclusions as a basis for investigating the sources of ore-forming fluids in the Abunabu mining area and the Tethys Himalayan metallogenic belt.Results: The analysed stibnites have 4He contents of 0.016 × 10−7–1.584 × 10–7 cm3 STP/g, 40Ar contents of 1.37 × 10−7–2.94 × 10–7 cm3 STP/g, 40Ar/36Ar ratios of 303.8–320.7, and 3He/4He (Ra) ratios of 0.021–0.351. These isotopic features indicate that the ore-forming fluids were primarily metamorphic fluids of crustal origin, with small amounts of magmatic-derived materials and modified air-saturated water with low 40Ar*/4He ratios. The δ34S values of stibnite vary within a narrow range of −4.9‰ to −3.5‰, with a mean value of −4.31‰, indicating a deep magmatic origin.Discussion: On the basis of these results and a compilation of data for sulphide deposits in the metallogenic belt, we infer that compositional variations in the He and Ar isotopes of the ore-forming fluids of each antimony deposit in the Tethys Himalayan metallogenic belt are independent of each other. This suggests that antimony deposits in the belt had similar ore-forming fluid sources and mixing processes and that differences in the metallogenic tectonic setting within the belt emerged only in the later stages of deposit evolution. Our new results and compiled data also show that antimony–gold deposits and lead–zinc–antimony polymetallic deposits in the Tethys Himalayan metallogenic belt differ in their sulphur isotopic compositions and that multiple sulphur sources were involved in each of these types of deposit.

Shallow portion of an active geothermal system revealed by multidisciplinary studies: The case of Le Biancane (Larderello, Italy)

The natural park of Le Biancane is located in the southern sector of the Larderello-Travale geothermal field (LTGF). It extends over an approximately 100,000 m2 area where the impermeable caprock is locally absent and deep fluids may directly reach the surface. Through a multidisciplinary approach including measurements of soil CO2 flux (total output of 11.5 t day−1), soil temperature (average 34.4 °C), stable isotope and chemical data on fluids from fumaroles (dominated by a mixture of geothermal gases and air or gases from air-saturated meteoric water), and structural analysis of the formation outcropping, we found that anomalous CO2 emissions are positively correlated with shallow temperature anomalies. These are in restricted locations adjacent to vents and fumaroles, where a network of well-connected fractures (preferentially NW-SE and NE-SW orientated and with steep dips) drains efficiently allowing upward migration of the deep fluids and the energy toward the surface.

Nitrogen, helium, and argon reveal the magmatic signature of fumarole gases and episodes of outgassing from upper-crustal magma reservoirs: The case of the Nisyros caldera (Aegean Arc, Greece)

The chemical composition of gases emitted by active volcanoes reflects both magma degassing and shallower processes, such as fluid-rock hydrothermal interaction and mixing with atmospheric-derived fluids. Untangling the magmatic fluid endmember within surface gas emission is therefore challenging, even with the use of well-known magma degassing tracers such as noble gases. Here, we investigate the deep magmatic fluid composition at the Nisyros caldera (Aegean Arc, Greece) by measuring nitrogen and noble gas abundances and isotopes in naturally degassing fumaroles. Gas samples were collected from 32 fumarolic vents at water-boiling temperature between 2018 and 2021. These fumaroles are admixtures of magmatic fluids typical of subduction zones, groundwater (or air saturated water, ASW), and air. The N2, He, and Ar composition of the magmatic endmember is calculated by reverse mixing modeling and shows N2/He = 31.8 ± 4.5, N2/Ar = 281.6, δ15N = +7 ± 3 ‰, 3He/4He = 6.2 Ra (where Ra is air 3He/4He), and 40Ar/36Ar = 551.6 ± 19.8. Although N2/He is significantly low with respect to typical values for arc volcanoes (1,000–10,000), the contribution of subducted sediments to the Aegean Arc magma generation is reflected by the positive δ15N values of Nisyros fumaroles. The low N2/He ratio indicates N2-depletion due to solubility-controlled differential degassing of an upper-crustal silicic (dacitic/rhyodacitic) melt in a high-crystallinity reservoir. We compare our 2018–2021 data with N2, He, and Ar values collected from the same fumaroles during a hydrothermal unrest following the seismic crisis in 1996–1997. Results show additions of both magmatic fluid and ASW during this unrest. In the same period, fumarolic vents display an increase in magmatic species relative to hydrothermal gas, such as CO2/CH4 and He/CH4 ratios, an increase of ∼50 °C in the equilibrium temperature of the hydrothermal system (up to 325 °C), and greater amounts of vapor separation. These variations reflect an episode of magmatic fluid expulsion during the seismic crisis. The excess of heat and mass supplied by the magmatic fluid injection is then dissipated through boiling of deeper and peripheral parts of the hydrothermal system. Reverse mixing modeling of fumarolic N2-He-Ar has therefore important ramifications not only to disentangle the magmatic signature from gases emitted during periods of dormancy, but also to trace episodes of magmatic outgassing and better understand the state of the upper crustal reservoir.

