Stable Hydrogen Isotope Composition Research Articles

The measurement of ambient air moisture stable isotope composition for the accurate estimation of evaporative losses

Accurate estimation of evaporative losses from a water body, using the Craig-Gordon model and the stable hydrogen and oxygen isotope composition of water, requires knowledge of the stable isotope composition of ambient air moisture. This is rarely measured in the field, and it is usually estimated assuming that recent rainfall remains in isotopic equilibrium with atmospheric moisture. However, the ambient air moisture stable isotope composition may vary significantly at different heights above the water body.In this study, we set up outdoor pan evaporation experiments and simultaneously measured the stable isotope composition of ambient moisture in the atmosphere at three different heights. Using these measurements, we calculated evaporative losses, compared them with the observed losses in the pan, and assessed the uncertainty introduced by differences in ambient moisture measurements.Three main steps in the experimental method:•Daily water sampling from the evaporation pan for analysis of stable hydrogen and oxygen isotope compositions.•Recording the stable isotope composition of ambient air moisture at three different heights using the Picarro L2130-i system over a period of experiments.•Calculating evaporative losses from the pan using the Craig-Gordon model and ambient air stable isotope composition measured at three different levels and comparing to the observed losses.

An explainable machine learning for geographical origin traceability of mussels Mytilus edulis based on stable isotope ratio and compositions of C, N, O and H

Geographical traceability of marine bivalves has been explored continually, however the traceability results have not been recognized owing to the absence of a reasonable explanation for a certain model prediction. To address this problem, we employed an explainable machine learning to identify the origin of mussels based on stable isotope ratio and compositions of carbon (C), nitrogen (N), oxygen (O), and hydrogen (H). Our findings proved that the Extreme gradient boosting (XGBoost) model may be the best model based upon its high accuracy (93.75 %), precision (93.75 %), recall (94.51 %), F1 score (93.72 %) and AUC (0.990). The feature impact for model out of XGBoost was interpreted by SHapley Additive exPlanations (SHAP) on global and local perspective. This study demonstrated the potential of explainable machine learning to elucidate the complex relationships between desirable geographical information of mussels and the selected features.

Anomalous stable hydrogen-oxygen isotope characteristics and water vapor sources of autumn precipitation in the Weihe River basin, Northwest China.

The extreme changes in autumn rain have significant impacts on the ecological environment of Weihe River basin. Based on 117 autumn rain samples and corresponding meteorological data from 2015 to 2021 at Yangling located in the middle of Weihe River basin, we investigated the stable hydrogen and oxygen isotope composition and water vapor sources of precipitation. The results showed that, (1) extreme changes in autumn rainfall in the study area occurred frequently in recent years, which could be divided into extreme-high autumn precipitation year (HAP, 2021), general autumn precipitation year (GAP, 2015-2017, 2019-2020) and extreme-low autumn precipitation year (LAP, 2018) based on the autumn rain index (ARI); (2) the stable isotopes of different types of precipitation differed significantly, with a pattern of LAP>GAP>HAP for both δ2H and δ18O values. the variations of d-excess values and the slopes and intercepts of the meteoric water lines of autumn rain showed opposite trends. The main factor controlling autumn rain anomaly was not the local meteorological parameters, but the El Nino-Southern Oscillation and the Indian Ocean dipole events, which could explain 99% and 93% of the autumn rain isotopic variations, respectively. These coupling phenomena affected water vapor transport intensity of the marine air mass to the northwest inland, which determined autumn rainfall amount and the stable hydrogen-oxygen isotope composition. Our results would be helpful for improving the understanding of autumn rain anomalies in West China, and provide basic data and theoretical support for regional hydrological model building, would thereby better serve water resources management and disaster prevention and reduction.

