Isoscapes West, Jason B; Bowen, Gabriel J; Dawson, Todd E
2009, 2014-07-30
eBook
Stable isotope ratio variation in natural systems reflects the dynamics of Earth systems processes and imparts isotope labels to Earth materials. Carbon isotope ratios of atmospheric CO2 record ...exchange of carbon between the biosphere and the atmosphere, the incredible journeys of migrating monarchs is documented by hydrogen isotopes in their wings, and water carries an isotopic record of its source and history as it traverses the atmosphere and land surface. Through these and many other examples, improved understanding of spatio-temporal isotopic variation in Earth systems is leading to innovative new approaches to scientific problem-solving. This volume provides a comprehensive overview of the theory, methods, and applications that are enabling new disciplinary and cross-disciplinary advances through the study of "isoscapes": isotopic landscapes."This impressive new volume shows scientists deciphering and using the natural isotope landscapes that subtly adorn our spaceship Earth.", Brian Fry, Coastal Ecology Institute, Louisiana State University, USA"An excellent timely must read and must-have reference book for anybody interested or engaged in applying stable isotope signatures to questions in e.g. Anthropology, Biogeochemistry, Ecology, or Forensic Science regarding chronological and spatial movement, changes, or distribution relating to animals, humans, plants, or water.", Wolfram Meier-Augenstein, Centre for Anatomy Human Identification, University of Dundee, UK"Natural resources are being affected by global change, but exactly where, how, and at what pace? Isoscapes provide new and remarkably precise answers.", John Hayes, Woods Hole Oceanographic Institution, USA"This exciting volume is shaping a new landscape in environmental sciences that is utilizing the remarkable advances in isotope research to enhance and extend the capabilities of the field.", Dan Yakir, Weizmann Institute of Science, Israel
Water stable isotopes (18O and 2H) are widely used as ideal tracers to track water through the soil and to separate evaporation from transpiration. Due to the technical developments in the last two ...decades, soil water stable isotope data have become easier to collect. Thus, the application of isotope methods in soils is growing rapidly. Studies that make use of soil water stable isotopes often have a multidisciplinary character since an interplay of processes that take place in the vadose zone has to be considered. In this review, we provide an overview of the hydrological processes that alter the soil water stable isotopic composition and present studies utilizing pore water stable isotopes. The processes that are discussed include the water input as precipitation or throughfall, the output as evaporation, transpiration, or recharge, and specific flow and transport processes. Based on the review and supported by additional data and modeling results, we pose a different view on the recently proposed two water world hypothesis. As an alternative to two distinct pools of soil water, where one pool is enriched in heavy isotopes and used by the vegetation and the other pool does not undergo isotopic fractionation and becomes recharge, the water gets successively mixed with newly introduced rainwater during the percolation process. This way, water initially isotopically enriched in the topsoil loses the fractionation signal with increasing infiltration depth, leading to unfractionated isotopic signals in the groundwater.
Key Points
We present how soil water stable isotopes provide valuable insight into water flow processes
We review the influential factors at the soil‐vegetation‐atmosphere interface altering soil water isotopes
We discuss current issues and challenges for soil water isotope studies
Nitrogen (N) capture by arbuscular mycorrhizal (AM) fungi from organic material is a recently discovered phenomenon. This study investigated the ability of two Glomus species to transfer N from ...organic material to host plants and examined whether the ability to capture N is related to fungal hyphal growth. Experimental microcosms had two compartments; these contained either a single plant of Plantago lanceolata inoculated with Glomus hoi or Glomus intraradices, or a patch of dried shoot material labelled with ¹⁵N and ¹³carbon (C). In one treatment, hyphae, but not roots, were allowed access to the patch; in the other treatment, access by both hyphae and roots was prevented. When allowed, fungi proliferated in the patch and captured N but not C, although G. intraradices transferred more N than G. hoi to the plant. Plants colonized with G. intraradices had a higher concentration of N than controls. Up to one-third of the patch N was captured by the AM fungi and transferred to the plant, while c. 20% of plant N may have been patch derived. These findings indicate that uptake from organic N could be important in AM symbiosis for both plant and fungal partners and that some AM fungi may acquire inorganic N from organic sources.