Progressive crushing 40Ar/39Ar dating of a gold-bearing quartz vein from the Liaotun Carlin-type gold deposit, Guangxi, southern China

Carlin-type gold deposits are among the largest hydrothermal gold deposits in the world. However, direct dating the metallogenic age of these deposits is difficult, because not all deposits provide material suitable for conventional radiometric methods. Syn-mineralization stage quartz veins from these deposits usually contain abundant fluid inclusions, which allow fluid inclusion 40Ar/39Ar dating. In this study, progressive crushing 40Ar/39Ar dating has been performed on a gold-bearing quartz vein from the Liaotun Carlin-type gold deposit in northwestern Guangxi, China. Argon isotopes liberated from the later steps yielded an isochron age of 200.7 ± 2.1 Ma. We infer that Ar-bearing gas was extracted from the primary fluid inclusions, and that the age of ca. 200.7 Ma reflects the timing of gold mineralization. The initial 40Ar/36Ar ratio corresponding to the isochron is 298.0 ± 4.3, which is statistically indistinguishable from the value for air, indicating that the ore-forming fluids probably mainly derived from gravitational pressure flow in the basin of air-saturated water. Our preliminary study shows the feasibility and great potential of 40Ar/39Ar dating of gases from fluid inclusions by progressive crushing of quartz veins to date the mineralization age and decipher the fluid origins of Carlin-type gold deposits.

Unraveling the origin of geothermal heat in absence of recent volcanism: The Santiago Papasquiaro hydrothermal area, Central-Eastern Sierra Madre Occidental, México

