Deliberate Tracer Experiments Research Articles

Compound-specific stable isotope analysis of nitrogen-containing intact polar lipids.

Compound-specific isotope analysis (CSIA) of nitrogen in amino acids has proven a valuable tool in many fields (e.g. ecology). Several intact polar lipids (IPLs) also contain nitrogen, and their nitrogen isotope ratios have the potential to elucidate food-web interactions or metabolic pathways. Here we have developed novel methodology for the determination of δ(15)N values of nitrogen-containing headgroups of IPLs using gas chromatography coupled with isotope-ratio mass spectrometry. Intact polar lipids with nitrogen-containing headgroups were hydrolyzed and the resulting compounds were derivatized by (1) acetylation with pivaloyl chloride for compounds with amine and hydroxyl groups or (2) esterification using acidified 2-propanol followed by acetylation with pivaloyl chloride for compounds with both carboxyl and amine groups. The δ(15)N values of the derivatives were subsequently determined using gas chromatography/combustion/isotope-ratio mass spectrometry. Intact polar lipids with ethanolamine and amino acid headgroups, such as phosphatidylethanolamine and phosphatidylserine, were successfully released from the IPLs and derivatized. Using commercially available pure compounds it was established that δ(15)N values of ethanolamine and glycine were not statistically different from the offline-determined values. Application of the technique to microbial cultures and a microbial mat showed that the method works well for the release and derivatization of the headgroup of phosphatidylethanolamine, a common IPL in bacteria. A method to enable CSIA of nitrogen of selected IPLs has been developed. The method is suitable for measuring natural stable nitrogen isotope ratios in microbial lipids, in particular phosphatidylethanolamine, and will be especially useful for tracing the fate of nitrogen in deliberate tracer experiments.

Investigation of Groundwater Flow Variations near a Recharge Pond with Repeat Deliberate Tracer Experiments

Determining hydraulic connections and travel times between recharge facilities and production wells has become increasingly important for permitting and operating managed aquifer recharge (MAR) sites, a water supply strategy that transfers surface water into aquifers for storage and later extraction. This knowledge is critical for examining water quality changes and assessing the potential for future contamination. Deliberate tracer experiments are the best method for determining travel times and identifying preferential flow paths between recharge sites over the time scales of weeks to a few years. This paper compares the results of two deliberate tracer experiments at Kraemer Basin, Orange County, CA, USA. Results from the first experiment, which was conducted in October 1998, showed that a region of highly transmissive sedimentary material extends down gradient from the basin for more than 3 km [1]. Mean groundwater velocities were determined to be approximately 2 km/year in this region based on the arrival time of the tracer center of mass. A second experiment was initiated in January 2008 to determine if travel times from this basin to monitoring and production wells changed during the past decade in response to new recharge conditions. Results indicate that flow near Kraemer Basin was stable, and travel times to most wells determined during both experiments agree within the experimental uncertainty.

Molecular and isotopic composition of foraminiferal organic linings

Fossil remnants of benthic foraminifera consist of carbonate tests and their organic linings. The macromolecular and stable isotopic composition of these benthic foraminiferal organic linings was characterized to evaluate their potential use as paleoclimate proxies. Using Curie point pyrolysis–GC–MS (Py–GC–MS) we show that benthic foraminiferal organic linings consist of protein and polysaccharides, bound together in a complex macromolecular structure. Both chitin derivatives and traces of guaiacols and syringols, usually assigned to lignin are found. Although the five species of benthic foraminifera all contain chitin derivatives and proteins, the relative contribution of these compounds tends to vary considerably. Oxygen stable isotopic analyses of the organic linings of the benthic foraminiferal species Ammonia tepida indicates that ∂18OOL values are in line with fractionation between seawater and organic matter. In contrast a ∂13C deliberate tracer experiment showed that metabolic carbon is the main source for the carbon fixed in the organic lining. The different pathways of carbon and oxygen stable isotopes into the foraminiferal linings have important implications for future proxy development as they reflect different components of the environment compared to the carbonate bound stable isotopes. Still, the future application of benthic foraminiferal organic linings and their isotopic values critically relies on improvements in calibration and sample size required for isotopic analyses.

Evaluating Travel Times Beneath an Artificial Recharge Pond Using Sulfur Hexafluoride

