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At least 181 records · Page 10Linked to original sources
USGS2001

Chemical analysis and modes of occurrence of selected trace elements in a Powder River basin coal and its corresponding simulated cleaned coal

This report provides semi-quantitative data on modes of occurrence of 19 elements in as-mined Powder River Basin coal and its corresponding simulated cleaned coal. The data are in support of the project "Prediction of Trace Element Removal from Coal" --a Cooperative Research and Development Agreement (CRADA) with CQ Inc. The purpose of this CRADA is to apply modes of occurrence information to coal cleaning procedures. Techniques used in this study include sequential selective leaching procedures, scanning electron microscopy, X-ray diffraction analysis, and electron microprobe analysis. Selective leaching results indicate that greater than 40 percent of the elements Co, U, Be, Ca, Fe, Mn, Ba, Zn, Cd, Pb are associated with HCIsoluble carbonates, iron oxides, or monosulfides, greater than 40 percent of the Al, Cr and Mo are associated with HF-soluble silicates, greater than 40 percent of the Ni, Cu, As and Sb are associated with acid-insoluble phases and/or organic matter, and greater than 50 percent of the Hg is associated with HMDs-soluble pyrite. Thirty percent of the Th was leached by HCI and 30 percent of this element was leached by HF. Scanning electron microscopy indicates that quartz, kaolinite, illite and iron oxide, possibly hematite, are the major minerals present. X-ray diffraction analysis confirmed that quartz, kaolinite and hematite are present, but did not determine illite, indicating that illite in these coals is of low abundance or is poorly crystalline. Electron microprobe data indicate that concentrations of the chalcophile elements As, Se, Cu, Ni, Zn, and Cd in most pyrite grains are at or below the detection limit of about 100-200 ppm in both the as-mined coal and its corresponding simulated cleaned coal product. The results of this project should aid in the development of models for predicting the response of potentially toxic trace elements in commercial coal cleaning procedures.

Open-File Report↗
USGS2024

Evidence of nitrate attenuation in intertidal and subtidal groundwater in a subterranean estuary at a Cape Cod embayment, East Falmouth, Massachusetts, 2015–16

Nitrogen dynamics in intertidal and nearshore subtidal groundwater (subterranean estuary) adjacent to the Seacoast Shores peninsula, Falmouth, Massachusetts, were investigated during 2015–16 by the U.S. Geological Survey. The peninsula is a densely populated residential area with septic systems and cesspools that are substantial sources of nitrogen to groundwater. The study area is in the Eel River, an estuarine saltwater embayment connected to the ocean adjacent to the western shore of the peninsula, that was the subject of an earlier study by Colman and others (2018, https://doi.org/10.3133/sir20185095 ) on nitrogen transport and transformations in groundwater between onshore and offshore locations. The previous study documented the distribution of nitrate concentrations and nitrate attenuation reactions in fresh groundwater beneath the peninsula and the estuary. The current study extended those observations with more detailed sampling and analysis of shallow groundwater from wells near discharge sites beneath the estuary. The current field investigation included sampling of existing wells and installation and sampling of clusters of wells and temporary sampling points in the subterranean estuary, including (1) shallow transects 0.3 to 1.2 meters (m) deep extending from 1 to 13.5 m offshore and (2) deeper wells (from 1.83 to 4.88 m deep) extending from 4.3 to 14.3 m offshore. Measurements of hydraulic-head gradients 2–5 m below the sediment/water interface in the intertidal and nearshore subtidal zones indicated that groundwater flow generally was upwards (towards the estuary) under all tide conditions in October 2016. The magnitude of the gradient was greatest during low tide conditions, indicating that groundwater discharge likely decreased during high tides. Measurements of specific conductance in shallow groundwater in the subterranean estuary in three transects perpendicular to shore were consistent with the existence of saltwater flow cells (infiltration of overlying saline water, mixing with fresh groundwater, and discharge to the overlying saline water) in the intertidal and nearshore subtidal regions. The size of these flow cells was variable in space and time and dependent on the elevation of the tide (spring or neap). At this location in the Eel River subterranean estuary, and offshore to at least 13.5 m, offshore flow of fresh groundwater apparently prevented a deeper saltwater wedge from discharging to the surface. Nitrate concentrations in shallow groundwater (30 to 122 centimeters [cm] depth) were variable in space and time, ranging from not detectable to 600 micromoles per liter (μmol/L) (8.4 milligrams per liter as N), and were highest in June 2016 at depths from 61 to 122 cm below the sediment/water interface and from 4 to 9 m offshore. Nitrate generally was not detectable in saline shallow groundwater at 30-cm depth or at any depth from 30 to 122 cm from 10 to 13.5 m offshore. Dissolved oxygen concentrations were suboxic (less than 16 μmol/L) in 60 percent of the sampled subterranean groundwater beneath the intertidal and subtidal zones. In the remaining sites, the range of dissolved oxygen concentrations was from 18 to 272 μmol/L and the median concentration was 43 μmol/L. Evidence for microbial nitrate reduction (denitrification and possibly anammox) was provided by the distribution of the reaction product nitrogen gas (excess N 2 , or N 2MIC ), as determined from analysis of the dissolved nitrogen gas and argon gas (Ar) concentrations in groundwater samples. Excess nitrogen gas provided evidence for nitrate reduction in shallow groundwater below the subtidal and, to a lesser extent, intertidal zones adjacent to the Seacoast Shores peninsula. These zones, where evidence for nitrate reduction was detected, were in fresh and brackish groundwater near subtidal or intertidal saltwater cells where discharging fresh groundwater mixed with infiltrating saline water. Infiltrating seawater may have supplied organic carbon, one of several potential electron donors that are required for denitrification. Other potential electron donors, such as organic carbon, iron, manganese, hydrogen, methane, ammonium, elemental sulfur, or sulfide phases, may have been supplied by the estuarine sediments. Drainage from surface runoff near the shore also may have supplied organic carbon to fresh groundwater near the intertidal saltwater cell. The highest amounts of nitrate converted to excess nitrogen gas were estimated to be in the range of 230 to 430 μmol/L in nearly fresh groundwater near the subtidal saltwater cell at depths of 61 to 122 cm below the sediment/water interface and from 10 to 13.5 m offshore. Evidence of denitrification within 10 m of the shore was sparse (generally limited to less than 50 μmol/L of N 2 -N) despite the presence of high nitrate concentrations. The spatial distribution of estimated nitrate reduction in the intertidal and nearshore subtidal fresh and brackish groundwater may be related to local variability in the distribution of reactive electron donors in those zones. Variations in the amount of nitrate reduction to nitrogen gas were not clearly related to potential aqueous electron donors such as dissolved organic carbon, nor to potential reaction products such as alkalinity, but may have been controlled by combinations of aqueous and solid-phase reactants. The distribution of relatively shallow fresh groundwater containing nitrate could indicate potential nitrate discharge areas in the lower intertidal zone and uncertain locations farther offshore; however, the data did not extend all the way to the sediment/water interface or to the offshore freshwater limit. This study confirmed substantial loss of nitrate from some of the fresh and brackish groundwater in shallow subestuarine sediments prior to discharge but did not quantify how much nitrate eventually discharged to the estuary.

