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81.
A geochemical and end‐member mixing analysis (EMMA) is undertaken in Devil Canyon catchment, located in southern California, to further understanding of watershed behaviour and source water contributions after an acute and extensive wildfire. Physical and chemical transformations in post‐fire watersheds are known to increase overland flow and decrease infiltration, mainly due to formation of a hydrophobic layer at, or near, the soil surface. However, less is known about subsurface flow response in burned watersheds. The current study incorporates EMMA to evaluate and quantify source water contributions before, and after, a catchment affected by wildfires in southern California during the fall of 2003. Pre‐ and post‐fire stream water data were available at several sampling sites within the catchment, allowing the identification of contributing water sources at varying spatial scales. Proposed end‐member observations (groundwater, overland flow, shallow subsurface flow) were also collected to constrain and develop the catchment mixing model. Post‐fire source water changes are more evident in the smaller and faster responding sub‐basin (interior sampling point). Early post‐fire storm events are dominated by overland flow with no significant soil water or groundwater flow contribution. Inter‐storm streamwater in this smaller basin shows an increase in groundwater and a decrease in soil water. In the larger, baseflow‐dominated system, source water components appear less affected by fire. A slight increase in lateral flow is observed with only a slight decrease in baseflow. Changes in the post‐fire flow regimes affect nutrient loading and chemical response of the basin. Relatively rapid recovery of the chaparral ecosystem is evidenced, with active re‐growth and evapotranspiration evidenced by the fourth post‐fire rainy season. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
82.
Lawrence M. Mayer Linda L. Schick Thomas S. Bianchi Laura A. Wysocki 《Marine Chemistry》2009,113(1-2):123-128
Several chemical markers of organic matter source and age are shown to be susceptible to light-induced alteration. To test for the photochemical lability of markers previously employed for sediments from the Louisiana coastal zone, we subjected sediments under resuspension conditions to simulated sunlight, and monitored changes in C:N and Br:OC ratios, δ13C, Δ14C, and lignin composition. Markers of terrigenous origin (high C:N, lignin) decreased and δ13C became enriched in sediments containing primarily terrigenous organic matter, while a marker of marine organic matter (Br:OC) decreased in samples containing significant contributions from this source. Preferential loss of 14C from all sediments indicated enhanced photochemical lability of organic matter of relatively recent origin, consistent with the changes in chemical markers. Most, but not all, experimental alterations are consistent with field distributions of these markers. Relatively small experimental changes in the markers in combination with confounding processes in the environment, however, prevent these parallel trends from providing any more than a consistency test for the importance of photochemical reactions in this region. 相似文献
83.
84.
Italo Foppiani John M. Hill Matteo Lombini Giovanni Bregoli Giuseppe Cosentino Emiliano Diolaiti Thomas M. Herbst Giancarlo Innocenti Daniel Meschke Douglas L. Miller Ralf-Rainer Rohloff Laura Schreiber 《Experimental Astronomy》2011,31(2-3):115-130
We describe the design, integration, and operation of the infrared test cameras for the commissioning of the Large Binocular Telescope. The design and construction phase lasted slightly more than one year from February 2007 to April 2008 and was the result of a joint collaboration among INAF Osservatorio Astronomico di Bologna, Università di Bologna Dipartimento di Astronomia (Italy) and the Max-Planck-Institut für Astronomie (Heidelberg, Germany). Thereafter, the camera was delivered to the LBT Observatory (USA) for commissioning of the telescope active optics and, more recently, for commissioning of the first light adaptive optics. 相似文献
85.
Chemistry of atmospheres formed during accretion of the Earth and other terrestrial planets 总被引:1,自引:0,他引:1
We used chemical equilibrium and chemical kinetic calculations to model chemistry of the volatiles released by heating different types of carbonaceous, ordinary and enstatite chondritic material as a function of temperature and pressure. Our results predict the composition of atmospheres formed by outgassing during accretion of the Earth and other terrestrial planets. Outgassing of CI and CM carbonaceous chondritic material produces H2O-rich (steam) atmospheres in agreement with the results of impact experiments. However, outgassing of other types of chondritic material produces atmospheres dominated by other gases. Outgassing of ordinary (H, L, LL) and high iron enstatite (EH) chondritic material yields H2-rich atmospheres with CO and H2O being the second and third most abundant gases. Outgassing of low iron enstatite (EL) chondritic material gives a CO-rich atmosphere with H2, CO2, and H2O being the next most abundant gases. Outgassing of CV carbonaceous chondritic material gives a CO2-rich atmosphere with H2O being the second most abundant gas. Our results predict that the atmospheres formed during accretion of the Earth and Mars were probably H2-rich unless the accreted material was dominantly CI and CM carbonaceous chondritic material. We also predict significant amounts of S, P, Cl, F, Na, and K in accretionary atmospheres at high temperatures (1500-2500 K). Finally, our results may be useful for interpreting spectroscopic observations of accreting extrasolar terrestrial planets. 相似文献
86.
