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Sample records for 15n isotope effects

  1. The 15N isotope effect in Escherichia coli: a neutron can make the difference.

    PubMed

    Filiou, Michaela D; Varadarajulu, Jeeva; Teplytska, Larysa; Reckow, Stefan; Maccarrone, Giuseppina; Turck, Christoph W

    2012-11-01

    Several techniques based on stable isotope labeling are used for quantitative MS. These include stable isotope metabolic labeling methods for cells in culture as well as live organisms with the assumption that the stable isotope has no effect on the proteome. Here, we investigate the (15) N isotope effect on Escherichia coli cultures that were grown in either unlabeled ((14) N) or (15) N-labeled media by LC-ESI-MS/MS-based relative protein quantification. Consistent protein expression level differences and altered growth rates were observed between (14) N and (15) N-labeled cultures. Furthermore, targeted metabolite analyses revealed altered metabolite levels between (14) N and (15) N-labeled bacteria. Our data demonstrate for the first time that the introduction of the (15) N isotope affects protein and metabolite levels in E. coli and underline the importance of implementing controls for unbiased protein quantification using stable isotope labeling techniques. PMID:22887715

  2. Insight on RDX degradation mechanism by Rhodococcus strains using 13C and 15N kinetic isotope effects.

    PubMed

    Bernstein, Anat; Ronen, Zeev; Gelman, Faina

    2013-01-01

    The explosive Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is known to be degraded aerobically by various isolates of the Rhodococcus species, with denitration being the key step, mediated by Cytochrome P450. Our study aimed at gaining insight into the RDX degradation mechanism by Rhodococcus species and comparing isotope effects associated with RDX degradation by distinct Rhodococcus strains. For these purposes, enrichment in (13)C and (15)N isotopes throughout RDX denitration was studied for three distinct Rhodococcus strains, isolated from soil and groundwater in an RDX-contaminated site. The observable (15)N enrichment throughout the reaction, together with minor (13)C enrichment, suggests that N-N bond cleavage is likely to be the key rate-limiting step in the reaction. The similarity in the kinetic (15)N isotope effect between the three tested strains suggests that either isotope-masking effects are negligible, or are of a similar extent for all tested strains. The lack of variability in the kinetic (15)N isotope effect allows the interpretation of environmental studies with greater confidence. PMID:23215036

  3. Use of a {sup 15}N isotope dilution method to assess contaminant effects on soil nitrification

    SciTech Connect

    Nason, G.E.; Dinwoodie, G.D.

    1995-12-31

    Ecologically relevant bioassays are needed to assess effects of contaminants on soil processes such as decomposition and nutrient cycling. This study was conducted to assess the potential of a soil-based nitrification bioassay. Soil samples adjusted to 0.03 MPa moisture content were amended with 0.1, 1.0, 10 and 100 mg kg{sup {minus}1} PCP or PCB, and 0.05, 0.5, 5 and 50 mg kg{sup {minus}1} Hg and preincubated for 7 days. A 2-d incubation was then started by addition of 10 mg kg{sup {minus}1} {sup 15}NO{sub 3}-N. Diethyl ether used as a carrier for PCP addition had little effect on inorganic nitrogen concentrations during the incubation. Net nitrogen mineralization and nitrification were unaffected by PCB. Higher amendment levels of both PCP and Hg resulted in increases in ammonium concentrations and decreases in net nitrification. {sup 15}N-nitrate pool dilution was sensitive to contamination and showed some gross nitrification was occurring even when net nitrification had ceased. Recoveries of Hg and PCB at the end of the study were greater than 90%. Recovery of PCP was 5%. Incubations carried out under sterile and non-sterile conditions indicated that both sorption and biological degradation were factors in the low PCP recovery.

  4. Effects of Four Different Restoration Treatments on the Natural Abundance of 15N Stable Isotopes in Plants

    PubMed Central

    Temperton, Vicky M.; Märtin, Lea L. A.; Röder, Daniela; Lücke, Andreas; Kiehl, Kathrin

    2012-01-01

    δ15N signals in plant and soil material integrate over a number of biogeochemical processes related to nitrogen (N) and therefore provide information on net effects of multiple processes on N dynamics. In general little is known in many grassland restoration projects on soil–plant N dynamics in relation to the restoration treatments. In particular, δ15N signals may be a useful tool to assess whether abiotic restoration treatments have produced the desired result. In this study we used the range of abiotic and biotic conditions provided by a restoration experiment to assess to whether the restoration treatments and/or plant functional identity and legume neighborhood affected plant δ15N signals. The restoration treatments consisted of hay transfer and topsoil removal, thus representing increasing restoration effort, from no restoration measures, through biotic manipulation to major abiotic manipulation. We measured δ15N and %N in six different plant species (two non-legumes and four legumes) across the restoration treatments. We found that restoration treatments were clearly reflected in δ15N of the non-legume species, with very depleted δ15N associated with low soil N, and our results suggest this may be linked to uptake of ammonium (rather than nitrate). The two non-legume species differed considerably in their δ15N signals, which may be related to the two species forming different kinds of mycorrhizal symbioses. Plant δ15N signals could clearly separate legumes from non-legumes, but our results did not allow for an assessment of legume neighborhood effects on non-legume δ15N signals. We discuss our results in the light of what the δ15N signals may be telling us about plant–soil N dynamics and their potential value as an indicator for N dynamics in restoration. PMID:22645597

  5. Effects of preservation methods of muscle tissue from upper-trophic level reef fishes on stable isotope values (δ13C and δ15N)

    PubMed Central

    Nelson, James A.; Rozar, Katherine L.; Adams, Charles S.; Wall, Kara R.; Switzer, Theodore S.; Winner, Brent L.; Hollander, David J.

    2015-01-01

    Research that uses stable isotope analysis often involves a delay between sample collection in the field and laboratory processing, therefore requiring preservation to prevent or reduce tissue degradation and associated isotopic compositions. Although there is a growing literature describing the effects of various preservation techniques, the results are often contextual, unpredictable and vary among taxa, suggesting the need to treat each species individually. We conducted a controlled experiment to test the effects of four preservation methods of muscle tissue from four species of upper trophic-level reef fish collected from the eastern Gulf of Mexico (Red Grouper Epinephelus morio, Gag Mycteroperca microlepis, Scamp Mycteroperca phenax, and Red Snapper Lutjanus campechanus). We used a paired design to measure the effects on isotopic values for carbon and nitrogen after storage using ice, 95% ethanol, and sodium chloride (table salt), against that in a liquid nitrogen control. Mean offsets for both δ13C and δ15N values from controls were lowest for samples preserved on ice, intermediate for those preserved with salt, and highest with ethanol. Within species, both salt and ethanol significantly enriched the δ15N values in nearly all comparisons. Ethanol also had strong effects on the δ13C values in all three groupers. Conversely, for samples preserved on ice, we did not detect a significant offset in either isotopic ratio for any of the focal species. Previous studies have addressed preservation-induced offsets in isotope values using a mass balance correction that accounts for changes in the isotope value to that in the C/N ratio. We tested the application of standard mass balance corrections for isotope values that were significantly affected by the preservation methods and found generally poor agreement between corrected and control values. The poor performance by the correction may have been due to preferential loss of lighter isotopes and corresponding

  6. Effects of preservation methods of muscle tissue from upper-trophic level reef fishes on stable isotope values (δ (13)C and δ (15)N).

    PubMed

    Stallings, Christopher D; Nelson, James A; Rozar, Katherine L; Adams, Charles S; Wall, Kara R; Switzer, Theodore S; Winner, Brent L; Hollander, David J

    2015-01-01

    Research that uses stable isotope analysis often involves a delay between sample collection in the field and laboratory processing, therefore requiring preservation to prevent or reduce tissue degradation and associated isotopic compositions. Although there is a growing literature describing the effects of various preservation techniques, the results are often contextual, unpredictable and vary among taxa, suggesting the need to treat each species individually. We conducted a controlled experiment to test the effects of four preservation methods of muscle tissue from four species of upper trophic-level reef fish collected from the eastern Gulf of Mexico (Red Grouper Epinephelus morio, Gag Mycteroperca microlepis, Scamp Mycteroperca phenax, and Red Snapper Lutjanus campechanus). We used a paired design to measure the effects on isotopic values for carbon and nitrogen after storage using ice, 95% ethanol, and sodium chloride (table salt), against that in a liquid nitrogen control. Mean offsets for both δ (13)C and δ (15)N values from controls were lowest for samples preserved on ice, intermediate for those preserved with salt, and highest with ethanol. Within species, both salt and ethanol significantly enriched the δ (15)N values in nearly all comparisons. Ethanol also had strong effects on the δ (13)C values in all three groupers. Conversely, for samples preserved on ice, we did not detect a significant offset in either isotopic ratio for any of the focal species. Previous studies have addressed preservation-induced offsets in isotope values using a mass balance correction that accounts for changes in the isotope value to that in the C/N ratio. We tested the application of standard mass balance corrections for isotope values that were significantly affected by the preservation methods and found generally poor agreement between corrected and control values. The poor performance by the correction may have been due to preferential loss of lighter isotopes and

  7. Effect of age and ration on diet-tissue isotopic (Δ13C, Δ15N) discrimination in striped skunks (Mephitis mephitis).

    PubMed

    Hobson, Keith A; Quirk, Travis W

    2014-01-01

    An important prerequisite for the effective use of stable isotopes in animal ecology is the accurate assessment of isotopic discrimination factors linking animals to their diets for a multitude of tissue types. Surprisingly, these values are poorly known in general and especially for mammalian carnivores and omnivores in particular. Also largely unknown are the factors that influence diet-tissue isotopic discrimination such as nutritional quality and age. We raised adult and juvenile striped skunks (Mephitis mephitis) in captivity on a constant omnivore diet (Mazuri Omnivore A 5635). Adults (n=6) and juveniles (n=3) were kept for 7 months and young (n=7) to the age of 50 days. We then examined individuals for stable carbon (δ(13)C) and nitrogen (δ(15)N) isotope values of hair, nails, lipid, liver, muscle, bone collagen and the plasma, and cellular fractions of blood. Discrimination values differed among age groups and were significantly higher for young compared with their mothers, likely due to the effects of weaning. Δ(15)N isotopic discrimination factors ranged from 3.14 (nails) to 5.6‰ (plasma) in adults and 4.3 (nails) to 5.8‰ (liver) for young. For Δ(13)C, values ranged from-3.3 (fat) to 3.0‰ (collagen) in adults and from-3.3 (fat) to 2.0‰ (collagen) in young. Our data provide an important tool for predicting diets and source of feeding for medium-sized mammalian omnivorous adults integrated over short (e.g. liver, plasma) through long (e.g. collagen) periods and underline the potential effects of age on isotopic values in omnivore diets. PMID:24506487

  8. Nitrogen stable isotope composition (δ15N) of vehicle-emitted NOx.

    PubMed

    Walters, Wendell W; Goodwin, Stanford R; Michalski, Greg

    2015-02-17

    The nitrogen stable isotope ratio of NOx (δ(15)N-NOx) has been proposed as a regional indicator for NOx source partitioning; however, knowledge of δ(15)N values from various NOx emission sources is limited. This study presents a detailed analysis of δ(15)N-NOx emitted from vehicle exhaust, the largest source of anthropogenic NOx. To accomplish this, NOx was collected from 26 different vehicles, including gasoline and diesel-powered engines, using a modification of a NOx collection method used by the United States Environmental Protection Agency, and δ(15)N-NOx was analyzed. The vehicles sampled in this study emitted δ(15)N-NOx values ranging from -19.1 to 9.8‰ that negatively correlated with the emitted NOx concentrations (8.5 to 286 ppm) and vehicle run time because of kinetic isotope fractionation effects associated with the catalytic reduction of NOx. A model for determining the mass-weighted δ(15)N-NOx from vehicle exhaust was constructed on the basis of average commute times, and the model estimates an average value of -2.5 ± 1.5‰, with slight regional variations. As technology improvements in catalytic converters reduce cold-start emissions in the future, it is likely to increase current δ(15)N-NOx values emitted from vehicles. PMID:25621737

  9. Endogenous N-losses in broilers estimated by a [15N]-isotope dilution technique: effect of dietary fat type and xylanase addition.

    PubMed

    Dänicke, S; Jeroch, H; Simon, O

    2000-01-01

    Male broilers were given a low protein diet (15.5% CP) spiked with [15N]H4HCO3 from day 12 to day 18 of age to label the endogenous N-constituents. Experimental diets were subsequently fed from day 19 to day 24 of age and consisted of a rye based diet (56% dietary inclusion) which contained either 10% soya oil (S) or 10% beef tallow (T), each of which was either unsupplemented (-) or supplemented (+) with a xylanase containing enzyme preparation (2700 IU/kg at pH 5.3). [15N]-atom percent excess (APE) of excreta, faeces and urine were monitored on a daily basis during both experimental periods. Furthermore, APE was measured in various tissues at the end of the experiment. The APE of urine on the last day of the experiment was between the APE of the pancreas and that of the jejunal tissue, an observation which supported the usefulness of using urinary APE as an indicator for the endogenous N-pool. Endogenous N-proportions were estimated by an isotope dilution technique at the end of the experiment by examination of the ratio of APE in faeces and urine. The endogenous N-proportion in the faeces was greatest in birds receiving the T(-) diet. The proportions were 0.321, 0.319, 0.451 and 0.289 in S(-), S(+), T(-) and T(+) fed groups, respectively. Xylanase addition reduced endogenous N-proportion, a factor which was used to correct apparent crude protein digestibility (85.6, 86.2, 84.3 and 88.5% in S(-), S(+), T(-) and T(+) fed birds, respectively) for endogenous losses resulting in almost equal true digestibilities of crude protein for all treatments (90.3, 90.6, 90.4 and 91.5%). The amounts of endogenous N in faces were estimated to be 87, 69, 244 and 81 mg per day per kg0.67 body weight in S(-), S(+), T(-) and T(+) fed birds, respectively. It was concluded that xylanase supplementation of a rye based broiler diet does not change endogenous N-secretions when the supplemental fat is soya oil. However, addition of tallow rather than soya oil increased these N

  10. Nitrogen use efficiency evaluation of aerobic rice under field capacity water potential using 15N isotopic tracer technique

    NASA Astrophysics Data System (ADS)

    Wahid, Ahmad Nazrul Abd; Rahim, Sahibin Abd; Rahim, Khairuddin Abdul; Harun, Abdul Rahim

    2015-09-01

    This study was carried out to evaluate the efficiency use of the nitrogen fertilizer on aerobic rice varieties MR219-4 and MR219-9 which were grown aerobically under field capacity water potential at the controlled environment area or shield house. Direct 15N isotope tracer method was used in this study, whereby the 15N isotope was utilized as a tracer for nitrogen nutrient uptake. 15N isotope presence in the samples is determined by using emission spectrometer analysis and percentage of total nitrogen is determined by using Kjeldahl method. 15N atom access value contained in the sample will be used in determining the effectiveness of the use of nitrogen in fertilizers through the specific calculation formulas. In this work, the data several data of nitrogen derived from fertilizer (Ndff), total nitrogen, nitrogen uptake and nitrogen use efficiency was obtained.

  11. Nitrogen use efficiency evaluation of aerobic rice under field capacity water potential using {sup 15}N isotopic tracer technique

    SciTech Connect

    Wahid, Ahmad Nazrul Abd; Rahim, Sahibin Abd; Rahim, Khairuddin Abdul; Harun, Abdul Rahim

    2015-09-25

    This study was carried out to evaluate the efficiency use of the nitrogen fertilizer on aerobic rice varieties MR219-4 and MR219-9 which were grown aerobically under field capacity water potential at the controlled environment area or shield house. Direct {sup 15}N isotope tracer method was used in this study, whereby the {sup 15}N isotope was utilized as a tracer for nitrogen nutrient uptake. {sup 15}N isotope presence in the samples is determined by using emission spectrometer analysis and percentage of total nitrogen is determined by using Kjeldahl method. {sup 15}N atom access value contained in the sample will be used in determining the effectiveness of the use of nitrogen in fertilizers through the specific calculation formulas. In this work, the data several data of nitrogen derived from fertilizer (Ndff), total nitrogen, nitrogen uptake and nitrogen use efficiency was obtained.

  12. Retrieving nitrogen isotopic signatures from fresh leaf reflectance spectra: disentangling δ15N from biochemical and structural leaf properties

    PubMed Central

    Hellmann, Christine; Große-Stoltenberg, André; Lauströ, Verena; Oldeland, Jens; Werner, Christiane

    2015-01-01

    Linking remote sensing methodology to stable isotope ecology provides a promising approach to study ecological processes from small to large spatial scales. Here, we show that δ15N can be detected in fresh leaf reflectance spectra of field samples along a spatial gradient of increasing nitrogen input from an N2-fixing invasive species. However, in field data it is unclear whether δ15N directly influences leaf reflectance spectra or if the relationship is based on covariation between δ15N and foliar nitrogen content or other leaf properties. Using a 15N-labeling approach, we experimentally varied δ15N independently of any other leaf properties in three plant species across different leaf developmental and physiological states. δ15N could successfully be modeled by means of partial least squares (PLSs) regressions, using leaf reflectance spectra as predictor variables. PLS models explained 53–73% of the variation in δ15N within species. Several wavelength regions important for predicting δ15N were consistent across species and could furthermore be related to known absorption features of N-containing molecular bonds. By eliminating covariation with other leaf properties as an explanation for the relationship between reflectance and δ15N, our results demonstrate that 15N itself has an inherent effect on leaf reflectance spectra. Thus, our study substantiates the use of spectroscopic measurements to retrieve isotopic signatures for ecological studies and encourages future development. Furthermore, our results highlight the great potential of optical measurements for up-scaling isotope ecology to larger spatial scales. PMID:25983740

  13. Effects of foliar boron application on seed composition, cell wall boron, and seed δ15N and δ13C isotopes in water-stressed soybean plants

    PubMed Central

    Bellaloui, Nacer; Hu, Yanbo; Mengistu, Alemu; Kassem, My A.; Abel, Craig A.

    2013-01-01

    Limited information is available on the effects of foliar boron (B) application on soybean seed composition. The objective of this research was to investigate the effects of foliar B on seed composition (protein, oil, fatty acids, and sugars). Our hypothesis was that since B is involved in nitrogen and carbon metabolism, it may impact seed composition. A repeated greenhouse experiment was conducted where half of the soybean plants was exposed to water stress (WS) and the other half was well-watered. Foliar boron (FB) in the form of boric acid was applied twice at a rate of 1.1 kg ha−1. The first application was during flowering stage, and the second application was during seed-fill stage. Treatments were water stressed plants with no FB (WS–B); water stressed plants with FB (WS+B); watered plants without FB (W–B), and watered plants with FB (W+B). The treatment W–B was used as a control. Comparing with WS–B plants, B concentration was the highest in leaves and seed of W+B plants (84% increase in leaves and 73% in seed). Seeds of W+B plants had higher protein (11% increase), oleic acid (27% increase), sucrose (up to 40% increase), glucose, and fructose comparing with W–B. However, seed stachyose concentrations increased by 43% in WS–B plants seed compared with W–B plants. Cell wall (structural) B concentration in leaves was higher in all plants under water stress, especially in WS–B plants where the percentage of cell wall B reached up to 90%. Water stress changed seed δ15N and δ13C values in both B applied and non-B applied plants, indicating possible effects on nitrogen and carbon metabolism. This research demonstrated that FB increased B accumulation in leaves and seed, and altered seed composition of well-watered and water stressed plants, indicating a possible involvement of B in seed protein, and oleic and linolenic fatty acids. Further research is needed to explain mechanisms of B involvement in seed protein and fatty acids. PMID:23888163

  14. Effects of foliar boron application on seed composition, cell wall boron, and seed δ(15)N and δ(13)C isotopes in water-stressed soybean plants.

    PubMed

    Bellaloui, Nacer; Hu, Yanbo; Mengistu, Alemu; Kassem, My A; Abel, Craig A

    2013-01-01

    Limited information is available on the effects of foliar boron (B) application on soybean seed composition. The objective of this research was to investigate the effects of foliar B on seed composition (protein, oil, fatty acids, and sugars). Our hypothesis was that since B is involved in nitrogen and carbon metabolism, it may impact seed composition. A repeated greenhouse experiment was conducted where half of the soybean plants was exposed to water stress (WS) and the other half was well-watered. Foliar boron (FB) in the form of boric acid was applied twice at a rate of 1.1 kg ha(-1). The first application was during flowering stage, and the second application was during seed-fill stage. Treatments were water stressed plants with no FB (WS-B); water stressed plants with FB (WS+B); watered plants without FB (W-B), and watered plants with FB (W+B). The treatment W-B was used as a control. Comparing with WS-B plants, B concentration was the highest in leaves and seed of W+B plants (84% increase in leaves and 73% in seed). Seeds of W+B plants had higher protein (11% increase), oleic acid (27% increase), sucrose (up to 40% increase), glucose, and fructose comparing with W-B. However, seed stachyose concentrations increased by 43% in WS-B plants seed compared with W-B plants. Cell wall (structural) B concentration in leaves was higher in all plants under water stress, especially in WS-B plants where the percentage of cell wall B reached up to 90%. Water stress changed seed δ(15)N and δ(13)C values in both B applied and non-B applied plants, indicating possible effects on nitrogen and carbon metabolism. This research demonstrated that FB increased B accumulation in leaves and seed, and altered seed composition of well-watered and water stressed plants, indicating a possible involvement of B in seed protein, and oleic and linolenic fatty acids. Further research is needed to explain mechanisms of B involvement in seed protein and fatty acids. PMID:23888163

  15. Factors Controlling the Stable Nitrogen Isotopic Composition (δ15N) of Lipids in Marine Animals.

    PubMed

    Svensson, Elisabeth; Schouten, Stefan; Hopmans, Ellen C; Middelburg, Jack J; Sinninghe Damsté, Jaap S

    2016-01-01

    Lipid extraction of biomass prior to stable isotope analysis is known to cause variable changes in the stable nitrogen isotopic composition (δ15N) of residual biomass. However, the underlying factors causing these changes are not yet clear. Here we address this issue by comparing the δ15N of bulk and residual biomass of several marine animal tissues (fish, crab, cockle, oyster, and polychaete), as well as the δ15N of the extracted lipids. As observed previously, lipid extraction led to a variable offset in δ15N of biomass (differences ranging from -2.3 to +1.8 ‰). Importantly, the total lipid extract (TLE) was highly depleted in 15N compared to bulk biomass, and also highly variable (differences ranging from -14 to +0.7 ‰). The TLE consisted mainly of phosphatidylcholines, a group of lipids with one nitrogen atom in the headgroup. To elucidate the cause for the 15N-depletion in the TLE, the δ15N of amino acids was determined, including serine because it is one of the main sources of nitrogen to N-containing lipids. Serine δ15N values differed by -7 to +2 ‰ from bulk biomass δ15N, and correlated well with the 15N depletion in TLEs. On average, serine was less depleted (-3‰) than the TLE (-7 ‰), possibly due to fractionation during biosynthesis of N-containing headgroups, or that other nitrogen-containing compounds, such as urea and choline, or recycled nitrogen contribute to the nitrogen isotopic composition of the TLE. The depletion in 15N of the TLE relative to biomass increased with the trophic level of the organisms. PMID:26731720

  16. Factors Controlling the Stable Nitrogen Isotopic Composition (δ15N) of Lipids in Marine Animals

    PubMed Central

    Svensson, Elisabeth; Schouten, Stefan; Hopmans, Ellen C.; Middelburg, Jack J.; Sinninghe Damsté, Jaap S.

    2016-01-01

    Lipid extraction of biomass prior to stable isotope analysis is known to cause variable changes in the stable nitrogen isotopic composition (δ15N) of residual biomass. However, the underlying factors causing these changes are not yet clear. Here we address this issue by comparing the δ15N of bulk and residual biomass of several marine animal tissues (fish, crab, cockle, oyster, and polychaete), as well as the δ15N of the extracted lipids. As observed previously, lipid extraction led to a variable offset in δ15N of biomass (differences ranging from -2.3 to +1.8 ‰). Importantly, the total lipid extract (TLE) was highly depleted in 15N compared to bulk biomass, and also highly variable (differences ranging from -14 to +0.7 ‰). The TLE consisted mainly of phosphatidylcholines, a group of lipids with one nitrogen atom in the headgroup. To elucidate the cause for the 15N-depletion in the TLE, the δ15N of amino acids was determined, including serine because it is one of the main sources of nitrogen to N-containing lipids. Serine δ15N values differed by -7 to +2 ‰ from bulk biomass δ15N, and correlated well with the 15N depletion in TLEs. On average, serine was less depleted (-3‰) than the TLE (-7 ‰), possibly due to fractionation during biosynthesis of N-containing headgroups, or that other nitrogen-containing compounds, such as urea and choline, or recycled nitrogen contribute to the nitrogen isotopic composition of the TLE. The depletion in 15N of the TLE relative to biomass increased with the trophic level of the organisms. PMID:26731720

  17. 15N2 formation and fast oxygen isotope exchange during pulsed 15N18O exposure of MnOx/CeO2

    SciTech Connect

    Kwak, Ja Hun; Szanyi, Janos

    2014-12-23

    Pulsing 15N18O onto an annealed 1% Mn16Ox/Ce16O2 catalyst resulted in very fast oxygen isotope exchange and 15N2 formation at 295 K. In the 1st 15N18O pulse, due to the presence of large number of surface oxygen defects, extensive 15N218O and 15N2 formations were observed. In subsequent pulses oxygen isotope exchange dominated as a result of highly labile oxygen in the oxide. We gratefully acknowledge the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy/Vehicle Technologies Program for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.

  18. Isotopic variability of cave bears (δ15N, δ13C) across Europe during MIS 3

    NASA Astrophysics Data System (ADS)

    Krajcarz, Magdalena; Pacher, Martina; Krajcarz, Maciej T.; Laughlan, Lana; Rabeder, Gernot; Sabol, Martin; Wojtal, Piotr; Bocherens, Hervé

    2016-01-01

    Collagen, the organic fraction of bone, records the isotopic parameters of consumed food for carbon (δ13C) and nitrogen (δ15N). This relationship of isotopic signature between diet and tissue is an important tool for the study of dietary preferences of modern and fossil animal species. Since the first information on the isotopic signature of cave bear was reported, numerous data from Europe have become available. The goal of this work is to track the geographical variation of cave bear collagen isotopic values in Europe during Marine Isotopic Stage 3 (about 60,000-25,000 yr BP). In this study the results of new δ13C and δ15N isotopic analyses of cave bear collagen from four Central-Eastern European sites are presented, as well as a review of all published isotopic data for cave bears of the same period. The main conclusion is a lack of geographical East-West pattern in the variations of δ13C and δ15N values of cave bear collagen. Moreover, no relationship was found between cave bear taxonomy and isotopic composition. The cave bears from Central-Eastern Europe exhibit δ13C and δ15N values near the average of the range of Central, Western and Southern European cave bears. Despite the fact that most cave bear sites follow an altitudinal gradient, separate groups of sites exhibit shift in absolute values of δ13C, what disturbs an altitude-related isotopic pattern. The most distinct groups are: high Alpine sites situated over 1500 m a.s.l. - in terms of δ13C; and two Romanian sites Peştera cu Oase and Urşilor - in case of δ15N. Although the cave bear isotopic signature is driven by altitude, the altitudinal adjustment of isotopic data is not enough to explain the isotopic dissimilarity of these cave bears. The unusually high δ15N signature of mentioned Romanian sites is an isolated case in Europe. Cave bears from relatively closely situated Central-Eastern European sites and other Romanian sites are more similar to Western European than to Romanian

  19. Effects of foliar boron application on seed composition, cell wall boron, and seed delta 15N and delta 13C isotopes in soybean are influenced by water stress

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Although the effect of foliar boron (B) application on yield and quality is well established for crops, limited information and controversial results still exist on the effects of foliar B application on soybean seed composition (seed protein, oil, fatty acids, and sugars). The objective of this res...

  20. Comparing isotope signatures of prey fish: does gut removal affect δ13C or δ15N?

    USGS Publications Warehouse

    Chipps, Steven R.; Fincel, Mark J.; VanDeHey, Justin A.; Wuestewald, Andrew

    2011-01-01

    Stable isotope analysis is a quick and inexpensive method to monitor the effects of food web changes on aquatic communities. Traditionally, whole specimens have been used when determining isotope composition of prey fish or age-0 recreational fishes. However, gut contents of prey fish could potentially alter isotope composition of the specimen, especially when recent foraging has taken place or when the gut contains non-assimilated material that would normally pass through fishes undigested. To assess the impacts of gut content on prey fish isotope signatures, we examined the differences in isotopic variation of five prey fish species using whole fish, whole fish with the gut contents removed, and dorsal muscle only. We found significant differences in both δ15N and δ13C between the three tissue treatments. In most cases, muscle tissue was enriched compared to whole specimens or gut-removed specimens. Moreover, differences in mean δ15N within a species were up to 2‰ among treatments. This would result in a change of over half a trophic position (TP) based on a 3.4‰ increase per trophic level. However, there were no apparent relationships between tissue isotope values in fish with increased gut fullness (more prey tissue present). We suggest that muscle tissue should be used as the standard tissue for determining isotope composition of prey fish or age-0 recreational fishes, especially when determining enrichment for mixing models, calculating TP, or constructing aquatic food webs.

  1. Nitrogen Isotopic Ratios in Cometary NH2: Implication for 15N-fractionation in Ammonia

    NASA Astrophysics Data System (ADS)

    Shinnaka, Yoshiharu; Kawakita, Hideyo; Jehin, Emmanuël; Decock, Alice; Hutsemékers, Damien; Manfroid, Jean; Arai, Akira

    2015-11-01

    Isotopic ratios in cometary molecules are diagnostic for the physico-chemical conditions where molecules formed and are processed, from the interstellar medium to the solar nebula. Usually temperatures at the molecular formation control the fractionation of the heavier element in molecular species, e.g., D-fractionation in water.In cometary volatiles, the 14N/15N ratios in CN have been well observed (Manfroid et al. 2009, A&A, 503, 613, and reference therein) and is consistent with the ratio in HCN (a most probable parent of CN) measured in few comets (Bockelée-Morvan et al. 2008, ApJ, 679, L49). Those ratios are enriched compared to the proto-solar value by a factor of ~3. In contrast to those Nitriles, there are only few reports on 14N/15N ratios in Ammonia (as Amine) (Rousselot et al. 2014, ApJ, 780, L17; Shinnaka et al. 2014, ApJ, 782, L16). Ammonia (NH3) is usually the most abundant and HCN is the second most abundant N-bearing volatiles in cometary ice. Especially, recent observations of 15NH2 revealed the 14N/15N ratios in NH3 are comparable to those of CN. However, from the viewpoint of theoretical work, the enrichment of 15N in cometary NH3 cannot be reproduced by current chemical network models. Information about the diversity of the 14N/15N ratios in NH3 of individual comets is needed to understand the formation mechanisms/environments of NH3 in the early solar system.To clarify the diversity of the 14N/15N ratios in cometary NH3, we determine the 14N/15N ratios in NH3 for more than ten comets individually which include not only Oort cloud comets but also short period comets by using the high-resolution optical spectra of NH2. These spectra were obtained with both the UVES mounted on the VLT in Chile and the HDS on the Subaru Telescope in Hawaii.The derived 14N/15N ratios in NH3 for more than ten comets show high 15N-enrichment compared with the elemental abundances of nitrogen in the Sun by about factor of ~3 and has no large diversity depending on

  2. A 15N-poor isotopic composition for the solar system as shown by Genesis solar wind samples.

    PubMed

    Marty, B; Chaussidon, M; Wiens, R C; Jurewicz, A J G; Burnett, D S

    2011-06-24

    The Genesis mission sampled solar wind ions to document the elemental and isotopic compositions of the Sun and, by inference, of the protosolar nebula. Nitrogen was a key target element because the extent and origin of its isotopic variations in solar system materials remain unknown. Isotopic analysis of a Genesis Solar Wind Concentrator target material shows that implanted solar wind nitrogen has a (15)N/(14)N ratio of 2.18 ± 0.02 × 10(-3) (that is, ≈40% poorer in (15)N relative to terrestrial atmosphere). The (15)N/(14)N ratio of the protosolar nebula was 2.27 ± 0.03 × 10(-3), which is the lowest (15)N/(14)N ratio known for solar system objects. This result demonstrates the extreme nitrogen isotopic heterogeneity of the nascent solar system and accounts for the (15)N-depleted components observed in solar system reservoirs. PMID:21700869

  3. Stable Isotope Tracking of Endangered Sea Turtles: Validation with Satellite Telemetry and δ15N Analysis of Amino Acids

    PubMed Central

    Seminoff, Jeffrey A.; Benson, Scott R.; Arthur, Karen E.; Eguchi, Tomoharu; Dutton, Peter H.; Tapilatu, Ricardo F.; Popp, Brian N.

    2012-01-01

    Effective conservation strategies for highly migratory species must incorporate information about long-distance movements and locations of high-use foraging areas. However, the inherent challenges of directly monitoring these factors call for creative research approaches and innovative application of existing tools. Highly migratory marine species, such as marine turtles, regularly travel hundreds or thousands of kilometers between breeding and feeding areas, but identification of migratory routes and habitat use patterns remains elusive. Here we use satellite telemetry in combination with compound-specific isotope analysis of amino acids to confirm that insights from bulk tissue stable isotope analysis can reveal divergent migratory strategies and within-population segregation of foraging groups of critically endangered leatherback sea turtles (Dermochelys coriacea) across the Pacific Ocean. Among the 78 turtles studied, we found a distinct dichotomy in δ15N values of bulk skin, with distinct “low δ15N” and “high δ15N” groups. δ15N analysis of amino acids confirmed that this disparity resulted from isotopic differences at the base of the food chain and not from differences in trophic position between the two groups. Satellite tracking of 13 individuals indicated that their bulk skin δ15N value was linked to the particular foraging region of each turtle. These findings confirm that prevailing marine isoscapes of foraging areas can be reflected in the isotopic compositions of marine turtle body tissues sampled at nesting beaches. We use a Bayesian mixture model to show that between 82 and 100% of the 78 skin-sampled turtles could be assigned with confidence to either the eastern Pacific or western Pacific, with 33 to 66% of all turtles foraging in the eastern Pacific. Our forensic approach validates the use of stable isotopes to depict leatherback turtle movements over broad spatial ranges and is timely for establishing wise conservation efforts in

  4. 15N-Cholamine – A Smart Isotope Tag for Combining NMR- and MS-Based Metabolite Profiling

    PubMed Central

    Tayyari, Fariba; Nagana Gowda, G. A.; Gu, Haiwei; Raftery, Daniel

    2013-01-01

    Recently, the enhanced resolution and sensitivity offered by chemoselective isotope tags have enabled new and enhanced methods for detecting hundreds of quantifiable metabolites in biofluids using nuclear magnetic resonance (NMR) spectroscopy or mass spectrometry. However, the inability to effectively detect the same metabolites using both complementary analytical techniques has hindered the correlation of data derived from the two powerful platforms and thereby the maximization of their combined strengths for applications such as biomarker discovery of the identification of unknown metabolites. With the goal of alleviating this bottleneck, we describe a smart isotope tag, 15N-cholamine, which possesses two important properties: an NMR sensitive isotope, and a permanent charge for MS sensitivity. Using this tag, we demonstrate the detection of carboxyl group containing metabolites in both human serum and urine. By combining the individual strengths of the 15N label and permanent charge, the smart isotope tag facilitates effective detection of the carboxyl-containing metabolome by both analytical methods. This study demonstrates a unique approach to exploit the combined strength of MS and NMR in the field of metabolomics. PMID:23930664

  5. Intraskeletal isotopic compositions (δ(13) C, δ(15) N) of bone collagen: nonpathological and pathological variation.

    PubMed

    Olsen, Karyn C; White, Christine D; Longstaffe, Fred J; von Heyking, Kristin; McGlynn, George; Grupe, Gisela; Rühli, Frank J

    2014-04-01

    Paleodiet research traditionally interprets differences in collagen isotopic compositions (δ(13) C, δ(15) N) as indicators of dietary distinction even though physiological processes likely play some role in creating variation. This research investigates the degree to which bone collagen δ(13) C and δ(15) N values normally vary within the skeleton and examines the influence of several diseases common to ancient populations on these isotopic compositions. The samples derive from two medieval German cemeteries and one Swiss reference collection and include examples of metabolic disease (rickets/osteomalacia), degenerative joint disease (osteoarthritis), trauma (fracture), infection (osteomyelitis), and inflammation (periostitis). A separate subset of visibly nonpathological skeletal elements from the German collections established normal intraindividual variation. For each disease type, tests compared bone lesion samples to those near and distant to the lesions sites. Results show that normal (nonpathological) skeletons exhibit limited intraskeletal variation in carbon- and nitrogen-isotope ratios, suggesting that sampling of distinct elements is appropriate for paleodiet studies. In contrast, individuals with osteomyelitis, healed fractures, and osteoarthritis exhibit significant intraskeletal differences in isotope values, depending on whether one is comparing lesions to near or to distant sites. Skeletons with periostitis result in significant intraskeletal differences in nitrogen isotope values only, while those with rickets/osteomalacia do not exhibit significant intraskeletal differences. Based on these results, we suggest that paleodiet researchers avoid sampling collagen at or close to lesion sites because the isotope values may be reflecting both altered metabolic processes and differences in diet relative to others in the population. PMID:24374993

  6. Effect of protein restriction on (15)N transfer from dietary [(15)N]alanine and [(15)N]Spirulina platensis into urea.

    PubMed

    Hamadeh, M J; Hoffer, L J

    2001-08-01

    Six normal men consumed a mixed test meal while adapted to high (1.5 g. kg(-1) x day(-1)) and low (0.3 g. kg(-1) x day(-1)) protein intakes. They completed this protocol twice: when the test meals included 3 mg/kg of [(15)N]alanine ([(15)N]Ala) and when they included 30 mg/kg of intrinsically labeled [(15)N]Spirulina platensis ([(15)N]SPI). Six subjects with insulin-dependent diabetes mellitus (IDDM) receiving conventional insulin therapy consumed the test meal with added [(15)N]Ala while adapted to their customary high-protein diet. Protein restriction increased serum alanine, glycine, glutamine, and methionine concentrations and reduced those of leucine. Whether the previous diet was high or low in protein, there was a similar increase in serum alanine, methionine, and branched-chain amino acid concentrations after the test meal and a similar pattern of (15)N enrichment in serum amino acids for a given tracer. When [(15)N]Ala was included in the test meal, (15)N appeared rapidly in serum alanine and glutamine, to a minor degree in leucine and isoleucine, and not at all in other circulating amino acids. With [(15)N]SPI, there was a slow appearance of the label in all serum amino acids analyzed. Despite the different serum amino acid labeling, protein restriction reduced the postmeal transfer of dietary (15)N in [(15)N]Ala or [(15)N]SPI into [(15)N]urea by similar amounts (38 and 43%, respectively, not significant). The response of the subjects with IDDM was similar to that of the normal subjects. Information about adaptive reductions in dietary amino acid catabolism obtained by adding [(15)N]Ala to a test meal appears to be equivalent to that obtained using an intrinsically labeled protein tracer. PMID:11440912

  7. Complementary constraints from carbon (13C) and nitrogen (15N) isotopes on the glacial ocean's soft-tissue biological pump

    NASA Astrophysics Data System (ADS)

    Schmittner, A.; Somes, C. J.

    2016-06-01

    A three-dimensional, process-based model of the ocean's carbon and nitrogen cycles, including 13C and 15N isotopes, is used to explore effects of idealized changes in the soft-tissue biological pump. Results are presented from one preindustrial control run (piCtrl) and six simulations of the Last Glacial Maximum (LGM) with increasing values of the spatially constant maximum phytoplankton growth rate μmax, which accelerates biological nutrient utilization mimicking iron fertilization. The default LGM simulation, without increasing μmax and with a shallower and weaker Atlantic Meridional Overturning Circulation and increased sea ice cover, leads to 280 Pg more respired organic carbon (Corg) storage in the deep ocean with respect to piCtrl. Dissolved oxygen concentrations in the colder glacial thermocline increase, which reduces water column denitrification and, with delay, nitrogen fixation, thus increasing the ocean's fixed nitrogen inventory and decreasing δ15NNO3 almost everywhere. This simulation already fits sediment reconstructions of carbon and nitrogen isotopes relatively well, but it overestimates deep ocean δ13CDIC and underestimates δ15NNO3 at high latitudes. Increasing μmax enhances Corg and lowers deep ocean δ13CDIC, improving the agreement with sediment data. In the model's Antarctic and North Pacific Oceans modest increases in μmax result in higher δ15NNO3 due to enhanced local nutrient utilization, improving the agreement with reconstructions there. Models with moderately increased μmax fit both isotope data best, whereas large increases in nutrient utilization are inconsistent with nitrogen isotopes although they still fit the carbon isotopes reasonably well. The best fitting models reproduce major features of the glacial δ13CDIC, δ15N, and oxygen reconstructions while simulating increased Corg by 510-670 Pg compared with the preindustrial ocean. These results are consistent with the idea that the soft-tissue pump was more efficient

  8. Depth-dependence in stable isotope ratio δ 15N of benthic POM consumers: The role of particle dynamics and organism trophic guild

    NASA Astrophysics Data System (ADS)

    Mintenbeck, K.; Jacob, U.; Knust, R.; Arntz, W. E.; Brey, T.

    2007-06-01

    The stable nitrogen isotope ratio (δ 15N) is an established indicator of trophic hierarchy in marine food-web studies. Most of these studies presume that spatial variation in the primary food source is negligible, although a water-depth-related increase in δ 15N of particulate organic matter (POM) has been found in many systems. We used the high-Antarctic Weddell Sea shelf and slope ecosystem to test whether such a depth-related change in δ 15N is reflected at higher trophic levels, i.e., benthic consumers of POM. In suspension feeders (SF) we found a significant increase in δ 15N with water depth of up to 9.8‰, whereas in deposit feeders (DF) a depth effect was barely detectable. Particle-size preferences of the two feeding guilds combined with particle-size-dependent sinking velocities and biogeochemical reworking of POM are discussed as the major causes of these differences. It is essential to marine food-web studies to take into account the general depth effect on POM δ 15N as well as potential feeding-guild-specific differences in the response of POM consumer tissue δ 15N to avoid serious bias and misinterpretation of stable-isotope-based trophic information.

  9. Organic vs. Conventional Grassland Management: Do 15N and 13C Isotopic Signatures of Hay and Soil Samples Differ?

    PubMed Central

    Klaus, Valentin H.; Hölzel, Norbert; Prati, Daniel; Schmitt, Barbara; Schöning, Ingo; Schrumpf, Marion; Fischer, Markus; Kleinebecker, Till

    2013-01-01

    Distinguishing organic and conventional products is a major issue of food security and authenticity. Previous studies successfully used stable isotopes to separate organic and conventional products, but up to now, this approach was not tested for organic grassland hay and soil. Moreover, isotopic abundances could be a powerful tool to elucidate differences in ecosystem functioning and driving mechanisms of element cycling in organic and conventional management systems. Here, we studied the δ15N and δ13C isotopic composition of soil and hay samples of 21 organic and 34 conventional grasslands in two German regions. We also used Δδ15N15N plant - δ15N soil) to characterize nitrogen dynamics. In order to detect temporal trends, isotopic abundances in organic grasslands were related to the time since certification. Furthermore, discriminant analysis was used to test whether the respective management type can be deduced from observed isotopic abundances. Isotopic analyses revealed no significant differences in δ13C in hay and δ15N in both soil and hay between management types, but showed that δ13C abundances were significantly lower in soil of organic compared to conventional grasslands. Δδ15N values implied that management types did not substantially differ in nitrogen cycling. Only δ13C in soil and hay showed significant negative relationships with the time since certification. Thus, our result suggest that organic grasslands suffered less from drought stress compared to conventional grasslands most likely due to a benefit of higher plant species richness, as previously shown by manipulative biodiversity experiments. Finally, it was possible to correctly classify about two third of the samples according to their management using isotopic abundances in soil and hay. However, as more than half of the organic samples were incorrectly classified, we infer that more research is needed to improve this approach before it can be efficiently used in practice

  10. Ammonia 15N/14N Isotope Ratio in the Jovian Atmosphere

    NASA Technical Reports Server (NTRS)

    Mahaffy, P.R.; Niemann, H. B.; Atreya, S. K.; Wong, M. H.; Owen, T. C; Einaudi, Franco (Technical Monitor)

    2000-01-01

    Data from the Galileo Probe Mass Spectrometer has been used to derive the N-15/N-14 isotope ratio in ammonia at Jupiter. Although the mass spectral interference from the water contribution to 18 amu makes an accurate derivation of the (N-15)H3/(N-14)H3 ratio difficult from measurements of the singly ionized signals at 18 and 17 amu, this interference is not present in the doubly charged 8.5 and 9.0 amu signals from (N-14)H3++ and (N-15)H3++ respectively. Although the count rate from the 9 amu signal is low during the direct sampling of the atmosphere, the ammonia signal was considerably enhanced during the first enrichment cell (EC1) experiment that measured gas sampled between 0.8 and 2.8 bar. Count rates at 9 amu in the EC1 experiment reach 60/second and measure ammonia sampled from 0.88 to 2.8 bar. In the EC1 measurements the 8.5 amu signal is not measured directly, but can be calculated from the ammonia contribution to 17 amu and the ratio of NH3 ions of a double to single charged observed during a high resolution mass scan taken near the end of the descent. The high resolution scan gives this ratio from ammonia sampled much deeper in the atmosphere. These results are described and compared with Infrared Space Observatory-Short Wavelength Spectrometer (ISO-SWS) observations that give this ratio at 400 mbar.

  11. Early life histories of the London poor using δ13C and δ15N stable isotope incremental dentine sampling.

    PubMed

    Henderson, Rowena C; Lee-Thorp, Julia; Loe, Louise

    2014-08-01

    High resolution incremental isotopic analysis of the dentine from early forming teeth, especially first molars (M1s), provides a means to assess the effects of poor childhood nutrition and healthcare on individuals in an assemblage where there are no infants to study. This approach is applied to an 18th and 19th century cemetery population associated with St Saviour's Almshouse burial ground in Southwark, London, to assess whether, or how, early dietary history, including weaning age, influenced health and nutritional status. The results show a general pattern in which non-breast milk foods were introduced before or by 6 months of age, as indicated by elevated δ(15) N during this period. Almost all individuals for which we also have second molar (M2) records, showed lower δ(15) N values from a very young age (>1 year) until approximately 8-10 years, compared to adult values. The overall results show a significant difference in δ(1) (3) C (p = 0 to 4sf, F = 17.327) and a weaker statistical difference in δ(15) N between males and females (p = 0.019, F = 5.581). One possible cause of this is a difference in the diet of males and females early in life, or alternatively, a greater susceptibility of males to nutritional deprivation compared to females. The latter argument is strengthened by a significant difference in the incidence of enamel hypoplasia between the males and females, with 7.7% of male teeth showing defects, compared to 3.9% of females. PMID:24898314

  12. STATISTICAL ESTIMATES OF VARIANCE FOR 15N ISOTOPE DILUTION MEASUREMENTS OF GROSS RATES OF NITROGEN CYCLE PROCESSES

    EPA Science Inventory

    It has been fifty years since Kirkham and Bartholmew (1954) presented the conceptual framework and derived the mathematical equations that formed the basis of the now commonly employed method of 15N isotope dilution. Although many advances in methodology and analysis have been ma...

  13. Tracking spatial distribution of human-derived wastewater from Davis Station, East Antarctica, using δ15N and δ13C stable isotopes.

    PubMed

    Corbett, Patricia A; King, Catherine K; Mondon, Julie A

    2015-01-15

    Stable isotope ratios, δ15N and δ13C were effectively used to determine the geographical dispersion of human derived sewage from Davis Station, East Antarctica, using Antarctic rock cod (Trematomus bernacchii). Fish within 0-4 km downstream of the outfall exhibited higher δ15N and δ13C values relative to reference sites. Nitrogen in particular showed a stepped decrease in δ15N with increasing distance from the discharge point by 1-2‰. Stable isotopes were better able to detect the extent of wastewater contamination than other techniques including faecal coliform and sterol measures. Uptake and assimilation of δ15N and δ13C up to 4 km from the outfall adds to growing evidence indicating the current level of wastewater treatment at Davis Station is not sufficient to avoid impact to the surrounding environment. Isotopic assimilation in T. bernacchii is a viable biomarker for investigation of initial sewage exposure and longer term monitoring in the future. PMID:25487089

  14. Validating the Incorporation of 13C and 15N in a Shorebird That Consumes an Isotopically Distinct Chemosymbiotic Bivalve

    PubMed Central

    van Gils, Jan A.; Ahmedou Salem, Mohamed Vall

    2015-01-01

    The wealth of field studies using stable isotopes to make inferences about animal diets require controlled validation experiments to make proper interpretations. Despite several pleas in the literature for such experiments, validation studies are still lagging behind, notably in consumers dwelling in chemosynthesis-based ecosystems. In this paper we present such a validation experiment for the incorporation of 13C and 15N in the blood plasma of a medium-sized shorebird, the red knot (Calidris canutus canutus), consuming a chemosymbiotic lucinid bivalve (Loripes lucinalis). Because this bivalve forms a symbiosis with chemoautotrophic sulphide-oxidizing bacteria living inside its gill, the bivalve is isotopically distinct from ‘normal’ bivalves whose food has a photosynthetic basis. Here we experimentally tested the hypothesis that isotope discrimination and incorporation dynamics are different when consuming such chemosynthesis-based prey. The experiment showed that neither the isotopic discrimination factor, nor isotopic turnover time, differed between birds consuming the chemosymbiotic lucinid and a control group consuming a photosynthesis-based bivalve. This was true for 13C as well as for 15N. However, in both groups the 15N discrimination factor was much higher than expected, which probably had to do with the birds losing body mass over the course of the experiment. PMID:26458005

  15. Validating the Incorporation of 13C and 15N in a Shorebird That Consumes an Isotopically Distinct Chemosymbiotic Bivalve.

    PubMed

    van Gils, Jan A; Ahmedou Salem, Mohamed Vall

    2015-01-01

    The wealth of field studies using stable isotopes to make inferences about animal diets require controlled validation experiments to make proper interpretations. Despite several pleas in the literature for such experiments, validation studies are still lagging behind, notably in consumers dwelling in chemosynthesis-based ecosystems. In this paper we present such a validation experiment for the incorporation of 13C and 15N in the blood plasma of a medium-sized shorebird, the red knot (Calidris canutus canutus), consuming a chemosymbiotic lucinid bivalve (Loripes lucinalis). Because this bivalve forms a symbiosis with chemoautotrophic sulphide-oxidizing bacteria living inside its gill, the bivalve is isotopically distinct from 'normal' bivalves whose food has a photosynthetic basis. Here we experimentally tested the hypothesis that isotope discrimination and incorporation dynamics are different when consuming such chemosynthesis-based prey. The experiment showed that neither the isotopic discrimination factor, nor isotopic turnover time, differed between birds consuming the chemosymbiotic lucinid and a control group consuming a photosynthesis-based bivalve. This was true for 13C as well as for 15N. However, in both groups the 15N discrimination factor was much higher than expected, which probably had to do with the birds losing body mass over the course of the experiment. PMID:26458005

  16. Tracing the diet of the monitor lizard Varanus mabitang by stable isotope analyses (δ15N, δ13C)

    NASA Astrophysics Data System (ADS)

    Struck, Ulrich; Altenbach, Alexander; Gaulke, Maren; Glaw, Frank

    2002-09-01

    In this study, we used analyses of stable isotopes of nitrogen (δ15N) and carbon (δ13C) to determine the trophic ecology of the monitor lizard Varanus mabitang. Stable isotopes from claws, gut contents, and soft tissues were measured from the type specimen. Samples from Varanus olivaceus, Varanus prasinus, Varanus salvator, the herbivorous agamid lizard Hydrosaurus pustulatus, and some plant matter were included for comparison. Our data show a rapid decrease in δ13C (about10‰) from food plants towards gut contents and soft tissues of herbivorous species. For the varanids, we found a significant linear correlation of decreasing δ13C and increasing δ15N from herbivorous towards carnivorous species. In terms of trophic isotope ecology, the type specimen of V. mabitang is a strict herbivore. Thus it differs significantly in its isotopic composition from the morphologically next closest related species V. olivaceus. The most highly carnivorous species is V. salvator, while δ15N values for V. prasinus and V. olivaceus are intermediate. Claws provide very valuable samples for such measurements, because they can be sampled from living animals without harm. Additionally, their range of variability is relatively small in comparison with measurements from soft tissues.

  17. The Titan 14N/ 15N and 12C/ 13C isotopic ratios in HCN from Cassini/CIRS

    NASA Astrophysics Data System (ADS)

    Vinatier, Sandrine; Bézard, Bruno; Nixon, Conor A.

    2007-11-01

    We report the detection of H 13CN and HC 15N in mid-infrared spectra recorded by the Composite Infrared Spectrometer (CIRS) aboard Cassini, along with the determination of the 12C/ 13C and 14N/ 15N isotopic ratios. We analyzed two sets of limb spectra recorded near 13-15° S (Tb flyby) and 83° N (T4 flyby) at 0.5 cm -1 resolution. The spectral range 1210-1310 cm -1 was used to retrieve the temperature profile in the range 145-490 km at 13° S and 165-300 km at 83° N. These two temperature profiles were then incorporated in the atmospheric model to retrieve the abundance profile of H 12C 14N, H 13CN and HC 15N from their bands at 713, 706 and 711 cm -1, respectively. The HCN abundance profile was retrieved in the range 90-460 km at 15° S and 165-305 km at 83° N. There is no evidence for vertical variations of the isotopic ratios. Constraining the isotopic abundance profiles to be proportional to the HCN one, we find C12/C13=89-18+22 at 15° S, and 68-12+16 at 83° N, two values that are statistically consistent. A combination of these results yields a 12C/ 13C value equal to 75±12. This global result, as well as the 15° S one, envelop the value in Titan's methane ( 82.3±1) [Niemann, H.B., and 17 colleagues, 2005. Nature 438, 779-784] measured at 10° S and is slightly lower than the terrestrial inorganic standard value (89). The 14N/ 15N isotopic ratio is found equal to 56-13+16 at 15° S and 56-9+10 at 83° N. Combining the two values yields 14N/ 15N = 56 ± 8, which corresponds to an enrichment in 15N of about 4.9 compared with the terrestrial ratio. These results agree with the values obtained from previous ground-based millimeter observations [Hidayat, T., Marten, A., Bézard, B., Gautier, D., Owen, T., Matthews, H.E., Paubert, G., 1997. Icarus 126, 170-182; Marten, A., Hidayat, T., Biraud, Y., Moreno, R., 2002. Icarus 158, 532-544]. The 15N/ 14N ratio found in HCN is ˜3 times higher than in N 2 [Niemann, H.B., and 17 colleagues, 2005. Nature 438, 779

  18. 15N Isotopic Crop Exchange Residue Studies Suggest that IPCC N Input Methodologies to Assess N2O-N Emissions Should be Reevaluated

    Technology Transfer Automated Retrieval System (TEKTRAN)

    It is difficult to quantify nitrogen (N) losses from agricultural systems to the environment, however we can use 15N isotopic techniques to conduct site specific studies to increase our knowledge about N management and fate. This manuscript synthesizes the review of two selected 15N isotopic studies...

  19. Paleobiological Implications of the Isotopic Signatures ( 13C, 15N) of Fossil Mammal Collagen in Scladina Cave (Sclayn, Belgium)

    NASA Astrophysics Data System (ADS)

    Bocherens, Hervé; Billiou, Daniel; Patou-Mathis, Marylène; Bonjean, Dominique; Otte, Marcel; Mariotti, André

    1997-11-01

    An isotopic investigation of upper Pleistocene mammal bones and teeth from Scladina cave (Sclayn, Belgium) demonstrated the very good quality of collagen preservation. A preliminary screening of the samples used the amount of nitrogen in whole bone and dentine in order to estimate the preserved amount of collagen before starting the extraction process. The isotopic abundances of fossil specimens from still-extant species are consistent with their trophic position. Moreover, the 15N isotopic abundance is higher in dentine than in bone in bears and hyenas, a phenomenon already observed in modern specimens. These results demonstrate that the isotopic compositions of samples from Scladina cave can be interpreted in ecological terms. Mammoths exhibit a high 15N isotopic abundance relative to other herbivores, as was the case in Siberian and Alaskan samples. These results suggest distinctive dietary adaptations in herbivores living in the mammoth steppe. Cave bears are clearly isotopically different from coeval brown bears, suggesting an ecological separation between species, with a pure vegetarian diet for cave bear and an omnivorous diet for brown bear.

  20. Soil and foliar nutrient and nitrogen isotope composition (δ(15)N) at 5 years after poultry litter and green waste biochar amendment in a macadamia orchard.

    PubMed

    Bai, Shahla Hosseini; Xu, Cheng-Yuan; Xu, Zhihong; Blumfield, Timothy J; Zhao, Haitao; Wallace, Helen; Reverchon, Frédérique; Van Zwieten, Lukas

    2015-03-01

    This study aimed to evaluate the improvement in soil fertility and plant nutrient use in a macadamia orchard following biochar application. The main objectives of this study were to assess the effects of poultry litter and green waste biochar applications on nitrogen (N) cycling using N isotope composition (δ(15)N) and nutrient availability in a soil-plant system at a macadamia orchard, 5 years following application. Biochar was applied at 10 t ha(-1) dry weight but concentrated within a 3-m diameter zone when trees were planted in 2007. Soil and leaf samples were collected in 2012, and both soil and foliar N isotope composition (δ(15)N) and nutrient concentrations were assessed. Both soil and foliar δ(15)N increased significantly in the poultry litter biochar plots compared to the green waste biochar and control plots. A significant relationship was observed between soil and plant δ(15)N. There was no influence of either biochars on foliar total N concentrations or soil NH4 (+)-N and NO3 (-)-N, which suggested that biochar application did not pose any restriction for plant N uptake. Plant bioavailable phosphorus (P) was significantly higher in the poultry litter biochar treatment compared to the green waste biochar treatment and control. We hypothesised that the bioavailability of N and P content of poultry litter biochar may play an important role in increasing soil and plant δ(15)N and P concentrations. Biochar application affected soil-plant N cycling and there is potential to use soil and plant δ(15)N to investigate N cycling in a soil-biochar-tree crop system. The poultry litter biochar significantly increased soil fertility compared to the green waste biochar at 5 years following biochar application which makes the poultry litter a better feedstock to produce biochar compared to green waste for the tree crops. PMID:25266060

  1. Stable isotope (13C, 15N and 34S) analysis of the hair of modern humans and their domestic animals.

    PubMed

    Bol, Roland; Pflieger, Christian

    2002-01-01

    Relationships between dietary status and recent migration were examined by delta(13)C, delta(15)N and delta(34)S analysis of hair samples from 43 modern humans living in a rural community in SW England. The isotopic content of 38 'local' hair samples was compared with that of five recently arrived individuals (from Canada, Chile, Germany and the USA). Hair samples from domestic animals (i.e. mainly cats, dogs, cows and horses) were analysed to examine the difference in delta(13)C, delta(15)N and delta(34)S values between herbivores and carnivores. Generally, modern human hair data from the triple stable isotope (delta(13)C, delta(15)N and delta(34)S) provided enough information to confirm the dietary status and origin of the individual subjects. The dietary intake was generally reflected in the animal hair delta(15)N and delta(13)C values, i.e. highest in the carnivores (cats). However, a non-local origin of food sources given to domesticated omnivores (i.e. dogs) was suggested by their hair delta(34)S values. PMID:12442295

  2. The effect of noncollinearity of 15N-1H dipolar and 15N CSA tensors and rotational anisotropy on 15N relaxation, CSA/dipolar cross correlation, and TROSY.

    PubMed

    Fushman, D; Cowburn, D

    1999-02-01

    Current approaches to 15N relaxation in proteins assume that the 15N-1H dipolar and 15N CSA tensors are collinear. We show theoretically that, when there is significant anisotropy of molecular rotation, different orientations of the two tensors, experimentally observed in proteins, nucleic acids, and small peptides, will result in differences in site-specific correlation functions and spectral densities. The standard treatments of the rates of longitudinal and transverse relaxation of amide 15N nuclei, of the 15N CSA/15N-1H dipolar cross correlation, and of the TROSY experiment are extended to account for the effect of noncollinearity of the 15N-1H dipolar and 15N CSA (chemical shift anisotropy) tensors. This effect, proportional to the degree of anisotropy of the overall motion, (D parallel/D perpendicular - 1), is sensitive to the relative orientation of the two tensors and to the orientation of the peptide plane with respect to the diffusion coordinate frame. The effect is negligible at small degrees of anisotropy, but is predicted to become significant for D parallel/D perpendicular > or = 1.5, and at high magnetic fields. The effect of noncollinearity of 15N CSA and 15N-1H dipolar interaction is sensitive to both gross (hydrodynamic) properties and atomic-level details of protein structure. Incorporation of this effect into relaxation data analysis is likely to improve both precision and accuracy of the derived characteristics of protein dynamics, especially at high magnetic fields and for molecules with a high degree of anisotropy of the overall motion. The effect will also make TROSY efficiency dependent on local orientation in moderately anisotropic systems. PMID:10070755

  3. Similarities and differences in 13C and 15N stable isotope ratios in two non-lethal tissue types from shovelnose sturgeon Scaphirhynchus platorynchus (Rafinesque, 1820)

    USGS Publications Warehouse

    DeVries, R. J.; Schramm, Harold L., Jr.

    2015-01-01

    We tested the hypothesis that δ13C and δ15N signatures of pectoral spines would provide measures of δ13C and δ15N similar to those obtained from fin clips for adult shovelnose sturgeon Scaphirhynchus platorynchus. Thirty-two shovelnose sturgeon (fork length [FL] = 500–724 mm) were sampled from the lower Mississippi River, USA on 23 February 2013. Isotopic relationships between the two tissue types were analyzed using mixed model analysis of covariance. Tissue types differed significantly for both δ13C (P < 0.01; spine: mean = −23.83, SD = 0.62; fin clip: mean = −25.74, SD = 0.97) and δ15N (P = 0.01; spine: mean = 17.01, SD = 0.51; fin clip: mean = 17.19, SD = 0.62). Neither FL nor the FL × tissue type interaction had significant (P > 0.05) effects on δ13C. Fin clip δ13C values were highly variable and weakly correlated (r = 0.16, P = 0.40) with those from pectoral spines. We found a significant FL-tissue type interaction for δ15N, reflecting increasing δ15N with FL for spines and decreasing δ15N with FL for fin clips. These results indicate that spines are not a substitute for fin clip tissue for measuring δ13C and δ15N for shovelnose sturgeon in the lower Mississippi River, but the two tissues have different turnover rates they may provide complementary information for assessing trophic position at different time scales.

  4. Mechanistic Determination of Nitrogen Removal By Advanced Soil-Based Wastewater Treatment Systems Using 15n Isotopes

    NASA Astrophysics Data System (ADS)

    Cooper, J.; Loomis, G.; Kalen, D.; Boving, T. B.; Morales, I.; Amador, J.

    2014-12-01

    Current levels of nitrogen removal by onsite wastewater treatment systems (OWTS) are inadequate, with release of N from OWTS contributing to environmental N pollution, especially in coastal zones where aquatic ecosystems are sensitive to eutrophication. Current mechanistic understand of N removal are limited and mainly attributed to denitrification in the drainfield. Loss of N from N2O production during nitrification, a sparsely researched topic, may be a significant mechanism in advanced OWTS systems that enhance O2 diffusion by sand filter pre-treatment, shallow placement of infiltrative areas and timed dosing controls to prevent drainfield saturation. Replicate (n=3) intact soil mesocosms were used with 15N isotope to evaluate the effectiveness and mechanisms of N removal in drainfields with a conventional wastewater delivery (pipe-and-stone, P&S) compared to two advanced types of drainfields, pressurized shallow narrow drainfield (SND) and Geomat (GEO), a variation of a SND drainfield. Over the 11 day experiment, dissolved O2 was 1.6 mg/L for P&S and 3.0 mg/L for SND and GEO. Removal of total N was 13.5% for P&S, 4.8% for SND and 5.4% for GEO. 15NH4 labeled nitrogen inputs to drainfields were transformed primarily to 15NO3 in all outputs. Consistent low 15N2O levels were present in P&S, with increasing levels of N2 peaking 48h after 15NH4 injection, suggesting denitrification dominated N removal. By contrast, SND and GEO 15N2O levels rose quickly, peaking 8h after 15NH4 injection, suggesting N loss by nitrification. When the whole system is considered, including sand filter removal, 26 - 27% of total N was removed by the SND and GEO systems, whereas 14% of total N was removed in the P&S system. Our results suggest the SND and GEO systems as a whole are capable of removing a greater mass of N than the P&S system.

  5. Differentiation of Pigment in Eggs Using Carbon ((13)C/(12)C) and Nitrogen ((15)N/(14)N) Stable Isotopes.

    PubMed

    Sun, Feng M; Shi, Guang Y; Wang, Hui W

    2016-07-01

    Consumers prefer natural and healthy food, but artificial pigments are often abused in egg products. The study aimed at differentiating the origin of pigments in eggs by applying the technique of carbon ((13)C/(12)C) and nitrogen ((15)N/(14)N) stable isotope analysis. Five hundred sixty laying hens were randomly distributed into 14 treatments, which were divided into four groups: maize, carophyll red pigment, carophyll yellow pigment, and a mixture of carophyll red and yellow pigments. Eggs were collected and pretreated to determe the values of the Roche Yolk Color Fan (RCF), δ(13)C, and δ(15)N. With increasing maize content, the RCF and δ(13)C values of yolks increased. Moreover, the RCF values in the three pigment groups were significantly influenced by the artificial colors, but δ(13)C values were not significantly different, regardless of the existence of pigment. The δ(15)N values in all treatments did not vary as regularly as the carbon stable isotope. A strong positive correlation was found between RCF and δ(13)C in the maize group, but no such correlation was be observed in the pigment groups. It is concluded that carbon stable isotope ratio analysis (δ(13)C) of the yolk can be used to differentiate the origin of the pigment added to eggs. PMID:27302905

  6. Stable isotope analysis (δ13C and δ15N) of soil nematodes from four feeding groups

    PubMed Central

    Griffiths, Bryan; Dyckmans, Jens; Schmidt, Olaf

    2016-01-01

    Soil nematode feeding groups are a long-established trophic categorisation largely based on morphology and are used in ecological indices to monitor and analyse the biological state of soils. Stable isotope ratio analysis (13C/12C and 15N/14N, expressed as δ13C and δ15N) has provided verification of, and novel insights into, the feeding ecology of soil animals such as earthworms and mites. However, isotopic studies of soil nematodes have been limited to date as conventional stable isotope ratio analysis needs impractically large numbers of nematodes (up to 1,000) to achieve required minimum sample weights (typically >100 µg C and N). Here, micro-sample near-conventional elemental analysis–isotopic ratio mass spectrometry (μEA–IRMS) of C and N using microgram samples (typically 20 µg dry weight), was employed to compare the trophic position of selected soil nematode taxa from four feeding groups: predators (Anatonchus and Mononchus), bacterial feeders (Plectus and Rhabditis), omnivores (Aporcelaimidae and Qudsianematidae) and plant feeder (Rotylenchus). Free-living nematodes were collected from conventionally and organically managed arable soils. As few as 15 nematodes, for omnivores and predators, were sufficient to reach the 20 µg dry weight target. There was no significant difference in δ15N (p = 0.290) or δ13C (p = 0.706) between conventional and organic agronomic treatments but, within treatments, there was a significant difference in N and C stable isotope ratios between the plant feeder, Rotylenchus (δ15N = 1.08 to 3.22 mUr‰, δ13C = –29.58 to –27.87 mUr) and all other groups. There was an average difference of 9.62 mUr in δ15N between the plant feeder and the predator group (δ15N = 9.89 to 12.79 mUr, δ13C = –27.04 to –25.51 mUr). Isotopic niche widths were calculated as Bayesian derived standard ellipse areas and were smallest for the plant feeder (1.37 mUr2) and the predators (1.73 mUr2), but largest for omnivores (3.83 mUr2

  7. Design and Operation of a Continuous 13C and 15N Labeling Chamber for Uniform or Differential, Metabolic and Structural, Plant Isotope Labeling

    PubMed Central

    Soong, Jennifer L; Reuss, Dan; Pinney, Colin; Boyack, Ty; Haddix, Michelle L; Stewart, Catherine E; Cotrufo, M. Francesca

    2014-01-01

    Tracing rare stable isotopes from plant material through the ecosystem provides the most sensitive information about ecosystem processes; from CO2 fluxes and soil organic matter formation to small-scale stable-isotope biomarker probing. Coupling multiple stable isotopes such as 13C with 15N, 18O or 2H has the potential to reveal even more information about complex stoichiometric relationships during biogeochemical transformations. Isotope labeled plant material has been used in various studies of litter decomposition and soil organic matter formation1-4. From these and other studies, however, it has become apparent that structural components of plant material behave differently than metabolic components (i.e. leachable low molecular weight compounds) in terms of microbial utilization and long-term carbon storage5-7. The ability to study structural and metabolic components separately provides a powerful new tool for advancing the forefront of ecosystem biogeochemical studies. Here we describe a method for producing 13C and 15N labeled plant material that is either uniformly labeled throughout the plant or differentially labeled in structural and metabolic plant components. Here, we present the construction and operation of a continuous 13C and 15N labeling chamber that can be modified to meet various research needs. Uniformly labeled plant material is produced by continuous labeling from seedling to harvest, while differential labeling is achieved by removing the growing plants from the chamber weeks prior to harvest. Representative results from growing Andropogon gerardii Kaw demonstrate the system's ability to efficiently label plant material at the targeted levels. Through this method we have produced plant material with a 4.4 atom%13C and 6.7 atom%15N uniform plant label, or material that is differentially labeled by up to 1.29 atom%13C and 0.56 atom%15N in its metabolic and structural components (hot water extractable and hot water residual components

  8. Isotope ratio mass spectrometry: delta13C and delta15 N analysis for tracing the origin of illicit drugs.

    PubMed

    Galimov, E M; Sevastyanov, V S; Kulbachevskaya, E V; Golyavin, A A

    2005-01-01

    Gas chromatography/combustion/mass spectrometry (GC-C-MS) and elemental analysis/mass spectrometry (EA-MS) techniques are proposed to estimate delta(13)C and delta(15)N values in heroin, morphine, cocaine and hemp leaves, for the purposes of tracing the geographical origins of seized drugs. The values of isotope ratios for pure drugs and drugs with impurities were compared. It was demonstrated that large samples (up to 3 x 10(-6) g C) were combusted completely, so that the results obtained were valid. The data are considered to be an essential supplement to a wide-scale database designed specifically for the delta(13)C and delta(15)N values of drugs. The potential forensic and academic significance of the results is discussed. PMID:15832288

  9. High resolution (13)C MRI with hyperpolarized urea: in vivo T(2) mapping and (15)N labeling effects.

    PubMed

    Reed, Galen D; von Morze, Cornelius; Bok, Robert; Koelsch, Bertram L; Van Criekinge, Mark; Smith, Kenneth J; Hong Shang; Larson, Peder E Z; Kurhanewicz, John; Vigneron, Daniel B

    2014-02-01

    (13)C steady state free precession (SSFP) magnetic resonance imaging and effective spin-spin relaxation time (T2) mapping were performed using hyperpolarized [(13)C] urea and [(13) C,(15)N2] urea injected intravenously in rats. (15)N labeling gave large T2 increases both in solution and in vivo due to the elimination of a strong scalar relaxation pathway. The T2 increase was pronounced in the kidney, with [(13) C,(15) N2] urea giving T2 values of 6.3±1.3 s in the cortex and medulla, and 11±2 s in the renal pelvis. The measured T2 in the aorta was 1.3±0.3 s. [(13)C] urea showed shortened T2 values in the kidney of 0.23±0.03 s compared to 0.28±0.03 s measured in the aorta. The enhanced T2 of [(13)C,(15)N2] urea was utilized to generate large signal enhancement by SSFP acquisitions with flip angles approaching the fully refocused regime. Projection images at 0.94 mm in-plane resolution were acquired with both urea isotopes, with [(13)C,(15) N2] urea giving a greater than four-fold increase in signal-to-noise ratio over [(13)C] urea. PMID:24235273

  10. Diurnal variations in the isotopic composition of atmospheric nitrate in coastal California: δ15N and Δ17O as tracers of daytime and nighttime nitrogen oxide chemistry

    NASA Astrophysics Data System (ADS)

    Vicars, W. C.; Morin, S.; Wagner, N.; Savarino, J.; Erbland, J.; Brown, S. S.; Williams, E. J.

    2012-12-01

    The comprehensive isotopic composition of atmospheric nitrate (i.e., δ17O, δ18O, and δ15N) can convey valuable information regarding reactive nitrogen oxide (NOx = NO2 and NO) sources, cycling, and removal pathways; however, interpretations derived from nitrate isotope ratio measurements have thus far been useful primarily in the analysis of annual or seasonal atmospheric trends, while isotopic effects associated with faster atmospheric processes (e.g., diurnal variations) are presently not well constrained. In order to assess the impact of temporal variability in atmospheric chemistry on nitrate stable isotope ratios, we have measured the size-resolved concentration and isotopic composition of atmospheric nitrate at a diurnal/semidiurnal resolution onboard the R/V Atlantis during a cruise along the coast of California. This campaign was a major component of the CalNex 2010 field study and consisted of two distinct cruises in the South Coast and San Francisco Bay regions from 14 - 31 May and 1 - 7 June, respectively. Significant differences in air mass origin and atmospheric chemistry were observed for these two regions with corresponding differences in the concentration and isotopic composition of nitrate. Measurements of the 17O-excess (Δ17O = δ17O - 0.52 * δ18O) of nitrate suggest that nocturnal processes involving the nitrate radical play an important role in terms of NOx sinks in the South Coast region, where atmospheric nitrate concentrations were elevated due to the influence of continental outflow and the Δ17O of nitrate averaged 25.3 ± 1.6‰; conversely, Δ17O averaged 22.3 ± 1.8‰ in the San Francisco Bay region suggesting that the daytime OH + NO2 reaction is a relatively more significant NOx loss mechanism in the predominantly marine air masses sampled in this area. A strong diurnal signal was observed for both the δ15N and Δ17O of atmospheric nitrate. In the case of Δ17O, this diurnal pattern can be interpreted quantitatively as a result

  11. 13N,15N isotope and kinetic evidence against hyponitrite as an intermediate in dentrification.

    PubMed

    Hollocher, T C; Garber, E; Cooper, A J; Reiman, R E

    1980-06-10

    13N- and 15N-labeling experiments were carried out with Paracoccus denitrificans, grown anaerobically on nitrate, to determine whether hyponitrite might be an obligatory intermediate in denitrification and a precursor of nitrous oxide. From experiments designed to trap [13N]- or [15N,15N]hyponitrite by dilution into authentic hyponitrite it was calculated that the intracellular concentration of a presumptive hyponitrite pool must be less than 0.4 mM. In order for a pool of this size to turn over rapidly enough to handle the flux of nitrogen during dentrifucation, the spontaneous rate of hyponitrite dehydration must be enhanced by a factor of several thousand through enzyme catalysis. Cell extracts failed to catalyze this reaction under a variety of conditions. It is concluded that hyponitrite cannot be an intermediate in dentrification. In addition, the assimilation of inorganic nitrogen was studied in P. denitrificans using 13N as tracer. At low concentrations (less than 10(-8) M) of labeled nitrate and nitrite 5 to 10% of the label was assimilated into non-volatile metabolites and 90 to 95% was reduced to N2. Similarly, with 15 mM [13N]nitrate, 5% of the label went into metabolites and 95% to N2. High pressure liquid chromatography analysis of the labeled metabolites indicated that the major pathway for assimilation of inorganic nitrogen in P. denitrificans under these conditions is through ammonia incorporation via the aspartase reaction. PMID:7372623

  12. Trophic guilds of generalist feeders in soil animal communities as indicated by stable isotope analysis (15N/14N).

    PubMed

    Oelbermann, K; Scheu, S

    2010-10-01

    We investigated if the commonly used aggregation of organisms into trophic guilds, such as detritivores and predators, in fact represent distinct trophic levels. Soil arthropods of a forest-meadow transect were ascribed a priori to trophic guilds (herbivores, detritivores, predators and necrovores), which are often used as an equivalent to trophic levels. We analysed natural variations in 15N/14N ratios of the animals in order to investigate the trophic similarity of organisms within (a priori defined) trophic guilds. Using trophic guilds as an equivalent to trophic level, the assumed stepwise enrichment of 15N by 3.4 per thousand per trophic level did not apply to detritivores; they were only enriched in 15N by on average 1.5 per thousand compared to litter materials. Predators on average were enriched in 15N by 3.5 per thousand compared to detritivores. Within detritvores and predators delta15N signatures varied markedly, indicating that these trophic guilds are dominated by generalist feeders which form a gradient of organisms feeding on different resources. The results indicate that commonly used trophic guilds, in particular detritivores and predators, do not represent trophic levels but consist of subguilds, i.e. subsets of organisms differing in resource utilization. In particular, in soil and litter food webs where trophic level omnivory is common, the use of distinct trophic levels may be inappropriate. Guilds of species delineated by natural variations of stable isotope ratios are assumed to more adequately represent the structure of litter and soil food webs allowing a more detailed understanding of their functioning. PMID:20109270

  13. Effect of body size and body mass on δ 13 C and δ 15 N in coastal fishes and cephalopods

    NASA Astrophysics Data System (ADS)

    Vinagre, C.; Máguas, C.; Cabral, H. N.; Costa, M. J.

