In-situ measurements of dissolved gases in xylem sap as tracers in plant physiology.

Trees transport gases from below ground into the atmosphere through the process of transpiration. Tracing gases transported through this mechanism continuously and under field conditions remains an experimental challenge. Here we measured gases dissolved in tree sap in-situ and in real time, aiming to simultaneously analyse the transport of several gases (He, Ar, Kr, N2, O2, CO2) from the soil, through the trees, into the atmosphere.

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.

Lake surface cooling drives littoral-pelagic exchange of dissolved gases.

The extent of littoral influence on lake gas dynamics remains debated in the aquatic science community due to the lack of direct quantification of lateral gas transport. The prevalent assumption of diffusive horizontal transport in gas budgets fails to explain anomalies observed in pelagic gas concentrations. Here, we demonstrate through high-frequency measurements in a eutrophic lake that daily convective horizontal circulation generates littoral-pelagic advective gas fluxes one order of magnitude larger than typical horizontal fluxes used in gas budgets.

In-situ experiment reveals CO enriched fluid migration in faulted caprock.

The sealing characteristics of the geological formation located above a CO storage reservoir, the so-called caprock, are essential to ensure efficient geological carbon storage. If CO were to leak through the caprock, temporal changes in fluid geochemistry can reveal fundamental information on migration mechanisms and induced fluid-rock interactions. Here, we present the results from a unique in-situ injection experiment, where CO-enriched fluid was continuously injected in a faulted caprock analogue.

Quantifying Carbon Cycling across the Groundwater-Stream-Atmosphere Continuum Using High-Resolution Time Series of Multiple Dissolved Gases.

The quantification of carbon cycling across the groundwater-stream-atmosphere continuum (GSAC) is crucial for understanding regional and global carbon cycling. However, this quantification remains challenging due to highly coupled carbon exchange and turnover in the GSAC. Here, we disentangled carbon cycling processes in a representative groundwater-stream-atmosphere transect by obtaining and numerically simulating high-resolution time series of dissolved He, Ar, Kr, O, CO, and CH concentrations.

Noble gas constraints on the fate of arsenic in groundwater.

Groundwater contamination of geogenic arsenic (As) remains a global health threat, particularly in south-east Asia. The prominent correlation often observed between high As concentrations and methane (CH) stimulated the analysis of the gas dynamics in an As contaminated aquifer, whereby noble and reactive gases were analysed. Results show a progressive depletion of atmospheric gases (Ar, Kr and N) alongside highly increasing CH, implying that a free gas phase comprised mainly of CH is formed within the aquifer.

Combined method of H/He apparent age and on-site helium analysis to identify groundwater flow processes and transport of perchloroethylene (PCE) in an urban area.

Urban groundwater management requires a thorough and robust scientific understanding of flow and transport processes. H/He apparent ages have been shown to efficiently help provide important groundwater-related information. However, this type of analysis is expensive as well as labor- and time-intensive, and hence limits the number of potential sampling locations.

Deconvolution and compensation of mass spectrometric overlap interferences with the miniRUEDI portable mass spectrometer.

The miniRUEDI is a portable mass spectrometer system designed for on-site analysis of gases in the environment during field work and at remote locations. For many gas species (e.g.

In situ observation of helium and argon release during fluid-pressure-triggered rock deformation.

Temporal changes in groundwater chemistry can reveal information about the evolution of flow path connectivity during crustal deformation. Here, we report transient helium and argon concentration anomalies monitored during a series of hydraulic reservoir stimulation experiments measured with an in situ gas equilibrium membrane inlet mass spectrometer. Geodetic and seismic analyses revealed that the applied stimulation treatments led to the formation of new fractures (hydraulic fracturing) and the reactivation of natural fractures (hydraulic shearing), both of which remobilized (He, Ar)-enriched fluids trapped in the rock mass.

A New in Situ Method for Tracing Denitrification in Riparian Groundwater.

The spatiotemporal dynamics of denitrification in groundwater are still not well-understood because of a lack of efficient methods to quantify this biogeochemical reaction pathway. Previous research used the ratio of N to argon (Ar) to quantify net production of N via denitrification by separating the biologically generated N component from the atmospheric-generated components. However, this method does not allow the quantification of the atmospheric components accurately because the differences in gas partitioning between N and Ar are being neglected.

