Search USGS⌕ Search

SEARCH · Search USGS

Results for “Solutions Journal”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31Linked to original sources
USGS2012

Ultraviolet irradiation effects incorporation of nitrate and nitrite nitrogen into aquatic natural organic matter

One of the concerns regarding the safety and efficacy of ultraviolet radiation for treatment of drinking water and wastewater is the fate of nitrate, particularly its photolysis to nitrite. In this study, 15 N NMR was used to establish for the first time that UV irradiation effects the incorporation of nitrate and nitrite nitrogen into aquatic natural organic matter (NOM). Irradiation of 15 N-labeled nitrate in aqueous solution with an unfiltered medium pressure mercury lamp resulted in the incorporation of nitrogen into Suwannee River NOM (SRNOM) via nitrosation and other reactions over a range of pH from approximately 3.2 to 8.0, both in the presence and absence of bicarbonate, confirming photonitrosation of the NOM. The major forms of the incorporated label include nitrosophenol, oxime/nitro, pyridine, nitrile, and amide nitrogens. Natural organic matter also catalyzed the reduction of nitrate to ammonia on irradiation. The nitrosophenol and oxime/nitro nitrogens were found to be susceptible to photodegradation on further irradiation when nitrate was removed from the system. At pH 7.5, unfiltered irradiation resulted in the incorporation of 15 N-labeled nitrite into SRNOM in the form of amide, nitrile, and pyridine nitrogen. In the presence of bicarbonate at pH 7.4, Pyrex filtered (cutoff below 290–300 nm) irradiation also effected incorporation of nitrite into SRNOM as amide nitrogen. We speculate that nitrosation of NOM from the UV irradiation of nitrate also leads to production of nitrogen gas and nitrous oxide, a process that may be termed photo-chemodenitrification. Irradiation of SRNOM alone resulted in transformation or loss of naturally abundant heterocyclic nitrogens.

Journal of Environmental Quality↗
USGS2020

Perceived constraints and negotiations to trout fishing in Georgia based on angler specialization level

Anglers face constraints that influence participation and dropout rates. Some recreational anglers may be able to negotiate constraints by altering the timing or frequency of participation, acquiring new skills, or modifying nonrecreational aspects such as family or work responsibilities. We consider data collected via a mail survey from Georgia-resident trout license holders to identify both perceived constraints and strategies used to negotiate them. To capture variation among anglers, survey responses were grouped by level of angler specialization using K -means cluster analysis, which resulted in a three-cluster solution of most, moderately, and least specialized anglers. Analyses of variance were used to detect potential differences among the three specialization clusters. Tests revealed that the least specialized anglers experienced constraints more intensely than the most or moderately specialized anglers. Likewise, least specialized anglers were less able to negotiate constraints when compared to the most or moderately specialized anglers. However, the least specialized anglers used negotiation strategies involving overcoming perceived lack of skill more intensely than their counterparts. The most intensely experienced constraints overall were lack of time due to work or family obligations and distance to Georgia’s trout waters from home. The most intensely used negotiation strategies overall were “learn to enjoy being outside and stress less about catching fish” and “encourage family or friends to go fishing with me.” This research benefits fishery managers by providing a method of identifying angling groups that perceive more constraints and are less likely to overcome these constraints through constraint negotiation strategies. With this information, managers may choose to tailor efforts towards reducing constraints for angling groups that have low participation and may drop out of the activity all together.