Controls on the hydrogen isotope composition of tetraether lipids in an autotrophic ammonia-oxidizing marine archaeon

The stable hydrogen isotope composition of persistent biomolecules is used as a palaeohydrological proxy. While much previous work has focused on plant leaf wax-derived n-alkanes, the potential of prokaryotic lipid biomarkers as carriers of H isotope signatures remains underexplored, particularly in the Archaea. Here we investigated H isotope distributions in the membrane lipids of the ammonia-oxidizing chemoautotroph Nitrosopumilus maritimus strain SCM1. Hydrogen isotope ratios were measured on the cleaved biphytane chains of tetraether membrane lipids extracted from steady-state continuous cultures cultivated at slow, medium, and fast growth rates. In contrast to recent work on bacterial fatty acids, where the direction and magnitude of isotopic fractionation varies widely (ca. 600‰ range) as a function of central C and energy metabolism, archaeal biphytane data in the present work are relatively invariant. The weighted average 2H/1H fractionation values relative to growth water (2εL/W) ranged from –272 to –260‰, despite a three-fold difference in doubling times (30.8–92.5 hr), yielding an average growth-rate effect <0.2‰ hr−1. These 2εL/W values are more negative than most heterotrophic microbial lipid H isotope measurements in the literature, and are on par with those from other autotrophic archaea, as well as with phytol from photoautotrophic algae. N. maritimus values of 2εL/W also varied systematically with the number of internal rings (cyclopentyl + cyclohexyl), increasing for each additional ring by 6.4 ± 2.7‰. Using an isotope flux-balance model in tandem with a comprehensive analysis of the sources of H in archaeal lipid biosynthesis, we use this observation to estimate the kinetic isotope effects (KIEs) of H incorporation from water; from reducing cofactors such as flavins and NADPH, and for the transhydrogenation reaction(s) that convert the electron-donor derived NADH into these cofactors. Consistent with prior studies on bacteria and plants, our results indicate the KIEs of reducing cofactors in archaea are highly fractionating, while those involving exchange of water protons are less so. When combined with the observation of minimal growth-rate sensitivity, our results suggest biphytanes of autotrophic 3HP/4HB utilizing Nitrososphaerota (a.k.a. Thaumarchaeota) may be offset from their growth waters by a nearly constant 2εL/W value. Together with the ring effect, this implies that all biphytanes originating from a common source should have a predictable ordering of their isotope ratios with respect to biphytane ring number, allowing precise reconstruction of the original δ2H value of the environmental water. Collectively, these patterns indicate archaeal biphytanes have potential as paleo-hydrological proxies, either as a complement or an alternative to leaf wax n-alkanes.

Application of concentration and 2-dimensional stable isotope measurements of methane to constrain sources and sinks in a seasonally stratified freshwater lake

Methane (CH4) emissions from aquatic systems have recently been comprised to account for up to 50% of global CH4 emissions, with lakes representing one of the largest CH4 sources within this pool. However, there is large uncertainty associated with CH4 emissions from freshwater environments to the atmosphere, because of a lack of understanding in the spatial and temporal dynamics of CH4 sources and sinks, as well as underlying mechanisms and processes. In this study, we investigated the concentrations and stable carbon (δ13C-CH4) and hydrogen (δ2H-CH4) isotope composition of CH4 in a small eutrophic lake (Lake Willersinnweiher) with seasonal stratification and its spatial and temporal variation. We found that while supersaturation of CH4 in the entire water column was present throughout the whole year, the isotopic composition of CH4 in sediment and water column varied depending on lake stratification, physiochemical conditions, and lake depth. During the stratification period, isotopic characteristics of pelagic surface water CH4 differed from littoral and sedimentary CH4, suggesting likely mixing of CH4 from different sources including vertical and lateral input as well as groundwater input and potentially oxic methane production in the mixed surface water layer. Aerobic CH4 oxidation indicated by a strong increase in both δ13C-CH4 and δ2H-CH4 values at the bottom of the oxycline was found to significantly reduce upward migrating CH4 released at the sediment-water interface. In the sediment, stable isotope characteristics of CH4 showed an increasing dominance of the acetoclastic CH4 formation pathway from the pelagic towards the littoral area. Furthermore, the occurrence of sulfate-dependent anaerobic methane oxidation in the sediment was suggested by an increase in δ13C-CH4 and δ2H-CH4 values. During the mixing period, the isotopic CH4 composition of the water column was distinctively less negative than during the stratification period potentially resulting from a greater impact of groundwater CH4 input compared to the stratification period. Our findings implicate that the application of concentrations and dual isotope measurements of CH4 is a promising approach for constraining CH4 sinks and sources in Lake Willersinnweiher and potentially other small lakes to clearly disentangle the complex CH4 dynamics in lakes both spatially and seasonally.