Research Article| April 01, 2005 Evaluating Travel Times Beneath an Artificial Recharge Pond Using Sulfur Hexafluoride DROR AVISAR; DROR AVISAR 1Department of Geological Sciences, University of California, Santa Barbara, CA 93106 Search for other works by this author on: GSW Google Scholar JORDAN F. CLARK JORDAN F. CLARK 1Department of Geological Sciences, University of California, Santa Barbara, CA 93106 Search for other works by this author on: GSW Google Scholar Author and Article Information DROR AVISAR 1Department of Geological Sciences, University of California, Santa Barbara, CA 93106 JORDAN F. CLARK 1Department of Geological Sciences, University of California, Santa Barbara, CA 93106 Publisher: Association of Environmental & Engineering Geologists First Online: 09 Mar 2017 Online ISSN: 1558-9161 Print ISSN: 1078-7275 © 2005 Association of Engineering Geologists Environmental & Engineering Geoscience (2005) 11 (4): 309–317. https://doi.org/10.2113/11.4.309 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation DROR AVISAR, JORDAN F. CLARK; Evaluating Travel Times Beneath an Artificial Recharge Pond Using Sulfur Hexafluoride. Environmental & Engineering Geoscience 2005;; 11 (4): 309–317. doi: https://doi.org/10.2113/11.4.309 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEnvironmental & Engineering Geoscience Search Advanced Search Abstract Draft rules for artificial recharge operations, which use recycled waste water as a source water, require minimum travel times to production wells in California. Deliberate tracer experiments are the accepted method for determining travel times. An example of a tracer experiment using sulfur hexafluoride is discussed at an artificial recharge site located within a regional water table depression. The study shows the complexity in interpreting travel times because of the influence of recharge rates and water production. It also demonstrates the effectiveness of recovering recharged water at spreading basins surrounded by production wells. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Possible errors in CO2air-sea transfer velocity from deliberate tracer releases and eddy covariance measurements due to near-surface concentration gradients

[1] The air-sea transfer velocity of CO2, kCO2, from a deliberate tracer experiment (DTE) and from eddy covariance measurements (ECM) during ASGAMAGE differed on average by a factor of ∼2.5, in spite of the fact that both methods were applied with maximum care. In an attempt to explain this difference, implicit assumptions were investigated critically using complementary one-dimensional (1-D) and 2-D models for the upper oceanic boundary layer and atmospheric surface layer. Simulations of a DTE and ECM facilitate examination of the possible impact of near-surface vertical gradients, horizontal inhomogeneity, and instationarity of the tracer concentration on the results from field experiments. The simulations suggest that vertical tracer concentration gradients due to physical processes might occur outside the diffusive boundary and that these might have escaped prior observation due to their confinement to the upper meter of the water column. Such gradients could then cause DTE to typically underestimate kCO2 by 10–25%, depending on ambient conditions, such as light penetration. Buffering of the seawater CO2 system renders ECM much less sensitive to near-surface gradients. However, inhomogeneity of the CO2 concentration in water might cause scatter in ECM due to inhomogeneity-related flux divergence in air. Additionally, in the case of instationarity a complex and strongly varying fine structure of vertical CO2 concentration profiles in water could cause inconsistencies with CO2 flux observations in air. Both mechanisms might explain several tens of percents of the scatter in the ECM, while systematic effects are ∼10%.

In situ evaluation of air‐sea gas exchange parameterizations using novel conservative and volatile tracers

Measurements of air‐sea gas exchange rates are reported from two deliberate tracer experiments in the southern North Sea during February 1992 and 1993. A conservative tracer, spores of the bacterium Bacillus globigii var. Niger, was used for the first time in an in situ air‐sea gas exchange experiment. This nonvolatile tracer is used to correct for dispersive dilution of the volatile tracers and allows three estimations of the transfer velocity for the same time period. The first estimation of the power dependence of gas transfer on molecular diffusivity in the marine environment is reported. This allows the impact of bubbles on estimates of the transfer velocity derived from changes in the helium/sulphur hexafluoride ratio to be assessed. Data from earlier dual tracer experiments are reinterpreted, and findings suggest that results from all dual tracer experiments are mutually consistent. The complete data set is used to test published parameterizations of gas transfer with wind speed. A gas ex‐ change relationship that shows a dependence on wind speed intermediate between those ofLiss and Merlivat [1986] and Wanninkhof [1992] is found to be optimal. The dual tracer data are shown to be reasonably consistent with global estimates of gas exchange based on the uptake of natural and bomb‐derived radiocarbon. The degree of scatter in the data when plotted against wind speed suggests that parameters not scaling with wind speed are also influencing gas exchange rates.

Evaluation of perfluoromethyldecalin as a deliberate tracer for the study of water mixing processes

A deliberate tracer experiment has been carried out in an enclosed lagoon in a coastal area. The tracer used was a perfluorocarbon, perfluoro- l-methyldecalin (PMD), analysed using liquid-liquid extraction and electron capture gas chromatography. The results show good recovery of the tracer, indicating that adsorption and volatilization did not occur to an appreciable extent over the short time period of the experiment. A mathematical model, PHOENICS, developed for simulation of flow systems, was used to simulate the experiment.

A deliberate tracer experiment in Santa Monica Basin

The mixing of heat and chemical constituents across density strata in the ocean plays a major role in ocean circulation and in the response of the climate to thermal and chemical perturbations. We are developing a tracer technique which, in conjunction with fluid dynamical measurements, promises to improve our understanding and our estimates of such diapycnal mixing. In a prototype tracer experiment in Santa Monica Basin, 50km west of Los Angeles, two tracers, sulphur hexafluoride (SF6) and per-fluorodecalin (PFD), have been injected on an isopycnal surface near the centre of the basin. After 50 days, the tracers had mixed along the isopycnal surface to nearly every part of the basin, although relatively little had penetrated to the basin walls. The diapycnal spreading of the tracer distributions during this first stage of the experiment yielded an apparent eddy diffusivity of 0.33±0.08 cm2s−1 at the ambient density gradient of 4.0±0.5×10−9g cm−4.