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991.
992.
Watershed mean transit times (MTTs) are used to characterize the hydrology of watersheds. Watershed MTTs could have important implications for water quality, as relatively long MTTs imply lengthier water retention, thereby allowing more time for pollutant transformation and more moderate release of pollutants into streams. Although estimates of MTTs are common for undisturbed watersheds, only a few studies to date have applied MTT models to urbanized watersheds. In the present study, we use δ18O to compare estimates of MTTs for paired suburban‐industrial and agricultural watersheds in Toronto, Canada. Although differences in precipitation δ18O between the two watersheds were negligible, there were significant differences in stream δ18O, suggesting differences in water transport pathways. Less damping between input precipitation δ18O and output stream δ18O in the suburban‐industrial watershed indicated a larger streamflow contribution from quick‐flow transport pathways. We applied three transit time models to quantify MTTs. Considering overall model fit, root mean square error, and uncertainty in model parameters, the exponential model performed the best of the three models. Optimized MTTs using this distribution across the suburban‐industrial subwatersheds ranged from 2.1 to 2.9 months, whereas those in the agricultural subwatersheds ranged from 2.7 to 7.5 months. The relatively small difference between urban and agricultural MTTs coincides with observations elsewhere. Model efficiencies could potentially be improved, and MTTs estimated more reliably, with a higher sampling frequency that captures a greater volume of overall discharge. Overall, this work provides a distinct first glimpse into the separation of MTTs between paired watersheds with such a large contrast in their land use. 相似文献
993.
Northern Svalbard represents a basement high surrounded by the Norwegian‐Greenland Sea/Fram Strait, Eurasian Basin, the Barents Shelf and the onshore Central Tertiary Basin (CTB). Published apatite fission track (AFT) data indicate Mesozoic differential, fault‐controlled uplift and exhumation of the region. Thermal history modelling of published and new AFT and (U–Th–Sm)/He ages of 51–153 Ma in the context of regional stratigraphy and geomorphology implies at least two, possibly three, uplift and exhumation stages since late Mesozoic, separated by episodes of subsidence and sediment deposition. Late Cretaceous/Palaeocene exhumation and subsequent burial appear to be related with the transition of compressional to transpressional collision of Svalbard and Greenland during the Eurekan Orogeny. Renewed exhumation since the Oligocene probably results from passive margin formation after the separation of Svalbard and Greenland, when a new offshore sedimentary basin opened west of Svalbard. Final uplift since the Miocene eventually re‐exposed the palaeosurface of northern Svalbard. 相似文献
994.
We compare horizontal velocities, vertical magnetic fields, and the evolution of trees of fragmenting granules (TFG, also named families of granules) derived in the quiet Sun at disk center from observations at solar minimum and maximum of the Solar Optical Telescope (SOT on board Hinode) and results of a recent 3D numerical simulation of the magneto-convection. We used 24-hour sequences of a 2D field of view (FOV) with high spatial and temporal resolution recorded by the SOT Broad band Filter Imager (BFI) and Narrow band Filter Imager (NFI). TFG were evidenced by segmentation and labeling of continuum intensities. Horizontal velocities were obtained from local correlation tracking (LCT) of proper motions of granules. Stokes V provided a proxy of the line-of-sight magnetic field (BLOS). The MHD simulation (performed independently) produced granulation intensities, velocity, and magnetic field vectors. We discovered that TFG also form in the simulation and show that it is able to reproduce the main properties of solar TFG: lifetime and size, associated horizontal motions, corks, and diffusive index are close to observations. The largest (but not numerous) families are related in both cases to the strongest flows and could play a major role in supergranule and magnetic network formation. We found that observations do not reveal any significant variation in TFG between solar minimum and maximum. 相似文献
995.
