Showing papers by "United States Geological Survey published in 1993"

Dissimilatory Metal Reduction

Abstract: Microorganisms can enzymatically reduce a variety of metals in metabolic processes that are not related to metal assimilation. Some microorganisms can conserve energy to support growth by coupling the oxidation of simple organic acids and alcohols, H2, or aromatic compounds to the reduction of Fe(III) or Mn(IV). This dissimilatory Fe(III) and Mn(IV) reduction influences the organic as well as the inorganic geochemistry of anaerobic aquatic sediments and ground water. Microorganisms that use U(VI) as a terminal electron acceptor play an important role in uranium geochemistry and may be a useful tool for removing uranium from contaminated environments. Se(VI) serves as a terminal electron acceptor to support anaerobic growth of some microorganisms. Reduction of Se(VI) to Se(O) is an important mechanism for the precipitation of selenium from contaminated waters. Enzymatic reduction of Cr(VI) to the less mobile and less toxic Cr(III), and reduction of soluble Hg(II) to volatile Hg(O) may affect the fate of these compounds in the environment and might be used as a remediation strategy. Microorganisms can also enzymatically reduce other metals such as technetium, vanadium, molybdenum, gold, silver, and copper, but reduction of these metals has not been studied extensively.

Geobacter metallireducens gen. nov. sp. nov., a microorganism capable of coupling the complete oxidation of organic compounds to the reduction of iron and other metals.

Abstract: The gram-negative metal-reducing microorganism, previously known as strain GS-15, was further characterized. This strict anaerobe oxidizes several short-chain fatty acids, alcohols, and monoaromatic compounds with Fe(III) as the sole electron acceptor. Furthermore, acetate is also oxidized with the reduction of Mn(IV), U(VI), and nitrate. In whole cell suspensions, the c-type cytochrome(s) of this organism was oxidized by physiological electron acceptors and also by gold, silver, mercury, and chromate. Menaquinone was recovered in concentrations comparable to those previously found in gram-negative sulfate reducers. Profiles of the phospholipid ester-linked fatty acids indicated that both the anaerobic desaturase and the branched pathways for fatty acid biosynthesis were operative. The organism contained three lipopolysaccharide hydroxy fatty acids which have not been previously reported in microorganisms, but have been observed in anaerobic freshwater sediments. The 16S rRNA sequence indicated that this organism belongs in the delta proteobacteria. Its closest known relative is Desulfuromonas acetoxidans. The name Geobacter metallireducens is proposed.

Seismicity Remotely Triggered by the Magnitude 7.3 Landers, California, Earthquake

Abstract: The magnitude 7.3 Landers earthquake of 28 June 1992 triggered a remarkably sudden and widespread increase in earthquake activity across much of the western United States. The triggered earthquakes, which occurred at distances up to 1250 kilometers (17 source dimensions) from the Landers mainshock, were confined to areas of persistent seismicity and strike-slip to normal faulting. Many of the triggered areas also are sites of geothermal and recent volcanic activity. Static stress changes calculated for elastic models of the earthquake appear to be too small to have caused the triggering. The most promising explanations involve nonlinear interactions between large dynamic strains accompanying seismic waves from the mainshock and crustal fluids (perhaps including crustal magma).

Reduction of Fe(III) in sediments by sulphate-reducing bacteria

Abstract: REDUCTION of ferric iron (Fe(III)) to ferrous iron (Fe(II)) is one of the most important geochemical reactions in anaerobic aquatic sediments because of its many consequences for the organic and inorganic chemistry of these environments1. In marine environments, sulphate-reducing bacteria produce H2S, which can reduce iron oxyhydroxides2 to form iron sulphides. The presence of siderite (FeCO3) in marine sediments is anomalous, however, as it is unstable in the presence of H2S. Previous work3,4 has suggested a bacterial origin of siderite. Here we describe geochemical and microbiological studies which suggest that contemporary formation of siderite concretions in a salt-marsh sediment results from the activity of sulphate-reducing bacteria. We find that, instead of reducing Fe(III) indirectly through the production of sulphide, some of these bacteria can reduce Fe(III) directly through an enzymatic mechanism, producing siderite rather than iron sulphides. Sulphate-reducing bacteria may thus be an important and previously unrecognized agent for Fe(III) reduction in aquatic sediments and ground waters.