Massachusetts↗
USGS2026

Treatability study to evaluate bioremediation of trichloroethene at Site K, former Twin Cities Army Ammunition Plant, Arden Hills, Minnesota, 2020–22

Executive Summary Chlorinated solvents, including trichloroethene (TCE) and other chlorinated volatile organic compounds (cVOCs), are widespread contaminants that can be treated by bioremediation approaches that enhance anaerobic reductive dechlorination. Reductive dechlorination can be enhanced either through the addition of an electron donor (biostimulation) or the addition of a known dechlorinating culture (bioaugmentation) along with an electron donor. Although bioremediation has been applied at many TCE-contaminated groundwater sites, application in source zones at sites where residual dense nonaqueous phase liquid (DNAPL) is present is more limited. In this study, laboratory and field treatability tests were completed to evaluate the potential application of anaerobic bioremediation for a shallow groundwater plume containing TCE in a perched alluvial aquifer at Site K, former Twin Cities Army Ammunition Plant, Arden Hills, Minnesota, which was on the National Priorities List as the New Brighton/Arden Hills Superfund site until 2019. In addition to the presence of residual DNAPL at the site, temporal variability in groundwater flow directions and input of oxygenated recharge were possible complicating factors for the application of enhanced anaerobic biodegradation in the shallow plume. The Site K plume extends beneath the footprint of Building 103, which was demolished in 2006, and soil excavations to a maximum depth of 6 feet (ft) below ground surface in 2014 were known to leave some deeper contaminated soil in place in the TCE source area. Groundwater treatment at the site, formalized as part of the 1997 Record of Decision, has been in operation since 1986 and consists of an extraction trench at the downgradient edge of the plume to collect groundwater, which is then pumped to an on-site air stripper. Groundwater concentrations in the plume have been relatively stable since treatment began, indicating a continued source of TCE in the aquifer. The desire for a destructive remedy that would enhance the removal of cVOCs in the aquifer at Site K and shorten the remediation timeframe led the U.S. Army to request that the U.S. Geological Survey conduct a groundwater treatability study to assess bioremediation. This report describes the U.S. Geological Survey bioremediation treatability study conducted during 2020–22, including pre-design site characterization to assist in formulating the bioremediation approach, laboratory experiments to support the design of the field pilot test, and implementation and 1-year performance monitoring results for the pilot test. Pre-design site characterization included the collection of soil cores for cVOC analysis and lithologic descriptions and the re-installment of three wells to obtain hydrologic measurements and initial groundwater chemistry. Relatively flat head gradients were measured at the site, and substantial decreases in water-level elevations occurred from spring to summer (May–July 2021). Continuous water-level monitoring indicated a rapid response to precipitation. Groundwater flow velocities were consistently less than 0.5 foot per day, and the pilot bioremediation test was therefore designed with short lateral distances (about 5 ft) between injection and individual monitoring points. Soil analyses confirmed that high volatile organic compound contamination was left in place in the source area. The highest concentrations were near or in clay at the base of the perched aquifer. Concentrations of cVOCs measured in the replaced wells were consistent with historical data and had a maximum TCE concentration of 57,700 micrograms per liter (μg/L), indicative of nearby residual DNAPL based on the general rule of observed concentrations exceeding 1 percent of solubility. The primary TCE daughter product detected was 1,2-cis-dichloroethene (cisDCE), which indicated limited reductive dechlorination in the plume. Groundwater in both the source and downgradient areas was relatively reducing during the pre-design characterization, particularly in the source area where methane concentrations greater than 400 μg/L were measured. Initial laboratory tests conducted using native aquifer microorganisms from the three replacement wells showed that anaerobic TCE biodegradation rates were low when biostimulated with the addition of sodium lactate as an electron donor, also known as a carbon donor, and resulted in the production of only cisDCE. Addition of a known dechlorinating culture, WBC-2, however, resulted in rapid biodegradation and production of ethene, verifying complete reductive dechlorination of TCE. Microcosms constructed with aquifer soil collected from the site were used to evaluate other electron donors besides lactate to support reductive dechlorination by WBC-2, including corn syrup as an alternative fast-release compound and whey, soy-based vegetable oil, and 3-D Microemulsion (Regenesis, San Clemente, California) as slow-release compounds. First-order rate constants for total organic chlorine removal in these WBC-2 amended microcosms were greatest with either lactate or vegetable oil as the donor, ranging between 