Hydrogen Isotope Ratios Research Articles

Hydrogen isotopic ratio by residual gas analysis during the JET DT campaigns

Abstract The analysis of hydrogen isotope content is crucial for understanding the operation of fusion devices. Hydrogen isotopic analysis in the core and plasma edge is conducted through neutron and spectroscopic diagnostics. In the case of exhaust gas, mass spectrometry is employed using residual gas analyzers (RGAs), along with optical gas analysis (OGA) utilizing an optical Penning gauge. The use of traditional quadrupole mass spectrometers for RGA encounters challenges during discharges with tritium gas due to signal overlap of different hydrogen molecules at the same mass number. This paper introduces a novel technique to address this issue through a cross-related analysis of RGA data with OGA results. Another consideration in mass spectrometry analysis is the instrument’s varying sensitivity concerning the gas mass number. The paper includes gas calibration data results for all the quadrupoles used in the JET gas analysis. Hydrogen isotopic ratios are calculated from RGA detected currents using simple formulas. The results of this procedure are presented for selected DT JET discharges in relation to the JET pulse time, and they are compared with corresponding optical data. Time-averaged hydrogen isotopic ratio values are computed for numerous discharges during the DT and T campaigns.

The effects of fingerprinting agents on the stable isotope ratios of polyethylene films

Traditional forensic chemical comparisons of polymeric materials are often affected by fingerprinting agents that enhance and visualise finger-marks. This can inhibit detailed analysis used to provide an association or discrimination between two samples. In this study, we have demonstrated that the method for polymer comparisons using isotope ratio mass spectrometry analysis is not affected by fingerprinting matter on the surface in contrast to other forensic instrumental tests. A selection of resealable bags was analysed for carbon and hydrogen isotope ratio values of bags that had been subject to various fingerprinting agents and compared to values of untreated bags. The results showed no significant difference between samples that had been fingerprinted from those that were untreated.

Sourcing and long-range transport of particulate organic matter in river bedload: Río Bermejo, Argentina

Abstract. Fluvial transport of organic carbon from the terrestrial biosphere to the oceans is an important term in the global carbon cycle. Traditionally, the long-term burial flux of fluvial particulate organic carbon (POC) is estimated using river suspended sediment flux; however, organic carbon can also travel in river bedload as coarse particulate organic matter (POMBed). Estimates of fluvial POC export to the ocean are highly uncertain because few studies document POMbed sources, flux, and evolution during long-range fluvial transport from uplands to ocean basins. This knowledge gap limits our ability to determine the global terrestrial organic carbon burial flux. In this study we investigate the flux, sources, and transformations of POMBed during fluvial transport over a ∼1300 km long reach of the Río Bermejo, Argentina, which has no tributary inputs. To constrain sourcing of POMBed, we analyzed the composition and stable hydrogen and carbon isotope ratios (δ2H, δ13C) of plant wax biomarkers from POMBed at six locations along the Río Bermejo and compared this to samples of suspended sediment, soil, leaf litter, and floating organic debris (POMfloat) from both the lowland and headwater river system. Across all samples, we found no discernible differences in n-alkane average chain length or nC29 δ13C, indicting a common origin for all sampled POMBed. Leaf litter and POMfloat nC29 δ2H values decrease with elevation, making it a useful proxy for POMBed source elevation. Biomarker δ2H values suggest that POMBed is a mix of distally derived headwater and locally recruited floodplain sources at all sampling locations. These results indicate that POMBed can be preserved during transport through lowland rivers for hundreds of kilometers. However, the POMBed flux decreases with increasing transport distance, suggesting mechanical comminution of these coarse organic particles and progressive transfer into the suspended load. Our provisional estimates suggest that the carbon flux from POMBed comprises less than 1 % of the suspended load POC flux in the Río Bermejo. While this represents a small portion of the river POC flux, this coarse, high-density material likely has a higher probability of deposition and burial in sedimentary basins, potentially allowing it to be more effective in long-term CO2 drawdown relative to fine suspended particles. Because the rate and ratio of POMBed transport versus comminution likely vary across tectonic and climatic settings, additional research is needed to determine the importance of POMBed in the global carbon cycle.

