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At least 1,747 records · Page 97Linked to original sources
USGS1983

The past is the key to the future

A new major frontier of geological research, which was initiated in the 1970's, involves predicting future geologic trends or events through study of the present and past, rather than trying to understand the past, often using what one knows about the present. Like most scientific frontiers, this one began from practical considerations—environmental concerns. The lack of formal recognition of this frontier results from fragmentation among many Federal agencies and highly focused mission-oriented programs ( e.g. , earthquake prediction, CO 2 , nuclear-energy safety, etc.). Most programs aim to predict only the next 50–100 years, but much longer periods of the past need to be studied to do this. Nuclear-waste disposal has sometimes been considered in terms of the next million years, a period of time permitting significant and broad geologic changes. Decreasing public interest in environmental concerns relegates many questions from the realm of applied research back to that of basic research. Most of these questions are so fascinating, however, that the frontier is still worth pursuing. Such questions include whether a phenomenon will or will not take place and the rates at which it can develop ( e.g. , how fast do rifts form, how fast can a caldera event begin, and how quickly can a glacial maximum arrive?). Common elements of all studies include the historic record, trends in the Quaternary, analogues in various periods of the geologic time scale, and allowance for phenomena never experienced before. Other examples of studies include the Cretaceous as a period of a climatic extreme, an especially interesting time period; establishing the amount of paleocloudiness, a particularly challenging and important research area; acid rain as a possible new phenomenon. Geochemistry has much to contribute to this frontier science.

Geochimica et Cosmochimica Acta↗
USGS1989

Reactive iron transport in an acidic mountain stream in Summit County, Colorado: A hydrologic perspective

A pH perturbation experiment was conducted in an acidic, metal-enriched, mountain stream to identify relative rates of chemical and hydrologic processes as they influence iron transport. During the experiment the pH was lowered from 4.2 to 3.2 for three hours by injection of sulfuric acid. Amorphous iron oxides are abundant on the streambed, and dissolution and photoreduction reactions resulted in a rapid increase in the dissolved iron concentration. The increase occurred simultaneously with the decrease in pH. Ferrous iron was the major aqueous iron species. The changes in the iron concentration during the experiment indicate that variation exists in the solubility properties of the hydrous iron oxides on the streambed with dissolution of at least two compartments of hydrous iron oxides contributing to the iron pulse. Spatial variations of the hydrologic properties along the stream were quantified by simulating the transport of a coinjected tracer, lithium. A simulation of iron transport, as a conservative solute, indicated that hydrologie transport had a significant role in determining downstream changes in the iron pulse. The rapidity of the changes in iron concentration indicates that a model based on dynamic equilibrium may be adequate for simulating iron transport in acid streams. A major challenge for predictive solute transport models of geochemical processes may be due to substantial spatial and seasonal variations in chemical properties of the reactive hydrous oxides in such streams, and in the physical and hydrologic properties of the stream.

Geochimica et Cosmochimica Acta↗
USGS1993

Oxygen buffering of Kilauea volcanic gases and the oxygen fugacity of Kilauea basalt