Noble gas composition and H/He groundwater ages in the Gardermoen Aquifer, Norway: Improved understanding of flow dynamics as a tool for water management.

This study presents a novel data set of noble gas compositions and H/He measurements in groundwater samples from the Gardermoen Aquifer in Norway. The motivation was to test the applicability of noble gases as tracers in constraining the conceptual model and improve the understanding of deeper parts of the aquifer. Flow models have been used as tools for water resource management at the Oslo international airport, which is located within the aquifer recharge area, and bordering towards protected nature reserves.

In-situ mass spectrometry improves the estimation of stream reaeration from gas-tracer tests.

The estimation of gas-exchange rates between streams and the atmosphere is of great importance for the fate of volatile compounds in rivers. For dissolved oxygen, this exchange process is called reaeration, and its accurate and precise estimation is essential for the quantification of metabolic rates. A common method for the determination of gas-exchange rates is through artificial gas-tracer tests with a proxy gas.

A Novel Approach To Quantify Air-Water Gas Exchange in Shallow Surface Waters Using High-Resolution Time Series of Dissolved Atmospheric Gases.

Gas exchange across the air-water interface is a key process determining the release of greenhouse gases from surface waters and a fundamental component of gas dynamics in aquatic systems. To experimentally quantify the gas transfer velocity in a wide range of aquatic settings, a novel method based on recently developed techniques for the in situ, near-continuous measurement of dissolved (noble) gases with a field portable mass spectrometer is presented. Variations in observed dissolved gas concentrations are damped and lagged with respect to equilibrium concentrations, being the result of (a) temperature (and thus solubility) variations, (b) water depth, and (c) the specific gas transfer velocity ( k).

Porewater salinity reveals past lake-level changes in Lake Van, the Earth's largest soda lake.

In closed-basin lakes, sediment porewater salinity can potentially be used as a conservative tracer to reconstruct past fluctuations in lake level. However, until now, porewater salinity profiles did not allow quantitative estimates of past lake-level changes because, in contrast to the oceans, significant salinity changes (e.g.

Diverging effects of isotopic fractionation upon molecular diffusion of noble gases in water: mechanistic insights through ab initio molecular dynamics simulations.

Atmospheric noble gases are routinely used as natural tracers to analyze gas transfer processes in aquatic systems. Their isotopic ratios can be employed to discriminate between different physical transport mechanisms by comparison to the unfractionated atmospheric isotope composition. In many applications of aquatic systems molecular diffusion was thought to cause a mass dependent fractionation of noble gases and their isotopes according to the square root ratio of their masses.

A Portable and Autonomous Mass Spectrometric System for On-Site Environmental Gas Analysis.

We developed a portable mass spectrometric system ("miniRuedi") for quantificaton of the partial pressures of He, Ne (in dry gas), Ar, Kr, N, O, CO, and CH in gaseous and aqueous matrices in environmental systems with an analytical uncertainty of 1-3%. The miniRuedi does not require any purification or other preparation of the sampled gases and therefore allows maintenance-free and autonomous operation. The apparatus is most suitable for on-site gas analysis during field work and at remote locations due to its small size (60 cm × 40 cm × 14 cm), low weight (13 kg), and low power consumption (50 W).

Improved Method for the Quantification of Methane Concentrations in Unconsolidated Lake Sediments.

There is conclusive evidence that the methods most commonly used to sample methane (CH4) dissolved in the pore water of lake sediments produce results that are likely to be affected by gas loss or gas exchange with the atmosphere. To determine the in situ amount of CH4 per unit mass of pore water in sediments, we developed and validated a new method that combines techniques developed for noble-gas analysis in pore waters with a standard headspace technique to quantify the CH4 present in the pore space in dissolved and gaseous form. The method was tested at two sites: Lake Lungern, where CH4 concentrations were close to saturation; and Lake Rotsee, where CH4 concentrations are known to exceed saturation and where CH4 bubble formation and gas ebullition are commonly observed.