    2011-11-01

    Carbon and nitrogen isotopes have been widely used in the investigation of trophic relations, energy pathways, trophic levels and migrations, under the assumption that δ 13C is independent of body size and that variation in δ 15N occurs exclusively due to ontogenetic changes in diet and not body size increase per se. However, several studies have shown that these assumptions are uncertain. Data from food-webs containing an important number of species lack theoretical support on these assumptions because very few species have been tested for δ 13C and δ 15N variation in captivity. However, if sampling comprises a wide range of body sizes from various species, the variation of δ 13C and δ 15N with body size can be investigated. While correlation between body size and δ 13C and δ 15N can be due to ontogenetic diet shifts, stability in such values throughout the size spectrum can be considered an indication that δ 13C and δ 15N in muscle tissues of such species is independent of body size within that size range, and thus the basic assumptions can be applied in the interpretation of such food webs. The present study investigated the variation in muscle δ 13C and δ 15N with body size and body mass of coastal fishes and cephalopods. It was concluded that muscle δ 13C and δ 15N did not vary with body size or mass for all bony fishes with only one exception, the dragonet Callionymus lyra. Muscle δ 13C and δ 15N also did not vary with body size or mass in cartilaginous fishes and cephalopods, meaning that body size/mass per se have no effect on δ 13C or δ 15N, for most species analysed and within the size ranges sampled. The assumption that δ 13C is independent of body size and that variation in δ 15N is not affected by body size increase per se was upheld for most organisms and can be applied to the coastal food web studied taking into account that C. lyra is an exception.

  14. Design and operation of a continuous 13C and 15N labeling chamber for uniform or differential, metabolic and structural, plant tissue isotope labeling

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Tracing heavy stable isotopes from plant material through the ecosystem provides the most sensitive information about ecosystem processes; from CO2 fluxes and soil organic matter formation to small-scale stable-isotope biomarker probing. Coupling multiple stable isotopes such as 13C with 15N, 18O o...

  15. Mangrove isotopic15N and δ13C) fractionation across a nitrogen vs. phosphorus limitation gradient

    USGS Publications Warehouse

    Mckee, Karen L.; Feller, Ilka C.; Popp, Marianne; Wanek, Wolfgang

    2002-01-01

    Mangrove islands in Belize are characterized by a unique switching from nitrogen (N) to phosphorus (P) limitation to tree growth from shoreline to interior. Fertilization has previously shown that Rhizophora mangle (red mangrove) fringe trees (5–6 m tall) growing along the shoreline are N limited; dwarf trees (!1.5 m tall) in the forestinterior are P limited; and transition trees (2–4 m tall) are co-limited by both N and P.  Growth patterns paralleled a landward decrease in soil flushing by tides and an increase in bioavailable N, but P availability remained consistently low across the gradient. Stable isotopic composition was measured in R. mangle leaves to aid in explaining this nutrient switching pattern and growth variation. Along control transects, leaf !15N decreased from "0.10‰ (fringe) to #5.38‰ (dwarf). The !15N of N-fertilized trees also varied spatially, but the values were consistently more negative (by $3‰) compared to control trees. Spatial variation in !15N values disappeared when the trees were fertilized with P, and values averaged "0.12‰, similar to that in control fringe trees. Neither variation in source inputs nor microbial fractionation could fully account for the observed patterns in !15N. The results instead suggest that the lower !15N values in transition and dwarf control trees were due to plant fractionation as a consequence of slower growth and lower N demand. P fertilization increased N demand and decreased fractionation. Although leaf !13C was unaffected by fertilization, values increased from fringe (#28.6‰) to transition (#27.9‰) to dwarf (#26.4‰) zones, indicating spatial variation in environmental stresses affecting stomatal conductance or carboxylation. The results thus suggest an interaction of external supply, internal demand, and plant ability to acquire nutrients under different hydro-edaphic conditions that vary across this tree-height gradient. The findings not only aid in understanding

  16. Evaluating mercury biomagnification in fish from a tropical marine environment using stable isotopes (delta13C and delta15N).

    PubMed

    Al-Reasi, Hassan A; Ababneh, Fuad A; Lean, David R

    2007-08-01

    Concentrations of total mercury (T-Hg) and methylmercury (MeHg) were measured in zooplankton and 13 fish species from a coastal food web of the Gulf of Oman, an arm of the Arabian Sea between Oman and Iran. Stable isotope ratios (delta13C and delta15N) also were determined to track mercury biomagnification. The average concentration of T-Hg in zooplankton was 21 +/- 8.0 ng g(-1) with MeHg accounting 10% of T-Hg. Total mercury levels in fish species ranged from 3.0 ng g(-1) (Sardinella longiceps) to 760 ng g(-1) (Rhizoprionodon acutus) with relatively lower fraction of MeHg (72%) than that found in other studies. The average trophic difference (Deltadelta13C) between zooplankton and planktivorous fish (Selar crumenopthalmus, Rastrelliger kanagurta, and S. longiceps) was higher (3.4 per thousandth) than expected, suggesting that zooplankton may not be the main diet or direct carbon source for these fish species. However, further sampling would be required to compensate for temporal changes in zooplankton and the influence of their lipid content. Trophic position inferred by delta15N and and slopes of the regression equations (log10[T-Hg] = 0.13[delta15N] - 3.57 and log10[MeHg] = 0.14[delta15N] - 3.90) as estimates of biomagnification indicate that biomagnification of T-Hg and MeHg was lower in this tropical ocean compared to what has been observed in arctic and temperate ecosystems and tropical African lakes. The calculated daily intake of methylmercury in the diet of local people through fish consumption was well below the established World Health Organization (WHO) tolerable daily intake threshold for most of the fish species except Euthynnus affinis, Epinephelus epistictus, R. acutus, and Thunnus tonggol, illustrating safe consumption of the commonly consumed fish species. PMID:17702328

  17. Characterising ontogenetic niche shifts in Nile crocodile using stable isotope (δ13C, δ15N) analyses of scute keratin.

    PubMed

    Radloff, Frans G T; Hobson, Keith A; Leslie, Alison J

    2012-09-01

    Nile crocodiles undergo a three to five order of magnitude increase in body size during their lifespan. This shift coincides with a change in resource and habitat use which influences the strength, type and symmetry of interactions with other species. Identifying size-specific crocodile groups displaying similar traits is important for conservation planning. Here, we illustrate how stable carbon (δ(13) C) and nitrogen (δ(15) N) isotope analysis of scute keratin, together with breakpoint modelling analysis can be used to characterise ontogenetic niche shifts. Using a sample set of 238 crocodiles from the Okavango Delta, Botswana (35-463 cm total length), we found prominent size-related changes in the scute keratin δ(13) C and δ(15) N profiles close to 40 and 119 cm snout-vent length. The first shift corroborated the findings of a traditional stomach-content study conducted on the same population at the same time, and the second conformed to known crocodile ecology. This approach can be used as a first approximation to identify size-specific groups within crocodile populations, and these can then be investigated further using isotopic or other methods. PMID:22462522

  18. Determination of Multimodal Isotopic Distributions: The Case of a (15)N Labeled Protein Produced into Hairy Roots.

    PubMed

    Trouillard, Romain; Hubert-Roux, Marie; Tognetti, Vincent; Guilhaudis, Laure; Plasson, Carole; Menu-Bouaouiche, Laurence; Coquet, Laurent; Guerineau, François; Hardouin, Julie; Ele Ekouna, Jean-Pierre; Cosette, Pascal; Lerouge, Patrice; Boitel-Conti, Michèle; Afonso, Carlos; Ségalas-Milazzo, Isabelle

    2015-06-16

    Isotopic labeling is widely used in various fields like proteomics, metabolomics, fluxomics, as well as in NMR structural studies, but it requires an efficient determination of the isotopic enrichment. Mass spectrometry is the method of choice for such analysis. However, when complex expression systems like hairy roots are used for production, multiple populations of labeled proteins may be obtained. If the isotopic incorporation determination is actually well-known for unimodal distributions, the multimodal distributions have scarcely been investigated. Actually, only a few approaches allow the determination of the different labeled population proportions from multimodal distributions. Furthermore, they cannot be used when the number of the populations and their respective isotope ratios are unknown. The present study implements a new strategy to measure the (15)N labeled populations inside a multimodal distribution knowing only the peptide sequence and peak intensities from mass spectrometry analyses. Noteworthy, it could be applied to other elements, like carbon and hydrogen, and extended to a larger range of biomolecules. PMID:25973921

  19. 15N investigation into the effect of a pollutant on the nitrogen metabolism of Tetrahymena pyriformis as a model for environmental medical research.

    PubMed Central

    Arndt, K; Hofmann, D; Gehre, M; Krumbiegel, P

    1998-01-01

    A pilot study was performed to examine the potential of stable isotope techniques for monitoring the impact of a harmful substance on the cellular nitrogen metabolism in the ciliate species Tetrahymena pyriformis. After identical cultivation periods of control cells and toluene-exposed cells in a defined culture medium enriched with [guanidino-15N2]l-arginine, a number of nitrogen-containing pools were analyzed: 1) quantity and 15N abundance of ammonia as the end product of nitrogen metabolism in the system; 2) pattern and 15N abundances of the protein-bound amino acids in the cells; 3) pattern and 15N abundances of free amino acids in the cells; and 4) pattern and 15N abundances of the amino acids in the culture medium. In addition to 15N emission spectrometry, a new gas chromatography/combustion interface-isotope ratio mass spectrometry/mass spectrometry analytical system was used. The production and 15N content of ammonia were higher in the toluene-exposed system by 30% and 43%, respectively, indicating higher deamination rates and greater arginine consumption. The toluene-exposed cells exhibited increased 15N abundances of protein-bound amino acids in alanine, aspartic acid, glutamic acid, and tyrosine. Furthermore, structural analyses revealed the presence of N[Omega]-acetylarginine and pyrrolidonecarboxylic acid--compounds that had not previously been detected in Tetrahymena pyriformis. Differences in the 15N-enrichment of free amino acids were also evident. This new effect-monitoring system designed to investigate the impact of a pollutant on protein metabolism by using a stable isotope-labeled cell culture is a powerful tool for environmental medical research. Images Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 PMID:9681977

  20. Establishing spatial trends in water chemistry and stable isotopes15N and δ13C) in the Elwha River prior to dam removal and salmon recolonization

    USGS Publications Warehouse

    Duda, J.J.; Coe, H.J.; Morley, S.A.; Kloehn, K.K.

    2011-01-01

    Two high-head dams on the Elwha River in Washington State (USA) have changed the migratory patterns of resident and anadromous fish, limiting Pacific salmon to the lower 7.9 km of a river that historically supported large Pacific salmon runs. To document the effects of the dams prior to their removal, we measured carbon and nitrogen stable isotope ratios of primary producers, benthic macroinvertebrates, and fish, and water chemistry above, between and below the dams. We found that δ15N was significantly higher in fish, stoneflies, black flies, periphyton and macroalgae where salmon still have access. Fish and chloroperlid stoneflies were enriched in δ13C, but the values were more variable than in δ15N. For some taxa, there were also differences between the two river sections that lack salmon, suggesting that factors other than marine-derived nutrients are structuring longitudinal isotopic profiles. Consistent with trophic theory, macroalgae had the lowest δ15N, followed by periphyton, macroinvertebrates and fish, with a range of 6.9, 6.2 and 7.7‰ below, between, and above the dams, respectively. Water chemistry analyses confirmed earlier reports that the river is oligotrophic. Phosphorous levels in the Elwha were lower than those found in other regional rivers, with significant differences among regulated, unregulated and reference sections. The removal of these dams, among the largest of such projects ever attempted, is expected to facilitate the return of salmon and their marine-derived nutrients (MDN) throughout the watershed, possibly altering the food web structure, nutrient levels and stable isotope values that we documented.

  1. Quantifying RDX biodegradation in groundwater using δ15N isotope analysis

    NASA Astrophysics Data System (ADS)

    Bernstein, Anat; Adar, Eilon; Ronen, Zeev; Lowag, Harald; Stichler, Willibald; Meckenstock, Rainer U.

    2010-01-01

    Isotope analysis was used to examine the extent of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) biodegradation in groundwater along a ca. 1.35-km contamination plume. Biodegradation was proposed as a natural attenuating remediation method for the contaminated aquifer. By isotope analysis of RDX, the extent of biodegradation was found to reach up to 99.5% of the initial mass at a distance of 1.15-1.35 km down gradient from the contamination sources. A range of first-order biodegradation rates was calculated based on the degradation extents, with average half-life values ranging between 4.4 and 12.8 years for RDX biodegradation in the upper 15 m of the aquifer, assuming purely aerobic biodegradation, and between 10.9 and 31.2 years, assuming purely anaerobic biodegradation. Based on the geochemical data, an aerobic biodegradation pathway was suggested as the dominant attenuation process at the site. The calculated biodegradation rate was correlated with depth, showing decreasing degradation rates in deeper groundwater layers. Exceptionally low first-order kinetic constants were found in a borehole penetrating the bottom of the aquifer, with half life ranging between 85.0 to 161.5 years, assuming purely aerobic biodegradation, and between 207.5 and 394.3 years, assuming purely anaerobic biodegradation. The study showed that stable isotope fractionation analysis is a suitable tool to detect biodegradation of RDX in the environment. Our findings clearly indicated that RDX is naturally biodegraded in the contaminated aquifer. To the best of our knowledge, this is the first reported use of RDX isotope analysis to quantify its biodegradation in contaminated aquifers.

  2. A facile method for expression and purification of (15)N isotope-labeled human Alzheimer's β-amyloid peptides from E. coli for NMR-based structural analysis.

    PubMed

    Sharma, Sudhir C; Armand, Tara; Ball, K Aurelia; Chen, Anna; Pelton, Jeffrey G; Wemmer, David E; Head-Gordon, Teresa

    2015-12-01

    Alzheimer's disease (AD) is a progressive neurodegenerative disease affecting millions of people worldwide. AD is characterized by the presence of extracellular plaques composed of aggregated/oligomerized β-amyloid peptides with Aβ42 peptide representing a major isoform in the senile plaques. Given the pathological significance of Aβ42 in the progression of AD, there is considerable interest in understanding the structural ensembles for soluble monomer and oligomeric forms of Aβ42. This report describes an efficient method to express and purify high quality (15)N isotope-labeled Aβ42 for structural studies by NMR. The protocol involves utilization of an auto induction system with (15)N isotope labeled medium, for high-level expression of Aβ42 as a fusion with IFABP. After the over-expression of the (15)N isotope-labeled IFABP-Aβ42 fusion protein in the inclusion bodies, pure (15)N isotope-labeled Aβ42 peptide is obtained following a purification method that is streamlined and improved from the method originally developed for the isolation of unlabeled Aβ42 peptide (Garai et al., 2009). We obtain a final yield of ∼ 6 mg/L culture for (15)N isotope-labeled Aβ42 peptide. Mass spectrometry and (1)H-(15)N HSQC spectra of monomeric Aβ42 peptide validate the uniform incorporation of the isotopic label. The method described here is equally applicable for the uniform isotope labeling with (15)N and (13)C in Aβ42 peptide as well as its other variants including any Aβ42 peptide mutants. PMID:26231074

  3. Compound-specific 15N stable isotope probing of N assimilation by the soil microbial biomass: a new methodological paradigm in soil N cycling

    NASA Astrophysics Data System (ADS)

    Charteris, A. F.; Knowles, T. D. J.; Michaelides, K.; Evershed, R. P.

    2015-10-01

    A compound-specific nitrogen-15 stable isotope probing (15N-SIP) technique is described which allows investigation of the fate of inorganic- or organic-N amendments to soils. The technique uses gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) to determine the δ15N values of individual amino acids (AAs; determined as N-acetyl, O-isopropyl derivatives) as proxies of biomass protein production. The δ15N values are used together with AA concentrations to quantify N assimilation of 15N-labelled substrates by the soil microbial biomass. The utility of the approach is demonstrated through incubation experiments using inorganic 15N-labelled substrates ammonium (15NH4+) and nitrate (15NO3-) and an organic 15N-labelled substrate, glutamic acid (15N-Glu). Assimilation of all the applied substrates was undetectable based on bulk soil properties, i.e. % total N (% TN), bulk soil N isotope composition and AA concentrations, all of which remained relatively constant throughout the incubation experiments. In contrast, compound-specific AA δ15N values were highly sensitive to N assimilation, providing qualitative and quantitative insights into the cycling and fate of the applied 15N-labelled substrates. The utility of this 15N-AA-SIP technique is considered in relation to other currently available methods for investigating the microbially-mediated assimilation of nitrogenous substrates into the soil organic N pool. This approach will be generally applicable to the study of N cycling in any soil, or indeed, in any complex ecosystem.

  4. Non-homogeneity of isotopic labelling in 15N gas flux studies: theory, some observations and possible lessons

    NASA Astrophysics Data System (ADS)

    Well, Reinhard; Buchen, Caroline; Deppe, Marianna; Eschenbach, Wolfram; Gattinger, Andreas; Giesemann, Anette; Krause, Hans-Martin; Lewicka-Szczebak, Dominika

    2015-04-01

    Quantifying dinitrogen (N2) and nitrous oxide (N2O) fluxes from different soil N pools and processes can be accomplished using the 15N tracer technique but this is subject to four different sources of bias (i. - iv.). This approach includes 15N labelling of selected N pools in soil and subsequent isotope analysis of all relevant N pools as well as of gas samples from enclosures, i.e. mixtures of soil-derived and atmospheric N2 and N2O. Depending on the processes of interest, there may be 15N labelling of one or several N pools, were several labelling treatment are needed in the latter case (e.g. Müller et al., 2004). Measuring pool-derived N2 or N2O has been shown to include two calculation problems, (i.) arising from multiple pools (e.g. Arah, 1992) and (ii.) dealing with the non-random distribution of N2 and N2O mole masses (Hauck et al., 1958). Non-randomness can be solved if m/z 28, 29 and 30 are correctly analysed and the 15N enrichment of one (to distinguish two pools, i.e. soil and atmosphere) or two pools (in case of three pools) is known (Spott & Stange, 2008). Moreover (iii.), NO3- pools generating N2 and N2O via denitrification can be identical or different, e.g. if N2O evolved from higher enriched NO3- in deeper soil was more reduced to N2 compared to N2O evolved from N2O from shallow soil with lower enrichment, or vice versa. Apportioning N2O fluxes to NH4+ (nitrification and/or nitrifier denitrification) and NO3- (denitrification) is often conducted by NO3-labeling, measuring δ15N of emitted N2O and applying mixing equations were the measured 15N enrichment of NH4+and NO3-pool is used. However, this assumes that the average 15N enrichment of NH4+and NO3-in the soil is identical to the enrichment in the active soil domain producing N2 and/or N2O. Violation of this precondition must lead to bias in source apportionment (iv.), but to our knowledge this has not been investigated until now. Here we present conceptual models and model calculations

  5. Dynamics of δ(15)N isotopic signatures of different intertidal macroalgal species: Assessment of bioindicators of N sources in coastal areas.

    PubMed

    Lemesle, Stéphanie; Erraud, Alexandre; Mussio, Isabelle; Rusig, Anne-Marie; Claquin, Pascal

    2016-09-15

    δ(15)N of annual (Ulva sp., Porphyra sp.) and perennial intertidal seaweed species (Chondrus crispus, Fucus sp.) collected on 17 sampling points along the French coast of the English Channel in 2012 and 2013 were assessed on their suitability as bioindicators of N pollution in coastal areas. A sine function applied for δ(15)N time series data showed for all the species the same seasonal trend with lowest δ(15)N values in April and highest in summer but with no significant interspecific differences of amplitude (α) and phase angle (ϕ). This model provides a useful tool for monitoring the inter-annual changes of N pollution. An interspecific variability of δ(15)N values was observed, probably due to their tolerance to emersion. An in vitro study for comparing the kinetic acquisition of the isotopic signal and N uptake mechanisms of each species underlined the influence of algal physiology on the δ(15)N interspecific variability. PMID:27349382

  6. Assessment of dissolved nutrients dispersal derived from offshore fish-farm using nitrogen stable isotope ratios (δ 15N) in macroalgal bioassays

    NASA Astrophysics Data System (ADS)

    García-Sanz, T.; Ruiz, J. M.; Pérez, M.; Ruiz, M.

    2011-02-01

    In this study, the dispersal of wastes from offshore fish farms was evaluated by analyzing nitrogen stable isotope ratios (δ 15N) in macroalgae incubated in the water column at sites located at an increasing distance from the fish cages. Bioassays were performed at three fish farms situated in separate localities with different nutritional conditions (Canary Islands, Murcia and Catalonia) and varying in size, species of fish reared and annual production. Macroalgal bioassays were carried out in two different directions (DI and DII) and they were replicated at each distance in order to evaluate the effect of small-scale variability on the spatial extent of fish farm wastes. The results obtained with δ 15N contribute to a better understanding of the application of nitrogen stable isotopes ratios in macroalgae as an effective bioindicator for tracing the dispersion of offshore fish farm wastes, and demonstrate that fish farm wastes can be traced even over distances of some km from the pollution source. In the Canary Islands, the maximum distance obtained for detection of fish farm wastes was between 450 and 700 m. Of the three installations studied, Murcia presented the greatest distance for detection of fish farm waste influence, ranging from between 1550 and 2450 m, whilst in Catalonia this distance was less than 120 m. In Catalonia, the results were masked by the influence of other sources of nitrogen, and thus fish farm wastes were detected at more reduced distances than expected. These results confirm that fish farm wastes can be traced using the nitrogen stable isotope ratios of macroalgae and that this method can also be useful for identifying areas of potential risk to some sensitive ecosystems, and as an early signal that changes in the community structure might occur.

  7. Nicotine, acetanilide and urea multi-level 2H-, 13C- and 15N-abundance reference materials for continuous-flow isotope ratio mass spectrometry.

    PubMed

    Schimmelmann, Arndt; Albertino, Andrea; Sauer, Peter E; Qi, Haiping; Molinie, Roland; Mesnard, François

    2009-11-01

    Accurate determinations of stable isotope ratios require a calibration using at least two reference materials with different isotopic compositions to anchor the isotopic scale and compensate for differences in machine slope. Ideally, the delta values of these reference materials should bracket the isotopic range of samples with unknown delta values. While the practice of analyzing two isotopically distinct reference materials is common for water (VSMOW-SLAP) and carbonates (NBS 19 and L-SVEC), the lack of widely available organic reference materials with distinct isotopic composition has hindered the practice when analyzing organic materials by elemental analysis/isotope ratio mass spectrometry (EA-IRMS). At present only L-glutamic acids USGS40 and USGS41 satisfy these requirements for delta13C and delta15N, with the limitation that L-glutamic acid is not suitable for analysis by gas chromatography (GC). We describe the development and quality testing of (i) four nicotine laboratory reference materials for on-line (i.e. continuous flow) hydrogen reductive gas chromatography-isotope ratio mass-spectrometry (GC-IRMS), (ii) five nicotines for oxidative C, N gas chromatography-combustion-isotope ratio mass-spectrometry (GC-C-IRMS, or GC-IRMS), and (iii) also three acetanilide and three urea reference materials for on-line oxidative EA-IRMS for C and N. Isotopic off-line calibration against international stable isotope measurement standards at Indiana University adhered to the 'principle of identical treatment'. The new reference materials cover the following isotopic ranges: delta2H(nicotine) -162 to -45 per thousand, delta13C(nicotine) -30.05 to +7.72 per thousand, delta15N(nicotine) -6.03 to +33.62 per thousand; delta15N(acetanilide) +1.18 to +40.57 per thousand; delta13C(urea) -34.13 to +11.71 per thousand, delta15N(urea) +0.26 to +40.61 per thousand (recommended delta values refer to calibration with NBS 19, L-SVEC, IAEA-N-1, and IAEA-N-2). Nicotines fill a gap as

  8. Resolving the bulk δ 15N values of ancient human and animal bone collagen via compound-specific nitrogen isotope analysis of constituent amino acids

    NASA Astrophysics Data System (ADS)

    Styring, Amy K.; Sealy, Judith C.; Evershed, Richard P.

    2010-01-01

    Stable nitrogen isotope analysis is a fundamental tool in assessing dietary preferences and trophic positions within contemporary and ancient ecosystems. In order to assess more fully the dietary contributions to human tissue isotope values, a greater understanding of the complex biochemical and physiological factors which underpin bulk collagen δ 15N values is necessary. Determinations of δ 15N values of the individual amino acids which constitute bone collagen are necessary to unravel these relationships, since different amino acids display different δ 15N values according to their biosynthetic origins. A range of collagen isolates from archaeological faunal and human bone ( n = 12 and 11, respectively), representing a spectrum of terrestrial and marine protein origins and diets, were selected from coastal and near-coastal sites at the south-western tip of Africa. The collagens were hydrolysed and δ 15N values of their constituent amino acids determined as N-acetylmethyl esters (NACME) via gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). The analytical approach employed accounts for 56% of bone collagen nitrogen. Reconstruction of bulk bone collagen δ 15N values reveals a 2‰ offset from bulk collagen δ 15N values which is attributable to the δ 15N value of the amino acids which cannot currently be determined by GC-C-IRMS, notably arginine which comprises 53% of the nitrogen unaccounted for (23% of the total nitrogen). The δ 15N values of individual amino acids provide insights into both the contributions of various amino acids to the bulk δ 15N value of collagen and the factors influencing trophic position and the nitrogen source at the base of the food web. The similarity in the δ 15N values of alanine, glutamate, proline and hydroxyproline reflects the common origin of their amino groups from glutamate. The depletion in the δ 15N value of threonine with increasing trophic level indicates a fundamental difference between

  9. Food partitioning of leaf-eating mangrove crabs ( Sesarminae): Experimental and stable isotope ( 13C and 15N) evidence

    NASA Astrophysics Data System (ADS)

    Kristensen, Ditte K.; Kristensen, Erik; Mangion, Perrine

    2010-05-01

    The feasibility of mangrove leaves as a full diet for sesarmid crabs has been questioned for decades. Since these leaves are nitrogen-poor, sesarmids probably obtain nitrogen from other sources to sustain growth. The aim of this study was to assess the food partitioning of the sesarmid species Neoepisesarma versicolor with emphasis on nitrogen allocation. The preference for animal tissue when crabs were pre-fed diets of different nitrogen content was determined in the laboratory. Furthermore, the possible in situ diet composition of N. versicolor was established from carbon and nitrogen stable isotope signature ( δ13C and δ15N) of freshly caught individuals and their potential food sources, using a concentration-dependent mixing model. N. versicolor showed significantly higher feeding preferences for fish meat when pre-fed leaf material without than with access to meat, indicating that this crab species can meet its nitrogen demand by ingesting animal tissue. The stable isotope mixing model based on in situ materials suggests that the diet of N. versicolor consists of ˜60% leaves in terms of biomass, leaving ˜40% for other sources such as animal tissue and benthic microorganisms. The biomass contribution from animal tissues, in form of e.g. other crustaceans and fish carcasses, was found to account for ˜15%. Despite the relative low biomass fraction, animal food sources may contribute with up to half of the nitrogen in the diet of N. versicolor. The quantity of ingested sediment most likely exceeds that of animal tissues. However, due to the low concentration of assimilable microalgae and other microorganism, we propose that sediment associated sources are less important as a nitrogen source for N. versicolor than hitherto presumed.

  10. A cross-shelf gradient in δ15N stable isotope values of krill and pollock indicates seabird foraging patterns in the Bering Sea

    NASA Astrophysics Data System (ADS)

    Jones, Nathan M.; Hoover, Brian A.; Heppell, Scott A.; Kuletz, Kathy J.

    2014-11-01

    Concurrent measurements of predator and prey δ15N isotope values demonstrated that a cross-shelf isotopic gradient can propagate through a marine food web from forage species to top-tier predators and indicate foraging areas at a scale of tens of kilometers. We measured δ13C and δ15N in muscle tissues of thick-billed murres (Uria lomvia) and black-legged kittiwakes (Rissa tridactyla), and in whole body tissues of walleye pollock (Gadus chalcogrammus) and krill (Thysanoessa spp), sampled across the continental shelf break in the Bering Sea in 2008 and in 2009. We found significant basin-shelf differences at fine scales (<100 km) in δ15N among murres but not kittiwakes, and no such differences in δ13C in either seabird species at that scale. We then quantified the multi-trophic signal and spatial structure of a basin-shelf δ15Nitrogen gradient in the central and southern Bering Sea, and used it to contrast foraging patterns of thick-billed murres and kittiwakes on the open ocean. Seabird muscle δ15N values were compared to baselines created from measurements in krill and pollock tissues sampled concurrently throughout the study area. Krill, pollock, and murre tissues from northern, shallow, shelf habitat (<200 m) were enriched 1-2‰ in δ15N relative to samples taken from deeper habitats (>200 m) to the south and west. Krill δ15N baseline values predicted 35-42% of the variability in murre tissue values. Patterns between kittiwakes and prey were less coherent. The persistence of strong spatial autocorrelation among sample values, and a congruence of geospatial patterns in δ15N among murre and prey tissues, suggest that murres forage repeatedly in specific areas. Murre isotope values showed distinct geospatial stratification, coincident with the spatial distribution of three colonies: St. Paul, St. George, and Bogoslof. This suggests some degree of foraging habitat partitioning among colonies.

  11. A stable isotope (δ13C and δ15N) perspective on human diet on Rapa Nui (Easter Island) ca. AD 1400-1900.

    PubMed

    Commendador, Amy S; Dudgeon, John V; Finney, Bruce P; Fuller, Benjamin T; Esh, Kelley S

    2013-10-01

    Ecological and environmental evidence suggests that Rapa Nui was among the most marginally habitable islands in Eastern Polynesia, with only a fraction of the biotic diversity found on archipelagos to the west, and capable of sustaining many fewer cultigens traditionally transported by Polynesian colonizers. However, archaeological evidence for human dietary adaptations under such restrictions is limited. Little is known about the particulars of the subsistence base and dietary changes on Rapa Nui that may be associated with a hypothesized late prehistoric decline in the quality and diversity of food sources. To better understand prehistoric Rapa Nui diet we examined stable carbon and nitrogen isotope compositions of human teeth along with archaeological faunal material thought to comprise the Rapa Nui food web. Our results indicate that contrary to previous zooarchaeological studies diet was predominantly terrestrial throughout the entire sequence of occupation, with reliance on rats, chickens and C3 plants. While a few individuals may have had access to higher trophic level marine resources, this is evident only later in time (generally post-AD 1600). A decline in (15)N through time was observed, and may be attributed to declines in available terrestrial proteins; however, presently we cannot rule out the effect of changing soil and plant baseline δ(15)N. Our results also suggest differential access to higher trophic level marine resources among contemporaneous populations, but more research is required to clarify this observation. PMID:23996514

  12. Multi-isotope ((15)N, (18)O and (13)C) indicators of sources and fate of nitrate in the upper stream of Chaobai River, Beijing, China.

    PubMed

    Li, Cai; Jiang, Yongbin; Guo, Xinyue; Cao, Yang; Ji, Hongbing

    2014-11-01

    Dual isotopes of nitrate ((15)N and (18)O) and carbon isotopes of dissolved inorganic carbon ((13)C) together with water chemistry were used to identify the sources and fate of nitrate in the upper stream of Chaobai River, north China. The results show that NO3(-) concentrations ranges from 0.03 mmol L(-1) to 0.80 mmol L(-1). Sampling sites from watershed with dominant forest land had higher NO3(-) concentrations and lower δ(15)N-NO3(-) (<10‰) in the wet season than in the dry season, while those from watershed with more anthropogenic activities had lower NO3(-) concentrations and higher δ(15)N-NO3(-) (>10‰) in the wet season. Compositions of isotopes and chemistry indicated that NO3(-) originated mainly from soil N, sewage and livestock wastes and atmospheric nitrogen. Furthermore, the mixing model suggested that soil N was the major NO3(-) source in the wet season, while the sewage and livestock wastes contributed the most in the dry season. Compared to rivers, the Miyun Reservoir had a higher contribution of atmospheric N and the N input from the upper rivers exerted significant influence over the reservoir. Mineralization and nitrification played an important role in N biogeochemistry based on the isotopes ((15)N and (18)O and (13)C) and chemical data. There appeared to be no significant denitrification in the watershed according to the three isotopes and chemical ions. The combined use of (15)N, (18)O and (13)C proved to be useful for further identification of the sources and fate of nitrate in watersheds with dominant forest land in the wet season. PMID:25283837

  13. Effects of lipid and urea extraction on δ15N values of deep-sea sharks and hagfish: Can mathematical correction factors be generated?

    NASA Astrophysics Data System (ADS)

    Churchill, Diana A.; Heithaus, Michael R.; Dean Grubbs, R.

    2015-05-01

    Stable isotope analysis is broadly employed to investigate diverse ecological questions. In order to make appropriate comparisons among multiple taxa, however, it is necessary to standardize values to account for interspecific differences in factors that affect isotopic ratios. For example, varying concentrations of soluble nitrogen compounds, such as urea or trimethylamine oxide, can affect the analysis and interpretation of δ15N values of sharks or hagfish. The goal of this study was to assess the effects of a standard chloroform/methanol extraction on the stable isotope values of muscle tissue obtained from 10 species of sharks and three species of hagfish collected from poorly-known deep-water (>200 m) communities. We detected significant differences in δ15N, %N, and C:N values as a result of extractions in 8 of 10 shark and all three hagfish species. We observed increased δ15N values, but shifts in %N and C:N values were not unidirectional. Mathematical normalizations for δ15N values were successfully created for four shark and two hagfish species. However, they were not successful for two shark species. Therefore, performing extractions of all samples is recommended.

  14. Landscape hydrology and scaling of nitrate 15N and 18O isotope composition in a semi-arid agroecosystem

    NASA Astrophysics Data System (ADS)

    Kelley, C. J.; Martin, R. A.; Keller, C. K.; Orr, C. H.; Huggins, D. R.; Evans, R. D.

    2014-12-01

    Understanding how pore- to hillslope-scale processes combine to control nutrient export at larger scales is a fundamental challenge in today's agroecosystems as the carbon and contamination footprints of production agriculture come under increasing scrutiny. At the Cook Agronomy Farm (CAF) Long-Term Agricultural Research (LTAR) station near Pullman, WA we are using in-field observations to track how local-scale hydrological routing and biogeochemical processing interact to control landscape-scale water and nutrient exports. Previous research at the CAF has shown that conservative tracers and reactive nutrient quantities (NO3-,and DOC concentrations, DOM quality) in landscape-scale drainage can be explained by straightforward mixing of waters from variably contributing areas. Nitrate stable isotope composition in subsurface drain effluent indicate that most leached nitrate originates from reduced nitrogen fertilizer applied to the CAF in the autumn, which undergoes nitrification and subsequent leaching. This occurs over a timespan of weeks to months. However, water samples from contributing areas exhibit nitrate d15N and d18O significantly greater than subsurface drain effluent at all locations, and time-series consistent with the occurrence of denitrification at some locations. Possible explanations include pore-scale processing of nitrogen that does not affect the other tracers (like EC, DOM quality, and DOC concentration), and landscape-scale transport pathways that bypass our field instruments. Through this work we are contributing to a broader understand of how global change and local factors and management practices interact to affect the fate of fertilizer N, which is a cross-cutting research theme of the national LTAR network.

  15. Assessing waterbird habitat use in coastal evaporative systems using stable isotopes (δ 13C, δ 15N and δD) as environmental tracers

    NASA Astrophysics Data System (ADS)

    Ramírez, Francisco; Abdennadher, Aida; Sanpera, Carola; Jover, Lluís; Wassenaar, Leonard I.; Hobson, Keith A.

    2011-04-01

    Isotopic patterns of biota across salinity gradients in man-made evaporative systems could assist in determining the use of these habitats by animals. Here we report δ 13C, δ 15N and δD measurements of a euryhaline fish, the Mediterranean toothcarp ( Aphanius fasciatus), inhabiting a range of salinities in the Thyna saltworks near Sfax (Tunisia). The contribution of these salinity niches to egg formation of two typically piscivorous bird species breeding in the area and feeding within saltworks, Little Tern ( Sternula albifrons) and Little Egret ( Egretta garzetta), was inferred trough a triple-isotope (δ 13C, δ 15N and δD) Bayesian mixing model. Isotopic trends for fish δ 15N and δD across the salinity gradient followed the equations: δ 15N = e (1.1 + 47.68/Salinity) and δD = -175.74 + Salinity + Salinity 2; whereas fish δ 13C increased as salinity rose (δ 13C = -10.83 + 0.02·Salinity), after a sudden drop in fish isotopic values for salinities >60 (Practical Salinity Scale) (average fish δ 13C for salinities <60 = -5.92‰). Both bird species fed largely on low hypersalinity ponds (salinity = 43; average contribution = 37% and 22% for Little Egrets and Little Terns, respectively), although the use of intermediate hypersalinities (salinities 63 and 70) by Little Terns also occurred (16% and 21%, respectively). Isotopic patterns across salinity gradients allow the use of isotopic measurements to inform studies of habitat occupancy within evaporative systems and provide further insights into how wildlife communities interact with them.

  16. The response of the foliar antioxidant system and stable isotopes (δ(13)C and δ(15)N) of white willow to low-level air pollution.

    PubMed

    Wuytack, Tatiana; AbdElgawad, Hamada; Staelens, Jeroen; Asard, Han; Boeckx, Pascal; Verheyen, Kris; Samson, Roeland

    2013-06-01

    In this study we aimed to determine and elucidate the effect of ambient air pollution on the foliar antioxidant system and stable carbon and nitrogen isotopes of white willow (Salix alba L.). We grew white willow in uniform potting soil in the near vicinity of sixteen air quality monitoring stations in Belgium where nitrogen dioxide (NO2), ozone, sulfur dioxide and particulate matter concentrations were continuously measured. The trees were exposed to ambient air during six months (April-September 2011), and, thereafter, the degree of lipid peroxidation and foliar content of antioxidant molecules (ascorbate, glutathione, polyphenols, flavonoids), antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, peroxidase) and foliar stable carbon (δ(13)C) and nitrogen (δ(15)N) isotopes were measured. We found that lipid peroxidation was caused by air pollution stress, arising from high ambient NO2 concentrations, as shown by an increased amount of malondialdehyde. The antioxidant system was activated by increasing the amount of polyphenols at monitoring stations with a high atmospheric NO2 and low O3 concentration, while no increase of key enzymes (e.g., ascorbate, glutathione) was observed. The δ(13)C also decreased with increasing NO2 concentrations and decreasing O3 concentrations, probably reflecting a decreased net photosynthesis and/or a concomitant decrease of (13)CO2 in the atmosphere. Shade also influenced foliar δ(13)C and the content of leaf ascorbate and glutathione. PMID:23562799

  17. Stable isotope ((13)C/(12)C and (15)N/(14)N) composition of the woolly rhinoceros Coelodonta antiquitatis horn suggests seasonal changes in the diet.

    PubMed

    Tiunov, Alexei V; Kirillova, Irina V

    2010-11-15

    The extinct woolly rhinoceros Coelodonta antiquitatis is a prominent member of the Mammuthus-Coelodonta faunal complex, but its biology is poorly known, partly because very few specimens with well-preserved soft tissues have been discovered to date. However, the permafrost-preserved horns of the woolly rhinoceros are recording structures which contain isotopic records of the diet, environmental conditions and physiological status of the animal during most of its life. In this study we report the first data on the pattern of carbon ((13)C/(12)C) and nitrogen ((15)N/(14)N) isotopic composition along the nasal horn of woolly rhinoceros. We found systematic variations in δ(13)C and δ(15)N values associated with morphologically expressed transverse banding of the horn. The comparative analysis of isotopic variation in keratinous tissues of extant and extinct herbivores suggests that the oscillation in isotopic composition of the horn was induced by seasonal changes in the diet. Although the compiled evidence is in part contradictory, we suggest that more positive δ(13)C and δ(15)N values associated with dark-colored and less dense zones of the horn indicate a summer diet. More dense and light-colored zones of the horn have lower δ(13)C and δ(15)N values possibly indicating a larger proportion of woody and shrub vegetation in the winter diet. The validity of these conclusions has to be proven in further investigations, but our data underline the potential of isotopic analysis for studies on diet and habitat use by extinct members of Pleistocene fauna. PMID:20941761

  18. Fossil Fuel Combustion-Related Emissions Dominate Atmospheric Ammonia Sources during Severe Haze Episodes: Evidence from (15)N-Stable Isotope in Size-Resolved Aerosol Ammonium.

    PubMed

    Pan, Yuepeng; Tian, Shili; Liu, Dongwei; Fang, Yunting; Zhu, Xiaying; Zhang, Qiang; Zheng, Bo; Michalski, Greg; Wang, Yuesi

    2016-08-01

    The reduction of ammonia (NH3) emissions is urgently needed due to its role in aerosol nucleation and growth causing haze formation during its conversion into ammonium (NH4(+)). However, the relative contributions of individual NH3 sources are unclear, and debate remains over whether agricultural emissions dominate atmospheric NH3 in urban areas. Based on the chemical and isotopic measurements of size-resolved aerosols in urban Beijing, China, we find that the natural abundance of (15)N (expressed using δ(15)N values) of NH4(+) in fine particles varies with the development of haze episodes, ranging from -37.1‰ to -21.7‰ during clean/dusty days (relative humidity: ∼ 40%), to -13.1‰ to +5.8‰ during hazy days (relative humidity: 70-90%). After accounting for the isotope exchange between NH3 gas and aerosol NH4(+), the δ(15)N value of the initial NH3 during hazy days is found to be -14.5‰ to -1.6‰, which indicates fossil fuel-based emissions. These emissions contribute 90% of the total NH3 during hazy days in urban Beijing. This work demonstrates the analysis of δ(15)N values of aerosol NH4(+) to be a promising new tool for partitioning atmospheric NH3 sources, providing policy makers with insights into NH3 emissions and secondary aerosols for regulation in urban environments. PMID:27359161

  19. Application of (13)C and (15)N stable isotope probing to characterize RDX degrading microbial communities under different electron-accepting conditions.

    PubMed

    Cho, Kun-Ching; Lee, Do Gyun; Fuller, Mark E; Hatzinger, Paul B; Condee, Charles W; Chu, Kung-Hui

    2015-10-30

    This study identified microorganisms capable of using the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) or its metabolites as carbon and/or nitrogen sources under different electron-accepting conditions using (13)C and (15)N stable isotope probing (SIP). Mesocosms were constructed using groundwater and aquifer solids from an RDX-contaminated aquifer. The mesocosms received succinate as a carbon source and one of four electron acceptors (nitrate, manganese(IV), iron(III), or sulfate) or no additional electron acceptor (to stimulate methanogenesis). When RDX degradation was observed, subsamples from each mesocosm were removed and amended with (13)C3- or ring-(15)N3-, nitro-(15)N3-, or fully-labeled (15)N6-RDX, followed by additional incubation and isolation of labeled nucleic acids. A total of fifteen 16S rRNA sequences, clustering in α- and γ-Proteobacteria, Clostridia, and Actinobacteria, were detected in the (13)C-DNA fractions. A total of twenty seven sequences were derived from different (15)N-DNA fractions, with the sequences clustered in α- and γ-Proteobacteria, and Clostridia. Interestingly, sequences identified as Desulfosporosinus sp. (in the Clostridia) were not only observed to incorporate the labeled (13)C or (15)N from labeled RDX, but also were detected under each of the different electron-accepting conditions. The data suggest that (13)C- and (15)N-SIP can be used to characterize microbial communities involved in RDX biodegradation, and that the dominant pathway of RDX biodegradation may differ under different electron-accepting conditions. PMID:25935409

  20. Route of tracer administration does not affect ileal endogenous nitrogen recovery measured with the 15N-isotope dilution technique in pigs fed rapidly digestible diets.

    PubMed

    Steendam, C A Carina; Verstegen, Martin W A; Tamminga, Seerp; Boer, Huug; van 't End, Marianne; Verstappen, Berthe; Caine, William R; Visser, G Henk

    2004-11-01

    The (15)N-isotope dilution technique ((15)N-IDT), with either pulse-dose oral administration or continuous i.v. administration of [(15)N]-l-leucine (carotid artery), both at 5 mg/(kg body weight . d), was used to measure ileal (postvalve T-cecum cannula) endogenous nitrogen recovery (ENR) in pigs (9 +/- 0.6 kg). Diets were cornstarch, enzyme-hydrolyzed casein with no (control) or high (4%) content of quebracho extract (Schinopsis spp.) rich in condensed tannins. Blood was sampled from a catheter in the external jugular vein. Mean plasma (15)N-enrichment at d 8-10 was higher (P = 0.0009) after i.v. than after oral administration [0.0356 vs. 0.0379 atom% excess (APE)]. Plasma (15)N-enrichment for i.v. infused pigs was 0.01117 APE higher (P < 0.0001) and for orally dosed pigs 0.0081 APE lower (P < 0.0001) at 11 h postprandial compared with 1 h postprandial. Apparent ileal N digestibility was higher (P < 0.0001) for the control (85.5%) than for the quebracho diet (69.5%). ENR was calculated from the ratio of (15)N-enrichment of plasma and digesta. The ENR for the quebracho diet was approximately 300% higher than for the control diet (6.03 vs. 1.94 g/kg dry matter intake, P < 0.001). The real N digestibility (92.2 +/- 0.4%) was equal for both diets (P = 0.1030) and both tracer methods (P = 0.9730). We concluded that oral administration of [(15)N]leucine provides reasonable estimates of ENR in pigs fed semipurified diets with high or low content of tannins; however, one must be careful in extrapolating this conclusion to studies with other protein sources or feeding frequencies. PMID:15514277

  1. Technical Note: Simultaneous measurement of sedimentary N2 and N2O production and new 15N isotope pairing technique

    NASA Astrophysics Data System (ADS)

    Hsu, T.-C.; Kao, S.-J.

    2013-04-01

    Dinitrogen (N2) and/or nitrous oxide (N2O) are produced through denitrification, anaerobic ammonium oxidation (anammox) or nitrification in sediments, of which entangled processes obfuscate the absolute rate estimation of gaseous nitrogen production from individual pathway. Recently, the classical isotope pairing technique (IPT), the most common 15N-nitrate enrichment method to quantify denitrification, has been modified by different researchers to (1) discriminate relative contribution of N2 production by denitrification from anammox or to (2) provide more accurate denitrification rate by considering both N2O and N2 productions. Both modified methods, however, have deficiencies such as overlooking N2O production in case 1 and neglecting anammox in case 2. In this paper, a new method was developed to refine previous methods. We installed cryogenic traps to pre-concentrate N2 and N2O separately, thus, allowing simultaneous measurement for two gases generated by one sample. The precision is better than 2% for N2 (m/z 28, m/z 29 and m/z 30), and 1.5% for N2O (m/z 44, m/z 45 and m/z 46). Based on the six m/z peaks of the two gases, we further revised IPT formulae to truthfully resolve the production rates of N2 and N2O contributed from 3 specific nitrogen removal processes, i.e. N2 and N2O from denitrification, N2 from anammox and N2O from nitrification. To validate the applicability of our new method, incubation experiments were conducted using sediment cores taken from the Danshuei estuary in Taiwan. We successfully determined the rates of aforementioned nitrogen removal processes. Moreover, N2O yield was as high as 66%, which no doubt would significantly bias previous IPT approaches when N2O was not considered. Our new method not only complements the previous IPT but also provides more comprehensive information to advance our understanding of nitrogen dynamics through the water-sediment interface.

  2. Identification of Nitrogen-Incorporating Bacteria in Petroleum-Contaminated Arctic Soils by Using [15N]DNA-Based Stable Isotope Probing and Pyrosequencing ▿ †

    PubMed Central

    Bell, Terrence H.; Yergeau, Etienne; Martineau, Christine; Juck, David; Whyte, Lyle G.; Greer, Charles W.

    2011-01-01

    Arctic soils are increasingly susceptible to petroleum hydrocarbon contamination, as exploration and exploitation of the Arctic increase. Bioremediation in these soils is challenging due to logistical constraints and because soil temperatures only rise above 0°C for ∼2 months each year. Nitrogen is often added to contaminated soil in situ to stimulate the existing microbial community, but little is known about how the added nutrients are used by these microorganisms. Microbes vary widely in their ability to metabolize petroleum hydrocarbons, so the question becomes: which hydrocarbon-degrading microorganisms most effectively use this added nitrogen for growth? Using [15N]DNA-based stable isotope probing, we determined which taxonomic groups most readily incorporated nitrogen from the monoammonium phosphate added to contaminated and uncontaminated soil in Canadian Forces Station-Alert, Nunavut, Canada. Fractions from each sample were amplified with bacterial 16S rRNA and alkane monooxygenase B (alkB) gene-specific primers and then sequenced using lage-scale parallel-pyrosequencing. Sequence data was combined with 16S rRNA and alkB gene C quantitative PCR data to measure the presence of various phylogenetic groups in fractions at different buoyant densities. Several families of Proteobacteria and Actinobacteria that are directly involved in petroleum degradation incorporated the added nitrogen in contaminated soils, but it was the DNA of Sphingomonadaceae that was most enriched in 15N. Bacterial growth in uncontaminated soils was not stimulated by nutrient amendment. Our results suggest that nitrogen uptake efficiency differs between bacterial groups in contaminated soils. A better understanding of how groups of hydrocarbon-degraders contribute to the catabolism of petroleum will facilitate the design of more targeted bioremediation treatments. PMID:21498745

  3. Isotopic variation ( δ15N, δ13C, and δ34S) with body size in post-larval estuarine consumers

    NASA Astrophysics Data System (ADS)

    Marie Wilson, Rachel; Chanton, Jeffrey; Lewis, Graham; Nowacek, Douglas

    2009-07-01

    Stable isotope analyses were conducted on fish and crabs in Apalachicola Bay, Florida (USA) to determine whether δ15N values are correlated with length within these species. Our objective was to define the smallest trophic unit of the system as a prelude to further isotopic evaluations of consumer trophic level in Apalachicola Bay. In some cases, the smallest trophic unit is the individual species; however, previous gut content analysis on organisms in this system indicated that subdivision by size class within species might be required. However, over the size ranges observed, there was no systematic change in the δ15N values of individual consumers. Analysis of the δ13C and δ34S values of these species reveal no obvious shifts in the utilization of organic matter sources with length that could be obscuring a trend in the δ15N signal. We find no isotopic evidence for a systematic trophic level increase within the species examined over the size ranges observed in this estuary. These results indicate that species rather than size class is the best predictor of trophic habit among these Apalachicola Bay consumers.

  4. Production of Secondary Radioactive Beams of He and Li Neutron-Rich Isotopes in the Fragmentation Reaction {sup 15}N(47 MeV/A)+{sup 9}Be

    SciTech Connect

    Milewska, Aleksandra

    2007-11-26

    Yields of neutron-rich isotopes of He and Li produced in the reaction {sup 15}N(47 MeV/A)+{sup 9}Be have been measured. The experiment was carried out at the fragment separator COMBAS of the Flerov Laboratory of Nuclear Reactions, JINR (Dubna). Ion beams accelerated with the U-400M cyclotron and thick target were used. The products were identified according to their magnetic rigidities and time of flight (TOF) via the separator. The path length of TOF was 7,5 m. As a result of fragmentation, beams of four isotopes of Lithium and two isotopes of Helium were obtained. The inclusive velocities of reaction products were obtained and isotopes yields were calculated.

  5. Combination of the (87)Sr/(86)Sr ratio and light stable isotopic values (δ(13)C, δ(15)N and δD) for identifying the geographical origin of winter wheat in China.

    PubMed

    Liu, Hongyan; Wei, Yimin; Lu, Hai; Wei, Shuai; Jiang, Tao; Zhang, Yingquan; Guo, Boli

    2016-12-01

    This study aims to investigate whether isotopic signatures can be used to develop reliable fingerprints for discriminating the geographical origin of Chinese winter wheat, and to evaluate the discrimination effects of δ(13)C, δ(15)N and δD, alone or with (87)Sr/(86)Sr. In this study, the values of δ(13)C, δ(15)N and δD, and the (87)Sr/(86)Sr ratios of wheat and provenance soils from three regions were determined. Significant differences were found in all parameters of wheat and (87)Sr/(86)Sr in soil extract (reflecting the bioavailable fraction of soil) among different regions. A significantly positive correlation was observed between the (87)Sr/(86)Sr ratios of wheat and soil extracts. An overall correct classification rate of 77.8% was obtained for discriminating wheat from three regions based on light stable isotopes (δ(13)C, δ(15)N, and δD). The correct classification rate of 98.1% could be obtained with the combination of the (87)Sr/(86)Sr ratio and the light stable isotopic values. PMID:27374544

  6. Nicotine, acetanilide and urea multi-level2H-,13C- and15N-abundance reference materials for continuous-flow isotope ratio mass spectrometry

    USGS Publications Warehouse

    Schimmelmann, A.; Albertino, A.; Sauer, P.E.; Qi, H.; Molinie, R.; Mesnard, F.

    2009-01-01

    Accurate determinations of stable isotope ratios require a calibration using at least two reference materials with different isotopic compositions to anchor the isotopic scale and compensate for differences in machine slope. Ideally, the S values of these reference materials should bracket the isotopic range of samples with unknown S values. While the practice of analyzing two isotopically distinct reference materials is common for water (VSMOW-SLAP) and carbonates (NBS 19 and L-SVEC), the lack of widely available organic reference materials with distinct isotopic composition has hindered the practice when analyzing organic materials by elemental analysis/isotope ratio mass spectrometry (EA-IRMS). At present only L-glutamic acids USGS40 and USGS41 satisfy these requirements for ??13C and ??13N, with the limitation that L-glutamic acid is not suitable for analysis by gas chromatography (GC). We describe the development and quality testing of (i) four nicotine laboratory reference materials for on-line (i.e. continuous flow) hydrogen reductive gas chromatography-isotope ratio mass-spectrometry (GC-IRMS), (ii) five nicotines for oxidative C, N gas chromatography-combustion-isotope ratio mass-spectrometry (GC-C-IRMS, or GC-IRMS), and (iii) also three acetanilide and three urea reference materials for on-line oxidative EA-IRMS for C and N. Isotopic off-line calibration against international stable isotope measurement standards at Indiana University adhered to the 'principle of identical treatment'. The new reference materials cover the following isotopic ranges: ??2Hnicotine -162 to -45%o, ??13Cnicotine -30.05 to +7.72%, ?? 15Nnicotine -6.03 to +33.62%; ??15N acetanilide +1-18 to +40.57%; ??13Curea -34.13 to +11.71%, ??15Nurea +0.26 to +40.61% (recommended ?? values refer to calibration with NBS 19, L-SVEC, IAEA-N-1, and IAEA-N-2). Nicotines fill a gap as the first organic nitrogen stable isotope reference materials for GC-IRMS that are available with different ??13N

  7. What can Δ 15N and Δ 18O isotopes tell us about sources, transport, and fate of nitrate in the Mississippi River Basin?

    NASA Astrophysics Data System (ADS)

    Battaglin, W. A.

    2003-12-01

    Water and nutrients, primarily nitrate (NO3) in Mississippi River discharge, affect the size and severity of the Gulf of Mexico hypoxic (depleted dissolved oxygen) zone. Approximately 120 water samples were collected from 16 sites on small streams and 6 sites on large rivers within the Mississippi River Basin in 1997-98 to see if NO3 sources and transformations can be identified using the stable isotopic ratios Δ 15N and Δ 18O. Results from Lagrangian sampling at the large river sites indicate that nitrate mass decreases slightly, while Δ 15N and Δ 18O isotope ratios are unchanged in the 1500 river kilometers between the Upper Mississippi-Ohio River confluence and the Gulf of Mexico. Results also show that Δ 15N and Δ 18O values from small streams draining lands dominated by row crops or livestock tended to be distinct from those dominated by urban or undeveloped land. Mean Δ 15N values at the 16 sites on small streams were most strongly correlated (Pearson's r) with manure production rate (0.64), percent residential land use (-0.45), and urea use rate (0.43). The best multiple linear regression (MLR) model for mean Δ 15N values (r2=0.69) used manure production rate and ammonium nitrate use rate as explanatory variables. Mean Δ 18O values were most strongly correlated with percent wetlands (0.72), mean NO3 concentration (-0.71), and percent residential land use (0.58). The best MLR model for mean Δ 18O values (r2=0.85) used percent residential land use, percent wetlands, and ammonium nitrate use rate as explanatory variables. Mean NO3 concentrations were most strongly correlated with percent row-crops land use (0.84), nitrogen-fertilizer use rate (0.74), and hog-manure production rate (0.66). The best MLR model for mean NO3 concentration (r2=0.85) used percent row-crops land use and percent grain-crops land use as explanatory variables. MLR equations developed from the 16 smaller streams were used to predict mean Δ 15N and Δ 18O values and NO3

  8. Nitrogen isotope exchange between NO and NO2 and its implications for δ15N variations in tropospheric NOx and atmospheric nitrate

    NASA Astrophysics Data System (ADS)

    Walters, Wendell W.; Simonini, Damian S.; Michalski, Greg

    2016-01-01

    The nitrogen (N) isotope exchange between nitric oxide (NO) and nitrogen dioxide (NO2) has been previously suggested to influence N stable isotope compositions (δ15N) of these molecules. However, there is disagreement in the magnitude of the N isotopic fractionation (αNO2>/NO) resulting from this exchange process between previous experimental and theoretical studies. To this end, we measured αNO2>/NO associated with this exchange reaction at various temperatures. Our results indicate αNO2>/NO to be 1.0403 ± 0.0015, 1.0356 ± 0.0015, and 1.0336 ± 0.0014 at 278 K, 297 K, and 310 K, respectively. These measured values are within experimental error of the values we calculated using a modified version of the Bigeleisen-Mayer equation corrected for accurate zero-point energies, indicating an agreement between experiment and theory. Modeling of this exchange reaction demonstrates that δ15N-NO2 may exhibit a diurnal and seasonal profile if N isotopic equilibrium is achieved.

  9. Trophic ecology of the supralittoral rocky shore (Roscoff, France): A dual stable isotope (δ 13C, δ 15N) and experimental approach

    NASA Astrophysics Data System (ADS)

    Laurand, Sandrine; Riera, Pascal

    2006-07-01

    The present study investigates the trophic transfers on the upper littoral rocky shore (i.e. the supralittoral zone together with the upper midlittoral and adlittoral) of northern Brittany. The population mainly consists of four invertebrate species: the littorinids Littorina saxatilis and Melarhaphe neritoides, the isopod Ligia oceanica and the insect Petrobius maritimus. The utilisation of food sources available to these grazers was examined in a laboratory microcosm feeding experiment and a field study using stable isotopes (δ 13C, δ 15N). The results indicated that although Ligia oceanica preferentially occurs in the supralittoral zone, its trophic subsidies originate mostly from the adlittoral and lower intertidal zones. The stable isotope data also suggested that adlittoral terrestrial organic material may be the major food source of Petrobius maritimus. δ 15N of Littorina saxatilis indicated a highly variable diet consisting of supralittoral lichens, midlittoral macroalgae and other food sources (e.g. microalgae). Both feeding experiments and stable isotope data show that only Melarhaphe neritoides has a clearly identifiable diet based on a mixture of lichens, mostly Verrucaria maura and Caloplaca marina, as estimated by an isotopic mixing model. Hence, the food web of this intertidal zone appears largely based on trophic subsidies from other habitats (i.e. upper and lower intertidal zones).

  10. Tracing the Cycling and Fate of the Explosive 2,4,6-Trinitrotoluene in Coastal Marine Systems with a Stable Isotopic Tracer, (15)N-[TNT].

    PubMed

    Smith, Richard W; Vlahos, Penny; Böhlke, J K; Ariyarathna, Thivanka; Ballentine, Mark; Cooper, Christopher; Fallis, Stephen; Groshens, Thomas J; Tobias, Craig

    2015-10-20

    2,4,6-Trinitrotoluene (TNT) has been used as a military explosive for over a hundred years. Contamination concerns have arisen as a result of manufacturing and use on a large scale; however, despite decades of work addressing TNT contamination in the environment, its fate in marine ecosystems is not fully resolved. Here we examine the cycling and fate of TNT in the coastal marine systems by spiking a marine mesocosm containing seawater, sediments, and macrobiota with isotopically labeled TNT ((15)N-[TNT]), simultaneously monitoring removal, transformation, mineralization, sorption, and biological uptake over a period of 16 days. TNT degradation was rapid, and we observed accumulation of reduced transformation products dissolved in the water column and in pore waters, sorbed to sediments and suspended particulate matter (SPM), and in the tissues of macrobiota. Bulk δ(15)N analysis of sediments, SPM, and tissues revealed large quantities of (15)N beyond that accounted for in identifiable derivatives. TNT-derived N was also found in the dissolved inorganic N (DIN) pool. Using multivariate statistical analysis and a (15)N mass balance approach, we identify the major transformation pathways of TNT, including the deamination of reduced TNT derivatives, potentially promoted by sorption to SPM and oxic surface sediments. PMID:26375037

  11. Dual element ((15)N/(14)N, (13)C/(12)C) isotope analysis of glyphosate and AMPA by derivatization-gas chromatography isotope ratio mass spectrometry (GC/IRMS) combined with LC/IRMS.

    PubMed

    Mogusu, Emmanuel O; Wolbert, J Benjamin; Kujawinski, Dorothea M; Jochmann, Maik A; Elsner, Martin

    2015-07-01

    To assess sources and degradation of the herbicide glyphosate [N-(phosphonomethyl) glycine] and its metabolite AMPA (aminomethylphosphonic acid), concentration measurements are often inconclusive and even (13)C/(12)C analysis alone may give limited information. To advance isotope ratio analysis of an additional element, we present compound-specific (15)N/(14)N analysis of glyphosate and AMPA by a two step derivatization in combination with gas chromatography/isotope ratio mass spectrometry (GC/IRMS). The N-H group was derivatized with isopropyl chloroformate (iso-PCF), and remaining acidic groups were subsequently methylated with trimethylsilyldiazomethane (TMSD). Iso-PCF treatment at pH <10 gave too low (15)N/(14)N ratios indicating an incomplete derivatization; in contrast, too high (15)N/(14)N ratios at pH >10 indicated decomposition of the derivative. At pH 10, and with an excess of iso-PCF by 10-24, greatest yields and accurate (15)N/(14)N ratios were obtained (deviation from elemental analyzer-IRMS: -0.2 ± 0.9% for glyphosate; -0.4 ± 0.7% for AMPA). Limits for accurate δ(15)N analysis of glyphosate and AMPA were 150 and 250 ng injected, respectively. A combination of δ(15)N and δ(13)C analysis by liquid chromatography/isotope ratio mass spectrometry (LC/IRMS) (1) enabled an improved distinction of commercial glyphosate products and (2) showed that glyphosate isotope values during degradation by MnO2 clearly fell outside the commercial product range. This highlights the potential of combined carbon and nitrogen isotopes analysis to trace sources and degradation of glyphosate. PMID:25967147

  12. Benthic macroinvertebrates and the use of stable isotopes (δ13C and δ15N) in the impact assessment of peatland use on boreal stream ecosystems

    NASA Astrophysics Data System (ADS)

    Nieminen, Mika L.; Daza Secco, Emmanuela; Nykänen, Hannu; Meissner, Kristian

    2013-04-01

    Stable isotope analysis (SIA) can provide insights into carbon flow dynamics and trophic positions of consumers in food webs. SIA is used in this study, where we assess the possible changes in the basal resources of Finnish boreal stream ecosystems and differences in the impact of two forms of peatland use, forestry and peat mining. About 30% of the total land area of Finland is classified as peatland, of which about 55% has been drained for forestry and about 0.6% is in peat production. Unlike forestry, peat production is regionally less scattered and can thus have measurable local impacts although the total area of peat production is small. Three watersheds were used as study areas. Within each watershed, one stream drains a subcatchment affected only by peat mining, whereas the other stream flows through a subcatchment affected by forestry. The two subcatchment streams merge to form a single stream flowing into a lake. Studied watersheds were subject to no other forms of land use. In addition to the impacted sites, we used two pristine natural mire and two natural forest catchments as controls. We analysed the stable isotopes of carbon (δ13C) and nitrogen (δ15N) from benthic macroinvertebrates, stream bank soil, stream sediment, and dissolved organic carbon (DOC) in stream water. Samples for stable isotope analyses were collected in the summer of 2011 and samples for invertebrate community analyses in the autumn of 2011. Upon sampling we measured several physical parameters at each sampling site. In addition, stream water samples collected in summer and autumn 2012 were analysed for CH4 and CO2 gas concentrations and autumn gas samples also for their δ13C values. Our initial SIA results of invertebrates suggest some degree of discrimination between different sources of OM and possible effects on feeding habits, presumably due to the quality of the basal resources. We will explore this result further by examining not only taxonomical structure, but also the

  13. Complete Measurement of Stable Isotopes in N2O (δ15N, δ15Nα, δ15Nβ, δ18O, δ17O) Using Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS)

    NASA Astrophysics Data System (ADS)

    Leen, J. B.; Gupta, M.

    2014-12-01

    Nitrate contamination in water is a worldwide environmental problem and source apportionment is critical to managing nitrate pollution. Fractionation caused by physical, chemical and biological processes alters the isotope ratios of nitrates (15N/14N, 18O/16O and 17O/16O) and biochemical nitrification and denitrification impart different intramolecular site preference (15N14NO vs. 14N15NO). Additionally, atmospheric nitrate is anomalously enriched in 17O compared to other nitrate sources. The anomaly (Δ17O) is conserved during fractionation processes, providing a tracer of atmospheric nitrate. All of these effects can be used to apportion nitrate in soil. Current technology for measuring nitrate isotopes is complicated and costly - it involves conversion of nitrate to nitrous oxide (N2O), purification, preconcentration and measurement by isotope ratio mass spectrometer (IRMS). Site specific measurements require a custom IRMS. There is a pressing need to make this measurement simpler and more accessible. Los Gatos Research has developed a next generation mid-infrared Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) analyzer to quantify all stable isotope ratios of N2O (δ15N, δ15Nα, δ15Nβ, δ18O, δ17O). We present the latest performance data demonstrating the precision and accuracy of the OA-ICOS based measurement. At an N2O concentration of 322 ppb, the analyzer quantifies [N2O], δ15N, δ15Na, δ15Nb, and δ18O with a precision of ±0.05 ppb, ±0.4 ‰, ±0.45 ‰, and ±0.6 ‰, and ±0.8 ‰ respectively (1σ, 100s; 1σ, 1000s for δ18O). Measurements of gas standards demonstrate accuracy better than ±1 ‰ for isotope ratios over a wide dynamic range (200 - 100,000 ppb). The measurement of δ17O requires a higher concentration (1 - 50 ppm), easily obtainable through conversion of nitrates in water. For 10 ppm of N2O, the instrument achieves a δ17O precision of ±0.05 ‰ (1σ, 1000s). This performance is sufficient to quantify atmospheric

  14. The Effect of N Fertilizer Placement on the Fate of Urea-15N and Yield of Winter Wheat in Southeast China

    PubMed Central

    Chen, Zhaoming; Wang, Huoyan; Liu, Xiaowei; Liu, Yongzhe; Gao, Shuaishuai; Zhou, Jianmin

    2016-01-01

    A field micro-plot experiment using nitrogen isotope (15N) labeling was conducted to determine the effects of placement methods (broadcast and band) and N rates (60, 150 and 240 kg ha–1) on the fate of urea-15N in the wheat–soil system in Guangde County of Anhui Province, China. N fertilizer applied in bands increased grain yield by 15% compared with broadcast application. The N fertilizer application rate had a significant effect on grain yield, straw yield and aboveground biomass, as well as on N uptake and N concentration of wheat. The recovery of urea-15N was a little higher for broadcast (34.0–39.0%) than for band treatment (31.2–38.2%). Most of the soil residual N was retained in the 0–20 cm soil layer. At the N rates of 60 and 240 kg ha–1, the residual 15N was higher for band (34.4 and 108.7 kg ha–1, respectively) than for broadcast application (29.6 and 88.4 kg ha–1, respectively). Compared with broadcast treatment, banded placement of N fertilizer decreased the N loss in the wheat–soil system. Band application one time is an alternative N management practice for winter wheat in this region. PMID:27082246

  15. Isotopic fractionation of nitrogen and carbon in Paleoarchean cherts from Pilbara craton, Western Australia: Origin of 15N-depleted nitrogen

    NASA Astrophysics Data System (ADS)

    Pinti, Daniele L.; Hashizume, Ko; Sugihara, Akiyo; Massault, Marc; Philippot, Pascal

    2009-07-01

    Nitrogen and carbon isotopic compositions, together with mineralogy and trace element geochemistry, were studied in a few kerogen-rich Paleoarchean cherts, a barite and a dolomitic stromatolite belonging to the eastern (Dixon Island Formation) and western (Dresser and Strelley Pool Chert Formations; North Pole Dome and Marble Bar) terranes of Pilbara Craton, Western Australia. The aim of the study was to search for 15N-depleted isotopic signatures, often found in kerogens of this period, and explain the origin of these anomalies. Trace elements suggest silica precipitation by hydrothermal fluids as the main process of chert formation with a contamination from volcanoclastic detritus. This is supported by the occurrence of hydrothermal-derived minerals in the studied samples indicating precipitation temperatures up to 350 °C. Only a dolomitic stromatolite from Strelley Pool shows a superchondritic Y/Ho ratio of 72 and a positive Eu/Eu * anomaly of 1.8, characteristic of chemical precipitates from the Archean seawater. The bulk δ 13C vs. δ 15N values measured in the cherts show a roughly positive co-variation, except for one sample from the North Pole (PI-85-00). The progressive enrichment in 15N and 13C from a pristine source having δ 13C ⩽ -36‰ and δ 15N ⩽ -4‰ is correlated with a progressive depletion in N content and to variations in Ba/La and Co/As ratios. These trends have been interpreted as a progressive hydrothermal alteration of the cherts by metamorphic fluids. Isotopic exchange at 350 °C between NH 4+(rock) and N 2(fluid) may explain the isotopic and elemental composition of N in the studied cherts. However, we need to assume isotopic exchange at 350 °C between carbonate C and graphite to explain the large 13C enrichment recorded. Only sample PI-85-00 shows a large N loss (90%) with a positive δ 15N value (+11‰), while C (up to 120 ppm and δ 13C -38‰) seems to be unaffected. This pattern has been interpreted as the result of

  16. Feeding and migration habits of white shark Carcharodon carcharias (Lamniformes: Lamnidae) from Isla Guadalupe inferred by analysis of stable isotopes delta15N and delta13C.

    PubMed

    Jaime-Rivera, Mario; Caraveo-Patiño, Javier; Hoyos-Padilla, Mauricio; Galván-Magaña, Felipe

    2014-06-01

    Stable isotope composition of marine top predator's tissues provides insight information of its trophic ecology and migratory behavior. Previous reports have shown that dermal tissues could record longer patterns of hunting and movement. Based on this, the aim of this study was to describe the feeding and migratory habits of the white shark from Isla Guadalupe, using stable isotopic analysis of dermis. We considered a small subset of many possible prey taxa that the sharks could have eaten throughout their migration: pinnipeds, squid and tuna. We grouped the data in five focal areas: Gulf of California, Coast of California, Isla Guadalupe, SOFA and Hawaii. We performed a Bayesian mixing model to study the trophic ecology of this top predator. Average isotopic values for dermis tissue of white shark were delta13C (-14.5 per thousand) and delta15N (19.1 per thousand). Corrected white shark dermal mean values to resemble muscle were delta13C (-16.6 per thousand) and delta15N (21.2 per thousand). Mixing model data from dermis showed predation in offshore areas such the SOFA and a main importance of pinnipeds as prey of the white shark in Isla Guadalupe. PMID:25102646

  17. Metabolic labeling with stable isotope nitrogen (15N) to follow amino acid and protein turnover of three plastid proteins in Chlamydomonas reinhardtii

    PubMed Central

    2014-01-01

    Background The length of time that a protein remains available to perform its function is significantly influenced by its turnover rate. Knowing the turnover rate of proteins involved in different processes is important to determining how long a function might progress even when the stimulus has been removed and no further synthesis of the particular proteins occurs. In this article, we describe the use of 15N-metabolic labeling coupled to GC-MS to follow the turnover of free amino acids and LC-MS/MS to identify and LC-MS to follow the turnover of specific proteins in Chlamydomonas reinhardtii. Results To achieve the metabolic labeling, the growth medium was formulated with standard Tris acetate phosphate medium (TAP) in which14NH4Cl was replaced with 15NH415NO3 and (14NH4)6Mo7O24.4H2O was replaced with Na2MoO4.2H2O. This medium designated 15N-TAP allowed CC-125 algal cells to grow normally. Mass isotopic distribution revealed successful 15N incorporation into 13 amino acids with approximately 98% labeling efficiency. Tryptic digestion of the 55 kDa SDS-PAGE bands from 14N- and 15N-labeled crude algal protein extracts followed by LC-MS/MS resulted in the identification of 27 proteins. Of these, five displayed peptide sequence confidence levels greater than 95% and protein sequence coverage greater than 25%. These proteins were the RuBisCo large subunit, ATP synthase CF1 alpha and beta subunits, the mitochondrial protein (F1F0 ATP synthase) and the cytosolic protein (S-adenosyl homocysteine hydroxylase). These proteins were present in both labeled and unlabeled samples. Once the newly synthesized 15N-labeled free amino acids and proteins obtained maximum incorporation of the 15N-label, turnover rates were determined after transfer of cells into 14N-TAP medium. The t½ values were determined for the three plastid proteins (RuBisCo, ATP synthase CF1 alpha and beta) by following the reduction of the 15N-fractional abundance over time. Conclusion We describe a more

  18. Multi-Isotope Secondary Ion Mass Spectrometry Combining Heavy Water 2H with 15N Labeling As Complementary Tracers for Metabolic Heterogeneity at the Single-Cell Level

    NASA Astrophysics Data System (ADS)

    Kopf, S.; McGlynn, S.; Cowley, E.; Green, A.; Newman, D. K.; Orphan, V. J.

    2014-12-01

    Metabolic rates of microbial communities constitute a key physiological parameter for understanding the in situ growth constraints for life in any environment. Isotope labeling techniques provide a powerful approach for measuring such biological activity, due to the use of isotopically enriched substrate tracers whose incorporation into biological materials can be detected with high sensitivity by isotope-ratio mass spectrometry. Nano-meter scale secondary ion mass spectrometry (NanoSIMS) combined with stable isotope labeling provides a unique tool for studying the spatiometabolic activity of microbial populations at the single cell level in order to assess both community structure and population diversity. However, assessing the distribution and range of microbial activity in complex environmental systems with slow-growing organisms, diverse carbon and nitrogen sources, or heterotrophic subpopulations poses a tremendous technical challenge because the introduction of isotopically labeled substrates frequently changes the nutrient availability and can inflate or bias measures of activity. Here, we present the use of hydrogen isotope labeling with deuterated water as an important new addition to the isotopic toolkit and apply it for the determination of single cell microbial activities by NanoSIMS imaging. This tool provides a labeling technique that minimally alters any aquatic chemical environment, can be administered with strong labels even in minimal addition (natural background is very low), is an equally universal substrate for all forms of life even in complex, carbon and nitrogen saturated systems, and can be combined with other isotopic tracers. The combination of heavy water labeling with the most commonly used NanoSIMS tracer, 15N, is technically challenging but opens up a powerful new set of multi-tracer experiments for the study of microbial activity in complex communities. We present the first truly simultaneous single cell triple isotope system

  19. A new strategy for sequential assignment of intrinsically unstructured proteins based on 15N single isotope labelling

    NASA Astrophysics Data System (ADS)

    Lopez, Juan; Ahuja, Puneet; Gerard, Melanie; Wieruszeski, Jean-Michel; Lippens, Guy

    2013-11-01

    We describe a new efficient strategy for the sequential assignment of amide resonances of a conventional 15N-1H HSQC spectrum of intrinsically unfolded proteins, based on composite NOESY-TOCSY and TOCSY-NOESY mixing times. These composite mixing times lead to a Hα-proton mediated unidirectional transfer of amide to amide proton. We have implemented the composite mixing times in an HSQC-NOESY-HSQC manner to obtain directional connectivity between amides of neighbouring residues. We experimentally determine the optimal mixing times for both transfer schemes, and demonstrate its use in the assignment for both a fragment of the neuronal tau protein and for α-synuclein.

  20. Effects of climate on deer bone δ15N and δ13C: Lack of precipitation effects on δ15N for animals consuming low amounts of C 4 plants

    NASA Astrophysics Data System (ADS)

    Cormie, A. B.; Schwarcz, H. P.

