Influence of hydrology on dissolvedorganic matter quantity and properties in a temporal Mediterranean stream = Influència de la hidrologia sobre la quantitat i disponibilitat de la matèria orgànica dissolta en una riera temporal mediterrània

The studies presented in this thesis focus on the biogeochemistry of dissolved organic matter (DOM) in an intermittent stream in a Mediterranean climate zone, with great emphasis on extreme hydrologic events: floods and the seasonal drought period. The changes in concentration and molecular weight, and the properties, especially those related to its origin, and bioavailability to the microbial community. The samplings were carried out during a wide span of years in order to characterize the concentration – discharge responses (C-Q) initially, and more intensively during the different periods of the hydrologic year (wet, drought and transitional periods) in order to capture the widest possible picture of the dissolved organic matter dynamics and processing. The last chapter is a review of different fluorescence spectroscopy and UV-vis absorbance methods applied in DOM characterization. The main conclusions from these works are: 1. The most probable C-Q response types represent only a 40% of all cases from the data set. Therefore, the majority of DOC and NO3-Q responses fall within some low probability C-Q response types. 2. The dry-wet transition does not present a typical C-Q response. Instead, it promotes the diversity of DOC-Q responses. The 33% of events comprised during this period contribute to the 41% of the total DOC-Q response diversity. On the other hand, it does not enhance NO3-Q responses. 3. The most important driver for the succession of NO3-Q responses is the periodicity of the magnitude of storms (ΔQ) is, while the effect of the seasonal temperature change (i.e., Tday), appears more perceptible after the removal of the signal of the weaker and more frequent rain episodes. 4. The occurrence of a severe summer dry period favored the mobilization and transport of labile DOC, as shown by the 56% of retention across the stream – riparian interface, during the following hydrological transition period. Furthermore, the DOC retention during this period was preferential from high to low molecular weight fractions. In the case of no apparent hydrological transition all DOC molecular weight fractions were equally conservative. 5. During both drought and rewetting periods DOC and DON bioavailability are not tied to a MW fraction. During the rewetting period, although there is no clear pattern of bioavailability according to any DOC MW fraction, 50% of cases at which DOCMW release is observed (BDOCMW<0) correspond to the LMW fraction. 6. In general, DOCMW dynamics fit within the framework that storm events enhance the input of larger molecular weight DOC fraction (higher than 1 kDa), but DONMW does not. Furthermore, the hydrologic characteristics of the rewetting period evidence an asynchronous mobilization of DOC and DON. 7. DOC bioavailability is heavily influenced by DON content rather than molecular weight. Furthermore, bioavailability seems to be regulated by the DOC:DON ratio presenting a threshold value of 13. The most remarkable case is that of DOCLMW that shifts from refractory to bioavailable when its DOC:DON ratio is lower than 13. 8. Drought causes a gradual hydrological fragmentation of the fluvial network enlarging the variability of DOM properties, and amplifying the biogeochemical variability of a fluvial system. 9. Sampling sites with lotic water bodies in summer show DOM properties similar to those observed in autumn under base flow hydrological conditions and reflect the prevalence of terrestrial inputs. In contrast, in isolated and lentic water bodies, DOM analyses reveal a supplementary contribution of autochthonous organic matter, originated by in situ microbial processes. 10. BDOC estimated during summer indicates an upper threshold of 40% that is also observed during the rewetting period. This allows asserting that the highest bioavailable DOC concentration can be reached during two ecosystem perturbations of opposite sign.Els articles presentats en aquesta tesi es centren en els aspectos biogeoquímics de la materia orgànica dissolta (DOM) en una riera temporal en una zona de clima mediterrani. Concretament, s’estudien els efectes dels events hidrològics extrems, les crescudes i les sequeres estacionals pròpies de la regió mediterrània, en la concentració i les propietats de la matèria orgànica dissolta. Els paràmetres utilitzats en la caracterizació de la DOM permeten principalment establir l’origen d’aquesta i establir la seva biodisponibilitat per a les comunitats microbianes del riu. En l’aspecte quantitatiu també es realitza un estudi més detallat mitjançant el fraccionament en diferents rangs de pes molecular. La recollida de dades inclou una sèrie temporal llarga que permet estudiar les despostes concentració – cabal (C-Q) tant del carboni orgànic dissolt com del nitrat, i d’uns mostreigs de camp intensius que permeten obtenir una imatge precisa dels diferents períodes de l’any hidrològic (període humit, de sequera i de transició hidrològica). Els resultats d’aquests treballs permeten copsar la variabilitat de les respostes C-Q, que en el cas del DOC veuen augmentada la seva variabilitat durant el període de transició hidrològica. En el cas del nitrat s’observa que les respostes es troben relacionades amb la magnitud y l’interval de temps entre episodis de precipitació. Pel que fa a la biodisponibilitat de les diferents fraccions moleculars, mentre que els estudis inicials apunten a una immobilització selectiva de les fraccions més grans a la interfase ripariana, estudis següents postren que la concentració de nitrogen orgànic dissolt és cabdal a l’hora de determinar si una fracció és biodisponible o no. A nivell hidrològic es conclou que tant durant la transició hidrològica com durant el període de transició hi ha una amplificació dels processos biogeoquímics que permeten estudiar el sistema fluvial amb més profunditat. No obstant, durant la fragmentació hidrològica es produeix una augment en la variabilitat biogeoquímica mentre que durant la transició hi ha una tendencia a l’homogeneïtzació