Volcanic gases collected during episode 1 of the Puu Oo eruption along the east rift zone of Kilauea Volcano, Hawaii, have uniform C-O-H-S-Cl-F compositions that are sharply depleted in CO 2 . The CO 2 -poor gases are typical of Type II volcanic gases ( gerlach and Graeber , 1985) and were emitted from evolved magma stored for a prolonged period of time in the east rift zone after releasing CO 2 -rich gases during an earlier period of temporary residence in the summit magma chamber. The samples are remarkably free of contamination by atmospheric gases and meteoric water. Thermodynamic evaluation of the analytical data shows that the episode 1 gases have equilibrium compositions appropriate for temperatures between 935 and 1032°C. Open- and closed-system equilibrium models of species distributions for the episode 1 gases show unequivocally that coexisting lavas buffered the gas oxygen fugacities during cooling. These models indicate that the f O 2 buffering process occurs by transfer of oxygen from the major species in the gas phase (H 2 O, CO 2 , SO 2 ) to the lava during cooling and that the transfer of oxygen also controls the fugacities of several minor and trace species (H 2 , CO, H 2 S, S 2 , Cl 2 , F 2 ), in addition to O 2 during cooling. Gas/lava exchanges of other components are apparently insignificant and exert little influence, compared to oxygen exchange, during cooling. Oxygen transfer during cooling is variable, presumably reflecting short-term fluctuations in gas flow rates. Higher flow rates restrict the time available for gas/lava oxygen transfer and result in gases with higher equilibrium temperatures. Lower flow rates favor f O 2 -constrained equilibration by oxygen transfer down to lower temperatures. Thus, the chemical equilibrium preserved in these gases is a heterogeneous equilibrium constrained by oxygen fugacity, and the equilibrium temperatures implied by the compositions of the gases reflect the temperatures at which gas/lava oxygen exchange ceased. This conclusion challenges the common assumption that volcanic gases are released from lava in a state of chemical equilibrium and then continue equilibrating homogeneously with falling temperature until reaction rates are unable to keep pace with cooling. No evidence is found, moreover, that certain gas species are kinetically more responsive and able to equilibrate down to lower temperatures than those of the last gas/lava oxygen exchange. Homogeneous reaction rates in the gas phase are apparently slow compared to the time it took for the gases to move from the last site of gas/lava equilibration to the site of collection. An earlier set of data for higher temperature CO 2 -rich Type I volcanic gases, which come from sustained summit lava lake eruptions supplied by magma that experienced substantially shorter periods of crustal storage, shows f O 2 buffering by oxygen transfer up to 1185°C. Oxygen fugacity measurements in drill holes into ponded lava flows suggest that buffering by oxygen transfer may control the f O 2 of residual gases down to several hundred degrees below the solidus in the early stages of cooling. Although the details of the f O 2 buffering mechanisms for oxygen transfer are unknown, the fact that f O 2 buffering is effective from molten to subsolidus conditions suggests that the reaction mechanisms must change with cooling as the reactants change from predominantly melt, to melt plus crystals, to glass plus crystals. Mass balance calculations suggest that redox reactions between the gas and ferrous/ferric iron in the lava are plausible mechanisms for the oxygen transfer and that the f O 2 of the gases is buffered by sliding ferrous/ferric equilibria in the erupting lavas. Contrary to expectations based on models predicting the oxidation of basalt by H 2 and CO escape during crustal storage, CO 2 -rich Type I gases and CO 2 -poor Type II gases have identical oxygen fugacities despite greatly different crustal storage and degassing histories. Volcanic gas data give a tightly constrained log f O 2 of NNO − 0.5 (±0.05) for subaerially erupted Kilauea basalt from liquidus to solidus temperatures, consistent with recent f O 2 determinations for the mantle source regions of ocean island basalts. Because the oxygen fugacities of volcanic gases emitted by subaerial lavas imply that the f O 2 of Kilauea basalt is unchanged during crustal storage, Kilauea basalt either arrives in the crust with an oxygen fugacity between NNO and FMQ, or it develops an oxygen fugacity in this range immediately upon arrival in the summit chamber.

Geochimica et Cosmochimica Acta↗
USGS1995

Frequency-moment distribution of deep earthquakes; Implications for the seismogenic zone at the bottom of slabs

We present a systematic investigation of the variation with depth of the frequency of earthquake occurrence vs. seismic moment based on 16 years of Harvard Centroid Moment Tensor (CMT) solutions. We analyze depth variations of earthquake size distribution in terms of variations in the absolute value of the slope of the regression of the logarithm of the population vs. seismic moment, a quantity known as the β parameter. The shallowest earthquakes (0–50 km depth) exhibit a well-defined and robust size distribution regime characterized by a discontinuous increase in β with increasing moment. Others have shown that this increase probably represents the effects of a physical limit in the dimensions of the area of seismogenic slip of shallow earthquake sources. The population of deep earthquakes in the depth interval 500–600 km shows two markedly different distributions. The deep earthquakes in the Tonga region feature an initially high β value (0.92) at small moments and a lower β value (0.41) at high moments. In contrast, the size distribution of non-Tonga deep events shows the reverse of those changes (β = 0.41 at low moment and β = 1.17 at higher moment). To help explain these observations, we propose a model of deep seismogenesis that assumes three-dimensional earthquake source regions that vary principally in their transverse dimensions. The two-β segment behavior in the Tonga region and other subduction zones is thought to represent, in part, constraints owing to the threshold of completeness of the CMT catalog and to its short time interval of sampling. We interpret the differences between Tonga and other deep Wadati-Benioff zones as being a consequence of Tonga's markedly higher subduction rate and, hence, its colder thermal structure and presumably thicker region of seismogenesis. We interpret the critical moments at which β values change in terms of variations in the transverse thickness of deep seismogenic zones and estimate that it is about 11 km for the Tonga region and about 3 km for other zones at depths of 500–600 km. These results are generally consistent with deep earthquakes being restricted to wedge-shaped regions of peridotite persisting metastably to as deep as 700 km in old, rapidly descending and hence cold slabs. Failure is thought to occur in metastable peridotite by transformational faulting. Great deep earthquakes present special challenges to any theory of deep earthquakes based on slab thermal structure. For example, a continuing question is how such large events can fit in a thermally controlled seismogenic zone that is diminishing in its transverse dimensions with increasing depth. The very concept of a scale-invariant earthquake size distribution may be inappropriate for these rare events and the unusual settings in which they are found.

