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251.
Effect of cross‐section interpolated bathymetry on 2D hydrodynamic model results in a large river 下载免费PDF全文
Two‐dimensional (2D) hydrodynamic models have been increasingly used to quantify aquatic habitat and stream processes, such as sediment transport, streambed morphological evolution, and inundation extents. Because river topography has a strong influence on predicted hydraulic conditions, 2D models require accurate and detailed bathymetric data of the stream channel and surrounding floodplains. Besides collection of mass points to construct high‐resolution three‐dimensional surfaces, bathymetries may be interpolated from cross‐sections. However, limited information is available on the effects of cross‐section spacing and the derived interpolated bathymetry on 2D model results in large river systems. Here, we investigated the effects of cross‐section spacing on flow properties simulated with 2D modeling at low, medium and high discharges in two morphologically different reaches, a simple (almost featureless with low sinuosity) and a complex (presenting pools, riffles, runs, contractions and expansions) reach of the Snake River (Idaho, USA), the tenth largest river in the United States in terms of drainage area. We compared the results from 2D models developed with complete channel bathymetry acquired with multibeam sonar data and photogrammetry, with 2D model results that were developed using interpolated topography from uniformly distributed transects. Results indicate that cross‐sections spaced equal to or greater than 2 times the average channel width (W*) smooths the bathymetry and suppresses flow structures. Conversely, models generated with cross‐sections spaced at 0.5 and 1 W* have stream flow properties, sediment mobility and spatial habitat distribution similar to those of the complete bathymetry. Furthermore, differences in flow properties between interpolated and complete topography models generally increase with discharge and with channel complexity. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
252.
Inorganic nitrogen control in wastewater treatment ponds from a fish farm (Orbetello, Italy): denitrification versus Ulva uptake 总被引:2,自引:0,他引:2
Bartoli M Nizzoli D Naldi M Vezzulli L Porrello S Lenzi M Viaroli P 《Marine pollution bulletin》2005,50(11):1386-1397
The aim of this study was to quantify the N removal efficiency of an Ulva-based phytotreatment system receiving wastewaters from a land-based fish farm (Orbetello, Italy), to identify the main biogeochemical pathways involved and to provide basic guidelines for treatment implementation and management. Fluxes of O2 and nutrients in bare and in Ulva colonised sediments were assessed by light/dark core incubations; denitrification by the isotope pairing technique and Ulva growth by in situ incubation of macroalgal disks in cages. O2 and nutrient budgets were estimated as sum of individual processes and further verified by 24-h investigations of overall inlet and outlet loads. Ulva uptake (up to 7.8 mmol Nm(-2) h(-1)) represented a net sink for water column and regenerated NH4+ whilst N removal via denitrification (10-170 micromol Nm(-2) h(-1)) accounted for a small percentage of inorganic nitrogen load (<5%). Laboratory experiments demonstrated a high potential for denitrification (over 800 microM Nm(-2) h(-1)) indicating that N loss could be enhanced. The control of Ulva standing stocks by optimised harvesting of surplus biomass may represent an effective strategy to maximise DIN removal and could result in the assimilation of approximately 50% of produced inorganic nitrogen. 相似文献
253.
Mount Etna is an open conduit volcano, characterised by persistent activity, consisting of degassing and explosive phenomena
at summit craters, frequent flank eruptions, and more rarely, eccentric eruptions. All eruption typologies can give rise to
lava flows, which represent the greatest hazard by the volcano to the inhabited areas. Historical documents and scientific
papers related to the 20th century effusive activity have been examined in detail, and volcanological parameters have been
compiled in a database. The cumulative curve of emitted lava volume highlights the presence of two main eruptive periods:
(a) the 1900–1971 interval, characterised by a moderate slope of the curve, amounting to 436 × 106 m3 of lava with average effusion rate of 0.2 m3/s and (b) the 1971–1999 period, in which a significant increase in eruption frequency is associated with a large issued lava
volume (767 × 106 m3) and a higher effusion rate (0.8 m3/s). The collected data have been plotted to highlight different eruptive behaviour as a function of eruptive periods and
summit vs. flank eruptions. The latter have been further subdivided into two categories: eruptions characterised by high effusion
rates and short duration, and eruptions dominated by low effusion rate, long duration and larger volume of erupted lava. Circular
zones around the summit area have been drawn for summit eruptions based on the maximum lava flow length; flank eruptions have
been considered by taking into account the eruptive fracture elevation and combining them with lava flow lengths of 4 and
6 km. This work highlights that the greatest lava flow hazard at Etna is on the south and east sectors of the volcano. This
should be properly considered in future land-use planning by local authorities. 相似文献
254.
