Denitrification of anthropogenic nitrogen in groundwater : measurement and modeling using stable isotopic and mass balance approaches

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2001.Includes bibliographical references.Denitrification is a microaerophilic, microbially-mediated process, by which nitrate is reduced to biologically-unavailable N2 gas; the reaction is generally coupled to the oxidation of organic carbon. We hypothesized that denitrification rates in groundwater in the Waquoit Bay watershed on Cape Cod, USA, were controlled by both nitrate and dissolved organic carbon (DOC) concentrations, and that groundwater DOC concentrations were inversely related to the thickness of the vadose (unsaturated) zone through which recharge occurred. We found that the deeper the vadose zone, the lower the concentration of DOC in groundwater near the water table; similarly, DOC concentrations decreased with increasing depth below the water table, suggesting quite active biogeochemical processing in these boundary environments. We used stable isotope and mass balance approaches to estimate denitrification rates in groundwater at two forested field sites and in a septic system plume. These sites provided a large range of groundwater nitrate and dissolved organic carbon (DOC) concentrations. At all sites, denitrification rates increased with increasing nitrate concentration. First order denitrification rate constants with respect to nitrate were highest where groundwater DOC concentrations were highest: k = 2.8 y-1 in the septic plume (~ 26 mf C 1-1), k = 1.6 y-1 at South Cape Beach (DOC = 0.8 to 23.4 mg C-1), and k = 0.25 y-1 at Crane Wildlife (0.1 to 1.9 mg C 1-), suggesting that, independent of nitrate, DOC concentrations exert significant control on denitrification rates. A simulation of N losses along groundwater flowpaths suggests that a saturating kinetics expression with respect to both nitrate and DOC best predicts nitrate concentrations measured at downgradient well ports (R2 = 0.96 for [NO3]model vs. [NC 3 imeas). In contrast, a saturating kinetics expression with respect to nitrate only, often overpredicts nitrate losses along groundwater flowpaths, particularly where DOC concentration are low, further confirming that DOC concentrations are an important control on groundwater denitrification rates. The magnitude of a nitrate source, its travel distance to shore, and the DOC concentration in groundwater are useful predictors of N downgradient. These relationships can help in designing strategies to control anthropogenic nitrogen loading.by Wendy Jeanne Pabich.Ph.D

X-rays and Gamma-rays from Cataclysmic Variables: The example case of Intermediate Polar V1223 Sgr

The accretion of matter onto intermediate polar White Dwarfs (IPWDs) seems to provide attractive conditions for acceleration of particles to high energies in a strongly magnetized turbulent region at the accretion disk inner radius. We consider possible acceleration of electrons and hadrons in such region and investigate their high energy radiation processes. It is concluded that accelerated electrons loose energy mainly on synchrotron process producing non-thermal X-ray emission. On the other hand, accelerated hadrons are convected onto the WD surface and interact with dense matter. As a result, high energy $\gamma$-rays from decay of neutral pions and secondary leptons from decay of charged pions appear. We show that GeV-TeV $\gamma$-rays can escape from the vicinity of the WD. Secondary leptons produce synchrotron radiation in the hard X-rays and soft $\gamma$-rays. As an example, we predict the X-ray and $\gamma$-ray emission from IPWD V1223 Sgr. Depending on the spectral index of injected particles, this high energy emission may be detected by the ${\it Fermi}$-LAT telescope and/or the future Cherenkov Telescope Array (CTA) observatory.Comment: 16 pages, 1 figure, accepted to MNRA

Optical depths for gamma-rays in the radiation field of a star heated by external X-ray source in LMXBs: Application to Her X-1 and Sco X-1

The surface of a low mass star inside a compact low mass X-ray binary system (LMXB) can be heated by the external X-ray source which may appear due to the accretion process onto a companion compact object (a neutron star or a black hole). As a result, the surface temperature of the star can become significantly higher than it is in the normal state resulting from thermonuclear burning. We wonder whether high energy electrons and gamma-rays, injected within the binary system, can efficiently interact with this enhanced radiation field. To decide this, we calculate the optical depths for the gamma-ray photons in the radiation field of such irradiated star as a function of the phase of the binary system. Based on these calculations, we conclude that compact low mass X-ray binary systems may also become sources of high energy gamma-rays since conditions for interaction of electrons and gamma-rays are quite similar to these ones observed within the high mass TeV gamma-ray binaries such as LS 5039 and LSI 303 +61. However, due to differences in the soft radiation field, the expected gamma-ray light curves can significantly differ between low mass and high mass X-ray binaries. As an example, we apply such calculations to two well known LMXBs: Her X-1 and Sco X-1. It is concluded that electrons accelerated to high energies inside these binaries should find enough soft photon target from the companion star for efficient gamma-ray production.Comment: 10 pages, 8 figures, accepted to A&

