δ2H Values Of Water Research Articles

Biochemical and biophysical drivers of the hydrogen isotopic composition of carbohydrates and acetogenic lipids.

The hydrogen isotopic composition (δ2H) of plant compounds is increasingly used as a hydroclimatic proxy; however, the interpretation of δ2H values is hampered by potential coeffecting biochemical and biophysical processes. Here, we studied δ2H values of water and carbohydrates in leaves and roots, and of leaf n-alkanes, in two distinct tobacco (Nicotiana sylvestris) experiments. Large differences in plant performance and biochemistry resulted from (a) soil fertilization with varying nitrogen (N) species ratios and (b) knockout-induced starch deficiency. We observed a strong 2H-enrichment in sugars and starch with a decreasing performance induced by increasing NO3-/NH4+ ratios and starch deficiency, as well as from leaves to roots. However, δ2H values of cellulose and n-alkanes were less affected. We show that relative concentrations of sugars and starch, interlinked with leaf gas exchange, shape δ2H values of carbohydrates. We thus provide insights into drivers of hydrogen isotopic composition of plant compounds and into the mechanistic modeling of plant cellulose δ2H values.

A multidisciplinary geochemical approach to geothermal resource exploration: The Spezzano Albanese thermal system, southern Italy

This work aims to define the geothermal conceptual model of the Spezzano Albanese thermal system located in the northern sector of the Calabria Region, along the western edge of the Sibari Plain. The study confirms that the deep thermal reservoir of Spezzano Albanese is mainly hosted within the permeable levels of the evaporite deposits of the Messinian succession including siltstones with manganese mineralisation, halite, and gypsum-arenites. The thermal waters show discharging temperature between 20.2 and 26.6 °C and a high compositional variability, from Na–Cl to Na–Ca–HCO3. The compositional evolution (from Na–Cl to Na–HCO3) is accompanied by a decrease in both salinity and the concentrations of most dissolved constituents, including Cl, Br, B, Li, Na, K, Mg, Ca, and Ba. These variations are due to mixing between the thermal endmember, rich in Cl and related components, and low-salinity, cold shallow waters (temperature between 17.5 and 22.7 °C). The study points out that the thermal endmember derives by halite dissolution and more complex water-rock interaction processes involving (1) the dissolution of other solid phases of the Messinian deposits, as also confirmed by δ34S values of dissolved sulphate and sulphide, and (2) the precipitation of secondary solid phases (e.g., barite). The geothermometric modelling suggests that the thermal groundwaters in the deep reservoir are probably in equilibrium with either (i) quartz, calcite, disordered dolomite, low-albite, and K-feldspar, as well as with pyrophyllite and poorly crystalline kaolinite (as proxies of clay minerals) at temperatures of 65.5 ± 4.5 °C or (ii) quartz, calcite, disordered dolomite, low-albite, disordered adularia, laumontite and saponites at temperatures of 56.1 ± 4.3 °C, based on the first and second geothermometric model, respectively.The δ18O and δ2H values of water confirm a meteoric origin for the thermal waters with average recharge altitudes between 745 and 857 m a.s.l. These elevations are compatible with the recharge from the western side of the Esaro valley where evaporite successions are found close to the surface.The isotopic value of the dissolved CO2 associated to the Spezzano Terme water highlights its likely microbial origin, as recognised for other thermal circuits hosted in sedimentary rocks of the southern Apennines. Furthermore, the thermal endmember shows a noteworthy enrichment in CH4 with respect to air due to the interaction of groundwater with sediments rich in organic matter. Although methane could have a biogenic origin, the presence of a minor component of thermogenic methane in the gas phase dissolved in the Spezzano Terme waters cannot be completely excluded.The data obtained in this study allow to assume that the recharge meteoric waters descend to a maximum depth of about 1.1–1.4 km below the main emergence area and then the regional NE-SW fault systems probably act as a preferential pathway for the ascent of the thermal waters towards the surface. These waters discharge at Spezzano Albanese, where the crystalline-metamorphic units cropping out immediately upstream of the emergence area act as cap-rock favouring the final ascent towards the surface of the thermal waters.