Jun-ichi Matsuda Teruyuki Maruoka Daniele Luigi Pinti Christian Koeberl 《Meteoritics & planetary science》1996,31(2):273-277
Abstract— A philippinite with a large bubble (volume ?5 cm3) was crushed in a specifically constructed device under vacuum. The total pressure, the major gas components, and the concentration and the isotopic composition of noble gases in the trapped gas were measured. The total gas pressure was found to be low, ~10?4 atm. Compared to terrestrial atmosphere, the abundances of He and Ne are considerably more enriched than the concentrations of the heavy noble gases. Unusually high 20Ne/22Ne and 21Ne/22Ne ratios were measured in the bubble gas. These ratios are higher than values expected for any steady state process and are interpreted to reflect very fast nonsteady state diffusion in the early stages of tektite formation. 相似文献
255.
Anita Cadoux Daniele L. Pinti Cyril Aznar Sergio Chiesa Pierre-Yves Gillot 《Lithos》2005,81(1-4):121-151
A new geochronological and geochemical study of the volcanic rocks of the Ponza and Palmarola Islands, Pontine Archipelago, has been carried out. This archipelago is located along the boundary between the Italian continental shelf and the opening Tyrrhenian basin. It is a key area to study volcanism related to the opening of the Tyrrhenian Sea. Ponza is the oldest felsic magmatic manifestation in the central Tyrrhenian area. Previous studies suggested that Ponza volcanic activity began before 5 Ma. Twenty-five new K–Ar ages constrain the volcanic activity (rhyolitic hyaloclastites and dykes) to the last 4.2 Ma, with two episodes of quiescence between 3.7 and 3.2 Ma and between 2.9 and 1.0 Ma. A new volcanic episode dated at 3.2–2.9 Ma has been identified on the central and southern Ponza, with emplacement of pyroclastic units. At 1.0 Ma, a trachytic episode ended the volcanic activity. The near island of Palmarola exhibits rhyolitic hyaloclastites and domes dated between 1.6 and 1.5 Ma, indicating that the island was entirely built during the Early Pleistocene in a short span of time of ca. 120 ka. Although only 6–8 km apart, the two islands display significantly different geochemical signatures. Ponza rhyolites show major and trace element compositions representative of orogenic magmas of subduction/collision zones: high-K calc-alkaline and metaluminous rhyolites (Agpaitic Index [AI] and Alumina Saturation Index [ASI] <1), high LILE/HFSE (Th/Ta=16–21) and LREE/HFSE ratios (La/Nb>3), and Nb–Ta negative anomalies. In Palmarola, the orogenic character is also present, but much less marked than in Ponza: rhyolites have a peralkaline character (AI>1), lower LILE/HFSE (Th/Ta=11–15), low LREE/HFSE ratios (La/Nb=1–2) close to those of anorogenic lavas, and the Nb–Ta negative anomalies are almost absent. Y/Nb ratios indicate different magmatic sources, one similar to island-arc or active continental margin basalts for Ponza rhyolites, and the others probably involving an OIB type component for Palmarola rhyolites and Ponza trachytes. Palmarola volcanics represent a transitional magmatism: although a preserved collisional geochemical imprint, they show geochemical features approaching those of anorogenic lavas erupted in a within-plate context. The change of magmatism evidenced in this study can be related to the tectonic evolution of the area. Indeed, Hf, Ta and Rb contents suggest that the oldest Pliocene rhyolites of Ponza would emplace in a syn- to late-collisional setting, while the younger Pleistocene rhyolites of Palmarola would be emplaced in a post-collisional setting in which the orogenic character (Th/Ta) decreases and mantle influence (Nb/Ta) increases. Geochemical modeling strongly suggests that the Palmarola rhyolites represent the waning stages of a subduction-related magmatism. The K–Ar datings allow us to estimate precisely the transition of magmatism to last less than 1.3 Ma. The transitional magmas may be the result of the upwelling of asthenospheric mantle inducing melting of a metasomatized lithospheric mantle and the mixing between these two sources. This upwelling could occur during the extension of the Tyrrhenian basin, caused by the slab retreat and steepening, or during a process of slab break-off starting in the Pliocene. 相似文献
256.
