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At least 1,693 records · Page 94Linked to original sources
USGS1984

Amino acid epimerization implies rapid sedimentation rates in Arctic Ocean cores

The palaeooceanography of the Arctic Ocean is less well known than any other ocean basin, due to difficulties in obtaining cores and in providing a secure chronological framework for those cores that have been raised. Most recent investigators have suggested that low sedimentation rates (0.05-0.1 cm kyr-1) have characterized the deep basins over the past 5 Myr (refs 1,2) despite the glacial-marine character of the sediment and proximity to major centres of shelf glaciation. These calculations have been primarily based on the down-core pattern in the inclination of magnetic minerals, supported by uranium-series, 14C and micropalaeontological evidence. Here we analyse amino acid diagnesis in foraminifera from two gravity cores raised from the floor of the Arctic Ocean, our results suggest that these cores span <200 kyr., conflicting with the earlier estimate of 3 Myr based on palaeomagnetic data. The chronology of other Arctic Ocean cores and previous palaeoenvironmental interpretations need re-evaluation. ?? 1984 Nature Publishing Group.

Nature↗
USGS2014

Prodigious degassing of a billion years of accumulated radiogenic helium at Yellowstone

Helium is used as a critical tracer throughout the Earth sciences, where its relatively simple isotopic systematics is used to trace degassing from the mantle, to date groundwater and to time the rise of continents 1 . The hydrothermal system at Yellowstone National Park is famous for its high helium-3/helium-4 isotope ratio, commonly cited as evidence for a deep mantle source for the Yellowstone hotspot 2 . However, much of the helium emitted from this region is actually radiogenic helium-4 produced within the crust by &alpha;-decay of uranium and thorium. Here we show, by combining gas emission rates with chemistry and isotopic analyses, that crustal helium-4 emission rates from Yellowstone exceed (by orders of magnitude) any conceivable rate of generation within the crust. It seems that helium has accumulated for (at least) many hundreds of millions of years in Archaean (more than 2.5 billion years old) cratonic rocks beneath Yellowstone, only to be liberated over the past two million years by intense crustal metamorphism induced by the Yellowstone hotspot. Our results demonstrate the extremes in variability of crustal helium efflux on geologic timescales and imply crustal-scale open-system behaviour of helium in tectonically and magmatically active regions.

Wyoming↗
USGS2025

Land application of biosolid, livestock, and drilling wastes to US farmland: A potential pathway for the redistribution of contaminants in the environment

In the United States (U.S.), waste byproducts generated from the treatment of municipal waste (biosolids), production of livestock (livestock waste), and drilling of oil and gas wells (drilling waste) are commonly applied to agricultural lands. Although this can be a cost-effective reuse/disposal practice, there is limited research on the potential for contaminant exposures and effects on ecosystems, wildlife, and human health from such land applications. In this study, we conducted extensive chemical, microbial, and toxicity analyses of biosolid, livestock, and drilling wastes just prior to land application on agricultural lands at 34 sites across the U.S. Twenty-two analytical methods were used to determine potential contaminant exposures profiles for 452 organic and 114 inorganic chemicals, nine microbial groups, estrogenicity, and cytotoxicity. Analytical results document unique and substantial chemical, microbial, and toxicity profiles for these land-applied wastes. Of the three waste byproducts, biosolids contained the greatest concentrations of household chemicals, pesticides, pharmaceuticals, per-/polyfluoroalkyl substances, calcium, and phosphorus. Livestock waste contained the greatest concentrations of total and leachable dissolved organic carbon, biogenic hormones, mycotoxins, plant estrogens, total inorganic nitrogen, and potassium. Drilling waste contained the greatest concentrations of BTEX compounds (benzene, toluene, ethylbenzene, and xylenes), polycyclic aromatic hydrocarbons, rare-earth elements, barium, strontium, and uranium–thorium series radioisotopes. Biosolid and livestock wastes had greater culturable heterotrophic bacteria, halophilic bacteria, Escherichia coli ( E. coli ), enterococci, and staphylococci concentrations, and greater microbial diversity than drilling waste. Bioassay analyses indicated that exposure to contaminants in livestock wastes and biosolids could result in estrogenic effects, whereas exposure to contaminants in drilling waste could result in cytotoxic effects. Our study documents that current reuse/disposal practices for biosolid, livestock, and drilling wastes on agricultural lands could provide a potential pathway for the redistribution of unique and complex contaminant mixtures into the environment that have bioactive, endocrine disrupting, and carcinogenic characteristics. Results of this study provide a snapshot of chemical compositions and concentrations that can be used to inform the development of best-management practices to help maximize beneficial reuse of these wastes and minimize risk to the environment and human health.

