Geology topics

John Karl Böhlke

Publications and source records attributed to John Karl Böhlke.

11 recordsLinked to original sources

USGS2016

Deposition, accumulation, and alteration of Cl−, NO3−, ClO4− and ClO3− salts in a hyper-arid polar environment: Mass balance and isotopic constraints

The salt fraction in permafrost soils/sediments of the McMurdo Dry Valleys (MDV) of Antarctica can be used as a proxy for cold desert geochemical processes and paleoclimate reconstruction. Previous analyses of the salt fraction in MDV permafrost soils have largely been conducted in coastal regions where permafrost soils are variably affected by aqueous processes and mixed inputs from marine and stratospheric sources. We expand upon this work by evaluating permafrost soil/sediments in University Valley, located in the ultraxerous zone where both liquid water transport and marine influences are minimal. We determined the abundances of Cl − , NO 3 − , ClO 4 − and ClO 3 − in dry and ice-cemented soil/sediments, snow and glacier ice, and also characterized Cl − and NO 3 − isotopically. The data are not consistent with salt deposition in a sublimation till, nor with nuclear weapon testing fall-out, and instead point to a dominantly stratospheric source and to varying degrees of post depositional transformation depending on the substrate, from minimal alteration in bare soils to significant alteration (photodegradation and/or volatilization) in snow and glacier ice. Ionic abundances in the dry permafrost layer indicate limited vertical transport under the current climate conditions, likely due to percolation of snowmelt. Subtle changes in ClO 4 − /NO 3 − ratios and NO 3 − isotopic composition with depth and location may reflect both transport related fractionation and depositional history. Low molar ratios of ClO 3 − /ClO 4 − in surface soils compared to deposition and other arid systems suggest significant post depositional loss of ClO 3 − , possibly due to reduction by iron minerals, which may have important implications for oxy-chlorine species on Mars. Salt accumulation varies with distance along the valley and apparent accumulation times based on multiple methods range from ∼10 to 30 kyr near the glacier to 70–200 kyr near the valley mouth. The relatively young age of the salts and relatively low and homogeneous anion concentrations in the ice-cemented sediments point to either a mechanism of recent salt removal, or to relatively modern permafrost soils (<1 million years). Together, our results show that near surface salts in University Valley serve as an end-member of stratospheric sources not subject to biological processes or extensive remobilization.

Geochimica et Cosmochimica Acta↗

USGS2014

Educational webtool illustrating groundwater age effects on contaminant trends in wells

No abstract available.

Groundwater↗

USGS2014

Soil, plant, and terrain effects on natural perchlorate distribution in a desert landscape

Perchlorate (ClO 4 − ) is a contaminant that occurs naturally throughout the world, but little is known about its distribution and interactions in terrestrial ecosystems. The objectives of this Amargosa Desert, Nevada study were to determine (i) the local-scale distribution of shallow-soil (0–30 cm) ClO 4 − with respect to shrub proximity (far and near) in three geomorphic settings (shoulder slope, footslope, and valley floor); (ii) the importance of soil, plant, and terrain variables on the hillslope-distribution of shallow-soil and creosote bush [ Larrea tridentata (Sessé & Moc. ex DC.) Coville] ClO 4 − ; and (iii) atmospheric (wet plus dry, including dust) deposition of ClO 4 − in relation to soil and plant reservoirs and cycling. Soil ClO 4 − ranged from 0.3 to 5.0 μg kg −1 . Within settings, valley floor ClO 4 − was 17× less near shrubs due in part to enhanced leaching, whereas shoulder and footslope values were ∼2× greater near shrubs. Hillslope regression models (soil, R 2 = 0.42; leaf, R 2 = 0.74) identified topographic and soil effects on ClO 4 − deposition, transport, and cycling. Selective plant uptake, bioaccumulation, and soil enrichment were evidenced by leaf ClO 4 − concentrations and Cl − /ClO 4 − molar ratios that were ∼8000× greater and 40× less, respectively, than soil values. Atmospheric deposition ClO 4 − flux was 343 mg ha −1 yr −1 , ∼10× that for published southwestern wet-deposition fluxes. Creosote bush canopy ClO 4 − (1310 mg ha−1) was identified as a previously unrecognized but important and active reservoir. Nitrate δ 18 O analyses of atmospheric deposition and soil supported the leaf-cycled–ClO 4 − input hypothesis. This study provides basic data on ClO 4 − distribution and cycling that are pertinent to the assessment of environmental impacts in desert ecosystems and broadly transferable to anthropogenically contaminated systems.