Species and biosynthetic effects cause uncorrelated variation in oxygen and hydrogen isotope compositions of plant organic compounds

Strong variation in plant organic compound δ2H and δ18O values such as leaf waxes or cellulose among species is commonly observed; however, the extent to which this isotopic variation is driven by leaf water or biochemical isotope effects is relatively unknown. Therefore, we compared variation in leaf water and organic compound δ2H and δ18O values (cellulose - δ2H and δ18O, and n-alkanes – δ2H) across 192 species grown in a botanical garden to assess covariation of isotope values (1) between elements in a given compound, (2) between different (organic) compounds of a given element, and (3) across different growing seasons. Our results suggest that variation in leaf water δ2H values are likely not a strong driver for the observed variation in organic compound δ2H values across species, and that this may also be true for δ18O values. Furthermore, even though correlation between leaf water δ2H and δ18O values appears to be transferred to organic compounds, the explanatory power of this correlation is strongly diminished (R2 < 0.04). This indicates that additional biochemical isotope fractionation leads to substantial variation in organic compound δ2H and possibly also δ18O values across species. Moreover, the low explanatory power of the correlation between cellulose and n-alkane δ2H values (R2 = 0.06) suggests that the biochemical pathways associated with the different compounds are accompanied by different isotope effects. Lastly, cellulose δ2H and δ18O values appeared sensitive to environmental differences between growing seasons, while differences in model-predicted source water δ18O and δ2H values and also climate were negligible between years. By contrast, the species pattern in n-alkane δ2H values was highly conserved between the two years. This indicates that the environmental forcing effects on isotope values were not equal between compounds. Therefore, we conclude that variation in organic compound δ2H (and possibly also δ18O) values among species and growing seasons was more strongly driven by biochemical isotope fractionation rather than by isotope values of plant water. This should be considered in the application of organic compound δ2H and δ18O values to reconstruct past climate, where invariable biochemical isotope fractionation is often assumed. Alternatively, organic compound δ2H and δ18O values could be further developed into a tool to extract plant metabolic information.

Apparent fractionation of hydrogen isotope from precipitation to leaf wax n-alkanes from natural environments and manipulation experiments

Knowledge of hydrogen isotopic fractionation (ε) of plant leaf waxes is the foundation for applying hydrogen isotope values (δ2H) in environmental reconstructions. In this work, we systematically investigated plant ε values (εalk/precipitation, εalk/soil water, εalk/leaf water and εalk/lake water, representing the isotopic fractionation between plant n-alkane δ2H and precipitation δ2H, soil water δ2H, leaf water δ2H and lake water δ2H) from the natural environments and manipulation experiments. The results show that the εalk/precipitation values of terrestrial plants have large variations (from −190 ‰ to −20 ‰) and become more negative with increasing aridity index. This phenomenon is possibly caused by the δ2H changes in source water (from precipitation to soil water and then to leaf water) during plant leaf wax synthesis under various evapotranspiration conditions in different climatic zones. The rainfall manipulation experiments show that leaf water δ2H values are generally higher than soil water δ2H values, and the latter are higher than precipitation δ2H values. This finding further demonstrates that the evapotranspiration effect on source water δ2H affects the quantification of the leaf wax apparent ε values (εalk/leaf water < εalk/soil water < εalk/precipitation). The εalk/lake water values of submerged plants display a smaller range (−153 ± 5 ‰) than the εalk/precipitation values of terrestrial plants, which is close to the terrestrial εalk/precipitation values in humid areas. Therefore, the biosynthetic ε value of terrestrial plant leaf waxes is relatively constant (ca. –153 ± 5 ‰), and the observed variable apparent εalk/precipitation values are possibly caused by the varied degree of evapotranspiration effect on the water that plants used in different climatic conditions. This effect should be considered when applying δ2H values of leaf waxes to trace environmental changes.