Physics of the Earth and Planetary Interiors↗
USGS1984

Fluvial sedimentation on a quivering craton: Influence of slight crustal movements on fluvial processes, upper Jurassic Morrison formation, western Colorado Plateau

One of the most important challenges facing the fluvial sedimentologist is identification of processes outside the stream channel that influence deposition of fluvial sediments. Detailed studies in the lower sequence of the Salt Wash Member (Morrison Formation, Upper Jurassic) demonstrate that crustal deformation at the site of deposition may considerably influence braided-stream processes. Late Jurassic crustal movements in the western part of the Colorado Plateau are interpreted largely from thickness variations and facies distribution, but other features such as vertical repetition of facies, coincidence with at least parts of present-day folds, and the geographic distribution of bedding parameters measured in the fluvial deposits, are also used as corroborating evidence of syndepositional tectonism. These features indicate that several of the large uplifts and basins in the region as well as some of the smaller folds within them were actively moving during deposition of the lower sequence. Tectonic activity altered the stream gradients, which in turn governed sinuosity, flow regime, energy levels, and sediment distribution. Cross-bedding studies indicate that reduced gradients within downwarped areas led to slight increases in sinuosity of the braided-stream channels and of the small sub-channels within them. The lowered gradients apparently resulted in a decrease in the depth of the channels and allowed the streams to flood more readily, producing abundant upper-flow regime horizontal laminations in the channel deposits. In addition, greater quantities of sediment containing higher proportions of sand were deposited in downwarped areas than in positive localities. The inability of the streams to transport bed load through downwarped areas indicates loss of stream energy. However, an increase in the quantity of upper-flow regime horizontal laminations in the same downwarped areas suggests that an increase in flow regime is not necessarily accompanied by an increase in energy levels, at least in regions of slight tectonic activity where the local configuration of the stream channels may change appreciably. Strata presently dip less than 2° throughout most of the region, and this relatively small amount of deformation reflects the combined effects of Late Jurassic, Cretaceous and Tertiary tectonism. This demonstrates that the amount of structural deformation at the site of deposition may appear to be insignificant, yet it can cause appreciable changes in the nature of braided-stream deposits.

Arizona, Utah↗
USGS1977

Immunization of sockeye salmon (Oncorhynchus nerka) against vibriosis using the hyperosmotic infiltration technique

Various procedures of hyperosmotic infiltration (HI) and intraperitoneal injection were used to vaccinate sockeye salmon ( Oncorhynchus nerka ) with killed Vibrio anguillarum . Excellent protection was evident against experimentally induced vibriosis in the groups immunized by HI with 10 × Hanks' balanced salt solution (HBSS), 1 × HBSS with 8.0% NaCl and 5.3% NaCl, as well as in the injected groups. Comparisons were made among the various immunization methods by vaccinating fish with ten-fold serial dilutions of bacterin, then challenging them by the water contact method after 6 or 9 weeks. Protection was somewhat better with 10 × HBSS than with 5.3% NaCl, and 1 × HBSS containing 8.0% NaCl was markedly superior to the vaccination of fish without hyperosmotic treatment. Agglutinin titers did not exceed 1 : 8 in any group.

