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131.
Pamela L. Nagler Armando Barreto-Muñoz Sattar Chavoshi Borujeni Christopher J. Jarchow Martha M. Gómez-Sapiens Hamideh Nouri Stefanie M. Herrmann Kamel Didan 《水文研究》2020,34(25):4851-4883
Hydrological and bioclimatic processes that lead to drought may stress plants and wildlife, restructure plant community type and architecture, increase monotypic stands and bare soils, facilitate the invasion of non-native plant species and accelerate soil erosion. Our study focuses on the impact of a paucity of Colorado River surface flows from the United States (U.S.) to Mexico. We measured change in riparian plant greenness and water use over the past two decades using remotely sensed measurements of vegetation index (VI), evapotranspiration (ET) and a new annualized phenology assessment metric (PAM) for ET. We measure these long-term (2000–2019) metrics and their short-term (2014–2019) response to an environmental pulse flow in 2014, as prescribed under Minute 319 of the 1944 Water Treaty between the two nations. In subsequent years, small-directed flows were provided to restoration areas under Minute 323. We use 250 m MODIS and 30 m Landsat imagery to evaluate three vegetation indices (NDVI, EVI, EVI2). We select EVI2 to parameterize an optical-based ET algorithm and test the relationship between ET from Landsat and MODIS by regression approaches. Our analyses show significant decreases in VIs and ET for both the 20-year and post-pulse 5-year periods. Over the last 20 years, EVI Landsat declined 34% (30% by EVIMODIS) and ETLandsat-EVI declined 38% (27% by ETMODIS-EVI), overall ca. 1.61 mm/day or 476 mm/year drop in ET; using PAM ETLandsat-EVI the drop was from 1130 to 654 mm/year. Over the 5 years since the 2014 pulse flow, EVILandsat declined 20% (13% by EVIMODIS) and ETLandsat-EVI declined 23% (4% by ETMODIS-EVI) with a 0.77 mm/day or a 209 mm/year 5-year drop in ET; using PAM ETLandsat-EVI the drop was from 863 to 654 mm/year. Data and change maps show the pulse flow contributed enough water to slow the rate of loss, but only for the very short-term (1–2 years). These findings are critically important as they suggest further deterioration of biodiversity, wildlife habitat and key ecosystem services due to anthropogenic diversions of water in the U.S. and Mexico and from land clearing, fires and plant-related drought which affect hydrological processes. 相似文献
132.
133.
Quantification of both normal and right‐lateral late Quaternary activity along the Kongur Shan extensional system,Chinese Pamir
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The Kongur Shan Extensional System (KES) is a ~250 km long normal fault system that bounds the Muji–Tashkorgan basin of the Chinese Pamir. It accommodates E–W extension due to the northward indentation of the Pamir salient, and its late Miocene activity has been the focus of tectonic studies. While the KES has a main normal component, ~WNW–ESE‐striking segments have an additional right‐lateral strike‐slip component. Here, we quantify late Quaternary horizontal and vertical slip rates at three locations along the KES, where active faults cut and offset abandoned geomorphic features. We find rates of >3–4 mm a?1 (horizontal) along the western Muji fault in the north and of ~1.7 mm a?1 (vertical) and ~1 mm a?1 (horizontal) along the Kongur Shan fault in the south during the late Pleistocene. These rates are consistent with GPS and late Miocene rates, and imply that E–W extension in the Muji–Tashkorgan basin is faster in the north than in the south. 相似文献
134.
Eiliv Larsen Astrid Lyså Ármann Höskuldsson Jan G. Davidsen Marie J. Nadeau Michael Power Georgios Tassis Stefan Wastegård 《第四纪科学杂志》2021,36(2):180-190
We provide the first documentation of tectonic deformation resulting from a volcanic eruption on the island of Jan Mayen. Vertical displacement of about 14 m southwest of the stratovolcano Beerenberg is associated with an eruption in ad 1732 on its southeastern flank. The age of the uplift event is bracketed by radiocarbon-dated driftwood buried by material deposited due to uplift, and by tephra from this eruption. Constraints, inferred from radiocarbon ages alone, allow for the possibility that uplift was completed prior to the ad 1732 eruption. However, the occurrence of tephra in the sediment column indicates that some displacement was ongoing during the eruption but ceased before the eruption terminated. We attribute the tectonic deformation to intrusion of shallow magma associated with the volcanic eruption. Our results complement previous studies of volcanic activity on Jan Mayan by providing precise age constraints for past volcanic activity. Also, it raises new hypotheses regarding the nature, timing and prevalence of precursor tectonic events to Jan Mayan eruptions. The uplift caused the complete isolation of a coastal lake by closing its outlet to the sea, thus landlocking the facultative migratory fish species Arctic charr (Salvelinus alpinus). 相似文献
135.