Georgia↗
USGS2018

Designing a protected area to safeguard imperiled species from urbanization

Reserve design is a process that can address ecological, social, and political factors to identify parcels of land needed to sustain wildlife populations and other natural resources. Acquisition of parcels for a large terrestrial reserve is difficult because it typically occurs over a long timeframe and thus invokes consideration of future conditions such as climate and urbanization changes. In central Florida, a new protected area, the Everglades Headwaters National Wildlife Refuge, has been authorized by the United States Government. The new refuge will host important threatened and endangered species and habitats, as well as be located to allow for species adaptation from climate change impacts. For this study we combined habitat objectives defined by the U.S. Fish and Wildlife Service and projections from two urbanization models to provide guidance for Everglades Headwaters National Wildlife Refuge design. We used Marxan with Zones to find near-optimal solutions for protecting explicit amounts of five target habitats. We identified parcels for inclusion into the reserve design that the model allocated among two zones representing different methods of protection: fee-simple purchase (up to 20,234 hectares authorized by the United States government), and conservation easement agreements (up to 40,469 hectares authorized). As expected, for all scenarios we found an increase in costs as the proportion of fee-simple purchases was increased, reflecting the lesser cost of easements, but the number of parcels required for protection differed little among scenarios. The two urbanization models showed considerable agreement over which habitat patches were not forecast to be developed, and showed some agreement over which parcels might be developed. The U.S. Fish and Wildlife Service may benefit from focusing on parcels that are selected frequently by our analyses under both urban scenarios because these parcels are more likely to be in areas where urbanization threats and demand for land is reduced. The reserve designs we generated met U.S. Fish and Wildlife Service habitat goals within fee and easement zone restrictions, and we found reserve configurations that fell well below the mandated size limit.

Florida↗
USGS2005

Coupled inverse modeling of vadose zone water, heat, and solute transport: Calibration constraints, parameter nonuniqueness, and predictive uncertainty

In this study, an inverse methodology is presented and used to evaluate the effect that calibration of a synthetic artificial recharge model, constrained by different combinations of measurements (pressure head, temperature, and concentration), has on estimated vadose zone model parameter-value nonuniqueness and predictive water, heat, and solute transport uncertainty. Several findings are arrived at following model calibration and predictive analysis. First, composite scaled sensitivities revealed that all calibration measurement combinations contributed to the estimation of 30 water, heat, and solute transport parameters by inverting a set of vadose zone transport equations that were coupled explicitly through dependent variables and implicitly through parameters and fluid properties. Second, despite excellent model quality and perfect match of simulated-to-measured dependent field variables, the limitations in information content of field measurements used to constrain the calibration process promoted correlation among parameters; correlation among parameters promoted parameter nonuniqueness; and parameter nonuniqueness promoted predictive uncertainty. Consequently, simulations by transport models calibrated against field information represent a single realization associated with some quantifiable range of predictive uncertainty. Third, a primary reduction in uncertainty was achieved by increasing the number of calibration-constraint measurements, but reductions in uncertainty appeared restricted implying a practical limit to parameterization detail. Fourth, for a fixed number of measurements, a less prominent reduction in the range of predictive uncertainty could be realized through selective use of measurement types to constrain the calibration process. Therefore, field measurement types used to constrain the calibration process should be matched to target predictions. Fifth, because correlation among parameters contributes to predictive uncertainty, it may be possible to further reduce predictive uncertainty by estimating parameters that also minimize the largest eigenvalue in the normalized eigenvector matrix.

Journal of Hydrology↗
USGS2011

Estimates of stress drop and crustal tectonic stress from the 27 February 2010 Maule, Chile, earthquake: Implications for fault strength

The great 27 February 2010 M w 8.8 earthquake off the coast of southern Chile ruptured a ∼600 km length of subduction zone. In this paper, we make two independent estimates of shear stress in the crust in the region of the Chile earthquake. First, we use a coseismic slip model constrained by geodetic observations from interferometric synthetic aperture radar (InSAR) and GPS to derive a spatially variable estimate of the change in static shear stress along the ruptured fault. Second, we use a static force balance model to constrain the crustal shear stress required to simultaneously support observed fore‐arc topography and the stress orientation indicated by the earthquake focal mechanism. This includes the derivation of a semianalytic solution for the stress field exerted by surface and Moho topography loading the crust. We find that the deviatoric stress exerted by topography is minimized in the limit when the crust is considered an incompressible elastic solid, with a Poisson ratio of 0.5, and is independent of Young's modulus. This places a strict lower bound on the critical stress state maintained by the crust supporting plastically deformed accretionary wedge topography. We estimate the coseismic shear stress change from the Maule event ranged from −6 MPa (stress increase) to 17 MPa (stress drop), with a maximum depth‐averaged crustal shear‐stress drop of 4 MPa. We separately estimate that the plate‐driving forces acting in the region, regardless of their exact mechanism, must contribute at least 27 MPa trench‐perpendicular compression and 15 MPa trench‐parallel compression. This corresponds to a depth‐averaged shear stress of at least 7 MPa. The comparable magnitude of these two independent shear stress estimates is consistent with the interpretation that the section of the megathrust fault ruptured in the Maule earthquake is weak, with the seismic cycle relieving much of the total sustained shear stress in the crust.

