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991.
992.
993.
Amy?L?Ryser Daniel?G?StrawnEmail author Matthew?A?Marcus Jodi?L?Johnson-Maynard Mickey?E?Gunter Gregory?M?ller 《Geochemical transactions》2005,6(1):1
Mining activities in the US Western Phosphate Resource Area (WPRA) have released Se into the environment. Selenium has several
different oxidation states and species, each having varying degrees of solubility, reactivity, and bioavailability. In this
study we are investigating the speciation of Se in mine-waste rocks. Selenium speciation was determined using bulk and micro-x-ray
absorption spectroscopy (XAS), as well as micro-x-ray fluorescence mapping. Rocks used for bulk-XAS were ground into fine
powders. Shale used for micro-XAS was broken along depositional planes to expose unweathered surfaces. The near edge region
of the XAS spectra (XANES) for the bulk rock samples revealed multiple oxidation states, with peaks indicative of Se(-II),
Se(IV), and Se(+VI) species. Micro-XANES analysis of the shale indicated that three unique Se-bearing species were present.
Using the XANES data together with ab initio fitting of the extended x-ray absorption fine structure region of the micro-XAS data (micro-EXAFS) the three Se-bearing species
were identified as dzharkenite, a di-selenide carbon compound, and Se-substituted pyrite. Results from this research will
allow for a better understanding of the biogeochemical cycling of Se in the WPRA. 相似文献
994.
The development of a cDNA array of coral genes and its application to investigate changes in coral gene expression associated with stressful conditions is described. The array includes both well-characterized and previously unidentified coral genes from Acropora cervicornis and Montastraea faveolata. Corals were exposed to either natural or anthropogenic stressors to elicit the expression of stress genes for isolation and incorporation onto the array. A total of 32 genes involved in protein synthesis, apoptosis, cell signaling, metabolism, cellular defense and inflammation were included on the array. Labeled cDNA from coral (Montastraea faveolata) exposed to elevated seawater temperature, salinity and ultraviolet light was tested against the microarray to determine patterns of gene expression associated with each stressor. Carbonic anhydrase, thioredoxin, a urokinase plasminogen activator receptor (uPAR) and three ribosomal genes demonstrated differential expression across all replicates on the array and between replicate colonies. Specific gene expression patterns produced in response to different stressors demonstrate the potential for gene expression profiling in characterizing the coral stress response. 相似文献
995.
The northwestern Argentina Tarija Basin: Stratigraphy, depositional systems, and controlling factors in a glaciated basin 总被引:1,自引:0,他引:1
The Tarija Basin, shared by Bolivia and Argentina, was subjected to glacial conditions during the Late Carboniferous and Early Permian. The Macharetí and Mandiyutí groups deposited during these times record in their facies advances and retreats of the Gondwanan ice cap. The lithostratigraphic subdivision of these groups presents stages with minor glacial influence in the basal formations of each group (Tupambi and Escarpment formations), whereas in the upper units, glacially related deposition prevails (Tarija and San Telmo formations). Typical facies deposited in relation to glacial settings are diamictites and mudstones mainly related to proglacial, lacustrine environments. During the stages of main ice retreat, deposition was dominated by fluvial and deltaic sandstones. Significant erosion and deep valley incision characterize the basal surfaces of both groups. Conversely, the stratigraphic surface that separates the sandy formations from the overlying diamictites tends to be rather flat. The dynamics of the glacial cap are not only reflected in the facies distribution but also were a key factor in creating accommodation space; the changes in the glacial-driven subsidence linked to the advance and retreat of the ice were its main control. 相似文献
996.
The effects of nutrient availability and litter quality on litter decomposition were measured in two oligotrophic phosphorus
(P)-limited Florida Everglades esturies, United States. The two estuaries differ, in that one (Shark River estuary) is directly
connected to the Gulf of Mexico and receives marine P, while the other (Taylor Slough estuary) does not receive marine P because
Florida Bay separates it from the Gulf of Mexico. Decomposition of three macrophytes.Cladium jamaicense, Eleochaaris spp., andJuncus roemerianus, was studied using a litter bag technique over 18 mo. Litter was exposed to three treatments: soil surface+macroinvertebrates
(=macro), soil surface without macroinvertebrates (=wet), and above the soil and water (=aerial). The third treatment replicated
the decomposition of standing dead leaves. Decomposition rates showed that litter exposed to the wet and macro treatments
decomposed significantly faster than the aerial treatment, where atmospheric deposition was the only source of nutrients.
Macroinvertebrates had no influence on litter decompostion rates.C. jamaicense decomposed faster at sites, with higher P, andEleocharis spp. decomposed significantly faster at sites with higher nitrogen (N). Initial tissue C:N and C:P molar ratios revealed
that the nutrient quality of litter of bothEleocharis spp. andJ. roemerianus was higher thanC. jamaicense, but onlyEleocharis spp. decomposed faster thanC. jamaicense. C. jamaicense litter tended to immobilize P, whileEleocharis spp. litter showed net remineralization of N and P. A comparison with other estuarine and wetland systems revealed the dependence
of litter decomposition on nutrient availability and litter quality. The results from this experiment suggest that Everglades
restoration may have an important effect on key ecosystem processes in the estuarine ecotone of this landscape. 相似文献
997.
Jun Hao Curtis Cleveland Eelin Lim Daniel R Strongin Martin AA Schoonen 《Geochemical transactions》2006,7(1):8-9
The chemolithoautotrophic bacterium, Acidithiobacillus ferrooxidans, commonly occurs in acid mine drainage (AMD) environments where it is responsible for catalyzing the oxidation of pyrite
and concomitant development of acidic conditions. This investigation reports on the growth of this bacterial species on the
pyrite surface and in the aqueous phase at a pH close to 2 as well as the role of adsorbed lipid in preventing pyrite dissolution.
Both acid washed pyrite and acid-washed pyrite coated with lipids were used as substrates in the studies. The choice of lipid,
1,2-bis(10,12-tricosadiynoyl)-sn-Glycero-3-Phosphocholine lipid (23:2 Diyne PC), a phosphocholine lipid, was based on earlier work that showed that this lipid
inhibits the abiotic oxidation rate of pyrite. Atomic force microscopy showed that under the experimental conditions used
in this study, the lipid formed ~4–20 nm layers on the mineral surface. Surface-bound lipid greatly suppresses the oxidation
process catalyzed by A. ferrooxidans. This suppression continued for the duration of the experiments (25 days maximum). Analysis of the bacterial population on
the pyrite surface and in solution over the course of the experiments suggested that the pyrite oxidation was dependent in
large part on the fraction of bacteria bound to the pyrite surface. 相似文献
998.
999.
Part of a small drainage basin on the Sevilleta National Wildlife Refuge (about 25 km north of Socorro, NM) was intensively instrumented with soil monitoring equipment to estimate natural ground-water recharge. Soil-moisture data were analysed with special attention to characterizing the influence of topography on the direction of vadose water flow paths in fine to medium aeolian sand. Moisture content data were obtained by the neutron scattering technique, and hydraulic head data were obtained using tensiometers. In addition, tracer experiments were conducted on a sandy hillslope to delineate the flow paths of vadose water. The results indicate that there is a strong lateral component to unsaturated flow on a hillslope, even in the absence of apparent sublayers of much lower permeability. Darcian calculations estimate the long-term, steady, deep flux beneath a concave location to be about 4 per cent of an assumed mean annual precipitation of 20 cm. The deep soil water flux downward varied by several orders of magnitude during the 17 month period of record. 相似文献
1000.