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41.
Gladys V. Melián Inés Galindo Nemesio M. Pérez Pedro A. Hernández Mario Fernández Carlos Ramírez Raúl Mora Guillermo E. Alvarado 《Pure and Applied Geophysics》2007,164(12):2465-2487
We report the results of four soil H2 surveys carried out in 2000–2003 at Poás volcano, Costa Rica, to investigate the soil H2 distribution and evaluate the diffuse H2 emission as a potential surveillance tool for Poás volcano. Soil gas H2 contents showed a wide range of concentration from 0.2 to 7,059 ppmV during the four surveys. Maps of soil gas H2 based on Sequential Gaussian Simulation showed low H2 concentration values in the soil atmosphere (<0.7 ppmV) for most of the study area, whereas high soil gas H2 values were observed inside the active crater of Poás. A significant increase in soil gas H2 concentration was observed inside the active crater during 2001 and 2002 with respect to year 2000, followed by a decrease
in 2003. The observed spatial and temporal variations of soil H2 concentration have been well correlated with seismicity, microgravimetry and fumarolic chemistry changes which occurred during
this study. These observations evidence changes in the shallow magmatic-hydrothermal system of Poás, and it might be related
to a potential magmatic intrusion during the period 1998–2004. Therefore, monitoring diffuse H2 emission of Poás has become an important geochemical tool for the monitoring of its volcanic activity. 相似文献
42.
D. Baines R. D. Oudmaijer A. Mora C. Eiroa John M. Porter B. Merín B. Montesinos D. de Winter A. Cameron J. K. Davies H. J. Deeg R. Ferlet C. A. Grady A. W. Harris M. G. Hoare K. Horne S. L. Lumsden L. F. Miranda A. Penny A. Quirrenbach 《Monthly notices of the Royal Astronomical Society》2004,353(2):697-704
43.
Juan Pesántez Christian Birkel Giovanny M. Mosquera Pablo Peña Viviana Arízaga-Idrovo Emma Mora William H. McDowell Patricio Crespo 《水文研究》2021,35(9):e14357
Monitoring the temporal variation of solute concentrations in streams at high temporal frequency can play an important role in understanding the hydrological and biogeochemical behaviour of catchments. UV–visible spectrometry is a relatively inexpensive and easily used tool to infer those concentrations in streams at high temporal resolution. However, it is not yet clear which solutes can be modelled with such an in-situ sensor. Here, we installed a UV–visible spectrometer probe (200–750 nm) in a high-altitude tropical Páramo stream to record the wavelength absorbance at a 5-min temporal resolution. For calibration, we simultaneously sampled stream water at a 4-h frequency from February 2018 to March 2019 for subsequent laboratory analysis. Absorbance spectra and laboratory-determined solute concentrations were used to identify the best calibration method and to determine which solute concentrations can be effectively inferred using in situ spectrometry through the evaluation of six calibration methods of different mathematical complexity. Based on the Nash – Sutcliffe efficiency (NSE) and Akaike information criterion metrics, our results suggest that multivariate methods always outperformed simpler strategies to infer solute concentrations. Eleven out of 21 studied solutes (Al, DOC, Ca, Cu, K, Mg, N, Na, Rb, Si and Sr) were successfully calibrated (NSE >0.50) and could be inferred using UV–visible spectrometry even with a reduced daily sampling frequency. It is worth noting that most calibrated solutes were correlated with wavelengths (WLs) in the low range of the spectra (i.e., UV range) and showed relatively good correlation with DOC. The latter suggests that estimation of metal concentrations could be possible in other streams with a high organic load (e.g., peat dominated catchments). In situ operation of spectrometers to monitor water quality parameters at high temporal frequency (sub-hourly) can enhance the protection of human water supplies and aquatic ecosystems as well as providing information for assessing catchment hydrological functioning. 相似文献
44.
