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  • 1
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    Isotopic composition of water in fog, rain, throughfall and stemflow in the Monte Verde, Costa Rica
    PANGAEA
    In:  Supplement to: Schmid, Simone; Burkard, Reto; Frumau, K F A; Tobón, C; Bruijnzeel, L Adrian; Siegwolf, Rolf T E; Eugster, Werner (2011): Using eddy covariance and stable isotope mass balance techniques to estimate fog water contributions to a Costa Rican cloud forest during the dry season. Hydrological Processes, 25, 429-437, https://doi.org/10.1002/hyp.7739
    Details
    Publication Date: 2023-05-12
    Description: Fog deposition, precipitation, throughfall and stemflow were measured in a windward tropical montane cloud forest near Monteverde, Costa Rica, for a 65-day period during the dry season of 2003. Net fog deposition was measured directly using the eddy covariance (EC) method and it amounted to 1.2 ± 0.1 mm/day (mean ± standard error). Fog water deposition was 5–9% of incident rainfall for the entire period, which is at the low end of previously reported values. Stable isotope concentrations (d18O and d2H) were determined in a large number of samples of each water component. Mass balance-based estimates of fog deposition were 1.0 ± 0.3 and 5.0 ± 2.7 mm/day (mean ± SE) when d18O and d2H were used as tracer, respectively. Comparisons between direct fog deposition measurements and the results of the mass balance model using d18O as a tracer indicated that the latter might be a good tool to estimate fog deposition in the absence of direct measurement under many (but not all) conditions. At 506 mm, measured water inputs over the 65 days (fog plus rain) fell short by 46 mm compared to the canopy output of 552 mm (throughfall, stemflow and interception evaporation). This discrepancy is attributed to the underestimation of rainfall during conditions of high wind.
    Keywords: Conductivity; DATE/TIME; Date/time end; Duration; Electrode; FIESTA; Fog Interception for the Enhancement of Streamflows in Tropical Areas; Isotope ratio mass spectrometry; Monitoring station; MONS; Monte_Verde; Monte Verde, Costa Rica; pH; Rain gauge; Sample type; Throughfall; δ18O, water; δ Deuterium, water
    Type: Dataset
    Format: text/tab-separated-values, 3600 data points
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  • 2
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    Insights into plant water uptake from xylem-water isotope measurements in two tropical catchments with contrasting moisture conditions (2016)
    Wiley
    Details
    Publication Date: 2016-03-09
    Description: Water transpired by trees has long been assumed to be sourced from the same subsurface water stocks that contribute to groundwater recharge and streamflow. However, recent investigations using dual water stable isotopes have shown an apparent ecohydrological separation between tree-transpired water and stream water. Here we present evidence for such ecohydrological separation in two tropical environments in Puerto Rico where precipitation seasonality is relatively low and where precipitation is positively correlated with primary productivity. We determined the stable isotope signature of xylem water of 30 mahogany ( Swietenia spp.) trees sampled during two periods with contrasting moisture status. Our results suggest that the separation between transpiration water and groundwater recharge/streamflow water might be related less to the temporal phasing of hydrologic inputs and primary productivity, and more to the fundamental processes that drive evaporative isotopic enrichment of residual soil water within the soil matrix. The lack of an evaporative signature of both groundwater and streams in the study area suggests that these water balance components have a water source that is transported quickly to deeper subsurface storage compared to waters that trees use. A Bayesian mixing model used to partition source water proportions of xylem water showed that groundwater contribution was greater for valley-bottom, riparian trees than for ridge-top trees. Groundwater contribution was also greater at the xeric site than at the mesic-hydric site. These model results (1) underline the utility of a simple linear mixing model, implemented in a Bayesian inference framework, in quantifying source water contributions at sites with contrasting physiographic characteristics, and (2) highlight the informed judgment that should be made in interpreting mixing model results, of import particularly in surveying groundwater use patterns by vegetation from regional to global scales. This article is protected by copyright. All rights reserved.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
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  • 3
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    Nongyrotropic electrons in guide field reconnection (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-02-26
