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Chemical and physical data are given for five samples of rock-forming apatite from diverse geologic environments in Nevada and Colorado. Four of these apatites contain rare-earth assemblages in which the cerium group is well represented but the yttrium group predominates. The fifth apatite contains a highly fractionated assemblage of the lighter (cerium group) rare earths similar to the assemblage typical of alkulic rocks.
Streamwater chemistry at Panola Mountain research catchment, Georgia, U.S.A., is explained as a mixture of representative soilwater solutions that are considered to be temporally invariant to a first approximation. The selection of three end-members from all sampled soil waters is evaluated by comparing the observed and predicted streamwater concentration of six solutes (alkalinity, sulfate, sodium, magnesium, calcium and dissolved silica), which are assumed to mix conservatively, and by assessing the consistency of the implied hydrograph separation with the hydrological mechanisms that are believed to be operating in this catchment. The percentage of variation in the streamwater solute concentrations explained by the end-member mixing analysis (EMMA) ranges from 82 to >97%, and the hydrograph separation is, intuitively, physically reasonable. If the correct end-members have been identified, the streamwater chemical response to different levels of acidic deposition can be predicted by examining the change in each end-member under different loads; no hydrological model is required. If a traditional hydrochemical model, which is driven by rainfall quantity and quality, is desired, this analysis provides an indication of the model structure that would be necessary to reproduce both streamwater and soilwater chemistry.
To test the transmissivity feedback hypothesis of runoff generation, surface and subsurface waters were monitored and sampled during the 1996 snowmelt at various topographic positions in a 41 ha forested headwater catchment at Sleepers River, Vermont. Two conditions that promote transmissivity feedback existed in the catchment during the melt period. First, saturated hydraulic conductivity increased toward land surface, from a geometric mean of 3.6 mm h-1 in glacial till to 25.6 mm h-1 in deep soil to 54.0 mm h-1 in shallow soil. Second, groundwater levels rose to within 0.3 m of land surface at all riparian sites and most hillslope sites at peak melt. The importance of transmissivity feedback to streamflow generation was tested at the catchment scale by examination of physical and chemical patterns of groundwater in near-stream (discharge) and hillslope (recharge/lateral flow) zones, and within a geomorphic hollow (convergent flow). The presence of transmissivity feedback was supported by the abrupt increase in streamflow as the water table rose into the surficial, transmissive zone; a flattening of the groundwater level vs. streamflow curve occurred at most sites. This relation had a clockwise hysteresis (higher groundwater level for given discharge on rising limb than at same discharge on falling limb) at riparian sites, suggesting that the riparian zone was the dominant source area during the rising limb of the melt hydrograph. Hysteresis was counterclockwise at hillslope sites, suggesting that hillslope drainage controlled the snowmelt recession. End member mixing analysis using Ca, Mg, Na, dissolved organic carbon (DOC), and Si showed that stream chemistry could be explained as a two-component mixture of groundwater high in base cations and an O-horizon/overland flow water high in DOC. The dominance of shallow flow paths during events was indicated by the high positive correlation of DOC with streamflow (r2 = 0.82). Despite the occurrence of transmissivity feedback, hillslope till and soil water were ruled out as end members primarily because their distinctive high-Si composition had little or no effect on streamwater composition. Till water from the geomorphic hollow had a chemistry very close to streamwater base flow, and may represent the base flow end member better than the more concentrated riparian groundwater. During snowmelt, streamwater composition shifted as this base flow was diluted - not by shallow groundwater from the hillslope, but rather by a more surficial O-horizon/overland flow water.Surface and subsurface waters were analyzed to test the transmissivity feedback of runoff generation during the 1996 snowmelt in a catchment at Sleepers River, Vermont. The importance of transmissivity feedback to stream flow generation was tested by examination of physical and chemical patterns of groundwater in near-stream and hillslope zones within a geomorphic hollow. End member mixing analysis of Ca, Mg, Na, dissolved organic carbon (DOC), and Si showed that stream chemistry could be explained as a two-component mixture of groundwater high in base cations and an O-horizon/overland flow water high in DOC. The dominance of shallow water paths during the events was indicated by the high positive correlation of DOC with streamflow (r2 = 0.82).