    1996-11-01

    We have examined the relationship of bone collagen δ15N and δ13C to climatic variables, humidity, temperature, and amount of precipitation using fifty-nine specimens of North American white-tailed deer ( Odocoileus virginianus) from forty-six different locations. In previous studies of African mammals there was a significant correlation between bone collagen δ15N and local amount of precipitation. Results presented here similarly show an increase in δ15N with decreasing amount of precipitation but only for 25% of the animals, namely those consuming more than 10% C 4 plants. These animals also exhibited a significant correlation between δ13C and temperature which mirrors previous observations for grasses suggesting that these deer consume grasses during times of population and nutrient stress. In contrast, even in dry areas containing high proportions of C 4 grasses, the majority of the deer had consumed low amounts of C 4 plants and these deer did not have δ15N which correlate with amount of precipitation. Only when deer deviated from their normal feeding pattern by consuming C 4 plants or grasses did their δ15N correlate with amount of rainfall. For these animals, consumption of C 4 plants or grasses may signal conditions of water and nutrient stress. An increase in δ15N of bone collagen may result from combined effects from excretion of concentrated urine (to conserve water) and increased internal recycling of nitrogen (to conserve nitrogen).

  1. Plan of study to determine if the isotopic ratios [delta]15 N and [delta]18 O can reveal the sources of nitrate discharged by the Mississippi River into the Gulf of Mexico

    USGS Publications Warehouse

    Battaglin, William A.; Kendall, Carol; Goolsby, Donald A.; Boyer, Laurie L.

    1997-01-01

    Nitrate and other nutrients discharged from the Mississippi River basin are suspected of causing a zone of depleted dissolved oxygen (hypoxic zone) in the Gulf of Mexico each summer. The hypoxic zone may have an adverse effect on aquatic life and commercial fisheries. Commercial fertilizers are the dominant source of nitrogen input to the Mississippi basin. Other nitrogen sources include animal waste, fixation of atmospheric nitrogen by legumes, precipitation, domestic and industrial effluent, and the soil. The inputs of nitrogen from most of these sources to the Mississippi basin can be estimated and the outputs in surface water can be measured. However, nitrogen from each source is affected differently by physical, chemical, and biological processes that control nitrogen cycling in terrestrial and aquatic systems. Hence, the relative contributions from the various sources of nitrogen to nitrate load in the Mississippi River are unknown because the different sources may not contribute proportionally to their inputs in the basin. It may be possible to determine the relative contributions of the major sources of nitrate in river water using the stable isotopic ratios d15N and d18O of the nitrate ion. A few researchers have used the d15N and/or d18O isotope ratios to determine sources of nitrate in ground water, headwater catchments, and small rivers, but little is known about the isotopic composition of nitrate in larger rivers. The objective of this study is to measure the isotopic composition of nitrate and suspended organic matter in the Mississippi River and its major tributaries, in discharge to the Gulf of Mexico, and in streamflow from smaller watersheds that have distinct sources of nitrogen (row crops, animal wastes, and urban effluents) or are minimally impacted by man (undeveloped). Samples from seven sites on the Mississippi River and its tributaries and from 17 sites in smaller watersheds within the Mississippi River basin will be analyzed for d15N and

  2. Nitrogen isotope effects induced by anammox bacteria

    PubMed Central

    Brunner, Benjamin; Contreras, Sergio; Lehmann, Moritz F.; Matantseva, Olga; Rollog, Mark; Kalvelage, Tim; Klockgether, Gabriele; Lavik, Gaute; Jetten, Mike S. M.; Kartal, Boran; Kuypers, Marcel M. M.

    2013-01-01

    Nitrogen (N) isotope ratios (15N/14N) provide integrative constraints on the N inventory of the modern ocean. Anaerobic ammonium oxidation (anammox), which converts ammonium and nitrite to dinitrogen gas (N2) and nitrate, is an important fixed N sink in marine ecosystems. We studied the so far unknown N isotope effects of anammox in batch culture experiments. Anammox preferentially removes 14N from the ammonium pool with an isotope effect of +23.5‰ to +29.1‰, depending on factors controlling reversibility. The N isotope effects during the conversion of nitrite to N2 and nitrate are (i) inverse kinetic N isotope fractionation associated with the oxidation of nitrite to nitrate (−31.1 ± 3.9‰), (ii) normal kinetic N isotope fractionation during the reduction of nitrite to N2 (+16.0 ± 4.5‰), and (iii) an equilibrium N isotope effect between nitrate and nitrite (−60.5 ± 1.0‰), induced when anammox is exposed to environmental stress, leading to the superposition of N isotope exchange effects upon kinetic N isotope fractionation. Our findings indicate that anammox may be responsible for the unresolved large N isotope offsets between nitrate and nitrite in oceanic oxygen minimum zones. Irrespective of the extent of N isotope exchange between nitrate and nitrite, N removed from the combined nitrite and nitrate (NOx) pool is depleted in 15N relative to NOx. This net N isotope effect by anammox is superimposed on the N isotope fractionation by the co-occurring reduction of nitrate to nitrite in suboxic waters, possibly enhancing the overall N isotope effect for N loss from oxygen minimum zones. PMID:24191043

  3. Inoculation of Bacillus sphaericus UPMB-10 to Young Oil Palm and Measurement of Its Uptake of Fixed Nitrogen Using the 15N Isotope Dilution Technique

    PubMed Central

    Zakry, Fitri Abdul Aziz; Shamsuddin, Zulkifli H.; Rahim, Khairuddin Abdul; Zakaria, Zin Zawawi; Rahim, Anuar Abdul

    2012-01-01

    There are increasing applications of diazotrophic rhizobacteria in the sustainable agriculture system. A field experiment on young immature oil palm was conducted to quantify the uptake of N derived from N2 fixation by the diazotroph Bacillus sphaericus strain UPMB-10, using the 15N isotope dilution method. Eight months after 15N application, young immature oil palms that received 67% of standard N fertilizer application together with B. sphaericus inoculation had significantly lower 15N enrichment than uninoculated palms that received similar N fertilizers. The dilution of labeled N served as a marker for the occurrence of biological N2 fixation. The proportion of N uptake that was derived from the atmosphere was estimated as 63% on the whole plant basis. The inoculation process increased the N and dry matter yields of the palm leaflets and rachis significantly. Field planting of young, immature oil palm in soil inoculated with B. sphaericus UPMB-10 might mitigate inorganic fertilizer-N application through supplementation by biological nitrogen fixation. This could be a new and important source of nitrogen biofertilizer in the early phase of oil palm cultivation in the field. PMID:22446306

  4. Trace elements and stable isotopes (delta13C and delta15N) in shallow and deep-water organisms from the East China Sea.

    PubMed

    Asante, Kwadwo Ansong; Agusa, Tetsuro; Mochizuki, Hiroko; Ramu, Karri; Inoue, Suguru; Kubodera, Tsunemi; Takahashi, Shin; Subramanian, Annamalai; Tanabe, Shinsuke

    2008-12-01

    Trace elements (22) and stable isotope ratios (delta15N and delta13C) were analyzed in marine organisms from shallow (SW) and deep-water (DW) of the East China Sea to understand biomagnification and prey source of trace elements. In the benthic marine organisms from DW, delta15N values were negatively correlated with Ba, Cu, Ag, Mo, Sr, As, and Co concentrations. This may be due to the specific accumulation in lower trophic animals and/or the biodilution through the food web in DW. Relationships between delta15N and concentrations of Co, Cr, Bi, and Tl in fish and Ag, Bi, V, Hg, and Tl in crustaceans showed positive correlations, suggesting that trophic position was affecting the concentrations of those elements in phyla, with higher trophic animals retaining higher concentrations than the lower trophic animals. Positive correlations between delta13C and Rb were observed in marine organisms. Therefore, Rb may be a possible substitute of delta13C as tracer of prey source in the East China Sea although further investigation is required. PMID:18583004

  5. A New Tool for NMR Crystallography: Complete (13)C/(15)N Assignment of Organic Molecules at Natural Isotopic Abundance Using DNP-Enhanced Solid-State NMR.

    PubMed

    Märker, Katharina; Pingret, Morgane; Mouesca, Jean-Marie; Gasparutto, Didier; Hediger, Sabine; De Paëpe, Gaël

    2015-11-01

    NMR crystallography of organic molecules at natural isotopic abundance (NA) strongly relies on the comparison of assigned experimental and computed NMR chemical shifts. However, a broad applicability of this approach is often hampered by the still limited (1)H resolution and/or difficulties in assigning (13)C and (15)N resonances without the use of structure-based chemical shift calculations. As shown here, such difficulties can be overcome by (13)C-(13)C and for the first time (15)N-(13)C correlation experiments, recorded with the help of dynamic nuclear polarization. We present the complete de novo (13)C and (15)N resonance assignment at NA of a self-assembled 2'-deoxyguanosine derivative presenting two different molecules in the asymmetric crystallographic unit cell. This de novo assignment method is exclusively based on aforementioned correlation spectra and is an important addition to the NMR crystallography approach, rendering firstly (1)H assignment straightforward, and being secondly a prerequisite for distance measurements with solid-state NMR. PMID:26485326

  6. Identifying the African Wintering Grounds of Hybrid Flycatchers Using a Multi–Isotope (δ2H, δ13C, δ15N) Assignment Approach

    PubMed Central

    Van Wilgenburg, Steven L.; Hobson, Keith A.; Folmer, Eelke; Font, Laura; Klaassen, Marcel

    2014-01-01

    Migratory routes and wintering grounds can have important fitness consequences, which can lead to divergent selection on populations or taxa differing in their migratory itinerary. Collared (Ficedula albicollis) and pied (F. hypoleuca) flycatchers breeding in Europe and wintering in different sub-Saharan regions have distinct migratory routes on the eastern and western sides of the Sahara desert, respectively. In an earlier paper, we showed that hybrids of the two species did not incur reduced winter survival, which would be expected if their migration strategy had been a mix of the parent species' strategies potentially resulting in an intermediate route crossing the Sahara desert to different wintering grounds. Previously, we compared isotope ratios and found no significant difference in stable-nitrogen isotope ratios (δ15N) in winter-grown feathers between the parental species and hybrids, but stable-carbon isotope ratios (δ13C) in hybrids significantly clustered only with those of pied flycatchers. We followed up on these findings and additionally analyzed the same feathers for stable-hydrogen isotope ratios (δ2H) and conducted spatially explicit multi-isotope assignment analyses. The assignment results overlapped with presumed wintering ranges of the two species, highlighting the efficacy of the method. In contrast to earlier findings, hybrids clustered with both parental species, though most strongly with pied flycatcher. PMID:24847717

  7. Qualitative study of substituent effects on NMR (15)N and (17)O chemical shifts.

    PubMed

    Contreras, Rubén H; Llorente, Tomás; Pagola, Gabriel I; Bustamante, Manuel G; Pasqualini, Enrique E; Melo, Juan I; Tormena, Cláudio F

    2009-09-10

    A qualitative approach to analyze the electronic origin of substituent effects on the paramagnetic part of chemical shifts is described and applied to few model systems, where its potentiality can be appreciated. The formulation of this approach is based on the following grounds. The influence of different inter- or intramolecular interactions on a second-order property can be qualitatively predicted if it can be known how they affect the main virtual excitations entering into that second-order property. A set of consistent approximations are introduced in order to analyze the behavior of occupied and virtual orbitals that define some experimental trends of magnetic shielding constants. This approach is applied first to study the electronic origin of methyl-beta substituent effects on both (15)N and (17)O chemical shifts, and afterward it is applied to a couple of examples of long-range substituent effects originated in charge transfer interactions such as the conjugative effect in aromatic compounds and sigma-hyperconjugative interactions in saturated multicyclic compounds. PMID:19685922

  8. Qualitative Study of Substituent Effects on NMR 15N and 17O Chemical Shifts

    NASA Astrophysics Data System (ADS)

    Contreras, Rubén H.; Llorente, Tomás; Pagola, Gabriel I.; Bustamante, Manuel G.; Pasqualini, Enrique E.; Melo, Juan I.; Tormena, Cláudio F.

    2009-08-01

    A qualitative approach to analyze the electronic origin of substituent effects on the paramagnetic part of chemical shifts is described and applied to few model systems, where its potentiality can be appreciated. The formulation of this approach is based on the following grounds. The influence of different inter- or intramolecular interactions on a second-order property can be qualitatively predicted if it can be known how they affect the main virtual excitations entering into that second-order property. A set of consistent approximations are introduced in order to analyze the behavior of occupied and virtual orbitals that define some experimental trends of magnetic shielding constants. This approach is applied first to study the electronic origin of methyl-β substituent effects on both 15N and 17O chemical shifts, and afterward it is applied to a couple of examples of long-range substituent effects originated in charge transfer interactions such as the conjugative effect in aromatic compounds and σ-hyperconjugative interactions in saturated multicyclic compounds.

  9. Biogeochemical Indicators in High- and Low-Arctic Marine and Terrestrial Avian Community Changes: Comparative Isotopic (13C, 15N, and 34S) Studies in Alaska and Greenland

    NASA Astrophysics Data System (ADS)

    Causey, D.; Bargmann, N. A.; Burnham, K. K.; Burnham, J. L.; Padula, V. M.; Johnson, J. A.; Welker, J. M.

    2011-12-01

    Understanding the complex dynamics of environmental change in northern latitudes is of paramount importance today, given documented rapid shifts in sea ice, plant phenology, temperatures, deglaciation, and habitat fidelity. This knowledge is particularly critical for Arctic avian communities, which are integral components by which biological teleconnections are maintained between the mid and northern latitudes. Furthermore, Arctic birds are fundamental to Native subsistence lifestyles and a focus for conservation activities. Avian communities of marine and terrestrial Arctic environments represent a broad spectrum of trophic levels, from herbivores (eg., geese Chen spp.), planktivores (eg., auklets Aethia spp.), and insectivores (eg., passerines: Wheatears Oenanthe spp., Longspurs Calcarius spp.), to predators of marine invertebrates (eg., eiders Somateria spp.), nearshore and offshore fish (eg., cormorants Phalacrocorax spp, puffins Fratercula spp.), even other bird species (eg., gulls Larus spp., falcons Peregrinus spp.). This diversity of trophic interconnections is an integral factor in the dynamics of Arctic ecosystem ecology, and they are key indicators for the strength and trajectories of change. We are especially interested in their feeding ecology, using stable isotope-diet relations to examine historical diets and to predict future feeding ecology by this range of species. Since 2009, we have been studying the foodweb ecology using stable isotopes (δ13C, δ15N, δ34S) of contemporaneous coastal and marine bird communities in High Arctic (Northwest Greenland) and Low Arctic (western Aleutian Islands, AK). We are quantifying the isotopic values of blood, organ tissues, and feathers, and have carried out comparisons between native and lipid-extracted samples. Although geographically distant, these communities comprise similar taxonomic and ecological congeners, including several species common to both (eg., Common Eider, Black-legged Kittiwake, Northern

  10. Stable Isotope (δ13C, δ15N, δ34S) Analysis and Satellite Telemetry Depict the Complexity of Gray Wolf (Canis lupus) Diets in Southwest Alaska

    NASA Astrophysics Data System (ADS)

    Stanek, A.; Watts, D. E.; Cohn, B. R.; Spencer, P.; Mangipane, B.; Welker, J. M.

    2010-12-01

    Throughout Alaska, gray wolves (Canis lupus) are a top predator of large ungulates. While they primarily rely on ungulates such as moose (Alces alces) and caribou (Rangifer tarandus) as food, they are opportunistic and use alternative resources. The variation and supplemental protein sources in wolf diet has not been studied extensively on live animals currently using the landscape. With large seasonal influxes of Pacific salmon (Oncorhynchus sp.) into Alaska, terrestrial carnivore use of marine species is of particular interest. Using stable isotope (δ13C, δ15N, δ34S) analysis of wolf guard hair and blood, this study aims to determine the proportion of marine derived nutrients (MDN) in the diet of wolf packs within and surrounding Lake Clark National Park and Preserve and Alaska Peninsula and Becharof National Wildlife Refuges in Southwest Alaska. Satellite telemetry from the animals sampled facilitates quantification of landscape use patterns in correspondence with isotopic traits. Wolf pack territories within and surrounding the Lake Clark region appear to vary in spatial extent and in availability of MDN, such as salmon. Initial analysis shows that two packs with smaller home ranges, centrally located around areas with greater salmon availability, have enriched δ15N values compared to packs that have larger home ranges not centralized around salmon spawning waters. This pattern of isotopic enrichment is found in red blood cells, blood serum and hair, representing diets over different time scales. The enrichment in both blood and hair indicates a sustained use of MDN over the previous six to nine months. In the Lake Clark region, simple mixing model estimates suggest that up to 30% of wolf pack diets may be from marine sources. In contrast, packs with larger home ranges and less access to salmon have stable isotope values representative of a terrestrial diet.

  11. Importance of bacterivory and preferential selection toward diatoms in larvae of Crepidula fornicata (L.) assessed by a dual stable isotope (13C, 15N) labeling approach

    NASA Astrophysics Data System (ADS)

    Leroy, Fanny; Riera, Pascal; Jeanthon, Christian; Edmond, Frédérique; Leroux, Cédric; Comtet, Thierry

    2012-05-01

    In Europe, the gastropod Crepidula fornicata is an invasive species characterized by a long reproductive period (from February to November). Thus, its larvae are exposed to variations in available food sources (in terms of quantity and quality). We aimed to investigate if bacteria could contribute to larval food both in presence or absence of phytoplankton, and to compare these results to seasonal variations of bacteria and phytoplankton abundances at a coastal site in the English Channel. First, ingestion of fluorescent beads of 0.5 to 2 μm diameter, showed that larvae were able to ingest particles of typical bacterial size. Then we used a dual stable isotope labeling approach which consisted in labeling a bacterial pelagic community with 15N and a diatom (Chaetoceros gracilis) culture with 13C, and supplying larvae with 15N-labeled bacteria, 13C-labeled diatoms, and both labeled sources. This technique has, to our knowledge, never been applied to invertebrate larvae. After 24 h of experiment, larvae were significantly enriched in all treatments: + 21.5‰ (∆δ13C) when supplied with diatoms, + 1364‰ (∆δ15N) when supplied with bacteria, and + 24‰ (∆δ13C) and + 135‰ (∆δ15N) when supplied with the two mixed sources. These results indicated that bacteria can contribute to the larval nutrition in C. fornicata, even in the presence of phytoplankton. Our results however suggested that larvae of C. fornicata preferentially used diatoms and showed that the supply of free bacteria did not alter the uptake of diatoms. Considering the seasonal variations of bacteria and phytoplankton abundances at the study site, these results suggested that bacteria may constitute a complementary resource for the larvae of C. fornicata when phytoplankton is abundant and may become a substitute resource when phytoplankton is less available. This approach offers promising perspectives to trace food sources and assess nitrogen and carbon fluxes between planktotrophic larvae

  12. Pan-Arctic concentrations of mercury and stable isotope ratios of carbon (δ(13)C) and nitrogen (δ(15)N) in marine zooplankton.

    PubMed

    Pomerleau, Corinne; Stern, Gary A; Pućko, Monika; Foster, Karen L; Macdonald, Robie W; Fortier, Louis

    2016-05-01

    Zooplankton play a central role in marine food webs, dictating the quantity and quality of energy available to upper trophic levels. They act as "keystone" species in transfer of mercury (Hg) up through the marine food chain. Here, we present the first Pan-Arctic overview of total and monomethylmercury concentrations (THg and MMHg) and stable isotope ratios of carbon (δ(13)C) and nitrogen (δ(15)N) in selected zooplankton species by assembling data collected between 1998 and 2012 from six arctic regions (Laptev Sea, Chukchi Sea, southeastern Beaufort Sea, Canadian Arctic Archipelago, Hudson Bay and northern Baffin Bay). MMHg concentrations in Calanus spp., Themisto spp. and Paraeuchaeta spp. were found to increase with higher δ(15)N and lower δ(13)C. The southern Beaufort Sea exhibited both the highest THg and MMHg concentrations. Biomagnification of MMHg between Calanus spp. and two of its known predators, Themisto spp. and Paraeuchaeta spp., was greatest in the southern Beaufort Sea. Our results show large geographical variations in Hg concentrations and isotopic signatures for individual species related to regional ecosystem features, such as varying water masses and freshwater inputs, and highlight the increased exposure to Hg in the marine food chain of the southern Beaufort Sea. PMID:26874765

  13. Fermentation and Cost-Effective 13C/15N Labeling of the Nonribosomal Peptide Gramicidin S for Nuclear Magnetic Resonance Structure Analysis.

    PubMed

    Berditsch, Marina; Afonin, Sergii; Steineker, Anna; Orel, Nataliia; Jakovkin, Igor; Weber, Christian; Ulrich, Anne S

    2015-06-01

    Gramicidin S (GS) is a nonribosomally synthesized decapeptide from Aneurinibacillus migulanus. Its pronounced antibiotic activity is attributed to amphiphilic structure and enables GS interaction with bacterial membranes. Despite its medical use for over 70 years, the peptide-lipid interactions of GS and its molecular mechanism of action are still not fully understood. Therefore, a comprehensive structural analysis of isotope-labeled GS needs to be performed in its biologically relevant membrane-bound state, using advanced solid-state nuclear magnetic resonance (NMR) spectroscopy. Here, we describe an efficient method for producing the uniformly (13)C/(15)N-labeled peptide in a minimal medium supplemented by selected amino acids. As GS is an intracellular product of A. migulanus, we characterized the producer strain DSM 5759 (rough-convex phenotype) and examined its biosynthetic activity in terms of absolute and biomass-dependent peptide accumulation. We found that the addition of either arginine or ornithine increases the yield only at very high supplementing concentrations (1% and 0.4%, respectively) of these expensive (13)C/(15)N-labeled amino acids. The most cost-effective production of (13)C/(15)N-GS, giving up to 90 mg per gram of dry cell weight, was achieved in a minimal medium containing 1% (13)C-glycerol and 0.5% (15)N-ammonium sulfate, supplemented with only 0.025% of (13)C/(15)N-phenylalanine. The 100% efficiency of labeling is corroborated by mass spectrometry and preliminary solid-state NMR structure analysis of the labeled peptide in the membrane-bound state. PMID:25795666

  14. Fermentation and Cost-Effective 13C/15N Labeling of the Nonribosomal Peptide Gramicidin S for Nuclear Magnetic Resonance Structure Analysis

    PubMed Central

    Berditsch, Marina; Afonin, Sergii; Steineker, Anna; Orel, Nataliia; Jakovkin, Igor; Weber, Christian

    2015-01-01

    Gramicidin S (GS) is a nonribosomally synthesized decapeptide from Aneurinibacillus migulanus. Its pronounced antibiotic activity is attributed to amphiphilic structure and enables GS interaction with bacterial membranes. Despite its medical use for over 70 years, the peptide-lipid interactions of GS and its molecular mechanism of action are still not fully understood. Therefore, a comprehensive structural analysis of isotope-labeled GS needs to be performed in its biologically relevant membrane-bound state, using advanced solid-state nuclear magnetic resonance (NMR) spectroscopy. Here, we describe an efficient method for producing the uniformly 13C/15N-labeled peptide in a minimal medium supplemented by selected amino acids. As GS is an intracellular product of A. migulanus, we characterized the producer strain DSM 5759 (rough-convex phenotype) and examined its biosynthetic activity in terms of absolute and biomass-dependent peptide accumulation. We found that the addition of either arginine or ornithine increases the yield only at very high supplementing concentrations (1% and 0.4%, respectively) of these expensive 13C/15N-labeled amino acids. The most cost-effective production of 13C/15N-GS, giving up to 90 mg per gram of dry cell weight, was achieved in a minimal medium containing 1% 13C-glycerol and 0.5% 15N-ammonium sulfate, supplemented with only 0.025% of 13C/15N-phenylalanine. The 100% efficiency of labeling is corroborated by mass spectrometry and preliminary solid-state NMR structure analysis of the labeled peptide in the membrane-bound state. PMID:25795666

  15. 15N techniques and analytical procedures. Indo/U. S. science and technology initiative. Research report

    SciTech Connect

    Porter, L.K.; Mosier, A.R.

    1992-05-01

    (15)N technology is used to explore many agricultural research topics, including the movement of nitrates to groundwater, use of fertilizer nitrogen by plants, ways to increase nitrogen fixation, and effects of management practices on denitrification. The publication reviews (15)N procedures and methods for handling and collecting samples, introducing isotopes into plants and soils, and for performing Kjeldahl analyses, isotope dilutions, Rittenberg oxidation conversions for isotope-ration analyses, and automated Dumas isotope-ratio analyses.

  16. Upper limits to the fractionation of isotopes due to atmospheric escape: Implications for potential 14N/15N in Pluto's atmosphere

    NASA Astrophysics Data System (ADS)

    Mandt, K.; Mousis, O.

    2014-12-01

    Formation and evolution of the solar system is studied in part using stable isotope ratios that are presumed to be primordial, or representative of conditions in the protosolar Nebula. Comets, meteorites and giant planet atmospheres provide measurements that can reasonably be presumed to represent primordial conditions while the terrestrial planets, Pluto and Saturn's moon Titan have atmospheres that have evolved over the history of the solar system. The stable isotope ratios measured in these atmospheres are, therefore, first a valuable tool for evaluating the history of atmospheric escape and once escape is constrained can provide indications of conditions of formation. D/H ratios in the atmosphere of Venus provide indications of the amount of water lost from Venus over the history of the solar system, while several isotope ratios in the atmosphere of Mars provide evidence for long-term erosion of the atmosphere. We have recently demonstrated that the nitrogen ratios, 14N/15N, in Titan's atmosphere cannot evolve significantly over the history of the solar system and that the primordial ratio for Titan must have been similar to the value recently measured for NH3 in comets. This implies that the building blocks for Titan formed in the protosolar nebula rather than in the warmer subnebula surrounding Saturn at the end of its formation. Our result strongly contrasts with works showing that 14N/15N in the atmosphere of Mars can easily fractionate from the terrestrial value to its current value due to escape processes within the lifetime of the solar system. The difference between how nitrogen fractionates in Mars and Titan's atmospheres presents a puzzle for the fractionation of isotopes in an atmosphere due to atmospheric escape. Here, we present a method aiming at determining an upper limit to the amount of fractionation allowed to occur due to escape, which is a function of the escape flux and the column density of the atmospheric constituent. Through this

  17. Chemical weathering and the role of sulfuric and nitric acids in carbonate weathering: Isotopes (13C, 15N, 34S, and 18O) and chemical constraints

    NASA Astrophysics Data System (ADS)

    Li, Cai; Ji, Hongbing

    2016-05-01

    Multiple isotopes (13C-DIC, 34S and 18O-SO42-, 15N and 18O-NO3-) and water chemistry were used to evaluate weathering rates and associated CO2 consumption by carbonic acid and strong acids (H2SO4 and HNO3) in a typical karst watershed (Wujiang River, Southwest China). The dual sulfate isotopes indicate that sulfate is mainly derived from sulfide oxidation in coal stratum and sulfide-containing minerals, and dual nitrate isotopes indicate that nitrate is mainly derived from soil N and nitrification. The correlation between isotopic compositions and water chemistry suggests that sulfuric and nitric acids, in addition to carbonic acid, are involved in carbonate weathering. The silicate and carbonate weathering rates are 7.2 t km-2 yr-1 and 76 t km-2 yr-1, respectively. In comparison with carbonate weathering rates (43 t km-2 yr-1) by carbonic acid alone, the subsequent increase in rates indicates significant enhancement of weathering when combined with sulfuric and nitric acids. Therefore, the role of sulfuric and nitric acids in the rock weathering should be considered in the global carbon cycle.

  18. Assessing sources of nitrate contamination in the Shiraz urban aquifer (Iran) using the δ(15)N and δ(18)O dual-isotope approach.

    PubMed

    Amiri, Haleh; Zare, Mohammad; Widory, David

    2015-01-01

    Nitrate ([Formula: see text]) is one of the major threats to the quality of the drinking water taken from the Shiraz aquifer. This aquifer undergoes high anthropogenic pressures from multiple local urban (including uncontrolled sewage systems), agricultural and industrial activities, resulting in [Formula: see text] concentrations as high as 149 mg L(-1), well above the 50 mg L(-1) guideline defined by the World Health Organisation. We coupled here classical chemical and dual isotope (δ(15)N and δ(18)O of [Formula: see text]) approaches trying to characterize sources and potential processes controlling the budget of this pollutant. Chemical data indicate that nitrate in this aquifer is explained by distinct end-members: while mineral fertilizers isotopically show to have no impact, our isotope approach identifies natural soil nitrification and organic [Formula: see text] (manure and/or septic waste) as the two main contributors. Isotope data suggest that natural denitrification may occur within the aquifer, but this conclusion is not supported by the study of other chemical parameters. PMID:25941866

  19. Insights into nitrogen allocation and recycling from nitrogen elemental analysis and 15N isotope labelling in 14 genotypes of willow.

    PubMed

    Brereton, Nicholas J B; Pitre, Frederic E; Shield, Ian; Hanley, Steven J; Ray, Michael J; Murphy, Richard J; Karp, Angela

    2014-11-01

    Minimizing nitrogen (N) fertilization inputs during cultivation is essential for sustainable production of bioenergy and biofuels. The biomass crop willow (Salix spp.) is considered to have low N fertilizer requirements due to efficient recycling of nutrients during the perennial cycle. To investigate how successfully different willow genotypes assimilate and allocate N during growth, and remobilize and consequently recycle N before the onset of winter dormancy, N allocation and N remobilization (to and between different organs) were examined in 14 genotypes of a genetic family using elemental analysis and (15)N as a label. Cuttings were established in pots in April and sampled in June, August and at onset of senescence in October. Biomass yield of the trees correlated well with yields recorded in the field. Genotype-specific variation was observed for all traits measured and general trends spanning these sampling points were identified when trees were grouped by biomass yield. Nitrogen reserves in the cutting fuelled the entirety of the canopy establishment, yet earlier cessation of this dependency was linked to higher biomass yields. The stem was found to be the major N reserve by autumn, which constitutes a major source of N loss at harvest, typically every 2-3 years. These data contribute to understanding N remobilization in short rotation coppice willow and to the identification of traits that could potentially be selected for in breeding programmes to further improve the sustainability of biomass production. PMID:24186940

  20. A mantle origin for Paleoarchean peridotitic diamonds from the Panda kimberlite, Slave Craton: Evidence from 13C-, 15N- and 33,34S-stable isotope systematics

    NASA Astrophysics Data System (ADS)

    Cartigny, Pierre; Farquhar, James; Thomassot, Emilie; Harris, Jeffrey W.; Wing, Bozwell; Masterson, Andy; McKeegan, Kevin; Stachel, Thomas

    2009-11-01

    In order to address diamond formation and origin in the lithospheric mantle underlying the Central Slave Craton, we report N- and C-stable isotopic compositions and N-contents and aggregation states for 85 diamonds of known paragenesis (73 peridotitic, 8 eclogitic and 4 from lower mantle) from the Panda kimberlite (Ekati Mine, Lac de Gras Area, Canada). For 12 peridotitic and two eclogitic sulfide inclusion-bearing diamonds from this sample set, we also report multiple-sulfur isotope ratios. The 73 peridotitic diamonds have a mean δ13C-value of - 5.2‰ and range from - 6.9 to - 3.0‰, with one extreme value at - 14.1‰. The associated δ15N-values range from - 17.0 to + 8.5‰ with a mean value of - 4.0‰. N-contents range from 0 to 1280 ppm. The 8 eclogitic diamonds have δ13C-values ranging from - 11.2 to - 4.4‰ with one extreme value at - 19.4‰. Their δ15N ranges from - 2.1 to + 7.9‰ and N-contents fall between 0 and 3452 ppm. Four diamonds with an inferred lower mantle origin are all Type II (i.e. nitrogen-free) and have a narrow range of δ13C values, between - 4.5 and - 3.5‰. The δ34S of the 14 analyzed peridotitic and eclogitic sulfide inclusions ranges from - 3.5 to +5.7‰. None of them provide evidence for anomalous δ33S-values; observed variations in δ33S are from +0.19 to - 0.33‰, i.e. within the 2 sigma uncertainties of mantle sulfur ( δ33S = 0‰). At Panda, the N contents and the δ13C of sulfide-bearing peridotitic diamonds show narrower ranges than silicate-bearing peridotitic diamonds. This evidence supports the earlier suggestion established from eclogitic diamonds from the Kaapvaal that sulfide-(±silicate) bearing diamonds sample a more restricted portion of sublithospheric mantle than silicate-(no sulfide) bearing diamonds. Our findings at Panda suggest that sulfide-bearing diamonds should be considered as a specific diamond population on a global-scale. Based on our study of δ34S, Δ 33S, δ15N and δ13C, we find no

  1. Carbon (δ13C) and Nitrogen (δ15N) Stable Isotope Signatures in Bat Fur Indicate Swarming Sites Have Catchment Areas for Bats from Different Summering Areas

    PubMed Central

    Segers, Jordi L.; Broders, Hugh G.

    2015-01-01

    Migratory patterns of bats are not well understood and traditional methods to study this, like capture-mark-recapture, may not provide enough detail unless there are many records. Stable isotope profiles of many animal species have been used to make inferences about migration. Each year Myotis lucifugus and M. septentrionalis migrate from summering roosts to swarming caves and mines in the fall, but the pattern of movement between them is not well understood. In this study, fur δ13C and δ15N values of 305 M. lucifugus and 200 M. septentrionalis were analyzed to make inferences about migration patterns between summering areas and swarming sites in Nova Scotia, Canada. We expected that there would be greater variability in δ13C and δ15N among individuals at swarming sites because it was believed that these sites are used by individuals originating from many summering areas. There was extensive overlap in the standard ellipse area, corrected for small sample sizes (SEAc), of bats at swarming sites and much less overlap in SEAc among groups sampled at summering areas. Meaningful inference could not be made on M. septentrionalis because their low variation in SEAc may have been the result of sampling only 3 summering areas. However, for M. lucifugus, swarming sites had larger SEAc than summering areas and predictive discriminant analysis assigned swarming bats to multiple summering areas, supporting the contention that swarming bats are mixed aggregations of bats from several summering areas. Together, these data support the contention that swarming sites have catchment areas for bats from multiple summering areas and it is likely that the catchment areas for swarming sites overlap. These data suggest that δ13C and δ15N profiling of bat fur offer some potential to make inferences about regional migration in bats. PMID:25923696

  2. Submillimeter Observations of Titan: Global Measures of Stratospheric Temperature, CO, HCN, HC3N, and the Isotopic Ratios 12C/13C and 14N/15N

    NASA Astrophysics Data System (ADS)

    Gurwell, Mark A.

    2004-11-01

    Interferometric observations of the atmosphere of Titan were performed with the Submillimeter Array on two nights in 2004 February to investigate the global average vertical distributions of several molecular species above the tropopause. Rotational transitions of CO, isomers of HCN, and HC3N were simultaneously recorded. The abundance of CO is determined to be 51+/-4 parts per million (ppm), constant with altitude. The vertical profile of HCN is dependent on the assumed temperature but generally increases from 30 parts per billion at the condensation altitude (~83 km) to 5 ppm at ~300 km. Furthermore, the central core of the HCN emission is strong and can be reproduced only if the upper stratospheric temperature increases with altitude. The isotopic ratios are determined to be 12C/13C=132+/-25 and 14N/15N=94+/-13 assuming the Coustenis & Bézard temperature profile. If the Lellouch temperature profile is assumed, the ratios decrease to 12C/13C=108+/-20 and 14N/15N=72+/-9. The vertical profile of HC3N is consistent with that derived by Marten et al.

  3. Quantification of soy protein using the isotope method (δ(13)C and δ(15)N) for commercial brands of beef hamburger.

    PubMed

    Ducatti, Rhani; de Almeida Nogueira Pinto, José Paes; Sartori, Maria Márcia Pereira; Ducatti, Carlos

    2016-12-01

    Hamburgers (beef patties) may be adulterated through the overuse of protein extenders. Among vegetables, soy protein is the best substitute for animal protein. These ingredients help to reduce the cost of producing a final product, and they maximize profits for fraudulent industries. Moreover, the ingestion of soy or other non-meat proteins by allergic individuals may present a health risk. In addition, monitoring by supervisory bodies is hampered by a lack of appropriate analytical methodologies. Within this context, the aim of this study was to determine and quantify the levels of added soy protein by determination of (15)N and (13)C stable isotopes. A total of 100 beef hamburger samples from 10 commercial brands were analyzed. Only three samples of the G brand were within the standards set the Brazilian legislation. The remaining 97 samples from 10 commercial brands contained >4% soy protein; therefore, they are adulterated and not in compliance with the current legislation. PMID:27501234

  4. Assessment of trace elements, POPs, (210)Po and stable isotopes ((15)N and (13)C) in a rare filter-feeding shark: The megamouth.

    PubMed

    Moura, Jailson Fulgencio de; Merico, Agostino; Montone, Rosalinda Carmela; Silva, Josilene; Seixas, Tércia Guedes; Godoy, José Marcus de Oliveira; Saint'Pierre, Tatiana Dillenburg; Hauser-Davis, Rachel Ann; Di Beneditto, Ana Paula Madeira; Reis, Estéfane Cardinot; Tavares, Davi Castro; Lemos, Leila Soledade; Siciliano, Salvatore

    2015-06-15

    With less than 60 records being reported worldwide, the megamouth (Megachasma pelagios) is today one of the least known shark species inhabiting our oceans. Therefore, information concerning the biology and ecology of this enigmatic organism is very scarce and limited to feeding behaviour and preferred habitat. The present work reports new data on the concentrations of trace elements, organic mercury, POPs and (210)Po in hepatic and muscular tissues of a specimen found stranded in the southeastern coast of Brazil. Additionally, we provide new evidence based on stable isotope analysis (δ(15)N and δ(13)C) confirming the preference for the pelagic habitat and the zooplanktivorous feeding behaviour of the megamouth. These results are consistent with the low concentrations of organic pollutant compounds and other elements measured in our samples. PMID:25858662

  5. [Effect of fertilization depth on 15N-urea absorption, utilization and loss in dwarf apple trees].

    PubMed

    Ding, Ning; Chen, Qian; Xu, Hai-gang; Ji, Meng-meng; Jiang, Han; Jiang, Yuan-mao

    2015-03-01

    Five-year-old 'Fuji'3/M26/M. hupehensis Rehd. seedlings were treated by 15N tracer to study the effects of fertilization depth (0, 20 and 40 cm) on 15N-urea absorption, distribution, utilization and loss in soil. The results showed that the plant leaf area, chlorophyll content and total N of apple leaves in 20 cm treatment were obviously higher than 0 cm and 40 cm treatments. The 15N derived from fertilizer (Ndff) in different organs of apple plant under different depths were significantly different, and the Ndff was the highest in roots at the full-bloom stage, and then in perennial branches. During the shoot rapid-growing and flower bud differentiation stage, the Ndff of new organs higher than that of the storage organs, and the Ndff of different organs were high level at fruit rapid-expanding stage, and the Ndff of fruit was the highest. The distribution ratio of 15N at fruit maturity stage was significantly different under fertilization depths, and that of the vegetative and repro- ductive organs of 20 cm treatment were obviously higher than 0 cm and 40 cm treatments, but that of the storage organs of 20 cm treatment was lower than 0 cm and 40 cm treatments. At fruit maturity stage, 15N utilization rate of apple plant of 20 cm treatment was 24.0%, which was obviously higher than 0 cm (14.1%) and 40 cm (7.6%) treatments, and 15N loss rate was 54.0%, which was obviously lower than 0 cm (67.8%) and 40 cm (63.5%) treatments. With the increase of fertilization depths, the N residue in soil increased sharply. PMID:26211056

  6. Application of δ13C and δ15N isotopic signatures of organic matter fractions sequentially separated from adjacent arable and forest soils to identify carbon stabilization mechanisms

    NASA Astrophysics Data System (ADS)

    Kayler, Z. E.; Kaiser, M.; Gessler, A.; Ellerbrock, R. H.; Sommer, M.

    2011-03-01

    Identifying the chemical mechanisms behind soil carbon bound in organo-mineral complexes is necessary to determine the degree to which soil organic carbon is stabilized belowground. We used the δ13C and δ15N isotopic signatures from two organic matter (OM) fractions from soil to identify the likely binding mechanisms involved. We used OM fractions hypothesized to contain carbon stabilized through organo-mineral complexes: (1) OM separated chemically with sodium pyrophosphate (OM(PY)) and (2) OM stabilized in microstructures found in the chemical extraction residue (OM(ER)). Furthermore, because the OM fractions were separated from five different soils with paired forest and arable land use histories, we could address the impact of land use change on carbon binding and processing mechanisms within these soils. We used partial least squares regression to analyze patterns in the isotopic signature of OM with established proxies of different binding mechanisms. Parsing soil OM into different fractions is a systematic method of dissection, however, we are primarily interested in how OM is bound in soil as a whole, requiring a means of re-assembly. Thus, we implemented the recent zonal framework described by Kleber et al. (2007) to relate our findings to undisturbed soil. The δ15N signature of OM fractions served as a reliable indicator for microbial processed carbon in both arable and forest land use types. The δ13C signature of OM fractions in arable sites did not correlate well with proxies of soil mineral properties while a consistent pattern of enrichment was seen in the δ13C of OM fractions in the forest sites. We found a significant difference in δ13C of pooled OM fractions between the forest and arable land use type although it was relatively small (<1‰). We found different binding mechanisms predominate in each land use type. The isotopic signatures of OM fractions from arable soils were highly related to the clay and silt size particles amount while

  7. Interference effects in proton scattering on {sup 15}N nuclei at intermediate energies

    SciTech Connect

    Ibraeva, E. T.; Zhusupov, M.A.; Imambekov, O.; Krassovitskiy, P. M.

    2010-08-15

    The differential cross section for proton scattering on {sup 15}N nuclei is calculated within Glauber diffraction theory at energies of 0.2, 0.6, and 1.0 GeV. Use is made of the shell-model wave function for the {sup 15}N nucleus. The contribution of single and double collisions to the Glauber operator {Omega} is taken into account. The sensitivity of the differential cross sections to the contributions of scattering on nucleons from different shells, to the parameters of the elementary pN amplitude, and to the energy of projectile protons is investigated. It is shown that the interference between amplitudes corresponding to different collision multiplicities, as well as between the amplitudes for scattering on nucleons from different shells, determines special features of the cross section.

  8. Spatial variation in the strength of mutualism between a jumping spider and a terrestrial bromeliad: Evidence from the stable isotope 15N

    NASA Astrophysics Data System (ADS)

    Romero, Gustavo Q.; Vasconcellos-Neto, João; Trivelin, Paulo C. O.

    2008-05-01

    Psecas chapoda, a neotropical jumping spider strictly associated with the terrestrial bromeliad Bromelia balansae in cerrados and semi-deciduous forests in South America, effectively contributes to plant nutrition and growth. In this study, our goal was to investigate if spider density caused spatial variations in the strength of this spider-plant mutualism. We found a positive significant relationship between spider density and δ15N values for bromeliad leaves in different forest fragments. Open grassland Bromeliads were associated with spiders and had higher δ15N values compared to forest bromeliads. Although forest bromeliads had no association with spiders their total N concentrations were higher. These results suggest that bromeliad nutrition is likely more litter-based in forests and more spider-based in open grasslands. This study is one of the few to show nutrient provisioning and conditionality in a spider-plant system.

  9. A stable isotope ( δ13C, δ15N) model for the North Water food web: implications for evaluating trophodynamics and the flow of energy and contaminants

    NASA Astrophysics Data System (ADS)

    Hobson, Keith A.; Fisk, Aaron; Karnovsky, Nina; Holst, Meike; Gagnon, Jean-Marc; Fortier, Martin

    fundamentally in transferring energy and carbon flux to higher trophic-level seabirds and marine mammals. We measured PCB 153 among selected organisms to investigate the behavior of bioaccumulating contaminants within the food web. Our isotopic model confirmed the trophic magnification of PCB 153 in this high-Arctic food web due to a strong correlation between contaminant concentration and organism δ15N values, demonstrating the utility of combining isotopic and contaminant approaches to food-web studies. Stable-carbon isotope analysis confirmed an enrichment in 13C between POM and ice algae (-22.3 vs. -17.7‰). Benthic organisms were generally enriched in 13C compared to pelagic species. We discuss individual species isotopic data and the general utility of our stable isotope model for defining carbon flux and contaminant flow through the North Water food web.

  10. Use of isotope effects as a probe of enzyme reaction mechanisms

    SciTech Connect

    Weiss, P.M.K.

    1987-01-01

    The use of multiple isotope effects has been extended to include both the variation of /sup 15/N isotope effects with deuterated and unlabeled substrates, and the use of solvent isotope effects in conjunction with /sup 13/C or /sup 15/N isotope effects. The deuterium isotope effect on the inhibition constant, /sup D/K/sub i/, of a competitive inhibitor has also been used to identify an active-site catalytic base. Phenylalanine ammonia lyase has been shown to catalyze the elimination of ammonia from the slow alternate substrate dihydrophenylalanine by an E1cb mechanism with a carbanion intermediate. This conclusion resulted from comparison of /sup 15/N isotope effects with 3-dideuterated and unlabeled substrates, and a deuterium isotope effect of 2.0 from dideuteration at C-3, with the equations for concerted, carbanion and carbonium ion mechanisms. Isotope effects with phenylalanine itself were smaller, but are also consistent with a carbanion mechanism, but with drastically increased commitments

  11. Precise Measurement of Phenylalanine δ15N Values via Elemental Analysis-Isotope Ratio Mass Spectrometry Following Purification with High-Pressure Liquid Chromatography: A New Tool for Fine-Scale Paleo-Nitrogen Cycle Reconstructions

    NASA Astrophysics Data System (ADS)

    Broek, T.; Walker, B. D.; Batista, F. C.; Andreasen, D.; Hill, T. M.; Guilderson, T. P.; McCarthy, M.

    2012-12-01

    Compound specific isotope analysis of individual amino acids (CSI-AA) in organic paleoarchives is emerging as a powerful tool for reconstructing the paleo-nitrogen (N) cycle. Because the δ15N of phenylalanine (Phe) remains almost unchanged with diagenesis or trophic transfer it has been demonstrated to be the most promising AA proxy for the δ15N of primary production. However, the precise measurement of AA δ15N values is currently limited by the standard gas chromatography-isotope ratio mass spectrometer (GC-IRMS) approach. The key problem with this approach is that GC-IRMS δ15N precision (±1‰) is almost an order of magnitude lower than typical bulk δ15N measurements (±0.1‰), posing a significant problem for assessing fine scale changes within paleo-climate records. Additionally, required instrumentation is both expensive, and not widely available. Here we present an offline approach in which Phe is purified via high-pressure liquid chromatography (HPLC), using an analytical scale, mixed-phase column and automated fraction collection. δ13C and δ15N values of the fractions are then determined via standard elemental analysis-isotope ratio mass spectrometry (EA-IRMS). We evaluate the precision of this HPLC-EA-IRMS method vs. traditional GC-IRMS for Phe δ15N values of isotopic AA standards and various proteinaceous marine samples (marine coral, sediment, and cyanobacteria). Typical HPLC-EA-IRMS δ15N precision is ±0.1‰ for isotopic AA standards and ±0.5‰ for marine coral, sediment, and cyanobacteria samples compared to ±0.5‰ and ±1.0‰ for AA standards and samples analyzed by GC-IRMS. In order to demonstrate the viability of our approach, we present a comparison of a Phe δ15N record produced from a deep-sea bamboo coral specimen from Monterey Bay, CA, using our offline HPLC-EA-IRMS method vs. standard GC-IRMS. Each method produced equivalent Phe δ15N values within error, however, the HPLC-EA-IRMS method produced Phe δ15N values with over

  12. Nitrate reductase 15N discrimination in Arabidopsis thaliana, Zea mays, Aspergillus niger, Pichea angusta, and Escherichia coli

    PubMed Central

    Carlisle, Eli; Yarnes, Chris; Toney, Michael D.; Bloom, Arnold J.

    2014-01-01

    Stable 15N isotopes have been used to examine movement of nitrogen (N) through various pools of the global N cycle. A central reaction in the cycle involves the reduction of nitrate (NO−3) to nitrite (NO−2) catalyzed by nitrate reductase (NR). Discrimination against 15N by NR is a major determinant of isotopic differences among N pools. Here, we measured in vitro 15N discrimination by several NRs purified from plants, fungi, and a bacterium to determine the intrinsic 15N discrimination by the enzyme and to evaluate the validity of measurements made using 15N-enriched NO−3. Observed NR isotope discrimination ranged from 22 to 32‰ (kinetic isotope effects of 1.022–1.032) among the different isozymes at natural abundance 15N (0.37%). As the fractional 15N content of substrate NO−3 increased from natural abundance, the product 15N fraction deviated significantly from that expected based on substrate enrichment and 15N discrimination measured at natural abundance. Additionally, isotopic discrimination by denitrifying bacteria used to reduce NO−3 and NO−2 in some protocols became a greater source of error as 15N enrichment increased. We briefly discuss potential causes of the experimental artifacts with enriched 15N and recommend against the use of highly enriched 15N tracers to study N discrimination in plants or soils. PMID:25071800

  13. 13C/12C and 15N/14N Isotope Analysis to Characterize Natural Degradation of Atrazine: Evidence from Parent and Daughter Compound Values

    NASA Astrophysics Data System (ADS)

    Elsner, Martin; Meyer, Armin

    2013-04-01

    The mobile and still herbicidal metabolites desethylatrazine (DEA) and desisopropylatrazine (DIA) are frequently detected together with its parent compound atrazine (Atz) in the aquatic environment. Interpretation of their transformation state is often difficult with current methods, which are mainly measuring concentrations. Alternatively, compound specific isotope analyses (CSIA) has become a novel tool to detect degradation processes of contaminants in groundwater. The aim of our study was to investigate on the lab scale 13C/12C and 15N/14N isotope trends in parent and daughter compounds associated with different degradation scenarios of atrazine likely to occur in the environment. Thus atrazine was dealkylated with (i) permanganate and (ii) the bacterium Rhodococcus sp. NI86/21. In both transformations, 13C/12C ratios of atrazine increased strongly (epsilon carbon/permanganate = -4.6 ± 0.6 ‰ and epsilon carbon/Rhodoccoccus = -3.8 ± 0.2 ‰) whereas nitrogen isotope fractionation was small. 13C/12C ratios of DEA showed the following trends. (i) When DEA was formed as only product (Atz + permanganate) 13C/12C remained constant, close to the initial value of Atz. (ii) When DEA was formed together with deisopropylatrazine (biodegradation of Atz) 13C/12C increased, but only within 2‰. (iii) When DEA and DIA was further biodegraded, 13C/12C increased for both metabolites up to 9‰. Thus strong enrichment of 13C/12C in the metabolites in comparison to Atz can give strong testimony for further breakdown of the metabolite.

  14. Effects of ruminally degradable nitrogen intake and in vitro addition of ammonia and propionate on the metabolic fate of L-[1-14C]alanine and L-[15N]alanine in isolated sheep hepatocytes.

    PubMed

    Mutsvangwa, T; Buchanan-Smith, J G; McBride, B W

    1997-04-01

    Isolated hepatocytes prepared from sheep fed a basal diet (bromegrass hay-corn, 50:50 wt/ wt, as-fed basis) with or without urea were used to determine the effects of added ammonia (as NH4Cl) and propionate on the partitioning of C from 1.25 mM L-[1-14C]alanine between oxidation and gluconeogenesis, and the flux of 15N from 1.25 mM L-[15N]alanine to [14N15N]urea and [15N15N]urea. Hepatocyte suspensions were incubated with NH4Cl (0, .31, .63, and 1.25 mM) and (or) propionate (0, .31, .63, and 1.25 mM) in the presence of either 1.25 mM L-[15N]alanine or 1.25 mM L-alanine plus 18.5 kBq of L-[1-14C]alanine. Feeding dietary urea did not affect [1-14C]alanine oxidation to 14CO2 (P = .601), or its conversion to [14C]glucose (P = .576) by isolated hepatocytes. Increasing in vitro concentrations of NH4Cl and propionate between 0 and 1.25 mM reduced [1-14C]alanine oxidation to 14CO2 (P < .001). Increasing NH4Cl concentration between 0 and 1.25 mM reduced [1-14C]alanine conversion to [14C]glucose in isolated hepatocytes (P < .001), whereas addition of propionate between 0 and 1.25 mM stimulated production of [14C]glucose from [1-14C]alanine (P < .001). Feeding urea did not affect in vitro rates of total urea production (P = .655) but increased the production of [14N15N]urea and [15N15N]urea (P < .05). Addition of NH4Cl increased total urea, [14N15N]urea, and [15N15N]urea production (P < .001), but reduced 15N isotopic enrichments of [14N15N]urea and [15N15N]urea (P < .001). Increasing propionate concentration between 0 and 1.25 mM reduced total urea production (P < .001), but [14N15N]urea and [15N15N]urea production was reduced only at 1.25 mM propionate (P < .001). We conclude that NH3 detoxification by isolated sheep hepatocytes increases amino acid deamination and this might have implications for nitrogen retention in ruminants consuming diets that promote considerable NH3 absorption from the digestive tract. PMID:9110231

  15. Global modeling of the 15N216O line positions within the framework of the polyad model of effective Hamiltonian and a room temperature 15N216O line list

    NASA Astrophysics Data System (ADS)

    Tashkun, S. A.; Perevalov, V. I.; Liu, A.-W.; Hu, S.-M.

    2016-05-01

    The global modeling of 15N216O line positions in the 4-12,516 cm-1 region has been performed using the polyad model of effective Hamiltonian. The effective Hamiltonian parameters were fitted to the line positions collected from an exhaustive review of the literature. The dimensionless weighted standard deviation of the fit is 1.31. The fitted set of 109 parameters allowed reproducing more than 18,000 measured line positions with an RMS value of 0.001 cm-1. A line list was calculated for a reference temperature 296 K, natural abundance (1.32×10-5), and an intensity cutoff 10-30 cm/molecule. The line list is based on the fitted set of the effective Hamiltonian parameters for 15N216O obtained in this work and the effective dipole moment parameters of the 15N216O and 14N216O isotopologues. Accurate values of the 15N216O total partition function are also given.

  16. Late Holocene monsoon climate of northeastern Taiwan inferred from elemental (C, N) and isotopic (δ13C, δ15N) data in lake sediments

    NASA Astrophysics Data System (ADS)

    Selvaraj, Kandasamy; Wei, Kuo-Yen; Liu, Kon-Kee; Kao, Shuh-Ji

    2012-03-01

    Little information exists about centennial-scale climate variability on oceanic islands in the western Pacific where the East Asian monsoon (EAM) strongly influences the climate, mountain ecosystem and the society. In this study, we investigate a 168 cm long sediment core recovered from Emerald Peak Lake in subalpine NE Taiwan for the contents of grain size, total organic carbon (TOC), C/N ratio, and stable isotopes (δ13C and δ15N) to reconstruct the monsoon climate and vegetation density during the late Holocene. Six radiocarbon (14C) ages obtained on plant remains used for the chronology indicate that the sediment core has been accumulated since ˜3770 cal BP with a mean sedimentation rate of 44.6 cm/ka. The sub-centennial resolution of our proxy records reveals strong fluctuations of the EAM and vegetation density for the past ˜3770 cal BP. The greater contents of coarse and medium sediments with overall decreasing trends from 3770 to 2000 cal BP suggest an increasing fine sediment influx from the catchment likely due to an increasing lake water level. Although low TOC content, C/N ratio, and enriched δ13C values in bulk and fine sediments during this interval suggest a sparsely vegetated catchment, increasing trends of TOC content and C/N ratio together with decreasing trends of δ13C and δ15N values indicate a strengthening pattern of summer monsoon. This is in contrast to a decreasing monsoon strength inferred from Dongge Cave δ18O record at that time, supporting the idea of anti-phasing of summer EAM and Indian summer monsoon. Since 2000 cal BP, higher content of fine sediments with high TOC content and C/N ratio but relatively depleted δ13C and low δ15N values suggest a high but stable lake water level and dense C3 plants, consistent with a stronger summer monsoon in a wet climate. Within this general trend, we interpret a prominent change of proxy parameters in sediments from ˜560 to 150 cal BP, as subtropical evidence for the Little Ice Age in NE

  17. Kinetic isotope effects for fast deuterium and proton exchange rates

    PubMed Central

    Mammoli, Daniele; Kadeřávek, Pavel; Pelupessy, Philippe; Bodenhausen, Geoffrey

    2016-01-01

    By monitoring the effect of deuterium decoupling on the decay of transverse 15N magnetization in D–15N spin pairs during multiple-refocusing echo sequences, we have determined fast D–D exchange rates k D and compared them with fast H–H exchange rates k H in tryptophan to determine the kinetic isotope effect as a function of pH and temperature. PMID:27009684

  18. Major Sources of Organic Matter in a Complex Coral Reef Lagoon: Identification from Isotopic Signatures (δ13C and δ15N).

    PubMed

    Briand, Marine J; Bonnet, Xavier; Goiran, Claire; Guillou, Gaël; Letourneur, Yves

    2015-01-01

    A wide investigation was conducted into the main organic matter (OM) sources supporting coral reef trophic networks in the lagoon of New Caledonia. Sampling included different reef locations (fringing, intermediate and barrier reef), different associated ecosystems (mangroves and seagrass beds) and rivers. In total, 30 taxa of macrophytes, plus pools of particulate and sedimentary OM (POM and SOM) were sampled. Isotopic signatures (C and N) of each OM sources was characterized and the composition of OM pools assessed. In addition, spatial and seasonal variations of reef OM sources were examined. Mangroves isotopic signatures were the most C-depleted (-30.17 ± 0.41 ‰) and seagrass signatures were the most C-enriched (-4.36 ± 0.72 ‰). Trichodesmium spp. had the most N-depleted signatures (-0.14 ± 0.03 ‰) whereas mangroves had the most N-enriched signatures (6.47 ± 0.41 ‰). The composition of POM and SOM varied along a coast-to-barrier reef gradient. River POM and marine POM contributed equally to coastal POM, whereas marine POM represented 90% of the POM on barrier reefs, compared to 10% river POM. The relative importance of river POM, marine POM and mangroves to the SOM pool decreased from fringing to barrier reefs. Conversely, the relative importance of seagrass, Trichodesmium spp. and macroalgae increased along this gradient. Overall, spatial fluctuations in POM and SOM were much greater than in primary producers. Seasonal fluctuations were low for all OM sources. Our results demonstrated that a large variety of OM sources sustain coral reefs, varying in their origin, composition and role and suggest that δ13C was a more useful fingerprint than δ15N in this endeavour. This study also suggested substantial OM exchanges and trophic connections between coral reefs and surrounding ecosystems. Finally, the importance of accounting for environmental characteristics at small temporal and spatial scales before drawing general patterns is highlighted. PMID

  19. Major Sources of Organic Matter in a Complex Coral Reef Lagoon: Identification from Isotopic Signatures (δ13C and δ15N)

    PubMed Central

    Briand, Marine J.; Bonnet, Xavier; Goiran, Claire; Guillou, Gaël; Letourneur, Yves

    2015-01-01

    A wide investigation was conducted into the main organic matter (OM) sources supporting coral reef trophic networks in the lagoon of New Caledonia. Sampling included different reef locations (fringing, intermediate and barrier reef), different associated ecosystems (mangroves and seagrass beds) and rivers. In total, 30 taxa of macrophytes, plus pools of particulate and sedimentary OM (POM and SOM) were sampled. Isotopic signatures (C and N) of each OM sources was characterized and the composition of OM pools assessed. In addition, spatial and seasonal variations of reef OM sources were examined. Mangroves isotopic signatures were the most C-depleted (-30.17 ± 0.41 ‰) and seagrass signatures were the most C-enriched (-4.36 ± 0.72 ‰). Trichodesmium spp. had the most N-depleted signatures (-0.14 ± 0.03 ‰) whereas mangroves had the most N-enriched signatures (6.47 ± 0.41 ‰). The composition of POM and SOM varied along a coast-to-barrier reef gradient. River POM and marine POM contributed equally to coastal POM, whereas marine POM represented 90% of the POM on barrier reefs, compared to 10% river POM. The relative importance of river POM, marine POM and mangroves to the SOM pool decreased from fringing to barrier reefs. Conversely, the relative importance of seagrass, Trichodesmium spp. and macroalgae increased along this gradient. Overall, spatial fluctuations in POM and SOM were much greater than in primary producers. Seasonal fluctuations were low for all OM sources. Our results demonstrated that a large variety of OM sources sustain coral reefs, varying in their origin, composition and role and suggest that δ13C was a more useful fingerprint than δ15N in this endeavour. This study also suggested substantial OM exchanges and trophic connections between coral reefs and surrounding ecosystems. Finally, the importance of accounting for environmental characteristics at small temporal and spatial scales before drawing general patterns is highlighted. PMID

  20. An economic approach to efficient isotope labeling in insect cells using homemade 15N-, 13C- and 2H-labeled yeast extracts.

    PubMed

    Opitz, Christian; Isogai, Shin; Grzesiek, Stephan

    2015-07-01

    Heterologous expression of proteins in insect cells is frequently used for crystallographic structural studies due to the high yields even for challenging proteins requiring the eukaryotic protein processing capabilities of the host. However for NMR studies, the need for isotope labeling poses extreme challenges in eukaryotic hosts. Here, we describe a robust method to achieve uniform protein (15)N and (13)C labeling of up to 90 % in baculovirus-infected insect cells. The approach is based on the production of labeled yeast extract, which is subsequently supplemented to insect cell growth media. The method also allows deuteration at levels of >60 % without decrease in expression yield. The economic implementation of the labeling procedures into a standard structural biology laboratory environment is described in a step-by-step protocol. Applications are demonstrated for a variety of NMR experiments using the Abelson kinase domain, GFP, and the beta-1 adrenergic receptor as examples. Deuterated expression of the latter provides spectra of very high quality of a eukaryotic G-protein coupled receptor. PMID:26070442

  1. THE DEVELOPMENT OF A PREDICTIVE TOLL USING LARGEMOUTH BASS (MICROPTERUS SALMOIDES) SCALES TO ESTIMATE MERCURY (HG) CONCENTRATIONS AND STABLE-NITROGEN (15N/14N) ISOTOPE RATIOS IN FISH MUSCLE TISSUE

    EPA Science Inventory

    Knowledge of the trophic structure of biota in aquatic sites offers potential for the construction of models to allow the prediction of contaminant bioaccumulation. Measurements of trophic position have been conducted using stable-nitrogen isotope ratios ( 15N) measured in fish m...

  2. Selection of effective macroalgal species and tracing nitrogen sources on the different part of Yantai coast, China indicated by macroalgal δ(15)N values.

    PubMed

    Wang, Yujue; Liu, Dongyan; Richard, Pierre; Di, Baoping

    2016-01-15

    To determine the dominant nitrogen sources and select effective macroalgal species for monitoring eutrophication along the Yantai coast, the total carbon (TOC), total nitrogen (TN) and nitrogen stable isotope ratio (δ(15)N) in macroalgal tissue were analyzed in conjunction with environmental variables in seawater along the Yantai coastline. The ranges of macroalgal tissue δ(15)N values together with dissolved inorganic nitrogen (DIN) composition indicated that except for the atmospheric deposition, there were three dominant types of nitrogen sources along the Yantai coast, with the agricultural fertilizer usage and factorial wastewater input at the S1 (Zhifu Island coast), the sewage discharge at S2 (the Moon Bay coast), the sewage discharge together with aquaculture impacts at S3 (Fisherman Wharf coast) and S4 (the Horse Island coast). Macroalgal growth were not limited by DIN but limited by P at S2, S3 and S4. Macroalgal species suitable or not for DIN source tracing along the Yantai coast were discussed. For sites with low DIN concentration, many species of three phyla could be used for DIN sources tracing with Laurencia okamurai, Gloiopeltis furcata and Ulva pertusa being ideal species. For site with high DIN concentration, however, species of Rhodophyta were not suitable and only Scytosiphon lomentaria and Monostroma nitidium were chosen. PMID:26519590

  3. Technical Note: Simultaneous measurement of sedimentary N2 and N2O production and a modified 15N isotope pairing technique

    NASA Astrophysics Data System (ADS)

    Hsu, T.-C.; Kao, S.-J.

    2013-12-01

    Dinitrogen (N2) and/or nitrous oxide (N2O) are produced through denitrification, anaerobic ammonium oxidation (anammox) or nitrification in sediments, of which entangled processes complicate the absolute rate estimations of gaseous nitrogen production from individual pathways. The classical isotope pairing technique (IPT), the most common 15N nitrate enrichment method to quantify denitrification, has recently been modified by different researchers to (1) discriminate between the N2 produced by denitrification and anammox or to (2) provide a more accurate denitrification rate under considering production of both N2O and N2. In case 1, the revised IPT focused on N2 production being suitable for the environments of a low N2O-to-N2 production ratio, while in case 2, anammox was neglected. This paper develops a modified method to refine previous versions of IPT. Cryogenic traps were installed to separately preconcentrate N2 and N2O, thus allowing for subsequent measurement of the two gases generated in one sample vial. The precision is better than 2% for N2 (m/z 28, m/z 29 and m/z 30), and 1.5% for N2O (m/z 44, m/z 45 and m/z 46). Based on the six m/z peaks of the two gases, the 15N nitrate traceable processes including N2 and N2O from denitrification and N2 from anammox were estimated. Meanwhile, N2O produced by nitrification was estimated via the production rate of unlabeled 44N2O. To validate the applicability of our modified method, incubation experiments were conducted using sediment cores taken from the Danshuei Estuary in Taiwan. Rates of the aforementioned nitrogen removal processes were successfully determined. Moreover, N2O yield was as high as 66%, which would significantly bias previous IPT approaches if N2O was not considered. Our modified method not only complements previous versions of IPT but also provides more comprehensive information to advance our understanding of nitrogen dynamics of the water-sediment interface.

  4. The signatures of stable isotopes δ 15N and δ 13C in anadromous and non-anadromous Coilia nasus living in the Yangtze River, and the adjacent sea waters

    NASA Astrophysics Data System (ADS)

    Wang, Lei; Tang, Wenqiao; Dong, Wenxia

    2015-12-01

    Stable isotopes are increasingly used to investigate seasonal migrations of aquatic organisms. This study employed stable isotopes ( δ 13C and δ 15N) for Coilia nasus from the lower Yangtze River and the adjacent East China Sea to distinguish different ecotypic groups, ascertain trophic nutrition positions, and reflect environmental influences on C. nasus. δ 13C signatures of C. nasus sampled from Zhoushan (ZS), Chongming (CM), and Jingjiang (JJ) waters were significantly higher than those from the Poyang Lake (PYL) ( P < 0.05). By contrast, δ 15N signatures of C. nasus in ZS, CM, and JJ groups were significantly lower than those in PYL group ( P < 0.05). Basing on δ 13C and δ 15N signatures, we could distinguish anadromous (ZS, CM, and JJ) and non-anadromous (PYL) groups. The trophic level (TL) of anadromous C. nasus ranged from 2.90 to 3.04, whereas that of non-anadromous C. nasus was 4.38. C. nasus occupied the middle and top nutrition positions in the marine and Poyang Lake food webs, respectively. C. nasus in Poyang Lake were significantly more enriched in δ 15N but depleted in δ 13C, suggesting that anthropogenic nutrient inputs and terrigenous organic carbon are important to the Poyang Lake food web. This study is the first to apply δ 15N and δ 13C to population assignment studies of C. nasus in the Yangtze River and its affiliated waters. Analysis of stable isotopes ( δ 15N and δ 13C) is shown to be a useful tool for discriminating anadromous and non-anadromous C. nasus.

  5. Spatio-temporal isotopic signatures (δ13 C and δ15 N) reveal that two sympatric West African mullet species do not feed on the same basal production sources.

    PubMed

    Le Loc'h, F; Durand, J-D; Diop, K; Panfili, J

    2015-04-01

    Potential trophic competition between two sympatric mullet species, Mugil cephalus and Mugil curema, was explored in the hypersaline estuary of the Saloum Delta (Senegal) using δ(13) C and δ(15) N composition of muscle tissues. Between species, δ(15) N compositions were similar, suggesting a similar trophic level, while the difference in δ(13) C compositions indicated that these species did not feed from exactly the same basal production sources or at least not in the same proportions. This result provides the first evidence of isotopic niche segregation between two limno-benthophageous species belonging to the geographically widespread, and often locally abundant, Mugilidae family. PMID:25846862

  6. EFFECT OF HIGH-ENERGY RESONANCES ON THE {sup 18}O(p, {alpha}){sup 15}N REACTION RATE AT AGB AND POST-AGB RELEVANT TEMPERATURES

    SciTech Connect

    La Cognata, M.; Spitaleri, C.; Mukhamedzhanov, A. M.

    2010-11-10

    The {sup 18}O(p, {alpha}){sup 15}N reaction is of great importance in several astrophysical scenarios, as it influences the production of key isotopes such as {sup 19}F, {sup 18}O, and {sup 15}N. Fluorine is synthesized in the intershell region of asymptotic giant branch (AGB) stars, together with s-elements, by {alpha} radiative capture on {sup 15}N, which in turn is produced in the {sup 18}O proton-induced destruction. Peculiar {sup 18}O abundances are observed in R-Coronae Borealis stars, having {sup 16}O/{sup 18}O {approx}< 1, hundreds of times smaller than the galactic value. Finally, there is no definite explanation of the {sup 14}N/{sup 15}N ratio in pre-solar grains formed in the outer layers of AGB stars. Again, such an isotopic ratio is influenced by the {sup 18}O(p, {alpha}){sup 15}N reaction. In this work, a high accuracy {sup 18}O(p, {alpha}){sup 15}N reaction rate is proposed, based on the simultaneous fit of direct measurements and of the results of a new Trojan Horse experiment. Indeed, current determinations are uncertain because of the poor knowledge of the resonance parameters of key levels of {sup 19}F. In particular, we have focused on the study of the broad 660 keV 1/2{sup +} resonance corresponding to the 8.65 MeV level of {sup 19}F. Since {Gamma} {approx} 100-300 keV, it determines the low-energy tail of the resonant contribution to the cross section and dominates the cross section at higher energies. Here, we provide a reaction rate that is a factor of two larger above T {approx} 0.5 10{sup 9} K based on our new improved determination of its resonance parameters, which could strongly influence present-day astrophysical model predictions.

  7. Revisiting the use of δ15N in meso-scale studies of marine food webs by considering spatio-temporal variations in stable isotopic signatures - The case of an open ecosystem: The Bay of Biscay (North-East Atlantic)

    NASA Astrophysics Data System (ADS)

    Chouvelon, T.; Spitz, J.; Caurant, F.; Mèndez-Fernandez, P.; Chappuis, A.; Laugier, F.; Le Goff, E.; Bustamante, P.

    2012-08-01

    Most of the recent framework directives and environmental policies argue for the development and the use of indicators - notably trophodynamic indicators - that should be able to follow ecosystems' evolution in space and time, particularly under anthropogenic perturbations. In the last decades, the use of stable carbon and nitrogen isotopes ratios has increased exponentially, particularly in studies of marine ecosystems' trophic structure and functioning. This method is principally based on the assumption that the isotopic composition of a consumer directly reflects that of its food. Nevertheless, few studies have attempted to define the limits of this tool, before using it and drawing ecological conclusions from isotopic analysis. This study aimed to assess the importance of considering spatio-temporal variations in isotopic signatures of consumers when using δ13C and especially δ15N values in open ecosystems with complex food webs, using the Bay of Biscay (North-East Atlantic) as a case study. To this end, more than 140 species from this marine ecosystem were analysed for the isotopic signatures in their muscle tissue. They were sampled from coastal to oceanic and deep-sea areas and at different latitudes, to evaluate spatial variations of isotopic signatures. Selected species were also sampled over several years and in two seasons to account for inter-annual and seasonal variations. In the Bay of Biscay temperate ecosystem, which is subject to both coastal and oceanic influences - two main river inputs and upwelling areas - , δ13C and δ15N values significantly decreased from inshore to offshore species, and to a lesser extent from benthic to pelagic organisms. River discharges appeared to be the first factor influencing δ13C and δ15N values in consumers. From the important spatial variations detected in δ15N values in particular, we suggest that in such contrasted ecosystem, nitrogen isotopic ratios may also be revisited as an indicator of the feeding

  8. Effects of ion binding on the backbone dynamics of calbindin D9k determined by 15N NMR relaxation.

    PubMed

    Akke, M; Skelton, N J; Kördel, J; Palmer, A G; Chazin, W J

    1993-09-21

    The backbone dynamics of apo- and (Cd2+)1-calbindin D9k have been characterized by 15N nuclear magnetic resonance spectroscopy. Spin-lattice and spin-spin relaxation rate constants and steady-state [1H]-15N nuclear Overhauser effects were measured at a magnetic field strength of 11.74 T by two-dimensional, proton-detected heteronuclear NMR experiments using 15N-enriched samples. The relaxation parameters were analyzed using a model-free formalism that characterizes the dynamics of the N-H bond vectors in terms of generalized order parameters and effective correlation times. The data for the apo and (Cd2+)1 states were compared to those for the (Ca2+)2 state [Kördel, J., Skelton, N. J., Akke, M., Palmer, A. G., & Chazin, W. J. (1992) Biochemistry 31, 4856-4866] to ascertain the effects on ion ligation on the backbone dynamics of calbindin D9k. The two binding loops respond differently to ligation by metal ions: high-frequency (10(9)-10(12) s-1) fluctuations of the N-terminal ion-binding loop are not affected by ion binding, whereas residues G57, D58, G59, and E60 in the C-terminal ion-binding loop have significantly lower order parameters in the apo state than in the metal-bound states. The dynamical responses of the four helices to binding of ions are much smaller than that for the C-terminal binding loop, with the strongest effect on helix III, which is located between the linker loop and binding site II. Significant fluctuations on slower time scales also were detected in the unoccupied N-terminal ion-binding loop of the apo and (Cd2+)1 states; the apparent rates were greater for the (Cd2+)1 state. These results on the dynamical response to ion binding in calbindin D9k provide insights into the molecular details of the binding process and qualitative evidence for entropic contributions to the cooperative phenomenon of calcium binding for the pathway in which the ion binds first in the C-terminal site. PMID:8373781

  9. Quantitation of metabolic compartmentation in hyperammonemic brain by natural abundance 13C-NMR detection of 13C-15N coupling patterns and isotopic shifts.

    PubMed

    Lapidot, A; Gopher, A

    1997-02-01

    In the present study, the removal of cerebral ammonia by glutamine synthetase (GS) and by reductive amination of 2-oxoglutarate by glutamate dehydrogenase in the presence of an amino donor group, was determined in hyperammonemic rabbit brains. The 15N enrichments of brain metabolite alpha-amino and amide positions of glutamine, glutamate, and alanine were determined by the indirect detection of 15N-labeled compounds of the 13C-15N spin coupling patterns of natural abundance 13C-NMR spectra. The 13C-NMR spectra of brain extracts were obtained from rabbits infused with 15NH4Cl with or without intraperitoneal infusion of the GS inhibitor, L-methionine DL-sulfoximine, in a reasonable acquisition time period. When 15NH4Cl was infused, [5-15N]glutamine and [2-15N]glutamine concentrations reached 5.2 mumol/100 mg protein and 3.6 mumol/100 mg protein, respectively, which indicates the relatively high activity of reductive amination of 2-oxoglutarate in the glutamate dehydrogenase reaction. The low concentration of [2-15N]glutamate, which is about 30% of that of [2-15N]glutamine obtained in this study, suggests that very little glutamine serves as a precursor of neuronal glutamate. When GS was inhibited by L-methionine DL-sulfoximine, a flux of 15NH4+ via the residual activity of GS was accompanied by an apparent increase of [2-15N]glutamate and [15N]alanine concentrations (2.9 mumol/100 mg protein and 1.8 mumol/100 mg protein, respectively). These findings and those obtained from 13C-13C isotopomer analysis (Lapidot and Gopher, 1994b) suggest that astrocytic 2-oxoglutarate is partially utilized (together with an amino group donor) as a precursor for neuronal glutamate in the hyperammonemic brain when GS is inhibited. This process can partly replace GS activity in metabolizing ammonia in the hyperammonemic rabbit brain. PMID:9057821

  10. Linking Isotopes and Panmixia: High Within-Colony Variation in Feather δ2H, δ13C, and δ15N across the Range of the American White Pelican

    PubMed Central

    Reudink, Matthew W.; Kyle, Christopher J.; McKellar, Ann E.; Somers, Christopher M.; Reudink, Robyn L. F.; Kyser, T. Kurt; Franks, Samantha E.; Nocera, Joseph J.

    2016-01-01

    Complete panmixia across the entire range of a species is a relatively rare phenomenon; however, this pattern may be found in species that have limited philopatry and frequent dispersal. American white pelicans (Pelecanus erythrorhyncos) provide a unique opportunity to examine the role of long-distance dispersal in facilitating gene flow in a species recently reported as panmictic across its broad breeding range. This species is also undergoing a range expansion, with new colonies arising hundreds of kilometers outside previous range boundaries. In this study, we use a multiple stable isotope (δ2H, δ13C, δ15N) approach to examine feather isotopic structuring at 19 pelican colonies across North America, with the goal of establishing an isotopic basemap that could be used for assigning individuals at newly established breeding sites to source colonies. Within-colony isotopic variation was extremely high, exceeding 100‰ in δ2H within some colonies (with relatively high variation also observed for δ13C and δ15N). The high degree of within-site variation greatly limited the utility of assignment-based approaches (42% cross-validation success rate; range: 0–90% success). Furthermore, clustering algorithms identified four likely isotopic clusters; however, those clusters were generally unrelated to geographic location. Taken together, the high degree of within-site isotopic variation and lack of geographically-defined isotopic clusters preclude the establishment of an isotopic basemap for American white pelicans, but may indicate that a high incidence of long-distance dispersal is facilitating gene flow, leading to genetic panmixia. PMID:26974163

  11. Changing gull diet in a changing world: a 150-year stable isotope (δ13C, δ15N) record from feathers collected in the Pacific Northwest of North America.