Cryogenic vacuum distillation vs Cavitron methods in ecohydrology: Extraction protocol effects on plant water isotopic values

Stable isotope ratios of hydrogen and oxygen in plant water are widely used for water tracing in ecohydrology studies. In this approach, plant water is extracted for isotopic analysis of δ2H and δ18O. Among the extraction methods, cryogenic vacuum distillation (CVD) has been the most popular, but its impact on the isotopic composition of plant water is currently under debate. Newer Cavitron method have been proposed to replace CVD method for xylem water extraction. These recommendations have been largely based on comparisons between Cavitron-xylem water with low temperatures CVD-xylem water. However, the CVD protocol (extraction temperature and time) varies widely across laboratories, and no direct, systematic comparison has yet been made between extraction temperature and time protocols vs. the Cavitron approach. Here we compared the isotopic values of xylem water from the same tree obtained through CVD extraction at 60 °C (60, 120, 240, 360 min), 100 °C (30, 60, 120, 240 min), 140 °C (15, 30, 60, 120, 240 min), and 200 °C (15, 30 min). Subsequently, we compared the results of CVD-xylem water with Cavitron-xylem water. Our data show that isotopic values for CVD-xylem water became more positive with increasing extraction time under the same extraction temperature. Such extractions also became more isotopically positive with increasing extraction temperature for the same extraction time. When total extraction efficiency exceeded 98 %, there was no δ18O difference in CVD-xylem water among any of the different protocols (p > 0.05). However, lower extraction temperatures resulted in more negative δ2H when compared to higher temperature extraction (p < 0.05). Cavitron-xylem water was close to CVD-xylem water (average difference of 3 ‰ for δ2H and 0.5 ‰ for δ18O, n = 79) when total extraction efficiency for CVD was below 98 %. But for extraction efficiencies beyond 98 %, the Cavitron-xylem water was more negative in δ2H (17.3 ‰, n = 70) and δ18O (1.7 ‰, n = 70) than CVD-xylem water. Compared to Cavitron-xylem water, CVD-xylem water at 200 °C with extraction efficiency > 98 % was closer to the soil water. Further study is necessary to conduct a complete cross-comparison between Cavitron and CVD at different temperatures with different species at various water and salt stress conditions. But our results suggest that abandoning CVD for plant water maybe premature until such complete comparison work is done.

From swamp to sea: Quantifying terrestrial dissolved organic carbon in a tropical shelf sea using hydrogen isotope ratios

Dissolved organic carbon (DOC) is a key component of coastal biogeochemical cycles, but its composition and reactivity depend on the relative contribution of autochthonous aquatic versus allochthonous terrigenous DOC (tDOC). In complex coastal waters, tDOC is commonly quantified using the bulk DOC stable carbon isotope ratio (δ13CDOC). However, several limitations can hamper the use of δ13CDOC in marine ecosystems, such as (1) the narrow and often overlapping separation of the autochthonous and allochthonous endmembers, and (2) mineralization of tDOC to dissolved inorganic carbon creates a reservoir effect such that autochthonous DOC can acquire a terrigenous-like δ13CDOC. The stable isotope ratio of non-exchangeable hydrogen in the DOC (δ2Hn) has emerged as a new tool that can potentially overcome these limitations: (1) δ2Hn has a large separation between aquatic and terrigenous endmembers (>50‰) and (2) it is not subject to reservoir effects caused by tDOC mineralization. Here, we evaluate the potential of δ2Hn obtained from solid phase-extracted dissolved organic matter (SPE-DOM), by comparing it to δ13CDOC and chromophoric DOM (CDOM) optical properties. We collected samples at a site in Southeast Asia’s Sunda Shelf that experiences substantial seasonal variation in tDOC input, driven primarily by the monsoon-induced physical advection of peatland-derived tDOC. Over a 1-year monthly time series, the terrigenous fraction of DOC (fterr) determined using δ2Hn of SPE-DOM and δ13CDOC of bulk DOC was well correlated (r2 = 0.42), and there was no significant difference in fterr between the two isotope systems. In fact, δ2Hn displayed slightly stronger correlations with salinity and CDOM optical properties compared to δ13CDOC. Our results indicate that δ2Hn of SPE-DOM is effective for quantifying tDOC across coastal gradients, potentially offering greater sensitivity than δ13CDOC, and is a viable alternative in settings where δ13CDOC is inadequate.

