Isotopic shift in streamflow relative to precipitation over 13 years: fractionation versus selection effects

In this paper we make comparisons between the observed oxygen and hydrogen stable isotope composition of leaf water and the predictions of the Craig-Gordon model of evaporative isotopic enrichment. Comparisons were made among two C3 species (Chenopodium album and Helianthus annuus) and two C4 species (Amaranthus retroflexus and Kochia scoparia), when plants were exposed to natural environmental conditions in the field. There were significant differences among the species for the hydrogen and oxygen isotopic composition of leaf water at mid-day. The Amaranthus and Helianthus plants had lower leaf water δD and δ18O values than did Kochia and Chenopodium. The observed leaf water δ values were significantly lower than those predicted by the evaporative enrichment model for all the species. The degree of discrepancy between the observed and modelled leaf water isotopic compositions differed among species. There was a strong linear relationship between the oxygen and hydrogen isotopic compositions of stem water, observed leaf water and the modelled leaf water for all species. The observed leaf water isotopic composition for the different species occurred at different points along the line connecting the stem water isotopic composition and the modelled leaf water isotopic composition in a plot of δD and δ18O. We interpret these linear relationships as mixing lines between the unfractionated source or stem water isotopic composition and the isotopic composition of water at the evaporation sites within leaves (as defined by the evaporative enrichment model).

Geochemical records of bivalve shells have been increasingly studied in the last decade to obtain information on climate conditions. In this paper we present stable isotope compositions of living and prehistoric shells of freshwater mussels (Unionidae) and their relationships with climate conditions in a shallow lake environment of Lake Balaton, West-Central Hungary. Physical conditions and stable oxygen isotope compositions of lake water samples were monitored where living bivalves were collected. Comparisons between seasonal variations in ambient temperature, water composition and within-shell isotopic variations indicate that the shells of Unio pictorum do reflect local changes at high resolution and thus can be used to study past conditions. Additionally, shells covering the last two decades were gathered at several locations along the lake in order to determine spatial and temporal variations in the shells’ isotopic compositions as a function of weather conditions. As an application, prehistoric shells collected in archaeological excavations were analysed in order to study past environmental variations. Climate variations during the Late Copper Age (5460–4870 cal. yr BP) have been assumed on the basis of geomorphological and archaeozoological observations at the site BalatonkeresztAor-RA©ti-dA±lA‘ (south of Lake Balaton), that suggested increasing humidity as a cause of changes in settlement location and domestic livestock husbandry. Stable carbon and oxygen isotope compositions of prehistoric bivalve shells were analyzed from excavations representing five archaeological subphases (BolerAiz subphase, 5460–5310 cal. yr BP; two transitional subphases around 5310 cal. yr BP; Early Classic subphase, 5310–5060 cal. yr BP; Late Classic subphase, 5040–4870 cal. yr BP). The analyses revealed significant negative C and O isotope shifts in the transitional subphases relative to the earlier and later subphases. The isotopic variations indicate that the local climate became relatively wet and possibly cold around 5310 cal. yr BP, then it returned to drier (and likely warmer) conditions during the Classic subphases. This interpretation is in agreement with previous studies on climate changes related to the “5.3 ky event” in the European continental area and the North Atlantic Region, indicating an Atlantic influence in the Carpathian Basin.

SummaryWe compiled hydrogen and oxygen stable isotope compositions (δ2H and δ18O) of leaf water from multiple biomes to examine variations with environmental drivers. Leaf water δ2H was more closely correlated with δ2H of xylem water or atmospheric vapour, whereas leaf water δ18O was more closely correlated with air relative humidity. This resulted from the larger proportional range for δ2H of meteoric waters relative to the extent of leaf water evaporative enrichment compared with δ18O. We next expressed leaf water as isotopic enrichment above xylem water (Δ2H and Δ18O) to remove the impact of xylem water isotopic variation. For Δ2H, leaf water still correlated with atmospheric vapour, whereas Δ18O showed no such correlation. This was explained by covariance between air relative humidity and the Δ18O of atmospheric vapour. This is consistent with a previously observed diurnal correlation between air relative humidity and the deuterium excess of atmospheric vapour across a range of ecosystems. We conclude that 2H and 18O in leaf water do indeed reflect the balance of environmental drivers differently; our results have implications for understanding isotopic effects associated with water cycling in terrestrial ecosystems and for inferring environmental change from isotopic biomarkers that act as proxies for leaf water.