Spatial variations in tap water isotopes across Canada: Tracing water from precipitation to distribution and assess regional water resources

With global warming and increasing water use, tap water resources need sustainable management. We used hydrogen and oxygen isotope analyses in tap water (i.e.,δ2H andδ18O values) to identify issues associated with tap water resources in Canada. We analyzed 576 summer tap samples collected from across Canada and 76 tap samples from three cities during different seasons and years. We classified the samples based on their sources: groundwater (TapGroundwater), river (TapRiver) and lake (TapLake).δ2H values in tap water correlate strongly with values predicted for local precipitation across Canada with a stronger correlation for TapGroundwaterand TapRiverthan for TapLake.We then constructed water balance models to predict theδ2H of surface water across Canada, and validated them against Canadian streamδ2H data.δ2H values in tap water correlate strongly with values predicted for local surface water, however, the water balance models improved the predictability only for TapRiverand TapLakeand not for TapGroundwater. TapGroundwaterδ2H values reflect theδ2H values of annually averaged precipitation, whereas TapRiverand TapLakeδ2H values reflect post-precipitation processes. We used theδ2H residuals between the observed and predictedδ2H values to assess regional processes influencing tap waterδ2H values across Canada. Regionally, snow/glacier melt contributes to all tap sources around the Rockies. Tap waters are highly evaporated across Western Canada, irrespective of their sources. In the Great Lakes and East Coast regions, tap waters are evaporated in many localities, particularly those using surface reservoirs and lakes. We propose the use of these isotopic baselines as a way forward for the monitoring of tap water resources at different scales. These isotopic baselines also have valuable applications in human forensic studies in Canada.

Permafrost degradation alters the environmental signals recorded in tree-ring lignin methoxy group δ2H in northeastern China

Climate warming has profoundly altered the status of permafrost and has caused extensive permafrost degradation in the Northern Hemisphere. However, long-term observations investigating the hydrological dynamics of permafrost and its ecological effects on plant growth are lacking. Previous studies have reported tree-ring stable hydrogen isotope ratios of lignin methoxy groups (δ2HLM) as an archive of hydrological signals. This study sampled tree-ring cores from a Larix gmelinii forest in Nanwenghe Forest Park, Northeastern China, and separately measured the tree-ring δ2HLM for earlywood and latewood from 1900 to 2020. Earlywood and latewood δ2HLM values, as well as the difference between them, showed no significant long-term trend from 1900 to 1987; however, they both exhibited significant increasing trends since 1988 at rates of 2.6 ‰ and 4.9 ‰ per decade, respectively. This variance changes the magnitude of the difference between the two chronologies and can be explained by the shift in source water δ2H values during tree growth. Based on a structural equation model analysis, when the influence of permafrost melting weakened due to permafrost degradation, the growing season temperature was better recorded in latewood δ2HLM through the effects of precipitation δ2H from July to September. Based on the environmental response of tree-ring δ2HLM in the permafrost region, permafrost degradation influences the source water δ2H values of trees, thereby affecting the expression of temperature signals in tree-ring δ2HLM. The novel results in this study provide a new perspective on permafrost degradation based on the dynamic responses of tree-ring δ2HLM to source water δ2H during permafrost degradation.

Mid- and long-chain leaf wax δ2H values in modern plants and lake sediments from mid-latitude North America

Compound-specific δ2H values of leaf wax n-alkanes are increasingly being used to infer past hydroclimates. However, differences in n-alkane production and apparent fractionation factors (εapp) among different plant groups complicate the relationships between n-alkane δ2H values and those of environmental water. Mid- and long-chain n-alkanes in sedimentary archives (i.e., n-C23 and n-C29) are thought to derive from aquatic and terrestrial plants, respectively, and track the isotopic composition of either lake water or precipitation. Yet, the relationship between n-C23 δ2H values and lake water δ2H values is not well constrained. Moreover, recent studies show that n-alkane production is greater in terrestrial plants than in aquatic plants, which has the potential to obscure n-alkane aquatic inputs to sedimentary archives. Here, we investigated n-alkane contributions to sedimentary archives from both aquatic and terrestrial plants by analyzing n-alkane δ2H values in plants and lake sediments at 29 sites across mid-latitude North America. We find that both aquatic and terrestrial plants synthesize n-C23 and that sedimentary n-C23 δ2H values parallel those of terrestrial plants and differ from those of aquatic plants. Our results indicate that across mid-latitude North America, both mid- and long-chain n-alkanes in lake sediments commonly derive from terrestrial higher plants challenging the assumption that submerged aquatic plants produce the n-C23-alkane preserved in lake sediments. Moreover, angiosperm and gymnosperm plants exhibit similar εapp values between n-C29 and mean annual precipitation (MAP) δ2H values across North America. Therefore, vegetation shifts between angiosperm and gymnosperm plants do not strongly affect εapp values between n-C29 and MAP. Our results show that both mid- and long-chain n-alkanes track the isotopic composition of MAP in temperate North America.