Compound-specific radiocarbon analysis of sedimentary fatty acids: Potential as a dating tool for lake sediments of Mt. Fuji volcanic region, Japan

Compound-specific radiocarbon analysis (CSRA) is a promising tool for dating sediment sequences where traditional dating methods are impractical. However, the applicability of CSRA of short-chain fatty acids as a dating tool remains poorly understood, especially in lacustrine settings. Accordingly, we determined the radiocarbon content (Δ14C) of individual fatty acids in sediments of Lake Yamanaka (central Japan), as well as their stable carbon and hydrogen isotope ratios, to evaluate the potential of CSRA as a dating tool in volcanic lake environments. We found that the Δ14C values of plant-derived (C24, C26, and C28) n-fatty acids (–99‰ to –149‰) were considerably lower than the Δ14C of charred plants (139‰) within the sediments and those of living aquatic plants (–52‰ to –58‰) in Lake Yamanaka, suggesting that contributions from pre-aged terrestrial and aquatic plant materials likely affect these acids. Similarly, the Δ14C of C16n-fatty acid (–95‰) in surface sediments was much lower than the Δ14C of modern aquatic plants (–52‰ to –58‰), as well as the Δ14C of dissolved organic carbon (DIC) in surface water (–48‰). Together with the stable isotope results, we conclude that in addition to autochthonous aquatic sources, contributions from pre-aged terrestrial carbon sources significantly affect the Δ14C of C16n-fatty acids. Comparing fatty acid Δ14C and concentration data across lakes within the Mt. Fuji region suggests that CSRA of the C16 acid provides valid chronological information only when the C16 originates exclusively from autochthonous aquatic sources, with minor allochthonous terrestrial input.

Theoretical and experimental constraints on hydrogen isotope equilibrium in C1-C5 alkanes

Stable isotope ratios of C1–C5 alkanes, the major constituents of subsurface gaseous hydrocarbons, can provide valuable insights on their origins, transport, and fates. Equilibrium isotope effects are fundamental to interpreting stable isotope signatures, as recognition of them in natural materials indicates reversible processes and constrains the temperatures of equilibrated systems. Hydrogen isotope equilibrium of C1–C5 alkanes is of particular interest because evidence shows that alkyl H can undergo isotopic exchange with coexisting compounds under subsurface conditions. We present the results of a combined experimental and theoretical effort to determine equilibrium hydrogen isotope distributions in mixtures of these hydrocarbon compounds. We created two mixtures: one with C1, C2 and C3 (where C1 indicates methane, C2 ethane, etc., hereinafter called ‘C1–C3 mixture’) and another one with C2, C3, iC4, nC4, iC5 and nC5 (hereinafter called ‘C2–C5 mixture’); in both cases, the mixtures were created to start out of hydrogen isotope equilibrium. We tested the performance of several metal catalysts as aids to H isotopic exchange by exposing these mixtures to different metal catalysts at 100 or 200 °C and analyzing the compound-specific hydrogen isotope ratios of the product gases. The C1–C3 mixture exchanged hydrogen isotopes among the starting gas components rapidly in the presence of Ru/Al2O3 at 200 °C. The isotope ratios reach a steady-state (presumably equilibrium) after 72 h of heating (up to 120 h). The hydrogen isotopic ratios of alkanes in the C2–C5 mixture shifted significantly in the presence of Rh/Al2O3 at 100 °C and C3-C5 compounds approached steady state after 70 h, whereas C2 had not yet reached a steady state D/H ratio after 216 h of heating. We evaluated the reaction progress of isotope exchange for each compound as a function of time with a reaction-network model informed by constraints on chemical kinetics. The model indicates that C3, iC4, nC4, iC5 and nC5 in the C2-C5 mixture reached internal isotope equilibrium after 70 h, hence we used their values to calculate experimental equilibrium results. We also calculated equilibrium isotope fractionations with the Bigeleisen-Mayer theorem using vibrational frequencies computed from the density functional theory (B3LYP/aug-cc-pVTZ). We included torsional conformers and explicit H positions in the calculations. We found that the experimental results from both the 200 ˚C C1–C3 experiment and 100 ˚C C2–C5 experiment are consistent with theoretical equilibrium results within experimental uncertainty. Additionally, our reaction-network model for catalyzed hydrogen isotope exchange between alkanes succeeded in fitting our experimental results. This modeling framework can be adjusted to simulate exchange in natural settings for constraining temperature histories and sources of natural gases.