The five most common species of Pacific salmon, Rainbow Trout (steelhead) Oncorhynchus spp., and Atlantic Salmon Salmo salar intermingle in the North Pacific Ocean and its freshwater tributaries. Efficient morphological methods for distinguishing among these species are sometimes limited by condition of the specimen (degraded or missing morphology), life history stage, or training of the observer. Researchers have successfully applied various genetic methods to distinguish among these species when morphological analyses are not possible, but they cannot easily incorporate these methods into standard fish and wildlife population monitoring analysis workflows. Here we test five 5′–3′ exonuclease (TaqMan) assays developed from mitochondrial genes and provide novel methods that take advantage of TaqMan output to distinguish among these species. We found that combinations of as few as two of the five assays were adequate to distinguish all species. TaqMan chemistry is designed to interrogate a single nucleotide locus. We also explore the basis for the variation in the observed scatter plot distributions (variation in florescent signals) and show that this variation is due to nucleotide diversity in and near the probe site. Because the SNPs underlying the assays developed here are all physically close to one another along the mitochondrial genome, the potential exists to develop a single DNA sequence-based assay to discriminate among salmon species. This single assay can be added to a genotyping-by-sequencing panel to identify and exclude nontarget species from analyses.
The distribution of contaminants in surface sediments has been measured and mapped as part of a U.S. Geological Survey study of the sediment quality and dynamics of Long Island Sound. Surface samples from 219 stations were analyzed for trace (Ag, Ba, Cd, Cr, Cu, Hg, Ni, Pb, V, Zn and Zr) and major (Al, Fe, Mn, Ca, and Ti) elements, grain size, and Clostridium perfringens spores. Principal Components Analysis was used to identify metals that may covary as a function of common sources or geochemistry. The metallic elements generally have higher concentrations in fine-grained deposits, and their transport and depositional patterns mimic those of small particles. Fine-grained particles are remobilized and transported from areas of high bottom energy and deposited in less dynamic regions of the Sound. Metal concentrations in bottom sediments are high in the western part of the Sound and low in the bottom-scoured regions of the eastern Sound. The sediment chemistry was compared to model results (Signell et al., 1998) and maps of sedimentary environments (Knebel et al., 1999) to better understand the processes responsible for contaminant distribution across the Sound. Metal concentrations were normalized to grain-size and the resulting ratios are uniform in the depositional basins of the Sound and show residual signals in the eastern end as well as in some local areas. The preferential transport of fine-grained material from regions of high bottom stress is probably the dominant factor controlling the metal concentrations in different regions of Long Island Sound. This physical redistribution has implications for environmental management in the region.
Congruous with earlier work, Martian soil along the Spirit Rover's traverse at Gusev crater can be divided into three broad groups by size: fines (<150 μ m), sand, and a mix of various grain sizes. The key chemical observation is greater homogeneity in fines relative to the other two, consistent with regional‐ and global‐scale sampling of chemical compositions by finer particle sizes. The mix class is generally more heterogeneous as are samples from the Columbia Hills within each class. Variation in the trace element Ni is consistent with a CI contribution not exceeding 3%, while that of Ti is compatible with Fe‐Ti oxide enrichment not exceeding 3%. Physical mixing models are poorly supported. Among many potential binary and three‐component mixing models, only two show some consistency with the soil data: typical fines with the opaline Si end‐member identified at Home Plate and typical fines with sulfates (bearing a variable mix of Ca, Fe, and Mg cations). We also infer that binary mixing transcends classes, contrasting strongly with terrestrial sediments, and that mixing trends are consistent with significant nonmixing contributions, perhaps including localized chemical alteration. The decoupling between chemistry and grain size classes also suggests that processes linking composition with grain size, such as heavy mineral sorting, may have been minimal or absent entirely. The primary exception to this is the correlation between Cl and Si, Cl‐S, and Al‐Si, which is strongest in the fines class.