Stable oxygen and hydrogen isotopic compositions (δ18O and δD) of plant xylem water and its potential water sources can provide new information for studying water sources, competitive interactions and water use patterns of plants. The contributions of different water sources to three plants, Hedysarum scoparium (HS), Caragana Korshinskii (CK) and Artemisia ordosica(AO), were investigated in the artificial sand-fixed vegetation of Shapotou, the southeastern margin of the Tengger Desert of northwestern China, based on meteorological data and δ18O and δD values of precipitation, groundwater, soil water and xylem water of HS, CK and AO. Our results indicated that water content throughout the soil profile and their competition balance for water uptake during different growth season. The results indicate that these sand-fixed plants have developed into a relatively stable stage and they are able to regulate their water use behavior as a response to the environmental conditions, which reinforces the effectiveness of plantation of native shrubs without irrigation in degraded areas.

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.

Influence of the North Atlantic Oscillation on δD and δ18O in meteoric water in the Armenian Highland

Peat cores are valuable archives of past environmental change because they accumulate plant organic matter over millennia. While studies have primarily focused on physical, ecological, and some biogeochemical proxies, cores from peatlands have increasingly been used to interpret hydroclimatic change using stable isotope analyses of cellulose preserved in plant remains. Previous studies indicate that the stable oxygen isotope compositions (δ18O) preserved in alpha cellulose extracted from specific plant macrofossils reflect the δ18O values of past peatland water and thereby provide information on long-term changes in hydrology in response to climate. Oxygen isotope analyses of peat cellulose (δ18Ocellulose) have been successfully developed from peat cores that accumulate the same species for millennia. However, to fully exploit the potential of this proxy in species-diverse fens, studies are needed that account for the isotopic variations caused by changes in dominant species composition. This study assesses variation in δ18O values among peatland plant species and how they relate to environmental waters in two fens informally named Horse Trail and Goldfin, located on the leeward (dry) and windward (wet) side, respectively, of the climatic gradient across the Kenai Peninsula, Alaska. Environmental water δ18O values at both fens reflect unmodified δ18O values of mean annual precipitation, although at Goldfin standing pools were slightly influenced by evaporation. Modern plant (mosses and Carex (sedges)) δ18Ocellulose values indicate that all Carex are higher (~2.5 ‰) than those of mosses, likely driven by their vascular structure and ecophysiological difference from non-vascular mosses. Moss δ18Ocellulose values within each peatland are similar among the species, and differences appear related to evaporation effects on environmental waters within hummocks and hollows. The plant taxa-environmental water δ18O differences are applied to the previously determined Horse Trail Fen untreated bulk δ18O record. Results include significant changes to inferred millennial-to-centennial scale hydroclimatic trends where dominant taxa shift from moss to Carex, indicating that modern calibration datasets are necessary for interpreting stable isotopes from fens, containing a mix of vascular and nonvascular plants. Accounting for isotopic offsets through macrofossil analysis and modern plant-water isotope measurements opens new opportunities for hydroclimatic reconstructions from fen peatlands.

Meltwaters dominate groundwater recharge in cold arid desert of Upper Indus River Basin (UIRB), western Himalayas

根据全球降水同位素观测网(GNIP)提供的昆明站大气降水氢氧稳定同位素数据及其气象资料，对昆明站1986~1992、1996~2003年共计15年的月均和年均大气降水氢氧同位素组成及其影响因素进行分析和研究。结果表明：昆明月均及年均同位素组成均落在中国和全球降水同位素的变化范围之内，并呈现明显的季节及年际变化。昆明大气降水中δD和δ18O主要受到水汽来源影响，而且在季节和年际尺度上存在较大差异。经计算得出：昆明雨季(5~10月)降水中氧同位素值81.7%受当地降水量控制，18.3%受气温影响，这说明昆明大气降水中δ18O受降水量和气温的协同影响，但以降水量对其影响为主；通过年降水量与西南季风指数对比证实，昆明年降水量与西南季风指数呈正相关性，但与δ18O呈显著的负相性，由此说明在季风影响显著的单一态地区，可以用降水δ18O值指示降水强度或季风强度，这种季风强度-大气降水量-δ18O三者之间的关系可为研究石笋中所蕴含的环境信息提供依据。另外，通过与香港降水同位素对比研究，发现二者的d值虽然均呈现旱季高于雨季的季节性变化趋势，但它们的平均d值几乎相同，由于昆明与香港所处地理位置和距离海洋远近的差异明显，说明二者的水汽来源不同，昆明降水主要受印度洋的西南季风控制，香港降水则主要来源于太平洋控制的东南季风。昆明大气降水线斜率和截距的季节及年际变化趋势可用云下二次蒸发和动力分馏效应来解释。 Using isotope and meteorology data at Kunming station from the GNIP, the average monthly and annual hydrogen and oxygen stable isotopic compositions and the main factors of 15 years (1986-1992 and 1996-2003) at Kunming station were analyzed. The average monthly and annual hydrogen and oxygen stable isotopic compositions fall within the scope of changes in China and the global isotopes of precipitation, and the seasonal and interannual variations are significant. Hydrogen and oxygen stable isotopic compositions of precipitation at Kunming are mainly influenced by vapor source. There exist obvious differences in the seasonal and interannual scales. The local precipitation amount and air temperature determine 81.7% and 18.3% oxygen isotope values in the rainy season, respectively. Even the δ18O in precipitation affected by the precipitation amount and air temperature, the precipitation amount has a stronger affect on the δ18O in precipitation than the air temperature. In addition, the relationship between annual precipitation and Indian monsoon indexes show a positive correlation, but a significant negative correlation with δ18O in precipitation, illustrating that δ18O in precipitation indicates monsoon or rainfall intensity. The relationship between monsoon intensity and precipitation amount and the δ18O in precipitation can provide a scientific support on the meaning of the isotope of the stalagmites. Comparing the isotopes of precipitation in Kunming with that from Hong Kong station, their d values have distinct seasonality with lower values in the rainy season and higher values in the dry season, but they have almost similar values. Nevertheless, geographical location and distance from sea are different, illustrating that the vapor sources are different. Precipitation in Kunming is affected mostly by southwest monsoon from Indian Ocean, but the rainfall in Hong Kong is mainly controlled by southeast monsoon from Pacific Ocean. The seasonal and interannual variation trends of slope and intercept of Kunming precipitation can be explained by below-cloud secondary evaporation and dynamic fractionation effect.