Do exchangeable hydrogens affect the evaluation of partial mycoheterotrophy in orchids? Insights from δ2H analysis in bulk, α-cellulose, and cellulose nitrate samples.

To evaluate the nutritional modes of orchids associated with 'rhizoctonia' fungi, analyses of hydrogen (δ2H), carbon (δ13C), and nitrogen (δ15N) stable isotope ratios are usually adopted. However, previous studies have not fully accounted for exchangeable hydrogens, which could affect these evaluations. Here, we performed standard δ13C, δ15N, and δ2H analyses on bulk samples. Additionally, we conducted δ2H analysis on α-cellulose and cellulose nitrate samples to investigate whether the heterogeneity of exchangeable hydrogens among plant species influences the assessment of nutritional modes. The δ2H of orchids were consistently higher than those of surrounding autotrophic plants, irrespective of the three pretreatments. Although the rhizoctonia-associated orchid exhibited lower δ13C, its δ2H was higher than those of the autotrophs. Notably, among all response variables, δ15N and δ2H exhibited high abilities for discriminating the nutritional modes of rhizoctonia-associated orchids. These results indicate that a time-efficient bulk sample analysis is an effective method for evaluating plant nutritional modes, as the heterogeneity of exchangeable hydrogens does not significantly impact the estimation. Using δ15N and δ2H benefits the assessment of partial mycoheterotrophy among rhizoctonia-associated orchids.

Large variability and 2H-depletion of Middle Miocene to Pleistocene alkenone hydrogen isotopes in the Equatorial Pacific reflect subsurface, low light haptophyte growth

Hydrogen isotope ratios of haptophyte derived long-chain alkenones (δ2HC37:2) have shown to be a useful tool for reconstructing past isotopic compositions of surface seawater (δ2HSSW). The δ2HSSW is related to global ice volume, sea surface salinity and the local hydrological cycle. Here, we present a hydrogen isotope record of alkenones spanning the last 14.5 Ma from IODP site U1338 in the east equatorial Pacific. The alkenone-based reconstructed δ2HSSW is substantially more negative and variable than reconstructed δ2HSSW based on published oxygen isotopes of coccolith carbonates. This suggests that factors other than the isotopic composition of seawater affect the hydrogen isotopic composition of alkenones. The relatively negative and highly variable δ2HC37:2 values are in line with published modern observations on alkenones from suspended particulate matter in the equatorial and north Pacific, with the highest values at relatively high light conditions at the surface and the lowest values at higher water depth and relatively low light conditions. This suggests that the relatively negative and highly variable δ2HC37:2 values in these Middle Miocene to Pleistocene sediments are likely derived from haptophytes growing below the sea surface under variable low light conditions. In regions where the contribution of alkenones from subsurface production, due to high subsurface nutrients, at low light intensities to the sediment is relatively high the δ2HC37:2 has to be interpreted with care as a proxy for δ2HSSW.

Source differentiation of BTEX compounds in groundwater contaminated due to refinery activities