Stable hydrogen and oxygen isotopes reveal aperiodic non-river evaporative solute enrichment in the solute cycling of rivers in arid watersheds

We investigated the spatial and temporal variations of the stable isotope composition of hydrogen (δD) and oxygen (δ18O) and the total dissolved ions (TDI) concentrations in the Okavango River in the middle Kalahari Desert. We aimed to elucidate the role of evaporation in controlling river solute enrichment from samples collected at a one- to two-month frequency from nine stations along a ∼460 km river transect for one year. We found that the δD and δ18O composition and the TDI concentrations increased downriver. Seasonal increases in the δD and δ18O composition and TDI concentrations during the hot, rainy season were subdued or decreased during the cool, dry season from pulse flooding. The δD and δ18O values of the samples plot along the Okavango Delta Evaporation Line consistent with evaporation. The effect of evaporation during river transit was related to the mean δD (δD = 0.07*River distance (km) − 37.9; R2 = 0.98) and mean d-excess (d-excess = −0.04*River distance (km) + 9.9; R2 = 0.94). The effect of evaporation on the river solute behavior is characterized by the mean d-excess and TDI concentrations (d-excess = −0.29*TDI (mg/L) + 15.0; R2 = 0.97). Some samples from this study and those compiled from published studies plot at greater than one sigma standard deviation above and below the mean TDI concentration vs. mean d-excess regression model line. We use these marked deviations from the mean TDI concentration vs. the mean d-excess regression model to suggest that additional solutes from river-floodplain-wetland-island interaction driven by pulse flooding are delivered into the river. While our findings support an evaporation-dominated solute enrichment during river transit at the seasonal scale, we conclude that intermittent hydrology (pulse flooding) plays an important role in the sub-seasonal spatiotemporal behavior of solutes in rivers in arid watersheds, which must be considered in solute cycling models.

Stable sulphur isotope (δ 34S) ratios in bird feathers from India indicate strong segregation between the Himalaya and Gangetic plain, and the rest of India

ABSTRACT Although stable hydrogen (δ 2H) and carbon (δ 13C) isotopic compositions of bird feathers have been increasingly used to understand the migration of birds through assignment of individuals to established isoscapes, far less is known about the structure of feather isoscapes based on stable sulphur isotope (δ 34S) assays. While δ 2H isoscapes have been used to investigate the migratory origins of the Globe Skimmer (Pantala flavescens) dragonfly in India, no isotope studies have been applied to avian migration patterns in that region. Here, based on museum collections, we report the feather δ 34S values of 13 avian species that included marine birds with expected 34S enriched feathers, resident birds throughout India and a single migratory species, Bar-headed Goose (Anser indicus). Feathers from the marine birds were the most enriched (20.6 ± 1.2 ‰, n = 10; range = 4.4 ‰) in 34S but terrestrial resident species also showed unexpectedly high δ 34S values (11.7 ± 4.8 ‰, n = 74; range = 19.9 ‰) throughout most of India but the Himalayan region and Gangetic plain typically showed δ 34S values less than 6.4 ‰. Our results show the utility of feather δ 34S studies to decipher avian and other animal migration between these two regions.

Diurnal Impact of Below-Cloud Evaporation on Isotope Compositions of Precipitation on the Southern Slope of the Altai Mountains, Central Asia

Precipitation is an important natural resource relating to regional sustainability in arid central Asia, and the stable oxygen and hydrogen isotopes provide useful tracers to understand precipitation processes. In this study, we collected the hourly meteorological data at several stations on the southern slope of the Altai Mountains in arid central Asia, from March 2017 to June 2022, and examined the diurnal impact of below-cloud evaporation on stable isotope compositions of precipitation. During nighttime, the changes in isotope compositions below cloud base are generally weak. The enhanced impact of below-cloud evaporation can be found after around 15:00, and the impact is relatively strong in the afternoon, especially from 18:00 to 22:00. Summer and spring usually have a larger impact of below-cloud evaporation than autumn, and the winter precipitation is generally not influenced by below-cloud evaporation. On an annual basis, the differences in evaporation-led isotope changes between daytime and nighttime are 1.1‰ for stable oxygen isotope compositions, 4.0‰ for stable hydrogen isotope compositions and 4.7‰ for deuterium excess. The period from 2:00 to 10:00 shows relatively low sensitivity to relative humidity, and from 14:00 to 22:00 the impacts are sensitive. Considering the fluctuations of precipitation isotope compositions, the impact of below-cloud evaporation does not greatly modify the seasonal environmental signals.