0.061 and 0.047 per day or corresponding half-lives of 11–15 days. Testing of commercial products in other WBC-2-bioaugmented microcosms led to selection for the field pilot test of an emulsified vegetable oil product that also contained some sodium lactate as a fast-release donor. Delaying the addition of WBC-2 relative to the donor in the microcosms resulted in the most rapid overall biodegradation rates. The selected design for the pilot test utilized three separate test plots, each about 30-ft wide and 60-ft long: plots GS1 and GS2 in the source area of the plume and plot GS3 in the downgradient area of the plume near the excavation trench. Each test plot had one injection well, one monitoring well upgradient from the injection point, and 12 surrounding monitoring wells in a grid to capture variable groundwater flow directions. Donor injections, which included a bromide tracer, were completed in October 2021, immediately following baseline sampling, and the WBC-2 culture was injected about 40 days later, between November 30 and December 2, 2021. Performance monitoring conducted until December 2022 included hydrologic measurements and analyses of cVOCs, redox-sensitive constituents, dissolved organic carbon, bromide, volatile fatty acids, compound-specific carbon isotopes, and microbial communities. The biogeochemical data collected during the pilot tests in the three treatment plots showed that enhanced, complete reductive dechlorination of cVOCs in the groundwater was achieved in the GS1 and GS3 plots. In contrast, evidence of distribution of the injected amendments and subsequent biodegradation was limited in GS2, which was in an area of more heterogeneous soil lithology and low water table elevations. The molar composition of volatile organic compounds in the GS1 and GS3 plots was dominated by ethene in wells that were reached by the injected amendments by the end of the monitoring period. In the GS1 and GS3 plots, similar patterns were observed of cVOC concentrations decreasing to near detection levels, or below, at some wells sampled in July and October 2022, whereas ethene became dominant and indicated sustained complete reductive dechlorination. Baseline cVOC concentrations were more than a factor of 10 higher in the groundwater in the GS1 plot than in GS3, but no apparent inhibition of complete dechlorination occurred. As expected from the initial pre-design site data and the laboratory experiments, enhanced dissolution of residual DNAPL coupled to biodegradation was evident in the GS1 plot, where a marked increase in dichloroethene (DCE) above the initial baseline and upgradient TCE and DCE concentrations occurred. DCE concentrations subsequently declined where DNAPL dissolution was evident, concurrent with production of vinyl chloride and then predominantly ethene. Thus, overall biodegradation rates outpaced the DNAPL dissolution and desorption and DCE production in the source area. This success in complete degradation to predominantly ethene was achieved even in areas where the DCE concentrations reached a maximum of about 30,000 μg/L. Compound specific isotope analysis of carbon in TCE, cisDCE, trans-1,2-dichloroethene, and vinyl chloride was conducted to provide another line of evidence of the occurrence and extent of anaerobic biodegradation. Along a flow path in each plot that was affected by the injected amendments, carbon isotopes in the TCE and daughter cVOCs in the groundwater became isotopically heavier, indicating biodegradation. Enhanced biodegradation rates calculated from the field tests in GS1 and GS3 showed half-lives of 36.9–75.3 days for DCE degradation and 9.48–38.5 days for ethene production. Notably, these ethene production rates calculated from the field tests are consistent with the results of WBC-2-bioaugmented microcosms amended with either lactate or vegetable oil, which had half-lives for total organic chlorine removal that ranged from 11 to 15 days. These rates indicated rapid enhanced biodegradation, which is promising for application of a full-scale bioremediation remedy. Ultimately, however, the mass of residual or sorbed TCE in the aquifer that remains accessible for dissolution and biodegradation would likely control the time required for a full-scale bioremediation effort to achieve performance goals for TCE and cisDCE specified in the Record of Decision for Site K. The field pilot tests showed that the relatively low hydraulic head gradients and temporal changes in groundwater flow directions in the shallow aquifer would add complexity to a full-scale bioremediation effort. The radius of influence (ROI) at GS1 and GS3 (16.3 ft and 12.7 ft, respectively) were close to the design ROI of 15 ft. The estimated ROI at GS2 was about four times the design ROI, but may be less reliable at this location owing to groundwater flow direction. In addition, the low temperatures following WBC-2 injection in late November to early December 2021, in combination with the low hydraulic head gradients, were probably major factors in the delay observed before the onset of enhanced biodegradation following injection of the culture. Additional test injections could be beneficial to optimize the timing of donor and culture injections with the variable temperatures and hydraulic head in the shallow aquifer.

