Isotope Fractionation Analysis Research Articles

How important are mangroves as a carbon source for decapod crustacean larvae in a tropical estuary?

In order to evaluate the importance of mangrove leaf detritus as a food source for deca- pod crustacean larvae, stable isotopes (δ 13 C and δ 15 N) were measured in the tissue of these larvae and other selected organisms. Decapod crustacean larvae and planktonic adult decapods, Lucifer faxoni and Acetes americanus, were sampled in the Itamaraca estuarine system, Brazil. For comparison with stable isotope values in the estuary, plankton and POM samples were also taken on the adjacent con- tinental shelf. In the Itamaraca estuarine system, δ 13 C of decapod larvae and the holoplanktonic decapods L. faxoni and A. americanus ranged from about -17 to -23‰ (mean: -19.8 ± 1.5‰). This indicates that the contribution of mangrove carbon (δ 13 C: -26.8‰) to larval nutrition was generally negligible. Among decapod larvae, porcellanid zoeae showed relatively low δ 13 C values, while penaeid shrimp postlarvae showed the highest δ 13 C. Porcellanid zoeae were thus the only decapod larvae with a considerable percentage (13 to 40%) of mangrove carbon in their tissue. However, these low values may also be due to a negative isotope shift that occurs during embryogenesis. Feed- ing experiments with zoeae of Petrolisthes armatus (Anomura: Porcellanidae) and Sesarma rectum (Brachyura: Grapsidae) showed assimilatory shifts of up to 1.0 ± 0.2‰ for 13 C and up to 1.4 ± 0.6‰ for 15 N. Analysis of embryonic isotope fractionation for 5 decapod crustacean species, P. armatus, S. rectum, Aratus pisonii, Uca thayeri, and U. maracoani, showed that larval tissue was 13 C-depleted by up to 3.8‰ and 15 N-depleted by up to 2.3‰ in relation to parental tissue.

Model analysis of oxygen isotope fractionation in humans due to disturbances of pulmonary gas exchange.

The lighter isotopic oxygen molecule 1602 passes through the human oxygen transport system with an approximately 0.8% higher rate than its heavier isotopic species 160180, leading to an overall fractionation effect which has recently been quantified (Schuster and Pflug, 1989). This effect has been measured in healthy persons at rest and during ergometer work (Schuster et al., 1994), situations of hyper-and hypoventilation have been studied (Heller et al., 1993), and patients suffering from anemia (Heller et al., 1994) or lung fibrosis have been investigated (Heller et al., this volume). All these situations affected the overall fractionation effect due to changes of processes of the oxygen transport system. Therefore it is supposed that this parameter and its change contains characteristic information with respect to the pattern of oxygen transport pathways and its variations. To understand the sources of the fractionation effects and their nature, model investigations are necessary. This study models changes of pulmonary gas exchange disturbances with respect to their influence on the overall fractionation effect so as to interpret experimental data.

Methanogenic Bacteria from the Bondyuzhskoe Oil Field: General Characterization and Analysis of Stable-Carbon Isotopic Fractionation

Selective enrichment culture techniques were employed to obtain mixed cultures of methanogenic rods and sarcina from surface flooding waters and deep subsurface ( approximately 1650 m) oil-bearing sedimentary rocks and formation waters sampled from an old oil field in the U.S.S.R. previously reported to display active biological methanogenesis. The methanogens were selectively isolated as colonies on agar petri dishes that were incubated in a novel container. The general cellular and growth features of three Methanobacterium isolates were determined. These strains grew optimally at 37 to 45 degrees C in anaerobic pressure tube cultures with a doubling time of 16 to 18 h on H(2)-CO(2) and proliferated as autotrophs. Acetate addition significantly enhanced the final cell yield. Growth of these strains was completely inhibited by either 0.6 g of sodium sulfide per liter or 31.0 of sodium chloride per liter, but growth was not inhibited by either 0.3 g of sodium sulfide per liter or 1.0 g of sodium sulfate per liter. One novel isolate, Methanobacterium sp. strain ivanov, was grown on H(2)-CO(2), and the stable-carbon isotopic fractionations that occurred during synthesis of methane, cell carbon, and lipids were determined. The results of this study were used to examine the anomalous relationship between the isotopic and chemical compositions of natural gas occurring in the deep subsurface environment of the oil field.