This study aims to identify sources of groundwater contamination in a refinery area using integrated compound-specific stable isotope analysis (CSIA), oil fingerprinting techniques, hydrogeological data, and distillation analysis. The investigations focused on determination of the origin of benzene, toluene, ethylbenzene, and xylenes (BTEX), and aliphatic hydrocarbons as well. Groundwater and floating oil samples were collected from extraction wells for analysis. Results indicate presence of active leaks in both the northern and southern zones. In the northern zone, toluene was found to primarily originate from oil products like aviation turbine kerosene (ATK or aviation fuel), kerosene, regular gasoline, and diesel fuel. Additionally, stable isotope ratios of carbon and hydrogen for ethylbenzene, o-xylene (ortho xylene) and p-xylene (para xylene) in zone A suggested the pollution originated from gasoline within the northern zone. The origin of super gasoline (with higher octane) identified in southern zone using δ13C and δ2H values of toluene in the floating oil and groundwater samples. Further, biodegradation of toluene likely occurred in southern zone according to δ13C and δ2H. The findings underscore the critical importance of integrating CSIA and fingerprinting techniques to effectively address the challenges of source identification and relying solely on each method independently is insufficient. Accordingly, comparing the GC-MS results of floating oil samples with ATK and jet fuel (JP4) standards can be effectively utilized for source differentiation. However, this method showed no practical application to distinguish different types of diesel or gasoline. The accuracy and reliability of source identification of BTEX compounds may significantly improve when hydrogeological data incorporates with stable isotopes analysis. Additionally, the results of this study will elevate the procedures for fuel-related contaminants source identification of the polluted groundwater that is crucial to develop effective remediation strategies.

The preservation of photosynthetic and hydrological signals in the carbon and hydrogen isotope compositions of n-fatty acids in the seasonal wetland soils of the Okavango Delta (Botswana)

The Okavango wetland (Botswana) is the world’s largest inland delta. A strong seasonality in water input leads to the contraction and extension of wetlands in the floodplains. The extreme evapotranspiration and little precipitation lead to a difference in the hydrogen isotope signature of rain, soil and river water. Biomarkers, such as plant waxes, are stored in the soils and preserved on geological timescales. To understand which signal is preserved in the stable isotope signatures of plant waxes, soils along a 250 m-long transect spanning waterlogged to dry soils were collected over several seasons and three years. In addition, plants, and plant and soil water were collected along this transect. First, carbon isotope ratios (δ13C) of plant waxes (i.e, n-fatty acids) were used to classify their metabolism. δ13C of bulk organic matter and individual n-fatty acids analyzed in the soils show a strong dependance on the type of vegetation found along the transect (C3 versus C4 plants). Hydrogen isotope ratios (δ2H) of water present in soil showed that shallow-rooted C4 grasses use superficial soil water, whereas the xylem water δ2H content in trees growing near the flooded channel indicated the use of river water. In addition, plant hydrogen fractionation between lipids and rain showed a strong influence of carbon metabolisms with larger fractionation for C3 plants compared with C4 grasses. n-fatty acid δ2H ratios in surface soils followed the hydrological variation in the Delta with its floods and dry periods. Hence δ2H of long-chain fatty acids seems to track the river-level variation rather than precipitation.

Revealing the ongoing speleogenetic processes in an underwater cave through the application of natural radionuclides and stable isotopes: case study from the hypogene Buda Thermal Karst

The underwater Molnár János Cave in the hypogene Buda Thermal Karst system (Budapest, Hungary) provides a unique site to study the effects of flowing groundwater and the interplay of fluids of different origin. The aim of the present study is to characterize the groundwater in different parts of the cave with temporal resolution, hence describe the recent speleogenetic processes within the cave. This study uses natural radioisotopes (uranium, radium, and radon) besides stable isotope ratios of oxygen and hydrogen to identify the different fluid components. The results show that the majority of the cave is situated in the flow path of the intermediate flow system, discharging in the Boltív Spring. Thus, the dominant recent speleogenetic processes are connected to this lukewarm groundwater. In contrast to previous views, typical hypogene processes, such as mixing corrosion involving thermal waters, are restricted to a narrower area in the cave, to the contact zone of lukewarm waters and the warmer upper water layer around the largest partially air-filled chamber (Kessler Hall). The warmer water layer is the result of free convection. In the air-filled chambers condensation-corrosion might be active. However, its effect is limited to the largest room (Kessler Hall), as it is open to surface conditions. More active mixing corrosion probably occurs deeper, in the area of the Northeastern Margin Fault, which is indicated by the radon content in the Boltív Spring. Regarding the temporal processes, the main driving force can be linked to the water level fluctuations of the Danube, which regulates the discharge of the regional flow-related thermal water upwelling, thus affecting the mixing ratio of the lukewarm waters transported by the intermediate flow systems and the thermal waters, representing the regional flow path, including basinal components.