Isotope ratios of heavy elements vary on the 1/10000 level in high temperature materials, providing a fingerprint of the processes behind their origin. Ensuring that the measured isotope ratio is ...precise and accurate depends on employing an efficient chemical purification technique and optimised analytical protocols. Exploiting the disparate speciation of Cu, Fe and Zn in HCl and HNO3, an anion exchange chromatography procedure using AG1‐×8 (200–400 mesh) and 0.4 × 7 cm Teflon columns was developed to separate them from each other and matrix elements in felsic rocks, basalts, peridotites and meteorites. It required only one pass through the resin to produce a quantitative and pure isolate, minimising preparation time, reagent consumption and total analytical blanks. A ThermoFinnigan Neptune Plus MC‐ICP‐MS with calibrator‐sample bracketing and an external element spike was used to correct for mass bias. Nickel was the external element in Cu and Fe measurements, while Cu corrected Zn isotopes. These corrections were made assuming that the mass bias for the spike and analyte element was identical, and it is shown that this did not introduce any artificial bias. Measurement reproducibilities were ± 0.03‰, ± 0.04‰ and ± 0.06‰ (2s) for δ57Fe, δ65Cu and δ66Zn, respectively.
Les rapports isotopiques des éléments lourds varient au niveau de la quatrième décimale dans les matériaux de haute température, fournissant ainsi un accès aux processus ayant participé à la formation de ces derniers. S'assurer que le rapport isotopique mesuré est précis et exact dépend de l'emploi d'une technique de purification chimique efficace et de protocoles analytiques optimisés. L'exploitation de la spéciation différentielle de Cu, Fe et Zn dans l'HCl et le HNO3 a permis le développement d'une procédure de chromatographie échangeuse d'anions utilisant de la résine anionique AG1‐X8 (200–400 mesh) et des colonnes en téflon (0.4 x 7 cm) pour séparer ces éléments à la fois les uns des autres mais aussi de ceux de la matrice dans des roches felsiques, des basaltes, des péridotites et des météorites. Il n'a fallu qu'un seul passage dans la résine pour produire un isolat mono élémentaire ultra pur, en minimisant le temps de préparation, la consommation de réactif et le blanc analytique total. En utilisant un MC‐ICP‐MS ThermoFinnigan Neptune plus, une alternance standard‐échantillon avec étalon externe a servi à corriger le biais de masse. Le Nickel était l'élément externe dans les mesures de Cu et de Fe alors que le Cu a été utilisé pour corriger les isotopes du Zn. Ces corrections ont été apportées en supposant que le biais de masse pour le spike et l'élément analysé était identique, et il est démontré que cela n'a pas introduit de biais artificiel. La reproductibilité des mesures a été de ± 0.03‰, ± 0.04‰ et ± 0.06‰ (2s) pour respectivement δ57Fe, δ65Cu et δ66Zn.
Food web ecology has revolutionized our understanding of ecological processes, but the drivers of food web properties like trophic position (TP) and food chain length are notoriously enigmatic. In ...terrestrial ecosystems, above‐ and belowground systems were historically compartmentalized into “green” and “brown” food webs, but the coupling of these systems by animal consumers is increasingly recognized, with potential consequences for trophic structure. We used stable isotope analysis (δ13C, δ15N) of individual amino acids to trace the flow of essential biomolecules and jointly measure multichannel feeding, food web coupling, and TP in a guild of small mammals. We then tested the hypothesis that brown energy fluxes to aboveground consumers increase terrestrial food chain length via cryptic trophic transfers during microbial decomposition. We found that the average small mammal consumer acquired nearly 70% of their essential amino acids (69.0% ± 7.6%) from brown food webs, leading to significant increases in TP across species and functional groups. Fungi were the primary conduit of brown energy to aboveground consumers, providing nearly half the amino acid budget for small mammals on average (44.3% ± 12.0%). These findings illustrate the tightly coupled nature of green and brown food webs and show that microbially mediated energy flow ultimately regulates food web structure in aboveground consumers. Consequently, we propose that the integration of green and brown energy channels is a cryptic driver of food chain length in terrestrial ecosystems.