Daniele Boyer Jean-Louis Le Mouël Vincent Courtillot 《Earth and Planetary Science Letters》1981,52(2):372-380
A very broad band (10?3 to 104 Hz) magnetotelluric investigation of the axial zone of the Ghoubbet-Asal rift (Djibouti) has revealed a shallow (2–4 km) magma chamber which can be mapped in some detail. The suggested roof of the chamber is shallowest very close to the Ardoukoba volcano which was built during the November 1978 rifting episode. 相似文献
257.
We investigate here recent (1980–2009) climate variability in the upper Karakoram, Northern Pakistan, of particular interest given the peculiar glacier behavior during the last two decades. Differently from other glacierized regions in the Hindu Kush–Karakoram–Himalaya region, glaciers in the Karakoram display limited ice thinning, and in some cases advancing has been detected. Climate analysis is required to describe recent (i.e., last three decades) variability, to aid highlighting of the factors driving glacier evolution. Starting from monthly data, we analyze seasonal values of total precipitation, number of wet days, maximum (max) and minimum (min) air temperature, max precipitation in 24 h, and cloud cover for 17 weather stations in the upper Karakoram, clustered within three climatic regions as per use of principal components analysis. We detect possible nonstationarity in each of these regions by way of (1) linear regression, (2) moving window average, and (3) Mann–Kendall test, also in progressive form, to detect the onset date of possible trends. We then evaluate linear correlation coefficients between Northern Atlantic Oscillation (NAO) index and climate variables to assess effectiveness of teleconnections, claimed recently to affect climate in this area. Also, we compare temperature within the investigated zone against global temperature anomalies, to evidence enhanced warming within this area. We found mostly nonsignificant changes of total precipitation, unless for few stations displaying increase in Chitral-Hindu Kush region and Northwest Karakoram, or Gilgit area, and decrease in Western Himalaya, Kotli region. Max precipitation is mostly unchanged, unless for slight increase in Chitral and Gilgit areas, and slight decrease in Kotli region. Number of wet days is mostly increasing in Gilgit area, and decreasing in Chitral area, with no clear signal in Kotli region. Min temperatures increase always but during Summer, when decreasing values are detected, especially for Gilgit and Chitral regions. Max temperatures are found to increase everywhere. Cloud cover is significantly increasing in Gilgit area, but decreasing otherwise, especially in Kotli region. Max temperature regime is significantly positively correlated against global thermal anomaly, while min temperature regime is nonsignificantly negatively correlated. Max and min temperatures seem mostly negatively correlated to NAO. Some dependence of trend intensity for the considered variables against altitude is found, different for each region, suggesting that investigation of weather variables at the highest altitudes is warranted to discriminate further climate variability in the area. 相似文献
258.
Quillon Harpham Olalla Gimeno Antonio Parodi Daniele D’Agostino 《Earth Science Informatics》2017,10(2):219-234
The purpose of this paper is to report on and analyse an international consultation into hydro-meteorological e-Science environments with the objective of identifying key functions and features together with exploring show-stopping issues and organisational structure. Transatlantic experiences were compared and contrasted. Including strong participation from both Europe and the USA with high quality responses from experienced practitioners, the consultation was undertaken as part of a joint initiative and took the form of an online questionnaire supported by a set of stakeholder interviews and other discussions. Topics included were functions and features such as provision of numerical models and data, usability, and ease of access; show-stopping issues such as flexibility, reliability and longevity; centralised and distributed structures, and funding models. The results demonstrated a broadly similar set of experiences and implied a future as an evolution of that which exists today. The consultation exercise ran alongside the development of the DRIHM e-Infrastructure which had, in itself, already benefitted from the prior DRIHMS consultation. Results were fed in to the development process at appropriate intervals allowing the consultation to shape the resultant services. 相似文献