The Global Carbon Dioxide Budget

Abstract: The increase in atmospheric CO[sub 2] levels during the last deglaciation was comparable in magnitude to the recent historical increase. However, global CO[sub 2] budgets for these changes reflect fundamental differences in rates and in sources and sinks. The modern oceans are a rapid net CO[sub 2] sink, whereas the oceans were a gradual source during the deglaciation. Unidentified terrestrial CO[sub 2] sinks are important uncertainties in both the deglacial and recent CO[sub 2] budgets. The deglacial CO[sub 2] budget represents a complexity of long-term dynamic behavior that is not adequately addressed by current models used to forecast future atmospheric CO[sub 2] levels.

Model for episodic flow of high-pressure water in fault zones before earthquakes

Abstract: In this model for the evolution of large crustal faults, water that originally came from the country rock saturates the initially highly porous and permeable fault zone. During shearing, the fault zone compacts and water flows back into the country rock, but the flow is arrested by silicate deposition that forms very low permeability seals between the fault zone and the country rock. Because of variations in temperature and mineralogical composition and the complex structure of the fault zone, a three-dimensional network of seals is formed in the fault zone itself; thus, the high-pressure fluid is not evenly distributed. As in deep oil reservoirs, the fluid will be confined to seal-bounded fluid compartments of various sizes and porosity that are not hydraulically connected with each other or with the hydrostatic regime in the country rock. When the seal between two of these compartments is ruptured, an electrical streaming potential will be generated by the sudden movement of fluid from the high-pressure compartment to the low-pressure compartment. When the pore pressure in the two compartments reaches its final equilibrium state, the average effective normal stress across them may be lower than it was initially, and, if the two compartments are large enough, this condition may trigger an earthquake. During an earthquake, many of the remaining seals will be ruptured, and the width of the fault zone will increase by failure of the geometric irregularities on the fault. This newly created, highly porous and permeable, but now wider fault zone will fill with water, and the process described above will be repeated. Thus, the process is an episodic one, with the water moving in and out of the fault zone, and each large earthquake should be preceded by an electrical and/or magnetic signal.

Near-Field Investigations of the Landers Earthquake Sequence, April to July 1992

Abstract: The Landers earthquake, which had a moment magnitude (M_w) of 7.3, was the largest earthquake to strike the contiguous United States in 40 years. This earthquake resulted from the rupture of five major and many minor right-lateral faults near the southern end of the eastern California shear zone, just north of the San Andreas fault. Its M_w 6.1 preshock and M_w 6.2 aftershock had their own aftershocks and foreshocks. Surficial geological observations are consistent with local and far-field seismologic observations of the earthquake. Large surficial offsets (as great as 6 meters) and a relatively short rupture length (85 kilometers) are consistent with seismological calculations of a high stress drop (200 bars), which is in turn consistent with an apparently long recurrence interval for these faults.

Scaling of the critical slip distance for seismic faulting with shear strain in fault zones

Abstract: THEORETICAL and experimentally based laws for seismic faulting contain a critical slip distance1–5, Dc, which is the slip over which strength breaks down during earthquake nucleation. On an earthquake-generating fault, this distance plays a key role in determining the rupture nucleation dimension6, the amount of premonitory and post-seismic slip7–10, and the maximum seismic ground acceleration1,11. In laboratory friction experiments, D c has been related to the size of surface contact junctions2,5,12; thus, the discrepancy between laboratory measurements of Dc (∼10−5m) and values obtained from modelling earthquakes (∼10−2m) has been attributed to differences in roughness between laboratory surfaces and natural faults5. This interpretation predicts a dependence of Dc on the particle size of fault gouge2 (breccia and wear material) but not on shear strain. Here we present experimental results showing that Dc scales with shear strain in simulated fault gouge. Our data suggest a new physical interpretation for the critical slip distance, in which Dc is controlled by the thickness of the zone of localized shear strain. As gouge zones of mature faults are commonly 102–103 m thick12–17, whereas laboratory gouge layers are 1–10 mm thick, our data offer an alternative interpretation of the discrepancy between laboratory and field-based estimates of Dc.