Minnesota↗
USGS2023

Creating oriented and precisely sectioned mineral mounts for in situ chemical analyses—An example using olivine for diffusion chronometry studies

Diffusion chronometry is now a widely applied methodology for determining the rates and timescales of geologic processes from the chemical zoning observed in minerals. Despite the popularity of the method, several challenges still remain during its application, including: (1) the random sectioning of minerals either in thin sections or grain mounts in which both off-center and oblique sections contribute substantial uncertainty to modeled timescales and (2) diffusion anisotropy needs to be accounted for in models, which generally requires determining the principal crystallographic axes of the mineral using electron backscatter diffraction, a technique that is both challenging and limiting because few scanning electron microscopes have an electron backscatter detector. This guide developed by the U.S. Geological Survey focuses on a step-by-step methodology for mounting individually oriented minerals that are sectioned through their cores prior to polishing for analytical work. Using this technique, one can significantly reduce the uncertainties associated with off-center sections and minimize or completely remove the need for determining crystallographic orientation via electron backscatter diffraction analyses. This report is presented as a guide for using the technique on olivine crystals but can be applied to any minerals that can be extracted for analysis. Two variations of the methodology are included here: (1) The individual crystal method that entails mounting individually sectioned single crystals and crystal groups and (2) the whole mount method in which multiple single crystals or crystal clusters are mounted and sectioned at the same time.

Techniques and Methods↗
USGS2013

Modeling the long-term fate of agricultural nitrate in groundwater in the San Joaquin Valley, California

Nitrate contamination of groundwater systems used for human water supplies is a major environmental problem in many parts of the world. Fertilizers containing a variety of reduced nitrogen compounds are commonly added to soils to increase agricultural yields. But the amount of nitrogen added during fertilization typically exceeds the amount of nitrogen taken up by crops. Oxidation of reduced nitrogen compounds present in residual fertilizers can produce substantial amounts of nitrate which can be transported to the underlying water table. Because nitrate concentrations exceeding 10 mg/L in drinking water can have a variety of deleterious effects for humans, agriculturally derived nitrate contamination of groundwater can be a serious public health issue. The Central Valley aquifer of California accounts for 13 percent of all the groundwater withdrawals in the United States. The Central Valley, which includes the San Joaquin Valley, is one of the most productive agricultural areas in the world and much of this groundwater is used for crop irrigation. However, rapid urbanization has led to increasing groundwater withdrawals for municipal public water supplies. That, in turn, has led to concern about how contaminants associated with agricultural practices will affect the chemical quality of groundwater in the San Joaquin Valley. Crop fertilization with various forms of nitrogen-containing compounds can greatly increase agricultural yields. However, leaching of nitrate from soils due to irrigation has led to substantial nitrate contamination of shallow groundwater. That shallow nitrate-contaminated groundwater has been moving deeper into the Central Valley aquifer since the 1960s. Denitrification can be an important process limiting the mobility of nitrate in groundwater systems. However, substantial denitrification requires adequate sources of electron donors in order to drive the process. In many cases, dissolved organic carbon (DOC) and particulate organic carbon (POC) are the primary electron donors driving active denitrification in groundwater. The purpose of this chapter is to use a numerical mass balance modeling approach to quantitatively compare sources of electron donors (DOC, POC) and electron acceptors (dissolved oxygen, nitrate, and ferric iron) in order to assess the potential for denitrification to attenuate nitrate migration in the Central Valley aquifer.