    Description: We apply a scalar measure of nongyrotropy to the electron pressure tensor in a 2D particle-in-cell simulation of guide field reconnection and assess the corresponding electron distributions and the forces that account for the nongyrotropy. The scalar measure reveals that the nongyrotropy lies in bands that straddle the electron diffusion region and the separatrices, in the same regions where there are parallel electric fields. Analysis of electron distributions and fields shows that the nongyrotropy along the inflow and outflow separatrices emerges as a result of multiple populations of electrons influenced differently by large and small-scale parallel electric fields and by gradients in the electric field. The relevant parallel electric fields include large-scale potential ramps emanating from the x-line and sub-ion inertial scale bipolar electron holes. Gradients in the perpendicular electric field modify electrons differently depending on their phase, thus producing nongyrotropy. Magnetic flux violation occurs along portions of the separatrices that coincide with the parallel electric fields. An inductive electric field in the electron E  ×  B drift frame thus develops, which has the effect of enhancing nongyrotropies already produced by other mechanisms and under certain conditions producing their own nongyrotropy. Particle tracing of electrons from nongyrotropic populations along the inflows and outflows shows that the striated structure of nongyrotropy corresponds to electrons arriving from different source regions. We also show that the relevant parallel electric fields receive important contributions not only from the nongyrotropic portion of the electron pressure tensor but from electron spatial and temporal inertial terms as well.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    Effects of Reforestation of a Degraded Imperata Grassland on Dominant Flow Pathways and Streamflow Responses in Leyte, the Philippines (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract Reforestation of degraded grasslands can increase the soil hydraulic conductivity and number of preferential flow pathways. However, it is not clear to what extent these changes affect streamflow responses and whether this depends on the event size. We, therefore, studied the hydrological response of two small catchments near Tacloban, Leyte (the Philippines): a degraded Imperata grassland catchment and a catchment that was reforested 23 years prior to our study. Precipitation, stream stage, and electrical conductivity were measured continuously from June to November 2013. Samples were taken from streamflow, precipitation, groundwater, and soil water for geochemical and stable isotope analyses. Streamflow and electrical conductivity changed rapidly during almost every event in the grassland catchment, but in the reforested catchment, these responses were much smaller and only occurred during large events. Streamflow was a mixture of groundwater and precipitation for both catchments, but the maximum event water contributions to streamflow were much larger for the degraded grassland than for the reforested catchment. The differences in the event water contributions and timing of the streamflow responses were observed across all event sizes, including a large tropical storm. Together with the low saturated hydraulic conductivity in the degraded catchment, these results suggest that overland flow occurred more frequently and was much more widespread in the degraded grassland than in the reforested catchment. We, therefore, conclude that reforestation of a degraded grassland can change the dominant flow pathways and restore the hydrological functioning if the forest soil is allowed to develop over a sufficiently long period.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Inner magnetospheric electron- temperature and spacecraft potential estimated from concurrent POLAR upper-hybrid frequency and relative potential measurements (2014)
    Wiley
    Details
    Publication Date: 2014-09-02
    Description: Direct measurement of low 〈 1 eV electron temperature is difficult to make in the earth's inner magnetosphere for electron densities ( N e ) 〈 3x10 2 cm -3 . We compute these quantities by solving current-balance equations in low density regions. Concurrent measurements from the POLAR spacecraft of the relative potential ( V S -V P ), between the spacecraft body and the electric field probe, and the electron density ( N e ), derived from upper hybrid frequency ( f UHR ), were used in the current balance equations to solve for the electron temperature ( T e ), V s and V p . Where V P is the probe potential and V S is the spacecraft potential relative to the nearby plasma. The assumption that the bulk plasma electrons are Maxwellian is used in the computations. Our dataset covered 1&1/2 years of measurements when f UHR was detectable ( L  〈 10). The following “averaged” T e vs. L relation for 3 〈  L  〈 5 was obtained: T e  = 0.58 + 0.49 ( L -3) eV. This expression is in reasonable agreement with extrapolations of ionospheric T e measurements by Akebono at lower altitudes. However the solution is sensitive to the photo-emission coefficients, substituting those of Scudder et al. [2000] with those of Escoubet et al. [1997] the T e curve shifted upwards by ~1 eV. Also the solution is sensitive to measurement error of V S -V P , applying a voltage shift of ±0.1 and ±0.2  V to V S -V P the relative median error for our data set was computed to be 0.27 and 1.04 respectively. We believe our T e values computed outside the plasmasphere are unrealistically low. We conclude that this method shows promise inside the plasmasphere, but should be used with caution. We also quantified the N e vs. V S -V P relationship. The running median N e vs. V S -V P curve shows no significant variation over the 1 ½ year period of the data set suggesting that the photo-emission coefficients did not change significantly over this time span. The Scudder et al. [2000] N e model, based on only one POLAR orbit, is in reasonable agreement (within a factor of 2) with our results.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Genome sequence of the PCE-dechlorinating bacterium Dehalococcoides ethenogenes (2005)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2005-01-08