A comparative (1)H NMR study of partially deuterated 1,3- and 1,4-diols has demonstrated that intramolecular hydrogen bonds of different geometry can give rise to equilibrium isotope shifts of opposite sign in hydrogen-bond-accepting solvents such as DMSO-d(6), acetone-d(6), and THF-d(8). The sign inversion is interpreted in terms of the ability of solvent molecules to form competitive intermolecular hydrogen bonds with the diol and in terms of the limiting chemical shifts for the interior and exterior hydroxyl groups. Deuterium is shown to prefer the intermolecular solvent hydrogen bond by 10.9 +/- 0.5 cal/mol for 1,4-diol 3 dissolved in DMSO-d(6) at room temperature. Pyridine-d(5) is shown to be capable of amplifying positive (downfield) isotope shifts measured in DMSO-d(6), in some cases by as much as a factor of 3. Its use is demonstrated for the assignment of the syn or anti relative configuration of 2,4-pentanediol and for the amplification of isotope shifts used to detect intramolecular hydrogen bonds in alpha- and beta-cyclodextrin. Studies in apolar solvents such as CD(2)Cl(2) and benzene-d(6) reveal that the isotope shift is negative (upfield) for all hydrogen bond geometries studied. Larger isotope shifts are measured in benzene-d(6), and a rationale for this amplification is presented. The use of apolar solvents is particularly useful for assigning the syn or anti configuration of 2,4-pentanediol.

To assess spatial, seasonal, and source variability in stable isotopic composition of human drinking waters throughout the entire USA, we have constructed a database of δ18O and δ2H of US tap waters. An additional purpose was to create a publicly available dataset useful for evaluating the forensic applicability of these isotopes for human tissue source geolocation. Samples were obtained at 349 sites, from diverse population centres, grouped by surface hydrologic units for regional comparisons. Samples were taken concurrently during two contrasting seasons, summer and winter. Source supply (surface, groundwater, mixed, and cistern) and system (public and private) types were noted. The isotopic composition of tap waters exhibits large spatial and regional variation within each season as well as significant at‐site differences between seasons at many locations, consistent with patterns found in environmental (river and precipitation) waters deriving from hydrologic processes influenced by geographic factors. However, anthropogenic factors, such as the population of a tap's surrounding community and local availability from diverse sources, also influence the isotopic composition of tap waters. Even within a locale as small as a single metropolitan area, tap waters with greatly differing isotopic compositions can be found, so that tap water within a region may not exhibit the spatial or temporal coherence predicted for environmental water. Such heterogeneities can be confounding factors when attempting forensic inference of source water location, and they underscore the necessity of measurements, not just predictions, with which to characterize the isotopic composition of regional tap waters. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Abstract. Rain-fed peatlands are dominated by peat mosses (Sphagnum sp.), which for their growth depend on nutrients, water and CO2 uptake from the atmosphere. As the isotopic composition of carbon (12,13C) and oxygen (16,18O) of these Sphagnum mosses are affected by environmental conditions, Sphagnum tissue accumulated in peat constitutes a potential long-term archive that can be used for climate reconstruction. However, there is inadequate understanding of how isotope values are influenced by environmental conditions, which restricts their current use as environmental and palaeoenvironmental indicators. Here we tested (i) to what extent C and O isotopic variation in living tissue of Sphagnum is species-specific and associated with local hydrological gradients, climatic gradients (evapotranspiration, temperature, precipitation) and elevation; (ii) whether the C isotopic signature can be a proxy for net primary productivity (NPP) of Sphagnum; and (iii) to what extent Sphagnum tissue δ18O tracks the δ18O isotope signature of precipitation. In total, we analysed 337 samples from 93 sites across North America and Eurasia using two important peat-forming Sphagnum species (S. magellanicum, S. fuscum) common to the Holarctic realm. There were differences in δ13C values between species. For S. magellanicum δ13C decreased with increasing height above the water table (HWT, R2=17 %) and was positively correlated to productivity (R2=7 %). Together these two variables explained 46 % of the between-site variation in δ13C values. For S. fuscum, productivity was the only significant predictor of δ13C but had low explanatory power (total R2=6 %). For δ18O values, approximately 90 % of the variation was found between sites. Globally modelled annual δ18O values in precipitation explained 69 % of the between-site variation in tissue δ18O. S. magellanicum showed lower δ18O enrichment than S. fuscum (−0.83 ‰ lower). Elevation and climatic variables were weak predictors of tissue δ18O values after controlling for δ18O values of the precipitation. To summarize, our study provides evidence for (a) good predictability of tissue δ18O values from modelled annual δ18O values in precipitation, and (b) the possibility of relating tissue δ13C values to HWT and NPP, but this appears to be species-dependent. These results suggest that isotope composition can be used on a large scale for climatic reconstructions but that such models should be species-specific.