Stream hydrological fragmentation drives bacterioplankton community composition

In Mediterranean intermittent streams, the hydrological fragmentation in summer and the successive water flow reconvergence in autumn allow exploring how local processes shape the microbial community within the same habitat. The objectives of this study were to determine how bacterial community composition responded to hydrological fragmentation in summer, and to evaluate whether the seasonal shifts in community composition predominate over the effects of episodic habitat fragmentation. The bacterial community was assessed along the intermittent stream Fuirosos (Spain), at different levels of phylogenetic resolution by in situ hybridization, fingerprinting, and 16S rRNA gene sequencing. The hydrological fragmentation of the stream network strongly altered the biogeochemical conditions with the depletion of oxidized solutes and caused changes in dissolved organic carbon characteristics. In the isolated ponds, beta-Proteobacteria and Actinobacteria increased their abundance with a gradual reduction of the alpha-diversity as pond isolation time increased. Moreover, fingerprinting analysis clearly showed a shift in community composition between summer and autumn. In the context of a seasonal shift, the temporary stream fragmentation simultaneously reduced the microbial dispersion and affected local environmental conditions (shift in redox regime and quality of the dissolved organic matter) tightly shaping the bacterioplankton community composition

Observation of Exclusive Gamma Gamma Production in p pbar Collisions at sqrt{s}=1.96 TeV

We have observed exclusive \gamma\gamma production in proton-antiproton collisions at \sqrt{s}=1.96 TeV, using data from 1.11 \pm 0.07 fb^{-1} integrated luminosity taken by the Run II Collider Detector at Fermilab. We selected events with two electromagnetic showers, each with transverse energy E_T > 2.5 GeV and pseudorapidity |\eta| < 1.0, with no other particles detected in -7.4 < \eta < +7.4. The two showers have similar E_T and azimuthal angle separation \Delta\phi \sim \pi; 34 events have two charged particle tracks, consistent with the QED process p \bar{p} to p + e^+e^- + \bar{p} by two-photon exchange, while 43 events have no charged tracks. The number of these events that are exclusive \pi^0\pi^0 is consistent with zero and is < 15 at 95% C.L. The cross section for p\bar{p} to p+\gamma\gamma+\bar{p} with |\eta(\gamma)| < 1.0 and E_T(\gamma) > 2.5$ GeV is 2.48^{+0.40}_{-0.35}(stat)^{+0.40}_{-0.51}(syst) pb.Comment: 7 pages, 4 figure

Shrinking a large dataset to identify variables associated with increased risk of Plasmodium falciparum infection in Western Kenya