Measurement of oxygen isotope ratios ((18)O/(16)O) of aqueous O2 in small samples by gas chromatography/isotope ratio mass spectrometry.

Rationale: Oxygen isotope fractionation of molecular O2 is an important process for the study of aerobic metabolism, photosynthesis, and formation of reactive oxygen species. The latter is of particular interest for investigating the mechanism of enzyme-catalyzed reactions, such as the oxygenation of organic pollutants, which is an important detoxification mechanism.

Methods: We developed a simple method to measure the δ(18) O values of dissolved O2 in small samples using automated split injection for gas chromatography coupled to isotope ratio mass spectrometry (GC/IRMS).

Determination of natural in vivo noble-gas concentrations in human blood.

Although the naturally occurring atmospheric noble gases He, Ne, Ar, Kr, and Xe possess great potential as tracers for studying gas exchange in living beings, no direct analytical technique exists for simultaneously determining the absolute concentrations of these noble gases in body fluids in vivo. In this study, using human blood as an example, the absolute concentrations of all stable atmospheric noble gases were measured simultaneously by combining and adapting two analytical methods recently developed for geochemical research purposes. The partition coefficients determined between blood and air, and between blood plasma and red blood cells, agree with values from the literature.

Conquering the outdoors with on-site mass spectrometry.

In recent years, mass spectrometers with a membrane inlet separating gases from water for final analysis have been used successfully for the on-site quantification of dissolved gases in surface waters. In 'classical' membrane inlet mass spectrometers (MIMS), the membrane directly separates the water from the high-vacuum environment of the mass spectrometer. The gas equilibrium MIMS (GE-MIMS) that is described in this review, however, makes use of an intermediate pressure reduction stage after the membrane inlet.

(220)Rn/(222)Rn isotope pair as a natural proxy for soil gas transport.

Radon (Rn) is a naturally occurring radioactive noble gas, which is ubiquitous in soil gas. Especially, its long-lived isotope (222)Rn (half-life: 3.82 d) gained widespread acceptance as a tracer for gas transport in soils, while the short-lived (220)Rn (half-life: 55.

Simultaneous analysis of noble gases, sulfur hexafluoride, and other dissolved gases in water.

We developed an analytical method for the simultaneous measurement of dissolved He, Ne, Ar, Kr, Xe, SF6, N2, and O2 concentrations in a single water sample. The gases are extracted from the water using a head space technique and are transferred into a vacuum system for purification and separation into different fractions using a series of cold traps. Helium is analyzed using a quadrupole mass spectrometer (QMS).

Argon concentration time-series as a tool to study gas dynamics in the hyporheic zone.

The oxygen dynamics in the hyporheic zone of a peri-alpine river (Thur, Switzerland), were studied through recording and analyzing the concentration time-series of dissolved argon, oxygen, carbon dioxide, and temperature during low flow conditions, for a period of one week. The argon concentration time-series was used to investigate the physical gas dynamics in the hyporheic zone. Differences in the transport behavior of heat and gas were determined by comparing the diel temperature evolution of groundwater to the measured concentration of dissolved argon.

Membrane inlet mass spectrometer for the quasi-continuous on-site analysis of dissolved gases in groundwater.

We developed a stand-alone system based on a membrane inlet mass spectrometer (MIMS) for measuring dissolved gas concentrations in groundwater under field conditions. The system permits the concentrations of dissolved gases (He, Ar, Kr, N(2), and O(2)) in groundwater to be determined quasi-continuously (every 12 min) with a precision of better than 4% for He and Kr, and with a precision of 1% for Ar, N(2), and O(2) in air-saturated water. The detection limits are below 3 × 10(-9) cm(3)(STP)(g) for the noble gases and below 400 × 10(-9)cm(3)(STP)(g) for N(2) and O(2).

(13)C/(12)C analysis of ultra-trace amounts of volatile organic contaminants in groundwater by vacuum extraction.

We developed a method for the vacuum extraction (VacEx) of volatile organic compounds (VOCs) from water samples for ultratrace determinations of carbon isotopic signatures. Our method permits compound-specific stable carbon isotope analysis (CSIA) at VOC concentrations as low as 0.03-1.