Aquaculture↗
USGS1977

DDE increased the toxicity of parathion to coturnix quail

Adult male Japanese quail (Coturnix coturnix) were exposed to DDE or chlordane in the diet and subsequently dosed with parathion or paraoxon. Pretreatment with 5 or 50 ppm DDE in the diet for 12 weeks resulted in increased cholinesterase (ChE) activity in plasma, but not in the brain. Dietary concentrations of 5 and 50 ppm DDE caused increased susceptibility of quail that were challenged with parathion or paraoxon. The increased mortality resulting from DDE pretreatment was reflected in brain ChE inhibition. The synergistic action of DDE was apparent after 3 days of exposure to 50 ppm DDE and 1 week of exposure to 5 ppm DDE. Birds exposed for 3 weeks to 5 or 50 ppm DDE retained their DDE-potentiated sensitivity to parathion after 2 weeks on clean diet. Chlordane pretreatment resulted in decreased susceptibility (antagonism) to parathion, but not to paraoxon dosage. Implications of differing responses in ChE and mortality among controls, DDE-, and chlordane-pretreated birds after parathion or paraoxon dosage are discussed.

Pesticide Biochemistry and Physiology↗
USGS1987

Higher resolution satellite remote sensing and the impact on image mapping

Recent advances in spatial, spectral, and temporal resolution of civil land remote sensing satellite data are presenting new opportunities for image mapping applications. The U.S. Geological Survey's experimental satellite image mapping program is evolving toward larger scale image map products with increased information content as a result of improved image processing techniques and increased resolution. Thematic mapper data are being used to produce experimental image maps at 1:100,000 scale that meet established U.S. and European map accuracy standards. Availability of high quality, cloud-free, 30-meter ground resolution multispectral data from the Landsat thematic mapper sensor, along with 10-meter ground resolution panchromatic and 20-meter ground resolution multispectral data from the recently launched French SPOT satellite, present new cartographic and image processing challenges. The need to fully exploit these higher resolution data increases the complexity of processing the images into large-scale image maps. The removal of radiometric artifacts and noise prior to geometric correction can be accomplished by using a variety of image processing filters and transforms. Sensor modeling and image restoration techniques allow maximum retention of spatial and radiometric information. An optimum combination of spectral information and spatial resolution can be obtained by merging different sensor types. These processing techniques are discussed and examples are presented.

Acta Astronautica↗
USGS1991

The interaction between biology and the management of aquatic macrophytes

‘Management’ refers to controlling nuisance aquatic species and to restoring or restructing aquatic plant communities. Producing stable, diverse, aquatic plant communities containing a high percentage of desirable species is a primary management goal. There are a variety of techniques including harvesting, herbicides, water-level fluctuation, sediment alteration, nutrient limitation, light alteration, and biological controls which can be used for managing macrophytes. These techniques are briefly reviewed along with discussions of biological considerations important to the efficacy of the technique and the environmental impacts of the technique. There is a growing interest in restoring and restructing aquatic plant communities. Techniques for community restoration are discussed as are emerging management technologies using growth regulators and bioengineering. New management technologies will probably be limited by costs and environmental impacts. In the near future, better macrophyte management will come through better planning and more effective use of present technology. The challenge is to make current planning and management techniques more effective through increased biological inputs. The potential for biological input ranges from subcellular biology to species biology, to community and ecosystem biology. Some information needs are identified.

Aquatic Botany↗
USGS2007

The geochemistry of pesticides

The mid-1970s marked a major turning point in human history, for it was at that moment that the ability of the Earth’s ecosystems to absorb most of the biological impacts of human activities appears to have been exceeded by the magnitude of those impacts. This conclusion is based partly upon estimates of the rate of carbon dioxide emission during the combustion of fossil fuels, relative to the rate of its uptake by terrestrial ecosystems ( Loh, 2002 ). A very different threshold, however, had already been crossed several decades earlier with the birth of the modern chemical industry, which produced novel substances for which no such natural assimilative capacity existed. Among these new chemical compounds, none has posed a greater challenge to the planet’s ecosystems than synthetic pesticides, compounds that have been intentionally released into the hydrologic system in vast quantities—several hundred million pounds of active ingredient (a.i.) per year in the United States alone ( Donaldson et al. , 2002 )—for many decades. To gauge the extent to which we are currently able to assess the environmental implications of this new development in the Earth’s history, this chapter presents an overview of current understanding regarding the sources, transport, fate, and biological effects of pesticides, their transformation products, and selected adjuvants in the hydrologic system. (Adjuvants are the so-called inert ingredients included in commercial pesticide formulations to enhance the effectiveness of the active ingredients.)