Large datasets are often not amenable to analysis using traditional single-step approaches. Here, our general objective was to apply imputation techniques, principal component analysis (PCA), elastic net and generalized linear models to a large dataset in a systematic approach to extract the most meaningful predictors for a health outcome. We extracted predictors for Plasmodium falciparum infection, from a large covariate dataset while facing limited numbers of observations, using data from the People, Animals, and their Zoonoses (PAZ) project to demonstrate these techniques: data collected from 415 homesteads in western Kenya, contained over 1500 variables that describe the health, environment, and social factors of the humans, livestock, and the homesteads in which they reside. The wide, sparse dataset was simplified to 42 predictors of P. falciparum malaria infection and wealth rankings were produced for all homesteads. The 42 predictors make biological sense and are supported by previous studies. This systematic data-mining approach we used would make many large datasets more manageable and informative for decision-making processes and health policy prioritization

Evidence for t\bar{t}\gamma Production and Measurement of \sigma_t\bar{t}\gamma / \sigma_t\bar{t}

Using data corresponding to 6.0/fb of ppbar collisions at sqrt(s) = 1.96 TeV collected by the CDF II detector, we present a cross section measurement of top-quark pair production with an additional radiated photon. The events are selected by looking for a lepton, a photon, significant transverse momentum imbalance, large total transverse energy, and three or more jets, with at least one identified as containing a b quark. The ttbar+photon sample requires the photon to have 10 GeV or more of transverse energy, and to be in the central region. Using an event selection optimized for the ttbar+photon candidate sample we measure the production cross section of, and the ratio of cross sections of the two samples. Control samples in the dilepton+photon and lepton+photon+\met, channels are constructed to aid in decay product identification and background measurements. We observe 30 ttbar+photon candidate events compared to the standard model expectation of 26.9 +/- 3.4 events. We measure the ttbar+photon cross section to be 0.18+0.08 pb, and the ratio of the cross section of ttbar+photon to ttbar to be 0.024 +/- 0.009. Assuming no ttbar+photon production, we observe a probability of 0.0015 of the background events alone producing 30 events or more, corresponding to 3.0 standard deviations.Comment: 9 pages, 3 figure

Measurement of the WZWZ Cross Section and Triple Gauge Couplings in ppˉp \bar p Collisions at s=1.96\sqrt{s} = 1.96 TeV

This Letter describes the current most precise measurement of the $WZ$ production cross section as well as limits on anomalous $WWZ$ couplings at a center-of-mass energy of 1.96 TeV in proton-antiproton collisions for the Collider Detector at Fermilab (CDF). $WZ$ candidates are reconstructed from decays containing three charged leptons and missing energy from a neutrino, where the charged leptons are either electrons or muons. Using data collected by the CDF II detector (7.1 fb$^{-1}$ of integrated luminosity), 63 candidate events are observed with the expected background contributing $8 \pm 1$ events. The measured total cross section $\sigma (p \bar p \to WZ) = 3.93_{-0.53}^{+0.60}(\text{stat})_{-0.46}^{+0.59}(\text{syst})$ pb is in good agreement with the standard model prediction of $3.50\pm 0.21$. The same sample is used to set limits on anomalous $WWZ$ couplings.Comment: Resubmission to PRD-RC after acceptance (27 July 2012

Search for the Higgs boson in events with missing transverse energy and b quark jets produced in proton-antiproton collisions at s**(1/2)=1.96 TeV

We search for the standard model Higgs boson produced in association with an electroweak vector boson in events with no identified charged leptons, large imbalance in transverse momentum, and two jets where at least one contains a secondary vertex consistent with the decay of b hadrons. We use ~1 fb-1 integrated luminosity of proton-antiproton collisions at s**(1/2)=1.96 TeV recorded by the CDF II experiment at the Tevatron. We find 268 (16) single (double) b-tagged candidate events, where 248 +/- 43 (14.4 +/- 2.7) are expected from standard model background processes. We place 95% confidence level upper limits on the Higgs boson production cross section for several Higgs boson masses ranging from 110 GeV/c2 to 140 GeV/c2. For a mass of 115 GeV/c2 the observed (expected) limit is 20.4 (14.2) times the standard model prediction.Comment: 8 pages, 2 figures, submitted to Phys. Rev. Let

