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At least 127 records · Page 7Linked to original sources
USGS1990

Monitoring long-term effects of offshore oil and gas development along the Southern California outer continental shelf and slope: Background environmental conditions in the Santa Maria Basin

Potential environmental impacts of materials discharged from oil and gas development and production platforms off the coast of southern California (Santa Maria Basin) are being monitored during an ongoing, long-term (fiveyear) field program. The study combines hypothesis testing of platform effects with basic research on the structure and dynamics of the regional ecosystem over a time series encompassing both seasonal and repeated annual scales. Oceanographic features and processes that are being measured focus on the benthos and include biological community indices and species abundances for hard-bottom and soft-bottom (macroinfauna and meiofauna) assemblages; levels and distributions of trace metals and hydrocarbons in bottom sediments, suspended particulates, animal tissues, and pore waters; water currents and otherphysical-oceanographicfeatures; various sedimentological properties (sediment grain size, total organic carbon, shear strength, distribution of mineral types, radioisotope profiles, and degrees of sediment mixing as a result of bioturbation); sediment and pollutant-transport processes; and animal-sediment-pollutant interactions. Synoptic measurement of these different environmental variables over the extended sampling period provides an opportunity to examine long-term variability in the benthic environment with respect to both natural and anthropogenic causes. Efforts to distinguish between natural variability and low-level cumulative impacts of drilling are given special attention. Results obtained during the first two years of sampling provide a basis for beginning to understand environmental processes and relations important in detecting and interpreting any subsequent impacts caused by drilling activities in this complex and productive region of the California outer continental shelf and slope. Background chemical, physical, and biological data generated during this period demonstrate that impacts of discharges from oil and gas operations should be detectable, if they occur, and should be distinguishable from natural environmental variability. Small inputs of barium and petroleum hydrocarbons have been detected and appear to be associated with the minor drilling activities that have occurred in the area thus far, however, these initial inputs have not led to any noticeable biological impacts. These initial results are hopefully of value for two reasons: (1) in providing a summary of basic chemical, physical, and biological features of the benthic environment within the Santa Maria Basin; and (2) in presenting information on research strategies that should be considered in designing studies dealing with similar resource-management problems in other parts of the world.

California↗
USGS2008

Effects of urbanization on stream ecosystems in the Willamette River basin and surrounding area, Oregon and Washington

This report describes the effects of urbanization on physical, chemical, and biological characteristics of stream ecosystems in 28 watersheds along a gradient of urbanization in the Willamette River basin and surrounding area, Oregon and Washington, from 2003 through 2005. The study that generated the report is one of several urban-effects studies completed nationally by the U.S. Geological Survey National Water-Quality Assessment Program. Watersheds were selected to minimize natural variability caused by factors such as geology, elevation, and climate, and to maximize coverage of different stages of urban development among watersheds. Because land use or population density alone often are not a complete measure of urbanization, a combination of land use, land cover, infrastructure, and socioeconomic variables were integrated into a multimetric urban intensity index (UII) to represent the degree of urban development in each watershed. Physical characteristics studied include stream hydrology, stream temperature, and habitat; chemical characteristics studied include sulfate, chloride, nutrients, pesticides, dissolved and particulate organic and inorganic carbon, and suspended sediment; and biological characteristics studied include algal, macroinvertebrate, and fish assemblages. Semipermeable membrane devices, passive samplers that concentrate trace levels of hydrophobic organic contaminants such as polycyclic aromatic hydrocarbons and polychlorinated biphenyls, also were used. The objectives of the study were to (1) examine physical, chemical, and biological responses along the gradient of urbanization and (2) determine the major physical, chemical, and landscape variables affecting the structure of aquatic communities. Common effects documented in the literature of urbanization on instream physical, chemical, and biological characteristics, such as increased contaminants, increased streamflow flashiness, increased concentrations of chemicals, and changes in aquatic community structure toward a more tolerant community associated with organically enriched conditions, generally were observed in this study. The strongest correlations to the UII and to many of the algal, macroinvertebrate, and fish assemblage metrics and community ordination involved water-chemistry metrics including the total pesticide concentration, toxic equivalents (extract assay from semipermeable membrane devices), and dissolved oxygen. Hydrologic variability metrics, such as flashiness, that normally are considered to be one of the main processes of urban disturbance had a strong association to the algal and fish assemblages in this study; however, the hydrologic variables for macroinvertebrates were secondary to the water-chemistry metrics mentioned above. Generally, the high urban intensity sites had high abundances of eutrophic and lower dissolved oxygen-indicating diatoms, high abundances of noninsects and tolerant insects, and high abundances of nonnative fish species. On the other hand, the low urban intensity sites had higher abundances of pollution sensitive diatoms, larger numbers of the sensitive macroinvertebrate EPT taxa (Ephemeroptera, Plecoptera and Trichoptera Orders), and fish assemblages with higher abundances of sensitive salmonids. The percent salmonid and macroinvertebrate EPT richness metrics plotted against the UII indicated a possible threshold response at about 25 on the UII, which is equivalent to an impervious surface value of about 5 percent. However, due to the added agricultural land use at sites within the 25 to 60 UII range, this possible threshold probably is not solely due to urbanization, but a combination of urban and agricultural land use. The effects of agricultural and urban land use could not be distinguished from each other, yet combined they provide a good assessment of overall watershed disturbance.