Book chapter↗
USGS2020

Natural gas hydrates: Status of potential as an energy resource

Gas hydrate is a widespread naturally-occurring combination of water and natural gases. Gas hydrate is found in shallow sediments of deepwater regions of the continental margins and in areas of continuous permafrost. Where gas supply is sufficient and migration pathways connect gas sources to favorable reservoirs, gas hydrate can accumulate to resource densities that may be attractive for gas production. Global research on the potential commercial viability of gas extraction from gas hydrates continues, predominantly in Asia and in the United States, where current efforts focus on the controlled destabilization of high-saturation deposits housed in sand and/or silt-rich reservoirs. This chapter reviews the current state of gas hydrate resource exploration and appraisal, the most promising production approaches identified to date, and the likely technical challenges to commercial production.

Book chapter↗
USGS2021

Ocean floor manganese deposits

Much of the dissolved Mn delivered to the oceans is slowly oxidized and precipitated alongside varying amounts of Fe into Mn and ferromanganese (FeMn) mineral deposits that occur extensively in the deep ocean wherever sediment accumulation is low and substrate is available. FeMn crusts grow as pavements on rock outcrops throughout the global ocean whereas nodules form as individual FeMn-encrusted particles on the sediment-covered abyssal plains. Both crusts and nodules are composed predominantly of Fe and Mn oxide minerals that precipitate from seawater and for some nodules also from porewaters of deep-sea sediment. In contrast, hydrothermal oxide deposits consist predominantly of Mn or Fe oxide. FeMn crusts and nodules exhibit very high specific surface areas that allow them to scavenge abundant metals and other elements, recording the history of the source waters. Crusts especially serve as an important record of paleoceanographic conditions over the past 70 + million years. Critical metals essential to many computer, military, and green technologies are enriched in crust and nodule deposits to concentrations high enough to compare with, or exceed, typical terrestrial deposits, and they can be considered as potential resources for mining in the near future. Twenty-three contracts pertaining to exploration for nodules and crusts have been signed with the International Seabed Authority, and resource/reserve, baseline, and environmental impact assessments are underway. Many challenges remain to be addressed before full-scale mining of marine FeMn deposits will occur. However, their unique genesis and the growing worldwide need for rare and critical metals keep these deep-ocean deposits relevant to industry, scientists, and governments.

Book chapter↗
USGS2012

GRACEnet: addressing policy needs through coordinated cross-location research

GRACEnet (Greenhouse gas Reduction through Agricultural Carbon Enhancement network) was conceived to build upon ongoing USDA Agricultural Research Service (ARS) research to improve soil productivity, while addressing the challenges and opportunities of interest in C sequestration from a climate change perspective. The vision for GRACEnet was and remains: Knowledge and information used to implement scientifically based agricultural management practices from the field to national policy scales on C sequestration, greenhouse gas (GHG) emissions, and environmental benefits. The national focus of GRACEnet uses a standardized approach by ARS laboratories and university and land manager (e.g. farmer and rancher) cooperators to assess C sequestration and GHG emission from different crop and grassland systems. Since 2002, GRACEnet has significantly expanded GHG mitigation science and delivered usable information to agricultural research and policy organizations. Recent developments suggest GRACEnet will have international impact by contributing leadership and technical guidance for the Global Research Alliance on Agricultural Greenhouse Gases.

Book chapter↗
USGS2012

The General Ensemble Biogeochemical Modeling System (GEMS) and its applications to agricultural systems in the United States: Chapter 18

The General Ensemble Biogeochemical Modeling System (GEMS) was es in individual models, it uses multiple site-scale biogeochemical models to perform model simulations. Second, it adopts Monte Carlo ensemble simulations of each simulation unit (one site/pixel or group of sites/pixels with similar biophysical conditions) to incorporate uncertainties and variability (as measured by variances and covariance) of input variables into model simulations. In this chapter, we illustrate the applications of GEMS at the site and regional scales with an emphasis on incorporating agricultural practices. Challenges in modeling soil carbon dynamics and greenhouse emissions are also discussed.