Effects of watershed land use on nitrogen concentrations and δ15 Nitrogen in groundwater

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Biogeochemistry 77 (2006): 199-215, doi:10.1007/s10533-005-1036-2.Eutrophication is a major agent of change affecting freshwater, estuarine, and marine systems. It is largely driven by transportation of nitrogen from natural and anthropogenic sources. Research is needed to quantify this nitrogen delivery and to link the delivery to specific land-derived sources. In this study we measured nitrogen concentrations and δ15N values in seepage water entering three freshwater ponds and six estuaries on Cape Cod, Massachusetts and assessed how they varied with different types of land use. Nitrate concentrations and δ15N values in groundwater reflected land use in developed and pristine watersheds. In particular, watersheds with larger populations delivered larger nitrate loads with higher δ15N values to receiving waters. The enriched δ15N values confirmed nitrogen loading model results identifying wastewater contributions from septic tanks as the major N source. Furthermore, it was apparent that N coastal sources had a relatively larger impact on the N loads and isotopic signatures than did inland N sources further upstream in the watersheds. This finding suggests that management priorities could focus on coastal sources as a first course of action. This would require management constraints on a much smaller population.This work was supported by funds from the Woods Hole Oceanographic Institution Sea Grant Program, from the Cooperative Institute for Coastal and Estuarine Environmental Technology, from Massachusetts Department of Environmental Protection to Applied Science Associates, Narragansett, RI, as well as from Palmer/McLeod and NOAA National Estuarine Research Reserve Fellowships to Kevin Kroeger. This work is the result of research sponsored by NOAA National Sea Grant College Program Office, Department of Commerce, under Grant No. NA86RG0075, Woods Hole Oceanographic Institution Sea Grant Project No. R/M-40

The Lactobacillus flora in vagina and rectum of fertile and postmenopausal healthy Swedish women

<p>Abstract</p> <p>Background</p> <p><it>Lactobacillus </it>species are the most often found inhabitants of vaginal ecosystem of fertile women. In postmenopausal women with low oestrogen levels, <it>Lactobacillus </it>flora is diminishing or absent. However, no studies have been performed to investigate the correlation between oestrogen levels and the lactobacilli in the gut. The aim of the present study was to investigate the relation in healthy women between vaginal and rectal microbial flora as well as possible variations with hormone levels.</p> <p>Methods</p> <p>Vaginal and rectal smears were taken from 20 healthy fertile women, average 40 years (range 28-49 years), in two different phases of the menstrual cycle, and from 20 postmenopausal women, average 60 years (range 52-85 years). Serum sex hormone levels were analyzed. Bacteria from the smears isolated on Rogosa Agar were grouped by Randomly Amplified Polymorphic DNA and identified by multiplex PCR and partial 16S rRNA gene sequencing.</p> <p>Results</p> <p><it>Lactobacillus crispatus </it>was more often found in the vaginal flora of fertile women than in that of postmenopausal (p = 0.036). Fifteen of 20 fertile women had lactobacilli in their rectal smears compared to 10 postmenopausal women (p = 0.071). There was no correlation between the number of bacteria in vagina and rectum, or between the number of bacteria and hormonal levels. Neither could any association between the presence of rectal lactobacilli and hormonal levels be found.</p> <p>Conclusion</p> <p><it>Lactobacillus crispatus </it>was more prevalent in the vaginal flora of fertile women, whereas the <it>Lactobacillus </it>flora of rectum did not correlate to the vaginal flora nor to hormonal levels.</p