Nitrate pollution of surface water has attracted global attention, and the issue is becoming increasingly significant in China. To identify the pollution status, sources, and potential ...non-carcinogenic health risks of nitrate in China's river water, nitrate data from 71 major rivers from 30 provinces were systematically collected. The spatial distribution of nitrate concentrations in river water was analyzed, and the main nitrate pollution sources were revealed based on the presence of nitrogen and oxygen isotopes of nitrate. The results show that approximately 7.83% of samples in China exceeded the national drinking water standard for nitrate (45 mg/L). The concentrations of nitrate in Mudan River (Linkou County), Haihe (Beijing), and Yangtze River estuary (Shanghai) exceed 90 mg/L, which indicates severe pollution. The characteristic values of δ15N and δ18O of river water in China range from −23.5‰ to 26.99‰ and − 12.7‰ to 83.5‰, indicate many sources including inorganic fertilizer, soil nitrogen, wastewater or manure. The primary sources of nitrate in river water of Northeast, Northwest, Southwest, and South China were manure, septic waste, inorganic fertilizer, and soil organic matter nitrification. Manure and septic waste were the major source of nitrate in Central, East, and North China. Correlation analysis revealed that the nitrate concentrations of surface water has a positive relationship with GDP, nitrogen fertilizer application usage, wastewater discharge, and population in China. Non-carcinogenic risk of nitrate was identified in 80% of the regions in China, and potential moderate non-carcinogenic risk areas are Shanghai, Beijing, and Shaanxi. It is urgent to solve the problem of pollution and prevent the further pollution of China's river water. Though the new “10-point Water Plan” issued by the Chinese government solved previous problems, it will take decades to control and repair polluted surface water.
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•The pollution of nitrate in river water increased gradually from west to east.•The distribution nitrate pollution was uneven from north to south.•The sources of nitrate in river water are varied and blending of mult-sources.•Nitrate pollution was impacted by GDP, fertilizer, wastewater, population.•80% of China present non-carcinogenic health risks, especially for children.
In this study, we measured Ni, Co, Cd, and Pb concentrations in the whole blood of farmers from southeast Brazil to address the factors influencing human exposure in this population. The factors ...included smoking, alcohol consumption, aging, body composition, gender, and feeding preferences, which were measured through carbon and nitrogen isotopic composition. We also calculated and compared the reference values (RVs) of the measured elements to evaluate ongoing exposure levels. We observed the influence of lifestyle habits on metal exposure; Cd levels were statistically higher in smokers, and alcohol consumption affected only Pb concentrations, with an association also observed with the frequency of alcohol ingestion. The metal levels were positively associated with both isotope values, indicating that feeding may be the dominant source of these elements in this population. We also observed the effect of endogenous sources measured through age, as increased Pb concentrations in both genders and higher Cd levels in older women, which is related to bone, kidney, and liver accumulation. The body mass index was negatively associated with Ni, Co, and Cd in women and positively in men. The negative associations may indicate that body fat may act as a reservoir for metals, reducing their availability in the blood in individuals with higher body mass and possibly influencing the assessment of exposure levels. The evaluated population presented elevated RVs for all elements: Ni 36, Co 3.3, Cd 16, and Pb 149 μg L−1. These values point to higher exposure in this population compared to other studies in Brazil and worldwide. These results emphasize an urgent need for monitoring programs for toxic substances in Brazil and evaluating possible health effects, given the ongoing environmental exposure associated with endogenous exposure and lifestyle habits that promote higher metal levels in this population.
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•Brazilian farms present elevated blood metal concentrations.•Lifestyle habits and exogenous/endogenous sources contribute to increased levels.•Blood C and N isotopes reflect metal levels, indicating the effect of feeding.•There is an urgent need to monitor toxic substances in Brazil.