Deep-sea corals have been shown to be useful archives of rapid changes in ocean chemistry during the last glacial cycle. Their aragonitic skeleton can be absolutely dated by U-Th data, freeing radiocarbon to be used as a water-mass proxy. For certain species of deep-sea corals, the growth rate allows time resolution that is comparable to ice cores. An additional proxy is needed to exploit this opportunity and turn radiocarbon data into rates of ocean overturning in the past.Neodymium isotopes in seawater can serve as a quasi-conservative water-mass tracer and initial results indicate that deep-sea corals may be reliable archives of seawater Nd isotopes. Here we present a systematic study exploring Nd isotopes as a water-mass proxy in deep-sea coral aragonite. We investigated five different genera of modern deep-sea corals (Caryophyllia, Desmophyllum, Enallopsamia, Flabellum, Lophelia), from global locations covering a large potential range of Nd isotopic compositions. Comparison with ambient seawater measurements yields excellent agreement and suggests that deep-sea corals are reliable archives for seawater Nd isotopes.A parallel study of Nd concentrations in these corals yields distribution coefficients for Nd between seawater and coral aragonite of 1-10, omitting one particular genus (Enallopsamia). The corals and seawater did however not come from exactly the same location, and further investigations are needed to reach robust conclusions on the incorporation of Nd into deep-sea coral aragonite.Lastly, we studied the viability of extracting the Nd isotope signal from fossil deep-sea corals by carrying out stepwise cleaning experiments. Our results show that physical removal of the ferromanganese coating and chemical pre-cleaning have the highest impact on Nd concentrations, but that oxidative/reductive cleaning is also needed to acquire a seawater Nd isotope signal. 相似文献
87.
This article analyzes the recent growth and configuration of Fair Trade networks connecting South African Rooibos tea producers with American consumer markets. As we demonstrate, Fair Trade’s growth in the Rooibos sector engages key issues of black empowerment, land reform, and sustainable development in post-Apartheid South Africa. Fair Trade networks provide small-scale black Rooibos producers with critical markets. Most significantly, the Wupperthal and Heiveld cooperatives have upgraded into processing and packaging and their jointly owned Fairpackers facility now exports shelf-ready Rooibos tea. Analyzing the nature of US Fair Trade Rooibos buyers and their South African sourcing arrangements, we identify key variations in Fair Trade commitment and engagement between mission-driven and market-driven distributors. While mission-driven buyers engage small-scale Rooibos cooperatives in multifaceted partnership networks, market-driven buyers pursue conventional sourcing strategies favoring purchases from large plantations and exporters. We conclude that tensions between a radical and commercial orientation toward Fair Trade in Rooibos tea networks in many ways mirror those in the broader movement. 相似文献
88.
Assessment of the role of facies heterogeneity at the fine scale by numerical transport experiments and connectivity indicators 总被引:2,自引:1,他引:1
The heterogeneity of facies at the scale of individual lithological levels controls, at a macroscopic scale, water flow and contaminant transport in porous sediments. In particular the presence of organized features such as permeable connected levels, has a significant effect on travel times and dispersion. Here, the effects of facies heterogeneity on flow and transport are studied for three blocks, whose volume is of the order of a cubic meter, dug from alluvial sediments from the Ticino valley (Italy). Using the results of numerical tracer experiments on these domains, the longitudinal dispersion coefficient is computed with an Eulerian approach based on the fit of the breakthrough curves with the analytical solution of the convective-dispersive transport equation. Moreover, the dispersion tensor is computed with a Lagrangian approach from the second order moments of particle distributions. Three types of connectivity indicators are tested: (1) connectivity function; (2) flow, transport and statistical connectivity; (3) original (intrinsic, normal and total) indicators of facies connectivity. The connectivity function provides the most complete information. Some of the transport and statistical connectivity indicators are correlated with dispersivity. The simultaneous analysis of the three indicators of facies connectivity emphasizes the fundamental geometrical features that control transport. 相似文献
89.
Groundwater inflow assessment is essential for the design of tunnel drainage systems, as well as for assessment of the environmental impact of the associated drainage. Analytical and empirical methods used in current engineering practice do not adequately account for the effect of the jointed-rock-mass anisotropy and heterogeneity. The impact of geo-structural anisotropy of fractured rocks on tunnel inflows is addressed and the limitations of analytical solutions assuming isotropic hydraulic conductivity are discussed. In particular, the study develops an empirical correction to the analytical formula frequently used to predict groundwater tunnel inflow. In order to obtain this, a discrete network flow modelling study was carried out. Numerical simulation results provided a dataset useful for the calibration of some empirical coefficient to correct the well-known Goodman’s equation. This correction accounts for geo-structural parameters of the rock masses such as joint orientation, aperture, spacing and persistence. The obtained empirical equation was then applied to a medium-depth open tunnel in Bergamo District, northern Italy. The results, compared with the monitoring data, showed that the traditional analytical equations give the highest overestimation where the hydraulic conductivity shows great anisotropy. On the other hand, the empirical relation allows a better estimation of the tunnel inflow. 相似文献
90.
Water quality and relationship between superficial and ground water in Rome (Aniene River basin,central Italy) 总被引:1,自引:1,他引:0
Francesco La Vigna Simone Ciadamidaro Roberto Mazza Laura Mancini 《Environmental Earth Sciences》2010,60(6):1267-1279
Chemical, physical, and biological features of streams and ground water of the North-Eastern area of Rome are jointly analyzed
in order to assess the status of water resources. Ground water was investigated with classical survey methods (pH, temperature,
and electric conductivity). Microbiological pollution, faunal composition, and stream surrounding area conditions of surface
waters were studied, in order to quantify the residual value of these ecosystems from both a human and an environmental point
of view. Results show a general impairment of the system and the comparison between superficial waters and shallow ground
waters makes it possible to detect the presence of a connection between the two levels. This relationship occurs as an exchange
from superficial waters (streams and rivers) to the shallow aquifers. Where superficial waters are contaminated, as in the
Tor Sapienza stream, pollutants move to the shallow aquifers too, due to the decreased pressure of the over-exploited aquifer.
Moreover, uncontrolled drilling activity, diffused in urban areas, makes it possible the connection between shallow and deep
ground water. Notwithstanding this, the mixing between superficial and deep ground water system in Rome is not very widespread
and, apparently, limited to restricted areas. 相似文献