Environmental Science: Processes & Impacts↗
USGS2001

Atomic weights of the elements 1999

The biennial review of atomic-weight, Ar(E), determinations and other cognate data have resulted in changes for the standard atomic weights of the following elements: from to nitrogen 14.006 74??0.000 07 14.0067??0.0002 sulfur 32.066??0.006 32.065??0.005 chlorine 35.4527??0.0009 35.453??0.002 germanium 72.61??0.02 72.64??0.01 xenon 131.29??0.02 131.293??0.006 erbium 167.26??0.03 167.259??0.003 uranium 238.0289??0.0001 238.028 91??0.000 03 Presented are updated tables of the standard atomic weights and their uncertainties estimated by combining experimental uncertainties and terrestrial variabilities. In addition, this report again contains an updated table of relative atomic mass values and half-lives of selected radioisotopes. Changes in the evaluated isotopic abundance values from those published in 1997 are so minor that an updated list will not be published for the year 1999. Many elements have a different isotopic composition in some nonterrestrial materials. Some recent data on parent nuclides that might affect isotopic abundances or atomic-weight values are included in this report for the information of the interested scientific community. ?? 2001 American Institute of Physics.

Journal of Physical and Chemical Reference Data↗
USGS2018

Enhancement and integration of airborne gamma-ray spectrometric and Landsat imagery for regolith mapping — Cape York Peninsula

Airborne gamma-ray spectrometric data (400-m line spacing), gathered for the National Geoscience Mapping Accord North Queensland Project, has proved invaluable for differentiating regolith types based on their potassium, thorium and uranium signatures. The ability of the gamma-ray signal to penetrate the vegetation cover and as much as 40 cm below the surface was a considerable advantage in North Queensland, where traditional mapping techniques are hindered by the thick vegetation cover and where deeply weathered sandy soils frequently mask underlying geology. Two image-processing techniques were used to enhance the gamma-ray data and integrate them with Landsat Thematic Mapper (TM) data. Firstly, a sun-angle illuminated high-pass filtered component (hillshade) of the gamma-ray image was added to a three-band false-colour composite image of the corrected gamma-ray data. The hillshade component highlighted local changes in the gamma-ray signal which related to changes in regolith materials and lithology, and sharpened boundaries associated with geomorphic features. Secondly, the gamma-ray image was integrated (pixel by pixel) with the high-frequency component of the corresponding TM band 5 scene. This allowed the imagery to be interpreted in a geomorphological and structural context. Broad lithological divisions and structural domains were identified in the imagery, but most of the variation within these groups relates to the regolith cover and to geomorphic features in the landscape. Subtle variations in lithology were effectively interpreted only when the responses of the regolith cover are known. The gamma-ray imagery provided an insight into the weathering and geomorphic history of the region. In addition, the imagery can also be interpreted as a ‘geomorphic activity map’, separating stable landforms with deep weathering from younger landforms with active erosion and stripping of the surficial cover. This allows past and present geomorphic processes to be interpreted from the imagery, which in turn provides more informed extrapolation of field results and prediction of regolith types. The imagery was highly useful for basement and regolith mapping. There is considerable potential for assisting with interpretation of both stream-sediment geochemical data and environmental studies, since the resulting imagery effectively maps the distribution of sediments in the landscape, and identifies areas of erosion and land degradation.