    Description: Dehalococcoides ethenogenes is the only bacterium known to reductively dechlorinate the groundwater pollutants, tetrachloroethene (PCE) and trichloroethene, to ethene. Its 1,469,720-base pair chromosome contains large dynamic duplicated regions and integrated elements. Genes encoding 17 putative reductive dehalogenases, nearly all of which were adjacent to genes for transcription regulators, and five hydrogenase complexes were identified. These findings, plus a limited repertoire of other metabolic modes, indicate that D. ethenogenes is highly evolved to utilize halogenated organic compounds and H2. Diversification of reductive dehalogenase functions appears to have been mediated by recent genetic exchange and amplification. Genome analysis provides insights into the organism's complex nutrient requirements and suggests that an ancestor was a nitrogen-fixing autotroph.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Seshadri, Rekha -- Adrian, Lorenz -- Fouts, Derrick E -- Eisen, Jonathan A -- Phillippy, Adam M -- Methe, Barbara A -- Ward, Naomi L -- Nelson, William C -- Deboy, Robert T -- Khouri, Hoda M -- Kolonay, James F -- Dodson, Robert J -- Daugherty, Sean C -- Brinkac, Lauren M -- Sullivan, Steven A -- Madupu, Ramana -- Nelson, Karen E -- Kang, Katherine H -- Impraim, Marjorie -- Tran, Kevin -- Robinson, Jeffrey M -- Forberger, Heather A -- Fraser, Claire M -- Zinder, Stephen H -- Heidelberg, John F -- New York, N.Y. -- Science. 2005 Jan 7;307(5706):105-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute for Genomic Research, 9712 Medical Center Drive, Rockville, MD 20850, USA. rekha@tigr.org〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15637277" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acids/biosynthesis ; Biodegradation, Environmental ; Chloroflexi/*genetics/*metabolism ; Gene Duplication ; Genes, Bacterial ; *Genome, Bacterial ; Hydrogen/metabolism ; Molecular Sequence Data ; Nitrogenase/genetics/metabolism ; Operon ; Oxidation-Reduction ; Oxidoreductases/genetics/metabolism ; Quinones/metabolism ; Sequence Analysis, DNA ; Tetrachloroethylene/*metabolism ; Transcription Factors/genetics/metabolism ; Water Pollutants, Chemical/metabolism
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 7
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    Global-scale regionalization of hydrologic model parameters (2016)
    Wiley
    Details
    Publication Date: 2016-04-21
    Description: Current state-of-the-art models typically applied at continental to global scales (hereafter called macro-scale) tend to use a priori parameters, resulting in suboptimal streamflow ( Q ) simulation. For the first time, a scheme for regionalization of model parameters at the global scale was developed. We used data from a diverse set of 1787 small-to-medium sized catchments (10-10000 km 2 ) and the simple conceptual HBV model to set up and test the scheme. Each catchment was calibrated against observed daily Q , after which 674 catchments with high calibration and validation scores, and thus presumably good-quality observed Q and forcing data, were selected to serve as donor catchments. The calibrated parameter sets for the donors were subsequently transferred to 0.5° grid cells with similar climatic and physiographic characteristics, resulting in parameter maps for HBV with global coverage. For each grid cell, we used the ten most similar donor catchments, rather than the single most similar donor, and averaged the resulting simulated Q , which enhanced model performance. The 1113 catchments not used as donors were used to independently evaluate the scheme. The regionalized parameters outperformed spatially-uniform (i.e., averaged calibrated) parameters for 79% of the evaluation catchments. Substantial improvements were evident for all major Köppen-Geiger climate types and even for evaluation catchments 〉 5000 km distant from the donors. The median improvement was about half of the performance increase achieved through calibration. HBV with regionalized parameters outperformed nine state-of-the-art macro-scale models, suggesting these might also benefit from the new regionalization scheme. The produced HBV parameter maps including ancillary data are available via http://water.jrc.ec.europa.eu/HBV/ . This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 8
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    Magnetospheric Electron-Velocity-Distribution Function Information from Wave Observations (2013)
    Wiley
    Details
    Publication Date: 2013-07-25