Despite precautions to protect cranes, a 3-year-old endangered Mississippi sandhill crane ( Grus canadensis pulla ) was found caught in a leghold trap in Gautier, Mississippi, on 11 November 1987. The bird could have been in the trap for up to 16 hr and was standing and struggling to escape when it was discovered. Serum chemistries of the crane on 12 November revealed elevated lactic dehydrogenase (2,880 IU/L), alanine aminotransferase (ALT) (152 IU/L), and aspartate aminotransferase (AST) (>1,000 IU/L) values. Following surgical amputation of a fractured toe, the bird never attempted to stand and was unable to stand even when manually supported. Radiographic and physical examination of both legs did not reveal any anatomical abnormalities. Despite medical care, including supportive therapy, no improvement was observed in the bird's ability to stand and to support itself, and the bird died on 19 November. Serum chemistries and the postmortem and histopathologic findings were compatible with capture myopathy described in other species. Because of the possible susceptibility of long-legged birds such as the Mississippi sandhill crane to capture myopathy, special care must be taken when trapping, handling, chemically immobilizing, and transporting these species. In addition, precautions must be taken when conducting a predator-control program to ensure that nontarget wildlife are unlikely to encounter traps. Capture myopathy has only rarely been observed in wild birds, and this case represents the first report in a Mississippi sandhill crane.
Boreal ecosystems represent a large carbon (C) reservoir and a substantial source of greenhouse gases. Hydrologic conditions dictate whether C leached from boreal soils is processed in catchments or flushed to less productive environments via the stream. This study quantified hydrologic and biogeochemical C loss from a boreal catchment underlain by frozen silt, where flowpaths may deepen as the active layer thaws over the summer. We hypothesized a decrease in the magnitude of C mineralization over the summer associated with changing flowpaths and decreasing hydrologic connectivity, organic matter lability, and nitrogen (N) availability. Conservative tracers were used to partition C and N loss between catchment export and biogeochemical processing. Coupling tracers with tributary and porewater chemistry indicated C and N cycling in soil flowpaths, with an exponential decrease over the summer. Nitrate was primarily reduced in hillslope flowpaths and the lack of N reaching the stream appeared to limit C mineralization. Stream export accounted for the greatest loss of C, removing 247 and 113 mol hr −1 in the early and late summer, respectively. Reactivity was related to hydrologic connectivity between the soils and stream, which was greatest early in the summer and following a large flood. While a warming climate may increase storage potential in thawed soils, the early‐season flush of labile material and late‐season runoff through mineral flowpaths may maintain high C export rates. Therefore, we highlight physical export as a dominant cause of aqueous C loss from silty catchments as the Arctic continues to thaw.
Mars Pathfinder obtained multispectral, elemental, magnetic, and physical measurements of soil and dust at the Sagan Memorial Station during the course of its 83 sol mission. We describe initial results from these measurements, concentrating on multispectral and elemental data, and use these data, along with previous Viking, SNC meteorite, and telescopic results, to help constrain the origin and evolution of Martian soil and dust. We find that soils and dust can be divided into at least eight distinct spectral units, based on parameterization of Imager for Mars Pathfinder (IMP) 400 to 1000 nm multispectral images. The most distinctive spectral parameters for soils and dust are the reflectivity in the red, the red/blue reflectivity ratio, the near-IR spectral slope, and the strength of the 800 to 1000 nm absorption feature. Most of the Pathfinder spectra are consistent with the presence of poorly crystalline or nanophase ferric oxide(s), sometimes mixed with small but varying degrees of well-crystalline ferric and ferrous phases. Darker soil units appear to be coarser-grained, compacted, and/or mixed with a larger amount of dark ferrous materials relative to bright soils. Nanophase goethite, akaganeite, schwertmannite, and maghemite are leading candidates for the origin of the absorption centered near 900 nm in IMP spectra. The ferrous component in the soil cannot be well-constrained based on IMP data. Alpha proton X-ray spectrometer (APXS) measurements of six soil units show little variability within the landing site and show remarkable overall similarity to the average Viking-derived soil elemental composition. Differences exist between Viking and Pathfinder soils, however, including significantly higher S and Cl abundances and lower Si abundances in Viking soils and the lack of a correlation between Ti and Fe in Pathfinder soils. No significant linear correlations were observed between IMP spectral properties and APXS elemental chemistry. Attempts at constraining the mineralogy of soils and dust using normative calculations involving mixtures of smectites and silicate and oxide minerals did not yield physically acceptable solutions. We attempted to use the Pathfinder results to constrain a number of putative soil and dust formation scenarios, including palagonitization and acid-fog weathering. While the Pathfinder soils cannot be chemically linked to the Pathfinder rocks by palagonitization, this study and McSween et al. [1999] suggest that palagonitic alteration of a Martian basaltic rock, plus mixture with a minor component of locally derived andesitic rock fragments, could be consistent with the observed soil APXS and IMP properties.