Oregon, Washington↗
USGS2009

Coastal Circulation and Sediment Dynamics in War-in-the-Pacific National Historical Park, Guam; measurements of waves, currents, temperature, salinity, and turbidity, June 2007-January 2008

Flow in and around coral reefs affects a number of physical, chemical and biologic processes that influence the health and sustainability of coral reef ecosystems. These range from the residence time of sediment and contaminants to nutrient uptake and larval retention and dispersal. As currents approach a coast they diverge to flow around reef structures, causing high horizontal and vertical shear. This can result in either the rapid advection of material in localized jets, or the retention of material in eddies that form in the lee of bathymetric features. The high complexity and diversity both within and between reefs, in conjunction with past technical restrictions, has limited our understanding of the nature of flow and the resulting flux of physical, chemical, and biologic material in these fragile ecosystems. Sediment, nutrients, and other pollutants from a variety of land-based activities adversely impact many coral reef ecosystems in the U.S. and around the world. These pollutants are transported in surface water runoff, groundwater seepage, and atmospheric fallout into coastal waters, and there is compelling evidence that the sources have increased globally as a result of human-induced changes to watersheds. In Guam, and elsewhere on U.S. high islands in the Pacific and Caribbean, significant changes in the drainage basins due to agriculture, feral grazing, fires, and urbanization have in turn altered the character and volume of land-based pollution released to coral reefs. Terrigenous sediment run-off (and the associated nutrients and contaminants often absorbed to it) and deposition on coral reefs are recognized to potentially have significant impact on coral health by blocking light and inhibiting photosynthesis, directly smothering and abrading coral, and triggering increases in macro algae. Studies that combine information on watershed, surface water- and groundwater-flow, transport and fate of sediment and other pollutants in the reef environment, and their impact on reef health and ecology are essential for effective reef management. Two of the main anthropogenic activities along west-central Guam's coastline that may impact the region's coral reef ecosystems include pollution and coastal land use/development, as discussed in the review by Porter and others (2005). The pollution threats include point-sources, such as municipal wastewater (Northern District, Hagatna, Naval Station Guam, and Agat-Santa Rita Waster Water Treatment Plants), cooling water (Tanguisson Steam and Cabras Power Plants), and numerous storm water, ballast water, and tank bottom draw outfalls; nonpoint sources include septic systems, urban runoff, illegal dumping, and groundwater discharges. Poor land-use practices include development without the use of runoff management measures, increased areal extent of impervious surfaces and decreased extent of vegetative barriers, and recreational off-road vehicle use. Furthermore, feral ungulates and illegal wildfires remove protective vegetative cover and generally result in increased soil erosion. While anthropogenic point-sources have been reduced in many areas due to better management practices, nonpoint sources have either stayed constant or increased. Between 1975 and 1999, it is estimated that Guam lost more than a quarter of its tree cover, and more than 750 wildfires each year have resulted in a greater proportion of badlands and other erosion-prone land surfaces with high erosion rates (Forestry and Soil Resources Division, 1999). Approximately 1.8 square kilometers (km2) of Asan Bay, west-central Guam, lies within the National Park Service's (NPS) War-in-the-Pacific National Historical Park's (WAPA) Asan Unit; the bay is the sink for material coming out of the Asan watershed. Anthropogenic modifications of the watersheds adjacent to Asan Bay, which include intentionally-set wildfires, construction, and agriculture (Minton, 2005), are believed to have increased over the past 25