California↗
USGS1998

The North American Bird Banding Program: Into the 21st century

The authors examined the legal, scientific, and philosophical underpinnings of the North American Bird Banding Program [BBP], with emphasis on the U.S. Bird Banding Laboratory [BBL], but also considering the Canadian Bird Banding Office [BBO]. In this report, we review the value of banding data, enumerate and expand on tile principles under which any modern BBP should operate, and from them derive our recommendations. These are cast into a Mission Statement, a Role and Function Statement, and a series of specific recommendations addressing five areas: (1) permitting procedures and practices; (2) operational issues; (3) data management; (4) BBL organization and staffing; and (5) implementation. Our major tenets and recommendations are as follows: banding provides valuable data for numerous scientific, management, and educational purposes, and its benefits far outweigh necessary biological and fiscal costs, especially those incurred by the BBL and BBO; because of the value of banding data for management of avian resources, including both game and nongame birds, government support of the program is fully justified and appropriate; all banding data, if collected to appropriate standards, are potentially valuable; there are many ways to increase the value of banding data such as by endorsing, promoting, and applying competence and/or training standards for permit issuance; promoting bander participation in well-designed projects; and by encouraging the use of banding data for meta-analytical approaches; the BBL should apply, promote, and encourage such standards, participation, and approaches; the BBP should be driven by the needs of users, including scientists and managers; all exchange of data and most communication between banders and the BBL should become electronic in the near future; the computer system at the BBL should be modernized to one designed for a true client-server relationship and storage of data in on-line relational databases; the BBL should continue to maintain high quality control and editing standards and should strive to bring all data in the database up to current standards; however, the BBL should transfer a major portion of the responsibility for editing banding data to the bander by providing software that will permit the bander to edit his/her own data electronically before submission to the BBL; the BBL should build the capacity to store additional data tied to original band records able to be pre-edited and submitted electronically, such as recapture data, appropriate data from auxiliary marking (e.g. resightings of color-marked birds), and other data that gain value when pooled from many banders (e.g., measurements); however, the BBL should only accept such data if they are collected using standardized methods and as part of an established program designed to utilize such data; now is the time to consider options for implementing a Western Hemisphere banding program, with leadership from the BBL; the Patuxent Electronic Data Processing Section should become part of the BBL; additional scientific and technical staff must be added to the BBL; an Implementation Team should be formed to expedite our recommendations, following timetables outlined in this document.

Journal of Field Ornithology↗
USGS1980

Emission spectra of the cations of some fluoro-substituted phenols in the gaseous phase

Emission spectra of the cations of 2,5- and 3,5-difluorophenol, of 2,3,4- and 2,4,5-trifluorophenol, of 2,3,5,6-tetrafluorophenol and of 2,3,4,5,6-pentafluorophenol have been obtained in the gas phase using low-energy electron beam excitation. The band systems are assigned to the B̃ (π −1 ) → X̃ (π −1 ) electronic transitions of these cations by reference to photoelectron spectroscopic data. The He(Iα) photoelectron spectra and the ionisation energies of ten fluoro-substituted phenols are reported. The symmetries of the four lowest electronic states of these cations are inferred from the radiative decay studies. The lifetimes of the lowest vibrational levels of the B̃ (π −1 ) state of the six fluoro-substituted phenol cations above have also been measured.

Journal of Electron Spectroscopy and Related Pheno↗
USGS2024

Estimating internal transmitter and external tag retention by Walleye in the Laurentian Great Lakes over multiple years

Objective Both electronic tags (e.g., acoustic and radio transmitters) and conventional external tags are used to evaluate movement and population dynamics of fish. External tags are also sometimes used to facilitate the recovery of internal electronic tags or other instrumentation because healing can make it difficult to identify fish with internal tags based on appearance alone. With both tag types, tag shedding and failure of electronic tags can affect accuracy and precision of study results. Methods We used a decade (2011–2021) of recapture data for Walleye Sander vitreus tagged in the Laurentian Great Lakes, where fish were double- or triple-tagged with external tags (T-bar, loop, or internal anchor tags) and internal acoustic transmitters, to quantify external tag and internal transmitter shedding and transmitter failure rates. Result In total, 1125 (33%) Walleye were recovered that had retained at least one external tag or internal transmitter. No confirmed cases of transmitter shedding were observed; 15 of 899 transmitters (2%) that were checked for functionality failed prior to the expected battery expiration. The retention of external T-bar tags 1 year after release differed depending on whether the tag was placed anterior or posterior to the secondary dorsal fin (anterior, fish length = 420 mm: 73% retention; anterior, fish length = 700 mm: 73%, posterior: 63%) but was <26% after 4 years for both tag positions and fish sizes. Internal anchor tags had an 88% 1-year retention probability and 81% 4-year retention probability. Loop tags had the highest 1-year retention (89%) but after 4 years retention (28–34% depending on agency) was comparable to that of T-bar tags. Conclusion Better understanding of tag retention characteristics through long-term tagging studies such as this can inform study design, be considered in model design, and ultimately improve inferences from mark–recapture studies.

North American Journal of Fisheries Management↗
USGS1999

Preliminary study on the mode of occurrence of arsenic in high arsenic coals from southwest Guizhou Province

Coal samples from high arsenic coal areas have been analyzed by electron micropbe analyzer (EMPA), scanning electron microscopy with an energy dispersive X-ray analyzer (SEM-EDX), X-ray diffinction analysis (XRD), low temperature ashing (LTA), transmission electron microscopy (TEM), X-ray absorption fine structure (XAFS), instnunent neutron activation analysis (INAA) and wet chemical analysis. Although some As-bearing minerals such as pyrite, arsenopyrite, realgar (?), As-bearing sulfate, and As-bearing clays are found in the high arsenic coals, their contents do not account for the abundance of arsenic in the some coals. Analysis of the coal indicates that arsenic exists mainly in the form of A s 5+ and A s 3+ , combined with compounds in the organic matrix. The occurrence of such exceptionally high arsenic contents in coal and the fact that the arsenic is dominantly organically associated are unique observations. The modes of occurrence of arsenic in high As-coals are discussed.