Origin, transport, and retention of fluvial sedimentary organic matter in South Africa's largest freshwater wetland, Mkhuze Wetland System

Abstract. Sedimentary organic matter (OM) analyses along a 130 km long transect of the Mkhuze River from the Lebombo Mountains to its outlet into Lake St Lucia, Africa's most extensive estuarine system, revealed the present active trapping function of a terminal freshwater wetland. Combining bulk OM analyses, such as Rock-Eval®, and source-specific biomarker analyses of plant-wax n-alkanes and their stable carbon (δ13C) and hydrogen (δD) isotopic composition showed that fluvial sedimentary OM originating from inland areas is mainly deposited in the floodplain and swamp area of the wetland system but not in the downstream lake area. A distinctly less degraded OM signature, i.e., a considerably lower degree of transformation of unstable components (higher I index) and lower contribution of refractory and persistent fractions (lower R index) as well as recognizably higher δD values compared to samples from upstream sub-environments, characterizes surface sediments of Lake St Lucia. The offset in δD indicates that the contributing vegetation, although similar to upstream vegetation inputs in terms of photosynthetic pathway (δ13C) and alkane distribution pattern, experienced different hydrological growth conditions. The results suggest that under current conditions hinterland sedimentary OM is deposited throughout the wetland system up to the Mkhuze Swamps, which ultimately captures the transported OM. Consequently, samples from the downstream located Lake St Lucia show locally derived signals instead of integrated signals encompassing the river catchment. This finding raises important constraints for future environmental studies as the assumption of watershed-integrated signals in sedimentary archives retrieved from downstream lakes or offshore might not hold true in certain settings.

Multiproxy records of temperature, precipitation and vegetation on the central Chinese Loess Plateau over the past 200,000 years

The strength of the East Asian Summer Monsoon (EASM) and associated moisture availability have been linked to the spatial distribution of occurrence of C3 and C4 vegetation on the Chinese Loess Plateau (CLP). Variations in the stable carbon isotopic composition of organic matter in loess-paleosol sequences from several locations on the CLP indicate that vegetation has shifted from mainly C3 plants during cool, dry glacials to more C4 plants during warm, wet interglacials. Although increased temperatures generally lead to an expansion of C4 vegetation, increased humidity has an opposite effect, as does increasing pCO2, leaving the exact driver(s) of vegetation change, and thus EASM strength, elusive. Here we reconstruct continuous, directly comparable records of air temperature, monsoon precipitation, and vegetation type over the past 200,000 years based on branched glycerol dialkyl glycerol tetraether (brGDGT) membrane lipids, plant leaf waxes and their isotopic stable carbon and hydrogen isotopic composition (δ13Cwax and δ2Hwax, respectively) preserved at Lingtai on the central CLP. BrGDGT-based temperatures vary between 12 and 21 °C over glacial-interglacial cycles, and consistently lead changes in loess proxies (grain size, magnetic susceptibility), as also observed elsewhere on the CLP. Variations in δ13Cwax are only minor (<2‰) and indicate that C3 plants have continuously dominated at Lingtai, in contrast to a nearby section where C4 plants flourished during interglacials. This difference can be explained by the site elevation (∼1300 m above sea level), resulting in air temperatures too low for widespread C4 vegetation occurrence. Instead, variations in the average chain length of the leaf waxes coinciding with large shifts in δ2Hwax (∼40‰) during glacial-interglacial transitions suggest that changes in rainfall source and seasonality may have pushed C3 woody vegetation present during glacials to more non-woody C3 vegetation during interglacials, as a result of differences in respective water-use efficiency. Our multiproxy records thus indicate that subtle changes in the C3 species composition can be used to reveal variations in EASM precipitation dynamics in elevated areas where temperature exerts a first order control on the vegetation type.

Signals of low grade organic matter alteration in the Upper Permian Kupferschiefer (Spremberg area, Eastern Germany) – A by-product of copper mineralization?