Open-File Report↗
USGS2016

Global perspectives on the urban stream syndrome

Urban streams commonly express degraded physical, chemical, and biological conditions that have been collectively termed the “urban stream syndrome”. The description of the syndrome highlights the broad similarities among these streams relative to their less-impaired counterparts. Awareness of these commonalities has fostered rapid improvements in the management of urban stormwater for the protection of downstream watercourses, but the focus on the similarities among urban streams has obscured meaningful differences among them. Key drivers of stream responses to urbanization can vary greatly among climatological and physiographic regions of the globe, and the differences can be manifested in individual stream channels even through the homogenizing veneer of urban development. We provide examples of differences in natural hydrologic and geologic settings (within similar regions) that can result in different mechanisms of stream ecosystem response to urbanization and, as such, should lead to different management approaches. The idea that all urban streams can be cured using the same treatment is simplistic, but overemphasizing the tremendous differences among natural (or human-altered) systems also can paralyze management. Thoughtful integration of work that recognizes the commonalities of the urban stream syndrome across the globe has benefitted urban stream management. Now we call for a more nuanced understanding of the regional, subregional, and local attributes of any given urban stream and its watershed to advance the physical, chemical, and ecological recovery of these systems.

Freshwater Science↗
USGS2005

Quantifying macropore recharge: Examples from a semi-arid area

The purpose of this paper is to illustrate the significantly increased resolution of determining macropore recharge by combining physical, chemical, and isotopic methods of analysis. Techniques for quantifying macropore recharge were developed for both small-scale (1 to 10 km2) and regional-scale areas in and semi-arid areas. The Southern High Plains region of Texas and New Mexico was used as a representative field site to test these methods. Macropore recharge in small-scale areas is considered to be the difference between total recharge through floors of topographically dosed basins and interstitial recharge through the same area. On the regional scale, macropore recharge was considered to be the difference between regional average annual recharge and interstitial recharge measured in the unsaturated zone. Stable isotopic composition of ground water and precipitation was used us an independent estimate of macropore recharge on the regional scale. Results of this analysis suggest that in the Southern High Plains recharge flux through macropores is between 60 and 80 percent of the total 11 mm/y. Between 15 and 35 percent of the recharge occurs by interstitial recharge through the basin floors. Approximately 5 percent of the total recharge occurs as either interstitial or matrix recharge between the basin floors, representing approximately 95 percent of the area. The approach is applicable to other arid and semi-arid areas that focus rainfall into depressions or valleys.The purpose of this paper is to illustrate the significantly increased resolution of determining macropore recharge by combining physical, chemical, and isotopic methods of analysis. Techniques for quantifying macropore recharge were developed for both small-scale (1 to 10 km2) and regional-scale areas in arid and semi-arid areas. The Southern High Plains region of Texas and New Mexico was used as a representative field site to test these methods. Macropore recharge in small-scale areas is considered to be the difference between total recharge through floors of topographically closed basins and interstitial recharge through the same area. On the regional scale, macropore recharge was considered to be the difference between regional average annual recharge and interstitial recharge measured in the unsaturated zone. Stable isotopic composition of ground water and precipitation was used as an independent estimate of macropore recharge on the regional scale. Results of this analysis suggest that in the Southern High Plains recharge flux through macropores is between 60 and 80 percent of the total 11 mm/y. Between 15 and 35 percent of the recharge occurs by interstitial recharge through the basin floors. Approximately 5 percent of the total recharge occurs as either interstitial or matrix recharge between the basin floors, representing approximately 95 percent of the area. The approach is applicable to other arid and semi-arid areas that focus rainfall into depressions or valleys.