Science in China, Series D: Earth Sciences↗
USGS2000

Enrichment of Geobacter species in response to stimulation of Fe(III) reduction in sandy aquifer sediments

Engineered stimulation of Fe(III) has been proposed as a strategy to enhance the immobilization of radioactive and toxic metals in metal-contaminated subsurface environments. Therefore, laboratory and field studies were conducted to determine which microbial populations would respond to stimulation of Fe(III) reduction in the sediments of sandy aquifers. In laboratory studies, the addition of either various organic electron donors or electron shuttle compounds stimulated Fe(III) reduction and resulted in Geobacter sequences becoming important constituents of the Bacterial 16S rDNA sequences that could be detected with PCR amplification and denaturing gradient gel electrophoresis (DGGE). Quantification of Geobacteraceae sequences with a PCR most-probable-number technique indicated that the extent to which numbers of Geobacter increased was related to the degree of stimulation of Fe(III) reduction. Geothrix species were also enriched in some instances, but were orders of magnitude less numerous than Geobacter species. Shewanella species were not detected, even when organic compounds known to be electron donors for Shewanella species were used to stimulate Fe(III) reduction in the sediments. Geobacter species were also enriched in two field experiments in which Fe(III) reduction was stimulated with the addition of benzoate or aromatic hydrocarbons. The apparent growth of Geobacter species concurrent with increased Fe(III) reduction suggests that Geobacter species were responsible for much of the Fe(III) reduction in all of the stimulation approaches evaluated in three geographically distinct aquifers. Therefore, strategies for subsurface remediation that involve enhancing the activity of indigenous Fe(III)-reducing populations in aquifers should consider the physiological properties of Geobacter species in their treatment design.

Microbial Ecology↗
USGS1990

Structure and morphology of magnetite anaerobically-produced by a marine magnetotactic bacterium and a dissimilatory iron-reducing bacterium

Intracellular crystals of magnetite synthesized by cells of the magnetotactic vibroid organism, MV-1, and extracellular crystals of magnetite produced by the non-magnetotactic dissimilatory iron-reducing bacterium strain GS-15, were examined using high-resolution transmission electron microscopy, electron diffraction and 57 Fe Mo¨ssbauer spectroscopy. The magnetotactic bacterium contained a single chain of approximately 10 crystals aligned along the long axis of the cell. The crystals were essentially pure stoichiometric magnetite. When viewed along the crystal long axis the particles had a hexagonal cross-section whereas side-on they appeared as rectangules or truncated rectangles of average dimension, 53 × 35 nm. These findings are explained in terms of a three-dimensional morphology comprising a hexagonal prism of 110 faces which are capped and truncated by 111 end faces. Electron diffraction and lattice imaging studies indicated that the particles were structurally well-defined single crystals. In contrast, magnetite particles produced by the strain, GS-15 were irregular in shape and had smaller mean dimensions (14 nm). Single crystals were imaged but these were not of high structural perfection. These results highlight the influence of intracellular control on the crystallochemical specificity of bacterial magnetites. The characterization of these crystals is important in aiding the identification of biogenic magnetic materials in paleomagnetism and in studies of sediment magnetization.

Earth and Planetary Science Letters↗
USGS1994

The geochemical evolution of low-molecular-weight organic acids derived from the degradation of petroleum contaminants in groundwater

The geochemical evolution of low-molecular-weight organic acids in groundwater downgradient from a crude-oil spill near Bemidji, Minnesota, was studied over a five year period (1986–1990). The organic acids are metabolic intermediates of the degradation of components of the crude oil and are structurally related to hydrocarbon precursors. The concentrations of organic acids, particularly aliphatic acids, increase as the microbial alteration of hydrocarbons progresses. The organic-acid pool changes in composition and concentration over time and in space as the degradation processes shift from Fe(III) reduction to methanogenesis. Over time, the aquifer system evolves into one in which the groundwater contains more oxidized products of hydrocarbon degradation and the reduced forms of iron, manganese, and nitrogen. Laboratory microcosm experiments with aquifer material support the hypothesis that organic acids observed in the groundwater originate from the microbial degradation of aromatic hydrocarbons under anoxic conditions. The geochemistry of two other shallow aquifers in coastal plain sediments, one contaminated with creosote waste and the other with gasoline, were compared to the Bemidji site. The geochemical evolution of the low-molecular-weight organic acid pool in these systems is controlled, in part, by the presence of electron acceptors available for microbially mediated electron-transfer reactions. The depletion of electron acceptors in aquifers leads to the accumulation of aliphatic organic acids in anoxic groundwater.

Geochimica et Cosmochimica Acta↗
USGS1986

Deformation microstructures of Barre granite: An optical, Sem and Tem study

New scanning electron microscope techniques have been developed for characterizing ductile deformation microstructures in felsic rocks. In addition, the thermomechanical history of the macroscopically undeformed Barre granite (Vermont, U.S.A.) has been reconstructed based on examination of deformation microstructures using optical microscopy, scanning electron microscopy, and transmission electron microscopy. The microstructures reveal three distinct events: 1. (1) a low-stress, high-temperature event that produced subgrains in feldspars, and subgrains and recrystallized grains in quartz; 2. (2) a high-stress, low-temperature event that produced a high dislocation density in quartz and feldspars; and 3. (3) a lowest-temperature event that produced cracks, oriented primarily along cleavage planes in feldspars, and parallel to the macroscopic rift in quartz. The first two events are believed to reflect various stages in the intrusion and cooling history of the pluton, and the last may be related to the last stages of cooling, or to later tectonism.