High-energy radiation from the massive binary system Eta Carinae

Context. The most massive binary system Eta Carinae has been recently established as a gamma-ray source by the AGILE and Fermi-LAT detectors. The high energy spectrum of this gamma-ray source is very intriguing. It shows two clear components and a lack of any evidence of variability with the orbital period of the binary system. Aims. We consider different scenarios for the acceleration of particles (both electrons and hadrons) and the production of the high energy radiation in the model of stellar wind collisions within the binary system Eta Carinae with the aim to explain the gamma-ray observations and predict the behaviour of the source at very high gamma-ray energies. Methods. The gamma-ray spectra calculated in terms of the specific models are compared with the observations of Eta Carinae, and the neutrino spectra produced in hadronic models are confronted with the atmospheric neutrino background and the sensitivity of 1 km2 neutrino telescope. Results. We show that spectral features can be explained in terms of the stellar wind collision model between the winds of the companion stars in which the acceleration of particles occurs on both sides of the double shock structure. The shocks from the Eta Carinae star and the companion star can accelerate particles to different energies depending on the different conditions determined by the parameters of the stars. The lack of strong GeV gamma-ray variability with the period of the binary system can be also understood in terms of such a model. Conclusions. We predict that the gamma-ray emission features at energies above  ~100 GeV will show significant variability (or its lack) depending on the acceleration and interaction scenario of particles accelerated within the binary system. For the hadronic models we predict the expected range of neutrino fluxes from the binary system Eta Carinae. This can be tested through observations with the large-scale neutrino telescopes, which will support or disprove the specific hadronic models

Electric Dipole and Current Induced Spin Resonances of Shallow Donor in ZnO

In this paper we present our observation of electric dipole spin resonance and current induced spin resonance in ZnO bulk crystals, both effects result from spin-orbit coupling. Electric dipole spin resonance originates from admixture of spin state due to spin-orbit interaction which leads to probability of spin-flip caused by electric component of microwave field. In current induced spin resonance phenomenon the electric component of microwave field induces electron motion leading to mean ac spin-orbit field that acts on electron spin. Spin-orbit interaction can be described in terms of the Rashba field, an effective magnetic field that induce spin resonance. In contrast to magnetic and electric dipole spin resonances the current induced resonance is characterized by dispersive-like line shape

Following up on a Margalevian concept: Interactions and exchanges among adjacent parcels of coastal landscapes

Some decades ago Margalef speculated that study of the exchanges across boundaries that separate different types of ecological systems would provide significant insights about properties and processes within the units that make up ecological mosaics. Although such boundaries might be difficult to define, it seemed likely that such exchanges among units would influence the function and structure of the adjoined systems. In this paper we explore exchanges across such ecological boundaries in coastal ecosystems in Cape Cod, Massachusetts, and elsewhere. We find that, indeed, definition of such boundaries is ambiguous, but study of the exchanges is more useful. In the Cape Cod system, water transport down-gradient is the dominant mechanism exerting influence on down-gradient systems. The direction of ecological control across such boundaries is largely asymmetrical, and properties of up-gradient units exert significant influence on down-gradient units. General properties of donor and receptor parcels are hard to discern, but clearly, parcels making up an ecological mosaic are not independent units, but are coupled by transfers from upgradient tesserae. Studies of controls of ecological systems need to include inter-unit influences as well as internal mechanisms.No disponibl

Plasma Prostaglandin E2 Metabolite Levels Predict Type 2 Diabetes Status and One-Year Therapeutic Response Independent of Clinical Markers of Inflammation

Over half of patients with type 2 diabetes (T2D) are unable to achieve blood glucose targets despite therapeutic compliance, significantly increasing their risk of long-term complications. Discovering ways to identify and properly treat these individuals is a critical problem in the field. The arachidonic acid metabolite, prostaglandin E2 (PGE2), has shown great promise as a biomarker of &beta;-cell dysfunction in T2D. PGE2 synthesis, secretion, and downstream signaling are all upregulated in pancreatic islets isolated from T2D mice and human organ donors. In these islets, preventing &beta;-cell PGE2 signaling via a prostaglandin EP3 receptor antagonist significantly improves their glucose-stimulated and hormone-potentiated insulin secretion response. In this clinical cohort study, 167 participants, 35 non-diabetic, and 132 with T2D, were recruited from the University of Wisconsin Hospital and Clinics. At enrollment, a standard set of demographic, biometric, and clinical measurements were performed to quantify obesity status and glucose control. C reactive protein was measured to exclude acute inflammation/illness, and white cell count (WBC), erythrocyte sedimentation rate (ESR), and fasting triglycerides were used as markers of systemic inflammation. Finally, a plasma sample for research was used to determine circulating PGE2 metabolite (PGEM) levels. At baseline, PGEM levels were not correlated with WBC and triglycerides, only weakly correlated with ESR, and were the strongest predictor of T2D disease status. One year after enrollment, blood glucose management was assessed by chart review, with a clinically-relevant change in hemoglobin A1c (HbA1c) defined as &ge;0.5%. PGEM levels were strongly predictive of therapeutic response, independent of age, obesity, glucose control, and systemic inflammation at enrollment. Our results provide strong support for future research in this area