A rainfall intensity-duration threshold for landslides in a humid- tropical environment, Puerto Rico

Abstract: Landslides are triggered by factors such as heavy rainfall, seismic activity, and construction on hillslopes. The leading cause of landslides in Puerto Rico is intense and/or prolonged rainfall. A ...

Methods for regression analysis of strong-motion data

Abstract: We introduce a new computational method for implementing Brillinger and Preisler's (1984, 1985) one-stage maximum-likelihood analysis of strong-motion data. We also reexamine two-stage methods and agree with Masuda and Ohtake (1992) that rigorous analysis requires off-diagonal terms in the weighting matrix for the second-stage regression but note that Masuda and Ohtake failed to account for the earthquake-to-earthquake component of variance. Analysis by Monte Carlo methods shows that both one-stage and two-stage methods, properly applied, are unbiased and that they have comparable uncertainties. Both give the same correct results when applied to the data that Fukushima and Tanaka (1990) have shown cannot be satisfactorily analyzed by ordinary least squares. The two-stage method is more efficient computationally, but for typical problems neither method requires enough time to make efficiency important. Of the two methods, only the two-stage method can readily be used with the techniques described by Toro (1981) and McLaughlin (1991) for overcoming the bias due to instruments that do not trigger.

Reduction of uranium by cytochrome c3 of Desulfovibrio vulgaris.

Abstract: The mechanism for U(VI) reduction by Desulfovibrio vulgaris (Hildenborough) was investigated. The H2-dependent U(VI) reductase activity in the soluble fraction of the cells was lost when the soluble fraction was passed over a cationic exchange column which extracted cytochrome c3. Addition of cytochrome c3 back to the soluble fraction that had been passed over the cationic exchange column restored the U(VI)-reducing capacity. Reduced cytochrome c3 was oxidized by U(VI), as was a c-type cytochrome(s) in whole-cell suspensions. When cytochrome c3 was combined with hydrogenase, its physiological electron donor, U(VI) was reduced in the presence of H2. Hydrogenase alone could not reduce U(VI). Rapid U(VI) reduction was followed by a subsequent slow precipitation of the U(IV) mineral uraninite. Cytochrome c3 reduced U(VI) in a uranium-contaminated surface water and groundwater. Cytochrome c3 provides the first enzyme model for the reduction and biomineralization of uranium in sedimentary environments. Furthermore, the finding that cytochrome c3 can catalyze the reductive precipitation of uranium may aid in the development of fixed-enzyme reactors and/or organisms with enhanced U(VI)-reducing capacity for the bioremediation of uranium-contaminated waters and waste streams.

Trace and Minor Elements in Coal

Abstract: Coal will be a major energy source in the United States and in many other countries well into the 21st century. Although coal is composed predominantly of organic matter, inorganic constituents in coal commonly attract more attention and can ultimately determine how the coal will be used.

The role of water exchange between a stream channel and its hyporheic zone in nitrogen cycling at the terrestrial-aquatic interface