    PubMed

    Blight, Louise K; Hobson, Keith A; Kyser, T Kurt; Arcese, Peter

    2015-04-01

    The world's oceans have undergone significant ecological changes following European colonial expansion and associated industrialization. Seabirds are useful indicators of marine food web structure and can be used to track multidecadal environmental change, potentially reflecting long-term human impacts. We used stable isotope (δ(13)C, δ(15)N) analysis of feathers from glaucous-winged gulls (Larus glaucescens) in a heavily disturbed region of the northeast Pacific to ask whether diets of this generalist forager changed in response to shifts in food availability over 150 years, and whether any detected change might explain long-term trends in gull abundance. Sampled feathers came from birds collected between 1860 and 2009 at nesting colonies in the Salish Sea, a transboundary marine system adjacent to Washington, USA and British Columbia, Canada. To determine whether temporal trends in stable isotope ratios might simply reflect changes to baseline environmental values, we also analysed muscle tissue from forage fishes collected in the same region over a multidecadal timeframe. Values of δ(13)C and δ(15)N declined since 1860 in both subadult and adult gulls (δ(13)C, ~ 2-6‰; δ(15)N, ~4-5‰), indicating that their diet has become less marine over time, and that birds now feed at a lower trophic level than previously. Conversely, forage fish δ(13)C and δ(15)N values showed no trends, supporting our conclusion that gull feather values were indicative of declines in marine food availability rather than of baseline environmental change. Gradual declines in feather isotope values are consistent with trends predicted had gulls consumed less fish over time, but were equivocal with respect to whether gulls had switched to a more garbage-based diet, or one comprising marine invertebrates. Nevertheless, our results suggest a long-term decrease in diet quality linked to declining fish abundance or other anthropogenic influences, and may help to explain regional

  12. Using nitrate dual isotopic composition (δ15N and δ18O) as a tool for exploring sources and cycling of nitrate in an estuarine system: Elkhorn Slough, California

    USGS Publications Warehouse

    Wankel, Scott D.; Kendall, Carol; Paytan, Adina

    2009-01-01

    Nitrate (NO-3 concentrations and dual isotopic composition (??15N and ??18O) were measured during various seasons and tidal conditions in Elkhorn Slough to evaluate mixing of sources of NO-3 within this California estuary. We found the isotopic composition of NO-3 was influenced most heavily by mixing of two primary sources with unique isotopic signatures, a marine (Monterey Bay) and terrestrial agricultural runoff source (Old Salinas River). However, our attempt to use a simple two end-member mixing model to calculate the relative contribution of these two NO-3 sources to the Slough was complicated by periods of nonconservative behavior and/or the presence of additional sources, particularly during the dry season when NO-3 concentrations were low. Although multiple linear regression generally yielded good fits to the observed data, deviations from conservative mixing were still evident. After consideration of potential alternative sources, we concluded that deviations from two end-member mixing were most likely derived from interactions with marsh sediments in regions of the Slough where high rates of NO-3 uptake and nitrification result in NO-3 with low ?? 15N and high ??18O values. A simple steady state dual isotope model is used to illustrate the impact of cycling processes in an estuarine setting which may play a primary role in controlling NO -3 isotopic composition when and where cycling rates and water residence times are high. This work expands our understanding of nitrogen and oxygen isotopes as biogeochemical tools for investigating NO -3 sources and cycling in estuaries, emphasizing the role that cycling processes may play in altering isotopic composition. Copyright 2009 by the American Geophysical Union.

  13. Comparative effect of salinity on growth, grain yield, water use efficiency, δ(13)C and δ(15)N of landraces and improved durum wheat varieties.

    PubMed

    Chamekh, Zoubeir; Ayadi, Sawsen; Karmous, Chahine; Trifa, Youssef; Amara, Hajer; Boudabbous, Khaoula; Yousfi, Salima; Serret, Maria Dolors; Araus, José Luis

    2016-10-01

    Supplemental irrigation with low-quality water will be paramount in Mediterranean agriculture in the future, where durum wheat is a major crop. Breeding for salinity tolerance may contribute towards improving resilience to irrigation with brackish water. However, identification of appropriate phenotyping traits remains a bottleneck in breeding. A set of 25 genotypes, including 19 landraces and 6 improved varieties most cultivated in Tunisia, were grown in the field and irrigated with brackish water (6, 13 and 18dSm(-1)). Improved genotypes exhibited higher grain yield (GY) and water use efficiency at the crop level (WUEyield or 'water productivity'), shorter days to flowering (DTF), lower N concentration (N) and carbon isotope composition (δ(13)C) in mature kernels and lower nitrogen isotope composition (δ(15)N) in the flag leaf compared with landraces. GY was negatively correlated with DTF and the δ(13)C and N of mature kernels and was positively correlated with the δ(15)N of the flag leaf. Moreover, δ(13)C of mature kernels was negatively correlated with WUEyield. The results highlight the importance of shorter phenology together with photosynthetic resilience to salt-induced water stress (lower δ(13)C) and nitrogen metabolism (higher N and δ(15)N) for assessing genotypic performance to salinity. PMID:27593462

  14. Protein Retention Assessment of Four Levels of Poultry By-Product Substitution of Fishmeal in Rainbow Trout (Oncorhynchus mykiss) Diets Using Stable Isotopes of Nitrogen (δ15N) as Natural Tracers

    PubMed Central

    Badillo, Daniel; Herzka, Sharon Z.; Viana, Maria Teresa

    2014-01-01

    This is second part from an experiment where the nitrogen retention of poultry by-product meal (PBM) compared to fishmeal (FM) was evaluated using traditional indices. Here a quantitative method using stable isotope ratios of nitrogen (δ15N values) as natural tracers of nitrogen incorporation into fish biomass is assessed. Juvenile rainbow trout (Oncorhynchus mykiss) were fed for 80 days on isotopically distinct diets in which 0, 33, 66 and 100% of FM as main protein source was replaced by PBM. The diets were isonitrogenous, isolipidic and similar in gross energy content. Fish in all treatments reached isotopic equilibrium by the end of the experiment. Two-source isotope mixing models that incorporated the isotopic composition of FM and PBM as well as that of formulated feeds, empirically derived trophic discrimination factors and the isotopic composition of fish that had reached isotopic equilibrium to the diets were used to obtain a quantitative estimate of the retention of each source of nitrogen. Fish fed the diets with 33 and 66% replacement of FM by PBM retained poultry by-product meal roughly in proportion to its level of inclusion in the diets, whereas no differences were detected in the protein efficiency ratio. Coupled with the similar biomass gain of fishes fed the different diets, our results support the inclusion of PBM as replacement for fishmeal in aquaculture feeds. A re-feeding experiment in which all fish were fed a diet of 100% FM for 28 days indicated isotopic turnover occurred very fast, providing further support for the potential of isotopic ratios as tracers of the retention of specific protein sources into fish tissues. Stable isotope analysis is a useful tool for studies that seek to obtain quantitative estimates of the retention of different protein sources. PMID:25226392

  15. Cross-basin heterogeneity in lanternfish (family Myctophidae) assemblages and isotopic niches (δ13C and δ15N) in the southern Tasman Sea abyssal basin

    NASA Astrophysics Data System (ADS)

    Flynn, A. J.; Kloser, R. J.

    2012-11-01

    A cross-basin (longitudinal) study of lanternfishes in the southern Tasman Sea abyssal basin during the austral winter of 2008 and 2009 found that mean biomass in the Western sector was higher than that in the Eastern sector, corresponding with cross-basin patterns in oceanographic heterogeneity and productivity. Dominant species over the abyssal basin differed from those previously recorded over the neighbouring continental slope. Vertical biomass profiles indicated diffuse night-time distributions in the Central sector and extensive diel vertical migrations in the Eastern sector. In the Western sector, macrocrustacean δ13C values were significantly higher, and δ15N significantly lower, than those in the Eastern sector. The results indicate a cross-basin difference in the primary productivity environment and 15N enrichment at the base of the foodweb. The cross-basin pattern in lanternfish δ15N values mirrored that for macrocrustaceans and was not correlated with standard length. Lanternfish δ13C values did not differ between sectors, but there were depth-wise differences, with values in the shallowest stratum (0-200 m) significantly higher than those in the deepest stratum (800-1000 m). Calculated trophic levels (TLs) of lanternfishes spanned the third trophic level and marked niche segregation was evident in the Eastern (mean TL 3.0-3.9) and Central (mean TL 2.5-3.6) sectors. Together, the results suggest that the Eastern and Western sectors are distinct sub-basin scale pelagic habitats, with implications for ecosystem modelling and future monitoring.

  16. Why is Mineral-Associated Organic Matter Enriched in 15N? Evidence from Grazed Pasture Soil

    NASA Astrophysics Data System (ADS)

    Baisden, W. T.; Wells, N. S.; Mudge, P. L.; Clough, T. J.; Schipper, L. A.; Ghani, A.; Stevenson, B.

    2014-12-01

    Throughout the scientific literature, measurements across soil depth and density fractions suggest that, with few exceptions, mineral-associated organic matter (OM) has higher δ15N than non-mineral-associated OM. This implies that the δ15N difference between N inputs and mineral-stabilized OM may characterize the microbial processes involved in stabilization and mineral association. Yet current understanding of observed N isotope fractionation in terrestrial ecosystems suggests the large isotope effects are expressed during inorganic N transformations from NH4 to gaseous loss pathways of NH3 volatilization and denitrification. How can the relative importance of N isotope fractionation during OM stabilization versus loss pathways be resolved? We recently examined N isofluxes when a temporary nitrogen excess is created by urine deposition in a New Zealand dairy pasture. We found that the N isotopic composition of volatilized NH3, and NO3 available for leaching or denitrification could not be linked back to the added N using Rayleigh distillation models. Instead, the results imply that the added N was immobilized, and the N available for losses was increasingly derived from mineralization of organic matter during the course of the experiment. These results are consistent with recent evidence of enhanced OM mineralization in urine patches, understanding of N isotope mass balances and long-standing evidence that gross mineralization and immobilization fluxes greatly exceed net mineralization and nitrification, except at very high N saturation. These results suggest that where 15N enrichment occurs due to fractionating loss pathways, the isotope effects are primarily transmitted to immobilized N, forming 15N enriched stabilized OM. This further explains earlier findings that the δ15N of soil OM represents an integrated indicator of losses, reflecting the intensity and duration of pastoral agriculture. We suggest that development of an indicator based on δ15N in

  17. Stable carbon ((12/13)C) and nitrogen ((14/15)N) isotopes as a tool for identifying the sources of cyanide in wastes and contaminated soils--a method development.

    PubMed

    Weihmann, Jenny; Mansfeldt, Tim; Schulte, Ulrike

    2007-01-23

    The occurrence of iron-cyanide complexes in the environment is of concern, since they are potentially hazardous. In order to determine the source of iron-cyanide complexes in contaminated soils and wastes, we developed a method based on the stable isotope ratios (13)C/(12)C and (15)N/(14)N of the complexed cyanide-ion (CN(-)). The method was tested on three pure chemicals and two industrials wastes: blast-furnace sludge (BFS) and gas-purifier waste (GPW). The iron-cyanide complexes were converted into the solid cupric ferrocyanide, Cu(2)[Fe(CN)(6)].7H(2)O, followed by combustion and determination of the isotope-ratios by continuous flow isotope ratio mass spectrometry. Cupric ferrocyanide was obtained from the materials by (i) an alkaline extraction with 1M NaOH and (ii) a distillate digestion. The [Fe(CN)(6)](4-) of the alkaline extraction was precipitated after adding Cu(2+). The CN(-) of the distillate digestion was at first complexed with Fe(2+) under inert conditions and then precipitated after adding Cu(2+). The delta(13)C-values obtained by the two methods differed slightly up to 1-3 per thousand for standards and BFS. The difference was larger for alkaline-extracted GPW (4-7 per thousand), since non-cyanide C was co-extracted and co-precipitated. Therefore the distillate digestion technique is recommended when determining the C isotope ratios in samples rich in organic carbon. Since the delta(13)C-values of BFS are in the range of -30 to -24 per thousand and of -17 to -5 per thousand for GPW, carbon seems to be a suitable tracer for identifying the source of cyanide in both wastes. However, the delta(15)N-values overlapped for BFS and GPW, making nitrogen unsuitable as a tracer. PMID:17386516

  18. Determination of the 2H/1H and 15N/14N ratios of Alkylpyrazines from coffee beans (Coffea arabica L. and Coffea canephoravar. robusta) by isotope ratio mass spectrometry.

    PubMed

    Richling, Elke; Preston, Christina; Kavvadias, Dominique; Kahle, Kathrin; Heppel, Christopher; Hummel, Silvia; König, Thorsten; Schreier, Peter

    2005-10-01

    The delta15N(AIR) and delta2H(VSMOW) data for several alkylpyrazines formed during the roasting process of coffee are reported. Samples of commercially available roasted (n = 9) as well as self-roasted (n = 8) coffee beans (Coffea arabica L. and Coffea canephora var. robusta) of different origins were investigated. By use of extracts prepared by simultaneous distillation extraction (SDE) and subsequently fractionated by liquid chromatography on silica gel, on-line capillary gas chromatography-isotope ratio mass spectrometry was employed in the combustion (C) and pyrolysis (P) modes (HRGC-C/P-IRMS) to determine the delta15N(AIR) and delta2H(VSMOW) values, respectively. In addition to the constituents of coffee beans, data for commercial synthetic alkylpyrazines and substances declared to be "natural" were determined. The delta15N(AIR) data for coffee alkylpyrazines under study-2-ethyl-5-methylpyrazine (1) and 2-ethyl-6-methylpyrazine (2) (measured as sum 1/2), 2-ethyl-3-methylpyrazine (3), 2-methylpyrazine (4), 2,5-dimethylpyrazine (5) and 2,6-dimethylpyrazine (6) (measured as sum 5/6), and 2,3-dimethylpyrazine (7), as well as 2,3,5-trimethylpyrazine (8)-varied in the range from +8.3 to -10.2 per thousand, thus revealing their biogeneration from amino acids (delta15N(AIR) ranging from +8 per thousand to -10 per thousand). The delta2H(VSMOW) values were determined in the range from -5 per thousand to -127 per thousand. Owing to the analytical differentiation observed between coffee alkylpyrazines and synthetic/"natural" samples of 3, 4, and 7, authenticity assessment of coffee-flavored products seems to be promising, provided that extended data will be available in the future. In the literature, there were no IRMS data available for the alkylpyrazines (1-8) under study. PMID:16190651

  19. NO3- Coordination in Aqueous Solutions by 15N/14N and 18O/natO Isotopic Substitution: What Can We Learn from Molecular Simulation?

    DOE PAGESBeta

    Chialvo, Ariel A.; Vlcek, Lukas

    2014-12-16

    We explore the deconvolution of the water-nitrate correlations by the first-order difference approach involving neutron diffraction of heavy- and null-aqueous solutions of KNO3 under 14N 15N and natON 18ON substitutions to achieve a full characterization of the first water coordination around the nitrate ion. For that purpose we performed isobaric-isothermal simulations of 3.5m KNO3 aqueous solutions at ambient conditions to generate the relevant radial distribution functions (RDF) required in the analysis (a) to identify the individual partial contributions to the total neutron weighted distribution function, (b) to isolate and assess the contribution of NO3 -!K+ pair formation, (c) to testmore » the accuracy of the NDIS-based coordination calculations and XRDbased assumptions, and (d) to describe the water coordination around both the nitrogen and oxygen sites of the nitrate ion.« less

  20. Stepwise enrichment of 15N along food chains: Further evidence and the relation between δ 15N and animal age

    NASA Astrophysics Data System (ADS)

    Minagawa, Masao; Wada, Eitaro

    1984-05-01

    The isotopic composition of nitrogen was measured in marine and fresh-water animals from the East China Sea, The Bering Sea, Lake Ashinoko and Usujiri intertidal zone. Primary producers, showed average δ15Nversus atmospheric nitrogen of +5.0%. (+3.4 to +7.5) in the Bering Sea and Lake Ashinoko, and +6.8%. (+6.0 to +7.6) in Usujiri intertidal zone. Blue green algae from the East China Sea show an average -0.55%. (-0.8 to +1.2). All consumers, Zooplankton, fish and bird exhibited Stepwise enrichment of 15N with increasing trophic level. The 15N enrichment at a single feeding process ranged from +1.3 to +5.3 averaging +3.4 ± 1.1%.. This isotopic fractionation seems to be independent of habitat. The effect of age in animals was obtained by analyzing two marine mussels. The soft tissue nitrogen showed +2.0%. enrichment relative to that of primary producers, and the magnitude was almost constant with shell ages ranging from 0 to 8 years. A similar 15N enrichment occurs in all Molluscs, Crustaceans, Insecta, Amphibia, Fish, Ave and Mammal species regardless of the difference in the form of excreted nitrogen and in laboratory cultured fish, brine shrimp and mice (+2.9 to +4.9%.). The excreted ammonia from guppy was sufficiently light to balance the concentration of 15N to animal body.

  1. sup 15 N NMR study on cyanide (C sup 15 N sup minus ) complex of cytochrome P-450 sub cam. Effects of d-camphor and putidaredoxin on the iron-ligand structure

    SciTech Connect

    Shiro, Yoshitsugu; Iizuka, Tetsutaro ); Makino, Ryu; Ishimura, Yuzuru ); Morishima, Isao )

    1989-11-27

    The cyanide (C{sup 15}N{sup {minus}}) complex of Pseudomonas putida cytochrome P-450 (P-450{sub cam}) exhibited well-resolved and hyperfine-shifted {sup 15}N NMR resonances arising from the iron-bound C{sup 15}N{sup {minus}} at 423 and 500 ppm in the absence and presence of the substrate, d-camphor, respectively. The values were smaller than those for cyanide complexes of myoglobin and hemoglobin ({approx} 1000 ppm) but fell into the same range as those for the cyanide complexes of peroxidases ({approx} 500 ppm). The {sup 15}N shift values of P-450{sub cam} were not incompatible with the existence of anionic ligand, such as cysteinyl thiolate anion, at the fifth coordination site of heme iron. The difference in the {sup 15}N chemical shift values between camphor-free and bound enzymes was inferred by the increase in the steric constraint to the Fe-C-N bond upon substrate binding.

  2. Cross-validation of δ15N and FishBase estimates of fish trophic position in a Mediterranean lagoon: The importance of the isotopic baseline

    NASA Astrophysics Data System (ADS)

    Mancinelli, Giorgio; Vizzini, Salvatrice; Mazzola, Antonio; Maci, Stefano; Basset, Alberto

    2013-12-01

    FishBase, a relational database freely available on the Internet, is to date widely used as a source of quantitative information on the trophic position of marine fish species. Here, we compared FishBase estimates for an assemblage of 30 fish species sampled in a Mediterranean lagoon (Acquatina lagoon, SE Italy) with their trophic positions calculated using nitrogen stable isotopes.

  3. Isotope Effects as New Proxies for Organic Pollutant Transformation.

    PubMed

    Hofstetter, Thomas B; Bolotin, Jakov; Pati, Sarah G; Skarpeli-Liati, Marita; Spahr, Stephanie; Wijker, Reto S

    2014-11-01

    Assessing the pathways and rates of organic pollutant transformation in the environment is a major challenge due to co-occurring transport and degradation processes. Measuring changes of stable isotope ratios (e.g. (13)C/(12)C, (2)H/(1)H, (15)N/(14)N) in individual organic compounds by compound-specific isotope analysis (CSIA) makes it possible to identify degradation pathways without the explicit need to quantify pollutant concentration dynamics. The so-called isotope fractionation observed in an organic pollutant is related to isotope effects of (bio)chemical reactions and enables one to characterize pollutant degradation even if multiple processes take place simultaneously. Here, we illustrate some principles of CSIA using benzotriazole, a frequently observed aquatic micropollutant, as example. We show subsequently how the combined C and N isotope fractionation analysis of nitroaromatic compounds reveals kinetics and mechanisms of reductive and oxidative reactions as well as their (bio)degradation pathways in the environment. PMID:26508486

  4. Compound-Specific δ15N Amino Acid Measurements in Littoral Mussels in the California Upwelling Ecosystem: A New Approach to Generating Baseline δ15N Isoscapes for Coastal Ecosystems

    PubMed Central

    Vokhshoori, Natasha L.; McCarthy, Matthew D.

    2014-01-01

    We explored δ15N compound-specific amino acid isotope data (CSI-AA) in filter-feeding intertidal mussels (Mytilus californianus) as a new approach to construct integrated isoscapes of coastal primary production. We examined spatial δ15N gradients in the California Upwelling Ecosystem (CUE), determining bulk δ15N values of mussel tissue from 28 sites between Port Orford, Oregon and La Jolla, California, and applying CSI-AA at selected sites to decouple trophic effects from isotopic values at the base of the food web. Bulk δ15N values showed a strong linear trend with latitude, increasing from North to South (from ∼7‰ to ∼12‰, R2 = 0.759). In contrast, CSI-AA trophic position estimates showed no correlation with latitude. The δ15N trend is therefore most consistent with a baseline δ15N gradient, likely due to the mixing of two source waters: low δ15N nitrate from the southward flowing surface California Current, and the northward transport of the California Undercurrent (CUC), with15N-enriched nitrate. This interpretation is strongly supported by a similar linear gradient in δ15N values of phenylalanine (δ15NPhe), the best AA proxy for baseline δ15N values. We hypothesize δ15NPhe values in intertidal mussels can approximate annual integrated δ15N values of coastal phytoplankton primary production. We therefore used δ15NPhe values to generate the first compound-specific nitrogen isoscape for the coastal Northeast Pacific, which indicates a remarkably linear gradient in coastal primary production δ15N values. We propose that δ15NPhe isoscapes derived from filter feeders can directly characterize baseline δ15N values across major biochemical provinces, with potential applications for understanding migratory and feeding patterns of top predators, monitoring effects of climate change, and study of paleo- archives. PMID:24887109

  5. Measurements of isotope effects in the photoionization of N2 and implications for Titan's atmosphere

    SciTech Connect

    Croteau, Philip; Randazzo, John B.; Kostko, Oleg; Ahmed, Musahid; Liang, Mao-Chang; Yung, Yuk L.; Boering, Kristie A.

    2010-12-30

    Isotope effects in the non-dissociative photoionization of molecular nitrogen (N2 + h nu -> N2+ + e-) may play a role in determining the relative abundances of isotopic species containing nitrogen in interstellar clouds and planetary atmospheres but have not been previously measured. Measurements of the photoionization efficiency spectra of 14N2, 15N14N, and 15N2 from 15.5 to 18.9 eV (65.6-80.0 nm) using the Advanced Light Source at Lawrence Berkeley National Laboratory show large differences in peak energies and intensities, with the ratio of the energy-dependent photoionization cross-sections, sigma(14N2)/sigma(15N14N), ranging from 0.4 to 3.5. Convolving the cross-sections with the solar flux and integrating over the energies measured, the ratios of photoionization rate coefficients are J(15N14N)/J(14N2)=1.00+-0.02 and J(15N2)/J(14N2)=1.00+-0.02, suggesting that isotopic fractionation between N2 and N2+ should be small under such conditions. In contrast, in a one-dimensional model of Titan's atmosphere, isotopic self-shielding of 14N2 leads to values of J(15N14N)/J(14N2) as large as ~;;1.17, larger than under optically thin conditions but still much smaller than values as high as ~;;29 predicted for N2 photodissociation. Since modeled photodissociation isotope effects overpredict the HC15N/HC14N ratio in Titan's atmosphere, and since both N atoms and N2+ ions may ultimately lead to the formation of HCN, estimates of the potential of including N2 photoionization to contribute to a more quantitative explanation of 15N/14N for HCN in Titan's atmosphere are explored.

  6. Life history of the individuals buried in the St. Benedict Cemetery (Prague, 15th-18th centuries): insights from (14)C dating and stable isotope (δ(13)C, δ(15)N, δ(18)O) analysis.

    PubMed

    Salesse, Kevin; Dufour, Élise; Castex, Dominique; Velemínský, Petr; Santos, Frédéric; Kuchařová, Hedvika; Jun, Libor; Brůžek, Jaroslav

    2013-06-01

    Funerary practices and bioarchaeological (sex and age) data suggest that a mortality crisis linked to an epidemic episode occurred during the fifth phase of the St. Benedict cemetery in Prague (Czech Republic). To identify this mass mortality episode, we reconstructed individual life histories (dietary and mobility factors), assessed the population's biological homogeneity, and proposed a new chronology through stable isotope analysis (δ(13)C, δ(18)O and δ(15)N) and direct radiocarbon dating. Stable isotope analysis was conducted on the bone and tooth enamel (collagen and carbonate) of 19 individuals from three multiple graves (MG) and 12 individuals from individual graves (IG). The δ(15)N values of collagen and the difference between the δ(13)C values of collagen and bone carbonate could indicate that the IG individuals had a richer protein diet than the MG individuals or different food resources. The human bone and enamel carbonate and δ(18)O values suggest that the majority of individuals from MG and all individuals from IG spent most of their lives outside of the Bohemian region. Variations in δ(18)O values also indicate that all individuals experienced residential mobility during their lives. The stable isotope results, biological (age and sex) data and eight (14)C dates clearly differentiate the MG and IG groups. The present work provides evidence for the reuse of the St. Benedict cemetery to bury soldiers despite the funeral protest ban (1635 AD). The Siege of Prague (1742 AD) by French-Bavarian-Saxon armies is identified as the cause of the St. Benedict mass mortality event. PMID:23588853

  7. Polyamine flux analysis by determination of heavy isotope incorporation from 13C, 15N-enriched amino acids into polyamines by LC-MS/MS.

    PubMed

    Cerrada-Gimenez, Marc; Häkkinen, Merja R; Vepsäläinen, Jouko; Auriola, Seppo; Alhonen, Leena; Keinänen, Tuomo A

    2012-02-01

    The study of polyamine flux, i.e. the circulating flow of polyamines through the interconnected biosynthetic and catabolic pathways, is of considerable interest because of the established links between the polyamine metabolism and many diseases, such as cancer and diabetes. To study polyamine flux in detail, a novel method based on following the label incorporation from the (13)C, (15)N-labeled polyamine precursors, arginine, methionine and ornithine, into polyamines by LC-MS/MS was implemented. This methodology was tested on three distinct cell lines with different spermidine/spermine-N (1)-acetyltransferase (SSAT) expression levels, i.e. non-transgenic, transgenic and knockout. These trials allowed the identification of the critical conditions for the successful polyamine flux measurement, such as the functional time frame of label incorporation, until plateau phase with the selected precursor is reached. The novel LC-MS/MS-based method for polyamine flux overcame the limitations of previous existing methodologies, with baseline separation of the different polyamine species and the exact quantification of the incorporated label. Moreover, the obtained results clearly show that the increased SSAT expression is associated with accelerated polyamine flux. PMID:21818565

  8. The effects of Paraloid B-72 and Butvar B-98 treatment and organic solvent removal on δ(13)C, δ(15)N, and δ(18)O values of collagen and hydroxyapatite in a modern bone.

    PubMed

    France, Christine A M; Giaccai, Jennifer A; Doney, Charlotte R

    2015-06-01

    Stable isotopes in bones are a powerful tool for diet, provenance, climate, and physiological reconstructions, but necessarily require well-preserved specimens unaltered by postmortem diagenesis or conservation practices. This study examines the effects of Paraloid B-72 and Butvar B-98, two common consolidants used in field and museum conservation, on δ(13)C, δ(15)N, and δ(18)O values from bone collagen and hydroxyapatite. The effects of solvent removal (100% acetone, 100% ethanol, 9:1 acetone:xylenes, 9:1 ethanol:xylenes) and drying methods (ambient air, vacuum, oven drying at 80°C) were also examined to determine if bones treated with these consolidants can successfully be cleaned and used for stable isotope analyses. Results show that introduction of Paraloid B-72 or Butvar B-98 in 100% acetone or 100% ethanol, respectively, with subsequent removal by the same solvents and drying at 80°C facilitates the most successful removal of consolidants and solvents. The δ(13)C values in collagen, δ(15)N in collagen, δ(18)O in hydroxyapatite phosphate, and δ(13)C in hydroxyapatite structural carbonate were unaltered by treatments with Paraloid or Butvar and subsequent solvent removal. The δ(18)O in hydroxyapatite structural carbonate showed nonsystematic variability when bones were treated with Paraloid and Butvar, which is hypothesized to be a result of hydroxyl exchange when bones are exposed to consolidants in solution. It is therefore recommended that δ(18)O in hydroxyapatite structural carbonate should not be used in stable isotope studies if bones have been treated with Paraloid or Butvar. PMID:25639211

  9. Defining fish community structure in Lake Winnipeg using stable isotopes (δ(13)C, δ(15)N, δ(34)S): implications for monitoring ecological responses and trophodynamics of mercury & other trace elements.

    PubMed

    Ofukany, Amy F A; Wassenaar, Leonard I; Bond, Alexander L; Hobson, Keith A

    2014-11-01

    The ecological integrity of freshwater lakes is influenced by atmospheric and riverine deposition of contaminants, shoreline development, eutrophication, and the introduction of non-native species. Changes to the trophic structure of Lake Winnipeg, Canada, and consequently, the concentrations of contaminants and trace elements measured in tissues of native fishes, are likely attributed to agricultural runoff from the 977,800 km(2) watershed and the arrival of non-native zooplankters and fishes. We measured δ(13)C, δ(15)N, and δ(34)S along with concentrations of 15 trace elements in 17 native fishes from the north and south basins of Lake Winnipeg in 2009 and 2010. After adjusting for differences in isotopic baseline values between the two basins, fishes in the south basin had consistently higher δ(13)C and δ(34)S, and lower δ(15)N. We found little evidence of biomagnification of trace elements at the community level, but walleye (Sander vitreus) and freshwater drum (Aplodinotus grunniens) had higher mercury and selenium concentrations with increased trophic position, coincident with increased piscivory. There was evidence of growth dilution of cobalt, copper, manganese, molybdenum, thallium, and vanadium, and bioaccumulation of mercury, which could be explained by increases in algal (and consequently, lake and fish) productivity. We conclude that the north and south basins of Lake Winnipeg represent very different communities with different trophic structures and trace element concentrations. PMID:25129159

  10. Mass-independent isotope effects.

    PubMed

    Buchachenko, Anatoly L

    2013-02-28

    Three fundamental properties of atomic nuclei-mass, spin (and related magnetic moment), and volume-are the source of isotope effects. The mostly deserved and popular, with almost hundred-year history, is the mass-dependent isotope effect. The first mass-independent isotope effect which chemically discriminates isotopes by their nuclear spins and nuclear magnetic moments rather than by their masses was detected in 1976. It was named as the magnetic isotope effect because it is controlled by magnetic interaction, i.e., electron-nuclear hyperfine coupling in the paramagnetic species, the reaction intermediates. The effect follows from the universal physical property of chemical reactions to conserve angular momentum (spin) of electrons and nuclei. It is now detected for oxygen, silicon, sulfur, germanium, tin, mercury, magnesium, calcium, zinc, and uranium in a great variety of chemical and biochemical reactions including those of medical and ecological importance. Another mass-independent isotope effect was detected in 1983 as a deviation of isotopic distribution in reaction products from that which would be expected from the mass-dependent isotope effect. On the physical basis, it is in fact a mass-dependent effect, but it surprisingly results in isotope fractionation which is incompatible with that predicted by traditional mass-dependent effects. It is supposed to be a function of dynamic parameters of reaction and energy relaxation in excited states of products. The third, nuclear volume mass-independent isotope effect is detected in the high-resolution atomic and molecular spectra and in the extraction processes, but there are no unambiguous indications of its importance as an isotope fractionation factor in chemical reactions. PMID:23301791

  11. Stable isotope methods: The effect of gut contents on isotopic ratios of zooplankton

    NASA Astrophysics Data System (ADS)

    Hill, J. M.; McQuaid, C. D.

    2011-05-01

    In the past decade there has been an increased awareness of the potential for methodological bias resulting from multiple pre-analytical procedures in foodweb interpretations based on stable isotope techniques. In the case of small organisms, this includes the effect of gut contents on whole body signatures. Although gut contents may not reflect actual assimilation, their carbon and nitrogen values will be isotopically lighter than after the same material has been assimilated. The potential skewing of isotopic ratios in whole organism samples is especially important for aquatic environments as many studies involve trophic relationships among small zooplankton. This is particularly important in pelagic waters, where herbivorous zooplankton comprise small taxa. Hence this study investigated the effect of gut contents on the δ13C and δ15N ratios of three size classes of zooplankton (1.0-2.0, 2.0-4.0 and >4.0 mm) collected using bongo net tows in the tropical waters of the south-west Indian Ocean. Animals were collected at night, when they were likely to be feeding, sieved into size classes and separated into genera. We focused on Euphausia spp which dominated zooplankton biomass. Three treatment types were processed: bulk animals, bulk animals without guts and tail muscle from each size class at 10 bongo stations. The δ15N ratios were influenced by zooplankton size class, presumably reflecting ontogenetic changes in diet. ANOVA post hoc results and correlations in δ15N signatures among treatments suggest that gut contents may not affect overall nitrogen signatures of Euphausia spp., but that δ13C signatures may be significantly altered by their presence. Carbon interpretations however, were complicated by potential effects of variation in chitin, lipids and metabolism among tissues and the possibility of opportunistic omnivory. Consequently we advocate gut evacuation before sacrifice in euphausiids if specific tissue dissection is impractical and recommend

  12. Simultaneous determination of stable isotopic compositions of nitrous oxide (δ15N and δ18O of N2O) and methane (δ13C of CH4) in nanomolar quantities from a single water sample

    NASA Astrophysics Data System (ADS)

    Hirota, A.; Tsunogai, U.; Komatsu, D. D.; Nakagawa, F.

    2010-12-01

    The stable isotopic compositions of nitrous oxide (δ15N of N2O and δ18O of N2O, respectively) and methane (δ13C of CH4) have provided us with some interesting geochemical insights. We have developed a rapid, sensitive, and automated analytical system to simultaneously determine the concentrations and stable isotopic compositions of nanomolar quantities of N2O and CH4 in the environmental water, by combining continuous-flow isotope-ratio mass spectrometry and a He-sparging system to extract and purify the dissolved gases. Our system, which is composed of a sparging bottle, a chemical trap, four cold traps and a capillary gas chromatograph that use ultra-pure helium as the carrier gas, achieves complete extraction of N2O and CH4 in a water sample and separation among N2O, CH4, and the other component gases. The flow path subsequent to gas chromatograph was periodically changed to pass the gases through the combustion furnace to convert CH4 and the other hydrocarbons into CO2, or to bypass the combustion furnace for the direct introduction of eluted N2O into the mass spectrometer, for determining the stable isotopic compositions through monitoring m/z = 44, 45, and 46, on the bases of CO2+ and N2O+, respectively. The analytical system can be operated automatically with sequential software programmed on a personal computer. The analytical precisions (the standard deviation of a single measurement) were better than 0.2‰ for δ15N of N2O and 0.3‰ for δ18O of N2O, in the case of more than 6.7 nmol N2O injection and better than 1.4‰ for δ15N of N2O and 2.6‰ for δ18O of N2O, in the case of more than 0.2 nmol N2O injection, respectively. Simultaneously, the analytical precisions were better than 0.07‰ for δ13C of CH4, in the case of more than 5.5 nmol CH4 infection and better than 2.1‰ for δ13C of CH4, when more than 0.024 nmol CH4 injection. In this manner, we can simultaneously determine stable isotopic compositions of a 120 mL water sample having

  13. Box-modeling of 15N/14N in mammals.

    PubMed

    Balter, Vincent; Simon, Laurent; Fouillet, Hélène; Lécuyer, Christophe

    2006-03-01

    The 15N/14N signature of animal proteins is now commonly used to understand their physiology and quantify the flows of nutrient in trophic webs. These studies assume that animals are predictably 15N-enriched relative to their food, but the isotopic mechanism which accounts for this enrichment remains unknown. We developed a box model of the nitrogen isotope cycle in mammals in order to predict the 15N/14N ratios of body reservoirs as a function of time, N intake and body mass. Results of modeling show that a combination of kinetic isotope fractionation during the N transfer between amines and equilibrium fractionation related to the reversible conversion of N-amine into ammonia is required to account for the well-established approximately 4 per thousand 15N-enrichment of body proteins relative to the diet. This isotopic enrichment observed in proteins is due to the partial recycling of 15N-enriched urea and the urinary excretion of a fraction of the strongly 15N-depleted ammonia reservoir. For a given body mass and diet delta15N, the isotopic compositions are mainly controlled by the N intake. Increase of the urea turnover combined with a decrease of the N intake lead to calculate a delta15N increase of the proteins, in agreement with the observed increase of collagen delta15N of herbivorous animals with aridity. We further show that the low delta15N collagen values of cave bears cannot be attributed to the dormancy periods as it is commonly thought, but inversely to the hyperphagia behavior. This model highlights the need for experimental investigations performed with large mammals in order to improve our understanding of natural variations of delta15N collagen. PMID:16328553

  14. Using d15 N in Fish Larvae as an Indicator of Watershed Sources of Anthropogenic Nitrogen: Response at Multiple Spatial Scales

    EPA Science Inventory

    The nitrogen stable isotope, 15N, is an effective tool to track anthropogenic N sources to aquatic ecosystems. It may be difficult to identify potential N sources, however, where 15N responds similarly to multiple, concurrent activities in the watershed that cause higher nutrient...

  15. Tracking atmospheric sulphur pollution from the study of Racomitrium lanuginosum mosses in Iceland: A multi-isotope approach (δ34S, 206Pb/204Pb, δ13C and δ15N)

    NASA Astrophysics Data System (ADS)

    Proust, E.; Widory, D.; Gautason, B.; Rogers, K.; Morrison, J.

    2010-12-01

    Among terrestrial plants, the applicability of mosses as monitoring organisms of atmospheric pollutants is a world-wide accepted technique due to their special biological and morphologic characteristics as nonvascular plants. They are commonly regarded as the best bioindicators of air quality because they can accumulate sulphur (S) and other elements to a far greater level than is necessary for their physiological needs. This study aims at using different isotope systematics δ34S, 206Pb/204Pb, δ13C and δ15N) to help understand the origin of S in the atmophsere of Reykjavik and its vicinity, and especially the potential contribution of surrounding geothermal plants. The selected Icelandic woolly fringe moss (Racomitrium lanuginosum (Hedw.) Brid.) is extremely common in lava fields and gravely and stony areas. Samples were taken in four distinct sampling sites around the city of Reykjavik: Bláfjöll area (south-eastern suburb of the city), and close to three power plants: Hellisheioarvirkjun (northern suburb of the city), Svartsengi (south-western suburb of the city) and Nesjavellir (north-eastern suburb of the city). Results show that, whatever the sampling context is, S is controlled by a binary mixing, between i) a high δ34S (around 16‰) end-member, characteristic of mosses from Hellisheioarvirkjun, and ii) a low δ34S (around -2‰) end-member, characteristic of mosses from Nesjavellir. The multi-isotope approach, confirms this binary relation and helps to constrain the different end-members involved.

  16. Assessment of temporal and spatial differences of source apportionment of nitrate in an urban river in China, using δ(15)N and δ(18)O values and an isotope mixing model.

    PubMed

    Zhang, Qianqian; Wang, Xiaoke; Sun, Feixiang; Sun, Jichao; Liu, Jingtao; Ouyang, Zhiyun

    2015-12-01

    Nitrate contamination in surface water has become an environmental problem widespread concern. In this study, environmental isotopes (δ(15)N-NO3 (-) and δ(18)O-NO3 (-)) and the chemical compositions of water samples from an urban river in Chongqing, China, were analyzed to evaluate the primary sources of nitrate pollution. A Bayesian isotope mixing model was applied to estimate the relative contributions of five potential NO3 (-) sources to river pollution (sewage/manure, soil N, NH4 (+) in fertilizer and precipitation, NO3 (-) fertilizer, and NO3 (-) in precipitation). The results show that the urban river was affected by NO3 (-) pollution from multiple sources. The major sources of NO3 (-) pollution in the dry season were sewage/manure (38-50 %) and soil N (22-26 %); in the wet season, the major sources of NO3 (-) pollution were sewage/manure (30-37 %), soil N (16-25 %), and precipitation (14-24 %). The higher contribution of N to the river water by precipitation indicates that atmospheric N deposition has become an important source of pollution in surface water in China. We conclude that domestic sewage is still the main contributor to NO3 (-) pollution in urban rivers in China. The discharge of domestic sewage into rivers should be prohibited as a priority measure to prevent NO3 (-) contamination. PMID:26527336

  17. δ15N patterns of Douglas-fir and red alder riparian forests in the Oregon Coast Range

    USGS Publications Warehouse

    Scott, E.E.; Perakis, S.S.; Hibbs, D.E.

    2008-01-01

    We used naturally occurring stable isotopes of N to compare N dynamics in near-stream and upslope environments along riparian catenas in N-fixing red alder (Alnus rubra) and Douglas-fir (Pseudotsuga menziesii) forests in the Coast Range of western Oregon. Based on the existing literature, we expected soil δ15N to be enriched closer to streams owing to inputs of isotopically heavy, marine-derived N by spawning salmon, higher rates of denitrification near the stream, or both. However, it has been unclear what effect red alder might have on soil δ15N patterns near streams. We found a consistent −1‰ δ15N signature in red alder foliage, and δ15N of total N in soils under red alder averaged 2.2‰ along sampling transects extending 20 m upslope from the stream. Surprisingly, δ15N of total N in soil under Douglas-fir was progressively depleted nearer to streams, opposite from the pattern expected from N losses by denitrification or N inputs from anadromous salmon. Instead, δ15N of total N in soil under Douglas-fir converged toward soil δ15N values typical of red alder sites. We consider that the historic presence of red alder may have contributed a legacy of lower soil δ15N nearer to streams on sites that are currently dominated by young Douglas-fir forest.

  18. Production of 15N-depleted biomass during cyanobacterial N2-fixation at high Fe concentrations

    NASA Astrophysics Data System (ADS)

    Zerkle, Aubrey L.; Junium, Christopher K.; Canfield, Donald E.; House, Christopher H.

    2008-09-01

    In this study we examine the effects of varying Fe, Mo, and P concentrations on δ15N fractionation during N2 fixation in the cyanobacterium Anabaena variabilis. We show that when grown in Fe-enriched media ([Fe] ≥ 50 nM), this organism produces biomass up to 3‰ lower in δ15N than when grown in Fe-limited media ([Fe] < 50 nM). A compilation of our data with previous measurements of δ15N in N2-fixing cyanobacteria reveals a general trend toward the production of more 15N-depleted biomass at higher Fe concentrations. We discuss our results in the context of negative δ15N values preserved in Archean and some Phanerozoic sediments, generally attributed to the production of marine organic matter with low δ15N by N2 fixation (and potentially NH4+ regeneration) during periods of fluctuating nutrient dynamics. We suggest that enhanced Fe availability during periods of widespread ocean anoxia can further stimulate the production of 15N-depleted biomass by N2-fixing organisms, contributing to the isotopic record.

  19. QUANTITATIVE 15N NMR SPECTROSCOPY

    EPA Science Inventory

    Line intensities in 15N NMR spectra are strongly influenced by spin-lattice and spin-spin relaxation times, relaxation mechanisms and experimental conditions. Special care has to be taken in using 15N spectra for quantitative purposes. Quantitative aspects are discussed for the 1...

  20. Coupling tree-ring delta13C and delta15N to test the effect of fertilization on mature Douglas-fir (Pseudotsuga menziesii var. glauca) stands across the Interior northwest, USA.

    PubMed

    Balster, Nick J; Marshall, John D; Clayton, Murray

    2009-12-01

    Nitrogen (N) fertilization causes long-term increases in biomass production in many N-limited forests around the world, but the mechanistic basis underlying the increase is often unclear. One possibility, especially in summer-dry climates, is that N fertilization increases the efficiency with which a finite water supply is consumed to support photosynthesis. This increase is achieved by a reduction in the canopy-integrated concentration of internal CO(2) and thus discrimination against (13)C. We used stable isotopes of carbon (delta(13)C) in tree rings to experimentally test the physiological impact of N fertilization on mature Douglas-fir (Pseudotsuga menziesii Franco var. glauca) stands across the geographic extent of the Intermountain West, USA. The concentration and the stable isotopes of N (delta(15)N) in tree rings were also used to assess the presence and activity of fertilizer N. We hypothesized that N fertilization would (i) increase delta(15)N and N concentration of stemwood relative to non-fertilized stands and (ii) increase stemwood delta(13)C as photosynthetic gas exchange responded to the additional N. This experiment included two rates of urea addition, 178 kg ha(-1) (low) and 357 kg ha(-1) (high), which were applied twice over a 6-year interval bracketed by the 18 years of wood production measured in this study. Foliar N concentrations measured the year after each fertilization treatment suggest that the fertilizer N had been assimilated by the trees (P < 0.001). The N fertilization significantly enriched stemwood delta(15)N by 1.3 per thousand at the low fertilization rate and by 2.4 per thousand at the high rate (P < 0.001) despite variation in soil N between sites. However, we found no significant effect of the N fertilizer on delta(13)C of the annual rings (P = 0.76). These data lead us to suggest that alternative mechanisms underlie the growth response to fertilizer, i.e., increase in canopy area and shifts in biomass allocation. PMID:19855101

  1. Evidence for a uniformly small isotope effect of nitrogen leaching loss: results from disturbed ecosystems in seasonally dry climates.

    PubMed

    Mnich, Meagan E; Houlton, Benjamin Z

    2016-06-01

    Nitrogen (N) losses constrain rates of plant carbon dioxide (CO2) uptake and storage in many ecosystems globally. N isotope models have been used to infer that ~30 % of terrestrial N losses occur via microbial denitrification; however, this approach assumes a small isotope effect associated with N leaching losses. Past work across tropical/sub-tropical forest sites has confirmed this expectation; however, the stable N isotope ratio (δ(15)N) of ecosystem leaching has yet to be systematically evaluated in seasonally dry climates or across major ecosystem disturbances. We here present new measurements of the δ(15)N of total dissolved N (TDN) in small streams, bulk deposition, and soil pools across eight watershed sites in California, including grassland, chaparral, and coastal redwood forest ecosystems, with and without fire, grazing, and forest harvesting. Regardless of the dominant vegetation type or disturbance regime, average δ(15)N of TDN in stream water differed only slightly (<~1 ‰) from that of bulk soil δ(15)N, revealing a uniformly small isotope effect associated with N leaching losses even under non-steady state conditions. Rather, lower input δ(15)N compared to TDN δ(15)N in streams pointed to fractionations via gaseous loss pathways as the dominant mechanism behind soil δ(15)N enrichment. We conclude that N leaching does not impart a major isotope effect across a broad range of ecosystems and conditions examined, thereby advancing the N gas-loss hypothesis as the principal explanation for variation in bulk soil δ(15)N. PMID:26343040

  2. Light-mediated 15N fractionation in Caribbean gorgonian octocorals: implications for pollution monitoring

    NASA Astrophysics Data System (ADS)

    Baker, D. M.; Kim, K.; Andras, J. P.; Sparks, J. P.

    2011-09-01

    The stable nitrogen isotope ratio ( δ 15N) of coral tissue is a useful recorder of anthropogenic pollution in tropical marine ecosystems. However, little is known of the natural environmentally induced fractionations that affect our interpretation of coral δ 15N values. In symbiotic scleractinians, light affects metabolic fractionation of N during photosynthesis, which may confound the identification of N pollution between sites of varied depth or turbidity. Given the superiority of octocorals for δ 15N studies, our goal was to quantify the effect of light on gorgonian δ 15N in the context of monitoring N pollution sources. Using field collections, we show that δ 15N declined by 1.4‰ over 20 m depth in two species of gorgonians, the common sea fan, Gorgonia ventalina, and the slimy sea plume, Pseudopterogorgia americana. An 8-week laboratory experiment with P. americana showed that light, not temperature causes this variation, whereby the lowest fractionation of the N source was observed in the highest light treatment. Finally, we used a yearlong reciprocal depth transplant experiment to quantify the time frame over which δ 15N changes in G. ventalina as a function of light regime . Over the year, δ 15N was unchanged and increased slightly in the deep control colonies and shallow colonies transplanted to the deep site, respectively. Within 6 months, colonies transplanted from deep to shallow became enriched by 0.8‰, mirroring the enrichment observed in the shallow controls, which was likely due to the combined effect of an increase in the source δ 15N and reduced fractionation. We conclude that light affects gorgonian δ 15N fractionation and should be considered in sampling designs for N pollution monitoring. However, these fractionations are small relative to differences observed between natural and anthropogenic N sources.

  3. Disentangling effects of growth and nutritional status on seabird stable isotope ratios

    USGS Publications Warehouse

    Sears, J.; Hatch, Shyla A.; O'Brien, D. M.

    2009-01-01

    A growing number of studies suggest that an individual's physiology affects its carbon and nitrogen stable isotope signatures, obscuring a signal often assumed to be only a reflection of diet and foraging location. We examined effects of growth and moderate food restriction on red blood cell (RBC) and feather ??15N and ??13C in rhinoceros auklet chicks (Cerorhinca monocerata), a piscivorous seabird. Chicks were reared in captivity and fed either control (75 g/day; n = 7) or ~40% restricted (40 g/day; n = 6) amounts of high quality forage fish. We quantified effects of growth on isotopic fractionation by comparing ??15N and ??13C in control chicks to those of captive, non-growing subadult auklets (n = 11) fed the same diet. To estimate natural levels of isotopic variation, we also collected blood from a random sample of free-living rhinoceros auklet adults and chicks in the Gulf of Alaska (n = 15 for each), as well as adult feather samples (n = 13). In the captive experiment, moderate food restriction caused significant depletion in ??15N of both RBCs and feathers in treatment chicks compared to control chicks. Growth also induced depletion in RBC ??15N, with chicks exhibiting lower ??15N when they were growing the fastest. As growth slowed, ??15N increased, resulting in an overall pattern of enrichment over the course of the nestling period. Combined effects of growth and restriction depleted ??15N in chick RBCs by 0.92???. We propose that increased nitrogen-use efficiency is responsible for 15N depletion in both growing and food-restricted chicks. ??15N values in RBCs of free-ranging auklets fell within a range of only 1.03???, while feather ??15N varied widely. Together, our captive and field results suggest that both growth and moderate food restriction can affect stable isotope ratios in an ecologically meaningful way in RBCs although not feathers due to greater natural variability in this tissue. ?? 2008 Springer-Verlag.

  4. Disentangling effects of growth and nutritional status on seabird stable isotope ratios.

    PubMed

    Sears, Justine; Hatch, Scott A; O'Brien, Diane M

    2009-02-01

    A growing number of studies suggest that an individual's physiology affects its carbon and nitrogen stable isotope signatures, obscuring a signal often assumed to be only a reflection of diet and foraging location. We examined effects of growth and moderate food restriction on red blood cell (RBC) and feather delta(15)N and delta(13)C in rhinoceros auklet chicks (Cerorhinca monocerata), a piscivorous seabird. Chicks were reared in captivity and fed either control (75 g/day; n = 7) or ~40% restricted (40 g/day; n = 6) amounts of high quality forage fish. We quantified effects of growth on isotopic fractionation by comparing delta(15)N and delta(13)C in control chicks to those of captive, non-growing subadult auklets (n = 11) fed the same diet. To estimate natural levels of isotopic variation, we also collected blood from a random sample of free-living rhinoceros auklet adults and chicks in the Gulf of Alaska (n = 15 for each), as well as adult feather samples (n = 13). In the captive experiment, moderate food restriction caused significant depletion in delta(15)N of both RBCs and feathers in treatment chicks compared to control chicks. Growth also induced depletion in RBC delta(15)N, with chicks exhibiting lower delta(15)N when they were growing the fastest. As growth slowed, delta(15)N increased, resulting in an overall pattern of enrichment over the course of the nestling period. Combined effects of growth and restriction depleted delta(15)N in chick RBCs by 0.92 per thousand. We propose that increased nitrogen-use efficiency is responsible for (15)N depletion in both growing and food-restricted chicks. delta(15)N values in RBCs of free-ranging auklets fell within a range of only 1.03 per thousand, while feather delta(15)N varied widely. Together, our captive and field results suggest that both growth and moderate food restriction can affect stable isotope ratios in an ecologically meaningful way in RBCs although not feathers due to greater natural variability in

  5. Tissue S/N ratios and stable isotopes (delta(34)S and delta(15)N) of epilithic mosses (Haplocladium microphyllum) for showing air pollution in urban cities in Southern China.

    PubMed

    Xiao, Hua-Yun; Tang, Cong-Guo; Xiao, Hong-Wei; Wang, Yan-Li; Liu, Xue-Yan; Liu, Cong-Qiang

    2010-05-01

    In urban cities in Southern China, the tissue S/N ratios of epilithic mosses (Haplocladium microphyllum), varied widely from 0.11 to 0.19, are strongly related to some atmospheric chemical parameters (e.g. rainwater SO(4)(2-)/NH(4)(+) ratios, each people SO(2) emission). If tissue S/N ratios in the healthy moss species tend to maintain a constant ratio of 0.15 in unpolluted area, our study cities can be divided into two classes: class I (S/N > 0.15, S excess) and class II (S/N < 0.15, N excess), possibly indicative of stronger industrial activity and higher density of population, respectively. Mosses in all these cities obtained S and N from rainwater at a similar ratio. Sulphur and N isotope ratios in mosses are found significantly linearly correlated with local coal delta(34)S and NH(4)(+)-N wet deposition, respectively, indicating that local coal and animal NH(3) are the major atmospheric S and N sources. PMID:19959268

  6. Structure effects in the 15N(n ,γ )16N radiative capture reaction from the Coulomb dissociation of 16N

    NASA Astrophysics Data System (ADS)

    Neelam, Shubhchintak, Chatterjee, R.

    2015-10-01

    Background: The 15N(n ,γ )16N reaction plays an important role in red giant stars and also in inhomogeneous big bang nucleosynthesis. However, there are controversies regarding spectroscopic factors of the four low-lying states of 16N, which have direct bearing on the total direct capture cross section and also on the reaction rate. Direct measurements of the capture cross section at low energies are scarce and available only at three energies below 500 keV. Purpose: The aim of this paper is to calculate the 15N(n ,γ )16N radiative capture cross section and its subsequent reaction rate by an indirect method and in that process investigate the effects of spectroscopic factors of different levels of 16N to the cross section. Method: A fully quantum mechanical Coulomb breakup theory under the aegis of post-form distorted wave Born approximation is used to calculate the Coulomb breakup of 16N on Pb at 100 MeV/u . This is then related to the photodisintegration cross section of 16N(γ ,n )15N and subsequently invoking the principle of detailed balance, the 15N(n ,γ )16N capture cross section is calculated. Results: The nonresonant capture cross section is calculated with spectroscopic factors from the shell model and those extracted (including uncertainties) from two recent experiments. The data seem to favor a more single particle nature for the low-lying states of 16N. The total neutron capture rate is also calculated by summing up nonresonant and resonant (significant only at temperatures greater than 1 GK) contributions and comparison is made with other charged particle capture rates. In the typical temperature range of 0.1 -1.2 GK, almost all the contributions to the reaction rate come from capture cross sections below 0.25 MeV. Conclusion: We have attempted to resolve the discrepancy in the spectroscopic factors of low-lying 16N levels and conclude that it would certainly be useful to perform a Coulomb dissociation experiment to find the low energy capture

  7. Effects of Boron Nutrition and Water Stress on Nitrogen Fixation, Seed δ15N and δ13C Dynamics, and Seed Composition in Soybean Cultivars Differing in Maturities

    PubMed Central

    Bellaloui, Nacer; Mengistu, Alemu

    2015-01-01

    Therefore, the objective of the current research was to investigate the effects of foliar B nutrition on seed protein, oil, fatty acids, and sugars under water stress conditions. A repeated greenhouse experiment was conducted using different maturity group (MG) cultivars. Plants were well-watered with no foliar B (W − B), well-watered with foliar B (W + B), water-stressed with no foliar B (WS − B), and water-stressed with foliar B (WS + B). Foliar B was applied at rate of 0.45 kg·ha−1 and was applied twice at flowering and at seed-fill stages. The results showed that seed protein, sucrose, fructose, and glucose were higher in W + B treatment than in W − B, WS + B, and WS − B. The increase in protein in W + B resulted in lower seed oil, and the increase of oleic in WS − B or WS + B resulted in lower linolenic acid. Foliar B resulted in higher nitrogen fixation and water stress resulted in seed δ15N and δ13C alteration. Increased stachyose indicated possible physiological and metabolic changes in carbon and nitrogen pathways and their sources under water stress. This research is beneficial to growers for fertilizer management and seed quality and to breeders to use 15N/14N and 13C/12C ratios and stachyose to select for drought tolerance soybean. PMID:25667936

  8. Total-body protein turnover in parenterally fed neonates: effects of energy source studied by using [15N]glycine and [1-13C]leucine.

    PubMed

    Pencharz, P; Beesley, J; Sauer, P; Van Aerde, J; Canagarayar, U; Renner, J; McVey, M; Wesson, D; Swyer, P

    1989-12-01

    The effects of nonprotein energy source (ie, glucose only vs glucose and lipid) on nitrogen retention and total-body protein turnover were studied in 20 parenterally fed newborn infants. All infants received approximately 3 g amino acids and 80-90 kcal.kg body wt.d. Total-body protein synthesis was estimated by using three constant-infusion, end-product methods: enrichment of urinary urea and ammonia in response to a [15N]glycine label and exhaled carbon dioxide enrichment in response to a [1-13C]leucine label. No differences were seen in nitrogen retention between the two energy sources. The estimate of total-body protein turnover obtained from the 13C label was similar to that obtained with the [15N]urea label. No differences in turnover rates were observed between the two diet groups. Use of the glucose-plus-lipid fuel system enhanced energy storage and the reutilization of amino acid for protein synthesis. PMID:2512806

  9. The theoretical investigation of solvent effects on the relative stability and 15N NMR shielding of antidepressant heterocyclic drug

    NASA Astrophysics Data System (ADS)

    Tahan, Arezoo; Khojandi, Mahya; Salari, Ali Akbar

    2016-01-01

    The density functional theory (DFT) and Tomasi's polarized continuum model (PCM) were used for the investigation of solvent polarity and its dielectric constant effects on the relative stability and NMR shielding tensors of antidepressant mirtazapine (MIR). The obtained results indicated that the relative stability in the polar solvents is higher than that in non-polar solvents and the most stable structure was observed in the water at the B3LYP/6-311++G ( d, p) level of theory. Also, natural bond orbital (NBO) interpretation demonstrated that by increase of solvent dielectric constant, negative charge on nitrogen atoms of heterocycles and resonance energy for LP(N10) → σ* and π* delocalization of the structure's azepine ring increase and the highest values of them were observed in water. On the other hand, NMR calculations showed that with an increase in negative charge of nitrogen atoms, isotropic chemical shielding (σiso) around them increase and nitrogen of piperazine ring (N19) has the highest values of negative charge and σiso among nitrogen atoms. NMR calculations also represented that direct solvent effect on nitrogen of pyridine ring (N15) is more than other nitrogens, while its effect on N19 is less than other ones. Based on NMR data and NBO interpretation, it can be deduced that with a decrease in the negative charge on nitrogen atoms, the intramolecular effects on them decrease, while direct solvent effect increases.

  10. The contamination of commercial 15N2 gas stocks with 15N-labeled nitrate and ammonium and consequences for nitrogen fixation measurements.

    PubMed

    Dabundo, Richard; Lehmann, Moritz F; Treibergs, Lija; Tobias, Craig R; Altabet, Mark A; Moisander, Pia H; Granger, Julie

    2014-01-01

    We report on the contamination of commercial 15-nitrogen (15N) N2 gas stocks with 15N-enriched ammonium, nitrate and/or nitrite, and nitrous oxide. 15N2 gas is used to estimate N2 fixation rates from incubations of environmental samples by monitoring the incorporation of isotopically labeled 15N2 into organic matter. However, the microbial assimilation of bioavailable 15N-labeled N2 gas contaminants, nitrate, nitrite, and ammonium, is liable to lead to the inflation or false detection of N2 fixation rates. 15N2 gas procured from three major suppliers was analyzed for the presence of these 15N-contaminants. Substantial concentrations of 15N-contaminants were detected in four Sigma-Aldrich 15N2 lecture bottles from two discrete batch syntheses. Per mole of 15N2 gas, 34 to 1900 µmoles of 15N-ammonium, 1.8 to 420 µmoles of 15N-nitrate/nitrite, and ≥21 µmoles of 15N-nitrous oxide were detected. One 15N2 lecture bottle from Campro Scientific contained ≥11 µmoles of 15N-nitrous oxide per mole of 15N2 gas, and no detected 15N-nitrate/nitrite at the given experimental 15N2 tracer dilutions. Two Cambridge Isotopes lecture bottles from discrete batch syntheses contained ≥0.81 µmoles 15N-nitrous oxide per mole 15N2, and trace concentrations of 15N-ammonium and 15N-nitrate/nitrite. 15N2 gas equilibrated cultures of the green algae Dunaliella tertiolecta confirmed that the 15N-contaminants are assimilable. A finite-differencing model parameterized using oceanic field conditions typical of N2 fixation assays suggests that the degree of detected 15N-ammonium contamination could yield inferred N2 fixation rates ranging from undetectable, <0.01 nmoles N L(-1) d(-1), to 530 nmoles N L(-1) d(-1), contingent on experimental conditions. These rates are comparable to, or greater than, N2 fixation rates commonly detected in field assays. These results indicate that past reports of N2 fixation should be interpreted with caution, and demonstrate that the purity of commercial 15N2

  11. δ15N Value Does Not Reflect Fasting in Mysticetes

    PubMed Central

    Aguilar, Alex; Giménez, Joan; Gómez–Campos, Encarna; Cardona, Luís; Borrell, Asunción

    2014-01-01

    The finding that tissue δ15N values increase with protein catabolism has led researchers to apply this value to gauge nutritive condition in vertebrates. However, its application to marine mammals has in most occasions failed. We investigated the relationship between δ15N values and the fattening/fasting cycle in a model species, the fin whale, a migratory capital breeder that experiences severe seasonal variation in body condition. We analyzed two tissues providing complementary insights: one with isotopic turnover (muscle) and one that keeps a permanent record of variations in isotopic values (baleen plates). In both tissues δ15N values increased with intensive feeding but decreased with fasting, thus contradicting the pattern previously anticipated. The apparent inconsistency during fasting is explained by the fact that a) individuals migrate between different isotopic isoscapes, b) starvation may not trigger significant negative nitrogen balance, and c) excretion drops and elimination of 15N-depleted urine is minimized. Conversely, when intensive feeding is resumed in the northern grounds, protein anabolism and excretion start again, triggering 15N enrichment. It can be concluded that in whales and other mammals that accrue massive depots of lipids as energetic reserves and which have limited access to drinking water, the δ15N value is not affected by fasting and therefore cannot be used as an indicatior of nutritive condition. PMID:24651388

  12. Mammalian DNA δ15N exhibits 40‰ intramolecular variation and is unresponsive to dietary protein level

    PubMed Central

    Strable, Maggie S.; Tschanz, Carolyn L.; Varamini, Behzad; Chikaraishi, Yoshito; Ohkouchi, Naohiko; Brenna, J. Thomas

    2014-01-01

    We report the first high precision characterization of molecular and intramolecular δ15N of nucleosides derived from mammalian DNA. The influence of dietary protein level on brain amino acids and deoxyribonucleosides was determined to investigate whether high protein turnover would alter amino acid 15N or 13C. Pregnant guinea pig dams were fed control diets, or high or low levels of dietary protein throughout gestation, and all pups were fed control diets. Cerebellar DNA of offspring was extracted at 2 and 120 days of life, nucleosides isolated and δ15N and δ13C characterized. Mean diet δ15N = 0.45±0.33‰, compared to cerebellar whole tissue and DNA δ15N = +4.1±0.7‰ and −4.5±0.4‰, respectively. Cerebellar deoxythymidine (dT), deoxycytidine (dC), deoxyadenosine (dA), and deoxyguanosine (dG) δ15N were +1.4±0.4, −2.1±0.9, −7.2±0.3, and −10.4±0.5‰, respectively. There were no changes in amino acid or deoxyribonucleoside δ15N due to dietary protein level. Using known metabolic relationships, we developed equations to calculate the intramolecular δ15N originating from aspartate (asp) in purines (pur) or pyrimidines (pyr), glutamine (glu), and glycine (gly) to be δ15NASP-PUR, δ15NASP-PYR, δ15NGLN, and δ15NGLY +11.9±2.3‰, +7.0±2.0‰, −9.1±2.4‰, and −31.8±8.9‰, respectively. A subset of twelve amino acids from food and brain had mean δ15N of 4.3±3.2‰ and 13.8±3.1‰, respectively, and δ15N for gly and asp were 12.6±2.2‰ and 15.2±0.8‰, respectively. A separate isotope tracer study detected no significant turnover of cerebellar DNA in the first six months of life. The large negative δ15N difference between gly and cerebellar purine N at the gly (7) position implies either that there is a major isotope effect during DNA synthesis, or that in utero gly has a different isotope ratio during rapid growth and metabolism than in adult life. Our data show that cerebellar nucleoside intramolecular δ15N vary over more than

  13. Synthesis of 5-aryl-4-(2-acetylaminobenzoyl)-1,2,3-triazoles with the /sup 15/N isotope at the terminal positions of the triazole rings and the tautomeric composition

    SciTech Connect

    Kurkovskaya, L.N.; Velezheva, V.S.; Sorokina, I.K.; Dmitrevskaya, L.I.; Zhil'nikov, V.G.

    1988-12-20

    A mixture of 4-(2-acetylaminobenzoyl)-5-phenyl(p-cumenyl)-1-/sup 15/N,2,3- and 4-(2-acetylaminobenzoyl)-5-phenyl(p-cumenyl)-1,2,3-/sup 15/N-triazoles was obtained from 1-acetyl-2-arylmethylene-3-indolinones and Na/sup 15/N/sub 3/ with the label at the terminal position. The tautomeric composition of the mixture, which corresponds to a state of equilibrium between the 2H and 3H forms of the triazole ring, was established by /sup 1/H (at low temperatures) and /sup 15/N NMR spectroscopy. The 4-(2-acetylaminobenzoyl)-5-aryl-1,2,3-triazoles are acylated at the sterically less hindered position 2 of the triazole ring.

  14. Uptake and fate of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in coastal marine biota determined using a stable isotopic tracer, (15)N - [RDX].

    PubMed

    Ballentine, Mark L; Ariyarathna, Thivanka; Smith, Richard W; Cooper, Christopher; Vlahos, Penny; Fallis, Stephen; Groshens, Thomas J; Tobias, Craig

    2016-06-01

    Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is globally one of the most commonly used military explosives and environmental contaminant. (15)N labeled RDX was added into a mesocosm containing 9 different coastal marine species in a time series experiment to quantify the uptake of RDX and assess the RDX derived (15)N retention into biota tissue. The (15)N attributed to munitions compounds reached steady state concentrations ranging from 0.04 to 0.67 μg (15)N g dw(-1), the bulk (15)N tissue concentration for all species was 1-2 orders of magnitude higher suggesting a common mechanism or pathway of RDX biotransformation and retention of (15)N. A toxicokinetic model was created that described the (15)N uptake, elimination, and transformation rates. While modeled uptake rates were within previous published values, elimination rates were several orders of magnitude smaller than previous studies ranging from 0.05 to 0.7 days(-1). These small elimination rates were offset by high rates of retention of (15)N previously not measured. Bioconcentration factors and related aqueous:organism ratios of compounds and tracer calculated using different tracer and non-tracer methods yielded a broad range of values (0.35-101.6 mL g(-1)) that were largely method dependent. Despite the method-derived variability, all values were generally low and consistent with little bioaccumulation potential. The use of (15)N labeled RDX in this study indicates four possible explanations for the observed distribution of compounds and tracer; each with unique potential implications for possible toxicological impacts in the coastal marine environment. PMID:27010164

  15. Continuous field measurement of N2O isotopologues using FTIR spectroscopy following 15N addition

    NASA Astrophysics Data System (ADS)

    Phillips, R. L.; Griffith, D. W.; Dijkstra, F. A.; Lugg, G.; Lawrie, R.; Macdonald, B.

    2012-12-01

    Anthropogenic additions of fertilizer nitrogen (N) have significantly increased the mole fraction of nitrous oxide (N2O) in the troposphere. Tracking the fate of fertilizer N and its transformation to N2O is important to advance knowledge of greenhouse gas emissions from soils. Transport and transformations are frequently studied using 15N labeling experiments, but instruments capable of continuous measurements of 15N-N2O at the surface of soil have only recently come to the fore. Our primary aim was to quantify emissions of N2O and the fraction of 15N emitted as N2O from an agricultural soil following 15N addition using a mobile Fourier Transform Infrared (FTIR) spectrometer. We set up a short-term field experiment on a coastal floodplain site near Nowra, New South Wales. We deployed an automated chamber system connected to a multi-pass cell (optical pathlength 24 m) and low resolution FTIR spectrometer to measure fluxes of all N2O isotopologues collected from five 0.25 m2 chambers every three hours. We measured N2O fluxes pre and post-application of 15N-labeled substrate as potassium nitrate (KNO3) or urea [CO(NH2)2] to the soil surface. Root mean square uncertainties for all isotopologue measurements were less than 0.3 nmol mol-1 for 1 minute average concentration measurements, and minimum detectable fluxes for each isotopologue were <0.1 ng N m-2 s-1. Emissions of all N2O isotopologues were evident immediately following 15N addition. Emissions of 14N15NO, 15N14NO and 15N15NO isotopologues subsided within 10 d, but 14N14NO fluxes were evident over the entire experiment. The figure provides an overview of the emissions. Cumulative 15N-N2O fluxes (sum of the three 15N isotopologues) per chamber for the 14 days following 15N addition ranged from 1.5 to 10.3 mg 15N-N2O m-2. The chambers were destructively sampled after 2 weeks and 15N analyzed in soil and plant material using isotope ratio mass spectrometry. Approximately 1% (range 0.7 - 1.9%) of the total amount of

  16. Stable isotope ratios as indicators of trophic status: Uncertainties imposed by geographic effects

    SciTech Connect

    Schell, D.M.

    1995-12-31

    Isotope ratios of carbon and nitrogen are often suggested as indicators to determine trophic status and carbon sources of marine organisms in explaining relative concentrations of pollutants. Whereas this technique is effective with organisms resident in ecosystems having homogeneous primary productivity regimes and uniform isotope ratios in the productivity base, it often is confounded by migratory movements by larger organisms across isotopic gradients. Tissues containing a temporal record such as baleen plates or whiskers show these effects clearly. Bowhead whales in Alaskan waters seasonally move across carbon isotope gradients of 5{per_thousand} in zooplankton and reflect these differences in the keratin of baleen plates and in overall body composition. However, no significant differences in {delta}{sup 15}N are evident regionally in northern Alaskan zooplankton. In contrast, the Southern Ocean is characterized by extreme latitudinal gradients in both {delta}{sup 13}C and {delta}{sup 15}N with the most pronounced effects occurring at the subtropical convergence. Prey taken by marine mammals south of this zone are depleted in both {sup 15}N and {sup 13}C by up to 8{per_thousand}. Data on southern right whales (Eubalaena glacialis), Bryde`s whale (Balaenoptera edenl), pygmy right whales (Caperea marginate) and antarctic fur seal (Arctocephalos gazella) show the effects of migratory movements across the gradient in both carbon and nitrogen isotope ratios. Similar patterns in marine mammal tissues from Australia, South Africa and South America indicate that the observed patterns are circumpolar. Within a given region, trophic effects shift {delta}{sup 15}N values consistent with observed feeding habits.

  17. Observation of kinetic tritium isotope effects by dynamic NMR. The tautomerism of porphyrin

    SciTech Connect

    Braun, J.; Limbach, H.H.; Williams, P.G.; Morimoto, Hiromi; Wemmer, D.E.

    1996-07-31

    As the knowledge of tritium isotope effects is desirable from a theoretical standpoint, we have applied {sup 3}H NMR in order to study these effects in the case of the double-hydron tautomerism of {sup 15} N-labeled porphyrin. In conclusion, the determination of kinetic tritium isotope effects is a powerful application of dynamic {sup 3}H NMR. In the case of the tautomerism of porphyrin, these effects support the stepwise hydron-tunneling mechanism and can serve to test multidimensional tunneling models in the future. 10 refs., 2 figs.

  18. Increased Plant Uptake of Nitrogen from 15N Depleted Fertilizer Using Plant Growth-Promoting Rhizobacteria

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The techniques of 15N isotope have been very useful for determining the behavior and fate of N in soil, including the use efficiency of applied N fertilizers by plants. Our objective in this study was to use 15N isotope techniques to demonstrate that a model plant growth-promoting rhizobacteria (PGP...

  19. Steady-State Nitrogen Isotope Effects of N2 and N2O Production in Paracoccus denitrificans

    PubMed Central

    Barford, Carol C.; Montoya, Joseph P.; Altabet, Mark A.; Mitchell, Ralph

    1999-01-01

    Nitrogen stable-isotope compositions (δ15N) can help track denitrification and N2O production in the environment, as can knowledge of the isotopic discrimination, or isotope effect, inherent to denitrification. However, the isotope effects associated with denitrification as a function of dissolved-oxygen concentration and their influence on the isotopic composition of N2O are not known. We developed a simple steady-state reactor to allow the measurement of denitrification isotope effects in Paracoccus denitrificans. With [dO2] between 0 and 1.2 μM, the N stable-isotope effects of NO3− and N2O reduction were constant at 28.6‰ ± 1.9‰ and 12.9‰ ± 2.6‰, respectively (mean ± standard error, n = 5). This estimate of the isotope effect of N2O reduction is the first in an axenic denitrifying culture and places the δ15N of denitrification-produced N2O midway between those of the nitrogenous oxide substrates and the product N2 in steady-state systems. Application of both isotope effects to N2O cycling studies is discussed. PMID:10049852

  20. Sinks for nitrogen inputs in terrestrial ecosystems: a meta-analysis of 15N tracer field studies

    USGS Publications Warehouse

    Templer, P.H.; Mack, M.C.; Chapin, F. S., III; Christenson, L.M.; Compton, J.E.; Crook, H.D.; Currie, W.S.; Curtis, C.J.; Dail, D.B.; D'Antonio, C. M.; Emmett, B.A.; Epstein, H.E.; Goodale, C.L.; Gundersen, P.; Hobbie, S.E.; Holland, K.; Hooper, D.U.; Hungate, B.A.; Lamontagne, S.; Nadelhoffer, K.J.; Osenberg, C.W.; Perakis, S.S.; Schleppi, P.; Schimel, J.; Schmidt, I.K.; Sommerkorn, M.; Spoelstra, J.; Tietema, A.; Wessel, W.W.; Zak, D.R.

    2012-01-01

    Effects of anthropogenic nitrogen (N) deposition and the ability of terrestrial ecosystems to store carbon (C) depend in part on the amount of N retained in the system and its partitioning among plant and soil pools. We conducted a meta-analysis of studies at 48 sites across four continents that used enriched 15N isotope tracers in order to synthesize information about total ecosystem N retention (i.e., total ecosystem 15N recovery in plant and soil pools) across natural systems and N partitioning among ecosystem pools. The greatest recoveries of ecosystem 15N tracer occurred in shrublands (mean, 89.5%) and wetlands (84.8%) followed by forests (74.9%) and grasslands (51.8%). In the short term (15N tracer application), total ecosystem 15N recovery was negatively correlated with fine-root and soil 15N natural abundance, and organic soil C and N concentration but was positively correlated with mean annual temperature and mineral soil C:N. In the longer term (3–18 months after 15N tracer application), total ecosystem 15N retention was negatively correlated with foliar natural-abundance 15N but was positively correlated with mineral soil C and N concentration and C: N, showing that plant and soil natural-abundance 15N and soil C:N are good indicators of total ecosystem N retention. Foliar N concentration was not significantly related to ecosystem 15N tracer recovery, suggesting that plant N status is not a good predictor of total ecosystem N retention. Because the largest ecosystem sinks for 15N tracer were below ground in forests, shrublands, and grasslands, we conclude that growth enhancement and potential for increased C storage in aboveground biomass from atmospheric N deposition is likely to be modest in these ecosystems. Total ecosystem 15N recovery decreased with N fertilization, with an apparent threshold fertilization rate of 46 kg N·ha-1·yr-1 above which most ecosystems showed net losses of applied 15N tracer in response to N fertilizer addition.