Ground Water↗
USGS1999

Fire and aquatic ecosystems in forested biomes of North America

Synthesis of the literature suggests that physical, chemical, and biological elements of a watershed interact with long‐term climate to influence fire regime, and that these factors, in concordance with the postfire vegetation mosaic, combine with local‐scale weather to govern the trajectory and magnitude of change following a fire event. Perturbation associated with hydrological processes is probably the primary factor influencing postfire persistence of fishes, benthic macroinvertebrates, and diatoms in fluvial systems. It is apparent that salmonids have evolved strategies to survive perturbations occurring at the frequency of wildland fires (10°–10 2 years), but local populations of a species may be more ephemeral. Habitat alteration probably has the greatest impact on individual organisms and local populations that are the least mobile, and reinvasion will be most rapid by aquatic organisms with high mobility. It is becoming increasingly apparent that during the past century fire suppression has altered fire regimes in some vegetation types, and consequently, the probability of large stand‐replacing fires has increased in those areas. Current evidence suggests, however, that even in the case of extensive high‐severity fires, local extirpation of fishes is patchy, and recolonization is rapid. Lasting detrimental effects on fish populations have been limited to areas where native populations have declined and become increasingly isolated because of anthropogenic activities. A strategy of protecting robust aquatic communities and restoring aquatic habitat structure and life history complexity in degraded areas may be the most effective means for insuring the persistence of native biota where the probability of large‐scale fires has increased.

Transactions of the American Fisheries Society↗
USGS1974

Alteration and fluid inclusion studies of the porphyry copper ore body at Bingham, Utah

Distribution patterns for biotitic alteration, sericitic alteration, and distinctive fluid-inclusion types in igneous host rocks of the porphyry copper ore body at Bingham, Utah, have been determined by petrographic examination of about 300 samples. These patterns are related to differences in original rock composition, variations in physical-chemical conditions during periods of intrusion and mineralization, and spatial position within the ore body. The distribution of biotitic (potassium-silicate) alteration assemblages and high-salinity fluid inclusions generally follows the crudely triangular form of the disseminated copper ore zone. Variations in abundance of hydrothermal biotite are attributed to differences in original mafic mineral content of the igneous host rocks. Biotitic alteration and initial copper mineralization were accomplished by high-salinity fluids concentrated during final crystallization of the monzonitic parent magma; genetic continuity between magmatic and hydrothermal stages is indicated . Pervasive sericitic alteration of plagioclase is confined to rocks in the northern one-third of the Bingham stock; a subzone of argillic alteration in the north-central part of the ore body occurs within the broader area of sericitic alteration. Fluids responsible for sericitic and argillic alteration were channeled by a broad zone of northeast-trending fractures. Hydrothermal minerals and high-salinity fluid inclusions occur within a large volume of shattered rock. Boiling of fluids during crystallization of the aplitic porphyry may account for the shattering. Sericitic (and argillic) alteration were apparently super-imposed on the earlier biotitic assemblage as the hydrothermal system cooled. Cooling and hydrolytic alteration were promoted by progressive introduction of meteoric waters. The many generations of inclusions trapped from boiling fluids in the temperature range 400 degrees to 600 degrees C suggest that the system was recharged repeatedly during the period of mineralization. Estimated fluid pressures of about 800 bars in the early stages of mineralization correspond to a lithostatic load of about 3 km; pressures were even lower (less than 200 bars) in the later stages and were probably controlled by hydrostatic conditions. Distribution patterns for biotitic alteration, sericitic alteration, and distinctive fluid-inclusion types in igneous host rocks of the porphyry copper ore body at Bingham, Utah, have been determined by petrographic examination of about 300 samples. These patterns are related to differences in original rock composition, variations in physical-chemical conditions during periods of intrusion and mineralization, and spatial position within the ore body.The distribution of biotitic (potassium-silicate) alteration assemblages and high-salinity fluid inclusions generally follows the crudely triangular form of the disseminated copper ore zone. Variations in abundance of hydrothermal biotite are attributed to differences in original mafic mineral content of the igneous host rocks. Biotitic alteration and initial copper mineralization were accomplished by high-salinity fluids concentrated during final crystallization of the monzonitic parent magma; genetic continuity between magmatic and hydrothermal stages is indicated.Pervasive sericitic alteration of plagioclase is confined to rocks in the northern one-third of the Bingham stock; a subzone of argillic alteration in the north-central part of the ore body occurs within the broader area of sericitic alteration. Fluids responsible for sericitic and argillic alteration were channeled by a broad zone of northeast-trending fractures.Hydrothermal minerals and high-salinity fluid inclusions occur within a large volume of shattered rock. Boiling of fluids during crystallization of the aplitic porphyry may account for the shattering. Sericitic (and argillic) alteration were apparently super-imposed on the earlier biotitic assemblage as the hydrothermal system cooled. Cooling and hydrolytic alteration were promoted by progressive introduction of meteoric waters. The many generations of inclusions trapped from boiling fluids in the temperature range 400 degrees to 600 degrees C suggest that the system was recharged repeatedly during the period of mineralization. Estimated fluid pressures of about 800 bars in the early stages of mineralization correspond to a lithostatic load of about 3 km; pressures were even lower (less than 200 bars) in the later stages and were probably controlled by hydrostatic conditions.