Nevada↗

USGS2014

Variation in the terrestrial isotopic composition and atomic weight of argon

The isotopic composition and atomic weight of argon (Ar) are variable in terrestrial materials. Those variations are a source of uncertainty in the assignment of standard properties for Ar, but they provide useful information in many areas of science. Variations in the stable isotopic composition and atomic weight of Ar are caused by several different processes, including (1) isotope production from other elements by radioactive decay (radiogenic isotopes) or other nuclear transformations (e.g., nucleogenic isotopes), and (2) isotopic fractionation by physical-chemical processes such as diffusion or phase equilibria. Physical-chemical processes cause correlated mass-dependent variations in the Ar isotope-amount ratios ( 40 Ar/ 36 Ar, 38 Ar/ 36 Ar), whereas nuclear transformation processes cause non-mass-dependent variations. While atmospheric Ar can serve as an abundant and homogeneous isotopic reference, deviations from the atmospheric isotopic ratios in other Ar occurrences limit the precision with which a standard atomic weight can be given for Ar. Published data indicate variation of Ar atomic weights in normal terrestrial materials between about 39.7931 and 39.9624. The upper bound of this interval is given by the atomic mass of 40 Ar, as some samples contain almost pure radiogenic 40 Ar. The lower bound is derived from analyses of pitchblende (uranium mineral) containing large amounts of nucleogenic 36 Ar and 38 Ar. Within this interval, measurements of different isotope ratios ( 40 Ar/ 36 Ar or 38 Ar/ 36 Ar) at various levels of precision are widely used for studies in geochronology, water–rock interaction, atmospheric evolution, and other fields.

Pure and Applied Chemistry↗

USGS2013

Hyporheic zone denitrification: controls on effective reaction depth and contribution to whole-stream mass balance

Stream denitrification is thought to be enhanced by hyporheic transport but there is little direct evidence from the field. To demonstrate at a field site, we injected 15 NO 3 − , Br (conservative tracer), and SF 6 (gas exchange tracer) and compared measured whole-stream denitrification with in situ hyporheic denitrification in shallow and deeper flow paths of contrasting geomorphic units. Hyporheic denitrification accounted for between 1 and 200% of whole-stream denitrification. The reaction rate constant was positively related to hyporheic exchange rate (greater substrate delivery), concentrations of substrates DOC and nitrate, microbial denitrifier abundance (nirS), and measures of granular surface area and presence of anoxic microzones. The dimensionless product of the reaction rate constant and hyporheic residence time, λ hz τ hz define a Damköhler number, Da den-hz that was optimal in the subset of hyporheic flow paths where Da den-hz ≈ 1. Optimal conditions exclude inefficient deep pathways transport where substrates are used up and also exclude inefficient shallow pathways that require repeated hyporheic entries and exits to complete the reaction. The whole-stream reaction significance, R s (dimensionless), was quantified by multiplying Da den-hz by the proportion of stream discharge passing through the hyporheic zone. Together these two dimensionless metrics, one flow-path scale and the other reach-scale, quantify the whole-stream significance of hyporheic denitrification. One consequence is that the effective zone of significant denitrification often differs from the full depth of the hyporheic zone, which is one reason why whole-stream denitrification rates have not previously been explained based on total hyporheic-zone metrics such as hyporheic-zone size or residence time.