  1. Dual optical marker Raman characterization of strained GaN-channels on AlN using AlN/GaN/AlN quantum wells and {sup 15}N isotopes

    SciTech Connect

    Qi, Meng; Li, Guowang; Protasenko, Vladimir; Zhao, Pei; Verma, Jai; Song, Bo; Ganguly, Satyaki; Zhu, Mingda; Hu, Zongyang; Yan, Xiaodong; Xing, Huili Grace; Jena, Debdeep; Mintairov, Alexander

    2015-01-26

    This work shows that the combination of ultrathin highly strained GaN quantum wells embedded in an AlN matrix, with controlled isotopic concentrations of Nitrogen enables a dual marker method for Raman spectroscopy. By combining these techniques, we demonstrate the effectiveness in studying strain in the vertical direction. This technique will enable the precise probing of properties of buried active layers in heterostructures, and can be extended in the future to vertical devices such as those used for optical emitters and for power electronics.

  2. Modeling Non-Steady Isotopic Effects Caused by Biological Kinetic Transient Complexation During Denitrification in Soils

    NASA Astrophysics Data System (ADS)

    Maggi, F.; Riley, W. J.

    2008-12-01

    The composition and location of 15N atoms on N2O molecules has been used to characterize soil biological N cycling and N2O surface emissions. Besides the complexity of the processes related to N2O transformations and movements (e.g., chain-like denitrification reaction, soil moisture and temperature dynamics, aqueous and gaseous advection and diffusion) which make interpretation of the isotopic N2O composition very difficult, a theoretical aspect has been overlooked. The theoretical formulation of biological kinetic reactions in isotopic applications makes common use of first-order and quasi steady-state assumptions, according to which the rates of change of the concentration of intermediate complexes can be neglected. When isotopically-labeled reactants are used, these assumptions are not necessarily accurate since isotopic effects during complexation occur at orders of magnitude that compare with the truncation used under first-order and quasi steady-state conditions. Both assumptions, in fact, always lead to a constant fractionation factor and may therefore yield incorrect estimates of the isotopic effect and a misleading interpretation of the reaction signature. We have analyzed the isotopic signature of denitrification in biogeochemical soil systems reported by Menyailo and Hungate (2006), where high 15N2O enrichment during N2O production and inverse isotope fractionation during N2O consumption could not be explained with first-order kinetics and the Rayleigh equation, or with quasi steady-state Monod kinetics. When the quasi steady-state assumption was relaxed, transient Monod kinetics accounting for isotopic effect occurring at the complexes accurately reproduced the observations and aided in interpretation of experimental isotopic signatures. These results may imply a substantial revision in using the Rayleigh equation for interpretation and in modeling biological kinetic isotope fractionation with first-order kinetics or quasi steady state Monod kinetics.

  3. Investigations into the effect of diet on modern human hair isotopic values.

    PubMed

    O'Connell, T C; Hedges, R E

    1999-04-01

    Carbon and nitrogen isotopic analysis of body tissues is one of the few techniques that can furnish quantitative information about the diet of archaeological humans. The study of the effects of various diets on modern human isotopic values can help to refine palaeodietary theories, and such work also enables the testing of palaeodietary theories independent of archaeological remains and interpretations. This report discusses the use of modern human hair as a sample material for isotopic analysis. The biogenic carbon and nitrogen isotopic signal is well preserved in hair, and the isotopic values of the keratin can be related to diet. We show that atmospheric and cosmetic contamination of hair keratin does not appear to affect the measured isotopic values. In a small study of Oxford residents, we demonstrate that the magnitude of the nitrogen isotopic values of hair keratin reflects the proportion of animal protein consumed in the diet: omnivores and ovo-lacto-vegetarians have higher delta15N than vegans. There was an observed relationship between the reported amount of animal protein eaten (either meat or secondary animal products) and the nitrogen isotopic values within the two groups of omnivores and ovo-lacto-vegetarians, indicating that an increasing amount of animal protein in the diet results in an increase in the delta15N of hair keratin. This provides the first independent support for a long-held theory that, for individuals within a single population, a diet high in meat equates to elevated nitrogen isotopic values in the body relative to others eating less animal protein. The implications of such results for the magnitude of the trophic level effect are discussed. Results presented here also permit a consideration of the effects of a change of diet in the short and long term on hair keratin isotopic values. PMID:10229386

  4. Growth Retardation and Altered Isotope Composition As Delayed Effects of PCB Exposure in Daphnia magna.

    PubMed

    Ek, Caroline; Gerdes, Zandra; Garbaras, Andrius; Adolfsson-Erici, Margaretha; Gorokhova, Elena

    2016-08-01

    Trophic magnification factor (TMF) analysis employs stable isotope signatures to derive biomagnification potential for environmental contaminants. This approach relies on species δ(15)N values aligning with their trophic position (TP). This, however, may not always be true, because toxic exposure can alter growth and isotope allocation patterns. Here, effects of PCB exposure (mixture of PCB18, PCB40, PCB128, and PCB209) on δ(15)N and δ(13)C as well as processes driving these effects were explored using the cladoceran Daphnia magna. A two-part experiment assessed effects of toxic exposure during and after exposure; juvenile daphnids were exposed during 3 days (accumulation phase) and then allowed to depurate for 4 days (depuration phase). No effects on survival, growth, carbon and nitrogen content, and stable isotope composition were observed after the accumulation phase, whereas significant changes were detected in adults after the depuration phase. In particular, a significantly lower nitrogen content and a growth inhibition were observed, with a concomitant increase in δ(15)N (+0.1 ‰) and decrease in δ(13)C (-0.1 ‰). Although of low magnitude, these changes followed the predicted direction indicating that sublethal effects of contaminant exposure can lead to overestimation of TP and hence underestimated TMF. PMID:27367056

  5. Experimental plant for simultaneous production of (14)N and (15)N by (15)N/(14)N exchange in NO, NO(2)-HNO(3) system under pressure.

    PubMed

    Axente, Damian; Marcu, Cristina; Muresan, Ancuţa; Kaucsar, Martin; Misan, Ioan; Popeneciu, Gabriel; Gligan, Nicolae; Cristea, Gabriela

    2010-06-01

    An experimental study on (14)N and (15)N simultaneous separation using the chemical exchange in NO, NO(2)-HNO(3) system under pressure is presented. The influence of the pressure and of the interstage 10 M HNO(3) flow rate on the separation of (14)N and (15)N was measured on a packed column with product and waste refluxers. At steady state and 1.8 atm (absolute), the isotopic concentration at the bottom of the separation column was 0.563 at% (15)N, and in the top of the column was 0.159 at% (15)N. The height equivalent to a theoretical plate and interstage 10 M HNO(3) flow rate values, obtained in these experimental conditions, allows the separation of (14)N highly depleted of (15)N and of (15)N at 99 at% (15)N concentration. PMID:20582793

  6. THE EFFECTS OF PARAMAGNETIC RELAXATION REAGENTS ON 15N SPIN RELAXATION AND THE USE OF GD(DPM)3 AS A NITROGEN-15 NUCLEAR MAGNETIC RESONANCE SPIN LABEL

    EPA Science Inventory

    Electron-nuclear relaxation times (T(1) sup e's) for (15)N and (13)C in natural abundance are measured for a series of amines of a wide range of pK(a)s using four paramagnetic relaxation reagents that are soluable in organic solutions. Cr(acac)3 and Cr(dpm)3 are seen to affect th...

  7. Pollution and Climate Effects on Tree-Ring Nitrogen Isotopes

    NASA Astrophysics Data System (ADS)

    Savard, M. M.; Bégin, C.; Marion, J.; Smirnoff, A.

    2009-04-01

    BACKGROUND Monitoring of nitrous oxide concentration only started during the last 30 years in North America, but anthropogenic atmospheric nitrogen has been significantly emitted over the last 150 years. Can geochemical characteristics of tree rings be used to infer past changes in the nitrogen cycle of temperate regions? To address this question we use nitrogen stable isotopes in 125 years-long ring series from beech specimens (Fagus grandifolia) of the Georgian Bay Islands National Park (eastern Ontario), and pine (Pinus strobus) and beech trees of the Arboretum Morgan near Montreal (western Quebec). To evaluate the reliability of the N stable isotopes in wood treated for removal of soluble materials, we tested both tree species from the Montreal area. The reproducibility from tree to tree was excellent for both pine and beech trees, the isotopic trends were strongly concordant, and they were not influenced by the heartwood-sapwood transition zone. The coherence of changes of the isotopic series observed for the two species suggests that their tree-ring N isotopic values can serve as environmental indicator. RESULTS AND INTERPRETATION In Montreal and Georgian Bay, the N isotopes show strong and similar parallel agreement (Gleichlaufigkeit test) with the climatic parameters. So in fact, the short-term isotopic fluctuations correlate directly with summer precipitation and inversely with summer and spring temperature. A long-term decreasing isotope trend in Montreal indicates progressive changes in soil chemistry after 1951. A pedochemical change is also inferred for the Georgian Bay site on the basis of a positive N isotopic trend initiated after 1971. At both sites, the long-term ^15N series correlate with a proxy for NOx emissions (Pearson correlation), and carbon-isotope ring series suggest that the same trees have been impacted by phytotoxic pollutants (Savard et al., 2009a). We propose that the contrasted long-term nitrogen-isotope changes of Montreal and

  8. Complete fusion of 15N+27Al

    NASA Astrophysics Data System (ADS)

    Prosser, F. W., Jr.; Racca, R. A.; Daneshvar, K.; Geesaman, D. F.; Henning, W.; Kovar, D. G.; Rehm, K. E.; Tabor, S. L.

    1980-05-01

    The total fusion cross section for the system 15N + 27Al has been measured over an energy range 27 MeV<=Elab<=70 MeV by detection of the fusion-evaporation residues. In addition elastic scattering was measured at six energies and fitted by optical model calculations. The fusion cross section for the system saturates at 1150+/-50 mb. The data can be well described by the model of Glas and Mosel, using a reasonable set of parameters. The model of Horn and Ferguson also describes the data well if an appropriate charge radius is used. Comparison is made between these results and the fusion cross sections for 16O + 26Mg and 18O + 24Mg, which lead to the same compound nucleus. The results for 15N + 27Al are quite similar to those for 18O + 24Mg, and the differences between the fusion cross sections for these two systems and those for 16O + 26Mg may be evidence for an entrance channel effect. NUCLEAR REACTIONS 15N+27Al, Elab=27-70 MeV; measured σfusion(E) measured dσdΩ elastic scattering; data fitted with Glas and Mosel model, Horn and Ferguson model.

  9. Effects of fasting and nutritional restriction on the isotopic ratios of nitrogen and carbon: a meta-analysis.

    PubMed

    Hertz, Eric; Trudel, Marc; Cox, Marlin K; Mazumder, Asit

    2015-11-01

    Many organisms experience fasting in their life time, and this physiological process has the potential to alter stable isotope values of organisms, and confound interpretation of food web studies. However, previous studies on the effects of fasting and starvation on stable isotopes show disparate results, and have never been quantitatively synthesized. We performed a laboratory experiment and meta-analysis to determine how stable isotopes of δ (15)N and δ (13)C change with fasting, and we tested whether moderators such as taxa and tissue explain residual variation. We collected literature data from a wide variety of taxa and tissues. We surveyed over 2000 papers, and of these, 26 met our selection criteria, resulting in 51 data points for δ (15)N, and 43 data points for δ (13)C. We determine that fasting causes an average increase in the isotopic value of organisms of 0.5‰ for δ (15)N and that the only significant moderator is tissue type. We find that the overall effect size for δ (13)C is not significant, but when the significant moderator of tissue is considered, significant increases in blood and whole organisms are seen with fasting. Our results show that across tissues and taxa, the nutritional status of an organism must be considered when interpreting stable isotope data, as fasting can cause large differences in stable isotope values that would be otherwise attributed to other factors. PMID:26640663

  10. Isotopic Incorporation and the Effects of Fasting and Dietary Lipid Content on Isotopic Discrimination in Large Carnivorous Mammals.

    PubMed

    Rode, K D; Stricker, C A; Erlenbach, J; Robbins, C T; Cherry, S G; Newsome, S D; Cutting, A; Jensen, S; Stenhouse, G; Brooks, M; Hash, A; Nicassio, N

    2016-01-01

    There has been considerable emphasis on understanding isotopic discrimination for diet estimation in omnivores. However, discrimination may differ for carnivores, particularly species that consume lipid-rich diets. Here, we examined the potential implications of several factors when using stable isotopes to estimate the diets of bears, which can consume lipid-rich diets and, alternatively, fast for weeks to months. We conducted feeding trials with captive brown bears (Ursus arctos) and polar bears (Ursus maritimus). As dietary lipid content increased to ∼90%, we observed increasing differences between blood plasma and diets that had not been lipid extracted (∆(13)Ctissue-bulk diet) and slightly decreasing differences between plasma δ(13)C and lipid-extracted diet. Plasma Δ(15)Ntissue-bulk diet increased with increasing protein content for the four polar bears in this study and data for other mammals from previous studies that were fed purely carnivorous diets. Four adult and four yearling brown bears that fasted 120 d had plasma δ(15)N values that changed by <±2‰. Fasting bears exhibited no trend in plasma δ(13)C. Isotopic incorporation in red blood cells and whole blood was ≥6 mo in subadult and adult bears, which is considerably longer than previously measured in younger and smaller black bears (Ursus americanus). Our results suggest that short-term fasting in carnivores has minimal effects on δ(13)C and δ(15)N discrimination between predators and their prey but that dietary lipid content is an important factor directly affecting δ(13)C discrimination and indirectly affecting δ(15)N discrimination via the inverse relationship with dietary protein content. PMID:27153128

  11. The use of delta(15)N in assessing sewage stress on coral reefs.

    PubMed

    Risk, Michael J; Lapointe, Brian E; Sherwood, Owen A; Bedford, Bradley J

    2009-06-01

    While coral reefs decline, scientists argue, and effective strategies to manage land-based pollution lag behind the extent of the problem. There is need for objective, cost-effective, assessment methods. The measurement of stable nitrogen isotope ratios, delta(15)N, in tissues of reef organisms shows promise as an indicator of sewage stress. The choice of target organism will depend upon study purpose, availability, and other considerations such as conservation. Algae are usually plentiful and have been shown faithfully to track sewage input. The organic matrix of bivalve shells can provide time series spanning, perhaps, decades. Gorgonians have been shown to track sewage, and can provide records potentially centuries-long. In areas where baseline data are lacking, which is almost everywhere, delta(15)N in gorgonians can provide information on status and trends. In coral tissue, delta(15)N combined with insoluble residue determination can provide information on both sewage and sediment stress in areas lacking baseline data. In the developed world, delta(15)N provides objective assessment in a field complicated by conflicting opinions. Sample handling and processing are simple and analysis costs are low. This is a method deserving widespread application. PMID:19286230

  12. Evidence for bias in measured δ15N values of terrestrial and aquatic organic materials due to pre-analysis acid treatment methods.

    PubMed

    Brodie, Chris R; Heaton, Tim H E; Leng, Melanie J; Kendrick, Christopher P; Casford, James S L; Lloyd, Jeremy M

    2011-04-30

    We investigate the effect of acid treatment methods on δ(15)N values from a range of environmental organic materials in the context of the increased application of 'dual-mode' isotope analysis (the simultaneous measurement of δ(13)C and δ(15)N from the same acid-treated sample). Three common methods are compared; (i) untreated samples; (ii) acidification followed by sequential water rinse (rinse method); and (iii) acidification in silver capsules (capsule method). The influence of capsule type (silver and tin) on δ(15)N is also independently assessed (as the capsule and rinse methods combust samples in different capsules; silver and tin, respectively). We find significant differences in δ(15)N values between methods and the precision of any one method varies significantly between sample materials and above the instrument precision (>0.3‰). The δ(15)N values of untreated samples did not produce the most consistent data on all sample materials. In addition, the capsule type appears to influence the measured δ(15)N value of some materials, particularly those combusted only in silver capsules. We also compare the new δ(15)N data with previously published δ(13)C data on the same materials. The response of δ(13)C and δ(15)N within and between methods and sample materials to acidification appears to be relatively disproportionate, which can influence the environmental interpretation of the measured data. In addition, statistical methods used to estimate inorganic nitrogen are shown to be seriously flawed. PMID:21452387

  13. Natural (15)N Abundance in Key Amino Acids from Lamb Muscle: Exploring a New Horizon in Diet Authentication and Assessment of Feed Efficiency in Ruminants.

    PubMed

    Cantalapiedra-Hijar, Gonzalo; Ortigues-Marty, Isabelle; Schiphorst, Anne-Marie; Robins, Richard J; Tea, Illa; Prache, Sophie

    2016-05-25

    Natural (15)N abundance (δ(15)N) varies between individual amino acids (AAs). We hypothesized that δ(15)N of nontransaminating and essential AAs ("source" AAs, such as phenylalanine) present in animal tissues could be used as a marker of dietary origin, whereas δ(15)N of transaminating AAs ("trophic" AAs, such as glutamic acid) could give more detailed insights into animal feed efficiency. Two diets based on dehydrated Lucerne pellets were tested in growing lambs, which promoted different feed efficiencies. No dietary effects were noted on δ(15)N of any AAs analyzed in lamb muscle. In addition, δ(15)N of phenylalanine was unexpectedly similar to that of glutamic acid, suggesting that δ(15)N of AAs is significantly derived from the metabolism of the rumen microbiota and, thus, are not suited for diet authentication in ruminants. In contrast, the δ(15)N of transaminating AAs facilitates an improved prediction of animal feed efficiency compared to the classical isotopic bulk N analysis. PMID:27148901

  14. Difference in delta(15)N signatures between nodulated roots and shoots of soybean is indicative of the contribution of symbiotic N(2) fixation to plant N.

    PubMed

    Wanek, Wolfgang; Arndt, Stefan K

    2002-05-01

    Symbiotic N(2) fixation has a variable effect on the (15)N abundance of different parts of legumes. Increases in fixation result in (15)N enrichment of nodules, while decreases, in combination with an increased uptake of mineral N, result in (15)N depletion of the root system. The difference between soybean shoot and below-ground delta(15)N (Deltadelta(15)N=delta(15)N(shoot)-delta(15)N(belowground)) was assessed in hydroponic culture over a range of rates of supply of mineral N. The fractional contribution of N(2) fixation to N uptake (%Ndfa) was determined using the natural abundance (NA) technique with ryegrass as a reference plant. Deltadelta(15)N and %Ndfa were highly correlated, and the relationship was tested using the same soybean cultivar grown in pots in N-rich soil. Estimates of %Ndfa derived from the NA method and from the Deltadelta(15)N approach yielded near-identical values. A literature survey showed similar relationships between %Ndfa and Deltadelta(15)N with different growth stages of soybeans grown under glasshouse and field conditions, different cowpea (Vigna unguiculata) cultivars in the field, and tagasaste (Chamaecytisus proliferus) in hydroponic culture. Possible confounding and species-specific (either plant or Rhizobium spp.) influences are discussed. The difference in delta(15)N signatures between nodulated roots and shoots is confirmed as a robust means of quantifying %Ndfa: it is independent of reference plants and offers the possibility of estimating %Ndfa in soils where the isotope composition of mineral N closely matches that of atmospheric N(2). PMID:11971922

  15. Carbon isotope effects associated with aceticlastic methanogenesis

    NASA Technical Reports Server (NTRS)

    Gelwicks, J. T.; Risatti, J. B.; Hayes, J. M.

    1994-01-01

    The carbon isotope effects associated with synthesis of methane from acetate have been determined for Methanosarcina barkeri 227 and for methanogenic archaea in sediments of Wintergreen Lake, Michigan. At 37 degrees C, the 13C isotope effect for the reaction acetate (methyl carbon) --> methane, as measured in replicate experiments with M. barkeri, was - 21.3% +/- 0.3%. The isotope effect at the carboxyl portion of acetate was essentially equal, indicating participation of both positions in the rate-determining step, as expected for reactions catalyzed by carbon monoxide dehydrogenase. A similar isotope effect, - 19.2% +/- 0.3% was found for this reaction in the natural community (temperature = 20 degrees C). Given these observations, it has been possible to model the flow of carbon to methane within lake sediment communities and to account for carbon isotope compositions of evolving methane. Extension of the model allows interpretation of seasonal fluctuations in 13C contents of methane in other systems.

  16. Carbon isotope effects associated with aceticlastic methanogenesis.

    PubMed

    Gelwicks, J T; Risatti, J B; Hayes, J M

    1994-02-01

    The carbon isotope effects associated with synthesis of methane from acetate have been determined for Methanosarcina barkeri 227 and for methanogenic archaea in sediments of Wintergreen Lake, Michigan. At 37 degrees C, the 13C isotope effect for the reaction acetate (methyl carbon) --> methane, as measured in replicate experiments with M. barkeri, was - 21.3% +/- 0.3%. The isotope effect at the carboxyl portion of acetate was essentially equal, indicating participation of both positions in the rate-determining step, as expected for reactions catalyzed by carbon monoxide dehydrogenase. A similar isotope effect, - 19.2% +/- 0.3% was found for this reaction in the natural community (temperature = 20 degrees C). Given these observations, it has been possible to model the flow of carbon to methane within lake sediment communities and to account for carbon isotope compositions of evolving methane. Extension of the model allows interpretation of seasonal fluctuations in 13C contents of methane in other systems. PMID:11536629

  17. Carbon isotope effects associated with aceticlastic methanogenesis.

    PubMed Central

    Gelwicks, J T; Risatti, J B; Hayes, J M

    1994-01-01

    The carbon isotope effects associated with synthesis of methane from acetate have been determined for Methanosarcina barkeri 227 and for methanogenic archaea in sediments of Wintergreen Lake, Michigan. At 37 degrees C, the 13C isotope effect for the reaction acetate (methyl carbon) --> methane, as measured in replicate experiments with M. barkeri, was - 21.3% +/- 0.3%. The isotope effect at the carboxyl portion of acetate was essentially equal, indicating participation of both positions in the rate-determining step, as expected for reactions catalyzed by carbon monoxide dehydrogenase. A similar isotope effect, - 19.2% +/- 0.3% was found for this reaction in the natural community (temperature = 20 degrees C). Given these observations, it has been possible to model the flow of carbon to methane within lake sediment communities and to account for carbon isotope compositions of evolving methane. Extension of the model allows interpretation of seasonal fluctuations in 13C contents of methane in other systems. PMID:11536629

  18. Effect of salinity and water stress during the reproductive stage on growth, ion concentrations, Delta 13C, and delta 15N of durum wheat and related amphiploids.

    PubMed

    Yousfi, Salima; Serret, Maria Dolores; Voltas, Jordi; Araus, José Luis

    2010-08-01

    The physiological performance of durum wheat and two related amphiploids was studied during the reproductive stage under different combinations of salinity and irrigation. One triticale, one tritordeum, and four durum wheat genotypes were grown in pots in the absence of stress until heading, when six different treatments were imposed progressively. Treatments resulted from the combination of two irrigation regimes (100% and 35% of container water capacity) with three levels of water salinity (1.8, 12, and 17 dS m(-1)), and were maintained for nearly 3 weeks. Gas exchange and chlorophyll fluorescence and content were measured prior to harvest; afterwards shoot biomass and height were recorded, and Delta(13)C, delta(15)N, and the concentration of nitrogen (N), phosphorus, and several ions (K(+), Na(+), Ca(2+), Mg(2+)) were analysed in shoot material. Compared with control conditions (full irrigation with Hoagland normal) all other treatments inhibited photosynthesis through stomatal closure, accelerated senescence, and decreased biomass. Full irrigation with 12 dS m(-1) outperformed other stress treatments in terms of biomass production and physiological performance. Biomass correlated positively with N and delta(15)N, and negatively with Na(+) across genotypes and fully irrigated treatments, while relationships across deficit irrigation conditions were weaker or absent. Delta(13)C did not correlate with biomass across treatments, but it was the best trait correlating with phenotypic differences in biomass within treatments. Tritordeum produced more biomass than durum wheat in all treatments. Its low Delta(13)C and high K(+)/Na(+) ratio, together with a high potential growth, may underlie this finding. Mechanisms relating delta(15)N and Delta(13)C to biomass are discussed. PMID:20660293

  19. Transient competitive complexation in biological kinetic isotope fractionation explains non-steady isotopic effects: Theory and application to denitrification in soils

    SciTech Connect

    Maggi, F.M.; Riley, W.J.

    2009-06-01

    The theoretical formulation of biological kinetic reactions in isotopic applications often assume first-order or Michaelis-Menten-Monod kinetics under the quasi-steady-state assumption to simplify the system kinetics. However, isotopic e ects have the same order of magnitude as the potential error introduced by these simpli cations. Both formulations lead to a constant fractionation factor which may yield incorrect estimations of the isotopic effect and a misleading interpretation of the isotopic signature of a reaction. We have analyzed the isotopic signature of denitri cation in biogeochemical soil systems by Menyailo and Hungate [2006], where high {sup 15}N{sub 2}O enrichment during N{sub 2}O production and inverse isotope fractionation during N{sub 2}O consumption could not be explained with first-order kinetics and the Rayleigh equation, or with the quasi-steady-state Michaelis-Menten-Monod kinetics. When the quasi-steady-state assumption was relaxed, transient Michaelis-Menten-Monod kinetics accurately reproduced the observations and aided in interpretation of experimental isotopic signatures. These results may imply a substantial revision in using the Rayleigh equation for interpretation of isotopic signatures and in modeling biological kinetic isotope fractionation with first-order kinetics or quasi-steady-state Michaelis-Menten-Monod kinetics.

  20. 13C and 15N fractionation of CH4/N2 mixtures during photochemical aerosol formation: Relevance to Titan

    NASA Astrophysics Data System (ADS)

    Sebree, Joshua A.; Stern, Jennifer C.; Mandt, Kathleen E.; Domagal-Goldman, Shawn D.; Trainer, Melissa G.

    2016-05-01

    The ratios of the stable isotopes that comprise each chemical species in Titan's atmosphere provide critical information towards understanding the processes taking place within its modern and ancient atmosphere. Several stable isotope pairs, including 12C/13C and 14N/15N, have been measured in situ or probed spectroscopically by Cassini-borne instruments, space telescopes, or through ground-based observations. Current attempts to model the observed isotope ratios incorporate fractionation resulting from atmospheric diffusion, hydrodynamic escape, and primary photochemical processes. However, the effect of a potentially critical pathway for isotopic fractionation - organic aerosol formation and subsequent deposition onto the surface of Titan - has not been considered due to insufficient data regarding fractionation during aerosol formation. To better understand the nature of this process, we have conducted a laboratory study to measure the isotopic fractionation associated with the formation of Titan aerosol analogs, commonly referred to as 'tholins', via far-UV irradiation of several methane (CH4) and dinitrogen (N2) mixtures. Analysis of the δ13C and δ15N isotopic signatures of the photochemical aerosol products using an isotope ratio mass spectrometer (IRMS) show that fractionation direction and magnitude are dependent on the initial bulk composition of the gas mixture. In general, the aerosols showed enrichment in 13C and 14N, and the observed fractionation trends can provide insight into the chemical mechanisms controlling photochemical aerosol formation.

  1. Fire effects on stable isotopes in a Sierran forested watershed.

    PubMed

    Saito, Laurel; Miller, Wally W; Johnson, Dale W; Qualls, Robert G; Provencher, Louis; Carroll, Erin; Szameitat, Peter

    2007-01-01

    This study tested the hypothesis that stable C and N isotope values in surface soil and litter would be increased by fire due to volatilization of lighter isotopes. The hypothesis was tested by: (1) performing experimental laboratory burns of organic and mineral soil materials from a watershed at combinations of temperature ranging 100 to 600 degrees C and duration ranging from 1 to 60 min; (2) testing field samples of upland soils before, shortly after, and 1 yr following a wildfire in the same watershed; and (3) testing field soil samples from a down-gradient ash/sediment depositional area in a riparian zone following a runoff event after the wildfire. Muffle furnace results indicated the most effective temperature range for using stable isotopes for tracing fire impacts is 200 to 400 degrees C because lower burn temperatures may not produce strong isotopic shifts, and at temperatures>or=600 degrees C, N and C content of residual material is too low. Analyses of field soil samples were inconclusive: there was a slightly significant effect of the wildfire on delta15N values in upland watershed analyses 1 yr postburn, while riparian zone analyses results indicated that delta13C values significantly decreased approximately 0.71 per thousand over a 9 mo post-fire period (p=0.015), and ash/sediment layer delta13C values were approximately 0.65 per thousand higher than those in the A horizon. The lack of field confirmation may have been due to overall wildfire burn temperatures being <200 degrees C and/or microbial recovery and vegetative growth in the field. Thus, the muffle furnace experiment supported the hypothesis, but it is as yet unconfirmed by actual wildfire field data. PMID:17215216

  2. Quantifying nitrate retention processes in a riparian buffer zone using the natural abundance of 15N in NO3-.

    PubMed

    Dhondt, Karel; Boeckx, Pascal; Van Cleemput, Oswald; Hofman, Georges

    2003-01-01

    Quantifying the relative importance of denitrification and plant uptake to groundwater nitrate retention in riparian zones may lead to methods optimising the construction of riparian zones for water pollution control. The natural abundance of 15N in NO3- has been shown to be an interesting tool for providing insights into the NO3- retention processes occurring in riparian zones. In this study, 15N isotope fractionation (variation in delta15N of the residual NO3-) due to denitrification and due to plant uptake was measured in anaerobic soil slurries at different temperatures (5, 10 and 15 degrees C) and in hydroponic systems with different plant species (Lolium perenne L., Urtica dioica L. and Epilobium hirsutum L.). It was found that temperature had no significant effect on isotope fractionation during denitrification, which resulted in a 15N enrichment factor epsilonD of -22.5 +/- 0.6 per thousand. On the other hand, nitrate uptake by plants resulted in 15N isotope fractionation, but was independent of plant species, leading to a 15N enrichment factor epsilonP of -4.4 +/- 0.3 per thousand. By relating these two laboratory-defined enrichment factors to a field enrichment factor for groundwater nitrate retention during the growing season (epsilonR = -15.5 +/- 1.0 per thousand ), the contribution of denitrification and plant uptake to groundwater nitrate retention could be calculated. The relative importance of denitrification and plant uptake to groundwater nitrate retention in the riparian buffer zone was 49 and 51% during spring, 53 and 47% during summer, and 75 and 25% during autumn. During wintertime, high micropore dissolved organic carbon (DOC) concentrations and low redox potentials due to decomposition of the highly productive riparian vegetation probably resulted in a higher denitrification rate and favoured other nitrate retention processes such as nitrate immobilisation or dissimilatory nitrate reduction to ammonium (DNRA). This could have biased the 15N

  3. Compound specific amino acid δ15N in marine sediments: A new approach for studies of the marine nitrogen cycle

    NASA Astrophysics Data System (ADS)

    Batista, Fabian C.; Ravelo, A. Christina; Crusius, John; Casso, Michael A.; McCarthy, Matthew D.

    2014-10-01

    The nitrogen (N) isotopic composition (δ15N) of bulk sedimentary N (δ15Nbulk) is a common tool for studying past biogeochemical cycling in the paleoceanographic record. Empirical evidence suggests that natural fluctuations in the δ15N of surface nutrient N are reflected in the δ15N of exported planktonic biomass and in sedimentary δ15Nbulk. However, δ15Nbulk is an analysis of total combustible sedimentary N, and therefore also includes mixtures of N sources and/or selective removal or preservation of N-containing compounds. Compound-specific nitrogen isotope analyses of individual amino acids (δ15NAA) are novel measurements with the potential to decouple δ15N changes in nutrient N from trophic effects, two main processes that can influence δ15Nbulk records. As a proof of concept study to examine how δ15NAA can be applied in marine sedimentary systems, we compare the δ15NAA signatures of surface and sinking POM sources with shallow surface sediments from the Santa Barbara Basin, a sub-oxic depositional environmental that exhibits excellent preservation of sedimentary organic matter. Our results demonstrate that δ15NAA signatures of both planktonic biomass and sinking POM are well preserved in such surface sediments. However, we also observed an unexpected inverse correlation between δ15N value of phenylalanine (δ15NPhe; the best AA proxy for N isotopic value at the base of the food web) and calculated trophic position. We used a simple N isotope mass balance model to confirm that over long time scales, δ15NPhe values should in fact be directly dependent on shifts in ecosystem trophic position. While this result may appear incongruent with current applications of δ15NAA in food webs, it is consistent with expectations that paleoarchives will integrate N dynamics over much longer timescales. We therefore propose that for paleoceanographic applications, key δ15NAA parameters are ecosystem trophic position, which determines relative partitioning of 15N

  4. Food webs in Mongolian grasslands: the analysis of 13C and 15N natural abundances.

    PubMed

    Kohzu, Ayato; Iwata, T; Kato, M; Nishikawa, J; Wada, Eitaro; Amartuvshin, N; Namkhaidorj, B; Fujita, N

    2009-09-01

    Overgrazing often lowers species richness and productivity of grassland communities. For Mongolian grassland ecosystems, a lack of detailed information about food-web structures makes it difficult to predict the effects of overgrazing on species diversity and community composition. We analysed the delta13C and delta15N signatures of herbaceous plants, arthropods (grouped by feeding habit), wild and domestic mammals, and humans in central Mongolia to understand the predominant food-web pathways in this grassland ecosystem. The delta13C and delta15N values of mammals showed little variation within species, but varied considerably with slope position for arthropods. The apparent isotopic discrimination between body tissue and hair of mammals was estimated as 2.0 per thousand for delta13C and 2.1 per thousand for delta15N, which was large enough to cause overestimation of the trophic level of mammals if not taken into account when using hair samples to measure isotopic enrichment. PMID:19507080

  5. Isotope effects of hydrogen and atom tunnelling

    NASA Astrophysics Data System (ADS)

    Buchachenko, A. L.; Pliss, E. M.

    2016-06-01

    The abnormally high mass-dependent isotope effects in liquid-phase hydrogen (deuterium) atom transfer reactions, which are customarily regarded as quantum effects, are actually the products of two classical effects, namely, kinetic and thermodynamic ones. The former is determined by the rate constants for atom transfer and the latter is caused by nonbonded (or noncovalent) isotope effects in the solvation of protiated and deuterated reacting molecules. This product can mimic the large isotope effects that are usually attributed to tunnelling. In enzymatic reactions, tunnelling is of particular interest; its existence characterizes an enzyme as a rigid molecular machine in which the residence time of reactants on the reaction coordinate exceeds the waiting time for the tunnelling event. The magnitude of isotope effect becomes a characteristic parameter of the internal dynamics of the enzyme catalytic site. The bibliography includes 61 references.

  6. (15)N NMR studies of a nitrile-modified nucleoside.

    PubMed

    Gillies, Anne T; Gai, Xin Sonia; Buckwalter, Beth L; Fenlon, Edward E; Brewer, Scott H

    2010-12-30

    Nitrile-modified molecules have proven to be excellent probes of local environments in biomolecules via both vibrational and fluorescence spectroscopy. The utility of the nitrile group as a spectroscopic probe has been expanded here to (15)N NMR spectroscopy by selective (15)N incorporation. The (15)N NMR chemical shift (δ((15)N)) of the (15)N-labeled 5-cyano-2'-deoxyuridine (C(15)NdU, 1a) was found to change from 153.47 to 143.80 ppm in going from THF-d(8) to D(2)O. A 0.81 ppm downfield shift was measured upon formation of a hydrogen-bond-mediated heterodimer between 2,6-diheptanamidopyridine and a silyl ether analogue of 1a in chloroform, and the small intrinsic temperature dependence of δ((15)N) of C(15)NdU was measured as a 0.38 ppm downfield shift from 298 to 338 K. The experiments were complemented with density functional theory calculations exploring the effect of solvation on the (15)N NMR chemical shift. PMID:21126044

  7. Biosynthetic uniform 13C,15N-labelling of zervamicin IIB. Complete 13C and 15N NMR assignment.

    PubMed

    Ovchinnikova, Tatyana V; Shenkarev, Zakhar O; Yakimenko, Zoya A; Svishcheva, Natalia V; Tagaev, Andrey A; Skladnev, Dmitry A; Arseniev, Alexander S

    2003-01-01

    Zervamicin IIB is a member of the alpha-aminoisobutyric acid containing peptaibol antibiotics. A new procedure for the biosynthetic preparation of the uniformly 13C- and 15N-enriched peptaibol is described This compound was isolated from the biomass of the fungus-producer Emericellopsis salmosynnemata strain 336 IMI 58330 obtained upon cultivation in the totally 13C, 15N-labelled complete medium. To prepare such a medium the autolysed biomass and the exopolysaccharides of the obligate methylotrophic bacterium Methylobacillus flagellatus KT were used. This microorganism was grown in totally 13C, 15N-labelled minimal medium containing 13C-methanol and 15N-ammonium chloride as the only carbon and nitrogen sources. Preliminary NMR spectroscopic analysis indicated a high extent of isotope incorporation (> 90%) and led to the complete 13C- and 15N-NMR assignment including the stereospecific assignment of Aib residues methyl groups. The observed pattern of the structurally important secondary chemical shifts of 1H(alpha), 13C=O and 13C(alpha) agrees well with the previously determined structure of zervamicin IIB in methanol solution. PMID:14658801

  8. Isotope effect of mercury diffusion in air

    PubMed Central

    Koster van Groos, Paul G.; Esser, Bradley K.; Williams, Ross W.; Hunt, James R.

    2014-01-01

    Identifying and reducing impacts from mercury sources in the environment remains a considerable challenge and requires process based models to quantify mercury stocks and flows. The stable isotope composition of mercury in environmental samples can help address this challenge by serving as a tracer of specific sources and processes. Mercury isotope variations are small and result only from isotope fractionation during transport, equilibrium, and transformation processes. Because these processes occur in both industrial and environmental settings, knowledge of their associated isotope effects is required to interpret mercury isotope data. To improve the mechanistic modeling of mercury isotope effects during gas phase diffusion, an experimental program tested the applicability of kinetic gas theory. Gas-phase elemental mercury diffusion through small bore needles from finite sources demonstrated mass dependent diffusivities leading to isotope fractionation described by a Rayleigh distillation model. The measured relative atomic diffusivities among mercury isotopes in air are large and in agreement with kinetic gas theory. Mercury diffusion in air offers a reasonable explanation of recent field results reported in the literature. PMID:24364380

  9. Individual protein balance strongly influences δ15N and δ13C values in Nile tilapia, Oreochromis niloticus

    NASA Astrophysics Data System (ADS)

    Gaye-Siessegger, Julia; Focken, Ulfert; Abel, Hansjörg; Becker, Klaus

    Although stable isotope ratios in animals have often been used as indicators of the trophic level and for the back-calculation of diets, few experiments have been done under standardized laboratory conditions to investigate factors influencing δ15N and δ13C values. An experiment using Nile tilapia [Oreochromis niloticus (L.)] was therefore carried out to test the effect of different dietary protein contents (35.4, 42.3, and 50.9%) on δ15N and δ13C values of the whole tilapia. The fish were fed the isoenergetic and isolipidic semi-synthetic diets at a relatively low level. δ15N and δ13C values of the lipid-free body did not differ between the fish fed the diets with different protein contents, but the trophic shift for N and C isotopes decreased with increasing protein accretion in the individual fish, for N from 6.5‰ to 4‰ and for C in the lipid-free body from 4‰ to 2.5‰. This is the first study showing the strong influence of the individual protein balance to the degree to which the isotopic signature of dietary protein was modified in tissue protein of fish. The extrapolation of the trophic level or the reconstruction of the diet of an animal from stable isotope ratios without knowledge of the individual physiological condition and the feeding rate may lead to erroneous results.

  10. Synthesis and biosynthesis of {sup 13}C-, {sup 15}N-labeled deoxynucleosides useful for biomolecular structural determinations

    SciTech Connect

    Ashburn, D.A.; Garcia, K.; Hanners, J.L.; Silks, L.A. III; Unkefer, C.J.

    1994-12-01

    Currently, there is a great emphasis on elucidating the structure, function, and dynamics of DNA. Much of the research involved in this study uses nuclear magnetic resonance (NMR) spectroscopy. Effective use of NMR spectroscopy for DNA molecules with mw > 10,000 requires stable isotope enrichment. We present strategies for site-specific isotopic labeling of the purine bases adenosine and guanosine and the biosynthesis of (U-{sup 13}C, {sup 15}N) DNA from methylotropic bacteria. With commercially available 6-chloropurine, an effective two-step route leads to 2{prime}-deoxy-(amino-{sup 15}N)adenosine (dA). The resulting d(amino-{sup 15}N)A is used in a series of reactions to synthesize 2{prime}-deoxy-(2-{sup 13}C,1,amino-{sup 15}N{sub 2})guanosine or any combination thereof. An improved biosynthesis of labeled DNA has been accomplished using Methylobacterium extorquens AS1. Each liter of growth medium contains 4 g of methanol to yield 1 g of lyophilized cells. As much as 200 mg of RNA per liter of culture has been obtained. We are currently developing large-scale isolation protocols. General synthetic pathways to oligomeric DNA will be presented.

  11. Studies with 15N-labeled ammonia and urea in the malnourished child

    PubMed Central

    Read, W. W. C.; McLaren, D. S.; Tchalian, Marie; Nassar, Siham

    1969-01-01

    Investigations using ammonium citrate-15N and urea-15N showed that children in the acute stage of kwashiorkor and marasmus receiving a diet of adequate protein content retained a considerable percentage of the label from both compounds. Excretion of both total 15N and urea-15N was subnormal and elimination was virtually completed 36 hr after administration of the isotope. During recovery from kwashiorkor total 15N excretion had approached normal a month after commencement of rehabilitation. Urea-15N excretion was still slightly subnormal after 3 months. In marasmus urea-15N formed a normal proportion of total 15N excretion after 1 month, although total 15N excretion then was still low. Ammonia nitrogen was retained to a greater extent than urea nitrogen in all cases. As it is known that a considerable amount of urea is degraded to ammonia in the gastrointestinal tract, it seems probable that urea nitrogen became available for use after this degradation. Examination of blood from one marasmic child after feeding ammonia-15N and from another after intravenous injection of urea-15N showed incorporation of the label into blood cells and plasma proteins. This did not occur in well nourished controls. It is concluded that ammonia and urea as sources of nonessential nitrogen may play an important part in protein metabolism in the malnourished child. PMID:5771193

  12. Isotope effects and spectroscopic assignments in the non-dissociative photoionization spectrum of N2

    NASA Astrophysics Data System (ADS)

    Randazzo, John B.; Croteau, Philip; Kostko, Oleg; Ahmed, Musahid; Boering, Kristie A.

    2014-05-01

    Photoionization efficiency spectra of 14N2, 15N14N, and 15N2 from 15.5 to 18.9 eV were measured using synchrotron radiation at the Advanced Light Source at Lawrence Berkeley National Laboratory with a resolution of 6 meV, and significant changes in peak energies and intensities upon isotopic substitution were observed. Previously, we reported the isotope shifts and their applications to Titan's atmosphere. Here, we report more extensive experimental details and tabulate the isotope shifts of many transitions in the N2 spectrum, including those for 15N14N, which have not been previously reported. The isotope shifts are used to address several long-standing ambiguities in spectral peak assignments just above the ionization threshold of N2. The feature at 15.677 eV (the so-called second "cathedral" peak) is of particular interest in this respect. The measured isotope shifts for this peak relative to 14N2 are 0.015 ± 0.001 eV for 15N2 and 0.008 ± 0.001 eV for 15N14N, which match most closely with the isotope shifts predicted for transitions to the (A 2Πu v' = 2)4sσg 1Πu state using Herzberg equations for the isotopic differences in harmonic oscillator energy levels plus the first anharmonic correction of 0.0143 eV for 15N2 and 0.0071 eV for 15N14N. More generally, the isotope shifts measured for both 15N2 and 15N14N relative to 14N2 provide new benchmarks for theoretical calculations of interferences between direct and indirect autoionization states which can interact to produce intricate resonant structures in molecular photoionization spectra in regions near ionization thresholds.

  13. Carbon isotope effects associated with autotrophic acetogenesis

    USGS Publications Warehouse

    Gelwicks, J.T.; Risatti, J.B.; Hayes, J.M.

    1989-01-01

    The carbon kinetic isotope effects associated with synthesis of acetate from CO2 and H2 during autotrophic growth of Acetobacterium woodii at 30??C have been measured by isotopic analyses of CO2, methyl-carbon, and total acetate. Closed systems allowing construction of complete mass balances at varying stages of growth were utilized, and the effects of the partitioning of carbon between CO2 and HCO3- were taken into account. For the overall reaction, total carbonate ??? total acetate, isotope effects measured in replicate experiments ranged from -59.0 ?? 0.9% to - 57.2 ?? 2.3z%. Taking into account all measurements, the weighted mean and standard deviation are -58.6 ?? 0.7%. There is no evidence for intramolecular ordering in the acetate. The carbon isotopic composition of sedimentary acetate, otherwise expected to be near that of sedimentary organic carbon, is likely to be depleted in environments in which autotrophic acetogenesis is occurring. ?? 1989.

  14. Carbon isotope effects associated with autotrophic acetogenesis.

    PubMed

    Gelwicks, J T; Risatti, J B; Hayes, J M

    1989-01-01

    The carbon kinetic isotope effects associated with synthesis of acetate from CO2 and H2 during autotrophic growth of Acetobacterium woodii at 30 degrees C have been measured by isotopic analyses of CO2, methyl-carbon, and total acetate. Closed systems allowing construction of complete mass balances at varying stages of growth were utilized, and the effects of the partitioning of carbon between CO2 and HCO3- were taken account. For the overall reaction, total carbonate --> total acetate, isotope effects measured in replicate experiments ranged from -59.0 +/- 0.9% to -57.2 +/- 2.3%. Taking into account all measurements, the weighted mean and standard deviation are -58.6 +/- 0.7%. There is no evidence for intramolecular ordering in the acetate. The carbon isotopic composition of sedimentary acetate, otherwise expected to be near that of sedimentary organic carbon, is likely to be depleted in environments in which autotrophic acetogenesis is occurring. PMID:11542159

  15. Carbon isotope effects associated with autotrophic acetogenesis

    NASA Technical Reports Server (NTRS)

    Gelwicks, J. T.; Risatti, J. B.; Hayes, J. M.

    1989-01-01

    The carbon kinetic isotope effects associated with synthesis of acetate from CO2 and H2 during autotrophic growth of Acetobacterium woodii at 30 degrees C have been measured by isotopic analyses of CO2, methyl-carbon, and total acetate. Closed systems allowing construction of complete mass balances at varying stages of growth were utilized, and the effects of the partitioning of carbon between CO2 and HCO3- were taken account. For the overall reaction, total carbonate --> total acetate, isotope effects measured in replicate experiments ranged from -59.0 +/- 0.9% to -57.2 +/- 2.3%. Taking into account all measurements, the weighted mean and standard deviation are -58.6 +/- 0.7%. There is no evidence for intramolecular ordering in the acetate. The carbon isotopic composition of sedimentary acetate, otherwise expected to be near that of sedimentary organic carbon, is likely to be depleted in environments in which autotrophic acetogenesis is occurring.

  16. Isotopic quantum effects in liquid methanol.

    PubMed

    Ludwig, Ralf

    2005-07-11

    Density functional calculations (B3 LYP/6-31+G*) on molecular clusters and a quantum cluster equilibrium (QCE) model were used to calculate thermodynamic and structural properties of four isotopically labeled methanol species. The method allowed the reproduction of the characteristic differences in boiling points and heats of vaporization. Structural changes were also detected and related to recent experimental findings. It was shown that isotopic effects clearly have a quantum-mechanical origin. PMID:15991271

  17. Sulfur Isotope Effects of Dissimilatory Sulfite Reductase

    PubMed Central

    Leavitt, William D.; Bradley, Alexander S.; Santos, André A.; Pereira, Inês A. C.; Johnston, David T.

    2015-01-01

    The precise interpretation of environmental sulfur isotope records requires a quantitative understanding of the biochemical controls on sulfur isotope fractionation by the principle isotope-fractionating process within the S cycle, microbial sulfate reduction (MSR). Here we provide the only direct observation of the major (34S/32S) and minor (33S/32S, 36S/32S) sulfur isotope fractionations imparted by a central enzyme in the energy metabolism of sulfate reducers, dissimilatory sulfite reductase (DsrAB). Results from in vitro sulfite reduction experiments allow us to calculate the in vitro DsrAB isotope effect in 34S/32S (hereafter, 34εDsrAB) to be 15.3 ± 2‰, 2σ. The accompanying minor isotope effect in 33S, described as 33λDsrAB, is calculated to be 0.5150 ± 0.0012, 2σ. These observations facilitate a rigorous evaluation of the isotopic fractionation associated with the dissimilatory MSR pathway, as well as of the environmental variables that govern the overall magnitude of fractionation by natural communities of sulfate reducers. The isotope effect induced by DsrAB upon sulfite reduction is a factor of 0.3–0.6 times prior indirect estimates, which have ranged from 25 to 53‰ in 34εDsrAB. The minor isotope fractionation observed from DsrAB is consistent with a kinetic or equilibrium effect. Our in vitro constraints on the magnitude of 34εDsrAB is similar to the median value of experimental observations compiled from all known published work, where 34εr−p = 16.1‰ (r–p indicates reactant vs. product, n = 648). This value closely matches those of MSR operating at high sulfate reduction rates in both laboratory chemostat experiments (34εSO4−H2S =  17.3 ± 1.5‰, 2σ) and in modern marine sediments (34εSO4−H2S =  17.3 ± 3.8‰). Targeting the direct isotopic consequences of a specific enzymatic processes is a fundamental step toward a biochemical foundation for reinterpreting the biogeochemical and geobiological sulfur isotope records in

  18. Sulfur Isotope Effects of Dissimilatory Sulfite Reductase.

    PubMed

    Leavitt, William D; Bradley, Alexander S; Santos, André A; Pereira, Inês A C; Johnston, David T

    2015-01-01

    The precise interpretation of environmental sulfur isotope records requires a quantitative understanding of the biochemical controls on sulfur isotope fractionation by the principle isotope-fractionating process within the S cycle, microbial sulfate reduction (MSR). Here we provide the only direct observation of the major ((34)S/(32)S) and minor ((33)S/(32)S, (36)S/(32)S) sulfur isotope fractionations imparted by a central enzyme in the energy metabolism of sulfate reducers, dissimilatory sulfite reductase (DsrAB). Results from in vitro sulfite reduction experiments allow us to calculate the in vitro DsrAB isotope effect in (34)S/(32)S (hereafter, [Formula: see text]) to be 15.3 ± 2‰, 2σ. The accompanying minor isotope effect in (33)S, described as [Formula: see text], is calculated to be 0.5150 ± 0.0012, 2σ. These observations facilitate a rigorous evaluation of the isotopic fractionation associated with the dissimilatory MSR pathway, as well as of the environmental variables that govern the overall magnitude of fractionation by natural communities of sulfate reducers. The isotope effect induced by DsrAB upon sulfite reduction is a factor of 0.3-0.6 times prior indirect estimates, which have ranged from 25 to 53‰ in (34)εDsrAB. The minor isotope fractionation observed from DsrAB is consistent with a kinetic or equilibrium effect. Our in vitro constraints on the magnitude of [Formula: see text] is similar to the median value of experimental observations compiled from all known published work, where (34)ε r-p = 16.1‰ (r-p indicates reactant vs. product, n = 648). This value closely matches those of MSR operating at high sulfate reduction rates in both laboratory chemostat experiments ([Formula: see text] 17.3 ± 1.5‰, 2σ) and in modern marine sediments ([Formula: see text] 17.3 ± 3.8‰). Targeting the direct isotopic consequences of a specific enzymatic processes is a fundamental step toward a biochemical foundation for reinterpreting the

  19. Modeling nuclear volume isotope effects in crystals

    PubMed Central

    Schauble, Edwin A.

    2013-01-01

    Mass-independent isotope fractionations driven by differences in volumes and shapes of nuclei (the field shift effect) are known in several elements and are likely to be found in more. All-electron relativistic electronic structure calculations can predict this effect but at present are computationally intensive and limited to modeling small gas phase molecules and clusters. Density functional theory, using the projector augmented wave method (DFT-PAW), has advantages in greater speed and compatibility with a three-dimensional periodic boundary condition while preserving information about the effects of chemistry on electron densities within nuclei. These electron density variations determine the volume component of the field shift effect. In this study, DFT-PAW calculations are calibrated against all-electron, relativistic Dirac–Hartree–Fock, and coupled-cluster with single, double (triple) excitation methods for estimating nuclear volume isotope effects. DFT-PAW calculations accurately reproduce changes in electron densities within nuclei in typical molecules, when PAW datasets constructed with finite nuclei are used. Nuclear volume contributions to vapor–crystal isotope fractionation are calculated for elemental cadmium and mercury, showing good agreement with experiments. The nuclear-volume component of mercury and cadmium isotope fractionations between atomic vapor and montroydite (HgO), cinnabar (HgS), calomel (Hg2Cl2), monteponite (CdO), and the CdS polymorphs hawleyite and greenockite are calculated, indicating preferential incorporation of neutron-rich isotopes in more oxidized, ionically bonded phases. Finally, field shift energies are related to Mössbauer isomer shifts, and equilibrium mass-independent fractionations for several tin-bearing crystals are calculated from 119Sn spectra. Isomer shift data should simplify calculations of mass-independent isotope fractionations in other elements with Mössbauer isotopes, such as platinum and uranium

  20. Modeling nuclear volume isotope effects in crystals.

    PubMed

    Schauble, Edwin A

    2013-10-29

    Mass-independent isotope fractionations driven by differences in volumes and shapes of nuclei (the field shift effect) are known in several elements and are likely to be found in more. All-electron relativistic electronic structure calculations can predict this effect but at present are computationally intensive and limited to modeling small gas phase molecules and clusters. Density functional theory, using the projector augmented wave method (DFT-PAW), has advantages in greater speed and compatibility with a three-dimensional periodic boundary condition while preserving information about the effects of chemistry on electron densities within nuclei. These electron density variations determine the volume component of the field shift effect. In this study, DFT-PAW calculations are calibrated against all-electron, relativistic Dirac-Hartree-Fock, and coupled-cluster with single, double (triple) excitation methods for estimating nuclear volume isotope effects. DFT-PAW calculations accurately reproduce changes in electron densities within nuclei in typical molecules, when PAW datasets constructed with finite nuclei are used. Nuclear volume contributions to vapor-crystal isotope fractionation are calculated for elemental cadmium and mercury, showing good agreement with experiments. The nuclear-volume component of mercury and cadmium isotope fractionations between atomic vapor and montroydite (HgO), cinnabar (HgS), calomel (Hg2Cl2), monteponite (CdO), and the CdS polymorphs hawleyite and greenockite are calculated, indicating preferential incorporation of neutron-rich isotopes in more oxidized, ionically bonded phases. Finally, field shift energies are related to Mössbauer isomer shifts, and equilibrium mass-independent fractionations for several tin-bearing crystals are calculated from (119)Sn spectra. Isomer shift data should simplify calculations of mass-independent isotope fractionations in other elements with Mössbauer isotopes, such as platinum and uranium. PMID

  1. Modeling nuclear volume isotope effects in crystals

    NASA Astrophysics Data System (ADS)

    Schauble, Edwin A.

    2013-10-01

    Mass-independent isotope fractionations driven by differences in volumes and shapes of nuclei (the field shift effect) are known in several elements and are likely to be found in more. All-electron relativistic electronic structure calculations can predict this effect but at present are computationally intensive and limited to modeling small gas phase molecules and clusters. Density functional theory, using the projector augmented wave method (DFT-PAW), has advantages in greater speed and compatibility with a three-dimensional periodic boundary condition while preserving information about the effects of chemistry on electron densities within nuclei. These electron density variations determine the volume component of the field shift effect. In this study, DFT-PAW calculations are calibrated against all-electron, relativistic Dirac-Hartree-Fock, and coupled-cluster with single, double (triple) excitation methods for estimating nuclear volume isotope effects. DFT-PAW calculations accurately reproduce changes in electron densities within nuclei in typical molecules, when PAW datasets constructed with finite nuclei are used. Nuclear volume contributions to vapor-crystal isotope fractionation are calculated for elemental cadmium and mercury, showing good agreement with experiments. The nuclear-volume component of mercury and cadmium isotope fractionations between atomic vapor and montroydite (HgO), cinnabar (HgS), calomel (Hg2Cl2), monteponite (CdO), and the CdS polymorphs hawleyite and greenockite are calculated, indicating preferential incorporation of neutron-rich isotopes in more oxidized, ionically bonded phases. Finally, field shift energies are related to Mössbauer isomer shifts, and equilibrium mass-independent fractionations for several tin-bearing crystals are calculated from 119Sn spectra. Isomer shift data should simplify calculations of mass-independent isotope fractionations in other elements with Mössbauer isotopes, such as platinum and uranium.

  2. The fate of nitrogen in grain cropping systems: a meta-analysis of 15N field experiments.

    PubMed

    Gardner, Jennifer B; Drinkwater, Laurie E

    2009-12-01

    Intensively managed grain farms are saturated with large inputs of nitrogen (N) fertilizer, leading to N losses and environmental degradation. Despite decades of research directed toward reducing N losses from agroecosystems, progress has been minimal, and the currently promoted best management practices are not necessarily the most effective. We investigated the fate of N additions to temperate grain agroecosystems using a meta-analysis of 217 field-scale studies that followed the stable isotope 15N in crops and soil. We compared management practices that alter inorganic fertilizer additions, such as application timing or reduced N fertilizer rates, to practices that re-couple the biogeochemical cycles of carbon (C) and N, such as organic N sources and diversified crop rotations, and analyzed the following response variables: 15N recovery in crops, total recovery of 15N in crops and soil, and crop yield. More of the literature (94%) emphasized crop recovery of 15N than total 15N recovery in crops and soil (58%), though total recovery is a more ecologically appropriate indicator for assessing N losses. Findings show wide differences in the ability of management practices to improve N use efficiency. Practices that aimed to increase crop uptake of commercial fertilizer had a lower impact on total 15N recovery (3-21% increase) than practices that re-coupled C and N cycling (30-42% increase). A majority of studies (66%) were only one growing season long, which poses a particular problem when organic N sources are used because crops recover N from these sources over several years. These short-term studies neglect significant ecological processes that occur over longer time scales. Field-scale mass balance calculations using the 15N data set show that, on average, 43 kg N x ha(-1) x yr(-1) was unaccounted for at the end of one growing season out of 114 kg N x ha(-1) x yr(-1), representing approximately 38% of the total 15N applied. This comprehensive assessment of

  3. High-resolution laser spectroscopy and magnetic effect of the B̃(2)E(')←X̃(2)A2(') transition of the (15)N substituted nitrate radical.

    PubMed

    Tada, Kohei; Teramoto, Kanon; Ishiwata, Takashi; Hirota, Eizi; Kasahara, Shunji

    2015-03-21

    Rotationally resolved high-resolution fluorescence excitation spectra of the 0-0 band of the B̃(2)E(')←X̃(2)A2(') transition of the (15)N substituted nitrate radical were observed for the first time, by crossing a jet-cooled molecular beam and a single-mode dye laser beam at right angles. Several thousand rotational lines were detected in the 15 080-15 103 cm(-1) region. We observed the Zeeman splitting of intense lines up to 360 G in order to obtain secure rotational assignment. Two, nine, and seven rotational line pairs with 0.0248 cm(-1) spacing were assigned to the transitions from the X̃(2)A2(') (υ″ = 0, k″ = 0, N″ = 1, J″ = 0.5 and 1.5) to the (2)E3/2(') (J' = 1.5), (2)E1/2(') (J' = 0.5), and (2)E1/2(') (J' = 1.5) levels, respectively, based on the ground state combination differences and the Zeeman splitting patterns. The observed spectrum was complicated due to the vibronic coupling between the bright B̃(2)E(') (υ = 0) state and surrounding dark vibronic states. Some series of rotational lines other than those from the X̃(2)A2(') (J = 0.5 and 1.5) levels were also assigned by the ground state combination differences and the observed Zeeman splitting. The rotational branch structures were identified, and the molecular constants of the B̃(2)E1/2(') (υ = 0) state were estimated by a deperturbed analysis to be T0 = 15 098.20(4) cm(-1), B = 0.4282(7) cm(-1), and DJ = 4 × 10(-4) cm(-1). In the observed region, both the (2)E1/2(') and (2)E3/2(') spin-orbit components were identified, and the spin-orbit interaction constant of the B̃(2)E(') (υ = 0) state was estimated to be -12 cm(-1) as the lower limit. PMID:25796244

  4. Nutrient regime shift in the western North Atlantic indicated by compound-specific δ15N of deep-sea gorgonian corals.

    PubMed

    Sherwood, Owen A; Lehmann, Moritz F; Schubert, Carsten J; Scott, David B; McCarthy, Matthew D

    2011-01-18

    Despite the importance of the nitrogen (N) cycle on marine productivity, little is known about variability in N sources and cycling in the ocean in relation to natural and anthropogenic climate change. Beyond the last few decades of scientific observation, knowledge depends largely on proxy records derived from nitrogen stable isotopes (δ(15)N) preserved in sediments and other bioarchives. Traditional bulk δ(15)N measurements, however, represent the combined influence of N source and subsequent trophic transfers, often confounding environmental interpretation. Recently, compound-specific analysis of individual amino acids (δ(15)N-AA) has been shown as a means to deconvolve trophic level versus N source effects on the δ(15)N variability of bulk organic matter. Here, we demonstrate the first use of δ(15)N-AA in a paleoceanographic study, through analysis of annually secreted growth rings preserved in the organic endoskeletons of deep-sea gorgonian corals. In the Northwest Atlantic off Nova Scotia, coral δ(15)N is correlated with increasing presence of subtropical versus subpolar slope waters over the twentieth century. By using the new δ(15)N-AA approach to control for variable trophic processing, we are able to interpret coral bulk δ(15)N values as a proxy for nitrate source and, hence, slope water source partitioning. We conclude that the persistence of the warm, nutrient-rich regime since the early 1970s is largely unique in the context of the last approximately 1,800 yr. This evidence suggests that nutrient variability in this region is coordinated with recent changes in global climate and underscores the broad potential of δ(15)N-AA for paleoceanographic studies of the marine N cycle. PMID:21199952

  5. Isotopic effects of nitrate photochemistry in snow: A field study at Dome C, Antarctica

    NASA Astrophysics Data System (ADS)

    Berhanu, T. A.; Erbland, J.; Savarino, J. P.

    2012-12-01

    Nitrate (NO3-) is the end product of NOx (NO+NO2) oxidation in the atmosphere and one of the most abundant anions present in the Antarctic snow pack. The comprehensive isotopic composition of nitrate (δ18O, Δ17O and δ15N) obtained from deep ice-cores may provide valuable information regarding the oxidative capacity of the atmosphere and could provide constraints on the global NOx budget. Nitrogen stable isotope ratios are typically thought to trace NOx sources while oxygen isotope ratios convey quantitative information regarding the oxidation pathways leading to nitrate formation. However, nitrate deposited at low accumulation sites in Polar Regions such as Dome C, Antarctica, is exposed to post depositional processes that modify its original isotopic composition. Among these processes, photolysis has been identified as the most significant mechanism leading to large nitrate mass loss and isotopic fractionation. Emission of NOx and OH from photolysis of nitrate, as well as formation of by-products such as HONO, can have a significant impact on the overlying boundary layer chemistry of polar regions. The quantitative effect of photolysis on the isotopic signature of nitrate is presently not well constrained and previous experimental and modelling studies have resulted in differing conclusions regarding the role of photolysis in the post processing of nitrate deposited to snow. In order to quantify the effect of photolysis on the isotopic composition of nitrate in snow, we have conducted a field study at Dome C, Antarctica. In this study, two snow sampling fields (1m wide, 2m long and 0.5m deep) within close proximity of each other were studied for the effect of UV light using a plexi glass filter experiment. The two fields were filled with wind blown snow at the beginning of December 2011 and then covered with plexi glass sheets. One of these sheets was equipped with a UV filter. Sampling was conducted every 10 days at a 2-5 cm depth resolution during the period

  6. Variable δ15N Diet-Tissue Discrimination Factors among Sharks: Implications for Trophic Position, Diet and Food Web Models

    PubMed Central

    Olin, Jill A.; Hussey, Nigel E.; Grgicak-Mannion, Alice; Fritts, Mark W.; Wintner, Sabine P.; Fisk, Aaron T.

    2013-01-01

    The application of stable isotopes to characterize the complexities of a species foraging behavior and trophic relationships is dependent on assumptions of δ15N diet-tissue discrimination factors (∆15N). As ∆15N values have been experimentally shown to vary amongst consumers, tissues and diet composition, resolving appropriate species-specific ∆15N values can be complex. Given the logistical and ethical challenges of controlled feeding experiments for determining ∆15N values for large and/or endangered species, our objective was to conduct an assessment of a range of reported ∆15N values that can hypothetically serve as surrogates for describing the predator-prey relationships of four shark species that feed on prey from different trophic levels (i.e., different mean δ15N dietary values). Overall, the most suitable species-specific ∆15N values decreased with increasing dietary-δ15N values based on stable isotope Bayesian ellipse overlap estimates of shark and the principal prey functional groups contributing to the diet determined from stomach content analyses. Thus, a single ∆15N value was not supported for this speciose group of marine predatory fishes. For example, the ∆15N value of 3.7‰ provided the highest percent overlap between prey and predator isotope ellipses for the bonnethead shark (mean diet δ15N = 9‰) whereas a ∆15N value < 2.3‰ provided the highest percent overlap between prey and predator isotope ellipses for the white shark (mean diet δ15N = 15‰). These data corroborate the previously reported inverse ∆15N-dietary δ15N relationship when both isotope ellipses of principal prey functional groups and the broader identified diet of each species were considered supporting the adoption of different ∆15N values that reflect the predators’ δ15N-dietary value. These findings are critical for refining the application of stable isotope modeling approaches as inferences regarding a species’ ecological role in their

  7. Variable δ(15)N diet-tissue discrimination factors among sharks: implications for trophic position, diet and food web models.

    PubMed

    Olin, Jill A; Hussey, Nigel E; Grgicak-Mannion, Alice; Fritts, Mark W; Wintner, Sabine P; Fisk, Aaron T

    2013-01-01

    The application of stable isotopes to characterize the complexities of a species foraging behavior and trophic relationships is dependent on assumptions of δ(15)N diet-tissue discrimination factors (∆(15)N). As ∆(15)N values have been experimentally shown to vary amongst consumers, tissues and diet composition, resolving appropriate species-specific ∆(15)N values can be complex. Given the logistical and ethical challenges of controlled feeding experiments for determining ∆(15)N values for large and/or endangered species, our objective was to conduct an assessment of a range of reported ∆(15)N values that can hypothetically serve as surrogates for describing the predator-prey relationships of four shark species that feed on prey from different trophic levels (i.e., different mean δ(15)N dietary values). Overall, the most suitable species-specific ∆(15)N values decreased with increasing dietary-δ(15)N values based on stable isotope Bayesian ellipse overlap estimates of shark and the principal prey functional groups contributing to the diet determined from stomach content analyses. Thus, a single ∆(15)N value was not supported for this speciose group of marine predatory fishes. For example, the ∆(15)N value of 3.7‰ provided the highest percent overlap between prey and predator isotope ellipses for the bonnethead shark (mean diet δ(15)N = 9‰) whereas a ∆(15)N value < 2.3‰ provided the highest percent overlap between prey and predator isotope ellipses for the white shark (mean diet δ(15)N = 15‰). These data corroborate the previously reported inverse ∆(15)N-dietary δ(15)N relationship when both isotope ellipses of principal prey functional groups and the broader identified diet of each species were considered supporting the adoption of different ∆(15)N values that reflect the predators' δ(15)N-dietary value. These findings are critical for refining the application of stable isotope modeling approaches as inferences regarding a

  8. 15N Hyperpolarization by Reversible Exchange Using SABRE-SHEATH

    PubMed Central

    2016-01-01

    NMR signal amplification by reversible exchange (SABRE) is a NMR hyperpolarization technique that enables nuclear spin polarization enhancement of molecules via concurrent chemical exchange of a target substrate and parahydrogen (the source of spin order) on an iridium catalyst. Recently, we demonstrated that conducting SABRE in microtesla fields provided by a magnetic shield enables up to 10% 15N-polarization (Theis, T.; et al. J. Am. Chem. Soc.2015, 137, 1404). Hyperpolarization on 15N (and heteronuclei in general) may be advantageous because of the long-lived nature of the hyperpolarization on 15N relative to the short-lived hyperpolarization of protons conventionally hyperpolarized by SABRE, in addition to wider chemical shift dispersion and absence of background signal. Here we show that these unprecedented polarization levels enable 15N magnetic resonance imaging. We also present a theoretical model for the hyperpolarization transfer to heteronuclei, and detail key parameters that should be optimized for efficient 15N-hyperpolarization. The effects of parahydrogen pressure, flow rate, sample temperature, catalyst-to-substrate ratio, relaxation time (T1), and reversible oxygen quenching are studied on a test system of 15N-pyridine in methanol-d4. Moreover, we demonstrate the first proof-of-principle 13C-hyperpolarization using this method. This simple hyperpolarization scheme only requires access to parahydrogen and a magnetic shield, and it provides large enough signal gains to enable one of the first 15N images (2 × 2 mm2 resolution). Importantly, this method enables hyperpolarization of molecular sites with NMR T1 relaxation times suitable for biomedical imaging and spectroscopy. PMID:25960823

  9. Effects of elemental composition on the incorporation of dietary nitrogen and carbon isotopic signatures in an omnivorous songbird

    SciTech Connect

    Pearson, Scott, F.; Levey, Douglas, J.; Greenberg, Catheryn, H.; Martinez del Rio, Carlos

    2003-02-28

    Pearson, S.F., D.J. Levey, C.H. Greenberg, and C.M. del Rio. 2003. Effects of elemental composition on the incorporation of dietary nitrogen and carbon isotopic signatures in an omnivorous songbird. Oecologia. 135:516-523. The use of stable isotopes to infer diet requires quantifying the relationship between diet and tissues and, in particular, knowing of how quickly isotopes turnover in different tissues and how isotopic concentrations of different food components change (discriminate) when incorporated into consumer tissues. We used feeding trials with wild-caught yellow-rumped warblers (Dendroica coronata) to determine d15N and d13C turnover rates for blood, d15N and d13C diet-tissue discrimination factors, and diet-tissue relationships for blood and feathers. After 3 weeks on a common diet, 36 warblers were assigned to one of four diets differing in the relative proportion of fruit and insects. Plasma half-life estimates ranged from 0.4 to 0.7 days for d13C and from 0.5 to 1.7 days for d15N. Half-life did not differ among diets. Whole blood half-life for d13C ranged from 3.9 to 6.1 days. Yellow-rumped warbler tissues were enriched relative to diet by 1.7.3.6% for nitrogen isotopes and by 1.2 to 4.3% for carbon isotopes, depending on tissue and diet. Consistent with previous studies, feathers were the most enriched and whole blood and plasma were the least enriched or, in the case of carbon, slightly depleted relative to diet. In general, tissues were more enriched relative to diet for birds with high percentages of insects. For all tissues, carbon and nitrogen isotope discrimination factors increased with carbon and nitrogen concentrations of diets. The isotopic signature of plasma increased linearly with the sum of the isotopic signature of the diet and the discrimination factor. Because the isotopic signature of tissues depends on both elemental concentration and isotopic signature of the diet, attempts to reconstruct diet from stable isotope signatures

  10. Uptake of stormwater nitrogen in bioretention systems demonstrated from 15N tracer techniques

    NASA Astrophysics Data System (ADS)

    Houdeshel, D.; Hultine, K. R.; Pomeroy, C. A.

    2012-12-01

    Bioretention stormwater management systems are engineered ecosystems that capture urban stormwater in order to reduce the harmful effects of stormwater pollution on receiving waters. Bioretention systems have been shown to be effective at reducing the volume of runoff, and thereby reduce the nutrient loading to receiving waters from urban areas. However, little work has been done to evaluate the treatment processes that are responsible for reductions in effluent nitrogen (N). We hypothesize that the pulses of inorganic nitrogen associated with urban runoff events are captured in the plat tissues within these systems and not adsorbed to the soil media, thus creating a long-term, sustainable treatment approach to reducing the total nutrient loading to receiving waters. Nitrogen treatment performance was tested on two bioretention systems in Salt Lake City, UT: 1) an upland native community that does not require irrigation in semi-arid climates, and 2) a wetland community that requires 250 l of daily irrigation to offset the relatively high evaporative demand in the region. Each cell is sized to treat a 2.5 cm storm from a 140 m2 impervious surface: the area of the bioretention system is 10 m2. To test the N removal performance of each system, runoff events were simulated to represent an average precipitation regime using a synthetic stormwater blend starting in January, 2012. Effluent was collected from an underdrain and analyzed for total nitrogen (TN); mass removal was calculated for each month by subtracting the TN mass added to the garden minus the TN mass that flowed out of the garden. To test the hypothesis that plants assimilate stormwater N, 4 g of 100 atom% 15N NH4NO3 tracer was used as the N source in the synthetic stormwater during the first 2,000 l synthetic storm event in May. This isotopic label was calculated to enrich the total N pool of each garden to 100‰ 15N/14Nair. New growth was harvested from each plant in both cells and analyzed for 15N

  11. Effects of sample preparation on stable isotope ratios of carbon and nitrogen in marine invertebrates: implications for food web studies using stable isotopes.

    PubMed

    Mateo, Miguel A; Serrano, Oscar; Serrano, Laura; Michener, Robert H

    2008-08-01

    Trophic ecology has benefitted from the use of stable isotopes for the last three decades. However, during the last 10 years, there has been a growing awareness of the isotopic biases associated with some pre-analytical procedures that can seriously hamper the interpretation of food webs. We have assessed the extent of such biases by: (1) reviewing the literature on the topic, and (2) compiling C and N isotopic values of marine invertebrates reported in the literature with the associated sample preparation protocols. The factors considered were: acid-washing, distilled water rinsing (DWR), sample type (whole individuals or pieces of soft tissues), lipid content, and gut contents. Two-level ANOVA revealed overall large and highly significant effects of acidification for both delta(13)C values (up to 0.9 per thousand decrease) and delta(15) N values (up to 2.1 per thousand decrease in whole individual samples, and up to 1.1 per thousand increase in tissue samples). DWR showed a weak overall effect with delta(13)C increments of 0.6 per thousand (for the entire data set) or decrements of 0.7 per thousand in delta(15) N values (for tissue samples). Gut contents showed no overall significant effect, whereas lipid extraction resulted in the greatest biases in both isotopic signatures (delta(13)C, up to -2.0 per thousand in whole individuals; delta(15)N, up to +4.3 per thousand in tissue samples). The study analyzed separately the effects of the various factors in different taxonomic groups and revealed a very high diversity in the extent and direction of the effects. Maxillopoda, Gastropoda, and Polychaeta were the classes that showed the largest isotopic shifts associated with sample preparation. Guidelines for the standardization of sample preparation protocols for isotopic analysis are proposed both for large and small marine invertebrates. Broadly, these guidelines recommend: (1) avoiding both acid washing and DWR, and (2) performing lipid extraction and gut

  12. Climate-Dependence of Plant-Soil 15N/14N Interactions Across Tropical Rainforests

    NASA Astrophysics Data System (ADS)

    Houlton, B. Z.; Sigman, D. M.; Hedin, L. O.

    2005-12-01

    In most areas of the world, the 15N/14N of bulk soils is higher than that of plant leaves, and the isotopic signatures of these two ecosystem N pools progressively diverge with increasing rainfall. However, both the cause for this isotopic trend and its implications for understanding interactions between climate and N cycles are largely unknown. We report 15N/14N measurements of nitrate, ammonium, and total dissolved N in soil extracts from a highly constrained rainfall sequence in Hawaii, across which this trend in ecosystem 15N/14N is captured, to examine the competing explanations for plant-soil 15N/14N uncouplings. While the isotopic influences of microbial transfers of N between nitrate and ammonium pools and plant-mycorrhizae interactions have been posited in plant-soil 15N/14N relationships, our data did not support an important role for either of these mechanisms. Instead, preferential regeneration of 14N during the breakdown of DON to ammonium explains why the 15N/14N of plants is lower than that of bulk soils. Fractionation at this step leads to two isotopically distinct N subcycles in each forest, a lower-15N/14N subcycle composed of ammonium, nitrate, and bulk plant biomass N that `spins' rapidly and a higher-15N/14N subcycle composed of bulk soil N and DON that is much less dynamic. The increased difference between soil and plant 15N/14N is due to changes in the impacts of nitrification and denitrification on the 15N/14N of ammonium and nitrate, coupled with a switch from nitrate to ammonium uptake by plants under the wettest conditions. For instance, the particularly large (~6 per mil) 15N/14N difference between plants and soils in the wettest sites is due to the lack of 15N-enrichment of ammonium by nitrification coupled with plant dependence on ammonium uptake only. Our results highlight the importance of interactions between DON breakdown, ecosystem N recycling, and gaseous N losses in the explaining the interactions between the 15N signatures of

  13. Community 15N isoscapes to resolve plant-plant-interactions at the spatial scale

    NASA Astrophysics Data System (ADS)

    Hellmann, Christine; Rascher, Katherine G.; Máguas, Cristina; Werner, Christiane

    2014-05-01

    Isoscapes have greatly improved our ability to understand biogeochemical processes on continental to global scales. However, the isoscapes framework may also have significant potential to resolve the spatial component of within-community interactions. For example, exotic plant invaders often exert strong impacts on ecosystem functioning, particularly regarding water-, carbon- and nutrient-cycles, but the spatial extent of such alterations is largely unknown. Here we show that massive N input by the N2-fixing exotic invasive Acacia longifolia to a Portuguese dune system can be traced using spatially resolved information on native plants' leaf δ15N. We found isotopic signatures of N to differ strongly between the native system (δ15N c. -10 o) and the atmospherically derived N in A. longifolia phyllodes (δ15N c. 0 o). Thus, sources of N for native plants could be readily distinguished. Leaf δ15N of a native, non-fixing species was increasingly enriched the closer the plant grew to the invader, indicating uptake of fixed N provided by A. longifolia. The enrichment was evident far beyond the stands of the invader, demonstrating that A. longifolia affected N budgets of native species up to a distance of 8 m exceeding the margin of the canopy. Furthermore, using the isoscapes approach, we were able to quantify the total area of N enrichment and could thus show that the area affected by invasion was at least 3.5 times larger than the area actually occupied by the invader. However, a native N2-fixing species had no such effects. Thus, downscaling isoscapes to the community level opens new frontiers in quantifying the spatial dimension of functional changes associated with plant invasions. Moreover, considering the feasibility and applicability of this approach, it may provide a promising tool to identify, quantify and monitor different types of functional plant-plant interactions within communities at a spatially explicit scale.