Utah↗
USGS2007

Physical and chemical characteristics of a metal-contaminated overbank deposit, west-central South Dakota, USA

The deposit along the Belle Fourche River is typically up to 2 m thick and extends about 90 m away from the channel along the insides of meander bends. The sediments contain above-background levels of copper, iron, manganese, zinc, and particularly arsenic. An influx at high streamflow of uncontaminated sediment from terraces and the premining floodplain as well as from tributaries causes arsenic concentrations in parts of the contaminated deposit that are farthest away from the channel to be two to three times less than arsenic concentrations in overbank sediment that is immediately adjacent to the channel.

South Dakota↗
USGS2000

Chemical and physical properties affecting strontium distribution coefficients of surficial-sediment samples at the Idaho National Engineering and Environmental Laboratory, Idaho

The U.S. Geological Survey and Idaho State University, in cooperation with the U.S. Department of Energy, conducted a study to determine strontium distribution coefficients (K d s) of surficial sediments at the Idaho National Engineering and Environmental Laboratory (INEEL). Batch experiments using synthesized aqueous solutions were used to determine K d s, which describe the distribution of a solute between the solution and solid phase, of 20 surficial-sediment samples from the INEEL. The K d s for the 20 surficial-sediment samples ranged from 36 to 275 ml/g. Many properties of both the synthesized aqueous solutions and sediments used in the experiments also were determined. Solution properties determined were initial and equilibrium concentrations of calcium, magnesium, and strontium, pH and specific conductance, and initial concentrations of potassium and sodium. Sediment properties determined were grain-size distribution, bulk mineralogy, whole-rock major-oxide and strontium and barium concentrations, and Brunauer-Emmett-Teller (BET) surface area. Solution and sediment properties were correlated with strontium K d s of the 20 surficial sediments using Pearson correlation coefficients. Solution properties with the strongest correlations with strontium K d s were equilibrium pH and equilibrium calcium concentration correlation coefficients, 0.6598 and –0.6518, respectively. Sediment properties with the strongest correlations with strontium K d s were manganese oxide (MnO), BET surface area, and the >4.75-mm-grain-size fraction correlation coefficients, 0.7054, 0.7022, and –0.6660, respectively. Effects of solution properties on strontium K d s were interpreted as being due to competition among similarly charged and sized cations in solution for strontium-sorption sites; effects of sediment properties on strontium K d s were interpreted as being surface-area related. Multivariate analyses of these solution and sediment properties resulted in r 2 values of 0.8071 when all five properties were used and 0.8043 when three properties, equilibrium pH, MnO, and BET surface area, were used.

Idaho↗
USGS2016

Physical and chemical constraints limit the habitat window for an endangered mussel

Development of effective conservation and restoration strategies for freshwater pearly mussels requires identification of environmental constraints on the distributions of individual mussel species. We examined whether the spatial distribution of the endangered Alasmidonta heterodon in Flat Brook, a tributary of the upper Delaware River, was constrained by water chemistry (i.e., calcium availability), bed mobility, or both. Alasmidonta heterodon populations were bracketed between upstream reaches that were under-saturated with respect to aragonite and downstream reaches that were saturated for aragonite during summer baseflow but had steep channels with high bed mobility. Variability in bed mobility and water chemistry along the length of Flat Brook create a “habitat window” for A. heterodon defined by bed stability (mobility index ≤1) and aragonite saturation (saturation index ≥1). We suggest the species may exist in a narrow biogeochemical window that is seasonally near saturation. Alasmidonta heterodon populations may be susceptible to climate change or anthropogenic disturbances that increase discharge, decrease groundwater inflow or chemistry, and thus affect either bed mobility or aragonite saturation. Identifying the biogeochemical microhabitats and requirements of individual mussel species and incorporating this knowledge into management decisions should enhance the conservation and restoration of endangered mussel species.