Organic matter (OM) is known to be an important reductant in many sediment-hosted base metal deposits. However, the precise nature of the interactions between OM and hydrothermal fluids is still debated, as is just how such interconnected reactions develop over geological timescales. We investigated the Kupferschiefer mineralization in two drill cores from the Spremberg-Graustein field in Eastern Germany focusing on the inventory of organonitrogen, -sulfur and -oxygen (NSO) compounds, which are most affected by organic–inorganic interactions with mineral surfaces, metals and aqueous fluids. Rather homogeneous deposition of type II marine organic matter, prevailing photic zone euxinia and an early oil window thermal maturity were documented using conventional hydrocarbon analysis. Furthermore, a slight level of hydrothermal alteration was detected in the lower part of drill core 121 h/72, in proximity to the epigenetic hematitic alteration zone known as ‘Rote Fäule’. A minor loss of extractable organic matter and especially long-chain n-alkanes was accompanied by significant enrichment in oxygenated compounds and increased molecular oxygen content detected by ultra-high resolution mass spectrometry (FT–ICR–MS). A strong enrichment of deuterium observed in the n-alkanes (up to −36‰) and isoprenoids (up to −20‰) indicates that hydrogen exchange with an evaporitic fluid occurred in the Spremberg Kupferschiefer over geological timescales at maximum temperatures not exceeding 110 °C. We therefore conclude that FT–ICR–MS, combined with determination of stable hydrogen isotope compositions, can provide valuable information about interaction time scales and the origin of mineralizing hydrothermal fluids.

Combining hydrochemistry and hydrogen and oxygen stable isotopes to reveal the influence of human activities on surface water quality in Chaohu Lake Basin

The input of pollutants caused by human activities induces the deterioration of surface water quality. To reveal the characteristics of surface water quality in Chaohu Lake Basin and the influence of human activities, the hydrochemistry and stable isotope composition of hydrogen and oxygen in lake water and inflow river water were analyzed. The results show that the hydrochemical type of lake water is the Na–Cl type,while river water is the Na–Cl, Ca–Cl and mixed types. The ion proportional coefficient method and principal component analysis show that surface water is controlled by weathering of evaporated salt rocks and silicate rocks, in which Cl- and SO42- are affected by fertilizers and sewage to some extent. There is a strong correlation between conventional ions and nutrient indexes, which indicates that dissolved ions are affected not only by rock weathering but also by human activities (such as the discharge of domestic sewage or nitrogen-containing wastewater and the use of fertilizers). The stable isotope values of hydrogen and oxygen in surface water are distributed at the lower right portion of the local precipitation line and are close to it, indicating that surface water mainly originates from precipitation. The high value of d-excess values in surface water indicates that evaporation is weak. As pollution indicators, EC, Cl- and NO3- indicates that the Nanfei River, Dianbu River, Shiwuli River and Pai River flow in northwestern of Chaohu Lake Basin through Hefei urban city are severely polluted, NO3- originates from manure and sewage. Rivers flowing through farmland areas are less polluted, and the use of agricultural fertilizer contributes greatly to NO3-.

Comparing isotopic estimates of paleoelevation from carbonates and volcanic glass from the Miocene-age Chucal Formation in northern Chile

Paleoaltimetry reconstructions of the Central Andes based on stable isotope data indicate variable timing and rates of uplift, reflecting the operation of multiple geodynamic mechanisms. There are a range of isotopic methods and proxies involved in these reconstructions, and it may be that biases inherent in some of these methods has led to misinterpretations. Here we explored the limitations of carbonate archives in reconstructing past elevations, including underestimation of paleoelevations by oxygen-isotope evaporative enrichment and carbonate formation in the subsurface. To conduct our test, we obtained stable isotope values of carbonates from the Western Cordillera in northern Chile at ~18.5–19.5°S, where previously published paleoaltimetry results from the same sections, based on the hydrogen stable isotope composition of volcanic glass, indicate that this region of the Andes has remained at high elevations (>4.4 km) since at least ~23 Ma. We present new oxygen and carbon isotopic, and clumped isotopic results, petrographic and sedimentologic observations, as well as major element abundance (ICP-MS and microprobe analyses) from lacustrine carbonates (marlstones) and cements in sandstones of the early Miocene Chucal Formation in the central Andes of northern Chile. The clumped isotope paleotemperature estimates range from 26 to 45 °C in lacustrine carbonates and 27 to 54 °C in cements. These results indicate that carbonates from this section do not reflect surface temperatures, suggesting clumped isotope resetting in a rock-buffered setting for marlstones and carbonate formation at depth in the presence of groundwater for cements in sandstones. In contrast, the oxygen and carbon isotopic values from carbonates appear to be primary and combined with Mg/Ca ratios and Na concentrations document the transition from lake deposition into a dominantly fluvial environment within the Chucal Formation, also indicating variable evaporative conditions during deposition. The paleoaltimetry estimates in carbonates significantly underestimate the results determined in volcanic glass, with paleoelevation results ranging between 1.4 km and 2.6 km in marlstones and from 2.6 and 3.6 km in cements.. The results presented in this study highlight the importance of using multiple proxies for paleoaltimetry reconstructions, especially in arid land settings where meteoric waters have been modified by evaporation.