Hydrogen Isotope Fingerprinting of Lipid Biomarkers in the Chinese Marginal Seas

AbstractThe hydrogen isotope ratio (δ2H) of lipid biomarkers from phytoplankton and terrestrial plants were measured in surface sediments from Chinese marginal seas (CMS), in order to evaluate processes affecting their spatial distribution, and by extension, the controls on organic carbon cycling in these dynamic marginal seas. The dinoflagellate sterol dinosterol and the microalgal sterol brassicasterol had low δ2H values (&lt;−300%) near the mouth of the Yangtze River. Near the mouth of the Yellow River, dinosterol again had low δ2H values but brassicasterol had intermediate (−292 to −281%) δ2H values. This discrepancy in the δ2H values of two phytoplankton sterols may be explained by the timing of dinoflagellate production relative to that of brassicasterol producers (e.g., diatoms). The δ2H values of C16:0 fatty acid, synthesized by all organisms, had intermediate δ2H values (−199 to −178%) near the Yangtze River and lowest δ2H C16:0 values (−216 to −206%) occurred near the old Yellow River delta. The lowest δ2H C28:0 values (&lt;−184%) occurred adjacent to rivers, suggesting that leaf‐wax lipids produced on the loess plateau, which are enriched in 2H, may contribute less to the nearshore environment than the offshore regions. Higher δ2H C28:0 values offshore may be explained by a larger contribution of leaf wax fatty acids from aerosols relative to river‐borne suspended particles. Lipid biomarker δ2H fingerprinting thus provides a new tool for deciphering the controls on organic carbon cycling and accumulation in the dynamic CMS.

Hydrogen isotope fractionation is controlled by CO2 in coccolithophore lipids

Hydrogen isotope ratios (δ2H) represent an important natural tracer of metabolic processes, but quantitative models of processes controlling H-fractionation in aquatic photosynthetic organisms are lacking. Here, we elucidate the underlying physiological controls of 2H/1H fractionation in algal lipids by systematically manipulating temperature, light, and CO2(aq) in continuous cultures of the haptophyte Gephyrocapsa oceanica. We analyze the hydrogen isotope fractionation in alkenones (αalkenone), a class of acyl lipids specific to this species and other haptophyte algae. We find a strong decrease in the αalkenone with increasing CO2(aq) and confirm αalkenone correlates with temperature and light. Based on the known biosynthesis pathways, we develop a cellular model of the δ2H of algal acyl lipids to evaluate processes contributing to these controls on fractionation. Simulations show that longer residence times of NADPH in the chloroplast favor a greater exchange of NADPH with 2H-richer intracellular water, increasing αalkenone. Higher chloroplast CO2(aq) and temperature shorten NADPH residence time by enhancing the carbon fixation and lipid synthesis rates. The inverse correlation of αalkenone to CO2(aq) in our cultures suggests that carbon concentrating mechanisms (CCM) do not achieve a constant saturation of CO2 at the Rubisco site, but rather that chloroplast CO2 varies with external CO2(aq). The pervasive inverse correlation of αalkenone with CO2(aq) in the modern and preindustrial ocean also suggests that natural populations may not attain a constant saturation of Rubisco with the CCM. Rather than reconstructing growth water, αalkenone may be a powerful tool to elucidate the carbon limitation of photosynthesis.

Identification of a primordial high D/H component in the matrix of unequilibrated ordinary chondrites