Queensland↗
USGS2005

Geochemical controls on microbial nitrate-dependent U(IV) oxidation

After reductive immobilization of uranium, the element may be oxidized and remobilized in the presence of nitrate by the activity of dissimilatory nitrate-reducing bacteria. We examined controls on microbially mediated nitrate-dependent U(IV) oxidation in landfill leachate-impacted subsurface sediments. Nitrate-dependent U(IV)-oxidizing bacteria were at least two orders of magnitude less numerous in these sediments than glucose- or Fe(II)-oxidizing nitrate-reducing bacteria and grew more slowly than the latter organisms, suggesting that U(IV) is ultimately oxidized by Fe(III) produced by nitrate-dependent Fe(II)-oxidizing bacteria or by oxidation of Fe(II) by nitrite that accumulates during organotrophic dissimilatory nitrate reduction. We examined the effect of nitrate and reductant concentration on nitrate-dependent U(IV) oxidation in sediment incubations and used the initial reductive capacity (RDC = [reducing equivalents] - [oxidizing equivalents]) of the incubations as a unified measurement of the nitrate or reductant concentration. When we lowered the RDC with progressively higher nitrate concentrations, we observed a corresponding increase in the extent of U(IV) oxidation, but did not observe this relationship between RDC and U(IV) oxidation rate, especially when RDC > 0, suggesting that nitrate concentration strongly controls the extent, but not the rate of nitrate-dependent U(IV) oxidation. On the other hand, when we raised the RDC in sediment incubations with progressively higher reductant (acetate, sulfide, soluble Fe(II), or FeS) concentrations, we observed progressively lower extents and rates of nitrate-dependent U(IV) oxidation. Acetate was a relatively poor inhibitor of nitrate-dependent U(IV) oxidation, while Fe(II) was the most effective inhibitor. Based on these results, we propose that it may be possible to predict the stability of U(IV) in a bioremediated aquifer based on the geochemical characteristics of that aquifer.

Geomicrobiology Journal↗
USGS2015

Dominance of 'Gallionella capsiferriformans' and heavy metal association with Gallionella -like stalks in metal-rich pH 6 mine water discharge

Heavy metal-contaminated, pH 6 mine water discharge created new streams and iron-rich terraces at a creek bank in a former uranium-mining area near Ronneburg, Germany. The transition from microoxic groundwater with ~5 m m Fe(II) to oxic surface water may provide a suitable habitat for microaerobic iron-oxidizing bacteria (FeOB). In this study, we investigated the potential contribution of these FeOB to iron oxidation and metal retention in this high-metal environment. We (i) identified and quantified FeOB in water and sediment at the outflow, terraces, and creek, (ii) studied the composition of biogenic iron oxides ( Gallionella -like twisted stalks) with scanning and transmission electron microscopy (SEM, TEM) as well as confocal laser scanning microscopy (CLSM), and (iii) examined the metal distribution in sediments. Using quantitative PCR, a very high abundance of FeOB was demonstrated at all sites over a 6-month study period. Gallionella spp. clearly dominated the communities, accounting for up to 88% of Bacteria , with a minor contribution of other FeOB such as Sideroxydans spp. and &lsquo; Ferrovum myxofaciens &rsquo;. Classical 16S rRNA gene cloning showed that 96% of the Gallionella -related sequences had &ge;97% identity to the putatively metal-tolerant &lsquo; Gallionella capsiferriformans ES-2&rsquo;, in addition to known stalk formers such as Gallionella ferruginea and Gallionellaceae strain R-1. Twisted stalks from glass slides incubated in water and sediment were composed of the Fe(III) oxyhydroxide ferrihydrite, as well as polysaccharides. SEM and scanning TEM-energy-dispersive X-ray spectroscopy revealed that stalk material contained Cu and Sn, demonstrating the association of heavy metals with biogenic iron oxides and the potential for metal retention by these stalks. Sequential extraction of sediments suggested that Cu (52&ndash;61% of total sediment Cu) and other heavy metals were primarily bound to the iron oxide fractions. These results show the importance of &lsquo; G. capsiferriformans &rsquo; and biogenic iron oxides in slightly acidic but highly metal-contaminated freshwater environments.