Understanding the identity and stability of the hydrolysis products of metals is required in order to predict their behavior in natural aquatic systems. Despite this need, the hydrolysis constants of many metals are only known over a limited range of temperature and ionic strengths. In this paper, we show that the hydrolysis constants of 31 metals [i.e. Mn(II), Cr(III), U(IV), Pu(IV)] are nearly linearly related to the values for Al(III) over a wide range of temperatures and ionic strengths. These linear correlations allow one to make reasonable estimates for the hydrolysis constants of +2, +3, and +4 metals from 0 to 300°C in dilute solutions and 0 to 100°C to 5 m in NaCl solutions. These correlations in pure water are related to the differences between the free energies of the free ion and complexes being almost equal $$ \Updelta {\text{G}}^\circ \left( {{\text{Al}}^{3 + } } \right) - \Updelta {\text{G}}^\circ \left( {{\text{Al}}\left( {\text{OH}} \right)_{j}^{{\left( {3 - j} \right)}} } \right) \cong \Updelta {\text{G}}^\circ \left( {{\text{M}}^{n + } } \right) - \Updelta {\text{G}}^\circ \left( {{\text{M}}\left( {\text{OH}} \right)_{j}^{{\left( {n - j} \right)}} } \right) $$ The correlation at higher temperatures is a result of a similar relationship between the enthalpies of the free ions and complexes $$ \Updelta {\text{H}}^\circ \left( {{\text{Al}}^{3 + } } \right) - \Updelta {\text{H}}^\circ \left( {{\text{Al}}\left( {\text{OH}} \right)_{j}^{3 - j} } \right) \cong \Updelta {\text{H}}^\circ \left( {{\text{M}}^{n + } } \right) - \Updelta {\text{H}}^\circ \left( {{\text{M}}\left( {\text{OH}} \right)_{j}^{n - j} } \right) $$ The correlations at higher ionic strengths are the result of the ratio of the activity coefficients for Al(III) being almost equal to that of the metal. $$ \gamma \left( {{\text{M}}^{n + } } \right)/\gamma \left( {{\text{M}}\left( {\text{OH}} \right)_{j}^{n - j} } \right) \cong \gamma \left( {{\text{Al}}^{3 + } } \right)/\gamma \left( {{\text{Al}}\left( {\text{OH}} \right)_{j}^{3 - j} } \right) $$ The results of this study should be useful in examining the speciation of metals as a function of pH in natural waters (e.g. hydrothermal fresh waters and NaCl brines). 相似文献
996.
Lead chloride formation constants at 25°C were derived from analysis of previous spectrophotometrically generated observations
of lead speciation in a variety of aqueous solutions (HClO4–HCl and NaCl–NaClO4 mixtures, and solutions of MgCl2 and CaCl2). Specific interaction theory analysis of these formation constants produced coherent estimates of (a) PbCl+,
\textPbCl20 {\text{PbCl}}_{2}^{0} , and PbCl3− formation constants at zero ionic strength, and (b) well-defined depictions of the dependence of these formation constants
on ionic strength. Accompanying examination of a recent IUPAC critical assessment of lead formation constants, in conjunction
with the spectrophotometrically generated formation constants presented in this study, revealed significant differences among
various subsets of the IUPAC critically selected data. It was found that these differences could be substantially reduced
through reanalysis of the formation constant data of one of the subsets. The resulting revised lead chloride formation constants
are in good agreement with the formation constants derived from the earlier spectrophotometrically generated data. Combining
these data sets provides an improved characterization of lead chloride complexation over a wide range of ionic strengths:
|
log \text Cl b 1 = 1. 4 9 1- 2.0 4 I 1/ 2 ( 1+ 1. 5 I 1/ 2 ) - 1 + 0. 2 3 8 I log \text Cl b 2 = 2.0 6 2- 3.0 6 I 1/ 2 ( 1+ 1. 5 I 1/ 2 ) - 1 + 0. 3 6 9 I log \text Cl b 3 = 1. 8 9 9- 3.0 6 I 1/ 2 ( 1+ 1. 5 I 1/ 2 ) - 1 + 0. 4 3 9 I. \begin{gathered} {\log}\,{}_{\text{ Cl}} \beta_{ 1} = 1. 4 9 1- 2.0 4\,I^{ 1/ 2} \left( { 1+ 1. 5\,I^{ 1/ 2} } \right)^{ - 1} +\,0. 2 3 8\,I \hfill \\ {\log}\,{}_{\text{ Cl}} \beta_{ 2} = 2.0 6 2- 3.0 6\,I^{ 1/ 2} \left( { 1+ 1. 5\,I^{ 1/ 2} } \right)^{ - 1} +\,0. 3 6 9\,I \hfill \\ {\log}\,{}_{\text{ Cl}} \beta_{ 3} = 1. 8 9 9- 3.0 6\,I^{ 1/ 2} \left( { 1+ 1. 5\,I^{ 1/ 2} } \right)^{ - 1} +\,0. 4 3 9\,I. \hfill \\ \end{gathered} 相似文献
997.