Measurement of the Helicity Fractions of W Bosons from Top Quark Decays Using Fully Reconstructed top-antitop Events with CDF II

We present a measurement of the fractions F_0 and F_+ of longitudinally polarized and right-handed W bosons in top quark decays using data collected with the CDF II detector. The data set used in the analysis corresponds to an integrated luminosity of approximately 318 pb -1. We select ttbar candidate events with one lepton, at least four jets, and missing transverse energy. Our helicity measurement uses the decay angle theta*, which is defined as the angle between the momentum of the charged lepton in the W boson rest frame and the W momentum in the top quark rest frame. The cos(theta*) distribution in the data is determined by full kinematic reconstruction of the ttbar candidates. We find F_0 = 0.85 +0.15 -0.22 (stat) +- 0.06 (syst) and F_+ = 0.05 +0.11 -0.05 (stat) +- 0.03 (syst), which is consistent with the standard model prediction. We set an upper limit on the fraction of right-handed W bosons of F_+ < 0.26 at the 95% confidence level.Comment: 11 pages, 2 figures, submitted to Phys. Rev.

Measurement of Ratios of Fragmentation Fractions for Bottom Hadrons in p-pbar Collisions at sqrt{s}=1.96 TeV

This paper describes the first measurement of b-quark fragmentation fractions into bottom hadrons in Run II of the Tevatron Collider at Fermilab. The result is based on a 360 pb-1 sample of data collected with the CDF II detector in p-pbar collisions at sqrt{s}=1.96 TeV. Semileptonic decays of B0, B+, and B_s mesons, as well as Lambda_b baryons, are reconstructed. For an effective bottom hadron p_T threshold of 7 GeV/c, the fragmentation fractions are measured to be f_u/f_d=1.054 +/- 0.018 (stat) +0.025-0.045(sys) +/- 0.058 (Br), f_s/(f_u+f_d)=0.160 +/- 0.005 (stat) +0.011-0.010 (sys) +0.057-0.034 (Br), and f_{Lambda_b}/(f_u+f_d)=0.281\pm0.012 (stat) +0.058-0.056 (sys) +0.128-0.086 (Br), where the uncertainty (Br) is due to uncertainties on measured branching ratios. The value of f_s/(f_u+f_d) agrees within one standard deviation with previous CDF measurements and the world average of this quantity, which is dominated by LEP measurements. However, the ratio f_{Lambda_b}/(f_u+f_d) is approximately twice the value previously measured at LEP. The approximately 2 sigma discrepancy is examined in terms of kinematic differences between the two production environments.Comment: Submitted to PRD, 54 pages, 53 plot

Measurement of σ(Λb)/σ(B0)×BR(Λb→Λcπ−)/BR(B0→D+π−)\sigma(\Lambda_b)/\sigma(B^0) \times BR(\Lambda_b\to\Lambda_c\pi^-) / BR(B^0\to D^+\pi^-) in ppˉp\bar{p} Collisions at s=1.96\sqrt{s}=1.96 TeV

We present the first observation of the baryon decay $\Lambda_b\to\Lambda_c\pi^-$ followed by $\Lambda_c\to p K^-\pi^+$ in 106 pb-1 of $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV in the CDF experiment. In order to reduce systematic error, the measured rate for $\Lambda_b$ decay is normalized to the kinematically similar meson decay $B^0\to D^+\pi^-$ followed by $D^+\to\pi^+K^-\pi^+$. We report the ratio of production cross sections ($\sigma$) times the ratio of branching fractions (BR) for the momentum region integrated above $p_T > 6$ GeV/c and pseudorapidity range $|\eta| < 1.3$: $\sigma(p\bar{p}\to \Lambda_b X) / \sigma (p\bar{p}\to B^0 X) \times BR(\Lambda_b\to\Lambda_c\pi^-) / BR(B^0\to D^+\pi^-) = 0.82 \pm 0.08(stat) \pm 0.11(syst) \pm 0.22 (BR(\Lambda_c\to p K^-\pi^+))$.Comment: Submitted to Phys.Rev.Let