New Jersey↗
USGS2009

Effects of coal storage in air on physical and chemical properties of coal and on gas adsorption

This paper investigates changes in the high-volatile bituminous Lower Block Coal Member from Indiana owing to moisture availability and oxidation in air at ambient pressure and temperature over storage time. Specifically, it investigates changes in chemistry, in surface area, and pore structure, as well as changes in methane and carbon dioxide adsorption capacities. Our results document that the methane adsorption capacity increased by 40%, whereas CO 2 adsorption capacity increased by 18% during a 13-month time period. These changes in adsorption are accompanied by changes in chemistry and surface area of the coal. The observed changes in adsorption capacity indicate that special care must be taken when collecting samples and preserving coals until adsorption characteristics are measured in the laboratory. High-pressure isotherms from partially dried coal samples would likely cause overestimation of gas adsorption capacities, lead to a miscalculation of coal-bed methane prospects, and provide deceptively optimistic prognoses for recovery of coal-bed methane or capture of anthropogenic CO 2 . ?? 2009 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗
USGS1999

An environmental tolerance index for ostracodes as indicators of physical and chemical factors in aquatic habitats

Continental ostracode occurrences reflect salinity, solute composition, temperature, flow conditions, and other environmental properties of the water they inhabit. Their occurrences also reflect the variability of many of these environmental parameters. Environmental tolerance indices (ETIs) offer a new way to express the nature of an ostracode's environment. As defined herein, ETIs range in value from zero to one, and may be calculated for continuous and binary variables. For continuous variables such as salinity, the ETI is the ratio of the range of values of salinity tolerated by an ostracode to the total range of salinity values from a representative database. In this investigation, the database of continuous variables consists of information from 341 sites located throughout the United States. Binary ETIs indicate whether an environmental variable such as flowing water affects ostracode presence or absence. The binary database consists of information from 784 sites primarily from Illinois, USA. ETIs were developed in this investigation to interpret paleohydrological changes implied by fossil ostracode successions. ETI profiles may be cast in terms of a weighted average, or on presence/absence. The profiles express ostracode tolerance of environmental parameters such as salinity or currents. Tolerance of a wide range of values is taken to indicate shallow water because shallow environments are conducive to thermal variability, short-term water residence, and the development of currents from wind-driven waves.

Conference Paper↗
USGS2019

Chemical and physical controls on mercury source signatures in stream fish from the northeastern United States

Streams in the northeastern U.S. receive mercury (Hg) in varying proportions from atmospheric deposition and legacy point sources, making it difficult to attribute shifts in fish concentrations directly back to changes in Hg source management. Mercury stable isotope tracers were utilized to relate sources of Hg to co-located fish and bed sediments from 23 streams across a forested to urban-industrial land-use gradient within this region. Mass-dependent isotopes (δ202Hg) in prey and game fish at forested sites were depleted (medians -0.95 and -0.83 ‰, respectively) in comparison to fish from urban-industrial settings (medians -0.26 and -0.38 ‰, respectively); the forested site group also had higher prey fish Hg concentrations. The separation of Hg isotope signatures in fish was strongly related to in-stream and watershed land-use indicator variables. Fish isotopes were strongly correlated with bed sediment isotopes, but the comparison of isotopic composition between fish and sediment was variable due to differing ecosystem-specific drivers controlling the extent of MeHg formation. The multivariable approach of analyzing watershed characteristics and stream chemistry reveals that the Hg isotope composition in fish is linked to current and historic Hg sources in the northeastern U.S. and can be used to trace bioaccumulated Hg.