Responses of hemocytes from the crayfish Procambarus zonangulus to stimulation by fungal cell walls (Zymosan A) were measured by flow cytometry. Changes in hemocyte physical characteristics were assessed flow cytometrically using forward- and sidescatter light parameters, and viability was measured by two-color fluorescent staining with calcein-AM and ethidium homodimer 1. The main effects of zymosan A on crayfish hemocytes were reduction in cell size and viability compared to control mixtures (hemocytes in buffer only). Adding diethyldithiocarbamic acid, an inhibitor of phenoloxidase, to hemocyte to zymosan mixtures delayed the time course of cell size reduction and cell death compared to zymosan-positive controls. The inclusion of trypsin inhibitor in reaction mixtures further delayed the reduction in hemocyte size and cell death, thereby indicating that a proteolytic cascade, along with prophenoloxidase activation, played a key role in generating signal molecules which mediate these cellular responses. In addition to traditional methods such as microscopy and protein chemistry, flow cytometry can provide a simple, reproducible, and sensitve method for evaluating invertebrate hemocyte responses to immunological stimuli.
This paper investigates changes in the high-volatile bituminous Lower Block Coal Member from Indiana owing to moisture availability and oxidation in air at ambient pressure and temperature over storage time. Specifically, it investigates changes in chemistry, in surface area, and pore structure, as well as changes in methane and carbon dioxide adsorption capacities. Our results document that the methane adsorption capacity increased by 40%, whereas CO 2 adsorption capacity increased by 18% during a 13-month time period. These changes in adsorption are accompanied by changes in chemistry and surface area of the coal. The observed changes in adsorption capacity indicate that special care must be taken when collecting samples and preserving coals until adsorption characteristics are measured in the laboratory. High-pressure isotherms from partially dried coal samples would likely cause overestimation of gas adsorption capacities, lead to a miscalculation of coal-bed methane prospects, and provide deceptively optimistic prognoses for recovery of coal-bed methane or capture of anthropogenic CO 2 . ?? 2009 Elsevier B.V. All rights reserved.
The emerging subdiscipline of hydrogeophysics is underdeveloped in undergraduate curricula relative to its importance in professional engineering/environmental practice. In 2001, the Bucknell Department of Geology initiated efforts to refocus an undergraduate geophysics course on near-surface geophysical methods for hydrologic, environmental, and engineering problems. In addition to offering students practical experience, treatment of hydrogeophysics provides important pedagogical opportunities. Field-based hydrogeophysics labs challenge students to integrate concepts from other geology courses, as well as from physics, math, and chemistry. We faced two challenges in revising our geophysics course: (1) access to wells for field exercises on borehole geophysics; and (2) the costs of acquiring and maintaining equipment. We pursued two strategies to solve these problems. First, we established an on-campus well field, which serves as a field laboratory for downhole and cross-hole experiments. Second, we incorporated field demonstrations and lectures by professional geoscientists, including alumni, into our courses. By adding field exercises to our syllabi and promoting undergraduate research, we are building a cutting-edge dataset that includes televiewer and standard wellbore logging, cross-hole tomography, and hydraulic-test data. Student-led analysis of these data has already provided valuable insights into the control of fractures on aquifer properties, and these observations are being combined with outcrop studies to place our results in a more regional context.