Indiana↗

USGS2013

U.S. Geological Survey water science strategy—Observing, understanding, predicting, and delivering water science to the Nation

Executive Summary This report expands the Water Science Strategy that began with the USGS Science Strategy, “Facing Tomorrow’s Challenges—U.S. Geological Survey Science in the Decade 2007–2017” (U.S. Geological Survey, 2007). This report looks at the relevant issues facing society and develops a strategy built around observing, understanding, predicting, and delivering water science for the next 5 to 10 years by building new capabilities, tools, and delivery systems to meet the Nation’s water-resource needs. This report begins by presenting the vision of water science for the USGS and the societal issues that are influenced by, and in turn influence, the water resources of our Nation. The essence of the Water Science Strategy is built on the concept of “water availability,” defined as spatial and temporal distribution of water quantity and quality, as related to human and ecosystem needs, as affected by human and natural influences. The report also describes the core capabilities of the USGS in water science—the strengths, partnerships, and science integrity that the USGS has built over its 134-year history.

Circular↗

USGS2012

Strategic directions for U.S. Geological Survey water science, 2012-2022 - Observing, understanding, predicting, and delivering water science to the Nation

Executive Summary This report expands the Water Science Strategy that was begun in the USGS Science Strategy, “Facing Tomorrow’s Challenges—U.S. Geological Survey Science in the Decade 2007–2017” (U.S. Geological Survey, 2007). The report looks at the relevant issues facing society and develops a strategy built around observing, understanding, predicting, and delivering water science for the next 5 to 10 years by building new capabilities, tools, and delivery systems to meet the Nation’s water-resource needs. This report begins by presenting the vision of water science for the USGS and the societal issues that are influenced by, and in turn influence, the water resources of our Nation. The essence of the Water Strategic Science Plan is built on the concept of “water availability,” defined as spatial and temporal distribution of water quantity and quality, as related to human and ecosystem needs, as affected by human and natural influences . The report also describes the core capabilities of the USGS in water science—the strengths, partnerships, and science integrity that the USGS has built over its 130-year history. Nine priority actions are presented in the report, which combine and elevate the numerous specific strategic actions listed throughout the report. Priority actions were developed as a means of providing the audience of this report with a list for focused attention, even if resources and time limit the ability of managers to address all of the strategic actions in the report. Priority actions focus on the following: Improve integrated science planning for water. Expand and enhance water-resource monitoring networks. Characterize the water cycle through development of state-of-the-art 3-D/4-D hydrogeologic framework models at multiple scales. Clarify the linkage between human water use (engineered hydrology) and the water cycle (natural hydrology). Advance ecological flow science. Provide flood-inundation science and information. Develop rapid deployment teams for water-related emergencies. Conduct integrated watershed assessment, research, and modeling. Deliver water data and analyses to the Nation. The body of the report is presented as a hierarchal set of 5 goals, 14 objectives, and 27 strategic actions that the USGS should undertake to advance water science through year 2022. The goals deal with: Providing society the information it needs regarding the amount and quality of water in all components of the water cycle at high temporal and spatial resolution, nationwide; Advancing our understanding of processes that determine water availability; Predicting changes in the quantity and quality of water resources in response to changing climate, population, land use, and management scenarios; Anticipating and responding to water-related emergencies and conflicts; and Delivering timely hydrologic data, analyses, and decision-support tools seamlessly across the Nation to support water-resource decisions. Scientific information produced on water resources would be without value if it were not communicated to society in a fashion that can inform decisions and actions. Therefore, the chapter following the goals describes how the USGS should inform, involve, and educate society about the science it produces. This includes discussions on local outreach and the use of social media for effective communication. This report concludes with a chapter devoted to the crosscutting science issues of the Water Mission Area with the other USGS Mission Areas: Climate and Land Use Change, Core Science Systems, Ecosystems, Energy and Minerals, Environmental Health Science, and Natural Hazards. Not one of these Mission Areas stands alone—all must work together and integrate their actions to fulfill the USGS science mission for the future. This final chapter identifies the important linkages that must be realized and maintained for this integration to occur.