Street-level methane emissions of Bucharest, Romania and the dominance of urban wastewater.

Atmospheric methane (CH4) continues to increase, but there are multiple anthropogenic source categories that can be targeted for cost-effective emissions reduction. Cities emit CH4 to the atmosphere from a mixture of anthropogenic CH4 sources, which include, but are not limited to, fugitive emissions from natural gas distribution systems, wastewater treatment facilities, waste-and rainwater networks, and landfills. Therefore, to target mitigation measures, it is important to locate and quantify local urban emissions to prioritize mitigation opportunities in large cities. Using mobile measurement techniques, we located street-level CH4 leak indications, measured flux rates, and determined potential source origins (using carbon and hydrogen stable isotopic composition along with ethane: CH4 ratios) of CH4 in Bucharest, Romania. We found 969 confirmed CH4 leak indication locations, where the maximum mole fraction elevation (above background) was 38.3 ppm (mean = 0.9 ppm ± 0.1 ppm s.e.; n = 2482). Individual leak indicator fluxes, derived using a previously established empirical relation, ranged up to around 15 metric tons CH4 yr-1 (mean = 0.8 metric tons yr-1 ± 0.05, s.e.; n = 969). The total estimated city emission rate is 1832 tons CH4 yr-1 (min = 1577 t yr-1 and max = 2113 t yr-1). More than half (58%–63%) of the CH4 elevations were attributed to biogenic wastewater, mostly from venting storm grates and manholes connecting to sewer pipelines. Hydrogen isotopic composition of CH4 and ethane:methane ratios were the most useful tracers of CH4 sources, due to similarities in carbon isotope ratios between wastewater gas and natural gas. The annual city-wide CH4 emission estimate of Bucharest exceeded emissions of Hamburg, Germany by 76% and Paris, France by 90%.

Evidence for anthropogenic, climatic and oceanographic variability off southwestern Morocco during the last three millennia

In order to obtain a better knowledge of oceanic changes in the Canary Upwelling region during the Late Holocene, marine surface samples and two sediment cores retrieved off southwestern Morocco, GeoB8601–3 and GeoB4223–1, were investigated for organic-walled dinoflagellate cysts (dinocysts). The results were compared with pollen, microcharcoal particles, geochemical records, stable hydrogen and carbon isotope composition (δ 2 H and δ 13 C) of plant-waxes of the same material. The dinocyst results indicate active upwelling prior to 750 BCE and a longer upwelling season between 750 BCE and 950 CE, which is attributed to increased northeast trade winds. After 950 CE, a marked increase of Lingulodinium machaerophorum and Gymnodinium species indicates high fluvial input probably due to a combination of climate (possibly negative NAO) and anthropogenic (terrestrial erosion related to Early Arab conquest) impacts. • We present a new compilation of modern dinocyst distribution off southwestern Morocco. • We investigate Late Holocene dinocyst records from two marine sediment cores. • We employ a multiproxy approach with pollen, microcharcoal and geochemical records. • An interplay of climate and anthropogenic controls were demonstrated.