Geobiology↗
USGS2014

Simulation of the effects of seasonally varying pumping on intraborehole flow and the vulnerability of public-supply wells to contamination

Public-supply wells with long screens in alluvial aquifers can produce waters of differing quality from different depths. Seasonal changes in quality are linked to seasonal changes in pumping rates that influence the distribution of flow into the well screens under pumping conditions and the magnitude and direction of intraborehole flow within the wells under ambient conditions. Groundwater flow and transport simulations with MODFLOW and MT3DMS were developed to quantify the effects of changes in average seasonal pumping rates on intraborehole flow and water quality at two long-screened, public-supply wells, in Albuquerque, New Mexico and Modesto, California, where widespread pumping has altered groundwater flow patterns. Simulation results indicate that both wells produce water requiring additional treatment to maintain potable quality in winter when groundwater withdrawals are reduced because less water is derived from parts of the aquifer that contain water requiring less treatment. Simulation results indicate that the water quality at both wells could be improved by increasing average winter-pumping rates to induce more lateral flow from parts of the aquifer that contain better quality water. Arsenic-bearing water produced by the Albuquerque well could be reduced from 55% to 45% by doubling average winter-pumping rate, while nitrate- and uranium-bearing water produced by the Modesto well could be reduced from 95% to 65% by nearly tripling the average winter-pumping rate. Higher average winter-pumping rates would also reduce the volume of intraborehole flow within both wells and prevent the exchange of poor quality water between shallow and deep parts of both aquifers.

California;New Mexico↗
USGS2014

Effects of seasonal operation on the quality of water produced by public-supply wells

Seasonal variability in groundwater pumping is common in many places, but resulting effects of seasonal pumping stress on the quality of water produced by public-supply wells are not thoroughly understood. Analysis of historical water-quality samples from public-supply wells completed in deep basin-fill aquifers in Modesto, California (134 wells) and Albuquerque, New Mexico (95 wells) indicates that several wells have seasonal variability in concentrations of contaminants of concern. In Modesto, supply wells are more likely to produce younger groundwater with higher nitrate and uranium concentrations during the summer (high) pumping season than during the winter (low) pumping season. In Albuquerque, supply wells are more likely to produce older groundwater with higher arsenic concentrations during the winter pumping season than during the summer pumping season. Seasonal variability in contaminant concentrations in Modesto is influenced primarily by effects of summer pumping on vertical hydraulic gradients that drive migration of shallow groundwater through the aquifer to supply wells. Variability in Albuquerque is influenced primarily by the period of time that a supply well is idle, allowing its wellbore to act as a conduit for vertical groundwater flow and contaminant migration. However, both processes are observed in each study area. Similar findings would appear to be likely in other alluvial basins with stratified water quality and substantial vertical head gradients. Results suggest that even in aquifers dominated by old groundwater, changes to seasonal pumping patterns and/or to depth of well completion can help reduce vulnerability to selected contaminants of either natural or anthropogenic origin.

Groundwater↗
USGS2015

Chemical considerations for an updated National assessment of brackish groundwater resources

Brackish groundwater (BGW) is increasingly used for water supplies where fresh water is scarce, but the distribution and availability of such resources have not been characterized at the national scale in the United States since the 1960s. Apart from its distribution and accessibility, BGW usability is a function of the chemical requirements of the intended use, chemical characteristics of the resource, and treatment options to make the resource compatible with the use. Here, we discuss relations between these three chemical factors using national-scale examples and local case studies. In a preliminary compilation of BGW data in the United States, five water types accounted for the major-ion composition of 70% of samples. PHREEQC calculations indicate that 57&ndash;77% of samples were oversaturated with respect to barite, calcite, or chalcedony. In the study, 5&ndash;14% of samples had concentrations of arsenic, fluoride, nitrate, or uranium that exceeded drinking-water standards. In case studies of the potential use of BGW for drinking water, irrigation, and hydraulic fracturing, PHREEQC simulations of a hypothetical treatment process resembling reverse osmosis (RO) showed that BGW had the potential to form various assemblages of mineral deposits (scale) during treatment that could adversely affect RO membranes. Speciation calculations showed that most boron in the irrigation example occurred as boric acid, which has relatively low removal efficiency by RO. Results of this preliminary study indicate that effective national or regional assessments of BGW resources should include geochemical characterizations that are guided in part by specific use and treatment requirements.

