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161.
The stability and structure of aqueous complexes formed by trivalent antimony (SbIII) with carboxylic acids (acetic, adipic, malonic, lactic, oxalic, tartaric, and citric acid), phenols (catechol), and amino acids (glycine) having O- and N-functional groups (carboxyl, alcoholic hydroxyl, phenolic hydroxyl and amine) typical of natural organic matter, were determined at 20 and 60 °C from solubility and X-ray absorption fine structure (XAFS) spectroscopy measurements. In organic-free aqueous solutions and in the presence of acetic, adipic, malonic acids and glycine, both spectroscopic and solubility data are consistent with the dominant formation of SbIII hydroxide species, , at strongly acid, acid-to-neutral and basic pH, respectively, demonstrating negligible complexing with mono-functional organic ligands (acetic) or those having non adjacent carboxylic groups (adipic, malonic). In contrast, in the presence of poly-functional carboxylic and hydroxy-carboxylic acids and catechol, SbIII forms stable 1:1 and 1:2 complexes with the studied organic ligands over a wide pH range typical of natural waters (3 < pH < 9). XAFS spectroscopy measurements show that in these species the central SbIII atom has a distorted pseudo-trigonal pyramidal geometry composed of the lone pair of 5s2 electrons of Sb and four oxygen atoms from two adjacent functional groups of the ligand (OC-OH and/or COH), forming a five-membered bidendate chelate cycle. Stability constants for these species, generated from Sb2O3 (rhomb.) solubility experiments, were used to model Sb complexing with natural humic acids possessing the same functional groups as those investigated in this study. Our predictions show that in an aqueous solution of pH between 2 and 10, containing 1 μg/L of Sb and 5 mg/L of dissolved organic carbon (DOC), up to 35% of total dissolved Sb binds to aqueous organic matter via carboxylic and hydroxy-carboxylic groups. This amount of complexed Sb for typical natural DOC concentrations is in agreement with that estimated from dialysis experiments performed with commercial humic acid in our work and those available in the literature for a range of standardized IHSS humic acids. Our results imply that a significant part of Sb is likely to be bound with humic acids via hydroxy-carboxylic moieties, in the form of bidendate complexes. However, following the strong chemical affinity of SbIII for reduced sulfur, some undefined fraction of SbIII might also be bound to the minor thiol-bearing moieties of humic acids; further studies are required to check this hypothesis. 相似文献
162.
163.
Outcrop studies reveal a common occurrence of tabular zones of significantly‐increased fracture intensity affecting otherwise well‐lithified rocks. These zones, called fracture corridors, can have a profound effect on multi‐phase fluid flow in the subsurface. Using standard geo‐modelling tools, it is possible to generate 3D realizations of reservoirs that contain distributions of such fracture corridors that are consistent with observations, including the vertical frequency in pseudo‐wells inserted into the model at random locations. These models can generate the inputs to flow simulation. The approach adopted here is to run the flow simulations in a single‐porosity representation where the flow effects of fractures are upscaled into equivalent cell‐based properties, preserving a clear spatial relationship between the input geology and the resulting cellular model. The simulated reservoir performance outcomes are very similar to those seen in real oilfields: extreme variability between wells, early water breakthrough, disappointing recoveries and patchy saturation distributions. Thus, a model based on fracture corridors can provide an explanation for the observed flow performance of a suitable field. However, the use of seismics to identify fracture corridors is not an easy task. New work is needed to predict the seismic responses of fracture corridor systems to be able to judge whether it is likely that we can robustly detect and characterize these flow‐significant features adequately. 相似文献
164.
165.
Anne Marie de Grosbois 《Environmental Geology》2009,58(4):915-918
166.
167.
Rachel Marie Wilson Jeffrey Chanton Graham Lewis Douglas Nowacek 《Estuaries and Coasts》2009,32(5):999-1010
Stable isotope ratios of carbon and sulfur were used to assess organic matter utilization of numerically abundant consumers
present in Apalachicola Bay, FL, USA. These results were used to infer nitrogen isotopic enrichment of organic matter sources
in an effort to establish baseline δ
15N enrichment for trophic evaluations. We compared results from concentration-independent and concentration-dependent mixing
models and found that the two methods resulted in widely different conclusions about the importance of organic matter sources
that varied ninefold in sulfur concentrations. Nitrogen isotopic enrichment was used to determine relative trophic positions
of consumer organisms. Source elemental concentrations of nitrogen were also considered in the calculation of relative trophic
levels in a concentration-dependent approach. Concentration-independent and concentration-dependent methods of calculating
trophic results were compared. While relative trophic levels of individual species varied continuously from approximately
1.7 to 3.5, comparisons of trophic level among consumers indicated four possible trophic groupings. Filter feeders (mussels
and oysters) made up the lowest trophic tier while teleost fishes made up the highest trophic tier. Invertebrates sampled
were assigned intermediate nondiscrete trophic levels. Because δ
15N values of important organic matter sources in the system were similar, the concentration-independent and concentration-dependent
methods did not result in significantly different conclusions about trophic level for any of the consumers examined. However,
a comparison of the two methods applied to a hypothetical case found that differences in base δ
15N values ranging approximately 4‰ resulted in significantly different trophic-level assignments when comparing the concentration-dependent
and concentration-independent methods of trophic-level calculations. Our results confirm that consideration of the elemental
concentrations of the base organisms is an important factor in determining source contributions and may affect trophic-level
calculations in systems with a sufficient range of base nitrogen enrichment. However, this result depended on the relative
isotopic signatures of the chosen sources and their elemental concentrations and should be considered individually for each
system. 相似文献
168.