桂西北喀斯特小流域降雨稳定氢氧同位素组成及影响因素

气候变化背景下，降雨稳定氢氧同位素的变化对以快速的地表-地下水文过程为主要特征的喀斯特生态水文研究有重要意义。以桂西北典型喀斯特峰丛洼地小流域为研究对象，测定2013年至2018年日尺度及2019年至2020年8场大雨或特大暴雨的雨水稳定氢氧同位素组成，分析降雨稳定氢氧同位素变化特征及其影响因素。结果表明，研究区夏半年以海洋性水汽为主，冬半年以干燥的大陆性气团为主，导致夏半年降水δD、δ¹⁸O和氘盈余值显著（P<0.05）低于冬半年。降水的稳定氢氧同位素存在显著的反温度效应和雨量效应，即δ¹⁸O值与温度呈显著（P<0.001）负相关，与降雨量呈显著（P<0.001）正相关。次降雨过程中，持续时间较长（>9.5 h）的降雨存在显著的（P<0.05）雨量效应，特大暴雨则不存在雨量效应，与大气或地理因素有关。研究区水汽来源及降水强度存在明显的时间差异，因此在开展喀斯特小流域生态水文过程研究时，需要关注降水稳定氢氧同位素组成在不同时间尺度上的变化特征。;In the context of global climate change, the variation of stable hydrogen and oxygen isotopes during rainfall is of great significance to study of the rapid surface-to-subsurface hydrologic processes in karst areas. We measured the hydrogen-oxygen isotope composition of water samples during the inter-annual scale rainfall from 2013 to 2018 and eight typical rainfalls (heavy rain to extremely heavy rain) from 2019 to 2020 in the karst area of northwest Guangxi. We also analyzed the variation characteristics of hydrogen-oxygen isotope and its influencing factors. The results show that the δD, δ¹⁸O, and d-excess in the summer half-year is significant (P<0.05) lower than the winter half-year. Hydrogen and oxygen isotopes stable in precipitation have anti-temperature effect and rainfall effect, that is, δ¹⁸O value has a significantly (P<0.001) negative linear relationship with temperature and a significantly (P<0.001) positive linear relationship with rainfall. In the process of rainfall, the rainfall effect was only observed in the long-duration (> 9.5 h) rainfall events. Extremely heavy rain does not have a rainfall effect and is related to atmospheric or geographical factors. These results suggest that studies on eco-hydrological processes should focus on the various characteristics of stable hydrogen and oxygen isotopic compositions of precipitation at different time scales.

Simultaneous, High-Precision Measurements of δ2H and δ13C in Nanomole Quantities of Acetate Using Electrospray Ionization-Quadrupole-Orbitrap Mass Spectrometry.

Stable hydrogen isotope compositions (2H/1H ratios) have been an invaluable tool for studying biogeochemical processes in nature, but the diversity of molecular targets amenable to such analysis is limited. Here, we demonstrate a new technique for measuring δ2H of biomolecules via Orbitrap mass spectrometry (MS) using acetate as a model analyte. Acetate was chosen as a target molecule because its production and consumption are central to microbial carbon cycling, yet the mechanisms behind acetate turnover remain poorly understood. δ2H of acetate could provide a useful constraint on these processes; however, it remains uncharacterized in nature due to analytical challenges. Electrospray ionization (ESI)-Orbitrap MS circumvents these challenges and delivers methyl-specific H-isotope compositions of acetate with nanomole sensitivity, enough to enable analyses of environmental samples. This approach quantifies the methyl-specific δ2H and molecular-average δ13C of acetate simultaneously while achieving <3 and <0.5‰ uncertainty, respectively. Using optimized ionization and Orbitrap parameters, this level of precision is obtained within 15 min using only 15 nmol of acetate. As a demonstration of our analytical approach, we cultured three acetogenic bacteria and found a large 2H-fractionation between acetate and water (>310‰ depletion) associated with the Wood-Ljungdahl pathway, while fermentation expressed a muted (∼80‰) fractionation. With its high precision and sensitivity, Orbitrap MS is a promising tool for investigating these signals in nature after offline purification. Furthermore, the ESI-Orbitrap method presented here could be applied to other molecules amenable to ESI, including central metabolites and sugars, greatly expanding the molecular targets used in hydrogen isotope biogeochemistry.

Estimates of the contribution of fog to wet atmospheric deposition in Czech mountain forests based on its stable hydrogen and oxygen isotope composition: preliminary results

Stable isotopes are increasingly being used in many scientific fields, including environmental sciences. In this study we measured the variation in the stable hydrogen and oxygen isotope composition of fog water, rain water (in the form of bulk falling precipitation) and throughfall water in the Šumava (the Bohemian Forest), Krkonoše (the Giant Mts.) and Jizerske hory (the Jizera Mts.) Mts. in October-November 2017. In total, 46 cumulative two-week samples were collected and analysed. Our results indicate that the overall stable hydrogen and oxygen isotope composition of fog and rain samples differed significantly, fog being isotopically enriched in the heavier isotopes 2H and 18O relative to rain. In contrast to our assumption, throughfall water was generally depleted in the heavier isotopes 2H and 18O relative to rainwater. Hence, the simple mixing model for most samples yielded an unrealistic percentage outside the reasonable range of 0–100%. For few samples, however, the estimated contribution of fog to throughfall ranged between 3 and 8% based on δ2H and 4 and 7% based on δ 18O, which is lower than that estimated for the same mountain regions by other authors using different methods and significantly lower than that reported for mountain ranges in neighbouring countries. Although using stable isotopes is a promising tool for determining the contribution of fog to the hydrological budget when assessing atmospheric deposition, the critical limitations are in the collection, manipulation and storing of the samples.

