Knowledge Base

Goal: Dairy cows undergo significant metabolic and endocrine changes during the transition from pregnancy to lactation, and impaired insulin action influences nutrient partitioning toward the fetus and the mammary gland. Because impaired insulin action during transition is thought to be related to elevated body condition and body fat mobilization, we hypothesized that over-conditioned cows with excessive body fat mobilization around calving may have impaired insulin metabolism compared with cows with low fat mobilization.

Goal: This study compares concentrations and isotopic compositions of CH4 sampled from domestic groundwater wells in Letcher County, Eastern Kentucky in order to characterize its occurrence and origins in relation to both neighboring hydraulically fractured natural gas wells and surface coal mines. The studied groundwater showed concentrations of CH4 ranging from 0.05 mg/L to 10 mg/L, thus, no immediate remediation is required. The δ13C values of CH4 ranged from −66‰ to −16‰, and δ2H values ranged from −286‰ to −86‰, suggesting an immature thermogenic and mixed biogenic/thermogenic origin. The occurrence of CH4 was not correlated with proximity to hydraulically fractured natural gas wells. Generally, CH4 occurrence corresponded with groundwater abundant in Na+, Cl−, and HCO3−, and with low concentrations of SO42−.

Goal: The production of a sparkling wine can be performed with different methods taking from a few weeks to several years, which often justifies a difference in added value for the consumer. This paper presents the use of isotope ratio δ(13)C measurements combined with physico-chemical analyses for the determination of mislabelling of sparkling wines produced by 'ancestral', 'traditional', 'closed tank' or 'gasification' methods. This work shows that the isotope composition of CO2 compared with that of the corresponding dried residue of wine (DRW) can assess whether carbonate CO2 in a sparkling wine originates from alcohol fermentation or from artificial gas addition. Isotopic ratios expressed as δ(13)CCO2 and δ(13)CDRW measurements have been obtained for each wine by Gas Bench isotopic ratio mass spectroscopy and cavity ring down infrared spectroscopy, respectively. When the difference between δ(13)CCO2 and δ(13)CDRW is negative, the presence of artificial CO2 can be undoubtedly inferred, which would exclude the production methods 'ancestral' or 'traditional' for instance. Other parameters such as alcohol content, sugar and acid distributions are also important to complete the analytical panel to aid fraud tracking.

Goal: In the southern California Bight (SCB), there has been a longstanding hypothesis that anthropogenic nutrient loading is insignificant compared to the nutrient loading from upwelling. However, recent studies have demonstrated that, in the nearshore environment, nitrogen (N) flux from wastewater effluent is equivalent to the N flux from upwelling. The isotopic composition of suspended particulate organic matter (POM) recorded low δ15NPN and δ13CPN values around the outfall under normal operations suggesting the incorporation of “nitrified” NO3− and wastewater dissolved organic carbon into POM. Our results demonstrate the critical role of nitrification in nitrogen cycling in the nearshore environment of urban oceans

Goal: Results presented here, based on techniques of multilabeled water isotope probing and measurement of 18O/16O ratios in PO4 moieties of intracellular biomolecules, which allows direct sampling of intracellular environments, demonstrate a significant metabolic water component in intracellular water that is consistent across multiple strains of bacteria when grown under similar conditions. The intracellular water probe presented here, based on PO4 δ18O in DNA/biomass, may be extended to other biomolecules and organisms.

Goal: Oil sands tailings ponds in northern Alberta, Canada have been producing biogenic gases via microbial metabolism of hydrocarbons for decades. Persistent methanogenic activity in tailings ponds without any known replenishment of nutrients such as fixed nitrogen (N) persuaded us to investigate whether N2 fixation or polyacrylamide (PAM; used as a tailings flocculant) could serve as N sources. Cultures comprising mature fine tailings (MFT) plus methanogenic medium supplemented with or deficient in fixed N were incubated under an N2 headspace.

Goal: Nitrous oxide (N2O) is an important greenhouse gas produced in soil and aquatic ecosystems. Its warming potential is 296 times higher than that of CO2. Most N2O emission measurements made so far are limited in temporal and spatial resolution causing uncertainties in the global N2O budget. Recent advances in laser spectroscopic techniques provide an excellent tool for area-integrated, direct and continuous field measurements of N2O fluxes using the eddy covariance method. By employing this technique on an agricultural site with four laser-based analysers, we show here that N2O exchange exhibits contrasting diurnal behaviour depending upon soil nitrogen availability. When soil N was high due to fertilizer application, N2O emissions were higher during daytime than during the night. However, when soil N became limited, emissions were higher during the night than during the day. These reverse diurnal patterns supported by isotopic analyses may indicate a dominant role of plants on microbial processes associated with N2O exchange. This study highlights the potential of new technologies in improving estimates of global N2O sources.