Open-File Report↗

USGS2008

Determination of the delta(15N/14N)of Ammonium (NH4+) in Water: RSIL Lab Code 2898

The purpose of the technique described by Reston Stable Isotope Laboratory (RSIL) lab code 2898 is to determine the N isotopic composition, delta(15N/14N), abbreviated as d15N, of ammonium (NH4+) in water (freshwater and saline water). The procedure involves converting dissolved NH4+ into NH3 gas by raising the pH of the sample to above 9 with MgO and subsequently trapping the gas quantitatively as (NH4)2SO4 on a glass fiber (GF) filter. The GF filter is saturated with NaHSO4 and pressure sealed between two gas-permeable polypropylene filters. The GF filter 'sandwich' floats on the surface of the water sample in a closed bottle. NH3 diffuses from the water through the polypropylene filter and reacts with NaHSO4, forming (NH4)2SO4 on the GF filter. The GF filter containing (NH4)2SO4 is dried and then combusted with a Carlo Erba NC 2500 elemental analyzer (EA), which is used to convert total nitrogen in a solid sample into N2 gas. The EA is connected to a continuous-flow isotope-ratio mass spectrometer (CF-IRMS), which determines the relative difference in ratios of the amounts of the stable isotopes of nitrogen (15N and 14N) of the product N2 gas and a reference N2 gas. The filters containing the samples are compressed in tin capsules and loaded into a Costech Zero-Blank Autosampler on the EA. Under computer control, samples then are dropped into a heated reaction tube that contains an oxidant, where combustion takes place in a He atmosphere containing an excess of O2 gas. To remove S-O gases produced from the NaHSO4, a plug of Ag-coated Cu wool is inserted at the bottom of the reaction tube. Combustion products are transported by a He carrier through a reduction furnace to remove excess O2, toconvert all nitrogen oxides to N2, and to remove any remaining S-O gases. The gases then pass through a drying tube to remove water. The gas-phase products, mainly N2 and a small amount of background CO2, are separated by a gas chromatograph (GC). The gas is then introduced into the IRMS through a Finnigan ConFlo II interface. The ConFlo II interface is used to introduce not only sample into the IRMS but also N2 reference gas and He for sample dilution. The flash combustion is quantitative, so no isotopic fractionation is involved. The IRMS is a Finnigan Delta V CF-IRMS with 10 cups and is capable of detecting ion beams with mass/charge (m/z) 28, 29, 30. The ion beams from N2 are as follows: m/z 28 = 14N14N, m/z 29 = 14N15N, and m/z 30 = 15N15N. The ion beam with m/z 30 also represents 14N16O, which may indicate contamination or incomplete reduction.

Techniques and Methods↗

USGS2006

Ground water beneath coastal bays of the Delmarva Peninsula: Ages and nutrients

To complement a large-scale geophysical investigation of occurrence and discharge of fresh water beneath Delaware, Maryland, and Virginia (Delmarva) coastal bays, we measured (1) salinity and nutrient concentrations in ground water samples from several offshore coring sites and (2) a suite of chemical and isotopic parameters, including age tracers, in ground water samples from a Delaware site. Samples were collected in a variety of Holocene and Plio-Pleistocene sediments in nearshore and offshore areas of the bays. Ground waters that were significantly fresher than overlying waters were found in plumes up to at least 15 m thick extending to more than 500 m offshore in some areas. Steep salinity and nutrient gradients occur within a few meters of the sediment surface in most locations studied. The zone of transition from deeper fresher waters to shallower brackish waters is generally thin near shore, but thickens and becomes more gradual offshore. Ground water ages at the Delaware site were mostly < 50 yr in both fresh waters and brackish waters up to 22 m below the bay bottom. Water chemistry and age data indicate that fresh water plumes beneath the estuary are active extensions of the surficial aquifer carrying nitrate from recharge areas on land, whereas brackish ground water surrounding the fresh water plumes is recharged beneath the estuary and contains ammonium and phosphate released by diagenesis of shallow estuarine sediments. Denitrification affects some of the fresh water nitrate before it mixes with brackish ground water or discharges to surface water.