Groundwater↗
USGS2006

Arsenic in ground water of the Western United States

Natural occurrences of ground water with moderate (10 to 50 micrograms per liter) to high (greater than 50 micrograms per liter) concentrations of arsenic are common throughout much of the Western United States. High concentrations of arsenic are generally associated with one of four geochemical environments: (1) basin-fill deposits of alluvial-lacustrine origin, particularly in semiarid areas, (2) volcanic deposits, (3) geothermal systems, and (4) uranium and gold-mining areas. These findings are based on an extensive literature review, compilation of unpublished reports and data, and the review of data bases containing more than 7,000 analyses of ground-water samples for arsenic. In the first two environments, arsenic appears to be associated with sediments derived, in part, from volcanic rocks of intermediate to acidic composition. Dissolved arsenic concentrations in water from volcanic aquifers in the same regions, however, may be low (less than 10 micrograms per liter). Solid phases (minerals, amorphous solids, and sedimentary organic matter) that supply the dissolved arsenic have not been identified in most areas. Alluvial and lacustrine sedimentary deposits appear to be an important source of arsenic in volcanic areas (such as Lane County, Oregon) and in areas underlain by basin-fill deposits (such as Carson Desert in Nevada and the Tulare Lake basin in California). Mobilization of arsenic in sedimentary aquifers may be, in part, a result of changes in the geochemical environment due to agricultural irrigation. In the deeper subsurface, elevated arsenic concentrations are associated with compaction caused by groundwater withdrawals.

Groundwater↗
USGS2006

The chemical quality of self-supplied domestic well water in the United States

Existing water quality data collected from domestic wells were summarized to develop the first national‐scale retrospective of self‐supplied drinking water sources. The contaminants evaluated represent a range of inorganic and organic compounds, and although the data set was not originally designed to be a statistical representation of national occurrence, it encompasses large parts of the United States including at least some wells sampled in every state and Puerto Rico. Inorganic contaminants were detected in many of the wells, and concentrations exceeded the U.S. EPA maximum contaminant levels (MCLs; federal drinking water standards used to regulate public drinking water quality) more often than organic contaminants. Of the inorganic constituents evaluated, arsenic concentrations exceeded the MCL (10 μg/L) in ∼11% of the 7580 wells evaluated, nitrate exceeded the MCL (10 mg/L) in ∼8% of the 3465 wells evaluated, uranium‐238 exceeded the MCL (30 μg/L) in ∼4% of the wells, and radon‐222 exceeded 300 and 4000 pCi/L (potential drinking water standards currently under review by the U.S. EPA) in ∼75% and 9% of the wells, respectively. The MCLs for total mercury and fluoride were each exceeded in <1% of the wells evaluated. The MCL was exceeded in <1% of all wells for all anthropogenically derived organic contaminants evaluated and was not exceeded for many contaminants. In addition, 10 contaminants evaluated do not currently have an MCL. Atrazine, however, was detected in 24% of the wells evaluated and was the most frequently detected organic contaminant of the 28 organic contaminants evaluated in this study. Simazine and metolachlor each were detected in ∼9% of all wells and tied for second in frequency of detection for organic contaminants. The third and fourth most frequently detected organic contaminants were methyl tert ‐butyl ether (MTBE) (6%) and chloroform (5%), respectively. Because the water quality of domestic wells is not federally regulated or nationally monitored, this study provides a unique, previously nonexistent, perspective on the quality of the self‐supplied drinking water resources used by ∼45 million Americans in the United States.

Ground Water Monitoring and Remediation↗
USGS2007

Preparation and certification of Re-Os dating reference materials: Molybdenites HLP and JDC

Two Re-Os dating reference material molybdenites were prepared. Molybdenite JDC and molybdenite HLP are from a carbonate vein-type molybdenum-(lead)-uranium deposit in the Jinduicheng-Huanglongpu area of Shaanxi province, China. The samples proved to be homogeneous, based on the coefficient of variation of analytical results and an analysis of variance test. The sampling weight was 0.1 g for JDC and 0.025 g for HLP. An isotope dilution method was used for the determination of Re and Os. Sample decomposition and pre-concentration of Re and Os prior to measurement were accomplished using a variety of methods: acid digestion, alkali fusion, ion exchange and solvent extraction. Negative thermal ionisation mass spectrometry and inductively coupled plasma-mass spectrometry were used for the determination of Re and 187 Os concentration and isotope ratios. The certified values include the contents of Re and Os and the model ages. For HLP, the Re content was 283.8 ± 6.2 μg g −1 , 187 Os was 659 ± 14 ng g −1 and the Re-Os model age was 221.4 ± 5.6 Ma. For JDC, the Re content was 17.39 ± 0.32 μg g −1 , 187 Os was 25.46 ± 0.60 ng g −1 and the Re-Os model age was 139.6 ± 3.8 Ma. Uncertainties for both certified reference materials are stated at the 95% level of confidence. Three laboratories (from three countries: PR. China, USA, Sweden) joined in the certification programme. These certified reference materials are primarily useful for Re-Os dating of molybdenite, sulfides, black shale, etc.