An understanding of modern relationships between the stable oxygen isotope composition (δ18O) of lake water and aquatic invertebrates is essential for the interpretation of paleoclimate records based on δ18O of organic remains of these organisms. We analyzed δ18O of lake water and invertebrate remains, including head capsules of chironomid larvae and resting eggs (ephippia) of planktonic Cladocera, in surface sediments from 31 large, deep, and stratified lakes along a latitudinal transect through Europe. The δ18O values measured for both lake water and aquatic invertebrate remains were compared to estimated δ18O in precipitation. A strong linear relationship between mean annual air temperature and δ18O of precipitation was observed along the north–south transect (r = 0.97), whereas the relationship between precipitation δ18O and lake‐water δ18O was weaker (r = 0.80). A strong positive correlation was observed between δ18O in lake water and aquatic invertebrates (r = 0.95 and 0.94 for chironomids and cladocerans, respectively). Although slopes of linear regressions between lake‐water δ18O and δ18O of both aquatic invertebrate groups are similar, a systematic offset between the absolute δ18O values of chironomids and cladocerans was observed; chironomids were on average 2.4‰ heavier than Cladocera. We attribute this offset to differences in ecology, metabolism, and/or behavior between benthic chironomid larvae and planktonic Cladocera. δ18O records based on subfossil chironomid and cladoceran remains have the potential to quantitatively characterize past lake‐water δ18O and, indirectly, past climatic changes.

Deuterium-induced isotope shifts in a series of ML n (L = statistical mixture of 3-oxido-2-phenylpropenal-d0, -1-d and -1,3-d2) were measured. The 13C NMR isotope shifts, δC(D) − δC(H), for the aldehydic CH of AlL3, Al(OiPr)2L, (CH3)2AlL, SiBr3L, SiL3+HBr2−, (CF3)3GeL, (EtO)4NbL, Rh(CO)2L, PdL2, SbCl4L and (EtO)4TaL are small and positive. The positive isotope shifts are unusual, but since they are small and temperature independent they are intrinsic. A relationship between these isotope shifts and the chemical shifts can be discerned and attributed to isotopic perturbation of resonance in an allylic cation. Copyright © 2000 John Wiley & Sons, Ltd.

The stable isotope composition of hydrogen (δ2H) and oxygen (δ18O) in monthly precipitation and river water (Sava River and Danube) samples in the Belgrade area gathered between 1992 and 2005 are determined. The local meteoric water line δ2H=7.8 (±0.2) δ18O+7.3(±1.6) (r 2=0.98, n=60, σ=0.52) for the whole period of observation is close to the global meteoric water line. The amount-weighted mean δ2H and δ18O values of precipitation were−65±27 ‰ and−9.4±3.4 ‰, respectively. Good correlation between δ18O values (r>rsim0.67) and ambient temperature and relative humidity was obtained. Stream-water data ranged from−94 to−60 ‰ for δ2H and from−11.0 to ∼5.7 ‰ for δ18O with highly statistically significant difference (p>0.01) between the Sava River and the Danube. In addition, the isotopic compositions of local precipitation and adjacent river water at monitoring sites were compared. Obtained data will give an opportunity to improve the knowledge of mixing stream water and local groundwater, and assessment of potential groundwater risks and pressures in the Belgrade basin.