Olaf Nehlich Benjamin T. Fuller Mandy Jay Alice Mora Colin I. Smith Michael P. Richards 《Geochimica et cosmochimica acta》2011,75(17):4963-4977
This study investigates the application of sulphur isotope ratios (δ34S) in combination with carbon (δ13C) and nitrogen (δ15N) ratios to understand the influence of environmental sulphur on the isotopic composition of archaeological human and faunal remains from Roman era sites in Oxfordshire, UK. Humans (n = 83), terrestrial animals (n = 11), and freshwater fish (n = 5) were analysed for their isotope values from four locations in the Thames River Valley, and a broad range of δ34S values were found. The δ34S values from the terrestrial animals were highly variable (−13.6‰ to +0.5‰), but the δ34S values of the fish were clustered and 34S-depleted (−20.9‰ to −17.3‰). The results of the faunal remains suggest that riverine sulphur influenced the terrestrial sulphur isotopic signatures. Terrestrial animals were possibly raised on the floodplains of the River Thames, where highly 34S-depleted sulphur influenced the soil. The humans show the largest range of δ34S values (−18.8‰ to +9.6‰) from any archaeological context to date. No differences in δ34S values were found between the males (−7.8 ± 6.0‰) and females (−5.3 ± 6.8‰), but the females had a linear correlation (R2 = 0.71; p < 0.0001) between their δ15N and δ34S compositions. These δ34S results suggest a greater dietary variability for the inhabitants of Roman Oxfordshire than previously thought, with some individuals eating solely terrestrial protein resources and others showing a diet almost exclusively based on freshwater protein such as fish. Such large dietary variability was not visible by analysing only the carbon and nitrogen isotope ratios, and this research represents the largest and most detailed application of δ34S analysis to examine dietary practices (including breastfeeding and weaning patterns) during the Romano-British Period. 相似文献
45.
Gerardo Herrera Davide Notti Juan Carlos Garc��a-Davalillo Oscar Mora Geraint Cooksley M��nica S��nchez Alain Arnaud Michele Crosetto 《Landslides》2011,8(2):195-206
This paper describes the use of the Stable Point Network technique, a Persistent Scatterer Interferometry SAR technique, for
the analysis of the Portalet landslide area (Central Pyrenees, Spain). For this purpose, different SAR datasets acquired by
ERS-1, ERS-2, ENVISAT and TerraSAR-X satellites have been analysed. The use of different SAR images acquired by satellite
radar sensors operating at different microwave lengths has allowed for a comparative assessment and illustration of the advantages
and disadvantages of these satellites for landslide detection and monitoring. In the introduction, differential interferometry
and the study area are briefly described. Then the specifics of the SPN processing and the results of the different datasets
are described and compared. In Analysis of the results: the Portalet landslide area, the Portalet landslide area is introduced
and the radar displacement measurements are analysed with available geo-information data. Additionally, X-band measurements
are compared with those gathered by a ground-based SAR for a previous project. Finally, the most relevant conclusions of this
work are discussed. 相似文献
46.
J. Espinha Marques J. Samper B. Pisani D. Alvares J. M. Carvalho H. I. Chaminé J. M. Marques G. T. Vieira C. Mora F. Sodré Borges 《Environmental Earth Sciences》2011,62(6):1219-1234
High-mountain basins provide a source of valuable water resources. This paper presents hydrological models for the evaluation
of water resources in the high-mountain Zêzere river basin in Serra da Estrela, Central Portugal. Models are solved with VISUAL BALAN v2.0, a code which performs daily water balances in the root zone,
the unsaturated zone and the aquifer and requires a small number of parameters. A lumped hydrological model fails to fit measured
stream flows. Its limitations are overcome by considering the dependence of the temperature and precipitation data with elevation
and the spatial variability in hydrogeomorphological variables with nine sub-basins of uniform parameters. Model parameters
are calibrated by fitting stream flow measurements in the Zêzere river. Computed stream flows are highly sensitive to soil
thickness, whereas computed groundwater recharge is most sensitive to the interflow and percolation recession coefficients.
Interflow is the main component of total runoff, ranging from 41 to 55% of annual precipitation. High interflows are favored
by the steep relief of the basin, by the presence of a high permeability soil overlying the fractured low permeability granitic
bedrock and by the extensive subhorizontal fracturing at shallow depths. Mean annual groundwater recharge ranges from 11 to
15% of annual precipitation. It has a significant uncertainty due to uncertainties in soil parameters. This methodology proves
to be useful to handle the research difficulties regarding a complex mountain basin in a context of data scarcity. 相似文献
47.
Chad S. Lane Sally P. Horn Claudia I. Mora Kenneth H. Orvis David B. Finkelstein 《Journal of Paleolimnology》2011,45(3):323-338
Continuous terrestrial records of paleoclimate and paleovegetation that extend to the late Pleistocene are rare for the circum-Caribbean
uplands. In this study we analyzed the bulk and compound-specific carbon isotope composition of lake sediments spanning this
period from Lago de las Morrenas 1 (LM1), a glacial lake in the highlands of southern Costa Rica, for evidence of climate
and vegetation changes that may not have been apparent in previous analyses. The stable carbon isotope ratios of n-alkanes typically derived from terrestrial plants (δ13CC27–C33) indicate an increased abundance of C4 plant taxa during the late Pleistocene and earliest Holocene that may be related to decreased atmospheric carbon dioxide
concentrations, increased aridity, or habitat availability. These n-alkane isotope ratios also provide evidence of more arid conditions during the early and late Holocene, and more mesic conditions
during the middle Holocene, a pattern prevalent in other paleoclimate records from the region that is thought to be related
to millennial-scale dynamics of the intertropical convergence zone (ITCZ). The sensitivity of the LM1 paleorecord to trade
wind dynamics provides further support for the role of millennial-scale shifts in ITCZ dynamics in driving neotropical environmental
change, and indicates that the effects of ITCZ migration were not limited to the lowlands. 相似文献
48.