Constraining parameter uncertainty for predicting oxygen and hydrogen isotope values in fruit.

Understanding δ18O and δ2H values of agricultural products like fruit is of particular scientific interest in plant physiology, ecology, and forensic studies. Applications of mechanistic stable isotope models to predict δ18O and δ2H values of water and organic compounds in fruit, however, are hindered by a lack of empirical parameterizations and validations. We addressed this lack of data by experimentally evaluating model parameter values required to model δ18O and δ2H values of water and organic compounds in berries and leaves from strawberry and raspberry plants grown at different relative humidities. Our study revealed substantial differences between leaf and berry isotope values, consistent across the different relative humidity treatments. We demonstrated that existing isotope models can reproduce water and organic δ18O and δ2H values for leaves and berries. Yet, these simulations require organ-specific model parameterization to accurately predict δ18O and δ2H values of leaf and berry tissue and water pools. We quantified these organ-specific model parameters for both species and relative humidity conditions. Depending on the required model accuracy, species- and environment-specific model parameters may be justified. The parameter values determined in this study thus facilitate applications of stable isotope models where understanding δ18O and δ2H values of fruit is of scientific interest.

Hydrogen and carbon isotope fractionation in modern plant wax n-alkanes from the Falkland Islands

The hydrogen isotopic composition of terrestrial plant waxes (δ2Hwax) is widely used to reconstruct past hydroclimate. δ2Hwax values reflect plant source water or precipitation δ2H (δ2Hprecip) values, and when extracted from sediment archives, records of past δ2Hprecip values can be generated. In order to better interpret these δ2Hwax records, modern calibrations between plant waxes and source water are required when vegetation and location diverge from plant calibrations in other regions. To date, no modern study has examined how δ2Hwax values and source water δ2H values relate in the southern mid- and high-latitude maritime climatic regions where the climate is affected by the Southern Hemisphere Westerly Wind Belt. We present the first modern calibration of δ2Hwax values on the Falkland Islands by analyzing n-alkane plant wax concentrations, δ2H and δ13C values from 11 of the most common plant species, one lichen species, and surface lake sediment samples from four sites on Mount Usborne on East Falkland. Based on plant wax concentrations, the most commonly observed plants on the landscape, Empetrum rubrum and Cortaderia pilosa, are contributing the most to the waxes in sediment archives. We calculate the fractionation between the n-C29 alkane δ2Hwax and δ2Hprecip values (ε2Hwax/precip) for all plant species to be –110 ± 17‰ (1σ, n = 22), which is similar to the global average ε2Hwax/precip. Observed and modelled monthly δ2Hprecip values indicate that δ2Hwax values can be interpreted as mean annual δ2Hprecip values, ultimately establishing the framework for utilizing plant wax-based paleoreconstructions from the mid-latitude maritime climatic regions.

Miocene to modern hydrothermal circulation and high topography during synconvergent extension in the Cordillera Blanca, Peru

AbstractThe Cordillera Blanca detachment in the highest elevations of the Peruvian Andes has been accommodating synconvergent extension since the late Miocene. Stable isotope analysis of synkinematic mica from its exhumed footwall shear zone provides new constraints on deep meteoric-hydrothermal circulation during ductile deformation and regional paleoelevation. Muscovite and biotite that deformed and/or grew synkinematically in the shear zone have δ2H values of −131‰ to −58‰ and −149‰ to −98‰ (versus Vienna standard mean ocean water, VSMOW), respectively. The δ2H value difference between coexisting muscovite and biotite is consistent with equilibrium fractionation of the same fluid at the same temperature. Calculated δ2H values of water (−107‰ to −78‰) in equilibrium with these micas are indistinguishable from those of present-day, deeply circulated (9–11 km) hot spring waters emanating from the fault. Such low-δ2H fluids indicate circulation of meteoric water to the depths of the brittle-ductile transition that cannot be explained by other mechanisms. Average recharge paleoelevation for water entering the shear zone based on hydrogen isotopes was 3400 + 500/–700 m (1σ). This is near, but ~500 m below, the present-day mean elevation of the catchments feeding modern hot springs of 3965 ± 880 m, and ~700 m below the 4200 + 700/–900 m mean recharge elevation derived from δ2H values of modern surface and thermal water. The consistency between modern and ancient fault-assisted hydrothermal systems and elevation suggests that high topography, steep relief, and meteoric-hydrothermal circulation have persisted throughout the history of the Cordillera Blanca detachment system.