Deuterium to hydrogen isotope ratios in unequilibrated ordinary chondrites (UOCs) which have undergone little-to-no thermal metamorphism pose an interesting problem when looking at water in the early Solar System. Bulk chondrite studies have shown that UOCs of the lowest subtypes have D/H ratios as high as comets from the outer Solar System, which, along with bulk UOC water abundances, decrease with thermal metamorphism. Since bulk UOC analyses represent a complex mixture of organic and hydrated phases, it is not clear what phase(s) is responsible for the high bulk D/H values. In this study, we report in situ secondary ion mass spectrometry (SIMS) measurements of the H isotope composition of the fine-grained matrix of UOCs with petrological subtypes ranging from 3.00 to 3.9. We find that for matrix areas in UOCs of petrologic subtype ≥3.2, correlations between D-rich organic material and D-poor phyllosilicates give relatively D-poor intrinsic water isotopic compositions, with δD values between −320 ± 91 ‰ and −71 ± 71 ‰, which are inherited from parent body accretion. Therefore, we conclude that OC parent bodies accreted D-poor water ice that had an H isotopic composition similar to that of CM and CV chondrite parent bodies. We find that matrix in UOCs of the lowest subtypes (Semarkona, Bishunpur, and Ngawi) show similar water and organic H isotope compositions to higher type UOCs. Our in situ analyses also show that matrix areas in these pristine UOCs contain a third, thus far unidentified, component that carries the high D/H signature, with δD values up to ∼6000 ‰. We propose that this component is pristine amorphous silicates preserved from the molecular cloud or early protoplanetary disc that is extremely sensitive to thermal and aqueous alteration on asteroidal parent bodies.

Stable Isotope Hydrology of Karst Groundwaters in Romania

In this article we present the first investigation of the stable isotope composition of groundwater in Romania, East-Central Europe, with a focus on the karst areas. Our aim is twofold: (1) to provide a countrywide map with the distribution of stable oxygen and hydrogen isotope ratios in groundwater, and (2) to assess the recharge patterns of karst water. We collected more than 600 water samples from springs and wells across Romania for stable isotope analyses and monitored in detail the stable isotope composition of the waters as they pass through five cave systems. Our data show a spatial distribution of the stable isotope composition of the groundwater with low values in the mountainous area and high values in the surrounding lowlands and the central Transylvanian Depression. However, waters in karst areas induce departures from this distribution, resulting from the fast (hours to days) transfer of waters from high (ponor) to low (spring) altitudes. Water emerging from the karst springs has generally lower δ values than before sinking through the ponors, thus indicating a substantial contribution of winter recharge through diffuse infiltration and seepage. This contribution results in overall dilution of the water entering through ponors, likely resulting in changes in the chemical composition of the water and diluting potential pollutants. Our data call for careful separation between karst and non-karst spring/well waters, as indiscriminate common treatment might lead to erroneous interpretations.

A new method to analysis synthetic acetic acid to vinegar: Hydrogen isotope ratio at the methyl site of acetic acid in vinegar by GC-IRMS

Acetic acid is the key organic substance used to verify the authenticity of vinegar. A new method for precisely determining acetic acid δDCH3 in vinegar via gas chromatography −pyrolytic-stable isotope ratio mass spectrometry (GC-P-IRMS) was established. The δDCH3 values were obtained via calibration with a series of standards. The optimised method demonstrated a repeatability standard deviation within 3 ‰. The standard deviation of accuracy of the new method compared with that of the SNIF-NMR method was within 2.6 ‰. The synthetic acetic acid δDCH3 values was −136.7 ‰ ± 29.6 ‰, and the δDCH3 value of acetic acid in vinegar was −414.9 ‰ ± 40.5 ‰, with significant isotopic distribution characteristics. This methodology serves as a supplementary method for measuring the δDCH3 value of acetic acid in vinegar. It has advantages over other methods in terms of time, sensitivity and operability. And provides a new idea for solving the problem of analyzing substances in the presence of exchangeable groups.

Continental-scale migration patterns and origin of Helicoverpa zea (Lepidoptera: Noctuidae) based on a biogeochemical marker.