    Description: [1]  The electron-velocity-distribution function was determined to be highly non-Maxwellian and more appropriate to a kappa distribution, with κ ≈ 2.0, near magnetic midnight in the low-latitude magnetosphere just outside a stable plasmasphere during extremely quiet geomagnetic conditions. The kappa results were based on sounder-stimulated Qn plasma resonances using the Radio Plasma Imager (RPI) on the IMAGE satellite; the state of the plasmasphere was determined from IMAGE/EUV observations. The Qn resonances correspond to the maximum frequencies of Bernstein-mode waves that are observed between the harmonics of the electron cyclotron frequency in the frequency domain above the upper-hybrid frequency . Here we present the results of a parametric investigation that included suprathermal electrons in the electron-velocity-distribution function used in the plasma-wave dispersion equation to calculate the Qn frequencies for a range of kappa and f pe /f ce values for Qn resonances from Q1 to Q9. The Qn frequencies were also calculated using a Maxwellian distribution and they were found to be greater than those calculated using a kappa distribution with the frequency differences increasing with increasing n for a fixed κ and with decreasing κ for a fixed n. The calculated f Qn values have been incorporated into the RPI BinBrowser software providing a powerful tool for rapidly obtaining information on the nature of the magnetospheric electron-velocity-distribution function and the electron number density N e . This capability enabled accurate (within a few percent) in-situ N e determinations to be made along the outbound orbital track as IMAGE moved away from the plasmapause. The extremely quiet geomagnetic conditions allowed IMAGE/EUV-extracted counts to be compared with the RPI-determined orbital-track N e profile. The comparisons revealed remarkably similar N e structures.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Current Structure and Non-Ideal Behavior at Magnetic Null Points in the Turbulent Magnetosheath (2013)
    Wiley
    Details
    Publication Date: 2013-03-19
    Description: [1]  The Poincaré index indicates the Cluster spacecraft tetrahedron entraps a number of three-dimensional magnetic nulls during an encounter with the turbulent magnetosheath. Previous researchers have found evidence for reconnection at one of the many filamentary current layers observed by Cluster in this region. We find that many of the entrained nulls are also associated with strong currents. We dissect the current structure of a pair of spiral nulls that may be topologically connected. At both nulls, we find a strong current along the spine, accompanied by a somewhat more modest current perpendicular to the spine that tilts the fan toward the axis of the spine. The current along the fan is comparable to the current along the spine. At least one of the nulls manifests a rotational flow pattern in the fan plane that is consistent with torsional spine reconnection as predicted by theory. These results emphasize the importance of examining the magnetic topology in interpreting the nature of currents and reconnection in three-dimensional turbulence.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 10
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    Reforesting severely degraded grassland in the Lesser Himalaya of Nepal: Effects on soil hydraulic conductivity and overland flow production (2013)
    Wiley
    Details
    Publication Date: 2013-11-01
    Description: [1]  Severely degraded hillslopes in the Lesser Himalaya challenge local communities as a result of the frequent occurrence of overland flow and erosion during the rainy season, and water shortages during the dry season. Reforestation is often perceived as an effective way of restoring pre-disturbance hydrological conditions but heavy usage of reforested land in the region has been shown to hamper full recovery of soil hydraulic properties. This paper investigates the effect of reforestation and forest usage on field-saturated soil hydraulic conductivities ( K fs ) near Dhulikhel, Central Nepal, by comparing degraded pasture, a footpath within the pasture, a 25-year-old pine reforestation, and little disturbed natural forest. The hillslope hydrological implications of changes in K fs with land-cover change were assessed via comparisons with measured rainfall intensities over different durations. High surface- and near-surface K fs in natural forest (82–232 mm h -1 ) rules out overland flow occurrence and favours vertical percolation. Conversely, corresponding K fs for degraded pasture (18–39 mm h -1 ) and foot path (12–26 mm h -1 ) were conducive to overland flow generation during medium to high intensity storms and thus to local flash flooding. Pertinently, surface- and near-surface K fs in the heavily used pine forest remained similar to those for degraded pasture. Estimated monsoonal overland flow totals for degraded pasture, pine forest and natural forest were 21.3%, 15.5% and 2.5% of incident rainfall, respectively, reflecting the relative ranking of surface K fs . Along with high water use by the pines, this lack of recovery of soil hydraulic properties under pine reforestation is shown to be a critical factor in the regionally observed decline in baseflows following large-scale planting of pines and has important implications for regional forest management.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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