Hydrogen isotopic fractionations during syntheses of lipid biomarkers in the seeds of broomcorn millet (Panicum miliaceum L.) under controlled environmental conditions

Compound specific hydrogen isotopic analyses have the potential to reveal the biosynthetic pathways of biomarkers and to reconstruct the effects of water stress in a plant, or in an ecosystem. Although C4 graminoids are of great geological interest and are some of the world's leading crops, there are few experimental studies of their biomarker responses to hydrological conditions. Here, we study a C4 graminoid, broomcorn millet, and compare the effects of controlled changes in environmental conditions on the distributions of n-alkane homologues and on the pentacyclic triterpene, miliacin, which is a biomarker for broomcorn millet; both were measured in the seeds of the graminoid. Broomcorn millet plants were propagated in hydroponic solutions with four different δ2H values for each of two growth chambers, differing in relative humidity (58 and 74%). Analyses of δ2H values of the lipid compounds (miliacin and n-alkanes) in seeds and water extracted from transpiring and non-transpiring organs allowed us to quantify the apparent (lipids vs. source water to plant) and biosynthetic (lipids vs. leaf water) fractionations during miliacin and n-alkane syntheses. Miliacin and n-alkane δ2H values were linearly related to leaf water δ2H values, permitting credible biosynthetic fractionations to be calculated for n-alkanes (average −149.5‰ ± 11) and miliacin (−118‰ ± 5). These biosynthetic fractionations were within the range of published values for compounds with their respective biosynthetic pathways, although a 2H-enrichment of miliacin compared to n-alkanes remains unexplained.Whereas a 16% decrease in relative humidity had no significant impact on the biosynthetic fractionation of miliacin, n-C25 and n-C27 alkanes, it led to a ~25‰ decrease in biosynthetic fractionation for n-C31 and n-C33 alkanes. This could be the consequence of a contribution of more depleted pools of hydrogen atoms in cytoplasmic water (compared to chloroplastic hydrogen pools) during the n-alkyl lipid elongation process. This finding suggests that the respective influences of source water δ2H values and relative humidity on the δ2H values of organic compounds may be discretely inferred by examining the δ2H values of compounds synthesized from distinct sources of hydrogen in cells. This provides clues to the biosynthetic fractionations in a C4 plant for compounds derived from distinct pathways, but also highlights specific issues related to seed lipids which require further research.

Validation and calibration of soil δ2H and brGDGTs along (E-W) and strike (N-S) of the Himalayan climatic gradient

Reconstructing the timing of mountain range uplift and the evolution of high-altitude plateaus is important when attempting to understand potential feedbacks between tectonics and climate at geological timescales. This requires proxies that are able to accurately reconstruct elevation during different time periods in the past. Often, the sensitivity of climatic parameters to elevation gradients, recorded in geological archives such as soils, is used to estimate paleoelevations. However, most proxies reflect an indirect response to elevation change, adding uncertainties to reconstructions. In this study, we aim to identify those sources of uncertainty with respect to elevation reconstructions and test if the combined application of two such proxies, i.e., stable isotopes (δ2H) of plant waxes in modern soils and surface waters and bacterial membrane lipids (brGDGTs) in soils, which can potentially reduce uncertainties in the estimation of (paleo-) elevation. We performed this study in four Himalayan catchments (from west to east: Sutlej, Alaknanda, Khudi, and Arun), of which each individual catchment is subject to a unique precipitation regime, relative influences of moisture sources, and vegetation cover. In total, we analyzed 275 surface water samples, 9 precipitation samples, 131 xylem water samples, and 60 soil samples, which were collected between 2009 and 2014.The following key observations were made: Soil nC31-alkane δ2H values (δ2Hwax) in the Sutlej, Alaknanda, Khudi, and Arun generally record surface water δ2H values, confirming that the first-order control on the plant wax isotopic signature is precipitation δ2H and, therefore, the elevation in orogenic settings. We identified aridity as the factor that introduces scatter to this relationship. BrGDGT-derived Mean Annual Temperature (MAT) correlates in a statistically significant manner with sample site elevation and a 14-year annual average of remotely sensed land-surface temperature, showing that the main process influencing the brGDGT distribution is the adiabatic cooling of air.In an effort to combine these proxies to improve uncertainties in elevation reconstruction, elevations were inferred from both the δ2Hwax and brGDGT distributions. Arid, high elevation sites appear to underestimate actual sample site elevations using δ2H values while sites subject to high (>23–25 °C) annual temperatures overestimate the actual sample site elevation using brGDGT distributions. Elevations inferred from both proxies under such paleoclimatic conditions should be interpreted with caution. Elevations derived from the brGDGT distribution appear to most accurately reconstruct elevation. However, we show that the difference in elevation between the two proxies, described by the proposed ΔElevation parameter, can provide information on the hydrological conditions of the soil’s depositional environment. In conclusion, we emphasize that knowledge of the sample site’s climatic conditions are essential to reconstruct elevation from paleoarchives. In particular, knowledge of moisture availability and annual air temperatures are important, as these have been found to cause the largest scatter in the observed data.