Antimony speciation in saline hydrothermal fluids: A combined X-ray absorption fine structure spectroscopy and solubility study 总被引:2,自引:0,他引:2
Gleb S. Pokrovski Anastassia Yu. Borisova Jean-Louis Hazemann Marie Tella 《Geochimica et cosmochimica acta》2006,70(16):4196-4214
Solubility of senarmontite (Sb2O3, cubic) in pure water and NaCl-HCl aqueous solutions, and local atomic structure around antimony in these fluids were characterized using in situ X-ray absorption fine structure (XAFS) spectroscopy at temperatures to 450 °C and pressures to 600 bars. These experiments were performed using a new X-ray cell which allows simultaneous measurement of the absolute concentration of the absorbing element in the fluid, and atomic environment around the absorber. Results show that aqueous Sb(III) speciation is dominated by the complex in pure water, mixed Sb-hydroxide-chloride complexes in acidic NaCl-HCl solutions (2 m NaCl-0.1 m HCl), and by Sb-chloride species in concentrated HCl solutions (3.5 m HCl). Interatomic Sb-O and Sb-Cl distances in these complexes range from 1.96 to 1.97 Å and from 2.37 to 2.47 Å, respectively. These structural data, together with senarmontite solubility determined from XAFS spectra, were complemented by batch-reactor measurements of senarmontite and stibnite (Sb2S3, rhombic) solubilities over a wide range of HCl and NaCl concentrations from 300 to 400 °C. Analysis of the whole dataset shows that Sb(III) speciation in high-temperature moderately acid (pH > 2-3) Cl-rich fluids is dominated by mixed hydroxy-chloride species like Sb(OH)2Cl° and Sb(OH)3Cl−, but other species containing two or three Cl atoms appear at higher acidities and moderate temperatures (?300 °C). Calculations using stability constants retrieved in this study indicate that mixed hydroxy-chloride complexes control antimony transport in saline high-temperature ore fluids at acidic conditions. Such species allow for a more effective Sb partitioning into the vapor phase during boiling and vapor-brine separation processes occurring in magmatic-hydrothermal systems. Antimony hydroxy-chloride complexes are however minor in the neutral low- to moderate-temperature solutions (?250-300 °C) typical of Sb deposits formation; the antimony speciation in these systems is dominated by Sb(OH)3 and potentially Sb-sulfide species. 相似文献
136.
Doppler Lidar Measurements of Vertical Velocity Spectra in the Convective Planetary Boundary Layer 总被引:1,自引:1,他引:0
We utilized a Doppler lidar to measure spectra of vertical velocity w from 390m above the surface to the top of the daytime convective boundary layer (CBL). The high resolution 2μm wavelength
Doppler lidar developed by the NOAA Environmental Technology Laboratory was used to detect the mean radial velocity of aerosol
particles. It operated continuously during the daytime in the zenith-pointing mode for several days in summer 1996 during
the Lidars-in-Flat-Terrain experiment over level farmland in central Illinois, U.S.A. The temporal resolution of the lidar
was about 1 s, and the range-gate resolution was about 30m. The vertical cross-sections were used to calculate spectra as
a function of height with unprecedented vertical resolution throughout much of the CBL, and, in general, we find continuity
of the spectral peaks throughout the depth of the CBL. We compare the observed spectra with previous formulations based on
both measurements and numerical simulations, and discuss the considerable differences, both on an averaged and a case-by-case
basis. We fit the observed spectra to a model that takes into account the wavelength of the spectral peak and the curvature
of the spectra across the transition from low wavenumbers to the inertial subrange. The curvature generally is as large or
larger than the von Kármán spectra. There is large case-to-case variability, some of which can be linked to the mean structure
of the CBL, especially the mean wind and the convective instability. We also find a large case-to-case variability in our
estimates of normalized turbulent kinetic energy dissipation deduced from the spectra, likely due for the most part to a varying
ratio of entrainment flux to surface flux. Finally, we find a relatively larger contribution to the low wavenumber region
of the spectra in cases with smaller shear across the capping inversion, and suggest that this may be due partly to gravity
waves in the inversion and overlying free atmosphere. 相似文献
137.
Anne Marie de Grosbois 《Environmental Earth Sciences》2010,60(3):671-676
Events
Upcoming international events 相似文献138.
139.
The objective of this study was to investigate the possible links between regional climate, fire and vegetation at the small spatial scale during the early and mid Holocene in southern Sweden using pollen, plant macrofossil and charcoal records from a small bog. The fire history was compared with climate reconstructions inferred from various proxy records in the study region. High fire activity is related to dry and warm climate around 8550, 7600, 5500–5100 and 4500 cal. a BC. Low fire activity ca. 6500–6000 and 4750 BC may correspond to the widespread ‘8.2 k event’ (ca. 6200 BC) recorded across the North Atlantic region, and a later, brief period of increased precipitation, respectively. The decrease in broadleaved trees culminating ca. 6500–6000 BC correlates with the ‘8.2 k event’. A long mid Holocene period with low fire activity (ca. 4350–1000 BC) agrees with the pattern emerging for Europe from the global charcoal database, and may correspond to generally wetter and cooler conditions. High fire activity ca. 8550 BC probably triggered the local establishment of Corylus. Warmer and drier conditions (and high fire activity) ca. 7600 BC might have favoured the establishment of Alnus, Quercus and Tilia. The fire‐adapted Pinus maintained important populations throughout the early and mid Holocene. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
140.