Maule↗
USGS2009

Stratigraphic controls on seawater intrusion and implications for groundwater management, Dominguez Gap area of Los Angeles, California, USA

Groundwater pumping has led to extensive water-level declines and seawater intrusion in coastal Los Angeles, California (USA). A SUTRA-based solute-transport model was developed to test the hydraulic implications of a sequence-stratigraphic model of the Dominguez Gap area and to assess the effects of water-management scenarios. The model is two-dimensional, vertical and follows an approximate flow line extending from the Pacific Ocean through the Dominguez Gap area. Results indicate that a newly identified fault system can provide a pathway for transport of seawater and that a stratigraphic boundary located between the Bent Spring and Upper Wilmington sequences may control the vertical movement of seawater. Three 50-year water-management scenarios were considered: (1) no change in water-management practices; (2) installation of a slurry wall; and (3) raising inland water levels to 7.6 m above sea level. Scenario 3 was the most effective by reversing seawater intrusion. The effects of an instantaneous 1-m sea-level rise were also tested using water-management scenarios 1 and 3. Results from two 100-year simulations indicate that a 1-m sea-level rise may accelerate seawater intrusion for scenario 1; however, scenario 3 remains effective for controlling seawater intrusion.

Hydrogeology Journal↗
USGS2025

Assessing gap-filled Landsat land surface temperature time-series data using different observational datasets

Landsat Analysis Ready Data (ARD)-based time-series present challenges in monitoring surface urban heat islands (SUHI) due to rapid changes in land surface temperature (LST) compared to cloud-free satellite observations. This research investigates the use of a spatiotemporal gap-filling model as a feasible and cost-effective solution to produce Landsat time-series LST products with both high spatial resolution and temporal frequency. The study identified and filled Landsat ARD thermal times-series data gaps due to missing data, cloud and shadow effects, and data quality. The accuracy of Landsat gap-filled products was assessed using randomly selected clear observations of Landsat and uncertainty products from the gap-filling model and was evaluated using various existing temperature datasets, including climate data from NOAA Global Historical Climate Network station observations, Daily Surface Weather and Climatological Summaries (DAYMET), and LST including MODIS, VIIRS and ECOSTRESS. The result suggests that the gap-filled Landsat LST has significant correlations with existing datasets including field observation and remote sensing data derived from other sensors that have similar monthly and seasonal variation patterns. The uncertainty maps show spatial distributions of uncertainty for gap-filled pixels that have high or low uncertainties. The Landsat gap-filled time-series datasets can be used to measure annual, seasonal, or even monthly landscape thermal conditions, which are useful for SUHI and relevant research, and to perform multi-decade time-series LST change analysis under climate change conditions.

International Journal of Remote Sensing↗
USGS2010

Rayleigh-wave phase-velocity maps and three-dimensional shear velocity structure of the western US from local non-plane surface wave tomography

We utilize two-and-three-quarter years of vertical-component recordings made by the Transportable Array (TA) component of Earthscope to constrain three-dimensional (3-D) seismic shear wave velocity structure in the upper 200 km of the western United States. Single-taper spectral estimation is used to compile measurements of complex spectral amplitudes from 44 317 seismograms generated by 123 teleseismic events. In the first step employed to determine the Rayleigh-wave phase-velocity structure, we implement a new tomographic method, which is simpler and more robust than scattering-based methods (e.g. multi-plane surface wave tomography). The TA is effectively implemented as a large number of local arrays by defining a horizontal Gaussian smoothing distance that weights observations near a given target point. The complex spectral-amplitude measurements are interpreted with the spherical Helmholtz equation using local observations about a succession of target points, resulting in Rayleigh-wave phase-velocity maps at periods over the range of 18–125 s. The derived maps depend on the form of local fits to the Helmholtz equation, which generally involve the nonplane-wave solutions of Friederich et al. In a second step, the phase-velocity maps are used to derive 3-D shear velocity structure. The 3-D velocity images confirm details witnessed in prior body-wave and surface-wave studies and reveal new structures, including a deep (>100 km deep) high-velocity lineament, of width ∼200 km, stretching from the southern Great Valley to northern Utah that may be a relic of plate subduction or, alternatively, either a remnant of the Mojave Precambrian Province or a mantle downwelling. Mantle seismic velocity is highly correlated with heat flow, Holocene volcanism, elastic plate thickness and seismicity. This suggests that shallow mantle structure provides the heat source for associated magmatism, as well as thinning of the thermal lithosphere, leading to relatively high stress concentration. Our images also confirm the presence of high-velocity mantle at 100 km depth beneath areas of suspected mantle delamination (southern Sierra Nevada; Grande Ronde uplift), low velocity mantle underlying active rift zones, and high velocity mantle associated with the subducting Juan de Fuca plate. Structure established during the Proterozoic appears to exert a lasting influence on subsequent volcanism and tectonism up to the Present.