Goal: It is now recognized that variations in the Δ17O of terrestrial materials resulting from purely mass dependent fractionations, though small, have geological significance. In this study, the δ18O and δ17O values of selected low temperature quartz and silica samples were measured in order to derive the quartz-water fractionation–temperature relationship for the three oxygen isotope system. A 18O/16O quartz-water fractionation equation valid for all temperatures was generated from published high temperature exchange experiments and ...

Goal: In forests of the humid subtropics of China, chronically elevated nitrogen (N) deposition, predominantly as ammonium (NH4+), causes significant nitrate (NO3−) leaching from well-drained acid forest soils on hill slopes (HS), whereas significant retention of NO3− occurs in near-stream environments (groundwater discharge zones, GDZ). To aid our understanding of N transformations on the catchment level, we studied spatial and temporal variabilities of concentration and natural abundance (δ15N and δ18O) of nitrate (NO3−) in soil pore water along a hydrological continuum in the N-saturated Tieshanping (TSP) catchment, southwest China. Our data show that effective removal of atmogenic NH4+ and production of NO3− in soils on HS were associated with a significant decrease in δ15N-NO3−, suggesting efficient nitrification despite low soil pH.

Goal: An “on-line” mixing system has been developed and evaluated for continuous oxygen isotope exchange between gas-phase CO2 and liquid water. The system is composed of three basic parts: equipment and materials used to introduce water and gas into a mixing reservoir, the mixing and exchange reservoir, and a vessel used to separate gas and water phases exiting the system. A series of experiments were performed to monitor the isotope exchange process over a range of temperatures (5–40 °C) and CO2 partial pressures (202–15,200 Pa).

Goal: Nitric oxide (NO) controls the atmosphere’s oxidative capacity. In soils, NO emissions are thought to be controlled by a tradeoff that develops in response to changes in soil moisture: dry soils limit substrate diffusion, whereas wet soils limit gas diffusivity, such that moist soils favor NO emissions. In drylands, however, NO emissions can be highest when soils are dry and immediately following rewetting. Aridity and vegetation interact to generate unexpected NO emission patterns. The shutdown in plant N uptake during the dry season causes NO emissions to increase, whereas arid conditions concentrate resources in dry soils, stimulating NO pulses upon rewetting. Chemistry governs the rapid initial NO pulse, whereas biological processes control later emissions as microbes recover from drought stress.

Goal: The stable carbon isotopic composition of dissolved organic matter (δ13C-DOC) reveals information about its source and extent of biological processing. Here we report the lowest δ13C-DOC values (−43.8‰) measured to date in surface waters. The streams were located in the High Arctic, a region currently experiencing rapid changes in climate and carbon cycling. Based on the widespread occurrence of methane cycling in permafrost regions and the detection of the pmoA gene, a proxy for aerobic methanotrophs, we conclude that the low δ13C-DOC values are due to organic matter partially derived from methanotrophs consuming biologically produced, 13C-depleted methane. These findings demonstrate the significant impact that biological activity has on the stream water chemistry exported from permafrost and glaciated environments. ..., occurrences of low δ13C-DOC values may be more widespread than previously recognized, with implications for understanding C cycling in these environments.

Goal: In order to better understand the chlorine and bromine stable isotope fractionation that occurs when chloride and bromide salts precipitate from their saturated solutions, we determined experimentally the equilibrium fractionation factors between precipitating pure salt minerals and their coexisting saturated brine at 22 °C. Fractionation factors (expressed as 103lnα(37Cl/35Cl)salt-brine and 103lnα81Br/79Brsalt-brine) obtained for 11 chloride and 7 bromide salts of geological and industrial interest show a relatively largerange of variation (from − 0.31 to + 0.41), with the salt that precipitates having either a lower or a higher isotope ratio than the brine from which they precipitate. A negative fractionation factor indicates that the brine has a larger isotope ratio than the precipitate, a positive factor that the precipitate has a larger isotope ratio.In these measurements the uncertainty is defined as the 1σ standard deviation of replicate determinations.

Goal: Examining how species use and partition resources within an environment can lead to a better understanding of community assembly and diversity. The rich early Late Miocene (early Vallesian) deposits at Rudabánya II (R. II) in northern central Hungary preserve an abundance of forest dwelling taxa, including the hominoid Rudapithecus hungaricus. Here we use the carbon and oxygen stable isotope compositions of tooth enamel carbonate from 10 genera of medium to large-bodied mammals to evaluate resource use and partitioning among the herbivore community, and to reconstruct the paleoenvironment of Rudapithecus. The range of stable carbon and oxygen isotope values (δ13C and δ18O) displayed by the R. II fauna indicates a variable forest environment, which included both open and closed canopy habitats. The relatively low δ13C and δ18O values found in all sampled taxa are consistent with high levels of precipitation and humidity.