Abstract: The subsurface riparian zone was examined as an ecotone with two interfaces. Inland is a terrestrial boundary, where transport of water and dissolved solutes is toward the channel and controlled by watershed hydrology. Streamside is an aquatic boundary, where exchange of surface water and dissolved solutes is bi-directional and flux is strongly influenced by channel hydraulics. Streamside, bi-directional exchange of water was qualitatively defined using biologically conservative tracers in a third order stream. In several experiments, penetration of surface water extended 18 m inland. Travel time of water from the channel to bankside sediments was highly variable. Subsurface chemical gradients were indirectly related to the travel time. Sites with long travel times tended to be low in nitrate and DO (dissolved oxygen) but high in ammonium and DOC (dissolved organic carbon). Sites with short travel times tended to be high in nitrate and DO but low in ammonium and DOC. Ammonium concentration of interstitial water also was influenced by sorption-desorption processes that involved clay minerals in hyporheic sediments. Denitrification potential in subsurface sediments increased with distance from the channel, and was limited by nitrate at inland sites and by DO in the channel sediments. Conversely, nitrification potential decreased with distance from the channel, and was limited by DO at inland sites and by ammonium at channel locations. Advection of water and dissolved oxygen away from the channel resulted in an oxidized subsurface habitat equivalent to that previously defined as the hyporheic zone. The hyporheic zone is viewed as stream habitat because of its high proportion of surface water and the occurrence of channel organisms. Beyond the channel’s hydrologic exchange zone, interstitial water is often chemically reduced. Interstitial water that has not previously entered the channel, groundwater, is viewed as a terrestrial component of the riparian ecotone. Thus, surface water habitats may extend under riparian vegetation, and terrestrial groundwater habitats may be found beneath the stream channel.

Considerations and applications of the illite/smectite geothermometer in hydrocarbon-bearing rocks of Miocene to Mississippian age

Abstract: Empirical relationships between clay mineral transformations and temperature provide a basis for the use of clay minerals as geothermometers. Clay-mineral geothermometry has been applied mainly to diagenetic, hydrothermal, and contact- and burial-metamorphic settings to better understand the thermal histories of migrating fluids, hydrocarbon source beds, and ore and mineral formation. Quantitatively, the most important diagenetic clay mineral reaction in sedimentary rocks is the pro- gressive transformation of smectite to illite via mixed-layer illite/smectite (I/S). Changes in both the illite/ smeetite ratio and ordering of t/S, as determined from X-ray powder diffraction profiles, correlate with changes in temperature due to burial depth. Although the smectite-to-illite reaction may be influenced by several factors, reaction progress appears to be strongly controlled by temperature. Studies show that the model proposed by Hoffman and Hower in 1979 is applicable in burial diagenetic settings from about 5 to 330 Ma, and includes most rocks about Miocene to Mississippian in age. Reliability of the I/S geothermometer is, however, dependent upon a good understanding of the rock's original clay-mineral composition. Changes in the ordering of I/S are particularly useful in the exploration for hydrocarbons because of the common coincidence between the temperatures for the conversion from random-to-ordered I/S and those for the onset of peak, or main phase, oil generation. Here, the utility of the I/S geothermometer is reviewed in hydrocarbon-bearing rocks of Miocene to Mississippian age. Using three common applica- tions, the I/S geothermometer is compared to other mineral geothermometers, organic maturation indices, and grades of indigenous hydrocarbons. Good agreement between changes in ordering of I/S and calculated maximum burial temperatures or hydrocarbon maturity suggests that I/S is a reliable semiquantitative geothermometer and an excellent measures of thermal maturity.

Dissimilatory Fe(III) Reduction by the Marine Microorganism Desulfuromonas acetoxidans.

Abstract: The ability of the marine microorganism Desulfuromonas acetoxidans to reduce Fe(III) was investigated because of its close phylogenetic relationship with the freshwater dissimilatory Fe(III) reducer Geobacter metallireducens. Washed cell suspensions of the type strain of D. acetoxidans reduced soluble Fe(III)-citrate and Fe(III) complexed with nitriloacetic acid. The c-type cytochrome(s) of D. acetoxidans was oxidized by Fe(III)-citrate and Mn(IV)-oxalate, as well as by two electron acceptors known to support growth, colloidal sulfur and malate. D. acetoxidans grew in defined anoxic, bicarbonate-buffered medium with acetate as the sole electron donor and poorly crystalline Fe(III) or Mn(IV) as the sole electron acceptor. Magnetite (Fe(3)O(4)) and siderite (FeCO(3)) were the major end products of Fe(III) reduction, whereas rhodochrosite (MnCO(3)) was the end product of Mn(IV) reduction. Ethanol, propanol, pyruvate, and butanol also served as electron donors for Fe(III) reduction. In contrast to D. acetoxidans, G. metallireducens could only grow in freshwater medium and it did not conserve energy to support growth from colloidal S reduction. D. acetoxidans is the first marine microorganism shown to conserve energy to support growth by coupling the complete oxidation of organic compounds to the reduction of Fe(III) or Mn(IV). Thus, D. acetoxidans provides a model enzymatic mechanism for Fe(III) or Mn(IV) oxidation of organic compounds in marine and estuarine sediments. These findings demonstrate that 16S rRNA phylogenetic analyses can suggest previously unrecognized metabolic capabilities of microorganisms.