Marie Jo Goupil 《Astrophysics and Space Science》2008,316(1-4):251-261
A first part gives a summary of the main conclusions stemmed from the different comparisons reported in this book. One main conclusion is: with some care in the computations, one is able to obtain frequency differences between different computations which are smaller than required by Corot challenges. This is true for high frequency modes. Small frequency differences are much less easily obtained for low frequencies around the fundamental radial mode frequency. Care here means: having the same physics, same constants of physics, same input stellar parameters, computing models and oscillations with enough self numerical consistent accuracy. The ESTA group has built reference grids of models and associated oscillation frequencies and made them available to the community. In a second part of the present paper, a study case is considered in order to show the need and the use of such reference grids. Finally some perspectives concerning the remaining tasks are suggested. 相似文献
169.
Long term monitoring for oil in the Exxon Valdez spill region 总被引:2,自引:1,他引:1
In the aftermath of the 1989 Exxon Valdez oil spill, a Long Term Environmental Monitoring Program (LTEMP) has been regularly sampling mussels (and some sediments) for polycyclic aromatic and saturated hydrocarbons (PAH and SHC) at sites in Port Valdez, Prince William Sound, and the nearby Gulf of Alaska region. After 1999, a decreasing trend appears in total PAH (TPAH) in tissues at all sites with current values below 100 ng/g dry weight (many below 50 ng/g). Currently, most samples reflect a predominantly dissolved-phase signal. This new low in TPAH likely represents ambient background levels. Synchrony in TPAH time-series and similarities in the hydrocarbon signatures portray regional-scale dynamics. The five inner Prince William Sound sites show similar composition and fluctuations that are different from the three Gulf of Alaska sites. The two Port Valdez sites represent a unique third region primarily influenced by the treated ballast water discharge from the Alyeska Marine Terminal. Prince William Sound has reverted to a stable environment of extremely low level contamination in which local perturbations are easily detected. 相似文献
170.
Marie Lothon Fleur Couvreux Sylvie Donier Françoise Guichard Pierre Lacarrère Donald H. Lenschow Joël Noilhan Frédérique Saïd 《Boundary-Layer Meteorology》2007,124(3):425-447
During the Hydrological-Atmospheric Pilot Experiment (HAPEX)-Sahel, which took place in Niger in the transitional period between
the wet and dry seasons, two French aircraft probed the Sahelian boundary layer to measure sensible and latent heat fluxes.
The measurements over the Niamey area often revealed organised structures of a few km scale that were associated with both
thermals and dry intrusions. We study the impact of these coherent structures using a single day’s aircraft-measured fluxes
and a numerical simulation of that day with a mesoscale model. The numerical simulation at high horizontal resolution (250 m)
contains structures that evolve from streaks in the early morning to cells by noon. This simulation shows distribution, variance
and skewness similar to the observations. In particular, the numerical simulation shows dry intrusions that can penetrate
deeply into the atmospheric boundary layer (ABL), and even reach the surface in some cases, which is in accordance with the
observed highly negatively skewed water vapour fluctuations. Dry intrusions and thermals organised at a few km scale give
skewed flux statistics and can introduce large errors in measured fluxes. We use the numerical simulation to: (i) evaluate
the contribution of the organised structures to the total flux, and (ii) estimate the impact of the organised structures on
the systematic and random errors resulting from the 1D sampling of the aircraft as opposed to the 2D numerical simulation
estimate. We find a significant contribution by the organised structures to the total resolved fluxes. When rolls occur, and
for a leg length of about 30 times the ABL depth, the 1D sampled flux is shown to be sometimes 20% lower than the corresponding
2D flux when the 1D sampling direction is the same as the main axis of the rolls, whereas the systematic error is much lower
when the direction of the leg is transverse to the rolls. In the case of cells, an underestimate of around 10% can still be
observed with the 1D approach independent of direction, due to poor sampling of the energy-containing scales. 相似文献