The electronic structure of magnesiowustite is investigated using self-consistent field X α scattered wave (SCF- X α-SW) molecular orbital calculations on (FeO 6 ) 10− and (FeMg 12 O 14 ) 2− clusters. Calculated one-electron transition energies are used to interpret the optical spectrum of (Mg, Fe)O. The results are applied to the electrical and thermal conductivity of the lower mantle. The spin pairing of Fe 2+ and the effect of pressure on bonding in magnesiowustite, with some inferences regarding the incorporation of oxygen in the outer core, is also addressed. The approach used here appears to give a reliable description of the energy and pressure dependence of the spin-allowed 5 T 2 g → 5 E g ligand field transition and the spin-pairing transition of Fe 2+ in (Mg, Fe)O. However, the oxygen to metal charge transfer transitions in (Mg, Fe)O are not as reliably determined insofar as the p - d band gap varies with cluster size and the energies of the charge transfer states cannot be found without including configurational interaction. Nevertheless, it is argued that the charge transfer transitions that are intrinsic to (Fe, Mg)O are of a sufficiently high energy to be irrelevant to the electrical and thermal conductivity of the lower mantle. This is especially true if Fe 2+ adopts the low-spin configuration. The geophysically significant properties of (Fe, Mg)O probably result from defect Fe 3+ .
Gas hydrate is an ice-like form of water and low molecular weight gas stable at temperatures of roughly -10ºC to 25ºC and pressures of ~3 to 30 MPa in geologic systems. Natural gas hydrates sequester an estimated one-sixth of Earth’s methane and are found primarily in deepwater marine sediments on continental margins, but also in permafrost areas and under continental ice sheets. When gas hydrate is removed from its stability field, its breakdown has implications for the global carbon cycle, ocean chemistry, marine geohazards, and interactions between the geosphere and the ocean-atmosphere system. Gas hydrate breakdown can also be artificially driven as a component of studies assessing the resource potential of these deposits. Furthermore, geologic processes and perturbations to the ocean-atmosphere system (e.g., warming temperatures) can cause not only dissociation, but also more widespread dissolution of hydrate or even formation of new hydrate in reservoirs. Linkages between gas hydrate and disparate aspects of Earth’s near-surface physical, chemical, and biological systems render an assessment of the rates and processes affecting the persistence of gas hydrate an appropriate Centennial Grand Challenge. This paper reviews the thermodynamic controls on methane hydrate stability and then describes the relative importance of kinetic, mass transfer, and heat transfer processes in the formation and breakdown (dissociation and dissolution) of gas hydrate. Results from numerical modeling, laboratory, and some fields studies are used to summarize the rates of hydrate formation and breakdown, followed by an extensive treatment of hydrate dynamics in marine and cryospheric gas hydrate systems.
The Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry completed its last review of the isotopic compositions of the elements as determined by isotope-ratio mass spectrometry in 2001. That review involved a critical evaluation of the published literature, element by element, and forms the basis of the table of the isotopic compositions of the elements (TICE) presented here. For each element, TICE includes evaluated data from the “best measurement” of the isotope abundances in a single sample, along with a set of representative isotope abundances and uncertainties that accommodate known variations in normal terrestrial materials. The representative isotope abundances and uncertainties generally are consistent with the standard atomic weight of the element A r ( E ) "> A r ( E ) Ar(E) and its uncertainty U[A r ( E )] "> U[A r ( E )] U[Ar(E)] recommended by CAWIA in 2001.
Numerous loose rocks with dimensions of a few centimeters to tens of centimeters and with no obvious physical relationship to outcrop rocks have been observed along the traverse of the Mars Exploration Rover Opportunity. To date, about a dozen of these rocks have been analyzed with Opportunity's contact instruments, providing information about elemental chemistry (Alpha Particle X‐ray Spectrometer), iron mineralogy and oxidation states (Mössbauer Spectrometer) and texture (Microscopic Imager). These “cobbles” appear to be impact related, and three distinct groups can be identified on the basis of chemistry and mineralogy. The first group comprises bright fragments of the sulfate‐rich bedrock that are compositionally and texturally indistinguishable from outcrop rocks. All other cobbles are dark and are divided into two groups, referred to as the “Barberton group” and the “Arkansas group,” after the first specimen of each that was encountered by Opportunity. Barberton group cobbles are interpreted as meteorites with an overall chemistry and mineralogy consistent with a mesosiderite silicate clast composition. Arkansas group cobbles appear to be related to Meridiani outcrop and contain an additional basaltic component. They have brecciated textures, pointing to an impact‐related origin during which local bedrock and basaltic material were mixed.