Hydrogen isotope fractionation in modern plants along a boreal-tundra transect in Alaska

An increasing number of studies from high latitude settings use the stable hydrogen isotope ratio (δ2H) of plant leaf waxes to quantify changes in past precipitation. Calibration of modern vegetation and source water use from these landscapes is important to more accurately reconstruct past hydroclimate variability using sedimentary leaf wax δ2H values. Here, we determine plant-water fractionations from 12 sites along a south-north transect in central Alaska, from Fairbanks to Deadhorse (64-70°N). We characterize the δ2H values of n-alkanes and n-alkanoic acids from modern plants and their xylem and leaf water δ2H values, as well as plant source water using surface soils, a soil core, and previously collected meteoric water data from the region. We find both transpiration (εLW/XW) and biosynthetic (εwax/LW) fractionation are sensitive to environmental controls with latitude, with increased leaf transpiration and biosynthetic fractionation to the north, potentially due to increased summer sunlight hours. Soil water δ2H values show near linear 2H enrichment toward the surface associated with evaporation, with the δ2H value ∼40 cm matching mean annual precipitation (MAP). Average net fractionation was calculated using xylem water and chain length weighted wax δ2H values (εwax/XW) and we find nearly the same mean values for both n-alkanes, −112 ± 27‰, and n-alkanoic acids, −110 ± 23‰, from 12 common high latitude vascular plants. To provide the range of likely net fractionations along this transect, we also calculate the average net fractionation using MAP, finding values are less negative than using xylem waters (εwax/MAP, −89 ± 28‰ for n-alkanes, and −86 ± 24‰ for n-alkanoic acids). To compare across studies, we determined the average εwax/MAP of n-alkanes from all available high latitude calibration studies and found more 2H enriched (smaller fractionations) for C27 (-87 ± 29‰), C29 (-87 ± 32‰), and C31 (-91 ± 31‰) than those of global εwax/MAP homolog averages. This new work in Alaska contributes to our growing understanding of plant water-wax fractionation in the high latitudes and is potentially important for the use of sedimentary δ2H values for paleoprecipitation estimates.

Cryogenic vacuum artifacts do not affect plant water‐uptake studies using stable isotope analysis

AbstractWater movement through the soil‐plant‐atmosphere continuum can be tracked through its hydrogen and oxygen isotopic composition. How the isotopic composition of water evolves as it moves through this continuum provides critical information on ecosystem hydrology and climate change. Cryogenic vacuum extraction is the most applied method to extract waters from soil and plant material for such studies. However, recent experiments where oven dried soils were spiked with a reference water suggest potential for these techniques to bias results. We present results from a greenhouse‐based plant water uptake and cryogenic vacuum distillation experiment using Salix viminalis cuttings. We tested the capacity for cryogenic vacuum extraction to recover irrigation water and the plant‐available water pool from 4 soils that were subject to continuous irrigation as would occur in nature. Results show that δ2H and δ18O values of extracted soil waters reflect those of irrigation water, but with some influence of evaporation that varied with differences in soil humic and clay content. This suggests that isotope effects observed in laboratory experiments with oven‐dried soils may not be relevant under natural conditions. Cryogenic vacuum extraction also recovered xylem water δ2H values that matched the δ2H values of extracted soil water but revealed small, consistent offsets between xylem and soil water δ18O values of 0.84 ± 1.13‰. Although these effects may not significantly bias water isotope sourcing applications, they do result in large extrapolation errors when estimating original source water isotope composition from extracted xylem waters using the back extrapolation to the global meteoric water line method.