Vermont↗
USGS2007

Iron- and 4-hydroxy-2-alkylquinoline-containing periplasmic inclusion bodies of Pseudomonas aeruginosa: A chemical analysis

Dark aggregated particles were seen on pellets of iron-rich, mid-logarithmic phase Pseudomonas aeruginosa. Transmission electron microscopy of these cells showed inclusion bodies in periplasmic vacuoles. Aggregated particles isolated from the spent medium of these cells contained iron as indicated by atomic absorption spectroscopy and by electron paramagnetic resonance spectroscopy that revealed Fe3+. Scanning electron microscopy/energy dispersive X-ray analysis of whole cells revealed the presence of iron-containing particles beneath the surface of the cell, indicating that the isolated aggregates were the intracellular inclusion bodies. Collectively, mass spectroscopy and nuclear magnetic resonance spectroscopy of the isolated inclusion bodies revealed the presence of 3,4-dihydroxy-2-heptylquinoline which is the Pseudomonas quinolone signaling compound (PQS) and an iron chelator; 4-hydroxy-2-heptylquinoline (pseudan VII), which is an iron chelator, antibacterial compound and precursor of PQS; 4-hydroxy-2-nonylquinoline (pseudan IX) which is an iron chelator and antibacterial compound; 4-hydroxy-2-methylquinoline (pseudan I), and 4-hydroxy-2-nonylquinoline N-oxide. ?? 2006 Elsevier Inc. All rights reserved.

Bioorganic Chemistry↗
USGS2004

Speciation and characterization of arsenic in gold ores and cyanidation tailings using X-ray absorption spectroscopy

The knowledge of mineralogy and molecular structure of As is needed to better understand the stability of As in wastes resulting from processing of gold ores. In this study, optical microscopy, scanning electron microscopy, electron microprobe, X-ray diffraction and X-ray absorption fine structure (XAFS) spectroscopy (including both XANES and EXAFS regimes) were employed to determine the mineralogical composition and local coordination environment of As in gold ores and process tailings from bench-scale tests designed to mimic a common plant practice. Arsenic-bearing minerals identified in the ores and tailings include iron (III) oxyhydroxides, scorodite (FeAsO4??2H2O), ferric arsenates, arseniosiderite (Ca2Fe3 (AsO4)3O2??3H2O), Ca-Fe arsenates, pharmacosiderite (KFe4 (AsO4)3(OH)4??6-7H2O), jarosite (K2Fe6(SO4)4 (OH)12) and arsenopyrite (FeAsS). Iron (III) oxyhydroxides contain variable levels of As from trace to about 22 wt% and Ca up to approximately 9 wt%. Finely ground ore and tailings samples were examined by bulk XAFS and selected mineral grains were analyzed by microfocused XAFS (micro-EXAFS) spectroscopy to reconcile the ambiguities of multiple As sources in the complex bulk EXAFS spectra. XANES spectra indicated that As occurs as As5+in all the samples. Micro-EXAFS spectra of individual iron (III) oxyhydroxide grains with varying As concentrations point to inner-sphere bidentate-binuclear arsenate complexes as the predominant form of As. There are indications for the presence of a second Fe shell corresponding to bidentate-mononuclear arrangement. Iron (III) oxyhydroxides with high As concentrations corresponding to maximum adsorption densities probably occur as nanoparticles. The discovery of Ca atoms around As in iron (III) oxyhydroxides at interatomic distances of 4.14-4.17 A?? and the coordination numbers suggest the formation of arseniosiderite-like nanoclusters by coprecipitation rather than simple adsorption of Ca onto iron (III) oxyhydroxides. Correlation of Ca with As in iron (III) oxyhydroxides as determined by electron microprobe analysis supports the coprecipitate origin for the presence of Ca in iron (III) oxyhydroxides. The samples containing higher abundances of ferric arsenates released higher As concentrations during the cyanidation tests. The presence of highly soluble ferric arsenates and Ca-Fe arsenates, and relatively unstable iron (III) oxyhydroxides with Fe/As molar ratios of less than 4 in the ore and process tailings suggests that not only the tailings in the impoundment will continue to release As, but also there is the potential for mobilization of As from the natural sources such as the unmined ore. ?? 2004 Elsevier Ltd.

Geochimica et Cosmochimica Acta↗
USGS2006

Recharge processes drive sulfate reduction in an alluvial aquifer contaminated with landfill leachate