In western Mexico, the central part of the Sierra Madre Occidental (SMO) large igneous province hosts several thermal springs with groundwater temperatures up to 74 ºC within late Eocene to Oligocene extensional structures. Given that in this region the last pulse of silicic volcanism ended >30 Ma ago this hydrothermal activity cannot be associated with cooling magma chambers and/or ongoing crustal thinning as in conventional geothermal sites. A possible explanation for the anomalous water temperature includes two non-mutual excluding processes: 1) heat production by radioactive decay of abundant U, Th, K radioisotopes in the silicic rocks forming the upper crust of the SMO and accumulated below the low conductive sediments filling the tectonic depressions, and 2) water heating by convection through deeply rooted faults. To prove this hypothesis, we studied the Santiago Papasquiaro hydrothermal area, located at the intersection between the NNW trending Santiago Papasquiaro half-graben and the NW trending San Luis-Tepehuanes fault system. We provide a detailed stratigraphy of the area supported by new U-Pb ages and we estimated heat production with in-situ gamma ray measurements of radioelements (U, Th, K), and groundwater He isotopes analyses.The stratigraphy of the region consists of 1) a Late Cretaceous-Paleocene continental volcanosedimentary succession (Garame Group), 2) Early Eocene rhyolitic lavas and ignimbrites, 3) Late Eocene volcanosedimentary succession, 4) Late Eocene-Early Oligocene pyroclastic succession capped by rhyolitic lavas and domes, and 5) a siliciclastic succession (Papasquiaro Formation) filling the graben interbedded with minor basaltic lavas (∼12–11 Ma) in its upper part. We also mapped two intermediate composition intrusive bodies, a Late Cretaceous (66 Ma) granodiorite and a Late Eocene (∼39 Ma) diorite.Heat production values are in the range of 1 µWm−3 to 8 µWm−3, with extreme values up to 310 µWm−3 for carbonaceous beds within the Garame Group. Late Cretaceous to Eocene volcanosedimentary and volcanic successions have lower heat production values than the Oligocene volcanic succession and the Oligocene-Quaternary siliciclastic succession. As a whole, heat production of Santiago Papasquiaro rocks exceeds the average for the upper crust as well as that of continental granite/rhyolite, being in the range of the high heat production granites worldwide, and above plutonic and volcanic rocks from other areas of Mexico. Noble gasses isotopes show a major crustal radiogenic input (79.4–96.1%), consistent with the radiogenic heat source hypothesis for the thermal springs, and a secondary mantle input (1.9 – 9.4%), which can be related to the ascent of mantle fluids through a deep crustal zone at the intersection of the regional structures. The isotopic He composition differs from the volcanic geothermal systems of Mexico such as Los Azufres, Los Humeros and from the unconventional geothermal area of the Juchipila Graben, located 300 km southeast in the same tectonic setting. The first two nearly represent a binary mixture between mantle and air saturated water end-members, whereas the latter also includes a minor crustal signal. Modeling of He isotopes data confirm that the 3He signature is associated to the ascent of mantle fluids through a deep crustal zone of highly fractured rocks at the intersection of regional structures. The signal of mantle fluids is diluted over the time by 4He sourced from the Oligocene high-heat production rocks.

Dissolution of the smithsonite–rhodochrosite (ZnCO3-MnCO3) solid solutions in aqueous solution at 25 °C

A series of smithsonite-rhodochrosite solid solutions [(Zn1-xMnx)CO3] (XMn = 0.00–1.00) were prepared in lab to study their dissolution process in aqueous solution. The molar ratios Mn/(Zn + Mn) of the synthetic solids (XMn) were very close to that of the starting mixtures. The X-ray diffraction (XRD) patterns of the synthetic solids showed continuously peak shifting to lower 2θ value with the increasing of XMn. For the dissolution in the nitrogen-degassed and the air-saturated water, the Zn and Mn contents in aqueous phase went up quickly to a constant value; after dissolution, the weak (200) peak of Zn5(CO3)2(OH)6 (hydrozincite) emerged in the XRD patterns of the solids with XMn = 0.00–0.30. For the dissolution in the carbon-dioxide-saturated water, the Zn and Mn contents in water reached high values quickly after 48 h ~ 120 h, and then declined to a stable value. After 270 d of dissolution, the aqueous molar ratios Mn/(Zn + Mn) were greater than or close to XMn of the corresponding solids. For the dissolution in the nitrogen-degassed, the air-saturated and the carbon-dioxide-saturated waters at 25 °C, the mean log IAP values (ion activity product) at the equilibrium state (≈ solubility product log Ksp) were determined to be −10.56, −10.54 and − 10.71 for smithsonite, and − 10.29, −10.26 and − 10.18 for rhodochrosite, respectively. With the increasing of XMn, the log IAP values increased non-linearly from −10.54 ~ −10.71 to −10.18 ~ −10.29, while the ΔGf° decreased linearly from −735.08 to −736.04 kJ/mol and − 813.99 to −814.63 kJ/mol. The constructed Lippmann diagrams showed that the (Zn1-xMnx)CO3 solid solutions dissolved incongruently, and the dissolution data points moved progressively up and exceeded the solutus curve, and then move along the (Zn1-xMnx)CO3 saturation curves from left to right or right to left for the solids with lower XMn (0.10–0.30) and higher XMn (0.40–0.90), respectively.