Insect migrations have ecological and economic impacts, particularly in agriculture. However, there is limited knowledge about the migratory movements of pests at the continental scale, which is an important factor influencing the spread of resistance genes. Understanding the migratory patterns of economic pests, like Helicoverpa zea (Boddie), is essential for improving Integrated Pest Management (IPM) and Insect Resistance Management (IRM) strategies. In this study, we used stable hydrogen isotopic ratios in wing tissue as a biogeochemical marker to examine migratory patterns and estimate the native origins of H. zea individuals collected across a wide latitudinal gradient in North America. Samples collected at higher latitudes (Ontario, Canada and Minnesota, USA) exhibited a greater proportion (60%-96%) of nonlocal individuals, with an increased probability of origin from the southeastern United States. Populations from mid-latitudes (Florida, North Carolina, and South Carolina) showed a blend of local and nonlocal (40%-60%) individuals. Finally, 15% of the southernmost population individuals (Puerto Rico) were classified as migratory, with some having a probability of origin at higher latitudes (>30°). Overall, our results provide evidence of a northward spring/summer migration of H. zea in North America and underscore the significance of the southeastern United States as a hub for genetic flow. In addition, based on stable hydrogen isotopic ratios, there is strong evidence of reverse (southward) migration of H. zea from the continental United States to Puerto Rico. Our study highlights the implications for IPM and IRM programs and the need for management strategies that account for both northward and southward migration patterns.

Stream water sourcing from high-elevation snowpack inferred from stable isotopes of water: a novel application of d-excess values

Abstract. About 80 % of the precipitation at the Colorado River's headwaters is snow, and the resulting snowmelt-driven hydrograph is a crucial water source for about 40 million people. Snowmelt from alpine and subalpine snowpack contributes substantially to groundwater recharge and river flow. However, the dynamics of snowmelt progression are not well understood because observations of the high-elevation snowpack are difficult due to challenging access in complex mountainous terrain as well as the cost and labor intensity of currently available methods. We present a novel approach to infer the processes and dynamics of high-elevation snowmelt contributions predicated upon stable hydrogen and oxygen isotope ratios observed in streamflow. We show that deuterium-excess (d-excess) values of stream water could serve as a comparatively cost-effective proxy for a catchment-integrated signal of high-elevation snowmelt contributions to catchment runoff. We sampled stable hydrogen and oxygen isotope ratios of the precipitation, snowpack, and stream water in the East River, a headwater catchment of the Colorado River, and the stream water of larger catchments at sites on the Gunnison River and Colorado River. The d-excess of snowpack increased with elevation; the upper subalpine and alpine snowpack (&gt; 3200 m) had substantially higher d-excess compared to lower elevations (&lt; 3200 m) in the study area. The d-excess values of stream water reflected this because d-excess values increased as the higher-elevation snowpack contributed more to stream water generation later in the snowmelt/runoff season. End-member mixing analyses based on the d-excess data showed that the share of high-elevation snowmelt contributions within the snowmelt hydrograph was on average 44 % and generally increased during melt period progression, up to 70 %. The observed pattern was consistent during 6 years for the East River, and a similar relation was found for the larger catchments on the Gunnison and Colorado rivers. High-elevation snowpack contributions were found to be higher for years with lower snowpack and warmer spring temperatures. Thus, we conclude that the d-excess of stream water is a viable proxy to observe changes in high-elevation snowmelt contributions in catchments at various scales. Inter-catchment comparisons and temporal trends of the d-excess of stream water could therefore serve as a catchment-integrated measure to monitor if mountain systems rely on high-elevation water inputs more during snow drought compared to years of average snowpack depths.

Biosynthetic and catabolic pathways control amino acid δ2H values in aerobic heterotrophs.

The hydrogen isotope ratios (δ2HAA values) of amino acids in all organisms are substantially fractionated relative to growth water. In addition, they exhibit large variations within microbial biomass, animals, and human tissues, hinting at rich biochemical information encoded in such signals. In lipids, such δ2H variations are thought to primarily reflect NADPH metabolism. Analogous biochemical controls for amino acids remain largely unknown, but must be elucidated to inform the interpretation of these measurements. Here, we measured the δ2H values of amino acids from five aerobic, heterotrophic microbes grown on different carbon substrates, as well as five Escherichia coli mutant organisms with perturbed NADPH metabolisms. We observed similar δ2HAA patterns across all organisms and growth conditions, which-consistent with previous hypotheses-suggests a first-order control by biosynthetic pathways. Moreover, δ2HAA values varied systematically with the catabolic pathways activated for substrate degradation, with variations explainable by the isotopic compositions of important cellular metabolites, including pyruvate and NADPH, during growth on each substrate. As such, amino acid δ2H values may be useful for interrogating organismal physiology and metabolism in the environment, provided we can further elucidate the mechanisms underpinning these signals.