  14. Eastern oyster (Crassostrea virginica) δ15N as a bioindicator of nitrogen sources: Observations and modeling

    PubMed Central

    Fertig, B.; Carruthers, T.J.B.; Dennison, W.C.; Fertig, E.J.; Altabet, M.A.

    2013-01-01

    Stable nitrogen isotopes15N) in bioindicators are increasingly employed to identify nitrogen sources in many ecosystems and biological characteristics of the eastern oyster (Crassostrea virginica) make it an appropriate species for this purpose. To assess nitrogen isotopic fractionation associated with assimilation and baseline variations in oyster mantle, gill, and muscle tissue δ15N, manipulative fieldwork in Chesapeake Bay and corresponding modeling exercises were conducted. This study (1) determined that five individuals represented an optimal sample size; (2) verified that δ15N in oysters from two locations converged after shared deployment to a new location reflecting a change in nitrogen sources; (3) identified required exposure time and temporal integration (four months for muscle, two to three months for gill and mantle); and (4) demonstrated seasonal δ15N increases in seston (summer) and oysters (winter). As bioindicators, oysters can be deployed for spatial interpolation of nitrogen sources, even in areas lacking extant populations. PMID:20381097

  15. Marking Drosophila suzukii (Diptera: Drosophilidae) With Rubidium or 15N.

    PubMed

    Klick, J; Yang, W Q; Bruck, D J

    2015-06-01

    Drosophila suzukii Matsumura (Diptera: Drosophilidae) has caused significant economic damage to berry and stone fruit production regions. Markers that are systemic in plants and easily transferred to target organisms are needed to track D. suzukii exploitation of host resources and trophic interactions. High and low concentrations of the trace element, rubidium (Rb), and the stable isotope, 15N, were tested to mark D. suzukii larvae feeding on fruits of enriched strawberry plants grown in containers under greenhouse conditions. Fly marker content and proportion of flies marked 1, 7, and 14 d after emergence from enriched fruits and fly dry mass were analyzed. Nearly 100% of the flies analyzed 14 d after emerging from 15N-enriched plants were marked, whereas only 30-75% and 0-3% were marked 14 d after emerging from high and low Rb concentration plants, respectively. Rapid Rb decay, strong 15N persistence, and the economics of using these markers in the field to elucidate D. suzukii pest ecology are discussed. PMID:26470275

  16. A Tale of Two Gases: Isotope Effects Associated with the Enzymatic Production of H2 and N2O

    NASA Astrophysics Data System (ADS)

    Yang, H.; Gandhi, H.; Kreuzer, H. W.; Moran, J.; Hill, E. A.; McQuarters, A.; Lehnert, N.; Ostrom, N. E.; Hegg, E. L.

    2014-12-01

    Stable isotopes can provide considerable insight into enzymatic mechanisms and fluxes in various biological processes. In our studies, we used stable isotopes to characterize both enzyme-catalyzed H2 and N2O production. H2 is a potential alternative clean energy source and also a key metabolite in many microbial communities. Biological H2 production is generally catalyzed by hydrogenases, enzymes that combine protons and electrons to produce H2 under anaerobic conditions. In our study, H isotopes and fractionation factors (α) were used to characterize two types of hydrogenases: [FeFe]- and [NiFe]-hydrogenases. Due to differences in the active site, the α associated with H2 production for [FeFe]- and [NiFe]-hydrogenases separated into two distinct clusters (αFeFe > αNiFe). The calculated kinetic isotope effects indicate that hydrogenase-catalyzed H2 production has a preference for light isotopes, consistent with the relative bond strengths of O-H and H-H bonds. Interestingly, the isotope effects associated with H2 consumption and H2-H2O exchange reactions were also characterized, but in this case no specific difference was observed between the different enzymes. N2O is a potent greenhouse gas with a global warming potential 300 times that of CO2, and the concentration of N2O is currently increasing at a rate of ~0.25% per year. Thus far, bacterial and fungal denitrification processes have been identified as two of the major sources of biologically generated N2O. In this study, we measured the δ15N, δ18O, δ15Nα (central N atom in N2O), and δ15Nβ (terminal N atom in N2O) of N2O generated by purified fungal P450 nitric oxide reductase (P450nor) from Histoplasma capsulatum. We observed normal isotope effects for δ18O and δ15Nα, and inverse isotope effects for bulk δ15N (the average of Nα and Nβ) and δ15Nβ. The observed isotope effects have been used in conjunction with DFT calculations to provide important insight into the mechanism of P450nor. Similar

  17. Effect of acidification on elemental and isotopic compositions of sediment organic matter and macro-invertebrate muscle tissues in food web research.

    PubMed

    Mazumder, Debashish; Iles, Jordan; Kelleway, Jeff; Kobayashi, Tsuyoshi; Knowles, Lisa; Saintilan, Neil; Hollins, Suzanne

    2010-10-30

    Stable isotope techniques in food web studies often focus on organic carbon in food sources which are subsequently assimilated in the tissue of consumer organisms through diet. The presence of non-dietary carbonates in bulk samples can affect their δ(13)C values, altering how their results are interpreted. Acidification of samples is a common practice to eliminate any inorganic carbon present prior to analysis. We examined the effects of pre-analysis acidification on two size fractions of sediment organic matter (SOM) from marine and freshwater wetlands and pure muscle tissue of a common freshwater invertebrate (Cherax destructor). The elemental content and isotopic ratios of carbon and nitrogen were compared between paired samples of acidified and control treatments. Our results showed that acidification does not affect the elemental or isotopic values of freshwater SOM. In the marine environment acidification depleted the δ(13)C and δ(15)N values of the fine fraction of saltmarsh and δ(15)N values of mangrove fine SOM. Whilst acidification did not change the elemental content of invertebrate muscle tissue, the δ(13)C and δ(15)N values were affected. We recommend to researchers considering using acidification techniques on material prepared for stable isotope analysis that a formal assessment of the effect of acidification on their particular sample type should be undertaken. Further detailed investigation to understand the impact of acidification on elemental and isotopic values of organic matter and muscular tissues is required. PMID:20872625

  18. Effects of boron nutrition and water stress on nitrogen fixation, seed d15N and d13C daynamics, and seed composition in soybean cultivars differing in maturities

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Water stress is a major abiotic stress factor, resulting in a major yield loss and poor seed quality. Little information is available on the effects of B nutrition on seed composition under water stress. Therefore, the objective of the current research was to investigate the effects of foliar B nutr...

  19. Biosynthetic preparation of L-(/sup 13/C)- and (/sup 15/N)glutamate by Brevibacterium flavum

    SciTech Connect

    Walker, T.E.; London, R.E.

    1987-01-01

    The biosynthesis of isotopically labeled L-glutamic acid by the microorganism Brevibacterium flavum was studied with a variety of carbon-13-enriched precursors. The purpose of this study was twofold: (i) to develop techniques for the efficient preparation of labeled L-glutamate with a variety of useful labeling patterns which can be used for other metabolic studies, and (ii) to better understand the metabolic events leading to label scrambling in these strains. B. flavum, which is used commercially for the production of monosodium glutamate, has the capability of utilizing glucose or acetate as a sole carbon source, and important criterion from the standpoint of developing labeling strategies. Unfortunately, singly labeled glucose precursors lead to excessive isotopic dilution which reduces their usefulness. Studies with (3-/sup 13/C)pyruvate indicate that this problem can in principle be overcome by using labeled three-carbon precursors; however, conditions could not be found which would lead to an acceptable yield of isotopically labeled L-glutamate. In contrast, (1-/sup 13/C)- or (2-/sup 13/C)acetate provides relatively inexpensive, readily available precursors for the production of selectively labeled, high enriched L-glutamate. The preparation of L-(/sup 15/N)glutamate from (/sup 15/N)ammonium sulfate was carried out and is a very effective labeling strategy. Analysis of the isotopic distribution in labeled glutamate provides details about the metabolic pathways in these interesting organisms.

  20. Challenges to the Application of δ15N measurements of the organic fraction of archaeological and fossil mollusk shells to assess paleoenvironmental change.

    NASA Astrophysics Data System (ADS)

    Andrus, C. F. T.

    2015-12-01

    Nitrogen isotope analysis of the organic fraction of mollusk shells is beginning to be applied to questions of past anthropogenic and natural environmental variation using samples from archaeological and fossil deposits. Fairly extensive proxy validation research has been conducted in the past decade, documenting the relationship between the δ15N of ambient particulate organic matter, mollusk soft tissues, and shell organic matrix. However, comparatively little research has addressed the potential effects of taphonomy and diagenesis on these proxy records. Assessing archaeological samples are especially complex in that humans may have transported and/or cooked shell prior to deposition. Shell δ15N data will be presented from modern and archaeological oyster (Crassostrea virginica) and clam shell (Mercenaria spp.) of various late Holocene ages and late Cretaceous Crassatellites vadosus shells. Archaeological shells show some loss of organic matter over time, yet some Cretaceous shells retain enough matrix to permit δ15N analysis. The Cretaceous samples required concentration of the remaining organic matrix by removing carbonate via acid pretreatment prior to EA-IRMS analysis, but modern and archaeological shells had sufficient organic matrix to permit analysis without acid pretreatment. The δ15N data from the archaeological shells do not display obvious alteration from the loss of organic matrix. The results of cooking experiments performed on modern oyster shells also indicate little alteration of δ15N values, unless the shell was heated to the point of disintegration. While these experiments indicate promise for the application of δ15N analysis of shell organic matter, the results are incomplete and lack ideal control over initial δ15N values in ancient samples used for comparisons. Future research, perhaps focused on compound-specific δ15N analysis and additional controlled experiments on moderns shells, may improve this assessment.

  1. Evaluating cleansing effects on trace elements and stable isotope values in feathers of oiled birds.

    PubMed

    Valladares, Sonia; Moreno, Roćio; Jover, Lluis; Sanpera, Carola

    2010-01-01

    Feathers of seabirds are widely used as a nondestructive tissue for pollution monitoring of trace elements, as well as convenient samples for trophic ecology studies by means of stable isotope analysis (SIA). Nevertheless, feathers can be occasionally impregnated with oil from deliberate ship discharges and from massive oil spill accidents. The feather structure makes them effective traps for particles and are subject to external contamination. It is unknown to what extent the oil adhered to feathers can change trace element concentrations or stable isotope signatures. This study has two primary objectives: (1) to assess if there are differences between trace element concentrations and stable isotope signatures of oiled and clean feathers, and (2) to determine if the cleansing of oiled feathers using commonly applied techniques such as sodium hydroxide (NaOH) washes in combination with an organic solvent (hexane) is more effective than using NaOH alone. In order to do this, we analysed trace elements (Se, Hg, Pb, Cu and Zn) and stable isotopes (delta(13)C and delta(15)N) of individual feathers of yellow-legged gulls (Larus michahellis) which were affected by the 2002 Prestige oil spill in Galicia (NW Spain). Two sets of feathers were analysed, one group were oil-free (Control group) and the other had oil adhered to its surface (Oiled group). We expected to find differences between control and oiled feathers when cleaning exclusively with NaOH and no differences when using hexane. Our results did not show significant differences between Control and Oiled groups as a consequence of the cleansing method used. Unexpectedly, the additional cleansing with hexane resulted in decreasing selenium concentrations and increasing zinc and delta(15)N values in all groups of feathers. PMID:19731016

  2. Microturbulence study of the isotope effect

    SciTech Connect

    Bustos, A.; Bañón Navarro, A.; Görler, T.; Jenko, F.

    2015-01-15

    The influence of the ion mass on the dynamics of magnetized plasmas is an important challenge in fusion research. The discrepancies between the improvement of the magnetic confinement with the ion mass in tokamak experiments and diffusive turbulent transport predictions have remained unexplained for several decades. We refer to this phenomenon as the isotope effect. In this paper, we study this effect with gyrokinetic theory using the GENE code. We find several sets of plasma parameters that correspond to low wavenumber turbulence for which the isotope effect is present, although the intensity is smaller than the experimental observations. We also relate these results to the zonal flow intensity of the system, which is characterized by the average shear flow rate.

  3. Nitrogen isotope fractionation during archaeal ammonia oxidation: Coupled estimates from isotopic measurements of ammonium and nitrite

    NASA Astrophysics Data System (ADS)

    Mooshammer, Maria; Stieglmeier, Michaela; Bayer, Barbara; Jochum, Lara; Melcher, Michael; Wanek, Wolfgang

    2014-05-01

    Ammonia-oxidizing archaea (AOA) are ubiquitous in marine and terrestrial environments and knowledge about the nitrogen (N) isotope effect associated with their ammonia oxidation activity will allow a better understanding of natural abundance isotope ratios, and therefore N transformation processes, in the environment. Here we examine the kinetic isotope effect for ammonia oxidation in a pure soil AOA culture (Ca. Nitrososphaera viennensis) and a marine AOA enrichment culture. We estimated the isotope effect from both isotopic signatures of ammonium and nitrite over the course of ammonia oxidation. Estimates of the isotope effect based on the change in the isotopic signature of ammonium give valuable insight, because these estimates are not subject to the same concerns (e.g., accumulation of an intermediate) as estimates based on isotopic measurements of nitrite. Our results show that both the pure soil AOA culture and a marine AOA enrichment culture have similar but substantial isotope effect during ammonia consumption (31-34 per mill; based on ammonium) and nitrite production (43-45 per mill; based on nitrite). The 15N fractionation factors of both cultures tested fell in the upper range of the reported isotope effects for archaeal and bacterial ammonia oxidation (10-41 per mill) or were even higher than those. The isotope fractionation for nitrite production was significantly larger than for ammonium consumption, indicating that (1) some intermediate (e.g., hydroxylamine) of ammonia oxidation accumulates, allowing for a second 15N fractionation step to be expressed, (2) a fraction of ammonia oxidized is lost via gaseous N forms (e.g., NO or N2O), which is 15N-enriched or (3) a fraction of ammonium is assimilated into AOA biomass, biomass becoming 15N-enriched. The significance of these mechanisms will be explored in more detail for the soil AOA culture, based on isotope modeling and isotopic measurements of biomass and N2O.

  4. Paleoenvironmental implications of taxonomic variation among δ15N values of chloropigments

    USGS Publications Warehouse

    Higgins, Meytal B.; Wolfe-Simon, Felisa; Robinson, Rebecca S.; Qin, Yelun; Saito, Mark A.; Pearson, Ann

    2011-01-01

    Natural variations in the ratios of nitrogen isotopes in biomass reflect variations in nutrient sources utilized for growth. In order to use δ15N values of chloropigments of photosynthetic organisms to determine the corresponding δ15N values of biomass – and by extension, surface waters – the isotopic offset between chlorophyll and biomass must be constrained. Here we examine this offset in various geologically-relevant taxa, grown using nutrient sources that may approximate ocean conditions at different times in Earth’s history. Phytoplankton in this study include cyanobacteria (diazotrophic and non-diazotrophic), eukaryotic algae (red and green), and anoxygenic photosynthetic bacteria (Proteobacteria), as well as environmental samples from sulfidic lake water. Cultures were grown using N2, NO3−, and NH4+ as nitrogen sources, and were examined under different light regimes and growth conditions. We find surprisingly high variability in the isotopic difference (δ15Nbiomass − δ15Nchloropigment) for prokaryotes, with average values for species ranging from −12.2‰ to +11.7‰. We define this difference as εpor, a term that encompasses diagenetic porphyrins and chlorins, as well as chlorophyll. Negative values of εpor reflect chloropigments that are 15N-enriched relative to biomass. Notably, this enrichment appears to occur only in cyanobacteria. The average value of εpor for freshwater cyanobacterial species is −9.8 ± 1.8‰, while for marine cyanobacteria it is −0.9 ± 1.3‰. These isotopic effects group environmentally but not phylogenetically, e.g., εpor values for freshwater Chroococcales resemble those of freshwater Nostocales but differ from those of marine Chroococcales. Our measured values of εpor for eukaryotic algae (range = 4.7–8.7‰) are similar to previous reports for pure cultures. For all taxa studied, values of εpor do not depend on the type of nitrogen substrate used for growth. The observed

  5. Refining cotton-wick method for 15N plant labelling.

    NASA Astrophysics Data System (ADS)

    Fustec, Joëlle; Mahieu, Stéphanie

    2010-05-01

    The symbiosis Fabaceae/Rhizobiaceae plays a critical role in the nitrogen cycle. It gives the plant the ability to fix high amounts of atmospheric N. A part of this N can be transferred to the soil via rhizodeposition. The contribution of Fabaceae to the soil N pool is difficult to measure, since it is necessary for assessing N benefits for other crops, for soil biological activity, and for reducing water pollution in sustainable agriculture (Fustec, 2009). The aim of this study was to test and improve the reliability of the 15N cotton-wick method for measuring the soil N derived from plant rhizodeposition (Mahieu et al., 2007). The effects of the concentration of the 15N-urea labelling solution and of the feeding frequency (continuous or pulses) on the assessment of nitrogen rhizodeposition were studied in two greenhouse experiments using the field pea (Pisum sativum L.) and the non-nodulating isoline P2. The plant parts and the soil were prepared for 15N:14N measurements for assessing N rhizodeposition (Mahieu et al., 2009). The fraction of plants' belowground nitrogen allocated to rhizodeposition in both Frisson pea and P2 was 20 to more than 50% higher when plants were labelled continuously than when they were labelled using fortnightly pulses. Our results suggested that when 15N root enrichment was high, nitrogen rhizodeposition was underestimated only for plants that were 15N-fed by fortnightly pulses, and not in plants 15N-fed continuously. This phenomenon was especially observed for plants relying on symbiotic N fixation for N acquisition; it may be linked to the concentration of the labelling solution. In conclusion, N rhizodeposition assessment was strongly influenced by the 15N-feeding frequency and the concentration of the labelling solution. The estimation of N rhizodeposition was more reliable when plants were labelled continuously with a dilute solution of 15N urea. Fustec et al. 2009. Agron. Sustain. Dev., DOI 10.1051/agro/2009003, in press. Mahieu

  6. Laboratory study of nitrate photolysis in Antarctic snow. II. Isotopic effects and wavelength dependence

    NASA Astrophysics Data System (ADS)

    Berhanu, Tesfaye A.; Meusinger, Carl; Erbland, Joseph; Jost, Rémy; Bhattacharya, S. K.; Johnson, Matthew S.; Savarino, Joël

    2014-06-01

    Atmospheric nitrate is preserved in Antarctic snow firn and ice. However, at low snow accumulation sites, post-depositional processes induced by sunlight obscure its interpretation. The goal of these studies (see also Paper I by Meusinger et al. ["Laboratory study of nitrate photolysis in Antarctic snow. I. Observed quantum yield, domain of photolysis, and secondary chemistry," J. Chem. Phys. 140, 244305 (2014)]) is to characterize nitrate photochemistry and improve the interpretation of the nitrate ice core record. Naturally occurring stable isotopes in nitrate (15N, 17O, and 18O) provide additional information concerning post-depositional processes. Here, we present results from studies of the wavelength-dependent isotope effects from photolysis of nitrate in a matrix of natural snow. Snow from Dome C, Antarctica was irradiated in selected wavelength regions using a Xe UV lamp and filters. The irradiated snow was sampled and analyzed for nitrate concentration and isotopic composition (δ15N, δ18O, and Δ17O). From these measurements an average photolytic isotopic fractionation of 15ɛ = (-15 ± 1.2)‰ was found for broadband Xe lamp photolysis. These results are due in part to excitation of the intense absorption band of nitrate around 200 nm in addition to the weaker band centered at 305 nm followed by photodissociation. An experiment with a filter blocking wavelengths shorter than 320 nm, approximating the actinic flux spectrum at Dome C, yielded a photolytic isotopic fractionation of 15ɛ = (-47.9 ± 6.8)‰, in good agreement with fractionations determined by previous studies for the East Antarctic Plateau which range from -40 to -74.3‰. We describe a new semi-empirical zero point energy shift model used to derive the absorption cross sections of 14NO3- and 15NO3- in snow at a chosen temperature. The nitrogen isotopic fractionations obtained by applying this model under the experimental temperature as well as considering the shift in width and center well

  7. Laboratory study of nitrate photolysis in Antarctic snow. II. Isotopic effects and wavelength dependence.

    PubMed

    Berhanu, Tesfaye A; Meusinger, Carl; Erbland, Joseph; Jost, Rémy; Bhattacharya, S K; Johnson, Matthew S; Savarino, Joël

    2014-06-28

    Atmospheric nitrate is preserved in Antarctic snow firn and ice. However, at low snow accumulation sites, post-depositional processes induced by sunlight obscure its interpretation. The goal of these studies (see also Paper I by Meusinger et al. ["Laboratory study of nitrate photolysis in Antarctic snow. I. Observed quantum yield, domain of photolysis, and secondary chemistry," J. Chem. Phys. 140, 244305 (2014)]) is to characterize nitrate photochemistry and improve the interpretation of the nitrate ice core record. Naturally occurring stable isotopes in nitrate ((15)N, (17)O, and (18)O) provide additional information concerning post-depositional processes. Here, we present results from studies of the wavelength-dependent isotope effects from photolysis of nitrate in a matrix of natural snow. Snow from Dome C, Antarctica was irradiated in selected wavelength regions using a Xe UV lamp and filters. The irradiated snow was sampled and analyzed for nitrate concentration and isotopic composition (δ(15)N, δ(18)O, and Δ(17)O). From these measurements an average photolytic isotopic fractionation of (15)ɛ = (-15 ± 1.2)‰ was found for broadband Xe lamp photolysis. These results are due in part to excitation of the intense absorption band of nitrate around 200 nm in addition to the weaker band centered at 305 nm followed by photodissociation. An experiment with a filter blocking wavelengths shorter than 320 nm, approximating the actinic flux spectrum at Dome C, yielded a photolytic isotopic fractionation of (15)ɛ = (-47.9 ± 6.8)‰, in good agreement with fractionations determined by previous studies for the East Antarctic Plateau which range from -40 to -74.3‰. We describe a new semi-empirical zero point energy shift model used to derive the absorption cross sections of (14)NO3 (-) and (15)NO3 (-) in snow at a chosen temperature. The nitrogen isotopic fractionations obtained by applying this model under the experimental temperature as well as considering the

  8. Laboratory study of nitrate photolysis in Antarctic snow. II. Isotopic effects and wavelength dependence

    SciTech Connect

    Berhanu, Tesfaye A.; Erbland, Joseph; Savarino, Joël; Meusinger, Carl; Johnson, Matthew S.; Jost, Rémy; Bhattacharya, S. K.

    2014-06-28

    Atmospheric nitrate is preserved in Antarctic snow firn and ice. However, at low snow accumulation sites, post-depositional processes induced by sunlight obscure its interpretation. The goal of these studies (see also Paper I by Meusinger et al. [“Laboratory study of nitrate photolysis in Antarctic snow. I. Observed quantum yield, domain of photolysis, and secondary chemistry,” J. Chem. Phys. 140, 244305 (2014)]) is to characterize nitrate photochemistry and improve the interpretation of the nitrate ice core record. Naturally occurring stable isotopes in nitrate ({sup 15}N, {sup 17}O, and {sup 18}O) provide additional information concerning post-depositional processes. Here, we present results from studies of the wavelength-dependent isotope effects from photolysis of nitrate in a matrix of natural snow. Snow from Dome C, Antarctica was irradiated in selected wavelength regions using a Xe UV lamp and filters. The irradiated snow was sampled and analyzed for nitrate concentration and isotopic composition (δ{sup 15}N, δ{sup 18}O, and Δ{sup 17}O). From these measurements an average photolytic isotopic fractionation of {sup 15}ε = (−15 ± 1.2)‰ was found for broadband Xe lamp photolysis. These results are due in part to excitation of the intense absorption band of nitrate around 200 nm in addition to the weaker band centered at 305 nm followed by photodissociation. An experiment with a filter blocking wavelengths shorter than 320 nm, approximating the actinic flux spectrum at Dome C, yielded a photolytic isotopic fractionation of {sup 15}ε = (−47.9 ± 6.8)‰, in good agreement with fractionations determined by previous studies for the East Antarctic Plateau which range from −40 to −74.3‰. We describe a new semi-empirical zero point energy shift model used to derive the absorption cross sections of {sup 14}NO{sub 3}{sup −} and {sup 15}NO{sub 3}{sup −} in snow at a chosen temperature. The nitrogen isotopic fractionations obtained by applying

  9. N and O isotope effects during nitrate assimilation by unicellular prokaryotic and eukaryotic plankton cultures

    NASA Astrophysics Data System (ADS)

    Granger, J.; Sigman, D. M.; Rohde, M. M.; Maldonado, M. T.; Tortell, P. D.

    2010-02-01

    In order to provide biological systematics from which to interpret nitrogen (N) and oxygen (O) isotope ratios of nitrate ( 15N/ 14N, 18O/ 16O, respectively) in the environment, we previously investigated the isotopic fractionation of nitrate during its assimilation by mono-cultures of eukaryotic algae ( Granger et al., 2004). In this study, we extended our analysis to investigate nitrate assimilation by strains of prokaryotic plankton. We measured the N and O isotope effects, 15ɛ and 18ɛ, during nitrate consumption by cultures of prokaryotic strains and by additional eukaryotic phytoplankton strains (where ɛ is the ratio of reaction rate constants of the light vs. heavy isotopologues, lightk and heavyk; ɛ = lightk/ heavyk - 1 × 1000, expressed in per mil). The observed 15ɛ ranged from 5‰ to 8‰ among eukaryotes, whereas it did not exceed 5‰ for three cyanobacterial strains, and was as low as 0.4‰ for a heterotrophic α-protoeobacterium. Eukaryotic phytoplankton fractionated the N and O isotopes of nitrate to the same extent (i.e., 18ɛ ˜ 15ɛ). The 18ɛ: 15ɛ among the cyanobacteria was also ˜1, whereas the heterotrophic α-proteobacterial strain, which showed the lowest 15ɛ, between 0.4‰ and 1‰, had a distinct 18ɛ: 15ɛ of ˜2, unlike any plankton strain observed previously. Equivalent N vs. O isotope discrimination is thought to occur during internal nitrate reduction by nitrate reductase, such that the cellular efflux of the fractionated nitrate into the medium drives the typically observed 18ɛ: 15ɛ of ˜1. We hypothesize that the higher in the 18ɛ: 15ɛ of the α-proteobacterium may result from isotope discrimination by nitrate transport, which is evident only at low amplitude of ɛ. These observations warrant investigating whether heterotrophic bacterial assimilation of nitrate decreases the community isotope effects at the surface ocean.

  10. Incorporation of 15N-labeled ammonia into glutamine amide groups by protein-glutaminase and analysis of the reactivity for α-lactalbumin.

    PubMed

    Miwa, Noriko; Shimba, Nobuhisa; Nakamura, Mina; Yokoyama, Keiichi; Nio, Noriki; Suzuki, Eiichiro; Sonomoto, Kenji

    2011-12-28

    Protein-glutaminase (PG) is an enzyme that catalyzes the deamidation of protein-bound glutamine residues. We found that an enzyme labeling technique (ELT), which is a stable isotope labeling method based on transglutaminase (TGase) reaction, is applicable for PG. PG catalyzed incorporation of (15)N-labeled ammonium ions into reactive glutamine amide groups in α-lactalbumin similarly to TGase and deamidated the most reactive glutamine amide group once labeled with (15)N. Furthermore, we investigated the effect of ammonium ions on the PG activity by peptide mapping, and more reactive glutamine residues were detected than were detected by the ELT in the presence of ammonium ions. This is probably because ammonium ions are competitive inhibitors, causing decreased reactivity for glutamine residues. We propose the reaction scheme of PG in the presence of the (15)N-labeled ammonium ions and show that the ELT method with PG is useful for evaluating the activity of PG. PMID:22060122

  11. Reconstruction of the oceanic nitrate inventory in the Pliocene Caribbean Sea: Foraminifera-bound δ15N - A new approach

    NASA Astrophysics Data System (ADS)

    Straub, M.; Haug, G. H.; Sigman, D. M.; Ren, H.

    2010-12-01

    The nitrate budget in the low-latitude surface ocean is mainly controlled by the opposing effects of denitrification and nitrate fixation. The state of the global ocean nitrate inventory highly affects primary production, which allows sequestering CO2 into the deep ocean. This may influence climate variability and control warm and cold periods in Earth history. Studies have shown that nitrogen isotopes reflect the nutrient status of the upper water column and therefore can be used as proxy for the state of the ocean’s ‘biological pump’. The nitrate inventory has mostly been reconstructed based on bulk sedimentary N-isotope measurements, which can be affected by syn- and post-sedimentary processes. Promising approaches to circumvent these potential biases are based on measurements of foraminifera-bound δ15N isotopes. In the subtropical and tropical ocean, planktonic foraminifera are a main component of the sinking particle flux. The organic compounds encapsulated within the foraminiferal tests are protected from sedimentary diagenetic processes and record a pristine signal of the nitrate composition of the upper water column. The novel method used in this study employs denitrifying bacteria (Pseudomonas chlororaphis and Pseudomonas aureofaciens) to produce nitrous oxide (N2O), recovered from the nitrate extracted from the organic matter sheltered within the foraminifera shell. The extracted N2O is analyzed for δ15N with a Gas bench II - IRMS and yields results with reproducible isotopic measurements of samples with nitrate concentrations down to 1 μM. Previous data from the investigated site (ODP Leg 165, Site 999A, Caribbean Sea), spanning the last 30’000 yrs using the same method, indicate a systematic difference between glacial and interglacial values. The glacial state is characterized by high δ15N values around ~ 5 ‰ (suggesting less N-fixation) and the interglacial by low δ15N values around ~ 3 ‰ (N-fixation increase). Pliocene data from

  12. 15N fractionation in star-forming regions and Solar System objects

    NASA Astrophysics Data System (ADS)

    Wirström, Eva; Milam, Stefanie; Adande, Gilles; Charnley, Steven B.; Cordiner, Martin A.

    2015-08-01

    A central issue for understanding the formation and evolution of matter in the early Solar System is the relationship between the chemical composition of star-forming interstellar clouds and that of primitive Solar System materials. The pristine molecular content of comets, interplanetary dust particles and carbonaceous chondrites show significant bulk nitrogen isotopic fractionation relative to the solar value, 14N/15N ~ 440. In addition, high spatial resolution measurements in primitive materials locally show even more extreme enhancements of 14N/15N < 100.The coherent 15N enrichment in comets from different formation zones suggests that these isotopic enhancements are remnants of the interstellar chemistry in the natal molecular cloud core and the outer protosolar nebula. Indeed, early chemical models of gas-phase ion-molecule nitrogen fractionation showed that HCN and HNC (nitriles) can hold significant 15N enrichments in cold dark clouds where CO is depleted onto dust grains. In addition, 15N fractionation in nitriles and amines (NH2, NH3) follow different chemical pathways. More recently we have shown that once the spin-state dependence in rates of reactions with H2 is included in the models, amines can either be enhanced or depleted in 15N, depending on the core’s evolutionary stage. Observed 15N fractionation in amines and nitriles therefore cannot be expected to be the same, instead their ratio is a potential chemical clock.Observations of molecular isotope ratios in dark cores are challenging. Limited published results in general show higher 15N/14N ratios in HCN and HNC than ammonia, but more measurements are necessary to confirm these trends. We will present recent results from our ongoing observing campaign of 14N/15N isotopic ratios in HCN, HNC and NH3 in dense cores and protostars which seem consistent with significant fractionation in nitriles as compared to other molecules in each object. The few 14N/15N ratios observed in N2H+ are similar to

  13. Massive isotopic effect in vacuum UV photodissociation of N2 and implications for meteorite data.

    PubMed

    Chakraborty, Subrata; Muskatel, B H; Jackson, Teresa L; Ahmed, Musahid; Levine, R D; Thiemens, Mark H

    2014-10-14

    Nitrogen isotopic distributions in the solar system extend across an enormous range, from -400‰, in the solar wind and Jovian atmosphere, to about 5,000‰ in organic matter in carbonaceous chondrites. Distributions such as these require complex processing of nitrogen reservoirs and extraordinary isotope effects. While theoretical models invoke ion-neutral exchange reactions outside the protoplanetary disk and photochemical self-shielding on the disk surface to explain the variations, there are no experiments to substantiate these models. Experimental results of N2 photolysis at vacuum UV wavelengths in the presence of hydrogen are presented here, which show a wide range of enriched δ(15)N values from 648‰ to 13,412‰ in product NH3, depending upon photodissociation wavelength. The measured enrichment range in photodissociation of N2, plausibly explains the range of δ(15)N in extraterrestrial materials. This study suggests the importance of photochemical processing of the nitrogen reservoirs within the solar nebula. PMID:25267643

  14. Massive isotopic effect in vacuum UV photodissociation of N2 and implications for meteorite data

    PubMed Central

    Chakraborty, Subrata; Muskatel, B. H.; Jackson, Teresa L.; Ahmed, Musahid; Levine, R. D.; Thiemens, Mark H.

    2014-01-01

    Nitrogen isotopic distributions in the solar system extend across an enormous range, from −400‰, in the solar wind and Jovian atmosphere, to about 5,000‰ in organic matter in carbonaceous chondrites. Distributions such as these require complex processing of nitrogen reservoirs and extraordinary isotope effects. While theoretical models invoke ion-neutral exchange reactions outside the protoplanetary disk and photochemical self-shielding on the disk surface to explain the variations, there are no experiments to substantiate these models. Experimental results of N2 photolysis at vacuum UV wavelengths in the presence of hydrogen are presented here, which show a wide range of enriched δ15N values from 648‰ to 13,412‰ in product NH3, depending upon photodissociation wavelength. The measured enrichment range in photodissociation of N2, plausibly explains the range of δ15N in extraterrestrial materials. This study suggests the importance of photochemical processing of the nitrogen reservoirs within the solar nebula. PMID:25267643

  15. Fate of nitrogen deposition and decomposed nitrogen from litter in a 15N-tracer mesocosm experiment

    NASA Astrophysics Data System (ADS)

    Nair, R.; Perks, M.; Mencuccini, M.

    2013-12-01

    Atmospheric deposition of anthropogenic-derived nitrogen may be a major driver of the 0.6-0.7 Pg y-1 increase in the carbon sink in historically N-limited northern and boreal forests, but the magnitude of its effect is still uncertain. A strong effect depends on the allocation of N to trees, because of their high C:N ratio in woody tissues, and isotope tracer experiments have shown that the majority of 15N tracers applied directly to the soil are lost via leeching or retained in soil pools rather than being acquired by tree root systems. However, ambient anthropogenic inputs of N to these systems are transported in the atmosphere and intercepted by foliage before they reach the soil system, while labelled fertilization experiments also can only explicitly trace the fate of the 15N-tracer from deposition, as opposed to changes in the fate of N from litter, where decomposition rates may be enhanced at low ambient levels of deposition, affecting the availability of N from this pool for tree nutrition. We present initial results from a potted Sitka Spruce mesocosm 15N-tracer experiment where ambient nitrogen deposition was supplemented with a minor (0.4 kg ha-1 y-1) input of additional N, applied to either the soil or the foliage. Either this deposition, or litter in the pots, was enriched in 15N, allowing the fate of the isotope from two different methods of deposition to be compared with that of nitrogen released from the litter under the deposition treatment.

  16. A novel method for trapping and analyzing 15N in NO for tracing NO sources

    NASA Astrophysics Data System (ADS)

    Kang, Ronghua; Mulder, Jan; Dörsch, Peter

    2016-04-01

    15N isotope tracing is an effective and direct approach to investigate the biological and chemical sources of nitric oxide (NO) in soil. However, NO is highly reactive and rapidly converted to nitrogen dioxide (NO2) in the presence of ozone. Various chemical conversions of NO to the more stable solutes nitrite (NO2-) and nitrate (NO3-) have been proposed, which allow analysing the 15N abundance without major fractionation. However, NO emissions from soils are usually small, posing major challenges to conversion efficiency and background contamination. Here we present a novel method in which NO is oxidized to NO2- by chromium trioxide (CrO3) prior to conversion to NO2- and NO3- in an alkaline hydrogen peroxide (H2O2) solution. Immediately following trapping, manganese dioxide (MnO2) and 5M HCl are added to remove excess H2O2, and to adjust the pH to around 6.0-7.0, respectively. The resulting solution can be stored until analysis and is none-toxic, allowing to use a modified denitrifier method (Zhu et al., submitted), where NO2- and NO3- are reduced quantitatively to nitrous oxide (N2O). Optimum NO conversion rates of > 90% even at extremely low initial NO concentration were obtained with 4% H2O2, 0.5 M NaOH, and 0.5 L min-1 gas flow rate. In a laboratory test, using NO gas with different 15N signals produced from unlabelled and labelled NO2-, we found an overall precision of 0.4‰ for unlabelled and 49.7‰ for NO enriched with 1.0 atom% 15N, respectively. This indicates that this method can be used for both natural abundance studies of NO, as well as in labelling studies tracing NO sources. Zhu J, Yu L, Bakken LR, Mørkved PT, Mulder J, Dörsch P. Controlled induction of denitrification in Pseudomonas aureofaciens: a modified denitrifier method for 15N and 18O analysis in NO3- from natural water samples by IRMS. Submitted.

  17. A spectacular nitrogen isotope anomaly in Bencubbin

    NASA Technical Reports Server (NTRS)

    Prombo, C. A.; Clayton, R. N.

    1985-01-01

    Results of isotopic measurements on an unusual stony-iron meteorite named Bencubbin, which was found in Western Australia in 1930, are reported. Nitrogen from both the metallic and stony parts of the Bencubbin meteorite was analyzed, and in both materials large excesses of (15)N were found, resulting in values of the (14)N/(15)N abundance ratios as low as 137. That is, (15)N is enriched in Bencubbin by about a factor of two relative to terrestrial nitrogen. This is the largest (15)N enrichment of any known natural material. The effect is so large that chemical processes are probably inadequate to account for it. Nuclear processes which may be responsible for the anomalous isotope abundance are discussed.

  18. Theoretical and experimental study of 15N NMR protonation shifts.

    PubMed

    Semenov, Valentin A; Samultsev, Dmitry O; Krivdin, Leonid B

    2015-06-01

    A combined theoretical and experimental study revealed that the nature of the upfield (shielding) protonation effect in 15N NMR originates in the change of the contribution of the sp(2)-hybridized nitrogen lone pair on protonation resulting in a marked shielding of nitrogen of about 100 ppm. On the contrary, for amine-type nitrogen, protonation of the nitrogen lone pair results in the deshielding protonation effect of about 25 ppm, so that the total deshielding protonation effect of about 10 ppm is due to the interplay of the contributions of adjacent natural bond orbitals. A versatile computational scheme for the calculation of 15N NMR chemical shifts of protonated nitrogen species and their neutral precursors is proposed at the density functional theory level taking into account solvent effects within the supermolecule solvation model. PMID:25891386

  19. Stellar Origins of Extremely 13C- and 15N-enriched Presolar SiC Grains: Novae or Supernovae?

    NASA Astrophysics Data System (ADS)

    Liu, Nan; Nittler, Larry R.; O'D. Alexander, Conel M.; Wang, Jianhua; Pignatari, Marco; José, Jordi; Nguyen, Ann

    2016-04-01

    Extreme excesses of 13C (12C/13C < 10) and 15N (14N/15N < 20) in rare presolar SiC grains have been considered diagnostic of an origin in classical novae, though an origin in core collapse supernovae (CCSNe) has also been proposed. We report C, N, and Si isotope data for 14 submicron- to micron-sized 13C- and 15N-enriched presolar SiC grains (12C/13C < 16 and 14N/15N < ˜100) from Murchison, and their correlated Mg-Al, S, and Ca-Ti isotope data when available. These grains are enriched in 13C and 15N, but with quite diverse Si isotopic signatures. Four grains with 29,30Si excesses similar to those of type C SiC grains likely came from CCSNe, which experienced explosive H burning occurred during explosions. The independent coexistence of proton- and neutron-capture isotopic signatures in these grains strongly supports heterogeneous H ingestion into the He shell in pre-supernovae. Two of the seven putative nova grains with 30Si excesses and 29Si depletions show lower-than-solar 34S/32S ratios that cannot be explained by classical nova nucleosynthetic models. We discuss these signatures within the CCSN scenario. For the remaining five putative nova grains, both nova and supernova origins are viable because explosive H burning in the two stellar sites could result in quite similar proton-capture isotopic signatures. Three of the grains are sub-type AB grains that are also 13C enriched, but have a range of higher 14N/15N. We found that 15N-enriched AB grains (˜50 < 14N/15N < ˜100) have distinctive isotopic signatures compared to putative nova grains, such as higher 14N/15N, lower 26Al/27Al, and lack of 30Si excess, indicating weaker proton-capture nucleosynthetic environments.

  20. A 115-year δ15N record of cumulative nitrogen pollution in California serpentine grasslands

    NASA Astrophysics Data System (ADS)

    Vallano, D.; Zavaleta, E. S.

    2010-12-01

    Until the 1980s, California’s biodiverse serpentine grasslands were threatened primarily by development and protected by reserve creation. However, nitrogen (N) fertilization due to increasing fossil fuel emissions in the expanding Bay Area is thought to be contributing to rapid, recent invasion of these ecosystems by exotic annual grasses that are displacing rare and endemic serpentine species. Documenting the cumulative effects of N deposition in this ecosystem can direct policy and management actions to mitigate the role of N deposition in its transformation. Natural abundance stable isotopes of N in vegetation have been increasingly used as bio-indicators of N deposition patterns and subsequent changes to plant N cycling and assimilation. However, the long-term record of atmospheric reactive N enrichment and the resulting changes in ecosystem N dynamics have yet to be adequately reconstructed in many ecosystems. Museum archives of vascular plant tissue are valuable sources of materials to reconstruct temporal and spatial isotopic patterns of N inputs to ecosystems. Here, we present N stable isotope data from archived and current specimens of an endemic California serpentine grassland species, leather oak (Quercus durata), since 1895 across the greater San Francisco Bay region. We measured spatial and temporal trends in stable isotope composition (δ15N and δ13C) and concentration (%N and %C) of historical and current samples of leather oak leaves from sites within the Bay Area, impacted by increasing development, and sites northeast of the Bay Area, with significantly lower rates of urbanization and industrialization. Specifically, we sampled dry museum and fresh leaf specimens from serpentine sites within Lake (n=27) and Santa Clara (n=30) counties dating from 1895 to 2010. Leaf δ15N values were stable from 1895 to the 1950s and then decreased strongly throughout the last 50 years as fossil fuel emissions rapidly increased in the Bay Area, indicating that

  1. (15)N methodologies for quantifying the response of N2-fixing associations to elevated [CO2]: A review.

    PubMed

    Chalk, Phillip M; Lam, Shu K; Chen, Deli

    2016-11-15

    Methodologies based on (15)N enrichment (E) and (15)N natural abundance (NA) have been used to obtain quantitative estimates of the response of biological N2 fixation (BNF) of legumes (woody, grain and forage) and actinorhizal plants grown in artificial media or in soil exposed to elevated atmospheric concentrations of carbon dioxide e[CO2] for extended periods of time, in growth rooms, greenhouses, open top chambers or free-air CO2 enrichment (FACE) facilities. (15)N2 has also been used to quantify the response of endophytic and free-living diazotrophs to e[CO2]. The primary criterion of response was the proportional dependence of the N2-fixing system on the atmosphere as a source of N. i.e. the symbiotic dependence (Patm). The unique feature of (15)N-based methods is their ability to provide time-integrated and yield-independent estimates of Patm. In studies conducted in artificial media or in soil using the E methodology there was either no response or a positive response of Patm to e[CO2]. The interpretation of results obtained in artificial media or with (15)N2 is straight forward, not being subject to the assumptions on which the E and NA soil-cultured methods are based. A variety of methods have been used to estimate isotopic fractionation attendant on the NA technique, the so-called 'B value', which attaches a degree of uncertainty to the results obtained. Using the NA technique, a suite of responses of Patm to e[CO2] has been published, from positive to neutral to sometimes negative effects. Several factors which interact with the response of N2-fixing species to e[CO2] were identified. PMID:27424117

  2. Effects of acid washing on stable isotope ratios of C and N in penaeid shrimp and seagrass: Implications for food-web studies using multiple stable isotopes

    SciTech Connect

    Bunn, S.E.; Kempster, M.A.; Loneragan, N.R.

    1995-05-01

    We investigated the effects of acid washing on the carbon and nitrogen composition and stable isotope ratios of C and N in shrimp (Metapenaeus spp.) and seagrass (Enhalus acoroides). Acid washing did not affect the mean {delta}{sup 13}C ratios for juvenile Metapenaeus moyebi and resulted in only an ecologically insignificant change (0.3%) in mean {delta}{sup 13}C ratios for larger metapenaeus bennettae. In contrast, acid washing increased the mean {delta}{sup 15}N signatures of shrimp tissue ({approximately}3%) and decreased that of seagrass ({approximately}1.8%) to a degree that may confound the interpretation of food webs. The increase in %C and %N in both shrimp and seagrass after acid washing suggests that the changes in isotope ratios are due to loss of molecules comparatively low in C and N. Treating samples by acid washing also resulted in an increase in the variation among individuals for both {delta}{sup 15}N and {delta}{sup 13}C, which would lead to a loss of statistical power for testing differences between species, sites, or seasons. 13 refs., 2 figs., 1 tab.

  3. Isotopic studies in Pacific Panama mangrove estuaries reveal lack of effect of watershed deforestation on food webs.

    PubMed

    Viana, Inés G; Valiela, Ivan; Martinetto, Paulina; Monteiro Pierce, Rita; Fox, Sophia E

    2015-02-01

    Stable isotopic N, C, and S in food webs of 8 mangrove estuaries on the Pacific coast of Panama were measured to 1) determine whether the degree of deforestation of tropical forests on the contributing watersheds was detectable within the estuarine food web, and 2) define external sources of the food webs within the mangrove estuaries. Even though terrestrial rain forest cover on the contributing watersheds differed between 23 and 92%, the effect of deforestation was not detectable on stable isotopic values in food webs present at the mouth of the receiving estuaries. We used stable isotopic measures to identify producers or organic sources that supported the estuarine food web. N isotopic values of consumers spanned a broad range, from about 2.7 to 12.3‰. Mean δ(15)N of primary producers and organic matter varied from 3.3 for macroalgae to 4.7‰ for suspended particulate matter and large particulate matter. The δ(13)C consumer data varied between -26 and -9‰, but isotopic values of the major apparent producers or organic matter sampled could not account for this range variability. The structure of the food web was clarified when we added literature isotopic values of microphytobenthos and coralline algae, suggesting that these, or other producers with similar isotopic signature, may be part of the food webs. PMID:25481652

  4. Global nitrogen cycle: pre-Anthropocene mass and isotope fluxes and effects of human perturbations

    NASA Astrophysics Data System (ADS)

    Joo, Y.; Li, D. D.; Lerman, A.; Mackenzie, F. T.

    2012-12-01

    The size of the largest nitrogen reservoir -- the Earth atmosphere -- and its long residence time of approximately 17 million years suggest that the global N cycle was likely to be balanced at geological time scales. After the industrial revolution, human activities, such as mining, fossil fuel burning, land use change, and artificial fertilization, have resulted in perturbations and numerous flux changes of the N cycle. The effects of human activities on the mass and isotopic composition of the N reservoirs can be predicted using a detailed N cycle model with estimated additions. For the pre-Anthropocene period, a balanced steady-state N cycle model was constructed based on the Redfield ratios and an extensive literature review. The model includes 14 N reservoirs in the domains of the atmosphere, land, and ocean. The biotic reservoirs on land and in the ocean (land plants and marine biota) interact with atmospheric N2 and dissolved inorganic N (DIN) in ocean and soil waters. DIN further interacts with dissolved organic N (DON), particulate organic matter (POM), and ocean sediments. Atmosphere supplies N to land and ocean domains mainly by N fixation, deposition, and dissolution, and these fluxes are balanced by denitrification and volatilization back to atmosphere. Riverine transport of dissolved and particulate N connects land and ocean domains. Once the cycle is mass-balanced, the isotopic composition of reservoir and the size of fractionation accompanying microbial transformations and transfers of N species between the reservoirs were estimated by numerical iteration of the flux equations based on the reported δ15N values and fractionation factors. The calculated fractionation factors tend to be smaller in magnitude than the experimentally measured ones in natural systems, which can be interpreted as an indication of N-limited conditions prevailing in pre-Anthropocene world: a smaller isotope fractionation can be interpreted as an indication of nitrogen

  5. The Contamination of Commercial 15N2 Gas Stocks with 15N–Labeled Nitrate and Ammonium and Consequences for Nitrogen Fixation Measurements

    PubMed Central

    Dabundo, Richard; Lehmann, Moritz F.; Treibergs, Lija; Tobias, Craig R.; Altabet, Mark A.; Moisander, Pia H.; Granger, Julie

    2014-01-01

    We report on the contamination of commercial 15-nitrogen (15N) N2 gas stocks with 15N-enriched ammonium, nitrate and/or nitrite, and nitrous oxide. 15N2 gas is used to estimate N2 fixation rates from incubations of environmental samples by monitoring the incorporation of isotopically labeled 15N2 into organic matter. However, the microbial assimilation of bioavailable 15N-labeled N2 gas contaminants, nitrate, nitrite, and ammonium, is liable to lead to the inflation or false detection of N2 fixation rates. 15N2 gas procured from three major suppliers was analyzed for the presence of these 15N-contaminants. Substantial concentrations of 15N-contaminants were detected in four Sigma-Aldrich 15N2 lecture bottles from two discrete batch syntheses. Per mole of 15N2 gas, 34 to 1900 µmoles of 15N-ammonium, 1.8 to 420 µmoles of 15N-nitrate/nitrite, and ≥21 µmoles of 15N-nitrous oxide were detected. One 15N2 lecture bottle from Campro Scientific contained ≥11 µmoles of 15N-nitrous oxide per mole of 15N2 gas, and no detected 15N-nitrate/nitrite at the given experimental 15N2 tracer dilutions. Two Cambridge Isotopes lecture bottles from discrete batch syntheses contained ≥0.81 µmoles 15N-nitrous oxide per mole 15N2, and trace concentrations of 15N-ammonium and 15N-nitrate/nitrite. 15N2 gas equilibrated cultures of the green algae Dunaliella tertiolecta confirmed that the 15N-contaminants are assimilable. A finite-differencing model parameterized using oceanic field conditions typical of N2 fixation assays suggests that the degree of detected 15N-ammonium contamination could yield inferred N2 fixation rates ranging from undetectable, <0.01 nmoles N L−1 d−1, to 530 nmoles N L−1 d−1, contingent on experimental conditions. These rates are comparable to, or greater than, N2 fixation rates commonly detected in field assays. These results indicate that past reports of N2 fixation should be interpreted with caution, and demonstrate that the purity of commercial 15N2

  6. The magnitude of spatial and temporal variation in δ15N and δ13C differs between taxonomic groups: Implications for food web studies

    NASA Astrophysics Data System (ADS)

    Hyndes, Glenn A.; Hanson, Christine E.; Vanderklift, Mathew A.

    2013-03-01

    Understanding variability in stable isotope abundance is essential for effective hypothesis testing and evaluating food sources, trophic levels and food web structure. The magnitude and sources of variability are likely to differ among taxonomic and functional groups. We aimed to quantify variability of δ13C and δ15N for 16 species representing seven distinct taxonomic groups of benthic invertebrates and autotrophs in a marine ecosystem. We quantified the magnitude of variability among individuals or shoots separated by metres, among eight sites separated by kilometres, and between two survey occasions separated by months. δ13C varied by as much as 7‰ for primary producers, 4‰ for consumers, while δ15N varied by as much as 9‰ and 2‰ respectively. Variation in δ15N of seagrass was largely accounted for by differences among sites, while variation in δ13C was mainly attributable to shoots collected a few metres apart. Compared to seagrasses, variation in macroalgae was mainly explained by differences between the two survey occasions for δ15N and among individuals collected a few metres apart for δ13C. Variation was generally lower for consumers and typically explained by differences among individuals for δ15N but displayed inconsistent patterns for δ13C. Dual isotope Bayesian mixing models showed that the potential contributions of food sources for herbivorous consumers varied among sites and between survey occasions, and also that there was high variability or uncertainty in the contributions of sources within sites. The relative consistency in the main sources of variation among broad taxonomic groups in autotrophs suggests that aspects of physiology that are phylogenetically conserved might be important influences on variation in natural abundances of stable isotopes. In comparison, the sources of variability were less consistent within and among broad consumer groups, suggesting complex interactions between consumers and their food sources.

  7. Increase of Natural 15N Enrichment of Soybean Nodules with Mean Nodule Mass 1

    PubMed Central

    Shearer, Georgia; Bryan, Barbara A.; Kohl, Daniel H.

    1984-01-01

    The 15N abundance of soybean (Glycine max L. Merrill var Harosoy) nodules is usually greater than it is for other tissues or for atmospheric N2. Results of experiments in which nodules were separated by size show that the magnitude of the 15N enrichment is correlated with nodule mass. The results support the hypothesis that 15N enrichment of nodules results from differential N isotopic fractionation for synthesis of nodule tissue versus synthesis of compounds for export from the nodule. The physiological significance of this hypothesis is that it requires that a substantial fraction of the N for nodule tissue synthesis in 15N-enriched nodules be N recently fixed within the same nodule. PMID:16663917

  8. Isotope effects on desorption kinetics of hydrogen isotopes implanted into stainless steel by glow discharge

    SciTech Connect

    Matsuyama, M.; Kondo, M.; Noda, N.; Tanaka, M.; Nishimura, K.

    2015-03-15

    In a fusion device the control of fuel particles implies to know the desorption rate of hydrogen isotopes by the plasma-facing materials. In this paper desorption kinetics of hydrogen isotopes implanted into type 316L stainless steel by glow discharge have been studied by experiment and numerical calculation. The temperature of a maximum desorption rate depends on glow discharge time and heating rate. Desorption spectra observed under various experimental conditions have been successfully reproduced by numerical simulations that are based on a diffusion-limited process. It is suggested, therefore, that desorption rate of a hydrogen isotope implanted into the stainless steel is limited by a diffusion process of hydrogen isotope atoms in bulk. Furthermore, small isotope effects were observed for the diffusion process of hydrogen isotope atoms. (authors)

  9. Using a Macroalgal δ15N Bioassay to Detect Cruise Ship Waste Water Effluent Inputs

    EPA Science Inventory

    Nitrogen stable isotopes are a powerful tool for tracking sources of N to marine ecosystems. I used green macroalgae as a bioassay organism to evaluate if the δ15N signature of cruise ship waste water effluent (CSWWE) could be detected in Skagway Harbor, AK. Opportunistic green...

  10. Tracing Nitrogen through Landscapes to Coastal Wetlands using d15N of Larval Fish

    EPA Science Inventory

    Our objective was to evaluate the use of the nitrogen stable isotope value (d15N) of larval fish as an indicator of incipient anthropogenic nitrogen loading to coastal wetlands in the Great Lakes. We sampled coastal wetlands in five Lake Superior south shore tributaries that had ...

  11. Effect of native and invasive cordgrass on Macoma petalum density, growth, and isotopic signatures

    NASA Astrophysics Data System (ADS)

    Brusati, Elizabeth D.; Grosholz, Edwin D.

    2007-02-01

    Ecosystem engineers can influence community and ecosystem dynamics by controlling resources, modifying the flow of energy or biomass, or changing physical characteristics of the habitat. Invasive hybrid cordgrass ( Spartina alterniflora × Spartina foliosa ) is an ecosystem engineer in salt marshes in San Francisco Bay, California, U.S.A. that raises intertidal elevations and may be either increasing C4 plant carbon input into food webs or tying up carbon in a form that is not usable by consumers. A manipulative experiment compared abundance, growth, and stable isotope (δ 13C and δ 15N) composition of the clam Macoma petalum (= M. balthica) among native marsh, hybrid Spartina, and mudflats in central San Francisco Bay. We found higher densities (individuals m -2) of M. petalum on mudflats compared to either native or hybrid Spartina ( p < 0.001). Macoma petalum shell growth was significantly greater in mudflats than in either vegetation type in 2002 ( p = 0.005) but not 2003. Differences in shell growth between native and hybrid Spartina were not significant. Stable isotope results showed differences between habitats in δ 13C but not δ 15N. Carbon signatures of M. petalum placed in Spartina were much more depleted than the isotopic signature of Spartina. Neither native nor hybrid Spartina appears to be a significant carbon source for M. petalum in San Francisco Bay, and we found no evidence that hybrid Spartina contributes carbon to M. petalum beyond what is provided by S. foliosa, despite the hybrid's much greater biomass. Our results show that loss of mudflat habitat, rather than increased input of C4 carbon, is the greatest effect of the invasion of hybrid Spartina on M. petalum.

  12. Combinatorial effects on clumped isotopes and their significance in biogeochemistry

    NASA Astrophysics Data System (ADS)

    Yeung, Laurence Y.

    2016-01-01

    The arrangement of isotopes within a collection of molecules records their physical and chemical histories. Clumped-isotope analysis interrogates these arrangements, i.e., how often rare isotopes are bound together, which in many cases can be explained by equilibrium and/or kinetic isotope fractionation. However, purely combinatorial effects, rooted in the statistics of pairing atoms in a closed system, are also relevant, and not well understood. Here, I show that combinatorial isotope effects are most important when two identical atoms are neighbors on the same molecule (e.g., O2, N2, and D-D clumping in CH4). When the two halves of an atom pair are either assembled with different isotopic preferences or drawn from different reservoirs, combinatorial effects cause depletions in clumped-isotope abundance that are most likely between zero and -1‰, although they could potentially be -10‰ or larger for D-D pairs. These depletions are of similar magnitude, but of opposite sign, to low-temperature equilibrium clumped-isotope effects for many small molecules. Enzymatic isotope-pairing reactions, which can have site-specific isotopic fractionation factors and atom reservoirs, should express this class of combinatorial isotope effect, although it is not limited to biological reactions. Chemical-kinetic isotope effects, which are related to a bond-forming transition state, arise independently and express second-order combinatorial effects related to the abundance of the rare isotope. Heteronuclear moeties (e.g., Csbnd O and Csbnd H), are insensitive to direct combinatorial influences, but secondary combinatorial influences are evident. In general, both combinatorial and chemical-kinetic factors are important for calculating and interpreting clumped-isotope signatures of kinetically controlled reactions. I apply this analytical framework to isotope-pairing reactions relevant to geochemical oxygen, carbon, and nitrogen cycling that may be influenced by combinatorial

  13. Highly 15N-Enriched Chondritic Clasts in the Isheyevo Meteorite

    SciTech Connect

    Bonal, L; Huss, G R; Krot, A N; Nagashima, K; Ishii, H A; Bradley, J P; Hutcheon, I D

    2009-01-14

    The metal-rich carbonaceous chondrites (CB and CH) have the highest whole-rock {sup 15}N enrichment ({delta}{sup 15}N up to +1500{per_thousand}), similar to {delta}{sup 15}N values reported in micron-sized regions (hotspots) of Interplanetary Dust Particles (IDPs) of possibly cometary origin and fine-grained matrices of unmetamorphosed chondrites. These {sup 15}N-rich hotspots are commonly attributed to low-temperature ion-molecule reactions in the protosolar molecular cloud or in the outer part of the protoplanetary disk. The nature of the whole-rock {sup 15}N enrichment of the metal-rich chondrites is not understood. We report a discovery of a unique type of primitive chondritic clasts in the CH/CB-like meteorite Isheyevo, which provides important constraints on the origin of {sup 15}N anomaly in metal-rich chondrites and nitrogen-isotope fractionation in the Solar System. These clasts contain tiny chondrules and refractory inclusions (5-15 {micro}m in size), and abundant ferromagnesian chondrule fragments (1-50 {micro}m in size) embedded in the partly hydrated, fine-grained matrix material composed of olivines, pyroxenes, poorly-organized aromatic organics, phyllosilicates and other hydrous phases. The mineralogy and oxygen isotope compositions of chondrules and refractory inclusions in the clasts are similar to those in the Isheyevo host, suggesting formation at similar heliocentric distances. In contrast to the previously known extraterrestrial samples, the fine-grained material in the clasts is highly and rather uniformly enriched in {sup 15}N, with bulk {delta}{sup 15}N values ranging between +1000 and +1300{per_thousand}; the {delta}{sup 15}N values in rare hotspots range from +1400 to +4000{per_thousand}. Since fine-grained matrices in the lithic clasts are the only component containing thermally unprocessed (during CAI and chondrule formation or during impact melting) materials that accreted into the metal rich chondrite parent body(ies), the {sup 15}N

  14. Can a secondary isotope effect be larger than a primary?

    PubMed

    Perrin, Charles L; Burke, Kathryn D

    2015-05-21

    Primary and secondary (18)O equilibrium isotope effects on the acidities of a variety of Brønsted and Lewis acids centered on carbon, boron, nitrogen, and phosphorus were computed by density-functional theory. For many of these acids, the secondary isotope effect was found to be larger than the primary isotope effect. This is a counterintuitive result, because the H atom that is lost is closer to the (18)O atom that is responsible for the primary isotope effect. The relative magnitudes of the isotope effects can be associated with the vibrational frequency and zero-point energy of the X═O vibrations, which are greater than those of the X-O vibrations. However, the difference between these contributions is small, and the major responsibility for the larger secondary isotope effect comes from the moment-of-inertia factor, which depends on the position of the (18)O atom relative to the principal axes of rotation. PMID:25879248

  15. 15N Content Reflects Development of Mycorrhizae and Nitrogen Dynamics During Primary Succession

    NASA Astrophysics Data System (ADS)

    Hobbie, E. A.; Jumpponen, A.

    2004-05-01

    Mycorrhizal fungi are ubiquitous symbionts on terrestrial plants that are particularly important for plant nitrogen nutrition. 15N content appears to be a useful marker of the mycorrhizal role in plant nitrogen supply because of an apparent fractionation against 15N during transfer of nitrogen from mycorrhizal fungi to host plants. Because plants developing during primary succession are gradually colonized by mycorrhizal fungi, such situations provide good opportunities to study interactions between mycorrhizal colonization and plant 15N content. Here, we present results of a study of nitrogen isotope patterns in ecosystem components during the first 100 years of ecosystem development after glacial retreat, and compare those patterns with those on adjacent mature terrain. Soils in primary succession were depleted in 15N relative to nitrogen-fixing plants. Nonmycorrhizal plants and plants generally colonized by ectomycorrhizal, ericoid, or arbuscular fungi showed similar 15N content very early in succession (-4 to -6‰ ), corresponding to low colonization levels of all plant species. Subsequent colonization of evergreen plants by ectomycorrhizal and ericoid fungi led to a 5-6‰ decline in 15N content, indicating transfer of 15N-depleted N from fungi to plants. The values recorded (-10 to -14‰ ) are among the lowest yet observed in vascular plants. Nonmycorrhizal plants and plants colonized by arbuscular mycorrhizal fungi did not decline in 15N content. Most ectomycorrhizal and saprotrophic fungi were similar in 15N content in early succession (-1 to -3‰ ), with the notable exception of ectomycorrhizal fungi suspected of proteolytic capabilities, which were 15N enriched relative to all other fungi. 15N contents in both plants and soil from the mature site were 5‰ greater than in recently exposed sites. We conclude that 1) the primary nitrogen source to this ecosystem must be atmospheric deposition, 2) low plant 15N content generally corresponds with greater

  16. Carbon-rich Presolar Grains from Massive Stars: Subsolar 12C/13C and 14N/15N Ratios and the Mystery of 15N

    NASA Astrophysics Data System (ADS)

    Pignatari, M.; Zinner, E.; Hoppe, P.; Jordan, C. J.; Gibson, B. K.; Trappitsch, R.; Herwig, F.; Fryer, C.; Hirschi, R.; Timmes, F. X.

    2015-08-01

    Carbon-rich grains with isotopic anomalies compared to the Sun are found in primitive meteorites. They were made by stars, and carry the original stellar nucleosynthesis signature. Silicon carbide grains of Type X and C and low-density (LD) graphites condensed in the ejecta of core-collapse supernovae. We present a new set of models for the explosive He shell and compare them with the grains showing 12C/13C and 14N/15N ratios lower than solar. In the stellar progenitor H was ingested into the He shell and not fully destroyed before the explosion. Different explosion energies and H concentrations are considered. If the supernova shock hits the He-shell region with some H still present, the models can reproduce the C and N isotopic signatures in C-rich grains. Hot-CNO cycle isotopic signatures are obtained, including a large production of 13C and 15N. The short-lived radionuclides 22Na and 26Al are increased by orders of magnitude. The production of radiogenic 22Ne from the decay of 22Na in the He shell might solve the puzzle of the Ne-E(L) component in LD graphite grains. This scenario is attractive for the SiC grains of type AB with 14N/15N ratios lower than solar, and provides an alternative solution for SiC grains originally classified as nova grains. Finally, this process may contribute to the production of 14N and 15N in the Galaxy, helping to produce the 14N/15N ratio in the solar system.

  17. Highly 15N-enriched chondritic clasts in the CB/CH-like meteorite Isheyevo

    NASA Astrophysics Data System (ADS)

    Bonal, L.; Huss, G. R.; Krot, A. N.; Nagashima, K.; Ishii, H. A.; Bradley, J. P.

    2010-11-01

    The metal-rich carbonaceous chondrites (CB and CH) have the highest whole-rock 15N-enrichments (δ 15N up to 1500‰) among planetary materials. They are also characterized by the absence of interchondrule fine-grained matrix. The only fine-grained material is present as lithic clasts, which experienced extensive aqueous alteration in contrast to the surrounding high-temperature components (chondrules, refractory inclusions, metal grains). Hence, the clasts are foreign objects that were incorporated at a late stage into the final parent body of Isheyevo. Their origin is poorly constrained. Based on mineralogy, petrography, and thermal processing of the aromatic carbonaceous component, different types of clasts have been previously identified in the CB/CH-like chondrite Isheyevo. Here, we focus on the rare lithic clasts characterized by the presence of anhydrous silicates (chondrules, chondrule fragments, and CAIs). Their mineralogy and oxygen isotopic compositions reveal them to be micro-chondrules, fragments of chondrules, and refractory inclusions related to those in the Isheyevo host, suggesting accretion in the same region. In contrast to previously studied IDPs or primitive chondritic matrices, the fine-grained material in the clasts we studied is highly and rather uniformly enriched in heavy nitrogen, with bulk δ 15N values ranging between 1000‰ and 1300‰. It is also characterized by the presence of numerous 15N hotspots (δ 15N ranging from 1400‰ to 4000‰). No bulk (δD <-240‰) or localized deuterium enrichments were observed. These clasts have the highest bulk enrichment in heavy nitrogen measured to date in a fine-grained material. They represent a unique material, of asteroidal or cometary origin, in our collection of cosmomaterials. We show that they were 15N-enriched before their incorporation in the final parent body of Isheyevo. They experienced an extensive aqueous alteration that most likely played a role in redistributing 15N over the

  18. Backbone dynamics of barstar: a (15)N NMR relaxation study.

    PubMed

    Sahu, S C; Bhuyan, A K; Majumdar, A; Udgaonkar, J B

    2000-12-01

    Backbone dynamics of uniformly (15)N-labeled barstar have been studied at 32 degrees C, pH 6.7, by using (15)N relaxation data obtained from proton-detected 2D (1)H-(15)N NMR spectroscopy. (15)N spin-lattice relaxation rate constants (R(1)), spin-spin relaxation rate constants (R(2)), and steady-state heteronuclear (1)H-(15)N NOEs have been determined for 69 of the 86 (excluding two prolines and the N-terminal residue) backbone amide (15)N at a magnetic field strength of 14.1 Tesla. The primary relaxation data have been analyzed by using the model-free formalism of molecular dynamics, using both isotropic and axially symmetric diffusion of the molecule, to determine the overall rotational correlation time (tau(m)), the generalized order parameter (S(2)), the effective correlation time for internal motions (tau(e)), and NH exchange broadening contributions (R(ex)) for each residue. As per the axially symmetric diffusion, the ratio of diffusion rates about the unique and perpendicular axes (D( parallel)/D( perpendicular)) is 0.82 +/- 0.03. The two results have only marginal differences. The relaxation data have also been used to map reduced spectral densities for the NH vectors of these residues at three frequencies: 0, omega(H), and omega(N), where omega(H),(N) are proton and nitrogen Larmor frequencies. The value of tau(m) obtained from model-free analysis of the relaxation data is 5.2 ns. The reduced spectral density analysis, however, yields a value of 5.7 ns. The tau(m) determined here is different from that calculated previously from time-resolved fluorescence data (4.1 ns). The order parameter ranges from 0.68 to 0.98, with an average value of 0.85 +/- 0.02. A comparison of the order parameters with the X-ray B-factors for the backbone nitrogens of wild-type barstar does not show any considerable correlation. Model-free analysis of the relaxation data for seven residues required the inclusion of an exchange broadening term, the magnitude of which ranges from 2

  19. Evaluating chlorine isotope effects from isotope ratios and mass spectra of polychlorinated molecules.

    PubMed

    Elsner, Martin; Hunkeler, Daniel

    2008-06-15

    Compound-specific chlorine isotope analysis receives much interest to assess the fate of chlorinated hydrocarbons in contaminated environments. This paper provides a theoretical basis to calculate isotope ratios and quantify isotope fractionation from ion-current ratios of molecular- and fragment-ion multiplets. Because both (35)Cl and (37)Cl are of high abundance, polychlorinated hydrocarbons consist of molecules containing different numbers of (37)Cl denoted as isotopologues. We show that, during reactions, the changes in isotopologue ratios are proportional to changes in the isotope ratio assuming a nonselective isotope distribution in the initial compound. This proportionality extents even to fragments formed in the ion source of a mass spectrometer such as C 2Cl 2 (double dechlorinated fragment of perchloroethylene, PCE). Fractionation factors and kinetic isotope effects (KIE) may, therefore, be evaluated from isotope, isotopologue or even fragment ratios according to conventional simple equations. The proportionality is exact with symmetric molecules such as dichloroethylene (DCE) and PCE, whereas it is approximately true with molecules containing nonreactive positions such as trichloroethylene (TCE). If in the latter case isotope ratios are derived from dechlorinated fragments, e.g., C 2HCl 2, it is important that fragmentation in the ion source affect all molecular positions alike, as otherwise isotopic changes in reactive positions may be underrepresented. PMID:18484745

  20. GC-MS determination of ratios of stable-isotope labelled to natural urea using [13C15N2]urea for studying urea kinetics in serum and as a means to validate routine methods for the quantitative assay of urea in dialysate.

    PubMed

    Wolthers, B G; Tepper, T; Withag, A; Nagel, G T; de Haan, T H; van Leeuwen, J J; Stegeman, C A; Huisman, R M

    1994-02-01

    A GC-MS determination of urea in serum or spent dialysate is described, using 13C15N2-labelled urea and assaying the area ratio of labelled to natural urea by mass fragmentographic monitoring of fragments m/e 153 and 156, after its eventual conversion into the trimethylsilylether-derivative of 2-hydroxypyrimidine. The procedure can be successfully applied in the follow-up of the disappearance of labelled urea in serum after intravenous injection in man, enabling kinetic parameters of urea to be established, e.g. for purposes of studying the effectiveness of dialysis procedures. Furthermore the method can be used for validation of routine methods for measuring urea in other fluids, in particular dialysate. Examples are given of both applications of the GC-MS method described. PMID:8033352

  1. Compound-specific 15N analysis of amino acids in 15N tracer experiments provide an estimate of newly synthesised soil protein from inorganic and organic substrates

    NASA Astrophysics Data System (ADS)

    Charteris, Alice; Michaelides, Katerina; Evershed, Richard

    2015-04-01

    Organic N concentrations far exceed those of inorganic N in most soils and despite much investigation, the composition and cycling of this complex pool of SOM remains poorly understood. A particular problem has been separating more recalcitrant soil organic N from that actively cycling through the soil system; an important consideration in N cycling studies and for the soil's nutrient supplying capacity. The use of 15N-labelled substrates as stable isotope tracers has contributed much to our understanding of the soil system, but the complexity and heterogeneity of soil organic N prevents thorough compound-specific 15N analyses of organic N compounds and makes it difficult to examine any 15N-labelled organic products in any detail. As a result, a significant proportion of previous work has either simply assumed that since the majority of soil N is organic, all of the 15N retained in the soil is organic N (e.g. Sebilo et al., 2013) or subtracted 15N-labelled inorganic compounds from bulk values (e.g. Pilbeam et al., 1997). While the latter approach is more accurate, these methods only provide an estimate of the bulk 15N value of an extremely complex and non-uniformly labelled organic pool. A more detailed approach has been to use microbial biomass extraction (Brookes et al., 1985) and subsequent N isotopic analysis to determine the 15N value of biomass-N, representing the fraction of 15N assimilated by microbes or the 15N cycling through the 'living' or 'active' portion of soil organic N. However, this extraction method can only generate estimates and some lack of confidence in its validity and reliability remains. Here, we present an alternative technique to obtain a measure of the assimilation of an applied 15N substrate by the soil microbial biomass and an estimate of the newly synthesized soil protein, which is representative of the magnitude of the active soil microbial biomass. The technique uses a stable isotope tracer and compound-specific 15N analysis, but

  2. Nitrogen stable isotopes in streams: effects of agricultural sources and transformations.

    PubMed

    Diebel, Matthew W; Vander Zanden, M Jake

    2009-07-01

    The nitrogen stable isotope ratio of biological tissue has been proposed as an indicator of anthropogenic N inputs to aquatic ecosystems, but overlap in the isotopic signatures of various N sources and transformations make definitive attribution of processes difficult. We collected primary consumer invertebrates from streams in agricultural settings in Wisconsin, U.S.A., to evaluate the relative influence of animal manure, inorganic fertilizer, and denitrification on biotic delta15N. Variance in biotic delta15N was explained by inorganic fertilizer inputs and the percentage of wetland land cover in the watershed, but not by animal manure inputs. These results suggest that denitrification of inorganic fertilizer is the primary driver of delta15N variability among the study sites. Comparison with previously collected stream water NO3-N concentrations at the same sites supports the role of denitrification; for a given N application rate, streams with high biotic delta15N had low NO3-N concentrations. The lack of a manure signal in biotic delta15N may be due its high ammonia content, which can be dispersed outside the range of its application by volatilization. Based on our findings and on agricultural census data for the entire United States, inorganic fertilizer is more likely than manure to drive variability in biotic delta15N and to cause excessive nitrogen concentrations in streams. PMID:19688921

  3. Effect of phosphorylation on hydrogen-bonding interactions of the active site histidine of the phosphocarrier protein HPr of the phosphoenolpyruvate-dependent phosphotransferase system determined by sup 15 N NMR spectroscopy

    SciTech Connect

    van Dijk, A.A.; de Lange, L.C.M.; Robillard, G.T. ); Bachovchin, W.W. )

    1990-09-04

    The phosphocarrier protein HPr of the phosphoenolpyruvate-dependent sugar transport system of Escherichia coli can exist in a phosphorylated and a nonphosphorylated form. During phosphorylation, the phosphoryl group is carried on a histidine residue, His15. The hydrogen-bonding state of this histidine was examined with {sup 15}N NMR. For this purpose we selectively enriched the histidine imidazole nitrogens with {sup 15}N by supplying an E. coli histidine auxotroph with the amino acid labeled either at the N{delta}1 and N{epsilon}2 positions or at only the N{delta}1 position. {sup 15}N NMR spectra of two synthesized model compound, phosphoimidazole and phosphomethylimidazole, were also recorded. The authors show that, prior to phosphorylation, the protonated His15 N{epsilon}2 is strongly hydrogen bonded, most probably to a carboxylate moiety. The H-bond should strengthen the nucleophilic character of the deprotonated N{delta}1, resulting in a good acceptor for the phosphoryl group. The hydrogen bond to the His15 N{delta}1 breaks upon phosphorylation of the residue. Implications of the H-bond structure for the mechanism of phosphorylation of HPr are discussed.