Flavio S. Anselmetti Ruth Drescher-Schneider Heinz Furrer Hans Rudolf Graf Sally E. Lowick Frank Preusser Marc A. Riedi 《Swiss Journal of Geoscience》2010,103(3):345-361
A 30 m-deep drill core from a glacially overdeepened trough in Northern Switzerland recovered a ~180 ka old sedimentary succession that provides new insights into the timing and nature of erosion–sedimentation processes in the Swiss lowlands. The luminescence-dated stratigraphic succession starts at the bottom of the core with laminated carbonate-rich lake sediments reflecting deposition in a proglacial lake between ~180 and 130 ka ago (Marine Isotope Stage MIS 6). Anomalies in geotechnical properties and the occurrence of deformation structures suggest temporary ice contact around 140 ka. Up-core, organic content increases in the lake deposits indicating a warming of climate. These sediments are overlain by a peat deposit characterised by pollen assemblages typical of the late Eemian (MIS 5e). An abrupt transition following this interglacial encompasses a likely hiatus and probably marks a sudden lowering of the water level. The peat unit is overlain by deposits of a cold unproductive lake dated to late MIS 5 and MIS 4, which do not show any direct influence from glaciers. An upper peat unit, the so-called «Mammoth peat», previously encountered in construction pits, interrupts this cold lacustrine phase and marks more temperate climatic conditions between 60 and 45 ka (MIS 3). In the upper part of the core, a succession of fluvial and alluvial deposits documents the Late Glacial and Holocene sedimentation in the basin. The sedimentary succession at Wehntal confirms that the glaciation during MIS 6 did not apparently cause the overdeepening of the valley, as the lacustrine basin fill covering most of MIS 6 is still preserved. Consequently, erosion of the basin is most likely linked to an older glaciation. This study shows that new dating techniques combined with palaeoenvironmental interpretations of sediments from such overdeepened troughs provide valuable insights into the past glacial history. 相似文献
998.
Wolfgang Schirmer Josef Weber Valerian Bachtadse Marcelle BouDagher-Fadel Friedrich Heller Frank Lehmkuhl Ioannis Panayides Ursula Schirmer 《Central European Journal of Geosciences》2010,2(4):514-523
Southern Cyprus is situated within a mosaic terrane that has been fragmented between the northward drifting African and Arabian plates and the Eurasian plate. Enormous uplift of the earth mantle in the Tróodos Mountains is explained by two models. The subduction model explains subduction along the Cyprean arc to be the driving force for uplift whereas after the restraining bend model westward squeezing of Cyprus along strike-slip faulting is responsible for the enormous uplift at restraining bends. Since its emergence as an island in early Miocene times, landscape formation on Cyprus has been strongly controlled by this uplift. Until the Plio-Pleistocene, a strait belt separated the southern unroofed ophiolitic core region-the Tróodos Mountains-from the folded Kyrenia range to the north. This former sea basin, nowadays the Mesaoría Basin, is linked with the Tróodos Mountains by a dissected glacis with a thick cover of river deposits. The highest and oldest river deposits (Apalós Formation) were studied in the Vlokkariá hill southwest of Lefkosía. The 45.5 m thick Apalós Formation of Early Pleistocene age exhibits 24 sedimentary units (Fluviatile Series). Their magnetostratigraphical characters align with the Matuyama chron including the Olduvai and Jaramillo subchrons thus comprising about 1.15 Ma within the Early Pleistocene. This fluvial stack indicates a very flat and deeply lying river environment flowing from a slowly uplifting Tróodos hinterland. It happened during the end of Early Pleistocene when the enhanced Tróodos uplift started the dissection of the stacked river plain. 相似文献
999.
Frank Kreienkamp Arne Spekat Wolfgang Enke 《Theoretical and Applied Climatology》2010,102(1-2):205-212
In this investigation, a circulation index was used which is capable of tracing blocked states of the hemispheric circulation which has a relevance for a mid-latitude window between 40° and 60°N and between 30°W and 30°E. Results with respect to the seasonality of blocking situations are presented. Additionally, it is shown to which degree the circulation conditions, as they are simulated by the ECHAM5-MPI/OM1 climate model, have a tendency to exhibit blocking. Finally, results are presented which indicate the developments in blocking if the index is applied to scenario runs of the model. 相似文献
1000.
A glacier parameterization scheme has been developed and implemented into the regional climate model REMO. The new scheme
interactively simulates the mass balance as well as changes of the areal extent of glaciers on a subgrid scale. The temporal
evolution and the general magnitude of the simulated glacier mass balance in the European Alps are in good accordance with
observations for the period 1958–1980, but the strong mass loss towards the end of the twentieth century is systematically
underestimated. The simulated decrease of glacier area in the Alps between 1958 and 2003 ranges from −17.1 to −23.6%. The
results indicate that observed glacier mass balances can be approximately reproduced within a regional climate model based
on simplified concepts of glacier-climate interaction. However, realistic results can only be achieved by explicitly accounting
for the subgrid variability of atmospheric parameters within a climate model grid box. 相似文献
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