Denitrification measurements in aquatic sediments: A comparison of three methods

Abstract: Measurements of denitrification using the acetylene inhibition,15N isotope tracer, and N2 flux methods were carried out concurrently using sediment cores from Vilhelmsborg so, Denmark, in an attempt to clarify some of the limitations of each technique. Three experimental treatments of overlying water were used: control, nitrate enriched, and ammonia enriched water. The N2 flux and15N tracer experiments showed high rates of coupled nitrification/denitrification in the sediments. The acetylene inhibition method did not capture any coupled nitrification/denitrification. This could be explained by acetylene inhibition of nitrification. A combined15N tracer/acetylene inhibition experiment demonstrated that acetylene inhibition of N2O reduction was incomplete and the method, therefore, only measured approximately 50% of the denitrification due to nitrate from the overlying water. Similar rates of denitrification due to nitrate in the overlying water were measured by the N2 flux method and the acetylene inhibition method, after correcting for the 50% efficiency of acetylene inhibition. Rates of denitrification due to nitrate from the overlying water measured by the15N tracer method, however, were only approximately 35% or less of those measured by the acetylene inhibition or N2 flux methods.

Tidal, Residual, Intertidal Mudflat (TRIM) Model and its Applications to San Francisco Bay, California

Abstract: A numerical model using a semi-implicit finite-difference method for solving the two-dimensional shallow-water equations is presented The gradient of the water surface elevation in the momentum equations and the velocity divergence in the continuity equation are finite-differenced implicitly, the remaining terms are finite-differenced explicitly The convective terms are treated using an Eulerian-Lagrangian method The combination of the semi-implicit finite-difference solution for the gravity wave propagation, and the Eulerian-Lagrangian treatment of the convective terms renders the numerical model unconditionally stable When the baroclinic forcing is included, a salt transport equation is coupled to the momentum equations, and the numerical method is subject to a weak stability condition The method of solution and the properties of the numerical model are given This numerical model is particularly suitable for applications to coastal plain estuaries and tidal embayments in which tidal currents are dominant, and tidally generated residual currents are important The model is applied to San Francisco Bay, California where extensive historical tides and current-meter data are available The model calibration is considered by comparing time-series of the field data and of the model results Alternatively, and perhaps more meaningfully, the model is calibrated by comparing the harmonic constants of tides and tidal currents derived from field data with those derived from the model The model is further verified by comparing the model results with an independent data set representing the wet season The strengths and the weaknesses of the model are assessed based on the results of model calibration and verification Using the model results, the properties of tides and tidal currents in San Francisco Bay are characterized and discussed Furthermore, using the numerical model, estimates of San Francisco Bay's volume, surface area, mean water depth, tidal prisms, and tidal excursions at spring and neap tides are computed Additional applications of the model reveal, qualitatively the spatial distribution of residual variables

Worldwide distribution of subaquatic gas hydrates

Abstract: Sediments containing natural gas hydrates occur worldwide on continental and insular slopes and rises of active and passive margins, on continental shelves of polar regions, and in deep-water (> 300 m) environments of inland lakes and seas. The potential amount of methane in natural gas hydrates is enormous, with current estimates at about 1019 g of methane carbon. Subaquatic gas hydrates have been recovered in 14 different areas of the world, and geophysical and geochemical evidence for them has been found in 33 other areas. The worldwide distribution of natural gas hydrates is updated here; their global importance to the chemical and physical properties of near-surface subaquatic sediments is affirmed.