  4. Effect of phosphorylation on hydrogen-bonding interactions of the active site histidine of the phosphocarrier protein HPr of the phosphoenolpyruvate-dependent phosphotransferase system determined by 15N NMR spectroscopy.

    PubMed

    van Dijk, A A; de Lange, L C; Bachovchin, W W; Robillard, G T

    1990-09-01

    The phosphocarrier protein HPr of the phosphoenolpyruvate-dependent sugar transport system of Escherichia coli can exist in a phosphorylated and a nonphosphorylated form. During phosphorylation, the phosphoryl group is carried on a histidine residue, His15. The hydrogen-bonding state of this histidine was examined with 15N NMR. For this purpose we selectively enriched the histidine imidazole nitrogens with 15N by supplying an E. coli histidine auxotroph with the amino acid labeled either at the N delta 1 and N epsilon 2 positions or at only the N delta 1 position. 15N NMR spectra of two synthesized model compounds, phosphoimidazole and phosphomethylimidazole, were also recorded. We show that, prior to phosphorylation, the protonated His15 N epsilon 2 is strongly hydrogen bonded, most probably to a carboxylate moiety. The H-bond should strengthen the nucleophilic character of the deprotonated N delta 1, resulting in a good acceptor for the phosphoryl group. The hydrogen bond to the His15 N delta 1 breaks upon phosphorylation of the residue. Implications of the H-bond structure for the mechanism of phosphorylation of HPr are discussed. PMID:2261470

  5. Plant community change mediates the response of foliar delta15N to CO2 enrichment in mesic grasslands

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rising atmospheric CO2 concentration may change the isotopic signature of plant N by altering plant and microbial processes involved in the N cycle. Isotope fractionation theory and limited experimental evidence indicate that CO2 may increase leaf delta15N by increasing plant community productivity,...

  6. Influence of open ocean nitrogen supply on the skeletal δ15N of modern shallow-water scleractinian corals

    NASA Astrophysics Data System (ADS)

    Wang, Xingchen T.; Sigman, Daniel M.; Cohen, Anne L.; Sinclair, Daniel J.; Sherrell, Robert M.; Cobb, Kim M.; Erler, Dirk V.; Stolarski, Jarosław; Kitahara, Marcelo V.; Ren, Haojia

    2016-05-01

    The isotopic composition of skeleton-bound organic nitrogen in shallow-water scleractinian corals (hereafter, CS-δ15N) is an emerging tool for studying the marine nitrogen cycle in the past. The CS-δ15N has been shown to reflect the δ15N of nitrogen (N) sources to corals, with most applications to date focusing on the anthropogenic/terrestrial N inputs to reef environments. However, many coral reefs receive their primary N sources from the open ocean, and the CS-δ15N of these corals may provide information on past changes in the open ocean regional and global N cycle. Using a recently developed persulfate/denitrifier-based method, we measured CS-δ15N in modern shallow-water scleractinian corals from 8 sites proximal to the open ocean. At sites with low open ocean surface nitrate concentrations typical of the subtropics and tropics, measured CS-δ15N variation on seasonal and annual timescales is most often less than 2‰. In contrast, a broad range in CS-δ15N (of ∼10‰) is measured across these sites, with a strong correlation between CS-δ15N and the δ15N of the deep nitrate supply to the surface waters near the reefs. While CS-δ15N can be affected by other N sources as well and can vary in response to local reef conditions as well as coral/symbiont physiological changes, this survey indicates that, when considering corals proximal to the open ocean, the δ15N of the subsurface nitrate supply to surface waters drives most of the CS-δ15N variation across the global ocean. Thus, CS-δ15N is a promising proxy for reconstructing the open ocean N cycle in the past.

  7. Nuclear Volume Effects in Equilibrium Stable Isotope Fractionations of Hg, Tl and Pb Isotope Systems

    NASA Astrophysics Data System (ADS)

    Yang, S.; Liu, Y.

    2014-12-01

    Many evidences showed that heavy isotope systems could be significantly fractionated as the consequence of the nuclear volume effect (NVE) or so-called nuclear field shift effect. Here we investigate NVEs of Hg, Tl and Pb isotope systems by using quantum chemistry computational methods with careful evaluation on quantum relativistic effects via the Dirac's formalism of full-electron wavefunction. Our results generally agree with previous studies but with noticeable differences in many cases. With the unique NVE driving force, equilibrium 202Hg/198Hg and 205Tl/203Tl isotopes can be fractionated up to 3.94‰ and 2.78‰ at 0℃, respectively, showing potentially large equilibrium isotope fractionations can be expected for future studies of these two isotope systems. Moreover, the NVE causes large mass-independent fractionations (MIF) for odd-mass isotopes (e.g., ∆199NVHg and ∆201NVHg) and small MIFs for even-mass isotopes (e.g., ∆200NVHg). For Pb isotope system, NVEs induce isotope fractionations up to 1.62‰ (207Pb/206Pb) and 4.06‰ (208Pb/206Pb) at 0℃. However, contributions from classical mass-dependent driving force are small, about 0.1-0.5‰ for 207Pb/206Pb and 0.2-0.9‰ for 208Pb/206Pb. We find that Pb4+-bearing species can be significantly enriched heavy isotopes than Pb2+-bearing species. Comparing to Pb0, Pb2+-bearing species even enrich lighter Pb isotopes. A very strange and interesting thing is that the beta value of Pb2+-bearing species can be smaller than the unity (1.000). Similar thing has been found on Tl+-bearing species. This is an impossible and unexplained situation if only based on classical mass-dependent isotope fractionation theory (e.g., Bigeleisen-Mayer equation). The consequence is that the different direction of beta values of Pb2+-bearing species will let the Pb isotope fractionation even larger when they fractionate with Pb4+-bearing species. Moreover, NVEs also cause mass-independent fractionation (MIF) of odd 207Pb

  8. Measuring denitrification after grassland renewal and grassland conversion to cropland by using the 15N gas-flux method

    NASA Astrophysics Data System (ADS)

    Buchen, Caroline; Eschenbach, Wolfram; Flessa, Heinz; Giesemann, Anette; Lewicka-Szczebak, Dominika; Well, Reinhard

    2015-04-01

    Denitrification, the reduction of oxidized forms of inorganic N to N2O and N2 is an important pathway of gaseous nitrogen losses. Measuring denitrification, especially the reduction of N2O to N2, expressed in the product ratio (N2O/(N2O + N2)), is rather difficult and hence rarely performed under field conditions. But using the 15N gas-flux method allows determining N transformation processes in their natural environment. In order to develop effective climate mitigation strategies understanding the N2O source is essential. We used the 15N gas-flux method to determine N2O and N2 emissions following grassland renewal and conversion techniques. Therefore we selected three different treatments: control (C), mechanical grassland renovation (GR) (autumn 2013) and grassland conversion to maize (GM) (spring 2014) from field plot trials on two different sites (Histic Gleysoil and Plaggic Anthrosol) near Oldenburg, Lower Saxony, Germany. We applied 15N labeled KNO3- (60 atom. % 15N) at a rate equivalent to common farming practices (150 kg N*ha-1) using needle injection of fertilizer solution in three different depths (10 cm, 15 cm, 20 cm) for homogeneous soil labeling up to 30 cm in microplots. During the first 10 days after application (May 2014) gas flux measurements from closed chambers were performed every second day and then weekly following a period of 8 weeks. Gas samples were analyzed for δ15N of N2 and N2O by IRMS according to Lewicka-Szczebak et al. (2013). Concentration and 15N enrichment of NO3- in soil water was determined on weekly samples using the SPIN-MAS technique (Stange et al. 2007). Fluxes of N2 and N2O evolved from the 15N labeled soil nitrogen pool were calculated using the equations of Spott et al. (2006). Peak events of N2 and N2O emissions occurred during the first 10 days of measurement, showing differences in soil types, as well as treatment variations. N2 fluxes up to 178 g*ha-1*day-1 and N2O fluxes up to 280 g*ha-1*day-1 were measured on the

  9. Using dual-bacterial denitrification to improve δ15N determinations of nitrates containing mass-independent 17O

    USGS Publications Warehouse

    Coplen, T.B.; Böhlke, J.K.; Casciotti, K.L.

    2004-01-01

    The bacterial denitrification method for isotopic analysis of nitrate using N2O generated from Pseudomonas aureofaciens may overestimate ??15N values by as much as 1-2??? for samples containing atmospheric nitrate because of mass-independent 17O variations in such samples. By analyzing such samples for ??15N and ??18O using the denitrifier Pseudomonas chlororaphis, one obtains nearly correct ??15N values because oxygen in N 2O generated by P. chlororaphis is primarily derived from H 2O. The difference between the apparent ??15N value determined with P. aureofaciens and that determined with P. chlororaphis, assuming mass-dependent oxygen isotopic fractionation, reflects the amount of mass-independent 17O in a nitrate sample. By interspersing nitrate isotopic reference materials having substantially different ?? 18O values with samples, one can normalize oxygen isotope ratios and determine the fractions of oxygen in N2O derived from the nitrate and from water with each denitrifier. This information can be used to improve ??15N values of nitrates having excess 17O. The same analyses also yield estimates of the magnitude of 17O excess in the nitrate (expressed as ??17O) that may be useful in some environmental studies. The 1-?? uncertainties of ??15N, ??18O and ??17O measurements are ??0.2, ??0.3 and ??5???, respectively. Copyright ?? 2004 John Wiley & Sons, Ltd.

  10. Carbon isotope effects in carbonate systems

    NASA Astrophysics Data System (ADS)

    Deines, Peter

    2004-06-01

    Global carbon cycle models require a complete understanding of the δ 13C variability of the Earth's C reservoirs as well as the C isotope effects in the transfer of the element among them. An assessment of δ 13C changes during CO 2 loss from degassing magmas requires knowledge of the melt-CO 2 carbon isotope fractionation. In order to examine the potential size of this effect for silicate melts of varying composition, 13C reduced partition functions were computed in the temperature range 275 to 4000 K for carbonates of varying bond strengths (Mg, Fe, Mn, Sr, Ba, Pb, Zn, Cd, Li, and Na) and the polymorphs of calcite. For a given cation and a given pressure the 13C content increases with the density of the carbonate structure. For a given structure the tendency to concentrate 13C increases with pressure. The effect of pressure (‰/10 kbar) on the size of the reduced partition function of aragonite varies with temperature; in the pressure range 1 to 10 5 bars the change is given by: Δ 13C p average=-0.01796+0.06635∗ 10 3/T+0.006875∗ 10 6/T2 For calcite III the pressure effect is on average 1.4× larger than that for aragonite at all temperatures. The nature of the cation in a given structure type has a significant effect on the carbon isotope fractionation properties. The tendency to concentrate 13C declines in the series magnesite, aragonite, dolomite, strontianite, siderite, calcite, smithonite, witherite, rhodochrosite, otavite, cerrusite. For divalent cations a general expression for an estimation of the reduced partition function (β) from the reduced mass (μ = [M Cation × M Carbonate]/[M Cation + M Carbonate]) is: 1000 lnβ=(0.032367-0.072563∗ 10 3/T-0.01073∗ 10 6/T2)∗μ-14.003+29.953∗ 10 3/T+9.4610∗ 10 6/T2 For Mg-calcite the 13C content varies with the Mg concentration. The fractionation between Mg-calcite (X = mole fraction of MgCO 3) and calcite is given by: 1000 ln(α MgCalite- Calcite)=[0.013702-0.10957× 10 3/T+1.35940× 10 6/T2

  11. Laboratory Study of Nitrate Photolysis in Antarctic Snow: Quantum Yield and Isotope Effects

    NASA Astrophysics Data System (ADS)

    Meusinger, C.; Berhanu, T. A.; Erbland, J.; Jost, R.; Bhattacharya, S. K.; Savarino, J. P.; Johnson, M. S.

    2013-12-01

    Post-depositional processes alter the nitrate concentration and its isotopic composition in the top layers of snow at low snow accumulation sites, such as Dome C, Antarctica. Available nitrate ice core records can provide input for studying past atmospheres and climate if such processes are understood. Photolysis of nitrate in the snowpack was shown to be the major nitrate loss mechanism from the snowpack. Here a laboratory study is presented that uses snow from Dome C and minimizes effects of desorption by flushing the snow with pure N2 at 100 % humidity during irradiation with UV light from a Xenon lamp. A selection of UV filters allowed examination of the 200 and 300 nm absorption bands of nitrate and to emulate actinic fluxes similar to those in Dome C. Irradiated snow was sampled in 1 cm sections and analyzed for nitrate concentration and isotopic composition (δ15N, δ18O and Δ17O); the actinic flux was measured at similar sections in the snow. The quantum yield was observed to decrease from 0.44 to 0.05 within what corresponds to weeks of UV exposure in Antarctica. The superposition of photolysis in two photochemical domains of nitrate in snow is proposed: one of photolabile nitrate and one of trapped or buried nitrate. The difference lies in the ability of reaction products to escape the snow crystal, versus undergoing secondary (recombination) chemistry. Modeled NOx emissions may be increased significantly due to the observed quantum yield in this study influencing predicted boundary layer chemistry including ozone concentrations. An average photolytic isotopic fractionation of 15ɛ = -15×1.2 ‰ was found for the experiments without a wavelength filter. These results are ascribed to excitation of the 200 nm nitrate absorption band. Blocking wavelengths shorter than 320 nm, approximating the actinic flux spectrum at Dome C, showed a photolytic fractionation constant of 15ɛ = -47.9 × 6.8 ‰ which lies within the fractionation determined in the field

  12. Determination of the δ15N of total nitrogen in solids; RSIL lab code 2893

    USGS Publications Warehouse

    Revesz, Kinga; Qi, Haiping; Coplen, Tyler B.

    2006-01-01

    The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 2893 is to determine the δ(15N/14N), abbreviated as δ15N , of total nitrogen in solid samples. A Carlo Erba NC 2500 elemental analyzer (EA) is used to convert total nitrogen in a solid sample into N2 gas. The EA is connected to a continuous flow isotope-ratio mass spectrometer (CF-IRMS), which determines relative difference in the isotope-amount ratios of stable nitrogen isotopes (15N/14N)of the product N2 gas. The combustion is quantitative; no isotopic fractionation is involved. Samples are placed in a tin capsule and loaded into the Costech Zero Blank Autosampler of the EA. Under computer control, samples are dropped into a heated reaction tube that contains an oxidant, where the combustion takes place in a helium atmosphere containing an excess of oxygen gas. Combustion products are transported by a helium carrier through a reduction tube to remove excess oxygen and convert all nitrous oxides into N2 and through a drying tube to remove water. The gas-phase products, mainly CO2 and N2, are separated by a gas chromatograph. The gas is then introduced into the isotope-ratio mass spectrometer (IRMS) through a Finnigan MAT (now Thermo Scientific) ConFlo II interface, which also is used to inject N2 reference gas and helium for sample dilution. The IRMS is a Thermo Scientific Delta V Plus CF-IRMS. It has a universal triple collector, two wide cups with a narrow cup in the middle, capable of measuring mass/charge (m/z) 28, 29, 30, simultaneously. The ion beams from N2 are as follows: m/z 28 = N2 = 14N14N; m/z 29 = N2 = 14N15N primarily; m/z 30 = NO = 14N16O primarily, which is a sign of contamination or incomplete reduction.

  13. Possible isotopic fractionation effects in sputtered minerals

    NASA Technical Reports Server (NTRS)

    Haff, P. K.; Watson, C. C.; Tombrello, T. A.

    1980-01-01

    A model which makes definite predictions for the fractionation of isotopes in sputtered material is discussed. The fractionation patterns are nonlinear, and the pattern for a particular set of isotopes depends on the chemical matrix within which those isotopes are contained. Calculations are presented for all nonmonoisotopic elements contained in the minerals perovskite, anorthite, ackermanite, enstatite, and troilite. All isotopes are fractionated at the level of approximately 4-6 deg/o per atomic mass unit. Oxygen is always positively fractionated (heavier isotopes sputtered preferentially), and heavier elements are generally negatively fractioned (light isotopes sputtered preferentially). The value of Delta (O-18:O-16) is always less by about 1.8 deg/o than a linear extrapolation based upon the calculated delta (O-17:O-16) value would suggest. The phenomenon of both negative and positive fractionation patterns from a single target mineral are used to make an experimental test of the proposed model.

  14. Stable nitrogen isotopes in coastal macroalgae: geographic and anthropogenic variability.

    PubMed

    Viana, Inés G; Bode, Antonio

    2013-01-15

    Growing human population adds to the natural nitrogen loads to coastal waters. Both anthropogenic and natural nitrogen is readily incorporated in new biomass, and these different nitrogen sources may be traced by the measurement of the ratio of stable nitrogen isotopes (δ(15)N). In this study δ(15)N was determined in two species of macroalgae (Ascophyllum nodosum and Fucus vesiculosus), and in nitrate and ammonium to determine the relative importance of anthropogenic versus natural sources of nitrogen along the coast of NW Spain. Both algal species and nitrogen sources showed similar isotopic enrichment for a given site, but algal δ(15)N was not related to either inorganic nitrogen concentrations or δ(15)N in the water samples. The latter suggests that inorganic nitrogen inputs are variable and do not always leave an isotopic trace in macroalgae. However, a significant linear decrease in macroalgal δ(15)N along the coast is consistent with the differential effect of upwelling. Besides this geographic variability, the influence of anthropogenic nitrogen sources is evidenced by higher δ(15)N in macroalgae from rias and estuaries compared to those from open coastal areas and in areas with more than 15×10(3) inhabitants in the watershed. These results indicate that, in contrast with other studies, macroalgal δ(15)N is not simply related to either inorganic nitrogen concentrations or human population size but depends on other factors as the upwelling or the efficiency of local waste treatment systems. PMID:23247291

  15. Mass balance and isotope effects during nitrogen transport through septic tank systems with packed-bed (sand) filters

    USGS Publications Warehouse

    Hinkle, S.R.; Böhlke, J.K.; Fisher, L.H.

    2008-01-01

    Septic tank systems are an important source of NO3- to many aquifers, yet characterization of N mass balance and isotope systematics following septic tank effluent discharge into unsaturated sediments has received limited attention. In this study, samples of septic tank effluent before and after transport through single-pass packed-bed filters (sand filters) were evaluated to elucidate mass balance and isotope effects associated with septic tank effluent discharge to unsaturated sediments. Chemical and isotopic data from five newly installed pairs and ten established pairs of septic tanks and packed-bed filters serving single homes in Oregon indicate that aqueous solute concentrations are affected by variations in recharge (precipitation, evapotranspiration), NH4+ sorption (primarily in immature systems), nitrification, and gaseous N loss via NH3 volatilization and(or) N2 or N2O release during nitrification/denitrification. Substantial NH4+ sorption capacity was also observed in laboratory columns with synthetic effluent. Septic tank effluent ??15N-NH4+ values were almost constant and averaged + 4.9??? ?? 0.4??? (1 ??). In contrast, ??15N values of NO3- leaving mature packed-bed filters were variable (+ 0.8 to + 14.4???) and averaged + 7.2??? ?? 2.6???. Net N loss in the two networks of packed-bed filters was indicated by average 10-30% decreases in Cl--normalized N concentrations and 2-3??? increases in ??15N, consistent with fractionation accompanying gaseous N losses and corroborating established links between septic tank effluent and NO3- in a local, shallow aquifer. Values of ??18O-NO3- leaving mature packed-bed filters ranged from - 10.2 to - 2.3??? (mean - 6.4??? ?? 1.8???), and were intermediate between a 2/3 H2O-O + 1/3 O2-O conceptualization and a 100% H2O-O conceptualization of ??18O-NO3- generation during nitrification.

  16. 15N Fractionation in Star-Forming Regions and Solar System Objects

    NASA Technical Reports Server (NTRS)

    Wirstrom, Eva; Milam, Stefanie; Adande, GIlles; Charnley, Steven; Cordiner, Martin

    2015-01-01

    A central issue for understanding the formation and evolution of matter in the early Solar System is the relationship between the chemical composition of star-forming interstellar clouds and that of primitive Solar System materials. The pristinemolecular content of comets, interplanetary dust particles and carbonaceous chondrites show significant bulk nitrogen isotopic fractionation relative to the solar value, 14N15N 440. In addition, high spatial resolution measurements in primitive materials locally show even more extreme enhancements of 14N15N 100.

  17. Evidence of magnetic isotope effects during thermochemical sulfate reduction

    PubMed Central

    Oduro, Harry; Harms, Brian; Sintim, Herman O.; Kaufman, Alan J.; Cody, George; Farquhar, James

    2011-01-01

    Thermochemical sulfate reduction experiments with simple amino acid and dilute concentrations of sulfate reveal significant degrees of mass-independent sulfur isotope fractionation. Enrichments of up to 13‰ for 33S are attributed to a magnetic isotope effect (MIE) associated with the formation of thiol-disulfide, ion-radical pairs. Observed 36S depletions in products are explained here by classical (mass-dependent) isotope effects and mixing processes. The experimental data contrasts strongly with multiple sulfur isotope trends in Archean samples, which exhibit significant 36S anomalies. These results support an origin other than thermochemical sulfate reduction for the mass-independent signals observed for early Earth samples. PMID:21997216

  18. Bomb-pulse 14C analysis combined with 13C and 15N measurements in blood serum from residents of Malmö, Sweden.

    PubMed

    Georgiadou, Elisavet; Stenström, Kristina Eriksson; Uvo, Cintia Bertacchi; Nilsson, Peter; Skog, Göran; Mattsson, Sören

    2013-05-01

    The (14)C content of 60 human blood serum samples from residents of Malmö (Sweden) in 1978, obtained from a biobank, has been measured to estimate the accuracy of (14)C bomb-pulse dating. The difference between the date estimated using the Calibomb software and sampling date varied between -3 ± 0.4 and +0.2 ± 0.5 years. The average age deviation of all samples was -1.5 ± 0.7 years, with the delay between production and consumption of foodstuffs being probably the dominating cause. The potential influence of food habits on the (14)C date has been evaluated using stable isotope δ(13)C and δ(15)N analysis and information about the dietary habits of the investigated individuals. Although the group consisting of lacto-ovo vegetarians and vegans (pooled group) was not completely separated from the omnivores in a stable isotopic trophic level diagram, this analysis proved to add valuable information on probable dietary habits. The age deviation of the sampling date from the respective Calibomb date was found strongly correlated with the δ(13)C values, probably due to influence from marine diet components. For the omnivore individuals, there were indications of seasonal effects on δ(13)C and the age deviation. No significant correlation was found between the age deviation and the δ(15)N values of any dietary group. No influence of sex or year of birth was found on neither the (14)C nor the δ(13)C and δ(15)N values of the serum samples. The data were also divided into two groups (omnivores and pooled group), based on the level of δ(15)N in the samples. The consumption of high δ(15)N-valued fish and birds can be responsible for this clustering. PMID:23358598

  19. Ecosystem N distribution and δ15N during a century of forest regrowth after agricultural abandonment

    USGS Publications Warehouse

    Compton, J.E.; Hooker, T.D.; Perakis, S.S.

    2007-01-01

    Stable isotope ratios of terrestrial ecosystem nitrogen (N) pools reflect internal processes and input–output balances. Disturbance generally increases N cycling and loss, yet few studies have examined ecosystem δ15N over a disturbance-recovery sequence. We used a chronosequence approach to examine N distribution and δ15N during forest regrowth after agricultural abandonment. Site ages ranged from 10 to 115 years, with similar soils, climate, land-use history, and overstory vegetation (white pine Pinus strobus). Foliar N and δ15N decreased as stands aged, consistent with a progressive tightening of the N cycle during forest regrowth on agricultural lands. Over time, foliar δ15N became more negative, indicating increased fractionation along the mineralization–mycorrhizal–plant uptake pathway. Total ecosystem N was constant across the chronosequence, but substantial internal N redistribution occurred from the mineral soil to plants and litter over 115 years (>25% of ecosystem N or 1,610 kg ha−1). Temporal trends in soil δ15N generally reflected a redistribution of depleted N from the mineral soil to the developing O horizon. Although plants and soil δ15N are coupled over millennial time scales of ecosystem development, our observed divergence between plants and soil suggests that they can be uncoupled during the disturbance-regrowth sequence. The approximate 2‰ decrease in ecosystem δ15N over the century scale suggests significant incorporation of atmospheric N, which was not detected by traditional ecosystem N accounting. Consideration of temporal trends and disturbance legacies can improve our understanding of the influence of broader factors such as climate or N deposition on ecosystem N balances and δ15N.

  20. Isotopically sensitive branching and its effect on the observed intramolecular isotope effects in cytochrome P-450 catalyzed reactions: a new method for the estimation of intrinsic isotope effects

    SciTech Connect

    Jones, J.P.; Korzekwa, K.R.; Rettie, A.E.; Trager, W.F.

    1986-10-29

    Two selectively deuterated n-octanes (octane-1-/sup 2/H/sub 3/ and octane-1,2,3-/sup 2/H/sub 7/) were synthesized and subjected to hydroxylation by phenobarbital-induced rat liver microsomes and purified cytochrome P-450b. The results of these experiments provide evidence which clarifies the interplay between a branched reaction pathway and the equilibration of an enzyme-substrate complex, in determining the magnitude of an observed isotope effect. An equation is derived that allows limits to placed on the intrinsic isotope effect. The equation is based on the observed isotope effect and the regioselectivity of a branch reaction pathway, catalyzed by an enzyme that forms two products via a single enzyme-substrate complex. The intrinsic isotope effect for the formation of 1-octanol was determined by this equation to lie between 9.5 and 9.8.

  1. The Effects of Stratospheric Chemistry and Transport on the Isotopic Compositions of Long-Lived Gases Measured at Earth's Surface

    NASA Astrophysics Data System (ADS)

    Kanu, A. M.; Boering, K. A.

    2014-12-01

    The isotopic compositions of a number of long-lived gases in Earth's atmosphere, including those for carbon dioxide (δ18O, Δ17O, and Δ14C), nitrous oxide (δ15N, δ15Nα, and δ18O), methane (δ13C and δD), and molecular hydrogen (δD) undergo large changes in the stratosphere. These changes arise from the often unique photochemical isotope fractionation occurring there as well as the long residence times and mean ages of stratospheric air with respect to exchange with the troposphere of up to 5 years. Stratospheric air then returns to the troposphere and, in each case, can affect the isotopic composition of these gases measured at Earth's surface. In this work, we estimate the effect of stratospheric isotope fractionation on free tropospheric isotope compositions of CO2, N2O, CH4, and H2 on an annual and global mean basis. To do so, we calculate net isotope fluxes between the stratosphere and troposphere empirically from the correlation of the measured isotope compositions of these species with measured N2O mixing ratios on whole air samples collected in the stratosphere from stratospheric aircraft and balloons coupled with independent information on the global, annually-averaged loss rate of N2O. In each case, the effect is large enough to include in global models. In addition, we present arguments and evidence that deconvolving the stratospheric influence on surface measurements from source (or other) signals on higher spatial and temporal scales than 'global' and 'annually-averaged' is also necessary when using surface measurements of isotopic compositions to constrain the magnitudes and geographic distributions of the sources of these gases to the atmosphere.

  2. Novel uses of isotope effects to elucidate enzyme reaction mechanisms

    SciTech Connect

    Hermes, J.D.

    1983-01-01

    A new technique (Multiple Isotope Effects) for determining enzyme reaction mechanisms and intrinsic isotope effects has been developed. By determining the /sup 13/C isotope effect on V/K with both a deuterated and unlabeled substrate, and the deuterium isotope effect on V/K, it is possible to tell whether the /sup 13/C-sensitive and deuterium-sensitive steps are the same or not and, if they are different, to determine which comes first in the mechanism. If the two isotope-sensitive steps are the same, 1) deuteration increases the size of the observed /sup 13/C isotope effect, and 2) the intrinsic /sup 13/C and deuterium isotope effects, and the commitments can be calculated. When the deuterium- and /sup 13/C-sensitive steps are different, deuteration decreases the size of the observed /sup 13/C isotope effect. The data fit the equation (/sup 13/(V/K)/sub H/ - 1)/(/sup 13/(V/K)/sub D/ - 1) = /sup D/(V/K)//sup D/K/sub eq/ when the deuterium-sensitive step comes first, but fit the equation (/sup 13/(V/K)/sub H/ - /sup 13/K/sub eq/)/(/sup 13/(V/K)/sub D/ - /sup 13/K/sub eq/) = /sup D/(V/K) when the /sup 13/C-sensitive step comes first.

  3. Identification of isotopically primitive interplanetary dust particles: A NanoSIMS isotopic imaging study

    SciTech Connect

    Floss, C; Stadermann, F J; Bradley, J P; Dai, Z R; Bajt, S; Graham, G; Lea, A S

    2005-09-02

    particles typically also contain numerous {sup 15}N-rich N-hotspots, occasional C isotopic anomalies, and abundant presolar silicate grains. In contrast, the other ''isotopically normal'' IDPs have normal bulk N isotopic compositions and, although some contain {sup 15}N-rich hotspots, none exhibit C isotopic anomalies and none contain presolar silicate or oxide grains. Thus, isotopically interesting IDPs can be identified and selected on the basis of their N isotopic compositions for further study. However, this distinction does not extend to H isotopic compositions. Although both H and N anomalies are frequently attributed to the survival of molecular cloud material in IDPs and, thus, should be more common in IDPs with anomalous bulk N compositions, D anomalies are as common in normal IDPs as they are in those characterized as isotopically primitive, based on their N isotopes. This may be due to different effects of secondary processing on the isotopic systems involved.

  4. δ13C and δ15N values in scales of Micropterus salmoides largemouth bass as a freshwater environmental indicator.

    PubMed

    Inamura, O; Zhang, J; Minagawa, M

    2012-01-15

    We have investigated the effectiveness of using the Micropterus salmoides largemouth bass, which is a top predator found throughout the world, as the index of a hydrosphere environment and its food chain. To this end, we used stable carbon and nitrogen isotope analysis (SIA). Largemouth bass were collected from eight dam reservoirs and two ponds in Toyama Prefecture, Japan. Toyama is located in central Japan and features a variety of distinct geographical environments, a result of the 3000-m elevation that changes over short distances, and abundant water systems. The mean δ(13)C and δ(15)N values for the lipid-extracted muscle of largemouth bass from all sampling locations showed large variability, but there were only small standard deviations at each sampling location. The isotope ratios for largemouth bass express the characteristics of each investigated hydrosphere environment and food chain. A very high correlation (δ(13)C: Y(scale) = 0.96 X(muscle) + 1.58, R(2) = 0.98, δ(15)N: Y(scale) = 0.92 X(muscle) - 1.15, R(2) = 0.95) of SIA values was found between largemouth bass scales and lipid-extracted muscles, which suggests that the more easily analyzed scales are useful as SIA samples for the monitoring and comparison of hydrosphere environments throughout the world. PMID:22215573

  5. Isotope Effects Associated with N2O Production By Fungal and Bacterial Nitric Oxide Reductases: Implications for Tracing Microbial Production Pathways

    NASA Astrophysics Data System (ADS)

    Ostrom, N. E.; Yang, H.; Gandhi, H.; Hegg, E. L.

    2014-12-01

    Site preference (SP), the difference in δ15N between the central (α) and outer (β) N atoms in N2O, has emerged as a conservative tracer of microbial N2O production. The key advantages of SP relative to bulk isotopes are (1) that it is independent of the isotope composition of the substrates of nitrification and denitrification and (2) has not been shown to exhibit fractionation during production. In pure microbial culture distinct SP values for N2O production from bacterial denitrification, including nitrifier-denitrification (-10 to 0 ‰), relative to hydroxylamine oxidation and fungal denitrification (33-37 ‰) provide a promising basis to resolve production pathways. In this study, we determined the δ15N, δ18O, δ15Nα, and δ15Nβ of N2O generated by purified fungal (P450nor) and bacterial nitric oxide reductases. The isotope values were used to calculate SP values, enrichment factors (e), and kinetic isotope effects (KIEs). Both O and Nα displayed normal isotope effects during enzymatic NO reduction by the P450nor with e values of -25.7‰ (KIE = 1.0264) and -12.6‰ (KIE = 1.0127), respectively. However, bulk nitrogen (average δ15N of Nα and Nβ) and Nβ exhibited inverse isotope effects with e values of 14.0‰ (KIE = 0.9862) and 36.1‰ (KIE = 0.9651), respectively. The observed inverse isotope effect in δ15Nβ is consistent with reversible binding of the first NO in the P450nor reaction mechanism. Experiments with bacterial nitric oxide reductase are ongoing, however, preliminary data indicates a inverse isotope effect in the α and β positions and a normal isotope effect in δ18O. In contrast to the constant SP observed during N2O production observed in microbial cultures, the SP measured for purified P450nor was not constant, increasing from ~15‰ to ~29‰ during the course of the reaction. Our results clearly indicate that fractionation of SP during N2O production by P450nor is not zero, and that SP values higher and lower than the

  6. Sedimentary records of δ(13)C, δ(15)N and organic matter accumulation in lakes receiving nutrient-rich mine waters.

    PubMed

    Widerlund, Anders; Chlot, Sara; Öhlander, Björn

    2014-07-01

    Organic C and total N concentrations, C/N ratios, δ(15)N and δ(13)C values in (210)Pb-dated sediment cores were used to reconstruct historical changes in organic matter (OM) accumulation in three Swedish lakes receiving nutrient-rich mine waters. Ammonium-nitrate-based explosives and sodium cyanide (NaCN) used in gold extraction were the major N sources, while lesser amounts of P originated from apatite and flotation chemicals. The software IsoSource was used to model the relative contribution of soil, terrestrial and littoral vegetation, and phytoplankton detritus in the lake sediments. In one lake the IsoSource modelling failed, suggesting the presence of additional, unknown OM sources. In two of the lakes sedimentary detritus of littoral vegetation and phytoplankton had increased by 15-20% and 20-35%, respectively, since ~1950, when N- and P-rich mine waters began to reach the lakes. Today, phytoplankton is the dominating OM component in these lake sediments, which appears to be a eutrophication effect related to mining operations. Changes in the N isotopic composition of biota, lake water, and sediments related to the use of ammonium-nitrate-based explosives and NaCN were evident in the two studied systems. However, N isotope signals in the receiving waters (δ(15)N~+9‰ to +19‰) were clearly shifted from the primary signal in explosives (δ(15)N-NO3=+3.4±0.3‰; δ(15)N-NH4=-8.0±0.3‰) and NaCN (δ(15)N=+1.1±0.5‰), and direct tracing of the primary N isotope signals in mining chemicals was not possible in the receiving waters. Systems where mine waters with a well known discharge history are a major point source of N with well-defined isotopic composition should, however, be suitable for further studies of processes controlling N isotope signatures and their transformation in aquatic systems receiving mine waters. PMID:24727038

  7. Enzymatic synthesis of guanine nucleotides labeled with 15N at the 2-amino group of the purine ring.

    PubMed

    Bouhss, A; Sakamoto, H; Palibroda, N; Chiriac, M; Sarfati, R; Smith, J M; Craescu, C T; Bârzu, O

    1995-02-10

    GMP and dGMP labeled with 15N at the 2-amino group of the purine ring was obtained enzymatically from NH4Cl (> 99 at.% 15N) and from IMP or dIMP, respectively, by several reactions involving IMP-dehydrogenase, GMP-synthetase, adenylate kinase, and creatine kinase. The first three enzymes were obtained by overexpression in Escherichia coli of the corresponding genes. The isotope content of the primary amino group of guanine determined by mass spectrometry after acid hydrolysis of nucleotides was found higher than 98 at.% 15N. The proton NMR spectrum of [15N]GMP in solution in the absence of nitrogen decoupling showed a doublet with a coupling constant of 92 Hz. When nitrogen decoupling was used during the acquisition time, the doublet was replaced by a single peak at 6.47 ppm, indicating that the corresponding proton is bound to 15N. PMID:7778777

  8. Sources of δ15N variability in sinking particulate nitrogen in the Cariaco Basin, Venezuela

    NASA Astrophysics Data System (ADS)

    Montes, Enrique; Thunell, Robert; Muller-Karger, Frank E.; Lorenzoni, Laura; Tappa, Eric; Troccoli, Luis; Astor, Yrene; Varela, Ramón

    2013-09-01

    Ten years of monthly observations of the δ15N of sinking particulate nitrogen (δ15N-PN (in ‰ versus atmospheric N2)=[(15N/14N)sample/(15N/14N)standard)-1]1000) in the Cariaco Basin, Venezuela, confirm that the basin's bottom sediments store information about nitrogen dynamics related to seasonal and interannual variability in regional surface ocean processes. During the upwelling period of the southern Caribbean Sea (February-April), the δ15N-PN is similar to that of the thermocline nitrate (˜3.5‰). This nitrate is imported into the Cariaco Basin with Subtropical Underwater (SUW), which wells up near the coast. Thus, particles generated by phytoplankton photosynthesis during this productive period bear a sub-tropical North Atlantic isotopic imprint of N2 fixation (low compared to the global average of nitrate δ15N≈5‰). During the non-upwelling period when surface waters are stratified (September-November), the δ15N-PN is also 3.5-4.0‰, and reflects a mixture of local N2 fixation within the mixed layer, inputs of terrigenous organic matter and SUW nitrate consumption by phytoplankton below the mixed layer, which most likely exerts the strongest control on the δ15N-PN signal during this time. In the transition periods of May-July and December-January, the δ15N-PN increases to 4.5-6.5‰. This coincides with maxima of continental material fluxes (terrestrial PON δ15N is >6‰) into the Cariaco Basin. The δ15N signal in the sediments of the Cariaco Basin thus provides information about the relative strength of the local coastal upwelling, the relative input of continental material via river runoff, and local N2 fixation. The findings contribute to interpretations of the basin's paleoclimatic nitrogen cycle variations based on observations of the sedimentary δ15N record at this location.

  9. Isotopic phonon effects in β-rhombohedral boron—non-statistical isotope distribution

    NASA Astrophysics Data System (ADS)

    Werheit, H.; Filipov, V.; Kuhlmann, U.; Schwarz, U.; Armbrüster, M.; Antadze, M.

    2012-05-01

    On the basis of the spectra of IR- and Raman-active phonons, the isotopic phonon effects in β-rhombohedral boron are analysed for polycrystalline 10B- and 11B-enriched samples of different origin and high-purity natB single crystals. Intra- and inter-icosahedral B-B vibrations are harmonic, hence meeting the virtual crystal approximation (VCA) requirements. Deviations from the phonon shift expected according to the VCA are attributed to the anharmonic share of the lattice vibrations. In the case of icosahedral vibrations, the agreement with calculations on α-rhombohedral boron by Shirai and Katayama-Yoshida is quite satisfactory. Phonon shifts due to isotopic disorder in natB are separated and determined. Some phonon frequencies are sensitive to impurities. The isotopic phonon effects yield valuable specific information on the nature of the different phonon modes. The occupation of regular boron sites by isotopes deviates significantly from the random distribution.

  10. Choice of dietary protein of vegetarians and omnivores is reflected in their hair protein 13C and 15N abundance.

    PubMed

    Petzke, Klaus J; Boeing, Heiner; Metges, Cornelia C

    2005-01-01

    Stable isotopic (15N, 13C) composition of tissues depends on isotopic pattern of food sources. We investigated whether the isotopic compositions of human hair protein and amino acids reflect the habitual dietary protein intake. Hair samples were analyzed from 100 omnivores (selected randomly out of the 1987-1988 German nutrition survey VERA), and from 15 ovo-lacto-vegetarians (OLV), and from 6 vegans recruited separately. Hair bulk and amino acid specific isotopic compositions were analyzed by isotope-ratio mass spectrometry (EA/IRMS and GC/C/IRMS, respectively) and the results were correlated with data of the 7 day dietary records. Hair bulk 15N and 13C abundances clearly reflect the particular eating habits. Vegans can be distinguished from OLV and both are significantly distinct from omnivores in both 15N and 13C abundances. 15N and 13C abundances rose with a higher proportion of animal to total protein intake (PAPI). Individual proportions of animal protein consumption (IPAP) were calculated using isotopic abundances and a linear regression model using animal protein consumption data of vegans (PAPI = 0) and omnivores (mean PAPI = 0.639). IPAP values positively correlated with the intake of protein, meat, meat products, and animal protein. Distinct patterns for hair amino acid specific 15N and 13C abundances were measured but with lower resolution between food preference groups compared with bulk values. In conclusion, hair 13C and 15N values both reflected the extent of animal protein consumption. Bulk isotopic abundance of hair can be tested for future use in the validation of dietary assessment methods. PMID:15880664

  11. 15N/14N variations in Cretaceous Atlantic sedimentary sequences: implication for past changes in marine nitrogen biogeochemistry

    USGS Publications Warehouse

    Rau, G.H.; Arthur, M.A.; Dean, W.E.

    1987-01-01

    At two locations in the Atlantic Ocean (DSDP Sites 367 and 530) early to middle Cretaceous organic-carbon-rich beds ("black shales") were found to have significantly lower ??15N values (lower 15N/14N ratios) than adjacent organic-carbon-poor beds (white limestones or green claystones). While these lithologies are of marine origin, the black strata in particular have ??15N values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools. In contrast, black, organic-carbon-rich beds at a third site (DSDP Site 603) contain predominantly terrestrial organic matter and have C- and N-isotopic compositions similar to organic matter of modern terrestrial origin. The recurring 15N depletion in the marine-derived Cretaceous sequences prove that the nitrogen they contain is the end result of an episodic and atypical biogeochemistry. Existing isotopic and other data indicate that the low 15N relative abundance is the consequence of pelagic rather than post-depositional processes. Reduced ocean circulation, increased denitrification, and, hence, reduced euphotic zone nitrate availability may have led to Cretaceous phytoplankton assemblages that were periodically dominated by N2-fixing blue-green algae, a possible source of this sediment 15N-depletion. Lack of parallel isotopic shifts in Cretaceous terrestrially-derived nitrogen (Site 603) argues that the above change in nitrogen cycling during this period did not extend beyond the marine environment. ?? 1987.

  12. Do Low 15N Values in Paleozoic Epeiric Basins Indicate High Rates of N Fixation?

    NASA Astrophysics Data System (ADS)

    Tuite, M. L.; Macko, S. A.

    2011-12-01

    As a consequence of the high energetic requirements of dinitrogen (N2) fixation, organic N produced by diazotrophic microorganisms typically exhibits δ15N values similar to atmospheric N2 (approximately 0%). Because the δ15N of organic-rich Paleozoic epeiric basin sediments often has values in the vicinity of 0%, it is frequently asserted that N2 fixation was the primary source of new reactive N for productivity. There are two broad reasons why recourse to widespread and intensive N fixation as the primary source of the organic N is problematic. First, there are substantial physiological and ecological constraints on marine N fixation that limit its extent in modern oceans primarily to open ocean basins. Second, preservation of an unaltered isotopic signature of diazotrophy in underlying sediments is not a likely outcome of oxic and anoxic diagenetic alteration and repeated cycles of mineralization and assimilation. Constraining the sources of reactive N for primary productivity is critical to understanding the N cycle in Paleozoic epeiric seas. In this study we report δ15N values from high organic matter Middle Ordovician through Late Devonian dysoxic and euxinic basinal sediments. We propose a nitrogen isotope mass balance model that incorporates the microbial ecology of a stratified water column and the biochemical stoichiometry of primary production and organic matter diagenesis. Results from the model support our contention that high rates of N fixation over extended time periods were not the cause of depleted nitrogen isotope values in organic-rich Paleozoic basinal sediments. Rather, the depleted values were a consequence of a diminished role for nitrification and subsequent N loss via denitrification and anammox, and the preferential preservation of a substantially 15N-depleted chlorophyll-influenced lipid fraction. The model may be applicable to earlier and later geological periods where high organic matter sediments feature depleted δ15N values.

  13. Isotopic Effects in Nuclear Fragmentation and GCR Transport Problems

    NASA Technical Reports Server (NTRS)

    Cucinotta, Francis A.

    2002-01-01

    Improving the accuracy of the galactic cosmic ray (GCR) environment and transport models is an important goal in preparing for studies of the projected risks and the efficiency of potential mitigations methods for space exploration. In this paper we consider the effects of the isotopic composition of the primary cosmic rays and the isotopic dependence of nuclear fragmentation cross sections on GCR transport models. Measurements are used to describe the isotopic composition of the GCR including their modulation throughout the solar cycle. The quantum multiple-scattering approach to nuclear fragmentation (QMSFRG) is used as the data base generator in order to accurately describe the odd-even effect in fragment production. Using the Badhwar and O'Neill GCR model, the QMSFRG model and the HZETRN transport code, the effects of the isotopic dependence of the primary GCR composition and on fragment production for transport problems is described for a complete GCR isotopic-grid. The principle finding of this study is that large errors ( 100%) will occur in the mass-flux spectra when comparing the complete isotopic-grid (141 ions) to a reduced isotopic-grid (59 ions), however less significant errors 30%) occur in the elemental-flux spectra. Because the full isotopic-grid is readily handled on small computer work-stations, it is recommended that they be used for future GCR studies.

  14. Changes in nitrogen isotopic compositions during composting of cattle feedlot manure: effects of bedding material type.

    PubMed

    Kim, Young-Joo; Choi, Woo-Jung; Lim, Sang-Sun; Kwak, Jin-Hyeob; Chang, Scott X; Kim, Han-Yong; Yoon, Kwang-Sik; Ro, Hee-Myong

    2008-09-01

    Temporal changes in delta(15)N of cattle feedlot manure during its composting with either rice hull (RHM) or sawdust (SDM) as bedding materials were investigated. Regardless of the bedding material used, the delta(15)N of total N in the manure increased sharply from +7.6 per thousand to +9.9 per thousand and from +11.4 per thousand to +14.3 per thousand, respectively, in RHM or SDM, within 10 days from the commencement of composting. Such increases could be attributed primarily to N loss via NH(3) volatilization and denitrification based on the very high delta(15)N values (greater than +20 per thousand) of NH(4)(+) and NO(3)(-) in the co-composted manure. The delta(15)N of total N in RHM was substantially lower (by more than 3 per thousand) than that in SDM, suggesting that the delta(15)N of the composted manure was affected not only by N loss but also by the type of bedding material used. Specifically, the higher N concentration in the rice hull than in the saw dust could lead to a greater (15)N isotope dilution. PMID:18077156

  15. Nitrogen source tracking with delta(15)N content of coastal wetland plants in Hawaii.

    PubMed

    Bruland, Gregory L; MacKenzie, Richard A

    2010-01-01

    Inter- and intra-site comparisons of the nitrogen (N) stable isotope composition of wetland plant species have been used to identify sources of N in coastal areas. In this study, we compared delta(15)N values from different herbaceous wetland plants across 34 different coastal wetlands from the five main Hawaiian Islands and investigated relationships of delta(15)N with land use, human population density, and surface water quality parameters (i.e., nitrate, ammonium, and total dissolved N). The highest delta(15)N values were observed in plants from wetlands on the islands of Oahu (8.7-14.6 per thousand) and Maui (8.9-9.2 per thousand), whereas plants from wetlands on the islands of Kauai, Hawaii, and Molokai had delta(15)N values usually <4 per thousand. The enrichment in delta(15)N values in plant tissues from wetlands on Oahu and Maui was most likely a result of the more developed and densely populated watersheds on these two islands. Urban development within a 1000-m radius and population density were positively correlated to average delta(15)N vegetation values from each wetland site (r = 0.56 and 0.51, respectively; p < 0.001). This suggested that site mean delta(15)N values from mixed stands of wetland plants have potential as indices of N sources in coastal lowland wetlands in Hawaii and that certain sites on Oahu and Maui have experienced significant anthropogenic N loading. This information can be used to monitor future changes in N inputs to coastal wetlands throughout Hawaii and the Pacific. PMID:20048329

  16. Potential effect of algal productivity in the San Joaquin River on nitrate concentrations and isotope ratios

    NASA Astrophysics Data System (ADS)

    Kendall, C.; Silva, S. R.; Young, M. B.; Volkmar, E. C.; Dahlgren, R. A.; Borglin, S. E.; Stringfellow, W. T.

    2008-12-01

    The d15N of algae in nitrate-rich rivers is often about 4 to 5 permil lower than the d15N of the nitrate used by the algae. In cases where the algal productivity significantly depletes the available nitrate pool, the uptake of nitrate can cause significant increases in the d15N and d18O of the residual nitrate, resulting in isotope values similar to what would be expected for a major contribution of human or animal waste to the river. Furthermore, progressive algal uptake also causes nitrate d18O and d15N values that plot along slopes of about 1:2, consistent with assimilation and/or denitrification. One way to resolve the question of whether the high nitrate d15N and d18O values reflect a waste source, assimilation, or denitrification is to compare the simultaneous changes in nitrate concentrations, algal quality and loads, nitrate d15N and d18O, and the d15N, d13C, and C:N of the particulate organic matter, which is often dominated by algae in large rivers. As part of a recent investigation of nitrate and organic matter sources to the San Joaquin River (SJR), samples were collected twice-weekly to monthly for over 2 years from 7 mainstem sites (as well as many major and minor tributary sites) and analyzed for a wide range of chemical constituents and isotope ratios. The average nitrate d15N of mainstem sites was +11 permil, with a range of +2 to +17; the average d18O was +5 permil, with a range of -1 to +18. The potential impact of algal uptake on isotope ratios in the SJR was modeled using isotope and chemical data from 2 Lagrangian experiments in the San Luis Drain, a simple concrete-lined canal which drains into the SJR, has only a single input of water, and has algae similar to that in the SJR and a high productivity rate (Volkmar et al., in prep.).

  17. Edge Effects on Foliar Stable Isotope Values in a Madagascan Tropical Dry Forest

    PubMed Central

    Crowley, Brooke E.; McGoogan, Keriann C.; Lehman, Shawn M.

    2012-01-01

    Edge effects represent an inevitable and important consequence of habitat loss and fragmentation. These effects include changes in microclimate, solar radiation, or temperature. Such abiotic effects can, in turn, impact biotic factors. They can have a substantial impact on species, communities, and ecosystems. Here we examine clinal variations in stable carbon and nitrogen isotope values for trees along an edge-interior gradient in the dry deciduous forest at Ankarafantsika National Park. We predicted that soil respiration and differences in solar irradiance would result in stratified δ13C values where leaves collected close to the forest floor would have lower δ13C values than those growing higher up in the canopy. We also anticipated that plants growing at the savannah-forest boundary would have higher δ13C and δ15N values than plants growing in the forest interior. As expected, we detected a small but significant canopy effect. Leaves growing below 2 m from the forest floor exhibit δ13C values that are, on average, 1.1‰ lower than those growing above this threshold. We did not, however, find any relationship between foliar δ13C and distance from the edge. Unpredictably, we detected a striking positive relationship between foliar δ15N values and increasing distance into the forest interior. Variability in physiology among species, anthropogenic influence, organic input, and rooting depth cannot adequately explain this trend. Instead, this unexpected relationship most likely reflects decreasing nutrient or water availability, or a shift in N-sources with increasing distance from the savannah. Unlike most forest communities, the trees at Ampijoroa are growing in nutrient-limited sands. In addition to being nutrient poor, these well-drained soils likely decrease the amount of soil water available to forest vegetation. Continued research on plant responses to edge effects will improve our understanding of the conservation biology of forest ecosystems in

  18. Kinetic fractionation of stable nitrogen isotopes during amino acid transamination

    NASA Astrophysics Data System (ADS)

    Macko, Stephen A.; Estep, Marilyn L. Fogel; Engel, Michael H.; Hare, P. E.

    1986-10-01

    This study evaluates a kinetic isotope effect involving 15N, during the transamination reactions catalyzed by glutamic oxalacetic transaminase. During the transfer of amino nitrogen from glutamic acid to oxaloacetate to form aspartic acid, 14NH 2 reacted 1.0083 times faster than 14NH 2. In the reverse reaction transferring NH 2 from aspartic acid to α-ketoglutarate, 14NH 2 was incorporated 1.0017 times faster than 15NH 2. Knowledge of the magnitude and sign of these isotope effects will be useful in the interpretation of the distribution of 15N in biological and geochemical systems.

  19. Fundamental studies on kinetic isotope effect (KIE) of hydrogen isotope fractionation in natural gas systems

    NASA Astrophysics Data System (ADS)

    Ni, Yunyan; Ma, Qisheng; Ellis, Geoffrey S.; Dai, Jinxing; Katz, Barry; Zhang, Shuichang; Tang, Yongchun

    2011-05-01

    Based on quantum chemistry calculations for normal octane homolytic cracking, a kinetic hydrogen isotope fractionation model for methane, ethane, and propane formation is proposed. The activation energy differences between D-substitute and non-substituted methane, ethane, and propane are 318.6, 281.7, and 280.2 cal/mol, respectively. In order to determine the effect of the entropy contribution for hydrogen isotopic substitution, a transition state for ethane bond rupture was determined based on density function theory (DFT) calculations. The kinetic isotope effect (KIE) associated with bond rupture in D and H substituted ethane results in a frequency factor ratio of 1.07. Based on the proposed mathematical model of hydrogen isotope fractionation, one can potentially quantify natural gas thermal maturity from measured hydrogen isotope values. Calculated gas maturity values determined by the proposed mathematical model using δD values in ethane from several basins in the world are in close agreement with similar predictions based on the δ 13C composition of ethane. However, gas maturity values calculated from field data of methane and propane using both hydrogen and carbon kinetic isotopic models do not agree as closely. It is possible that δD values in methane may be affected by microbial mixing and that propane values might be more susceptible to hydrogen exchange with water or to analytical errors. Although the model used in this study is quite preliminary, the results demonstrate that kinetic isotope fractionation effects in hydrogen may be useful in quantitative models of natural gas generation, and that δD values in ethane might be more suitable for modeling than comparable values in methane and propane.

  20. Fundamental studies on kinetic isotope effect (KIE) of hydrogen isotope fractionation in natural gas systems

    USGS Publications Warehouse

    Ni, Y.; Ma, Q.; Ellis, G.S.; Dai, J.; Katz, B.; Zhang, S.; Tang, Y.

    2011-01-01

    Based on quantum chemistry calculations for normal octane homolytic cracking, a kinetic hydrogen isotope fractionation model for methane, ethane, and propane formation is proposed. The activation energy differences between D-substitute and non-substituted methane, ethane, and propane are 318.6, 281.7, and 280.2cal/mol, respectively. In order to determine the effect of the entropy contribution for hydrogen isotopic substitution, a transition state for ethane bond rupture was determined based on density function theory (DFT) calculations. The kinetic isotope effect (KIE) associated with bond rupture in D and H substituted ethane results in a frequency factor ratio of 1.07. Based on the proposed mathematical model of hydrogen isotope fractionation, one can potentially quantify natural gas thermal maturity from measured hydrogen isotope values. Calculated gas maturity values determined by the proposed mathematical model using ??D values in ethane from several basins in the world are in close agreement with similar predictions based on the ??13C composition of ethane. However, gas maturity values calculated from field data of methane and propane using both hydrogen and carbon kinetic isotopic models do not agree as closely. It is possible that ??D values in methane may be affected by microbial mixing and that propane values might be more susceptible to hydrogen exchange with water or to analytical errors. Although the model used in this study is quite preliminary, the results demonstrate that kinetic isotope fractionation effects in hydrogen may be useful in quantitative models of natural gas generation, and that ??D values in ethane might be more suitable for modeling than comparable values in methane and propane. ?? 2011 Elsevier Ltd.

  1. Heavy atom labeled nucleotides for measurement of kinetic isotope effects.

    PubMed

    Weissman, Benjamin P; Li, Nan-Sheng; York, Darrin; Harris, Michael; Piccirilli, Joseph A

    2015-11-01

    Experimental analysis of kinetic isotope effects represents an extremely powerful approach for gaining information about the transition state structure of complex reactions not available through other methodologies. The implementation of this approach to the study of nucleic acid chemistry requires the synthesis of nucleobases and nucleotides enriched for heavy isotopes at specific positions. In this review, we highlight current approaches to the synthesis of nucleic acids enriched site specifically for heavy oxygen and nitrogen and their application in heavy atom isotope effect studies. This article is part of a special issue titled: Enzyme Transition States from Theory and Experiment. PMID:25828952

  2. Vapor Pressure Isotope Effects and the Stable Isotope Geochemistry of the Martian Surface

    NASA Astrophysics Data System (ADS)

    Eiler, J. M.

    2002-12-01

    The stable isotope geochemistry of light elements (H, C, N, O and S) is a tool in the search for evidence of life on bodies other than the earth for several reasons: the elements in question are used by all known or easily imagined life forms; several mass spectrometric and spectroscopic methods for measuring their isotopic compositions exist and are appropriate for in situ analysis on other planets; it is known that 'vital effects' generate large (percent) isotopic fractionations; and studies of extant and former life on earth provide models for interpreting such data. However, the evidence stable isotope geochemistry provides is generally interpretable as a signature for life only in the context of a rich understanding of isotopic variations produced by non biological processes in the same environments. Several candidates in the search for extra-terrestrial life (Mars and the Jovian satellites) are bodies having volatile-element geochemical cycles that operate at lower temperatures than the earth's surface and involve phase-changes that do not occur on the earth (e.g., condensation/sublimation of CO2). We review new experimental data (both recently published and unpublished) describing isotopic fractionations accompanying phase changes of CO2, H2O below 240 K, NH3 and CO, compile them with previous data to derive general principles of low-temperature stable isotope fractionations, and discuss their significance for the stable isotope geochemistry of the surface of Mars. One example of the issues constrained by these data (the Martian CO2 cycle) is discussed here. The Martian surface is strongly influenced by condensation/sublimation and adsorption/desorption of CO2. The isotopic consequences of these processes are an attractive goal for in situ observations of atmosphere, ice and/or adsorbed gas because they provide a record of Martian atmospheric dynamics and atmosphere-surface interactions over a range of time-scales. Furthermore, these isotopic signals

  3. Site-Selective Synthesis of (15)N- and (13)C-Enriched Flavin Mononucleotide Coenzyme Isotopologues.

    PubMed

    Neti, Syam Sundar; Poulter, C Dale

    2016-06-17

    Flavin mononucleotide (FMN) is a coenzyme for numerous proteins involved in key cellular and physiological processes. Isotopically labeled flavin is a powerful tool for studying the structure and mechanism of flavoenzyme-catalyzed reactions by a variety of techniques, including NMR, IR, Raman, and mass spectrometry. In this report, we describe the preparation of labeled FMN isotopologues enriched with (15)N and (13)C isotopes at various sites in the pyrazine and pyrimidine rings of the isoalloxazine core of the cofactor from readily available precursors by a five-step chemo-enzymatic synthesis. PMID:27176708

  4. Vertical δ13C and δ15N changes during pedogenesis

    NASA Astrophysics Data System (ADS)

    Brunn, Melanie; Spielvogel, Sandra; Wells, Andrew; Condron, Leo; Oelmann, Yvonne

    2015-04-01

    The natural abundance of soil organic matter (SOM) stable C and N isotope ratios are subjected to vertical changes throughout the soil profile. This vertical distribution is a widely reported phenomenon across varieties of ecosystems and constitutes important insights of soil carbon cycling. In most ecosystems, SOM becomes enriched in heavy isotopes by several per mill in the first few centimeters of the topsoil. The enrichment of 13C in SOM with soil depth is attributed to biological and physical-chemical processes in soil e.g., plant physiological impacts, microbial decomposition, sorption and transport processes. Such vertical trends in 13C and 15N abundance have rarely been related to SOM composition during pedogenesis. The aims of our study were to investigate short and long-term δ13C and δ15N depth changes and their interrelations under progressing pedogenesis and ecosystem development. We sampled soils across the well studied fordune progradation Haast-chronosequence, a dune ridge system under super-humid climate at the West Coast of New Zealand's South Island (43° 53' S, 169° 3' E). Soils from 11 sites with five replicates each covered a time span of around 2870 yr of soil development (from Arenosol to Podzol). Vertical changes of δ13C and δ15N values of SOM were investigated in the organic layers and in 1-cm depth intervals of the upper 10 cm of the mineral soil. With increasing soil depth SOM became enriched in δ13C by 1.9 ± SE 0.1 o and in δ15N by 6.0 ± 0.4 ‰˙Litter δ13C values slightly decreased with increasing soil age (r = -0.61; p = 0.00) likely due to less efficient assimilation linked to nutrient limitations. Fractionation processes during mycorrhizal transfer appeared to affect δ15N values in the litter. We found a strong decrease of δ15N in the early succession stages ≤ 300 yr B.P. (r = -0.95; p = 0.00). Positive relations of vertical 13C and 15N enrichment with soil age might be related to decomposition and appeared to be

  5. Solvent isotope effects on nucleophilic displacement reactions

    SciTech Connect

    Spiegel, G.W.

    1981-01-01

    The kinetic solvent isotope effect, KSIE, (k/sub H/sub 2/O//k/sub D/sub 2/O/), at 25.0/sup 0/C and ionic strength, I, equal to 0.20 +- 0.02 M was measured for the nucleophilic displacement of iodine ion from iodomethane, iodoacetamide, and iodoacetate ion, thiophene from S-Methylthiophenium ion, and tosylate ion from methyl tosylate by bromide ion, chloride ion, acetate ion, hydroxide ion, water, ammonia, ethylenediamine, n-butylamine, piperazine, piperidine, quinuclidine, and 1,4-Diazabicyclo(2.2.2)octane (DABCO), and the monoprotonated cations of ethylenediamine, piperazine, and DABCO. By means of solvent partition measurements at 25.0/sup 0/C and I = 0.02 M between H/sub 2/O and D/sub 2/O and a common immiscible organic solvent, the ground state activity coefficients in D/sub 2/O, the solution in H/sub 2/O being chosen as the reference state, were determined for the nitrogen-containing nucleophiles (except ammonia) and the substrates methyl tosylate, iodoacetamide, and iodoacetic acid. The solubilities at 25.0/sup 0/C of the picrate and tetraphenylborate salts of the monoprotonated cationic forms of ethylenediamine, piperazine, and DABCO were measured to determine the activity coefficients in D/sub 2/O of these ions relative to an H/sub 2/O reference state. Applying the Eyring equation, the activity coefficients of the transition states in D/sub 2/O, reference state H/sub 2/O, were calculated.

  6. Scale-dependent linkages between nitrate isotopes and denitrification in surface soils: implications for isotope measurements and models.

    PubMed

    Hall, Steven J; Weintraub, Samantha R; Bowling, David R

    2016-08-01

    Natural abundance nitrate (NO3 (-)) isotopes represent a powerful tool for assessing denitrification, yet the scale and context dependence of relationships between isotopes and denitrification have received little attention, especially in surface soils. We measured the NO3 (-) isotope compositions in soil extractions and lysimeter water from a semi-arid meadow and lawn during snowmelt, along with the denitrification potential, bulk O2, and a proxy for anaerobic microsites. Denitrification potential varied by three orders of magnitude and the slope of δ(18)O/δ(15)N in soil-extracted NO3 (-) from all samples measured 1.04 ± 0.12 (R (2) = 0.64, p < 0.0001), consistent with fractionation from denitrification. However, δ(15)N of extracted NO3 (-) was often lower than bulk soil δ(15)N (by up to 24 ‰), indicative of fractionation during nitrification that was partially overprinted by denitrification. Mean NO3 (-) isotopes in lysimeter water differed from soil extractions by up to 19 ‰ in δ(18)O and 12 ‰ in δ(15)N, indicating distinct biogeochemical processing in relatively mobile water versus soil microsites. This implies that NO3 (-) isotopes in streams, which are predominantly fed by mobile water, do not fully reflect terrestrial soil N cycling. Relationships between potential denitrification and δ(15)N of extracted NO3 (-) showed a strong threshold effect culminating in a null relationship at high denitrification rates. Our observations of (1) competing fractionation from nitrification and denitrification in redox-heterogeneous surface soils, (2) large NO3 (-) isotopic differences between relatively immobile and mobile water pools, (3) and the spatial dependence of δ(18)O/δ(15)N relationships suggest caution in using NO3 (-) isotopes to infer site or watershed-scale patterns in denitrification. PMID:27102809

  7. Isotope effects and spectroscopic assignments in the non-dissociative photoionization spectrum of N{sub 2}

    SciTech Connect

    Randazzo, John B.; Croteau, Philip; Kostko, Oleg; Ahmed, Musahid; Boering, Kristie A.

    2014-05-21

    Photoionization efficiency spectra of {sup 14}N{sub 2}, {sup 15}N{sup 14}N, and {sup 15}N{sub 2} from 15.5 to 18.9 eV were measured using synchrotron radiation at the Advanced Light Source at Lawrence Berkeley National Laboratory with a resolution of 6 meV, and significant changes in peak energies and intensities upon isotopic substitution were observed. Previously, we reported the isotope shifts and their applications to Titan's atmosphere. Here, we report more extensive experimental details and tabulate the isotope shifts of many transitions in the N{sub 2} spectrum, including those for {sup 15}N{sup 14}N, which have not been previously reported. The isotope shifts are used to address several long-standing ambiguities in spectral peak assignments just above the ionization threshold of N{sub 2}. The feature at 15.677 eV (the so-called second “cathedral” peak) is of particular interest in this respect. The measured isotope shifts for this peak relative to {sup 14}N{sub 2} are 0.015 ± 0.001 eV for {sup 15}N{sub 2} and 0.008 ± 0.001 eV for {sup 15}N{sup 14}N, which match most closely with the isotope shifts predicted for transitions to the (A {sup 2}Π{sub u} v{sup ′} = 2)4sσ{sub g} {sup 1}Π{sub u} state using Herzberg equations for the isotopic differences in harmonic oscillator energy levels plus the first anharmonic correction of 0.0143 eV for {sup 15}N{sub 2} and 0.0071 eV for {sup 15}N{sup 14}N. More generally, the isotope shifts measured for both {sup 15}N{sub 2} and {sup 15}N{sup 14}N relative to {sup 14}N{sub 2} provide new benchmarks for theoretical calculations of interferences between direct and indirect autoionization states which can interact to produce intricate resonant structures in molecular photoionization spectra in regions near ionization thresholds.

  8. Characterising Redox-Related Isotope Effects

    NASA Astrophysics Data System (ADS)

    Black, J. R.; John, S.; Young, E. D.; Kavner, A.

    2008-12-01

    Redox processes have played a pivotal role in shaping Earth's interior and surface and making life possible. A record of this evolution is found within stable isotope signatures arising from chemical redox changes occurring in our continents, oceans and atmosphere over time. Experimental and theoretical studies of redox- related transition metal isotope fractionation provide a physical basis to understand how isotopes are fractionated under natural conditions, relating geochemical signatures to earth processes from which they arise. Here we present experimental evidence that charge transfer processes drive the fractionation of stable isotopes of Fe and Zn, and the magnitude of fractionation can be tuned as a function of redox potential and other physical variables. To quantitatively evaluate isotopic signatures of redox processes, we have conducted electrochemical experiments measuring the fractionation of Fe and Zn isotopes during their electrodeposition from aqueous solution: M2+ + 2e- = M(s). The electrochemical cell consisted of anodic and cathodic half- cells separated by a salt bridge, and connected to a potentiostat which applied an adjustable constant voltage (vs. Ag/AgCl). Metallic Fe and Zn plated on glassy carbon electrodes was recovered in acid for analysis of the stable isotope composition on a Thermo-Finnigan Neptune MC-ICP-MS. Results are reported as a large delta difference between the isotopic composition (56Fe/54Fe and 66Zn/64Zn) of plated metal relative to the stock solution. The results show some clear trends; fractionation is a function of applied voltage (overpotential: η = E- E0 Volts), ranging from Δ56Fe ~ -4 to -0.9 ‰, and Δ66Zn ~ - 5.5 to -4 ‰ at η = -0.5 to -1.25 V and -0.1 to -0.5 V, respectively. Temperature affects fractionation in a counter-intuitive manner, with fractionation increasing with increasing temperature (at η = -1.0 V: Δ56Fe ~ -1.25 ‰ at 0°C and -1.62 ‰ at 35°C). The results can be explained in terms of two

  9. Nitrogen dynamics in a Western Boundary Upwelling System (Cabo Frio, Brazil) based on δ15N-nitrate and δ15N of sinking particle signals

    NASA Astrophysics Data System (ADS)

    Fontana, L.; Belem, A. L.; Venancio, I.; Duarte, C.; Chiara, S. D.; Albuquerque, A. L.

    2014-12-01

    To improve the efficiency of upwelling to control nitrogen dynamic in the ocean, better understanding of the occurring processes is necessary. This research explores δ15N of nitrate and sinking particles on a western boundary upwelling System (Cabo Frio, Brazil). The Continental Shelf of southeastern Brazil is dominated by the oligotrophic Brazil Current, whose instabilities promote the coastal upwelling of South Atlantic Central Water (SACW), and consequently increases of primary productivity. The coastal upwelling system plays an important role in the nitrogen dynamics on the Cabo Frio Upwelling System (CFUS). However, the interactions between biological induced processes, including biological N-fixation and nitrate inputs from upwelled waters in CFUS still have not been well explored. Then, this study aims clarify N-dynamics on CFUS based on a cross-shelf approach. δ15N-nitrate was characterized for each water masses present on the shelf (South Atlantic Central Water, Tropical Water and Coastal Water) and associated with physicochemical parameters (T/S, nutrients), as well as the δ15N of sinking particles at different depths (from surface to the bottom water). Samples were collected in a time interval of 1 month during ~4 years (2011 to 2014). Cross-shelf gradients of nitrogen species concentration (ammonium + nitrite + nitrate) and stable isotopes were observed. The δ15N of nitrate and sinking particles were interpreted according to the prevailing processes of the N-transformations. Considering the region as N-limited (N:P < 16), processes as biological N-fixation seems to be dominant on oligotrophic Tropical Waters. Coastal upwelled SACW showed δ15N-nitrate signature within the global average of deep ocean (5-6‰) characterizing the inner and mid-shelf conditions, where the input of new nitrate from upwelling is rapidly used by organisms in the euphotic zone without any fractionation. On the other hands, the dominance of N-limited Tropical Waters on the

  10. (15)N CSA tensors and (15)N-(1)H dipolar couplings of protein hydrophobic core residues investigated by static solid-state NMR.

    PubMed

    Vugmeyster, Liliya; Ostrovsky, Dmitry; Fu, Riqiang

    2015-10-01

    In this work, we assess the usefulness of static (15)N NMR techniques for the determination of the (15)N chemical shift anisotropy (CSA) tensor parameters and (15)N-(1)H dipolar splittings in powder protein samples. By using five single labeled samples of the villin headpiece subdomain protein in a hydrated lyophilized powder state, we determine the backbone (15)N CSA tensors at two temperatures, 22 and -35 °C, in order to get a snapshot of the variability across the residues and as a function of temperature. All sites probed belonged to the hydrophobic core and most of them were part of α-helical regions. The values of the anisotropy (which include the effect of the dynamics) varied between 130 and 156 ppm at 22 °C, while the values of the asymmetry were in the 0.32-0.082 range. The Leu-75 and Leu-61 backbone sites exhibited high mobility based on the values of their temperature-dependent anisotropy parameters. Under the assumption that most differences stem from dynamics, we obtained the values of the motional order parameters for the (15)N backbone sites. While a simple one-dimensional line shape experiment was used for the determination of the (15)N CSA parameters, a more advanced approach based on the "magic sandwich" SAMMY pulse sequence (Nevzorov and Opella, 2003) was employed for the determination of the (15)N-(1)H dipolar patterns, which yielded estimates of the dipolar couplings. Accordingly, the motional order parameters for the dipolar interaction were obtained. It was found that the order parameters from the CSA and dipolar measurements are highly correlated, validating that the variability between the residues is governed by the differences in dynamics. The values of the parameters obtained in this work can serve as reference values for developing more advanced magic-angle spinning recoupling techniques for multiple labeled samples. PMID:26367322

  11. Kinetic H/D/T isotope and solid state effects on the tautomerism of the conjugate porphyrin monoanion

    SciTech Connect

    Braun, J.; Limbach, H.H.; Schwesinger, R.; Williams, P.G.; Morimoto, Hiromi; Wemmer, D.E.

    1996-11-13

    Using dynamic NMR spectroscopy, the kinetic isotope effects of the degenerate single hydron transfer in the conjugate {sup 15}N-labeled porphyrin anion Por-H{sup -} dissolved in organic solvents have been measured as a function of temperature. Por-H{sup -} was generated by dissolving the labeled parent compound porphyrin together with the phosphazene base 1,1,1,5,5, 5-hexakis(dimethylamino)-3-[1,1,2, 2-tetramethylpropylimino]-3-[[tris(dimethylamino)- phosphoran yliden]amino]-1{lambda}{sup 5},3{lambda}{sup 5},5{lambda}{sup 5} 1,1,4-triphosphazadiene (tHept-P{sup 4}) in organic solvents. In addition, by reaction of porphyrin with the base 1,1,1,5,5, 5-tetrakis[tris(dimethylamino)phosphoranylidene]amino phosphonium fluoride(P{sup 5}{sup +}F{sup -}) Por-H{sup -} could be embedded into the solid state and its tautomerism followed by {sup 15}N CPMAS NMR. Surprisingly, within the margin of error, the generacy of the tautomerism was not lifted in the solid state and the rate constants of the proton transfer were identical in the liquid and the solid. The kinetic isotope effects at 240 K (extrapolated) are given by k{sup H}/k{sup D} = 34 and k{sup H}/k{sup T} = 152. The size and the temperature dependence of the isotope effects indicates a proton tunneling mechanism as in the parent porphyrin where this process is nondegenerate. 29 refs., 9 figs., 3 tabs.

  12. Mineralogy and isotope chemistry of FUN (fractionation and nuclear isotope effects) and F (fractionation) CAIs

    NASA Astrophysics Data System (ADS)

    Krot, Alexander

    To understand the origin and formation conditions of FUN (Fractionation and Unidentified Nuclear isotope effects) and F (fractionation) Ca,Al-rich inclusions (CAIs), and their significance for constraining the origin of 26Al and O-isotopic compositions of the primordial dust and gas in the early Solar System, we propose to study mineralogy, petrology, oxidation state of Ti, trace element abundances, and O-, Mg-, Si-, Ca-, and Ti- isotope compositions of FUN and F CAIs previously identified in CV and CR chondrites. Twelve out of ~20 FUN and F CAIs known will be available for mineralogical study and isotope measurements; these include 1623-5, C1, EK1-4-1, CG-14, BG82DH8, B7F6, B7H10, BG82HB1, KT-1, AXCAI-2771, TE, and Gao-Guenie (b) #3. We will also search for additional FUN and F inclusions among Allende and Efremovka CAIs with large mass-dependent fractionation effects in Mg. This interdisciplinary research will be done in collaboration with I. Hutcheon (NanoSIMS), G. Huss (SIMS), S. Sutton (XANES), R. Mendybaev and A. Davis (evaporation experiments), F. Ciesla (modeling of evolution of O-isotope reservoirs in the solar nebula), and B. Meyer (modeling of Galactic chemical evolution of O-isotope compositions of dust and gas in the protosolar molecular cloud, and of stellar origin of short-lived radionuclides). The research proposed here is highly relevant to the Science Goals and Objectives of NASA and the Origins of Solar Systems Program, specifically ascertain the content, origin, and history of the solar system, and the potential for life elsewhere and increase the understanding of the chemical origin of the Solar System and the processes by which its planets and small bodies have evolved to their present states¿. Our interdisciplinary research (mineralogical and isotopic studies of the earliest solar-system solids, and astrophysical modeling) is designed to understand the origin of 26Al-poor CAIs with large mass-dependent isotope fractionation effects, and

  13. Mineralogy and isotope chemistry of FUN (fractionation and nuclear isotope effects) and F (fractionation) CAIs

    NASA Astrophysics Data System (ADS)

    Krot, Alexander

    To understand the origin and formation conditions of FUN (Fractionation and Unidentified Nuclear isotope effects) and F (fractionation) Ca,Al-rich inclusions (CAIs), and their significance for constraining the origin of 26Al and O-isotopic compositions of the primordial dust and gas in the early Solar System, we propose to study mineralogy, petrology, oxidation state of Ti, trace element abundances, and O-, Mg-, Si-, Ca-, and Ti- isotope compositions of FUN and F CAIs previously identified in CV and CR chondrites. Twelve out of ~20 FUN and F CAIs known will be available for mineralogical study and isotope measurements; these include 1623-5, C1, EK1-4-1, CG-14, BG82DH8, B7F6, B7H10, BG82HB1, KT-1, AXCAI-2771, TE, and Gao-Guenie (b) #3. We will also search for additional FUN and F inclusions among Allende and Efremovka CAIs with large mass-dependent fractionation effects in Mg. This interdisciplinary research will be done in collaboration with I. Hutcheon (NanoSIMS), G. Huss (SIMS), S. Sutton (XANES), R. Mendybaev and A. Davis (evaporation experiments), F. Ciesla (modeling of evolution of O-isotope reservoirs in the solar nebula), and B. Meyer (modeling of Galactic chemical evolution of O-isotope compositions of dust and gas in the protosolar molecular cloud, and of stellar origin of short-lived radionuclides). The research proposed here is highly relevant to the Science Goals and Objectives of NASA and the Origins of Solar Systems Program, specifically ascertain the content, origin, and history of the solar system, and the potential for life elsewhere and increase the understanding of the chemical origin of the Solar System and the processes by which its planets and small bodies have evolved to their present states. Our interdisciplinary research (mineralogical and isotopic studies of the earliest solar-system solids, and astrophysical modeling) is designed to understand the origin of 26Al-poor CAIs with large mass-dependent isotope fractionation effects, and

  14. Can the intramolecular distribution of 15N in N2O be used to source partition N2O emitted from soil

    NASA Astrophysics Data System (ADS)

    Decock, Charlotte; Six, Johan

    2014-05-01

    N2O is a potent greenhouse gas and plays an important role in the depletion of stratospheric ozone. Hence, many efforts are now geared towards quantifying and mitigating N2O emissions from soil in various ecosystems. This requires an in-depth understanding of the mechanisms and processes underlying N2O emissions, which has been methodologically challenging. Recently, it has been suggested that the intramolecular distribution of 15N in the N2O molecule (known as site preference or SP) can indicate which processes contribute to N2O fluxes. Here, we follow a framework of important validation steps to review the potential of SP to source partition N2O emitted from soils. In individual studies, significant effects of soil moisture content and soil type on SP values from soil-emitted N2O have been observed, supporting that SP could be a useful tool to source-partition N2O emitted from soil. While process-specific SP values based on pure culture studies have been used in isotope mixing and fractionation models to source partition N2O in environmental samples, effects of confounding factors such as unaccounted pathways, microbial community composition, process rate, and soil heterogeneity remain poorly quantified. This urges continued research to determine SP values for distinct N2O producing and consuming processes under controlled laboratory conditions for soils from a variety of ecosystems and environments. As mechanisms underlying N2O production and consumption are plentiful and complex, we recommend the creation of large isotope databases complemented with the development of more advanced models that take into account δ15N and δ18O of precursors, variability of overall isotope effects, and bulk δ15N, δ18O, and SP of N2O, as well as traditional proxies such as soil moisture content and C and N availability.