Natural attenuation of contaminants in groundwater depends on an adequate supply of electron acceptors to stimulate biodegradation. In an alluvial aquifer contaminated with leachate from an unlined municipal landfill, the mechanism of recharge infiltration was investigated as a source of electron acceptors. Water samples were collected monthly at closely spaced intervals in the top 2 m of the saturated zone from a leachate-contaminated well and an uncontaminated well, and analyzed for δ 18 O, δ 2 H, non-volatile dissolved organic carbon (NVDOC), SO 4 2− , NO 3 − and Cl − . Monthly recharge amounts were quantified using the offset of the δ 18 O or δ 2 H from the local meteoric water line as a parameter to distinguish water types, as evaporation and methanogenesis caused isotopic enrichment in waters from different sources. Presence of dissolved SO 4 2− in the top 1 to 2 m of the saturated zone was associated with recharge; SO 4 2− averaged 2.2 mM, with maximum concentrations of 15 mM. Nitrate was observed near the water table at the contaminated site at concentrations up to 4.6 mM. Temporal monitoring of δ 2 H and SO 4 2− showed that vertical transport of recharge carried SO 4 2− to depths up to 1.75 m below the water table, supplying an additional electron acceptor to the predominantly methanogenic leachate plume. Measurements of δ 34 S in SO 4 2− indicated both SO 4 2− reduction and sulfide oxidation were occurring in the aquifer. Depth-integrated net SO 4 2− reduction rates, calculated using the natural Cl − gradient as a conservative tracer, ranged from 7.5 × 10 − 3 to 0.61 mM·d − 1 (over various depth intervals from 0.45 to 1.75 m). Sulfate reduction occurred at both the contaminated and uncontaminated sites; however, median SO 4 2− reduction rates were higher at the contaminated site. Although estimated SO 4 2− reduction rates are relatively high, significant decreases in NVDOC were not observed at the contaminated site. Organic compounds more labile than the leachate NVDOC may be present in the root zone, and SO 4 2− reduction may be coupled to methane oxidation. The results show that sulfur (and possibly nitrogen) redox processes within the top 2 m of the aquifer are directly related to recharge timing and seasonal water level changes in the aquifer. The results suggest that SO 4 2− reduction associated with the infiltration of recharge may be a significant factor affecting natural attenuation of contaminants in alluvial aquifers.

Journal of Contaminant Hydrology↗
USGS2000

Fractionation of selenium isotopes during bacterial respiratory reduction of selenium oxyanions

Reduction of selenium oxyanions by microorganisms is an important process in the biogeochemical cycling of selenium. Numerous bacteria can reduce Se oxyanions, which are used as electron acceptors during the oxidation of organic matter in anoxic environments. In this study, we used a double spike ( 82 Se and 74 Se) thermal ionization mass spectrometry technique to quantify the isotopic fractionation achieved by three different species of anaerobic bacteria capable of accomplishing growth by respiratory reduction of selenate [SeO 4 2− or Se(VI)] or selenite [SeO 3 2− or Se(IV)] to Se(IV) or elemental selenium [Se(0)] coupled with the oxidation of lactate. Isotopic discrimination in these closed system experiments was evaluated by Rayleigh fractionation equations and numerical models. Growing cultures of Bacillus selenitireducens , a haloalkaliphile capable of growth using Se(IV) as an electron acceptor, induced a 80 Se/ 76 Se fractionation of −8.0 ± 0.4‰ (instantaneous ϵ value) during reduction of Se(IV) to Se(0). With Bacillus arsenicoselenatis , a haloalkaliphile capable of growth using Se(VI) as an electron acceptor, fractionations of −5.0 ± 0.5‰ and −6.0 ± 1.0‰ were observed for reduction of Se(VI) to Se(IV) and reduction of Se(IV) to Se(0), respectively. In growing cultures of Sulfurospirillum barnesii , a freshwater species capable of growth using Se(VI), fractionation was small initially, but near the end of the log growth phase, it increased to −4.0 ± 1.0‰ and −8.4 ± 0.4‰ for reduction of Se(VI) to Se(IV) and reduction of Se(IV) to Se(0), respectively. Washed cell suspensions of S. barnesii induced fractionations of −1.1 ± 0.4‰ during Se(VI) reduction, and −9.1 ± 0.5% for Se(IV) reduction, with some evidence for smaller values (e.g., −1.7‰) in the earliest-formed Se(0) results. These results demonstrate that dissimilatory reduction of selenate or selenite induces significant isotopic fractionation, and suggest that significant Se isotope ratio variation will be found in nature.

Geochimica et Cosmochimica Acta↗
USGS2023

High voltage: The molecular properties of redox-active dissolved organic matter in northern high-latitude lakes

Redox-active functional groups in dissolved organic matter (DOM) are crucial for microbial electron transfer and methane emissions. However, the extent of aquatic DOM redox properties across northern high-latitude lakes and their relationships with DOM composition have not been thoroughly described. We quantified electron donating capacity (EDC) and electron accepting capacity (EAC) in lake DOM from Canada to Alaska and assessed their relationships with parameters from absorbance, fluorescence, and ultrahigh resolution mass spectrometry (FT-ICR MS) analyses. EDC and EAC are strongly tied to aromaticity and negatively related to aliphaticity and protein-like content. Redox-active formulae spanned a range of aromaticity, including highly unsaturated phenolic formulae, and correlated negatively with many aliphatic N and S-containing formulae. This distribution illustrates the compositional diversity of redox-sensitive functional groups and their sensitivity to ecosystem properties such as local hydrology and residence time. Finally, we developed a reducing index ( RI ) to predict EDC in aquatic DOM from FT-ICR MS spectra and assessed its robustness using riverine DOM. As the hydrology of the northern high-latitudes continues to change, we expect differences in the quantity and partitioning of EDC and EAC within these lakes, which have implications for local water quality and methane emissions.

Environmental Science & Technology↗