Oceanic basalts show variation in their iron and magnesium isotope compositions. One hypothesis for the origin of this is source variation: radiogenic isotope and trace element abundance studies have ...long argued that the Earth's upper mantle is geochemically heterogeneous and that subducted crust is a major contributor to this diversity. In contrast, a recent hypothesis posits that stable isotopes record disequilibrium during melt transport and so provide novel insight into the melting process. In this study we investigate the first of these hypotheses, that source heterogeneity explains global Fe-Mg isotope systematics. We compile a global dataset of oceanic basalt Fe and Mg isotopes and complement this with new Fe-Mg isotope data from locations possessing some of the most extreme radiogenic isotope ratios for their setting: ocean island basalts from the Cook-Austral and Society islands and a Mid-Atlantic Ridge basalt. Despite both Fe and Mg isotope systems having the ability to trace recycled crustal material in the mantle, their global systematics are very different in this dataset. The global compilation of primitive oceanic basalts records heavier Fe (higher δ57Fe) isotope compositions than bulk silicate earth (BSE), but a mixture of heavier and lighter Mg isotope compositions than BSE. By employing a coupled Fe-Mg equilibrium isotope fractionation model during mantle melting we show that much of this isotopic variability can be generated by the mixed melts produced by melting of peridotite mantle containing moderate amounts of recycled crust as a discrete lithology. The Fe isotope composition of the melts is controlled by the bulk isotope composition of the recycled crust (expected to be considerably heavier than BSE, but variable). In contrast, the Mg isotope composition is controlled by source mineralogy. Olivine-poor lithologies such as recycled crust are able to generate large Mg isotope fractionations during melting, both positive and negative (± 0.1‰) relative to the mantle source, depending on the presence of spinel, clinopyroxene or garnet. These melt Mg isotope fractionations are consistent with the Mg isotope compositions of mid-ocean ridge basalts generated by variable depths of mantle melting. Our equilibrium model provides a baseline to test hypotheses of Fe-Mg isotope variability in basalts: our results show that contributions from recycled crust-derived melts, generated in spinel-, pyroxene-, and garnet-bearing mineral assemblages in the mantle, would be able to produce much of the Fe-Mg isotope variability seen in the global compilation of primitive oceanic basalts, without requiring isotopically extreme mantle components (e.g., carbonate with a light Mg isotope signature) or disequilibrium fractionation. However some basalt variability in ocean island settings may indeed fall outside the paradigm of pyroxenite heterogeneity – whilst we consider carbonates unlikely to be important, disequilibrium processes may in these cases play a role.
•Most oceanic basalt δ57Fe–δ26Mg is consistent with small pyroxenite contributions.•Basalt δ57Fe–δ26Mg constrain mantle composition and lithology respectively.•MORB δ26Mg forms a coherent global array with ridge depth.•Some basalt δ57Fe–δ26Mg are not matched by pyroxenite & equilibrium fractionation.
Mixing models are statistical tools that use biotracers to probabilistically estimate the contribution of multiple sources to a mixture. These biotracers may include contaminants, fatty acids, or ...stable isotopes, the latter of which are widely used in trophic ecology to estimate the mixed diet of consumers. Bayesian implementations of mixing models using stable isotopes (e.g., MixSIR, SIAR) are regularly used by ecologists for this purpose, but basic questions remain about when each is most appropriate. In this study, we describe the structural differences between common mixing model error formulations in terms of their assumptions about the predation process. We then introduce a new parameterization that unifies these mixing model error structures, as well as implicitly estimates the rate at which consumers sample from source populations (i.e., consumption rate). Using simulations and previously published mixing model datasets, we demonstrate that the new error parameterization outperforms existing models and provides an estimate of consumption. Our results suggest that the error structure introduced here will improve future mixing model estimates of animal diet.
According to the River Continuum Concept, headwater streams are richer in allochthonous (e.g. terrestrial leaves) than autochthonous (e.g. algae) sources of organic matter for consumers. However, ...compared to algae, leaf litter is of lower food quality, particularly ω‐3 polyunsaturated fatty acids (n‐3 PUFA), and would constrain the somatic growth, maintenance, and reproduction of stream invertebrates. It may be thus assumed that shredders, such as Gammarus, receive lower quality diets than grazers, e.g. Ecdyonurus, that typically feed on algae.
The objective of this study was to assess the provision of dietary PUFA from leaf litter and algae to the shredder Gammarus and the grazer Ecdyonurus. Three different diets (algae, terrestrial leaves, and an algae–leaf litter mix) were supplied to these macroinvertebrates in a flume experiment for 2 weeks. To differentiate how diet sources were retained in these consumers, algae were isotopically labelled with 13C.
Both consumers became enriched with 13C in all treatments, demonstrating that both assimilated algae. For Gammarus, n‐3 PUFA increased, whereas n‐6 PUFA stayed constant. By contrast, the n‐3 PUFA content of Ecdyonurus decreased as a consequence of declining algal supply.
Results from compound‐specific stable isotope analysis provided evidence that the long‐chain n‐3 PUFA eicosapentaenoic acid (EPA) in both consumers was more enriched in 13C than the short‐chain n‐3 PUFA α‐linolenic acid, suggesting that EPA was taken up directly from algae and not from heterotrophic biofilms on leaf litter. Both consumers depended on algae as their carbon and EPA source and retained their EPA from high‐quality algae.
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