  15. Origin and decomposition of sinking particulate organic matter in the deep water column inferred from the vertical distributions of its δ15N, δ13 and δ14

    NASA Astrophysics Data System (ADS)

    Nakatsuka, Takeshi; Handa, Nobuhiko; Harada, Naomi; Sugimoto, Tatsuhiro; Imaizumi, Shigemi

    1997-12-01

    Sinking particles were analyzed for their nitrogen isotopic ratio δ15N) of total particulate nitrogen (PN), stable carbon isotopic ratio ( δ13C) and radioactive isotopic ratio ( δ14C) of total particulate organic carbon (POC), at three different latitudinal (temperate, subpolar and equatorial) and geomorphological (trench, proximal abyssal plain and distal abyssal plain) sites in the western North Pacific Ocean using year-long time series sediment trap systems, to clarify the common vertical trends of the isotopic signals in deep water columns. Although the δ15N and δ13C values of sinking particulate organic matter (POM) were partly affected by the resuspension of sedimentary POM from the sea floor, especially in the trench, the changes in δ15N and δ13C values owing to the resuspension could be corrected by calculation of the isotopic mass balance from δ14C of sinking POC. After this correction, common downward decreasing trends in δ15N and δ13C values were obtained in the deep water columns, irrespective of the latitudes and depths. These coincidental isotopic signals between δ15N and δ13C values provide new constraints for the decomposition process of sinking POM, such as the preferential degradation of 15N- and 13C-rich compounds and the successive re-formation of the sinking particles by higher trophic level organisms in the deep water column.

  16. Evaluating δ(15)N-body size relationships across taxonomic levels using hierarchical models.

    PubMed

    Reum, Jonathan C P; Marshall, Kristin N

    2013-12-01

    Ecologists routinely set out to estimate the trophic position of individuals, populations, and species composing food webs, and nitrogen stable isotopes (δ(15)N) are a widely used proxy for trophic position. Although δ(15)N values are often sampled at the level of individuals, estimates and confidence intervals are frequently sought for aggregations of individuals. If individual δ(15)N values are correlated as an artifact of sampling design (e.g., clustering of samples in space or time) or due to intrinsic groupings (e.g., life history stages, social groups, taxonomy), such estimates may be biased and exhibit overly optimistic confidence intervals. However, these issues can be accommodated using hierarchical modeling methods. Here, we demonstrate how hierarchical models offer an additional quantitative tool for investigating δ(15)N variability and we explicitly evaluate how δ(15)N varies with body size at successively higher levels of taxonomic aggregation in a diverse fish assemblage. The models take advantage of all available data, better account for uncertainty in parameters estimates, may improve inferences on coefficients corresponding to groups with small to moderate sample sizes, and partition variation across model levels, which provides convenient summaries of the 'importance' of each level in terms of unexplained heterogeneity in the data. These methods can easily be applied to diet-based studies of trophic position. Although hierarchical models are well-understood and established tools, their benefits have yet to be fully reaped by stable isotope and food web ecologists. We suggest that hierarchical models can provide a robust framework for conceptualizing and statistically modeling trophic position at multiple levels of aggregation. PMID:23812110

  17. Interaction of yeast iso-1-cytochrome c with cytochrome c peroxidase investigated by [15N, 1H] heteronuclear NMR spectroscopy.

    PubMed

    Worrall, J A; Kolczak, U; Canters, G W; Ubbink, M

    2001-06-19

    The interaction of yeast iso-1-cytochrome c with its physiological redox partner cytochrome c peroxidase has been investigated using heteronuclear NMR techniques. Chemical shift perturbations for both 15N and 1H nuclei arising from the interaction of isotopically enriched 15N cytochrome c with cytochrome c peroxidase have been observed. For the diamagnetic, ferrous cytochrome c, 34 amides are affected by binding, corresponding to residues at the front face of the protein and in agreement with the interface observed in the 1:1 crystal structure of the complex. In contrast, for the paramagnetic, ferric protein, 56 amides are affected, corresponding to residues both at the front and toward the rear of the protein. In addition, the chemical shift perturbations were larger for the ferric protein. Using experimentally observed pseudocontact shifts the magnetic susceptibility tensor of yeast iso-1-cytochrome c in both the free and bound forms has been calculated with HN nuclei as inputs. In contrast to an earlier study, the results indicate that there is no change in the geometry of the magnetic axes for cytochrome c upon binding to cytochrome c peroxidase. This leads us to conclude that the additional effects observed for the ferric protein arise either from a difference in binding mode or from the more flexible overall structure causing a transmittance effect upon binding. PMID:11401551

  18. Steric effects on the primary isotope dependence of secondary kinetic isotope effects in hydride transfer reactions in solution: caused by the isotopically different tunneling ready state conformations?

    PubMed

    Maharjan, Binita; Raghibi Boroujeni, Mahdi; Lefton, Jonathan; White, Ormacinda R; Razzaghi, Mortezaali; Hammann, Blake A; Derakhshani-Molayousefi, Mortaza; Eilers, James E; Lu, Yun

    2015-05-27

    The observed 1° isotope effect on 2° KIEs in H-transfer reactions has recently been explained on the basis of a H-tunneling mechanism that uses the concept that the tunneling of a heavier isotope requires a shorter donor-acceptor distance (DAD) than that of a lighter isotope. The shorter DAD in D-tunneling, as compared to H-tunneling, could bring about significant spatial crowding effect that stiffens the 2° H/D vibrations, thus decreasing the 2° KIE. This leads to a new physical organic research direction that examines how structure affects the 1° isotope dependence of 2° KIEs and how this dependence provides information about the structure of the tunneling ready states (TRSs). The hypothesis is that H- and D-tunneling have TRS structures which have different DADs, and pronounced 1° isotope effect on 2° KIEs should be observed in tunneling systems that are sterically hindered. This paper investigates the hypothesis by determining the 1° isotope effect on α- and β-2° KIEs for hydride transfer reactions from various hydride donors to different carbocationic hydride acceptors in solution. The systems were designed to include the interactions of the steric groups and the targeted 2° H/D's in the TRSs. The results substantiate our hypothesis, and they are not consistent with the traditional model of H-tunneling and 1°/2° H coupled motions that has been widely used to explain the 1° isotope dependence of 2° KIEs in the enzyme-catalyzed H-transfer reactions. The behaviors of the 1° isotope dependence of 2° KIEs in solution are compared to those with alcohol dehydrogenases, and sources of the observed "puzzling" 2° KIE behaviors in these enzymes are discussed using the concept of the isotopically different TRS conformations. PMID:25941865

  19. Determining the nitrogen and oxygen isotope effects of microbial denitrification

    NASA Astrophysics Data System (ADS)

    Philp, C.; Martin, T. S.; Casciotti, K. L.

    2013-12-01

    The nitrogen cycle describes how nitrogen, a critical nutrient for life, moves throughout the ground, oceans, and atmosphere. An essential component of the nitrogen cycle is denitrification, in which bioavailable nitrogen is transformed into nitrous oxide and nitrogen gas and can no longer be harnessed by most organisms. We can further understand the importance of this nitrogen cycle process by examining the N and O isotope effects of microbial denitrification. We have cultured four denitrifying bacteria: P. stutzeri, P. putida, P. aureofaciens, and P. aeruginosa. After providing them with an initial amount of nitrite we tracked the rate at which each type of bacteria consumed the nitrite through a time series experiment. We then measured the N and O isotope ratios of the nitrite at each time point using a gas-source isotope ratio mass spectrometer. The subsequent isotope effects calculated using the Rayleigh equation provide an important tool for modeling denitrification in the environment.

  20. Tracing sewage water by 15N in a mangrove ecosystem to test its bioremediation ability.

    PubMed

    Lambs, Luc; Léopold, Audrey; Zeller, Bernd; Herteman, Mélanie; Fromard, Francois

    2011-10-15

    Mangrove forests could be a simple and effective alternative to conventional sewage treatment, particularly for island communities given its low cost and low maintenance. Due to their high adaptation capacity, these plants are able to tolerate and bioremediate the high levels of nutrients and pollutants found in sewage water. This solution could be applied to small tropical islands with high population density such as Mayotte in the Indian Ocean. This paper reports on a trial by stable isotopic (15)N tracing of such a bioremediation process on pre-treated wastewater near the village of Malamani, in the middle of the large coastal mangrove in the bay near Chirongui. The first results show a boost in the mangrove growth, but a longer period of observation is needed to confirm the beneficial effects, and also to clarify the role of the local crab population, whose engineering activities play an important part in the ecosystem. The exact denitrification process is not yet understood, and the mass balance equation also reveals loss of nitrogen-containing compounds, which needs to be analyzed more closely. PMID:21913255

  1. Macroalgae δ15N values in well-mixed estuaries: Indicator of anthropogenic nitrogen input or macroalgae metabolism?

    NASA Astrophysics Data System (ADS)

    Raimonet, Mélanie; Guillou, Gaël; Mornet, Françoise; Richard, Pierre

    2013-03-01

    Although nitrogen stable isotope ratio (δ15N) in macroalgae is widely used as a bioindicator of anthropogenic nitrogen inputs to the coastal zone, recent studies suggest the possible role of macroalgae metabolism in δ15N variability. Simultaneous determinations of δ15N of dissolved inorganic nitrogen (DIN) along the land-sea continuum, inter-species variability of δ15N and its sensitivity to environmental factors are necessary to confirm the efficiency of macroalgae δ15N in monitoring nitrogen origin in mixed-use watersheds. In this study, δ15N of annual and perennial macroalgae (Ulva sp., Enteromorpha sp., Fucus vesiculosus and Fucus serratus) are compared to δ15N-DIN along the Charente Estuary, after characterizing δ15N of the three main DIN sources (i.e. cultivated area, pasture, sewage treatment plant outlet). During late winter and spring, when human activities produce high DIN inputs, DIN sources exhibit distinct δ15N signals in nitrate (NO) and ammonium (NH): cultivated area (+6.5 ± 0.6‰ and +9.0 ± 11.0‰), pasture (+9.2 ± 1.8‰ and +12.4‰) and sewage treatment plant discharge (+16.9 ± 8.7‰ and +25.4 ± 5.9‰). While sources show distinct δN- in this multiple source catchment, the overall mixture of NO sources - generally >95% DIN - leads to low variations of δN-NO at the mouth of the estuary (+7.7 to +8.4‰). Even if estuarine δN-NO values are not significantly different from pristine continental and oceanic site (+7.3‰ and +7.4‰), macroalgae δ15N values are generally higher at the mouth of the estuary. This highlights high anthropogenic DIN inputs in the estuary, and enhanced contribution of 15N-depleted NH in oceanic waters. Although seasonal variations in δN-NO are low, the same temporal trends in macroalgae δ15N values at estuarine and oceanic sites, and inter-species differences in δ15N values, suggest that macroalgae δ15N values might be modified by the metabolic response of macroalgae to environmental parameters (e

  2. Food webs of two intermittently open estuaries receiving 15N-enriched sewage effluent

    NASA Astrophysics Data System (ADS)

    Hadwen, Wade L.; Arthington, Angela H.

    2007-01-01

    Carbon and nitrogen stable isotope signatures were used to assess the response of food webs to sewage effluent discharged into two small intermittently open estuaries in northern New South Wales, Australia. One of these systems, Tallows Creek, has a history of direct sewage inputs, whilst the other, Belongil Creek, receives wastewater via an extensive wetland treatment system. The food webs of both systems were driven by algal sources of carbon, reflecting high autotrophic productivity in response to the nutrients entering the system from sewage effluent. All aquatic biota collected from Tallows Creek had significantly enriched δ15N signatures relative to their conspecifics from Belongil Creek, indicating that sewage nitrogen had been assimilated and transferred throughout the Tallows Creek food web. These δ15N values were higher than those reported from studies in permanently open estuaries receiving sewage effluent. We suggest that these enriched signatures and the transfer of nitrogen throughout the entire food web reflect differences in hydrology and associated nitrogen cycling processes between permanently open and intermittently open estuaries. Although all organisms in Tallows Creek were generally 15N-enriched, isotopically light (less 15N-enriched) individuals of estuary perchlet ( Ambassis marianus) and sea mullet ( Mugil cephalus) were also collected. These individuals were most likely recent immigrants into Tallows Creek, as this system had only recently been opened to the ocean. This isotopic discrimination between resident (enriched) and immigrant (significantly less enriched) individuals can provide information on fish movement patterns and the role of heavily polluted intermittently open estuaries in supporting commercially and recreationally valuable estuarine species.

  3. Hydrogen in vanadium: Site occupancy and isotope effects

    NASA Astrophysics Data System (ADS)

    Xin, Xiao; Johansson, Robert; Wolff, Max; Hjörvarsson, Björgvin

    2016-04-01

    We discuss the influence of site occupancy on the absorption of the hydrogen isotopes H and D in thin V(001) layers. By growing V(001) under biaxial compressive strain in Fe/V(001) superlattices, the hydrogen (H as well as D) is forced to reside exclusively in octahedral (Oz) sites, even at the lowest concentrations. A weakening of the isotope effects is observed when hydrogen resides in octahedral as compared to tetrahedral sites.

  4. Variation in foliar [sup 15]N abundance and the availability of soil nitrogen on Walker Branch Watershed

    SciTech Connect

    Garten, C.T. Jr. )

    1993-10-01

    Spatial patterns in natural [sup 15]N abundance ([sigma][sup 15]N) in soil, soil solutions, and non-N[sub 2]-fixing plants were studied in the deciduous forest on Walker Branch Watershed near Oak Ridge, Tennessee. This study was undertaken to test the hypothesis that foliar [sigma][sup 15]N values are related to the availability of inorganic nitrogen in mineral soil. Soils collected in or near valley bottoms on the watershed had higher levels of net nitrogen mineralization and net nitrification potential than those sampled from ridges and slopes. More positive foliar [sigma][sup 15]N values occurred in valley bottoms, which, relative to other positions on the watershed, were characterized by greater availability of soil nitrogen and lower C-to-N ratios in the O[sub 1]-horizon, in the surface mineral soil, and in autumn leaf fall. Although leaf nitrogen concentrations changed significantly over the course of the growing season, there was little seasonal variation in foliar [sigma][sup 15]N values. A hypothesis about the relative importance of different sources of nitrogen to the forest and how nitrogen cycling varies with topography in this nitrogen-deficient ecosystem was derived, in part, from spatial patterns in natural [sup 15]N abundance. There appear to be two processes affecting the topographic patterns in foliar [sup 15]N abundance on this watershed: (1) greater uptake from isotopically heavy pools of inorganic soil nitrogen by plants in valley bottoms, and (2) uptake of isotopically light ammonium-N in atmospheric deposition by plants on ridges and slopes (where the availability of inorganic soil nitrogen to plant roots is more limited). Results from this study indicate that foliar [sigma][sup 15]N values are positively correlated with net nitrification potential in surface soil. 34 refs., 13 figs., 8 tabs.

  5. Species specific and environment induced variation of δ13C and δ15N in alpine plants

    PubMed Central

    Yang, Yang; Siegwolf, Rolf T. W.; Körner, Christian

    2015-01-01

    Stable carbon and nitrogen isotope signals in plant tissues integrate plant-environment interactions over long periods. In this study, we hypothesized that humid alpine life conditions are narrowing the scope for significant deviations from common carbon, water and nitrogen relations as captured by stable isotope signals. We explored the variation in δ13C and δ15N in 32 plant species from tissue type to ecosystem scale across a suite of locations at c. Two thousand five hundred meter elevation in the Swiss Alps. Foliar δ13C and δ15N varied among species by about 3–4‰ and 7–8‰ respectively. However, there was no overall difference in means of δ13C and δ15N for species sampled in different plant communities or when bulk plant dry matter harvests of different plant communities were compared. δ13C was found to be highly species specific, so that the ranking among species was mostly maintained across 11 habitats. However, δ15N varied significantly from place to place in all species (a range of 2.7‰) except in Fabaceae (Trifolium alpinum) and Juncaceae (Luzula lutea). There was also a substantial variation among individuals of the same species collected next to each other. No difference was found in foliar δ15N of non-legumes, which were either collected next to or away from the most common legume, T. alpinum. δ15N data place Cyperaceae and Juncaceae, just like Fabaceae, in a low discrimination category, well separated from other families. Soil δ15N was higher than in plants and increased with soil depth. The results indicate a high functional diversity in alpine plants that is similar to that reported for low elevation plants. We conclude that the surprisingly high variation in δ13C and δ15N signals in the studied high elevation plants is largely species specific (genetic) and insensitive to obvious environmental cues. PMID:26097487

  6. Oxygen isotope geochemistry of the amphiboles: Isotope effects of cation substitutions in minerals

    SciTech Connect

    Kohn, M.J.; Valley, J.W.

    1998-06-01

    The occurrence of coexisting amphiboles in rocks and the likelihood of concurrent isotope closure allows equilibrium oxygen isotope fractionations among the amphiboles to be recovered from natural samples. Oxygen isotope analyses of mineral separates using laser fluorination show that coexisting amphiboles increasingly partition {sup 18}O in the order: hornblende {much_lt} gedrite < cummingtonite {le} anthophyllite. The observed fractionations at {approximately}575 C are: {Delta}(Ged-Hbl) = 0.8%, {Delta}(Cum-Hbl) = 0.9, {Delta}(Cum-Ged) = 0.2, {Delta}(Ath-Ged) = 0.3, and {Delta}(Ath-Hbl) > 0.9. Previously published data for hornblende, actinolite, glaucophane, and garnet show that {Delta}(Act-Hbl) {approximately} 0.2, {Delta}(Gin-Grt) {much_gt} 1, and {Delta}(Hbl-Grt) {approximately} 0. Thus, glaucophane strongly partitions {sup 18}O relative to the calcic amphiboles. The fractionation between two amphiboles of arbitrary composition can be predicted from the known fractionations for mica endmembers, pyroxene endmembers, and exchange components. Applications of the exchange component method reproduce measured amphibole fractionations to within {+-}0.1 to {+-}0.2%, whereas other predictive methods cause misfit for typical metamorphic hornblende of {ge}0.5% at 575 C. Although the isotope effects of cation exchanges may be small at high-T, they magnify dramatically for minerals formed in surficial, diagenetic, and low-T metamorphic environments. Different composition clays are predicted to have equilibrium {delta}{sup 18}O differences of 2--9%. If the isotope fractionation can be determined for one mineral endmember, then calibrated exchanges allow accurate prediction of the isotope fractionations for intermediate compositions of most ortho-, ring-, chain-, and sheet-silicates.

  7. Effects of lipid extraction on stable isotope ratios in avian egg yolk: Is arithmetic correction a reliable alternative?

    USGS Publications Warehouse

    Oppel, S.; Federer, R.N.; O'Brien, D. M.; Powell, A.N.; Hollmén, Tuula E.

    2010-01-01

    Many studies of nutrient allocation to egg production in birds use stable isotope ratios of egg yolk to identify the origin of nutrients. Dry egg yolk contains >50% lipids, which are known to be depleted in 13C. Currently, researchers remove lipids from egg yolk using a chemical lipid-extraction procedure before analyzing the isotopic composition of protein in egg yolk. We examined the effects of chemical lipid extraction on ??13C, ??15N, and ??34S of avian egg yolk and explored the utility of an arithmetic lipid correction model to adjust whole yolk ??13C for lipid content. We analyzed the dried yolk of 15 captive Spectacled Eider (Somateriafischeri) and 20 wild King Eider (S. spectabilis) eggs, both as whole yolk and after lipid extraction with a 2:1 chloroform:methanol solution. We found that chemical lipid extraction leads to an increase of (mean ?? SD) 3.3 ?? 1.1% in ??13C, 1.1 ?? 0.5% in ??15N, and 2.3 ?? 1.1% in ??34S. Arithmetic lipid correction provided accurate values for lipid-extracted S13C in captive Spectacled Eiders fed on a homogeneous high-quality diet. However, arithmetic lipid correction was unreliable for wild King Eiders, likely because of their differential incorporation of macronutrients from isotopically distinct environments during migration. For that reason, we caution against applying arithmetic lipid correction to the whole yolk ??13C of migratory birds, because these methods assume that all egg macronutrients are derived from the same dietary sources. ?? 2010 The American Ornithologists' Union.

  8. Determination of organic milk authenticity using carbon and nitrogen natural isotopes.

    PubMed

    Chung, Ill-Min; Park, Inmyoung; Yoon, Jae-Yeon; Yang, Ye-Seul; Kim, Seung-Hyun

    2014-10-01

    Natural stable isotopes of carbon and nitrogen ((12)C, (13)C, (14)N, (15)N) have abundances unique to each living creature. Therefore, measurement of the stable isotope ratio of carbon and nitrogen (δ(13)C=(13)C/(12)C, δ(15)N=(15)N/(14)N) in milk provides a reliable method to determine organic milk (OM) authenticity. In the present study, the mean δ(13)C value of OM was higher than that of conventional milk (CM), whereas the mean δ(15)N value of OM was lower than that of CM; nonetheless both δ(13)C and δ(15)N values were statistically different for the OM and CM (P<0.05). Furthermore, the values of δ(13)C and δ(15)N were found to differ statistically with the collection date and the milk brand (P<0.05). The combination of δ(13)C and δ(15)N values was more effective than either value alone in distinguishing between OM and CM. The results of the present study, which is based on preliminary data from a limited sample size and sampling period, could be highly valuable and helpful for consumers, the food industry, and/or government regulatory agencies as it can prevent fraudulent labelling of organic food. Further studies include additional analyses of other milk brands and analyses over longer time periods in order to accurately determine OM authenticity using stable isotopes of carbon and nitrogen. PMID:24799230

  9. Using macroalgal δ15N bioassay to detect cruise ship waste water effluent inputs in Skagway, AK

    EPA Science Inventory

    Nitrogen stable isotopes are a powerful tool for tracking sources of N to marine ecosystems. I used green macroalgae as a bioassay organism to evaluate if the δ15N signature of cruise ship waste water effluent (CSWWE) could be detected in Skagway Harbor, AK. Opportunistic green...

  10. Isotopic evidence for nitrification in the Antarctic winter mixed layer

    NASA Astrophysics Data System (ADS)

    Smart, Sandi M.; Fawcett, Sarah E.; Thomalla, Sandy J.; Weigand, Mira A.; Reason, Chris J. C.; Sigman, Daniel M.

    2015-04-01

    We report wintertime nitrogen and oxygen isotope ratios (δ15N and δ18O) of seawater nitrate in the Southern Ocean south of Africa. Depth profile and underway surface samples collected in July 2012 extend from the subtropics to just beyond the Antarctic winter sea ice edge. We focus here on the Antarctic region (south of 50.3°S), where application of the Rayleigh model to depth profile δ15N data yields estimates for the isotope effect (the degree of isotope discrimination) of nitrate assimilation (1.6-3.3‰) that are significantly lower than commonly observed in the summertime Antarctic (5-8‰). The δ18O data from the same depth profiles and lateral δ15N variations within the mixed layer, however, imply O and N isotope effects that are more similar to those suggested by summertime data. These findings point to active nitrification (i.e., regeneration of organic matter to nitrate) within the Antarctic winter mixed layer. Nitrite removal from samples reveals a low δ15N for nitrite in the winter mixed layer (-40‰ to -20‰), consistent with nitrification, but does not remove the observation of an anomalously low δ15N for nitrate. The winter data, and the nitrification they reveal, explain the previous observation of an anomalously low δ15N for nitrate in the temperature minimum layer (remnant winter mixed layer) of summertime depth profiles. At the same time, the wintertime data require a low δ15N for the combined organic N and ammonium in the autumn mixed layer that is available for wintertime nitrification, pointing to intense N recycling as a pervasive condition of the Antarctic in late summer.

  11. Mass Fractionation Laws, Mass-Independent Effects, and Isotopic Anomalies

    NASA Astrophysics Data System (ADS)

    Dauphas, Nicolas; Schauble, Edwin A.

    2016-06-01

    Isotopic variations usually follow mass-dependent fractionation, meaning that the relative variations in isotopic ratios scale with the difference in mass of the isotopes involved (e.g., δ17O ≈ 0.5×δ18O). In detail, however, the mass dependence of isotopic variations is not always the same, and different natural processes can define distinct slopes in three-isotope diagrams. These variations are subtle, but improvements in analytical capabilities now allow precise measurement of these effects and make it possible to draw inferences about the natural processes that caused them (e.g., reaction kinetics versus equilibrium isotope exchange). Some elements, in some sample types, do not conform to the regularities of mass-dependent fractionation. Oxygen and sulfur display a rich phenomenology of mass-independent fractionation, documented in the laboratory, in the rock record, and in the modern atmosphere. Oxygen in meteorites shows isotopic variations that follow a slope-one line (δ17O ≈ δ18O) whose origin may be associated with CO photodissociation. Sulfur mass-independent fractionation in ancient sediments provides the tightest constraint on the oxygen partial pressure in the Archean and the timing of Earth's surface oxygenation. Heavier elements also show departures from mass fractionation that can be ascribed to exotic effects associated with chemical reactions such as magnetic effects (e.g., Hg) or the nuclear field shift effect (e.g., U or Tl). Some isotopic variations in meteorites and their constituents cannot be related to the terrestrial composition by any known process, including radiogenic, nucleogenic, and cosmogenic effects. Those variations have a nucleosynthetic origin, reflecting the fact that the products of stellar nucleosynthesis were not fully homogenized when the Solar System formed. Those anomalies are found at all scales, from nanometer-sized presolar grains to bulk terrestrial planets. They can be used to learn about stellar

  12. Magnetic isotope and magnetic field effects on the DNA synthesis

    PubMed Central

    Buchachenko, Anatoly L.; Orlov, Alexei P.; Kuznetsov, Dmitry A.; Breslavskaya, Natalia N.

    2013-01-01

    Magnetic isotope and magnetic field effects on the rate of DNA synthesis catalysed by polymerases β with isotopic ions 24Mg2+, 25Mg2+ and 26Mg2+ in the catalytic sites were detected. No difference in enzymatic activity was found between polymerases β carrying 24Mg2+ and 26Mg2+ ions with spinless, non-magnetic nuclei 24Mg and 26Mg. However, 25Mg2+ ions with magnetic nucleus 25Mg were shown to suppress enzymatic activity by two to three times with respect to the enzymatic activity of polymerases β with 24Mg2+ and 26Mg2+ ions. Such an isotopic dependence directly indicates that in the DNA synthesis magnetic mass-independent isotope effect functions. Similar effect is exhibited by polymerases β with Zn2+ ions carrying magnetic 67Zn and non-magnetic 64Zn nuclei, respectively. A new, ion–radical mechanism of the DNA synthesis is suggested to explain these effects. Magnetic field dependence of the magnesium-catalysed DNA synthesis is in a perfect agreement with the proposed ion–radical mechanism. It is pointed out that the magnetic isotope and magnetic field effects may be used for medicinal purposes (trans-cranial magnetic treatment of cognitive deceases, cell proliferation, control of the cancer cells, etc). PMID:23851636

  13. N-loss isotope effects in the Peru oxygen minimum zone studied using a mesoscale eddy as a natural tracer experiment

    NASA Astrophysics Data System (ADS)

    Bourbonnais, Annie; Altabet, Mark A.; Charoenpong, Chawalit N.; Larkum, Jennifer; Hu, Haibei; Bange, Hermann W.; Stramma, Lothar

    2015-06-01

    Mesoscale eddies in Oxygen Minimum Zones (OMZs) have been identified as important fixed nitrogen (N) loss hotspots that may significantly impact both the global rate of N-loss as well as the ocean's N isotope budget. They also represent "natural tracer experiments" with intensified biogeochemical signals that can be exploited to understand the large-scale processes that control N-loss and associated isotope effects (ɛ; the ‰ deviation from 1 in the ratio of reaction rate constants for the light versus heavy isotopologues). We observed large ranges in the concentrations and N and O isotopic compositions of nitrate (NO3-), nitrite (NO2-), and biogenic N2 associated with an anticyclonic mode-water eddy in the Peru OMZ during two cruises in November and December 2012. In the eddy's center where NO3- was nearly exhausted, we measured the highest δ15N values for both NO3- and NO2- (up to ~70‰ and 50‰) ever reported for an OMZ. Correspondingly, N deficit and biogenic N2-N concentrations were also the highest near the eddy's center (up to ~40 µmol L-1). δ15N-N2 also varied with biogenic N2 production, following kinetic isotopic fractionation during NO2- reduction to N2 and, for the first time, provided an independent assessment of N isotope fractionation during OMZ N-loss. We found apparent variable ɛ for NO3- reduction (up to ~30‰ in the presence of NO2-). However, the overall ɛ for N-loss was calculated to be only ~13-14‰ (as compared to canonical values of ~20-30‰) assuming a closed system and only slightly higher assuming an open system (16-19‰). Our results were similar whether calculated from the disappearance of DIN (NO3- + NO2-) or from the appearance of N2 and changes in isotopic composition. Further, we calculated the separate ɛ values for NO3- reduction to NO2- and NO2- reduction to N2 of ~16-21‰ and ~12‰, respectively, when the effect of NO2- oxidation could be removed. These results, together with the relationship between N and O of NO

  14. Phonon-isotope scattering and thermal conductivity in materials with a large isotope effect: A first-principles study

    NASA Astrophysics Data System (ADS)

    Lindsay, L.; Broido, D. A.; Reinecke, T. L.

    2013-10-01

    The interplay between phonon-isotope and phonon-phonon scattering in determining lattice thermal conductivities in semiconductors and insulators is examined using an ab initio Boltzmann transport equation approach. We identify materials with large enhancements to their thermal conductivities with isotopic purification, known as the isotope effect, and we focus in particular on results for beryllium-VI compounds and cubic germanium carbide. We find that germanium carbide and beryllium selenide have very large room temperature isotope effects of 450%, far larger than in any other material. Thus, isotopic purification in these materials gives surprisingly high intrinsic room temperature thermal conductivities, over 1500 Wm-1 K-1 for germanium carbide and over 600 Wm-1 K-1 for beryllium selenide, well above those of the best metals. In compound semiconductors, a large mass ratio of the constituent atoms and large isotope mixture for the heavier atom gives enhanced isotope scattering. A frequency gap between acoustic and optic phonons (also due to a large mass ratio) and bunching of the acoustic phonon branches give weak anharmonic scattering. Combined, weak anharmonic phonon scattering and strong isotope scattering give a large isotope effect in the materials examined here. The physical insights discussed in this work will help guide the efficient manipulation of thermal transport properties of compound semiconductors through isotopic modification.

  15. The confounding effects of source isotopic heterogeneity on consumer-diet and tissue-tissue stable isotope relationships.

    PubMed

    Codron, Daryl; Sponheimer, Matt; Codron, Jacqui; Newton, Ian; Lanham, John L; Clauss, Marcus

    2012-08-01

    Stable isotope analysis of consumer tissues document patterns of resource use because data are linearly related to isotope compositions of their source(s) (i.e., food, water, etc.). Deviations in parameters estimated for these relationships can arise from variations in consumer tissue-diet spacing (Δ(TS)) and the level of isotopic heterogeneity in the source(s). We present a set of simple hypotheses that distinguish between the effects of Δ(TS) and source isotope heterogeneity. The latter may arise via mixed diets, during tissue turnover, or by isotopic routing of dietary components. We apply these concepts to stable carbon and nitrogen isotope relationships between gut contents and body tissues of large mammal herbivores from mixed C(3)/C(4) South African savannas and test predictions based on the compound- and/or time-specific data archived within each material. Predicted effects of source isotope heterogeneity are readily detected in carbon isotope relationships between materials representing different time periods or comprising bulk versus protein-only diet components. Differences in Δ(TS) of carbon isotopes across mammal herbivore species with very different feeding niches (and diet isotope compositions) are likely to be small or non-existent in these habitats. Variations in Δ(TS) estimated for nitrogen isotopes are much greater, leading to inconsistencies that cannot be explained by diet or trophic level effects alone. The effects of source heterogeneity on isotopic relationships generate numerical artefacts that have been misinterpreted as variations in Δ(TS). We caution against generalized application of hypotheses based on assumptions of source isotopic homogeneity, even for single diets commonly used in laboratory studies. More careful consideration of how heterogeneity affects consumer-diet relationships is needed for many field and laboratory systems. PMID:22349754

  16. Plant community change mediates the response of foliar δ(15)N to CO 2 enrichment in mesic grasslands.

    PubMed

    Polley, H Wayne; Derner, Justin D; Jackson, Robert B; Gill, Richard A; Procter, Andrew C; Fay, Philip A

    2015-06-01

    Rising atmospheric CO2 concentration may change the isotopic signature of plant N by altering plant and microbial processes involved in the N cycle. CO2 may increase leaf δ(15)N by increasing plant community productivity, C input to soil, and, ultimately, microbial mineralization of old, (15)N-enriched organic matter. We predicted that CO2 would increase aboveground productivity (ANPP; g biomass m(-2)) and foliar δ(15)N values of two grassland communities in Texas, USA: (1) a pasture dominated by a C4 exotic grass, and (2) assemblages of tallgrass prairie species, the latter grown on clay, sandy loam, and silty clay soils. Grasslands were exposed in separate experiments to a pre-industrial to elevated CO2 gradient for 4 years. CO2 stimulated ANPP of pasture and of prairie assemblages on each of the three soils, but increased leaf δ(15)N only for prairie plants on a silty clay. δ(15)N increased linearly as mineral-associated soil C declined on the silty clay. Mineral-associated C declined as ANPP increased. Structural equation modeling indicted that CO2 increased ANPP partly by favoring a tallgrass (Sorghastrum nutans) over a mid-grass species (Bouteloua curtipendula). CO2 may have increased foliar δ(15)N on the silty clay by reducing fractionation during N uptake and assimilation. However, we interpret the soil-specific, δ(15)N-CO2 response as resulting from increased ANPP that stimulated mineralization from recalcitrant organic matter. By contrast, CO2 favored a forb species (Solanum dimidiatum) with higher δ(15)N than the dominant grass (Bothriochloa ischaemum) in pasture. CO2 enrichment changed grassland δ(15)N by shifting species relative abundances. PMID:25604918

  17. Effect of storage on the isotopic composition of nitrate in bulk precipitation.

    PubMed

    Spoelstra, John; Schiff, Sherry L; Jeffries, Dean S; Semkin, Ray G

    2004-09-15

    Stable isotopic analysis of atmospheric nitrate is increasingly employed to study nitrate sources and transformations in forested catchments. Large volumes have typically been required for delta18O and delta15N analysis of nitrate in precipitation due to relatively low nitrate concentrations. Having bulk collectors accumulate precipitation over an extended time period allows for collection of the required volume as well as reducing the total number of analyses needed to determine the isotopic composition of mean annual nitrate deposition. However, unfiltered precipitation left in collectors might be subject to microbial reactions that can alter the isotopic signature of nitrate in the sample. Precipitation obtained from the Turkey Lakes Watershed was incubated under conditions designed to mimic unfiltered storage in bulk precipitation collectors and monitored for changes in nitrate concentration, delta15N, and delta18O. Results of this experiment indicated that no detectable nitrate production or assimilation occurred in the samples during a two-week incubation period and that atmospheric nitrate isotopic ratios were preserved. The ability to collect unfiltered precipitation samples for an extended duration without alteration of nitrate isotope ratios is particularly useful at remote study sites where daily retrieval of samples may not be feasible. PMID:15487778

  18. Nuclear quantum effects and kinetic isotope effects in enzyme reactions.

    PubMed

    Vardi-Kilshtain, Alexandra; Nitoker, Neta; Major, Dan Thomas

    2015-09-15

    Enzymes are extraordinarily effective catalysts evolved to perform well-defined and highly specific chemical transformations. Studying the nature of rate enhancements and the mechanistic strategies in enzymes is very important, both from a basic scientific point of view, as well as in order to improve rational design of biomimetics. Kinetic isotope effect (KIE) is a very important tool in the study of chemical reactions and has been used extensively in the field of enzymology. Theoretically, the prediction of KIEs in condensed phase environments such as enzymes is challenging due to the need to include nuclear quantum effects (NQEs). Herein we describe recent progress in our group in the development of multi-scale simulation methods for the calculation of NQEs and accurate computation of KIEs. We also describe their application to several enzyme systems. In particular we describe the use of combined quantum mechanics/molecular mechanics (QM/MM) methods in classical and quantum simulations. The development of various novel path-integral methods is reviewed. These methods are tailor suited to enzyme systems, where only a few degrees of freedom involved in the chemistry need to be quantized. The application of the hybrid QM/MM quantum-classical simulation approach to three case studies is presented. The first case involves the proton transfer in alanine racemase. The second case presented involves orotidine 5'-monophosphate decarboxylase where multidimensional free energy simulations together with kinetic isotope effects are combined in the study of the reaction mechanism. Finally, we discuss the proton transfer in nitroalkane oxidase, where the enzyme employs tunneling as a catalytic fine-tuning tool. PMID:25769515

  19. Identifying vital effects in Halimeda algae with Ca isotopes

    NASA Astrophysics Data System (ADS)

    Blättler, C. L.; Stanley, S. M.; Henderson, G. M.; Jenkyns, H. C.

    2014-03-01

    Geochemical records of biogenic carbonates provide some of the most valuable records of the geological past, but are often difficult to interpret without a mechanistic understanding of growth processes. In this experimental study, Halimeda algae are used as a test organism to untangle some of the specific factors that influence their skeletal composition, in particular their Ca-isotope composition. Algae were stimulated to precipitate both calcite and aragonite by growth in artificial Cretaceous seawater. The Ca-isotope fractionation of the algal calcite is much smaller than that for the algal aragonite, similar to the behaviour observed in inorganic precipitates. However, the carbonate from Halimeda is isotopically heavier than inorganic forms, likely due to Rayleigh distillation within the algal intercellular space. In identifying specific vital effects and the magnitude of their influence on Ca-isotope ratios, this study suggests that mineralogy has a first-order control on the Ca-isotope budget of the carbonate sink and the Ca-isotope composition of seawater.

  20. Early-stage changes in natural (13)C and (15)N abundance and nutrient dynamics during different litter decomposition.

    PubMed

    Gautam, Mukesh Kumar; Lee, Kwang-Sik; Song, Byeong-Yeol; Lee, Dongho; Bong, Yeon-Sik

    2016-05-01

    Decomposition, nutrient, and isotopic (δ(13)C and δ(15)N) dynamics during 1 year were studied for leaf and twig litters of Pinus densiflora, Castanea crenata, Erigeron annuus, and Miscanthus sinensis growing on a highly weathered soil with constrained nutrient supply using litterbags in a cool temperate region of South Korea. Decay constant (k/year) ranged from 0.58 to 1.29/year, and mass loss ranged from 22.36 to 58.43 % among litter types. The results demonstrate that mass loss and nutrient dynamics of decomposing litter were influenced by the seasonality of mineralization and immobilization processes. In general, most nutrients exhibited alternate phases of rapid mineralization followed by gradual immobilization, except K, which was released throughout the field incubation. At the end of study, among all the nutrients only N and P showed net immobilization. Mobility of different nutrients from decomposing litter as the percentage of initial litter nutrient concentration was in the order of K > Mg > Ca > N ≈ P. The δ(13)C (0.32-6.70 ‰) and δ(15)N (0.74-3.90 ‰) values of residual litters showed nonlinear increase and decrease, respectively compared to initial isotopic values during decomposition. Litter of different functional types and chemical quality converged toward a conservative nutrient use strategy through mechanisms of slow decomposition and slow nutrient mobilization. Our results indicate that litter quality and season, are the most important regulators of litter decomposition in these forests. The results revealed significant relationships between litter decomposition rates and N, C:N ratio and P, and seasonality (temperature). These results and the convergence of different litters towards conservative nutrient use in these nutrient constrained ecosystems imply optimization of litter management because litter removal can have cascading effects on litter decomposition and nutrient availability in these systems. PMID:26915037

  1. Accelerating quantum instanton calculations of the kinetic isotope effects.

    PubMed

    Karandashev, Konstantin; Vaníček, Jiří

    2015-11-21

    Path integral implementation of the quantum instanton approximation currently belongs among the most accurate methods for computing quantum rate constants and kinetic isotope effects, but its use has been limited due to the rather high computational cost. Here, we demonstrate that the efficiency of quantum instanton calculations of the kinetic isotope effects can be increased by orders of magnitude by combining two approaches: The convergence to the quantum limit is accelerated by employing high-order path integral factorizations of the Boltzmann operator, while the statistical convergence is improved by implementing virial estimators for relevant quantities. After deriving several new virial estimators for the high-order factorization and evaluating the resulting increase in efficiency, using ⋅Hα + HβHγ → HαHβ + ⋅ Hγ reaction as an example, we apply the proposed method to obtain several kinetic isotope effects on CH4 + ⋅ H ⇌ ⋅ CH3 + H2 forward and backward reactions. PMID:26590524

  2. Asymptotic Normalization Coefficients from the {sup 15}N({sup 3}He,d){sup 16}O Reaction and the Astrophysical Factor for the {sup 15}N(p,{gamma}){sup 16}O Capture

    SciTech Connect

    Burjan, V.; Bem, P.; Hons, Z.; Kroha, V.; Mrazek, J.; Novak, J.; Piskor, S.; Simeckova, E.; Vincour, J.; Cherubini, S.; La Cognata, M.; Pizzone, R. G.; Romano, S.; Spitaleri, C.; Tumino, A.; Gagliardi, C. A.; Mukhamedzhanov, A. M.; Plunkett, A.; Trache, L.; Tribble, R. E.

    2008-05-12

    The angular distributions of the {sup 15}N({sup 3}He,d){sup 16}O reaction were measured with the aim to determine the direct capture rate of the astrophysical reaction {sup 15}N(p, {gamma}){sup 16}O by deducing asymptotic normalization coefficients (ANC). The {sup 15}N(p,{gamma}){sup 16}O reaction is a part of the CNO cycle having importance in the nucleosynthesis of the N and O isotopes. The measurement was carried out on the cyclotron U120M of NPI CAS at the energy 25.74 MeV of {sup 3}He ions in a gas chamber containing the high purity {sup 15}N isotope. The preliminary results of corresponding spectroscopic factors and ANC's were used for the estimation of the S-factor for the direct capture {sup 15}N(p,{gamma}){sup 16}O. Using the widths of the resonances E{sub R} = 312 and 962 keV, the total S-factor was determined within the framework of the R-matrix approach.

  3. Natural abundance 14N and 15N solid-state NMR of pharmaceuticals and their polymorphs

    DOE PAGESBeta

    Veinberg, Stanislav L.; Johnston, Karen E.; Jaroszewicz, Michael J.; Kispal, Brianna M.; Mireault, Christopher R.; Kobayashi, Takeshi; Pruski, Marek; Schurko, Robert W.

    2016-06-08

    14N ultra-wideline (UW), 1H{15N} indirectly-detected HETCOR (idHETCOR) and 15N dynamic nuclear polarization (DNP) solid-state NMR (SSNMR) experiments, in combination with plane-wave density functional theory (DFT) calculations of 14N EFG tensors, were utilized to characterize a series of nitrogen-containing active pharmaceutical ingredients (APIs), including HCl salts of scopolamine, alprenolol, isoprenaline, acebutolol, dibucaine, nicardipine, and ranitidine. Here, a case study applying these methods for the differentiation of polymorphs of bupivacaine HCl is also presented. All experiments were conducted upon samples with naturally-abundant nitrogen isotopes. For most of the APIs, it was possible to acquire frequency-stepped UW 14N SSNMR spectra of stationarymore » samples, which display powder patterns corresponding to pseudo-tetrahedral (i.e., RR'R"NH+ and RR'NH2+) or other (i.e., RNH2 and RNO2) nitrogen environments.« less

  4. Efficient methods and practical guidelines for simulating isotope effects.

    PubMed

    Ceriotti, Michele; Markland, Thomas E

    2013-01-01

    The shift in chemical equilibria due to isotope substitution is frequently exploited to obtain insight into a wide variety of chemical and physical processes. It is a purely quantum mechanical effect, which can be computed exactly using simulations based on the path integral formalism. Here we discuss how these techniques can be made dramatically more efficient, and how they ultimately outperform quasi-harmonic approximations to treat quantum liquids not only in terms of accuracy, but also in terms of computational cost. To achieve this goal we introduce path integral quantum mechanics estimators based on free energy perturbation, which enable the evaluation of isotope effects using only a single path integral molecular dynamics trajectory of the naturally abundant isotope. We use as an example the calculation of the free energy change associated with H/D and (16)O/(18)O substitutions in liquid water, and of the fractionation of those isotopes between the liquid and the vapor phase. In doing so, we demonstrate and discuss quantitatively the relative benefits of each approach, thereby providing a set of guidelines that should facilitate the choice of the most appropriate method in different, commonly encountered scenarios. The efficiency of the estimators we introduce and the analysis that we perform should in particular facilitate accurate ab initio calculation of isotope effects in condensed phase systems. PMID:23298033

  5. Quantum instanton evaluation of the kinetic isotope effects

    SciTech Connect

    Vanicek, Jiri; Miller, William H.; Castillo, Jesus F.; Aoiz, F.Javier

    2005-04-19

    A general quantum-mechanical method for computing kinetic isotope effects is presented. The method is based on the quantum instanton approximation for the rate constant and on the path integral Metropolis Monte-Carlo evaluation of the Boltzmann operator matrix elements. It computes the kinetic isotope effect directly, using a thermodynamic integration with respect to the mass of the isotope, thus avoiding the more computationally expensive process of computing the individual rate constants. The method is more accurate than variational transition-state theories or the semiclassical instanton method since it does not assume a single reaction path and does not use a semiclassical approximation of the Boltzmann operator. While the general Monte-Carlo implementation makes the method accessible to systems with a large number of atoms, we present numerical results for the Eckart barrier and for the collinear and full three-dimensional isotope variants of the hydrogen exchange reaction H+H{sub 2} {yields} H{sub 2}+H. In all seven test cases, for temperatures between 250 K and 600 K, the error of the quantum instanton approximation for the kinetic isotope effects is less than {approx}10%.

  6. Isotopic Changes During Digestion: Protein

    NASA Astrophysics Data System (ADS)

    Tuross, N.

    2013-12-01

    Nutrient and hydrological inputs traverse a complicated route of pH, enzymatic and cellular processes in digestion in higher animals. The end products of digestion are the starting products for biosynthesis that are often used to interpret past life-ways. Using an artificial gut system, the isotopic changes (dD, d18O, d13C and d15N) of protein are documented. Three separate protein sources are subjected to the conditions, chemical and enzymatic, found in the stomach and upper small intestine with only a small shift in the oxygen isotopic composition of the proteins observed. Middle to lower small intestine parameters produced both greater isotopic effects and significantly lower molecular weight products. The role of the gastric enterocyte and the likely involvement of the internal milieu of this cell in the isotopic composition of amino acids that are transported to the liver are reported.

  7. δ15N as a Potential Paleoenvironmental Proxy for Nitrogen Loading in Chesapeake Bay

    NASA Astrophysics Data System (ADS)

    Black, H. D.; Andrus, C. F.; Rick, T.; Hines, A.

    2013-12-01

    Stable isotope analysis of Eastern Oyster (Crassostrea virginica) and other mollusk shells from archaeological sites is a useful means of acquiring paleoenvironmental data. Recently, nitrogen isotopes have been identified as a potential new proxy in these shells. δ15N content in mollusk shells is affected by numerous anthropogenic and natural influences and may be used as an environmental proxy for nitrogen loading conditions. Chesapeake Bay is well known for both historic and modern pollution problems from numerous anthropogenic sources, such as fertilizer runoff, sewage discharge, and densely populated land use and serves as an ideal study location for long-term nitrogen loading processes. Longer records of these processes may be recorded in abundant archaeological remains around the bay, however, little is known about the stability of δ15N and %N in shell material over recent geologic time. In this study, 90 archaeological C. virginica shells were collected by the Smithsonian Institution from the Rhode River Estuary within Chesapeake Bay and range in age from ~150 to 3200 years old. Twenty-two modern C. virginica shells were also collected from nearby beds in the bay. All shell samples were subsampled from the resilifer region of the calcitic shell using a hand-held micro drill and were analyzed using EA-IRMS analysis to determine the potential temporal variability of δ15N and %N as well as creating a baseline for ancient nitrogen conditions in the bay area. Modern POM water samples and C. virginica soft tissues were also analyzed in this study to determine the degree of seasonal variation of δ15N and %N in Chesapeake Bay.

  8. Elucidating the trophodynamics of four coral reef fishes of the Solomon Islands using δ15N and δ13C

    NASA Astrophysics Data System (ADS)

    Greenwood, N. D. W.; Sweeting, C. J.; Polunin, N. V. C.

    2010-09-01

    Size-related diet shifts are important characteristics of fish trophodynamics. Here, body size-related changes in muscle δ15N and δ13C of four coral reef fishes, Acanthurus nigrofuscus (herbivore), Chaetodon lunulatus (corallivore) , Chromis xanthura (planktivore) and Plectropomus leopardus (piscivore) were investigated at two locations in the Solomon Islands. All four species occupied distinct isotopic niches and the concurrent δ13C' values of C. xanthura and P. leopardus suggested a common planktonic production source. Size-related shifts in δ15N, and thus trophic level, were observed in C. xanthura, C. lunulatus and P. leopardus, and these trends varied between location, indicating spatial differences in trophic ecology. A literature review of tropical fishes revealed that positive δ15N-size trends are common while negative δ15N-size trends are rare. Size-δ15N trends fall into approximately equal groups representing size-based feeding within a food chain, and that associated with a basal resource shift and occurs in conjunction with changes in production source, indicated by δ13C. The review also revealed large scale differences in isotope-size trends and this, combined with small scale location differences noted earlier, highlights a high degree of plasticity in the reef fishes studied. This suggests that trophic size analysis of reef fishes would provide a productive avenue to identify species potentially vulnerable to reef impacts as a result of constrained trophic behaviour.

  9. Endogenous and environmental factors influence the dietary fractionation of 13C and 15N in hissing cockroaches Gromphadorhina portentosa.

    PubMed

    McCue, Marshall D

    2008-01-01

    Since DeNiro and Epstein's discovery that the (13)C and (15)N isotopic signatures of animals approximate those of their respective diets, the measurement of stable isotope signatures has become an important tool for ecologists studying the diets of wild animals. This study used Madagascar hissing cockroaches (Gromphadorhina portentosa) to examine several preexisting hypotheses about the relationship between the isotopic composition of an animal and its diet. Contrary to my predictions, the results revealed that the tissues of adult cockroaches raised for two generations on a diet of known isotopic composition did not demonstrate enrichment of heavy stable isotopes. Moreover, the (15)N signatures of cockroaches were neither influenced by periods of rapid growth (i.e., 300-fold increase in dry body mass over 120 d) nor by imposed periods of starvation lasting up to 80 d. The offspring born to mothers raised on known diets were enriched in (15)N. Diet-switching experiments showed that turnover times of (13)C were highly correlated with age and ranged from 9 to 10 d to 60 to 75 d in subadults and adults, respectively. Adults subjected to diet switches differed from the subadults in that the adults achieved equilibrated isotopic signatures that were shifted approximately 1.0 per thousand toward their respective original diets. Lipid fractions of adult cockroaches averaged 2.9 per thousand more depleted in (13)C than in lipid-free fractions, but no changes in (13)C were observed in aging adults. Exposure to reduced ambient temperature from 33 degrees C to 23 degrees C over 120 d did not influence isotopic signatures of tissues. Overall, the results of this study reveal that different endogenous and exogenous factors can influence the isotopic signatures of cockroaches. These findings reinforce the need to conduct controlled studies to further examine environmental factors that influence the relationships between the isotopic signatures of animals and their diets. PMID

  10. Isolation and measurement of 15N2 from respiratory gases of animals administered 15N-labeled substances.

    PubMed

    Springer, D L; Reed, D J; Dost, F N

    1981-01-01

    A method is described for collection of metabolic 15N2 from in vitro preparations or intact rats administered 15N-containing compounds. The methods enables routine collection and mass spectrometric measurement of as little as 10 mumol 15N2 respired by a rat over a 24-h period. A device is described that includes either an animal chamber or a tissue reaction vessel in a closed recycling atmosphere, with automatic O2 replenishment and removal of CO2 and water. It is capable of sustaining moderate vacuum and is coupled to a high-vacuum manifold designed to process the contained atmosphere and respiratory gases. The starting atmosphere is an 80:20 mix of sulfur hexafluoride and O2. Recovery of 15N2 gas from the system without an animal present was 101.3 +/- 5.75%. When 15N2 gas was very slowly infused iv into an animal, recovery was 89.1 +/- 5.38%. Use of the method in studies of the fate of [15N]hydrazine in rats indicated that about 15% of the administered hydrazine is rapidly converted to 15N2, followed by slower conversion of an additional 7-10% over the next several hours. PMID:7328697

  11. Negligible Isotopic Effect on Dissociation of Hydrogen Bonds.

    PubMed

    Ge, Chuanqi; Shen, Yuneng; Deng, Gang-Hua; Tian, Yuhuan; Yu, Dongqi; Yang, Xueming; Yuan, Kaijun; Zheng, Junrong

    2016-03-31

    Isotopic effects on the formation and dissociation kinetics of hydrogen bonds are studied in real time with ultrafast chemical exchange spectroscopy. The dissociation time of hydrogen bond between phenol-OH and p-xylene (or mesitylene) is found to be identical to that between phenol-OD and p-xylene (or mesitylene) in the same solvents. The experimental results demonstrate that the isotope substitution (D for H) has negligible effects on the hydrogen bond kinetics. DFT calculations show that the isotope substitution does not significantly change the frequencies of vibrational modes that may be along the hydrogen bond formation and dissociation coordinate. The zero point energy differences of these modes between hydrogen bonds with OH and OD are too small to affect the activation energy of the hydrogen bond dissociation in a detectible way at room temperature. PMID:26967376

  12. The effect of the recent 17O(p,α)14N and 18O(p,α)15N fusion cross section measurements in the nucleosynthesis of AGB stars

    NASA Astrophysics Data System (ADS)

    Palmerini, S.; Sergi, M. L.; La Cognata, M.; Lamia, L.; Pizzone, R. G.; Spitaleri, C.

    2015-01-01

    The Trojan Horse Method (THM) has been used to investigate the low-energy cross sections of the 17O(p,α)14N and 18O(p,α)15N fusion reactions and to extract the strengths of the resonances that more contribute to the reaction rates at astrophysical energies. Moreover, the strength of the 65 keV resonance in the 17O(p,α)14N reaction, measured by means of the THM, has been used to renormalize the corresponding resonance strength in the 17O + p radiative capture channel. Since, proton-induced fusion reactions on 17O and 18O belong to the CNO cycle network for H-burning in stars, the new estimates of the cross sections have been introduced into calculations of Asymptotic giant branch (AGB) star nucleosynthesis to determine their impact on astrophysical environments. Results of nucleosynthesis calculations have been compared with geochemical analysis of "presolar" grains. These solids form in the cold and dusty envelopes that surround AGB stars and once that have been ejected by stellar winds, come to us as inclusions in meteorites providing invaluable benchmarks and constraints for our knowledge of fusion reactions in astrophysical environments.

  13. Partitioning Residue-derived and Residue-induced Emissions of N2O Using 15N-labelled Crop Residues

    NASA Astrophysics Data System (ADS)

    Farrell, R. E.; Carverhill, J.; Lemke, R.; Knight, J. D.

    2014-12-01

    Estimates of N2O emissions in Canada indicate that 17% of all agriculture-based emissions are associated with the decomposition of crop residues. However, research specific to the western Canadian prairies (including Saskatchewan) has shown that the N2O emission factor for N sources in this region typically ranges between 0.2 and 0.6%, which is well below the current IPCC default emission factor of 1.0%. Thus, it stands to reason that emissions from crop residues should also be lower than those calculated using the current IPCC emission factor. Current data indicates that residue decomposition, N mineralization and N2O production are affected by a number of factors such as C:N ratio and chemical composition of the residue, soil type, and soil water content; thus, a bench-scale incubation study was conducted to examine the effects of soil type and water content on N2O emissions associated with the decomposition of different crop residues. The study was carried out using soils from the Black, Dark Brown, Brown, and Gray soil zones and was conducted at both 50% and 70% water-filled pore space (WFPS); the soils were amended with 15N-labeled residues of wheat, pea, canola, and flax, or with an equivalent amount of 15N-labeled urea; 15N2O production was monitored using a Picarro G5101-i isotopic N2O analyzer. Crop residue additions to the soils resulted in both direct and indirect emissions of N2O, with residue derived emissions (RDE; measured as 15N2O) generally exceeding residue-induced emissions (RIE) at 50% WFPS—with RDEs ranging from 42% to 88% (mean = 58%) of the total N2O. Conversely, at 70% WFPS, RDEs were generally lower than RIEs—ranging from 21% to 83% (mean = 48%). Whereas both water content and soil type had an impact on N2O production, there was a clear and consistent trend in the emission factors for the residues; i.e., emissions were always greatest for the canola residue and lowest for the wheat residue and urea fertilizer; and intermediate for pea

  14. Rivermouth alteration of agricultural impacts on consumer tissue δ15N

    USGS Publications Warehouse

    Larson, James H.; Richardson, William B.; Vallazza, Jonathan M.; Nelson, J. C.

    2013-01-01

    Terrestrial agricultural activities strongly influence riverine nitrogen (N) dynamics, which is reflected in the δ15N of riverine consumer tissues. However, processes within aquatic ecosystems also influence consumer tissue δ15N. As aquatic processes become more important terrestrial inputs may become a weaker predictor of consumer tissue δ15N. In a previous study, this terrestrial-consumer tissue δ15N connection was very strong at river sites, but was disrupted by processes occurring in rivermouths (the ‘rivermouth effect’). This suggested that watershed indicators of N loading might be accurate in riverine settings, but could be inaccurate when considering N loading to the nearshore of large lakes and oceans. In this study, the rivermouth effect was examined on twenty-five sites spread across the Laurentian Great Lakes. Relationships between agriculture and consumer tissue δ15N occurred in both upstream rivers and at the outlets where rivermouths connect to the nearshore zone, but agriculture explained less variation and had a weaker effect at the outlet. These results suggest that rivermouths may sometimes be significant sources or sinks of N, which would cause N loading estimates to the nearshore zone that are typically made at discharge gages further upstream to be inaccurate. Identifying definitively the controls over the rivermouth effect on N loading (and other nutrients) will require integration of biogeochemical and hydrologic models.

  15. Effects of elemental composition on the incorporation of dietary nitrogen and carbon isotopic signatures in an omnivorous songbird.

    PubMed

    Pearson, Scott F; Levey, Douglas J; Greenberg, Cathryn H; Martínez Del Rio, Carlos

    2003-05-01

    The use of stable isotopes to infer diet requires quantifying the relationship between diet and tissues and, in particular, knowing of how quickly isotopes turnover in different tissues and how isotopic concentrations of different food components change (discriminate) when incorporated into consumer tissues. We used feeding trials with wild-caught yellow-rumped warblers (Dendroica coronata) to determine delta15N and delta13C turnover rates for blood, delta15N and delta13C diet-tissue discrimination factors, and diet-tissue relationships for blood and feathers. After 3 weeks on a common diet, 36 warblers were assigned to one of four diets differing in the relative proportion of fruit and insects. Plasma half-life estimates ranged from 0.4 to 0.7 days for delta13C and from 0.5 to 1.7 days for delta15N . Half-life did not differ among diets. Whole blood half-life for delta13C ranged from 3.9 to 6.1 days. Yellow-rumped warbler tissues were enriched relative to diet by 1.7-3.6% for nitrogen isotopes and by -1.2 to 4.3% for carbon isotopes, depending on tissue and diet. Consistent with previous studies, feathers were the most enriched and whole blood and plasma were the least enriched or, in the case of carbon, slightly depleted relative to diet. In general, tissues were more enriched relative to diet for birds on diets with high percentages of insects. For all tissues, carbon and nitrogen isotope discrimination factors increased with carbon and nitrogen concentrations of diets. The isotopic signature of plasma increased linearly with the sum of the isotopic signature of the diet and the discrimination factor. Because the isotopic signature of tissues depends on both elemental concentration and isotopic signature of the diet, attempts to reconstruct diet from stable isotope signatures require use of mixing models that incorporate elemental concentration. PMID:16228250

  16. Does avian malaria infection affect feather stable isotope signatures?

    PubMed

    Yohannes, Elizabeth; Palinauskas, Vaidas; Valkiūnas, Gediminas; Lee, Raymond W; Bolshakov, Casimir V; Bensch, Staffan

    2011-12-01

    It is widely accepted that stable isotope ratios in inert tissues such as feather keratin reflect the dietary isotopic signature at the time of the tissue synthesis. However, some elements such as stable nitrogen isotopes can be affected by individual physiological state and nutritional stress. Using malaria infection experiment protocols, we estimated the possible effect of malaria parasite infections on feather carbon (δ(13)C) and nitrogen (δ(15)N) isotope signatures in juvenile common crossbills Loxia curvirostra. The birds were experimentally infected with Plasmodium relictum (lineage SGS1) and P. ashfordi (GRW2), two widespread parasites of passerines. Experimental birds developed heavy parasitemia of both parasites and maintained high levels throughout the experiment (33 days). We found no significant difference between experimental and control birds in both δ(13)C and δ(15)N values of feathers re-grown. The study shows that even heavy primary infections of malaria parasites do not affect feather δ(13)C and δ(15)N isotopic signatures. The results of this experiment demonstrate that feather isotope values of wild-caught birds accurately reflect the dietary isotopic sources at the time of tissue synthesis even when the animal's immune system might be challenged due to parasitic infection. PMID:21671039

  17. Assessment of the effects of cage fish-farming on damselfish-associated food chains using stable-isotope analyses.

    PubMed

    Jan, Rong-Quen; Kao, Shuh-Ji; Dai, Chang-Feng; Ho, Cheng-Tze

    2014-09-15

    To assess the effect of cage fish-farming on the coral reef ecosystem off Xiaoliuchiu Island, southern Taiwan, geographical differences in the food chain of each of two damselfishes, Pomacentrus vaiuli and Chromis margaritifer, were examined using a stable-isotope approach. For each damselfish, individuals were found to consume similar foods at all sites. However, specimens collected at sites near the cage farm (as the experimental sites) exhibited lower δ(13)C and higher δ(15)N signatures compared to those from reference sites. Similar trends also occurred in the zooplankton and detritus, two major food sources for both damselfishes. This finding indicates that particulate organic matter released by the farm may have entered the coral reef ecosystem through the pelagic food chain. Artificial reef emplacement is recommended to provide extra habitats under cage farms to support additional pelagic-feeding fish populations, thereby reducing environmental impacts of cage farming on coral reefs. PMID:25103907

  18. Preparation of 13C and 15N labelled RNAs for heteronuclear multi-dimensional NMR studies.

    PubMed

    Nikonowicz, E P; Sirr, A; Legault, P; Jucker, F M; Baer, L M; Pardi, A

    1992-09-11

    A procedure is described for the efficient preparation of isotopically enriched RNAs of defined sequence. Uniformly labelled nucleotide 5'triphosphates (NTPs) were prepared from E.coli grown on 13C and/or 15N isotopically enriched media. These procedures routinely yield 180 mumoles of labelled NTPs per gram of 13C enriched glucose. The labelled NTPs were then used to synthesize RNA oligomers by in vitro transcription. Several 13C and/or 15N labelled RNAs have been synthesized for the sequence r(GGCGCUUGCGUC). Under conditions of high salt or low salt, this RNA forms either a symmetrical duplex with two U.U base pairs or a hairpin containing a CUUG loop respectively. These procedures were used to synthesize uniformly labelled RNAs and a RNA labelled only on the G and C residues. The ability to generate milligram quantities of isotopically labelled RNAs allows application of multi-dimensional heteronuclear magnetic resonance experiments that enormously simplify the resonance assignment and solution structure determination of RNAs. Examples of several such heteronuclear NMR experiments are shown. PMID:1383927

  19. Towards interpreting nitrate-δ15N records in ice cores in terms of nitrogen oxide sources

    NASA Astrophysics Data System (ADS)

    Hastings, M. G.; Buffen, A. M.

    2011-12-01

    The isotopic composition of nitrate preserved in ice cores offers unique potential for reconstructing past contributions of nitrogen oxides (NOx = NO and NO2) to the atmosphere. Sources of NOx imprint a nitrogen stable isotopic15N) signature, which can be conserved during subsequent oxidation to form nitrate. Major sources of NOx include fossil fuels combustion, biomass burning, microbial processes in soils, and lightning, and thus a quantitative tracer of emissions would help detail connections between the atmosphere, the biosphere, and climate. Unfortunately, the δ15N signatures of most NOx sources are not yet well enough constrained to allow for quantitative partitioning, though new methodology for directly collecting NOx for isotopic analysis is promising (Fibiger and Hastings, A43D-0265, AGU 2010). Still, a growing network of ice core δ15N records may offer insight into source signatures, as different sources are important to different regions of the world. For example, a 300-year ice core record of nitrate-δ15N from Summit, Greenland shows a clear and significant 12% (vs. N2) decrease since the Preindustrial that reflects emissions from fossil fuel combustion and/or soils related to changing agricultural practices in North America and Europe. Over the same time period, Antarctic ice cores show no such trend in δ15N. This would be consistent with previous work suggesting that biomass burning and/or stratospheric intrusion of NOx produced from N2O oxidation are dominant sources for nitrate formation at high southern latitudes. In comparison to the polar records, nitrate in tropical ice cores should represent more significant inputs from lightning, microbial processes in soils, and biomass burning. This may be reflected in new results from a high-elevation site in the Peruvian Andes that shows strong seasonal δ15N cycles of up to 15% (vs. N2). We compare and contrast these records in an effort to evaluate the contribution of NOx sources to nitrate over

  20. Millennial scale oscillations in bulk δ15N and δ13C over the Mid- to Late Holocene seen in proteinaceous corals from the North Pacific Subtropical Gyre

    NASA Astrophysics Data System (ADS)

    Glynn, D. S.; Mccarthy, M. D.; McMahon, K.; Guilderson, T. P.

    2014-12-01

    The North Pacific Subtropical Gyre (NPSG) is the largest continuous ecosystem on this planet and is an important regulator of biogeochemical cycling and carbon sequestration. With evidence of its expansion in a warming climate, it is necessary to develop a more complete understanding of the variability in productivity and nutrient dynamics in this important ecosystem through time. We constructed a long-term, high resolution record of bulk record of stable nitrogen (δ15N) and carbon isotopes (δ13C) from multiple proteinaceous deep sea corals around Hawaii extending back ~5300 years with few gaps. Our data confirms the decreasing trend in δ15N since the Little Ice Age (1850s), which matches previously published results in part attributed to anthropogenic climate change (e.g. Sherwood et al. 2014). However, while the rate of change since the Little Ice Age (δ15N declines ~1‰ over ~150yrs) remains by far the most rapid throughout the longer record, there also appear to be longer-term (near-millennial scale) climatic oscillations of even greater magnitude (δ15N shifts ~1.5-2‰ over ~1000yrs). After removal of the Seuss Effect, δ13C values also declined ~1.5‰ since the Little Ice Age. Furthermore, there also appear to be oscillations in δ13C of ~1-2‰ over millennial timescales. These results reveal the existence of previously unrecognized long-term oscillations in NPSG biogeochemical cycles, which are likely linked to changes in phytoplankton species composition, food web dynamics, and/or variability in source nutrients and productivity possibly caused by changes in climate. This study provides insight into nutrient dynamics in the NPSG over the past five millennia, and offers a historical baseline to better analyze the effects of current anthropogenic climate forcing.

  1. Identification of novel hydrazine metabolites by 15N-NMR.

    PubMed

    Preece, N E; Nicholson, J K; Timbrell, J A

    1991-05-01

    15N-NMR has been used to study the metabolism of hydrazine in rats in vivo. Single doses of [15N2]hydrazine (2.0 mmol/kg: 98.6% g atom) were administered to rats and urine collected for 24 hr over ice. A number of metabolites were detected by 15N-NMR analysis of lyophilized urine. Ammonia was detected as a singlet at 0 ppm and unchanged [15N2]hydrazine was present in the urine detectable as a singlet at 32 ppm. Peaks were observed at 107 and 110 ppm which were identified as being due to the hydrazido nitrogen of acetylhydrazine and diacetylhydrazine, respectively. A resonance at 85 ppm was ascribed to carbazic acid, resulting from reaction of hydrazine with carbon dioxide. A singlet detected at 316 ppm was thought to be due to the hydrazono nitrogen of the pyruvate hydrazone. The resonance at 56 ppm was assigned to 15N-enriched urea, this together with the presence of ammonia indicates that the N-N bond of hydrazine is cleaved in vivo, possibly by N-oxidation, and the resultant ammonia is incorporated into urea. A doublet centred at 150 ppm and a singlet at 294 ppm were assigned to a metabolite which results from cyclization of the 2-oxoglutarate hydrazone. Therefore 15N-NMR spectroscopic analysis of urine has yielded significant new information on the metabolism of hydrazine. PMID:2018564

  2. Long-term 15N tracking from biological N fixation across different plant and humus components of the boreal forest

    NASA Astrophysics Data System (ADS)

    Arroniz-Crespo, Maria; Jones, David L.; Zackrisson, Olle; Nilsson, Marie-Charlotte; DeLuca, Thomas H.

    2014-05-01

    Biological N2 fixation by cyanobacteria associated with feather mosses is an important cog in the nitrogen (N) cycle of boreal forests; still, our understanding of the turnover and fate of N fixed by this association remains greatly incomplete. The 15N signature of plants and soil serves as a powerful tool to explore N dynamics in forest ecosystems. In particular, in the present study we aimed to investigate the contribution of N2 fixation to δ15N signatures of plants and humus component of the boreal forest. Here we present results from a long-term (7 years) tacking of labelled 15N2 across the humus layer, seedlings of the tree species Pinus sylvestris, two common dwarf shrub species (Empetrum hermaphroditum and Vaccinium vitis-idaea) and the feather moss Pleurozium schreibery. The enriched experiment was conducted in 2005 in a natural boreal forest in northern Sweden. Two different treatments (10% 15N2 headspace enrichment and control) were setup in nine different plots (0.5 x 0.5 m) within the forest. We observed a significant reduction of δ15N signature of the 15N-enriched moss that could be explained by a growth dilution effect. Nevertheless, after 5 years since 15N2 enrichment some of the label 15N was still detected on the moss and in particular in the dead tissue. We could not detect a clear transfer of the labelled 15N2 from the moss-cyanobacteria system to other components of the ecosystem. However, we found consistence relationship through time between increments of δ15N signature of some of the forest components in plots which exhibited higher N fixation rates in the moss. In particular, changes in natural abundance δ15N that could be associated with N fixation were more apparent in the humus layer, the dwarf shrub Vaccinium vitis-idaea and the pine seedlings when comparing across plots and years.

  3. Identifying vital effects in Halimeda algae with Ca isotopes

    NASA Astrophysics Data System (ADS)

    Blättler, C. L.; Stanley, S. M.; Henderson, G. M.; Jenkyns, H. C.

    2014-12-01

    Geochemical records of biogenic carbonates provide some of the most valuable records of the geological past, but are often difficult to interpret without a mechanistic understanding of growth processes. In this experimental study, Halimeda algae are used as a test organism to untangle some of the specific factors that influence their skeletal composition, in particular their Ca-isotope composition. Algae were stimulated to precipitate both calcite and aragonite by growth in artificial Cretaceous seawater, resulting in experimental samples with somewhat malformed skeletons. The Ca-isotope fractionation of the algal calcite (-0.6‰) appears to be much smaller than that for the algal aragonite (-1.4‰), similar to the behaviour observed in inorganic precipitates. However, the carbonate from Halimeda has higher Ca-isotope ratios than inorganic forms by approximately 0.25‰, likely because of Rayleigh distillation within the algal intercellular space. In identifying specific vital effects and the magnitude of their influence on Ca-isotope ratios, this study suggests that mineralogy has a first-order control on the marine Ca-isotope cycle.

  4. Seasonal variation in stable carbon and nitrogen isotope values of bats reflect environmental baselines.

    PubMed

    Popa-Lisseanu, Ana G; Kramer-Schadt, Stephanie; Quetglas, Juan; Delgado-Huertas, Antonio; Kelm, Detlev H; Ibáñez, Carlos

    2015-01-01

    The stable carbon and nitrogen isotope composition of animal tissues is commonly used to trace wildlife diets and analyze food chains. Changes in an animal's isotopic values over time are generally assumed to indicate diet shifts or, less frequently, physiological changes. Although plant isotopic values are known to correlate with climatic seasonality, only a few studies restricted to aquatic environments have investigated whether temporal isotopic variation in consumers may also reflect environmental baselines through trophic propagation. We modeled the monthly variation in carbon and nitrogen isotope values in whole blood of four insectivorous bat species occupying different foraging niches in southern Spain. We found a common pattern of isotopic variation independent of feeding habits, with an overall change as large as or larger than one trophic step. Physiological changes related to reproduction or to fat deposition prior to hibernation had no effect on isotopic variation, but juvenile bats had higher δ13C and δ15N values than adults. Aridity was the factor that best explained isotopic variation: bat blood became enriched in both 13C and 15N after hotter and/or drier periods. Our study is the first to show that consumers in terrestrial ecosystems reflect seasonal environmental dynamics in their isotope values. We highlight the danger of misinterpreting stable isotope data when not accounting for seasonal isotopic baselines in food web studies. Understanding how environmental seasonality is integrated in animals' isotope values will be crucial for developing reliable methods to use stable isotopes as dietary tracers. PMID:25700080

  5. δ 13C and δ 15N biogeographic trends in rocky intertidal communities along the coast of South Africa: Evidence of strong environmental signatures

    NASA Astrophysics Data System (ADS)

    Hill, Jaclyn M.; McQuaid, Christopher D.

    2008-11-01

    Ecosystem dynamics driven by top-down controls have been well documented in rocky intertidal communities, while the effects of bottom-up influences are comparatively poorly understood. We hypothesized that large-scale signatures of the physical environment may be identifiable along the South African coastline as it is subject to two very different current systems (Benguela and Agulhas Currents) that profoundly influence primary production and thus both food type and availability. Through stable isotope analysis, we examined biogeographic patterns in multiple trophic levels at four sites along a 1400-km stretch of South African coastline and investigated the dietary role of macroalgal-derived organic carbon in rocky intertidal communities. The general positioning of trophic groups was comparable across all sites, with animals from the same trophic levels grouping together and with a δ 15N fractionation of 1-2‰ between levels. The species found at all sites demonstrated east-west δ 15N enrichment, presumably reflecting a biogeographic shift in nitrogen sources linked to upwelling on the west coast. Filter-feeders gave particularly clear results. Using discriminant analysis, mussels could be categorized into four geographic groups based on carbon and nitrogen signatures: east coast, southeast coast, south-west coast and west coast. Barnacles and polychaetes showed similar geographic groupings to mussels, but with shifts in actual values (1‰ depletion in δ 13C and 3‰ enrichment in δ 15N relative to mussels). This suggests that fractionation varies between species within a trophic level. IsoSource models showed that Ulva sp. made large contributions to the diets of two microalgal grazers ( Siphonaria capensis and Scutellastra granularis) and this dietary dependence increased when moving from west to east coast, along the shoreline. Additionally, IsoSource models determined that relative to phytoplankton, macroalgae accounted for upwards of 60% of suspended