A primary source of dissolved inorganic carbon (DIC) in the Black Creek aquifer of South Carolina is carbon dioxide produced by microbially mediated oxidation of sedimentary organic matter. Groundwater chemistry data indicate, however, that the available mass of inorganic electron acceptors (oxygen, Fe(III), and sulfate) and observed methane production is inadequate to account for observed CO 2 production. Although sulfate concentrations are low (approximately 0.05–0.10 mM) in aquifer water throughout the flow system, sulfate concentrations are greater in confining-bed pore water (0.4–20 mM). The distribution of culturable sulfate-reducing bacteria in these sediments suggests that this concentration gradient is maintained by greater sulfate-reducing activity in sands than in clays. Calculations based on Fick's Law indicate that possible rates of sulfate diffusion to aquifer sediments are sufficient to explain observed rates of CO 2 production (about 10 −5 mmoll −1 year −1 ), thus eliminating the apparent electron-acceptor deficit. Furthermore, concentrations of dissolved hydrogen in aquifer water are in the range characteristic of sulfate reduction (2–6 nM), which provides independent evidence that sulfate reduction is the predominant terminal electron-accepting process in this system. The observed accumulation of pyrite- and calcite-cemented sandstones at sand-clay interfaces is direct physical evidence that these processes have been continuing over the history of these sediments.
Geologic map units contain much information about the mineralogy, chemistry, and physical attributes of the rocks mapped. This paper presents information from regional-scale geologic maps in Maryland and Virginia, which are in the southern part of the Chesapeake Bay watershed in the eastern United States. The geologic map information is discussed and analyzed in relation to water chemistry data from shallow wells and stream reaches in the area. Two environmental problems in the Chesapeake Bay watershed are used as test examples. The problems, high acidity and high nitrate concentrations in streams and rivers, tend to be mitigated by some rock and sediment types and not by others. Carbonate rocks (limestone, dolomite, and carbonate-cemented rocks) have the greatest capacity to neutralize acidic ground water and surface water in contact with them. Rocks and sediments having high carbon or sulfur contents (such as peat and black shale) potentially contribute the most toward denitrification of ground water and surface water in contact with them. Rocks and sediments that are composed mostly of quartz, feldspar, and light-colored clay (rocks such as granite and sandstone, sediments such as sand and gravel) tend not to alter the chemistry of waters that are in contact with them. The testing of relationships between regionally mapped geologic units and water chemistry is in a preliminary stage, and initial results are encouraging.Geologic map units contain much information about the mineralogy, chemistry, and physical attributes of the rocks mapped. This paper presents information from regional-scale geologic maps in Maryland and Virginia, which are in the southern part of the Chesapeake Bay watershed in the eastern United States. The geologic map information is discussed and analyzed in relation to water chemistry data from shallow wells and stream reaches in the area. Two environmental problems in the Chesapeake Bay watershed are used as test examples. The problems, high acidity and high nitrate concentrations in streams and rivers, tend to be mitigated by some rock and sediment types and not by others. Carbonate rocks (limestone, dolomite, and carbonate-cemented rocks) have the greatest capacity to neutralize acidic ground water and surface water in contact with them. Rocks and sediments having high carbon or sulfur contents (such as peat and black shale) potentially contribute the most toward denitrification of ground water and surface water in contact with them. Rocks and sediments that are composed mostly of quartz, feldspar, and light-colored clay (rocks such as granite and sandstone, sediments such as sand and gravel) tend not to alter the chemistry of waters that are in contact with them. The testing of relationships between regionally mapped geologic units and water chemistry is in a preliminary stage, and initial results are encouraging.