Delaware, Maryland, Virginia↗

USGS2003

Atomic weights of the elements. Review 2000 (IUPAC Technical Report)

A consistent set of internationally accepted atomic weights has long been an essential aim of the scientific community because of the relevance of these values to science and technology, as well as to trade and commerce subject to ethical, legal, and international standards. The standard atomic weights of the elements are regularly evaluated, recommended, and published in updated tables by the Commission on Atomic Weights and Isotopic Abundances (CAWIA) of the International Union of Pure and Applied Chemistry (IUPAC). These values are invariably associated with carefully evaluated uncertainties. Atomic weights were originally determined by mass ratio measurements coupled with an understanding of chemical stoichiometry, but are now based almost exclusively on knowledge of the isotopic composition (derived from isotope-abundance ratio measurements) and the atomic masses of the isotopes of the elements. Atomic weights and atomic masses are now scaled to a numerical value of exactly 12 for the mass of the carbon isotope of mass number 12. Technological advances in mass spectrometry and nuclear-reaction energies have enabled atomic masses to be determined with a relative uncertainty of better than 1 ×10−7 . Isotope abundances for an increasing number of elements can be measured to better than 1 ×10−3 . The excellent precision of such measurements led to the discovery that many elements, in different specimens, display significant variations in their isotope-abundance ratios, caused by a variety of natural and industrial physicochemical processes. While such variations increasingly place a constraint on the uncertainties with which some standard atomic weights can be stated, they provide numerous opportunities for investigating a range of important phenomena in physical, chemical, cosmological, biological, and industrial processes. This review reflects the current and increasing interest of science in the measured differences between source-specific and even sample-specific atomic weights. These relative comparisons can often be made with a smaller uncertainty than is achieved in the best calibrated “absolute ” (=SI-traceable) atomic-weight determinations. Accurate determinations of the atomic weights of certain elements also influence the values of fundamental constants such as the Avogadro, Faraday, and universal gas constants. This review is in two parts: the first summarizes the development of the science of atomic-weight determinations during the 20th century; the second summarizes the changes and variations that have been recognized in the values and uncertainties of atomic weights, on an element-by-element basis, in the latter part of the 20th century.

Pure and Applied Chemistry↗

USGS2003

Isotope geochemistry and chronology of offshore ground water beneath Indian River Bay, Delaware

Results of geophysical surveys in Indian River Bay, Delaware, indicate a complex pattern of salinity variation in subestuarine ground water. Fresh ground-water plumes up to about 20 meters thick extending hundreds of meters offshore are interspersed with saline ground water, with varying degrees of mixing along the salinity boundaries. It is possible that these features represent pathways for nutrient transport and interaction with estuarine surface water, but the geophysical data do not indicate rates of movement or nutrient sources and reactions. In the current study, samples of subestuarine ground water from temporary wells with short screens placed 3 to 22 meters below the sediment-water interface were analyzed chemically and isotopically to determine the origins, ages, transport pathways, and nutrient contents of the fresh and saline components. Apparent ground-water ages determined from chlorofluorocarbons (CFCs), sulfur hexafluoride (SF6), tritium (3H), and helium isotopes (3He and 4He) commonly were discordant, but nevertheless indicate that both fresh and saline ground waters ranged from a few years to at least 50 years in age. Tritium-helium (3H-3He) ages, tentatively judged to be most reliable, indicate that stratified offshore freshwater plumes originating in distant recharge areas on land were bounded by relatively young saline water that was recharged locally from the overlying estuary. Undenitrified and partially denitrified nitrate of agricultural or mixed origin was transported laterally beneath the estuary in oxic and suboxic fresh ground water. Ammonium produced by anaerobic degradation of organic matter in estuarine sediments was transported downward in suboxic saline ground water around the freshwater plumes. Many of the chemical and isotopic characteristics of the subestuarine ground waters are consistent with conservative mixing of the fresh (terrestrial) and saline (estuarine) endmember water types. These data indicate that freshwater plumes detected by geophysical surveys beneath Indian River Bay represent lateral continuations of the active surficial nitrate-contaminated freshwater flow systems originating on land, but they do not indicate directly the magnitude of fresh ground-water discharge or nutrient exchange with the estuary. There is evidence that some of the terrestrial ground-water nitrate is reduced before discharging directly beneath the estuary. Local estuarine sediment-derived ammonium in saline pore water may be a substantial benthic source of nitrogen in offshore areas of the estuary.

Delaware↗