Geostandards and Geoanalytical Research↗
USGS2021

A revised position for the primary strand of the Pleistocene-Holocene San Andreas fault in southern California

The San Andreas fault has the highest calculated time-dependent probability for large-magnitude earthquakes in southern California. However, where the fault is multistranded east of the Los Angeles metropolitan area, it has been uncertain which strand has the fastest slip rate and, therefore, which has the highest probability of a destructive earthquake. Reconstruction of offset Pleistocene-Holocene landforms dated using the uranium-thorium soil carbonate and beryllium-10 surface exposure techniques indicates slip rates of 24.1 ± 3 millimeter per year for the San Andreas fault, with 21.6 ± 2 and 2.5 ± 1 millimeters per year for the Mission Creek and Banning strands, respectively. These data establish the Mission Creek strand as the primary fault bounding the Pacific and North American plates at this latitude and imply that 6 to 9 meters of elastic strain has accumulated along the fault since the most recent surface-rupturing earthquake, highlighting the potential for large earthquakes along this strand.

California↗
USGS2005

Dating the growth of oceanic crust at a slow-spreading ridge

Nineteen uranium-lead zircon ages of lower crustal gabbros from Atlantis Bank, Southwest Indian Ridge, constrain the growth and construction of oceanic crust at this slow-spreading midocean ridge. Approximately 75% of the gabbros accreted within error of the predicted seafloor magnetic age, whereas ???25% are significantly older. These anomalously old samples suggest either spatially varying stochastic intrusion at the ridge axis or, more likely, crystallization of older gabbros at depths of ???5 to 18 kilometers below the base of crust in the cold, axial lithosphere, which were uplifted and intruded by shallow-level magmas during the creation of Atlantis Bank.

Science↗
USGS1964

Isotopic composition of lead and strontium from Ascension and Gough islands

Isotopic composition of lead and strontium has been determined in a series of rock samples from two islands on the Mid-Atlantic Ridge. Both interand intra-island variations exist in the abundance of radiogenic isotopes of both elements. Lead from basalt of Ascension Island has a Pb 206 -Pb 204 ratio of 19.5, while the corresponding ratio at Gough Island is only 18.4. The Pb 208 -Pb 204 ratios from the two islands do not differ. Conversely, strontium from basalt of Ascension Island is less radiogenic than that from Gough Island basalts. The trachytes of both islands have lead and strontium that is more radiogenic than that found in the basalts. The inter-island differences indicate the existence of regional variations in the uranium-lead and rubidium-strontium ratios of the upper mantle source of these rocks and show that isotope compositions are a means for investigating chemical heterogeneities in the mantle.

Science↗
USGS1966

Genetic relations of oceanic basalts as indicated by lead isotopes

The isotopic compositions of lead and the concentrations of lead, uranium, and thorium in samples of oceanic tholeiite and alkali suites are determined, and the genetic relations of the oceanic basalts are discussed. Lead of the oceanic tholeiites has a varying lead-206 : lead-204 ratio between 17.8 and 18.8, while leads of the alkali basalt suites from Easter Island and Guadalupe Island are very radiogenic with lead-206 : lead-204 ratios between 19.3 and 20.4. It is concluded that (i) the isotopic composition of lead in oceanic tholeiite suggests that the upper mantle source region of the tholeiite was differentiated from an original mantle material more than 1 billion years ago and that the upper mantle is not homogeneous at the present time, (ii) less than 20 million years was required for the crystal differentiation within the alkali suite from Easter Island, (iii) no crustal contamination was involved in the course of differentiation of rocks from Easter Island; however, some crustal contamination may have affected Guadalupe Island rocks, and (iv) alkali basalt may be produced from the tholeiite in the oceanic region by crystal differentiation. Alternatively the difference in the isotopic composition of lead in oceanic basalts may be produced by partial melting at different depths of a differentiated upper mantle.

Science↗