Seasonal variability in temperature trends and atmospheric circulation systems during the Eemian (Last Interglacial) based on n-alkanes hydrogen isotopes from Northern Finland

The Last Interglacial warm period, the Eemian (ca. 130–116 thousand years ago), serves as a reference for projected future climate in a warmer world. However, there is a limited understanding of the seasonal characteristics of interglacial climate dynamics, especially in high latitude regions. In this study, we aim to provide new insights into seasonal trends in temperature and moisture source location, linked to shifts in atmospheric circulation patterns, for northern Fennoscandia during the Eemian. Our study is based on the distribution and stable hydrogen isotope composition (δD) of n-alkanes in a lake sediment sequence from the Sokli paleolake in NE Finland, placed in a multi-proxy framework. The δD values of predominantly macrophyte-derived mid-chain n-alkanes are interpreted to reflect lake water δD variability influenced by winter precipitation δD (δDprec), ice cover duration and deuterium (D)-depleted meltwater. The δD values of terrestrial plant-derived long-chain n-alkanes primarily reflect soil water δD variability modulated by summer δDprec and by the evaporative enrichment of soil and leaf water. The δDprec variability in our study area is mostly attributed to the temperature effect and the moisture source location linked to the relative dominance between D-depleted continental and polar air masses and D-enriched North Atlantic air masses. The biomarker signal further corroborates earlier diatom-based studies and pollen-inferred January and July temperature reconstructions from the same sediment sequence. Three phases of climatic changes can be identified that generally follow the secular variations in seasonal insolation: (i) an early warming trend succeeded by a period of strong seasonality (ii) a mid-optimum phase with gradually decreased seasonality and cooler summers, and (iii) a late climatic instability with a cooling trend. Superimposed on this trend, two abrupt cooling events occur in the early and late Eemian. The Sokli δD variability is generally in good agreement with other North Atlantic and Siberian records, reflecting major changes in the atmospheric circulation patterns during the Eemian as a response to orbital and oceanic forcings.

The spatial patterns and impact factors of stable oxygen and hydrogen isoscapes in pond water: A case study on the water-source forests of the Hani terraced fields in Yunnan, China

Isoscapes are useful tools for studies concerned with hydroclimatic processes, at multiple scales, and their effects on water resources. However, few studies have been conducted on the application of landscape ecology methods for the characterization of isoscape patterns and their impact factors. In this work, measurements of stable hydrogen and oxygen isotope composition were performed on 112 pond-water samples from the water-source forest of the Hani terraced fields. The spatial gradients of pond-water isotope compositions, and the altitude factor of these gradients, were then analysed according to the topography of the study area, using spatial interpolation and gradient analysis methods. It was found that: 1) The pond-water evaporation line (PWEL) of the study area was δD = 6.28δ18O − 5.5 (R2 = 0.96, n = 112). The gradient and intercept of the PWEL were lower than those of the global meteoric water line (GMWL) and local meteoric water line (LMWL), indicative of intense evaporation. 2) Inverse distance weighting (IDW) interpolation, natural neighbourhood interpolation, spline interpolation, Kriging and Co-Kriging (with altitude as an auxiliary variable) were compared, and IDW interpolation was demonstrated to be the most precise of these methods. IDW interpolation demonstrated that pond-water δ18O values generally increased with decreased altitude, in E-W, S-N and SE-NW directions across the study area. 3) Gradient analysis demonstrated that δ18O generally decreased with increased altitude across the whole-region and at watershed-scales. The δ18O was significantly correlated with altitude on virtually all transects. Therefore, altitude is one of the key factors for the spatial pattern in the stable isotope compositions of the study area’s pond water. This was less pronounced in the E-W transect across the study area, as its isotope compositions were affected by watershed-level patterns. In summary, this work has established a new approach for the analysis of water-body isoscapes and their altitude factor by adopting methods of pattern analysis from landscape ecology.