Environmental Science & Technology↗
USGS1998

Chemistry of unsaturated zone gases sampled in open boreholes at the crest of Yucca Mountain, Nevada: Data and basic concepts of chemical and physical processes in the mountain

Boreholes open to the unsaturated zone at the crest of Yucca Mountain, Nevada, were variously sampled for CO 2 (including 13 C and 14 C), CH 4 , N 2 , O 2 , Ar, CFC-11, CFC-12, and CFC-113 from 1986 to 1993. Air enters the mountain in outcrops, principally on the eastern slope, is enriched in CO 2 by mixing with soil gas, and is advected to the mountain crest, where it returns to the atmosphere. The CFC data indicate that travel times of the advecting gas in the shallow Tiva Canyon hydrogeologic unit are ≤5 years. The 14 C activities are postbomb to depths of 100 m, indicating little retardation of 14 CO 2 in the shallow flow systems. The 14 C activities from 168 to 404 m in the Topopah Spring hydrogeologic unit are 85–90 pMC at borehole USW-UZ6. The CFC data show that the drilling of USW-UZ6 in 1984 has altered the natural system by providing a conduit through the Paintbrush Nonwelded unit, allowing flow from Topopah Spring outcrops in Solitario Canyon on the west to USW-UZ6, upward in the borehole through the Paintbrush, to the shallow Tiva Canyon flow systems, and out of the mountain.

Nevada↗
USGS2006

Phase equilibria constraints on the chemical and physical evolution of the campanian ignimbrite

The Campanian Ignimbrite is a > 200 km3 trachyte-phonolite pyroclastic deposit that erupted at 39.3 ?? 0.1 ka within the Campi Flegrei west of Naples, Italy. Here we test the hypothesis that Campanian Ignimbrite magma was derived by isobaric crystal fractionation of a parental basaltic trachyandesitic melt that reacted and came into local equilibrium with small amounts (5-10 wt%) of crustal rock (skarns and foid-syenites) during crystallization. Comparison of observed crystal and magma compositions with results of phase equilibria assimilation-fractionation simulations (MELTS) is generally very good. Oxygen fugacity was approximately buffered along QFM+1 (where QFM is the quartz-fayalite-magnetite buffer) during isobaric fractionation at 0.15 GPa (???6 km depth). The parental melt, reconstructed from melt inclusion and host clinopyroxene compositions, is found to be basaltic trachyandesite liquid (51.1 wt% SiO2, 9.3 wt% MgO, 3 wt% H2O). A significant feature of phase equilibria simulations is the existence of a pseudo-invariant temperature, ???883??C, at which the fraction of melt remaining in the system decreases abruptly from ???0.5 to < 0.1. Crystallization at the pseudo-invariant point leads to abrupt changes in the composition, properties (density, dissolved water content), and physical state (viscosity, volume fraction fluid) of melt and magma. A dramatic decrease in melt viscosity (from 1700 Pa s to ???200 Pa s), coupled with a change in the volume fraction of water in magma (from ??? 0.1 to 0.8) and a dramatic decrease in melt and magma density acted as a destabilizing eruption trigger. Thermal models suggest a timescale of ??? 200 kyr from the beginning of fractionation until eruption, leading to an apparent rate of evolved magma generation of about 10-3 km3/year. In situ crystallization and crystal settling in density-stratified regions, as well as in convectively mixed, less evolved subjacent magma, operate rapidly enough to match this apparent volumetric rate of evolved magma production. ?? Copyright 2007 Oxford University Press.

Journal of Petrology↗
USGS1998

Benthic invertebrate distributions in the San Joaquin River, California, in relation to physical and chemical factors

The invertebrate fauna of nontidal portions of the lower San Joaquin River and its major tributaries is described in relation to water quality and habitat using canonical correspondence analysis, autecological metrics, and indicator species analysis. A large-scale (basin-wide) pattern in community response to salinity (sulfate-bicarbonate type) was detected when standardized, stable substratum was sampled. Community structure, taxa richness, and EPT (ephemeropterans, plecopterans, and trichopterans) richness varied with dissolved solids concentration (55-1700 mg total dissolved solids. L-1), and distributions of many taxa indicated salinity optima. Distinct assemblages associated with either high or low salinity were evident over this range. Large-scale patterns in community structure were unrelated to pesticide distributions. Structure and taxa richness of invertebrate assemblages in sand substratum varied both with salinity and with microhabitat heterogeneity. The benthic fauna generally was dominated by a taxa-poor assemblage of specialized psammophilous species, contributing to a weaker relationship between community structure and water quality than was observed using standardized substratum. Habitat types and associated dominant species were characterized using indicator species analysis. Species assemblages did not vary substantially with irrigation regime or fiver discharge, indicating that structure of invertebrate communities was a conservative measure of water quality.

California↗