Isotope (δ13C, δ15N, δ2H) diet–tissue discrimination in African grey parrot Psittacus erithacus: implications for forensic studies

ABSTRACTDiet–tissue isotopic relationships established under controlled conditions are informative for determining the dietary sources and geographic provenance of organisms. We analysed δ13C, δ15N, and non-exchangeable δ2H values of captive African grey parrot Psittacus erithacus feathers grown on a fixed mixed-diet and borehole water. Diet–feather Δ13C and Δ15N discrimination values were +3.8 ± 0.3 ‰ and +6.3 ± 0.7 ‰ respectively; significantly greater than expected. Non-exchangeable δ2H feather values (−62.4 ± 6.4 ‰) were more negative than water (−26.1 ± 2.5 ‰) offered during feather growth. There was no positive relationship between the δ13C and δ15N values of the samples along each feather with the associated samples of food offered, or the feather non-exchangeable hydrogen isotope values with δ2H values of water, emphasising the complex processes involved in carbohydrate, protein, and income water routing to feather growth. Understanding the isotopic relationship between diet and feathers may provide greater clarity in the use of stable isotopes in feathers as a tool in determining origins of captive and wild-caught African grey parrots, a species that is widespread in aviculture and faces significant threats to wild populations. We suggest that these isotopic results, determined even in controlled laboratory conditions, be used with caution.

Using hydrogen isotopes of freshwater fish tissue as a tracer of provenance.

Hydrogen isotope (δ2H) measurements of consumer tissues in aquatic food webs are useful tracers of diet and provenance and may be combined with δ13C and δ15N analyses to evaluate complex trophic relationships in aquatic systems. However, δ2H measurements of organic tissues are complicated by analytical issues (e.g., H exchangeability, lack of matrix‐equivalent calibration standards, and lipid effects) and physiological mechanisms, such as H isotopic exchange with ambient water during protein synthesis and the influence of metabolic water. In this study, δ2H (and δ15N) values were obtained from fish muscle samples from Lake Winnipeg, Canada, 2007–2010, and were assessed for the effects of species, feeding habits, and ambient water δ2H values. After lipid removal, we used comparative equilibration to calibrate muscle δ2H values to nonexchangeable δ2H equivalents and controlled for H isotopic exchange between sample and laboratory ambient water vapor. We then examined the data for evidence of trophic δ2H enrichment by comparing δ2H values with δ15N values. Our results showed a significant logarithmic correlation between fork length and δ2H values, and no strong relationships between δ15N and δ2H. This suggests the so‐called apparent trophic compounding effect and the influence of metabolic water into tissue H were the potential mechanisms for δ2H enrichment. We evaluated the importance of water in controlling δ2H values of fish tissues and, consequently, the potential of H isotopes as a tracer of provenance by taking account of confounding variables such as body size and trophic effects. The δ2H values of fish appear to be a good tracer for tracking provenance, and we present a protocol for the use of H isotopes in aquatic ecosystems, which should be applicable to a broad range of marine and freshwater fish species. We advise assessing size effects or working with fish of relatively similar mass when inferring fish movements using δ2H measurements.

N-Alkane biosynthetic hydrogen isotope fractionation is not constant throughout the growing season in the riparian tree Salix viminalis