Book chapter↗
USGS2013

Hormonal control of euryhalinity

Hormones play a critical role in maintaining body fluid balance in euryhaline fishes during changes in environmental salinity. The neuroendocrine axis senses osmotic and ionic changes, then signals and coordinates tissue-specific responses to regulate water and ion fluxes. Rapid-acting hormones, e.g. angiotensins, cope with immediate challenges by controlling drinking rate and the activity of ion transporters in the gill, gut, and kidney. Slow-acting hormones, e.g. prolactin and growth hormone/insulin-like growth factor-1, reorganize the body for long-term acclimation by altering the abundance of ion transporters and through cell proliferation and differentiation of ionocytes and other osmoregulatory cells. Euryhaline species exist in all groups of fish, including cyclostomes, and cartilaginous and teleost fishes. The diverse strategies for responding to changes in salinity have led to differential regulation and tissue-specific effects of hormones. Combining traditional physiological approaches with genomic, transcriptomic, and proteomic analyses will elucidate the patterns and diversity of the endocrine control of euryhalinity.

Book chapter↗
USGS2013

Smolt physiology and endocrinology

Hormones play a critical role in maintaining body fluid balance in euryhaline fishes during changes in environmental salinity. The neuroendocrine axis senses osmotic and ionic changes, then signals and coordinates tissue-specific responses to regulate water and ion fluxes. Rapid-acting hormones, e.g. angiotensins, cope with immediate challenges by controlling drinking rate and the activity of ion transporters in the gill, gut, and kidney. Slow-acting hormones, e.g. prolactin and growth hormone/insulin-like growth factor-1, reorganize the body for long-term acclimation by altering the abundance of ion transporters and through cell proliferation and differentiation of ionocytes and other osmoregulatory cells. Euryhaline species exist in all groups of fish, including cyclostomes, and cartilaginous and teleost fishes. The diverse strategies for responding to changes in salinity have led to differential regulation and tissue-specific effects of hormones. Combining traditional physiological approaches with genomic, transcriptomic, and proteomic analyses will elucidate the patterns and diversity of the endocrine control of euryhalinity.

Book chapter↗
USGS2019

Conservation of temporary wetlands

Temporary wetlands are characterized by frequent drying resulting in a unique, highly specialized assemblage of often rare or specialized plant and animal species. They are found on all continents and in a variety of landscape settings. Although accurate estimates of the abundance of temporary wetlands are available in only a few countries, global estimations identify a decline in number and quality. The key environmental factors driving the structure of ecological communities in temporary wetlands are the duration, timing, frequency and predictability of the aquatic and dry phases, which varies greatly with region and hydrogeomorphic setting. Temporary wetlands have been historically neglected, but improved social awareness of the functions and values of, and increases in scientific interest, suggest that this is changing. They play an ecological role in both global cycles (i.e., CO 2 emissions) and biodiversity (in proportion to their size, they contribute disproportionately to regional and global biodiversity). Moreover, they provide valuable ecosystem services including wildlife habitat, nutrient flux to adjacent ecosystems, flood control, water filtration, and cultural services. Effective conservation of temporary wetlands requires addressing threats (i.e., inconsistent and inadequate regulatory protections; climate change; changes in land use) and management challenges (i.e., management at both local and landscape scales; incomplete understanding of the ecosystem services provided by them; the need to enhance inventories). The most suitable approaches for conserving temporary wetlands include (1) regulations or other forms of protection; (2) sustainable management; (3) restoration and creation; and (4) collaborative conservation.

Book chapter↗
USGS2015

The role of water in unconventional in situ energy resource extraction technologies

Global trends toward developing new energy resources from lower grade, larger tonnage deposits that are not generally accessible using “conventional” extraction methods involve variations of subsurface in situ extraction techniques including in situ oil shale retorting , hydraulic fracturing of petroleum reservoirs, and in situ recovery of uranium. Although these methods are economically feasible and perhaps result in a smaller above-ground land-use footprint, there remain uncertainties regarding potential subsurface impacts to groundwater. This chapter provides an overview of the role of water in these technologies and the opportunities and challenges for water reuse and recycling.

Book chapter↗