Target rocks,impact glasses,and melt rocks from the Lonar crater,India: Highly siderophile element systematics and Sr‐Nd‐Os isotopic signatures 下载免费PDF全文
Toni Schulz Ambre Luguet Wencke Wegner David van Acken Christian Koeberl 《Meteoritics & planetary science》2016,51(7):1323-1339
The Lonar crater is a ~0.57‐Myr‐old impact structure located in the Deccan Traps of the Indian peninsula. It probably represents the best‐preserved impact structure hosted in continental flood basalts, providing unique opportunities to study processes of impact cratering in basaltic targets. Here we present highly siderophile element (HSE) abundances and Sr‐Nd and Os isotope data for target basalts and impactites (impact glasses and impact melt rocks) from the Lonar area. These tools may enable us to better constrain the interplay of a variety of impact‐related processes such as mixing, volatilization, and contamination. Strontium and Nd isotopic compositions of impactites confirm and extend earlier suggestions about the incorporation of ancient basement rocks in Lonar impactites. In the Re‐Os isochron plot, target basalts exhibit considerable scatter around a 65.6 Myr Re‐Os reference isochron, most likely reflecting weathering and/or magma replenishment processes. Most impactites plot at distinctly lower 187Re/188Os and 187Os/188Os ratios compared to the target rocks and exhibit up to two orders of magnitude higher abundances of Ir, Os, and Ru. Moreover, the impactites show near‐chondritic interelement ratios of HSE. We interpret our results in terms of an addition of up to 0.03% of a chondritc component to most impact glasses and impact melt rocks. The magnitude of the admixture is significantly lower than the earlier reported 12–20 wt% of extraterrestrial component for Lonar impact spherules, reflecting the typical difference in the distribution of projectile component between impact glass spherules and bulk impactites. 相似文献
49.
Juan A. Alfonso Helga Handt Abrahan Mora Yaneth Vásquez José Azocar Eunice Marcano 《Marine pollution bulletin》2013
The oyster Crassostrea rhizophorae is a bivalve abundant in Venezuelan estuaries and consumed by local populations. No known values have been reported on trace metals in oysters from the central Venezuelan coast. We report the concentrations of Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V and Zn in the soft parts of C. rhizophorae, which were collected bimonthly between March 2008 and March 2009, at two sampling areas from the Central Venezuelan Coast: Buche estuary and Mochima estuary. Our results show that for each metal there is a similar temporal variation pattern. The concentrations of the heavy metals reported in this work are useful as reliable baselines and can be used for comparison in future environment studies. Concentrations in C. rhizophorae from the Buche estuary can be interpreted to be high on a global scale for Cd, Cu, Ni and Mn, indicating atypically raised bioavailabilities. 相似文献
50.
Joanna K. York George B. McManus Wim J. Kimmerer Anne M. Slaughter Toni R. Ignoffo 《Estuaries and Coasts》2014,37(3):576-588
We investigated trophic relationships involving microzooplankton in the low salinity zone of the San Francisco Estuary (SFE) as part of a larger effort aimed at understanding the dynamics of the food web supporting the endangered delta smelt, Hypomesus transpacificus. We performed 14 cascade experiments in which we manipulated the biomass of a copepod (Limnoithona tetraspina, Pseudodiaptomus forbesi, or Acartiella sinensis) and quantified responses of lower trophic levels including bacterioplankton, phytoplankton, and microzooplankton. Microzooplankton comprised a major food source for copepods; 9 out of 14 experiments showed removal of at least one group of microzooplankton by copepods. In contrast, the impact of copepods on phytoplankton was indirect; increased copepod biomass led to greater growth of phytoplankton in 3 of 14 experiments. Estimated clearance rates on microzooplankton were 4 mL day?1 for L. tetraspina and 2–6 mL day?1 for P. forbesi, whereas A. sinensis consumed mainly copepod nauplii. Complex trophic interactions, including omnivory, among copepods, microzooplankton, and different components of the phytoplankton likely obscured clear trends. The food web of the SFE is probably less efficient than previously thought, providing poor support to higher trophic levels; this inefficient food web is almost certainly implicated in the continuing low abundance of fishes, including the delta smelt that use the low salinity zone of the San Francisco Estuary. 相似文献