Compound-specific δ2H values of leaf wax n-alkanes have emerged as a potentially powerful paleohydrological proxy. Research suggests terrestrial plant n-alkane δ2H values are strongly correlated with meteoric water δ2H values, and may provide information on temperature, relative humidity, evaporation, and precipitation. This is based upon several assumptions, including that biosynthetic fractionation of n-alkanes during synthesis is constant within a single species. Here we present a multi-isotope study of the n-alkanes of riparian Salix viminalis growing in Norwich, UK. We measured n-alkane δ2H, leaf water δ2H, xylem water δ2H, and bulk foliar δ13C and evaluated the variability of n-alkane δ2H values and net biosynthetic fractionation (εlw-wax) over a whole growing season. S. viminalis n-alkane δ2H values decreased by 40‰ between the start of the growing season in April and the time when they stabilized in July. Variation in leaf and xylem water δ2H did not explain this variability. εlw-wax varied from −116‰ during leaf expansion in April to −156‰ during the stable phase. This suggests that differential biosynthetic fractionation was responsible for the strong seasonal trends in S. viminalis n-alkane δ2H values. We suggest that variability in εlw-wax is driven by seasonal differences in the carbohydrate source and thus the NADPH used in n-alkane biosynthesis, with stored carbohydrates utilized during spring and recent occurring growing season assimilates used later in the season. This is further supported by bulk foliar δ13C values, which are 13C-enriched during the period of leaf flush, relative to the end of the growing season. Our results challenge the assumption that biosynthetic fractionation is constant for a given species, and suggest that 2H-enriched stored assimilates are an important source for n-alkane biosynthesis early in the growing season. These findings have implications for the interpretation of sedimentary n-alkanes and call for a careful design of calibration studies using contemporary samples.

Seasonal variation of leaf wax n-alkane production and δ2H values from the evergreen oak tree, Quercus agrifolia

In order to understand the timing of leaf wax synthesis in higher plants, we analysed the variability in leaf wax n-alkane concentration, composition (expressed as average chain length (ACL)), and δ2Hwax values as well as plant source water δ2H values (xylem and leaf water) in the evergreen tree Quercus agrifolia over a period of 9 months, beginning with leaf flush. We identified three distinct periods of leaf development with the first month following leaf flush being characterized by de novo synthesis and possibly removal of n-alkanes. During the following 3 months, n-alkane concentrations increased sevenfold and δ2Hwax and ACL values increased, suggesting this period was the major leaf wax n-alkane formation period. During the remaining 4 months of the experiment, stable values suggest cessation of leaf wax n-alkane formation. We find that n-alkane synthesis in Q. agrifolia takes place over 4 months, substantially longer than that observed for deciduous trees.

2H/1H ratio of hopanes, tricyclic and tetracyclic terpanes in oils and source rocks from the Potiguar Basin, Brazil

We report the hydrogen isotope ratio 2H/1H (expressed as δ2H values) of 8 selected hopanes, tricyclic and tetracyclic terpanes from oils and source rocks in the Potiguar Basin, and of associated formation water. Hopanes ranged in δ2H value from −79‰ to −142‰, whereas tri- and tetracyclic terpanes (TTTs) ranged from −137‰ to −225‰. Formation water δ2H values ranged from −23‰ to −32‰. The most significant pattern in the data is the systematic 2H enrichment of hopanes relative to TTTs, by an average of 45‰ in oils and 78‰ in source rock extracts. The hopanes appear close to hydrogen isotopic equilibrium with coeval formation water, whereas TTTs are significantly more 2H depleted. Given the similarities in structure between the two compound classes, it is unlikely that hopanes would be exchanged completely while the others would not. More likely, both classes have undergone a limited extent of exchange, but with the hopanes being biosynthesized with δ2H values closer to equilibrium. Our data suggest that at least some primary environmental and/or biotic information can be retained in the δ2H values of biomarkers in oils and extracts, and is not completely obscured by hydrogen exchange.

B-HIVE: Beeswax hydrogen isotopes as validation of environment, part II. Compound-specific hydrogen isotope analysis

Abstract Hydrogen isotope analysis has proven a useful tool to understand region-of-origin of food items and biologic materials. Here its application is extended to compound-specific hydrogen isotope analysis of authentic Apis mellifera beeswax and normal-alkanes in order to elicit geographic information. We found A. mellifera produced a characteristic distribution of hydrocarbons that was present in both lipid extracts from beeswax and liquid honey. We observed significant correlations between hydrogen (δ2H) isotope values of beeswax-extracted n-alkanes and both mean annual precipitation and tap water δ2H values. These data suggest the geographical variation in water δ2H values was reflected in beeswax n-alkane δ2H values while isotopic variation was likely related to local environment as potentially influenced by plant varietal. Further, extraction of n-alkanes from liquid honey is shown to be a viable method to expand compound-specific isotope analysis to liquid honeys.