Geophysical Journal International↗
USGS2000

Evaluation and application of the transient-pulse technique for determining the hydraulic properties of low permeability rocks: Part 2: Experimental application

In Part 1 of this study, the general solution to the transient-pulse test (Hsieh et al. 1981) was extended to evaluate quantitatively the transient variations in hydraulic head and the corresponding distributions of hydraulic gradient within a test specimen. In addition, the conditions and the validity of using the expression proposed by Brace et al. (1968) to compute the low permeability of a rock specimen from a transient-pulse test were examined. Some theoretical considerations related to the optimal design of a transient-pulse test were also discussed. Part 2 presents a relatively general and convenient approach for determining not only the hydraulic conductivity and specific storage of a specimen directly from a transient-pulse test, but also the compressive storage of the fluid reservoirs. The accuracy and efficiency of this method are demonstrated through (1) the comparison of the compressibility of the fluid-reservoir (permeating) system back-calculated from the transient-pulse tests with the value obtained from calibration tests, and (2) its application to a series of experimental studies designed to investigate the effects of confining pressure on the hydraulic properties of Shirahama sandstone and Inada granite, two rock types available widely in Japan.

Geotechnical Testing Journal↗
USGS2003

Location of long-period events below Kilauea Volcano using seismic amplitudes and accurate relative relocation

We present methods for improving the location of long-period (LP) events, deep and shallow, recorded below Kilauea Volcano by the permanent seismic network. LP events might be of particular interest to understanding eruptive processes as their source mechanism is assumed to directly involve fluid transport. However, it is usually difficult or impossible to locate their source using traditional arrival time methods because of emergent wave arrivals. At Kilauea, similar LP waveform signatures suggest the existence of LP multiplets. The waveform similarity suggests spatially close sources, while catalog solutions using arrival time estimates are widely scattered beneath Kilauea's summit caldera. In order to improve estimates of absolute LP location, we use the distribution of seismic amplitudes corrected for station site effects. The decay of the amplitude as a function of hypocentral distance is used for inferring LP location. In a second stage, we use the similarity of the events to calculate their relative positions. The analysis of the entire LP seismicity recorded between January 1997 and December 1999 suggests that a very large part of the LP event population, both deep and shallow, is generated by a small number of compact sources. Deep events are systematically composed of a weak high-frequency onset followed by a low-frequency wave train. Aligning the low-frequency wave trains does not lead to aligning the onsets indicating the two parts of the signal are dissociated. This observation favors an interpretation in terms of triggering and resonance of a magmatic conduit. Instead of defining fault planes, the precise relocation of similar LP events, based on the alignment of the high-energy low-frequency wave trains, defines limited size volumes. Copyright 2003 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗
USGS1973

Critically refracted waves in a spherically symmetric radially heterogeneous Earth model

A theoretical analysis of acoustic waves refracted by a spherical boundary across which velocity and density increase abruptly and below which velocity and density may either increase or decrease continuously with depth is formulated in terms of waves generated at a harmonic point source and scattered by a radially heterogeneous spherical body. Through the application of an Earth-flattening transformation on the radial solution and the Watson transform on the sum over eigenfunctions, the solution to the spherical problem for high frequencies is expressed as an integral for the corresponding half-space problem in which the effect of boundary curvature maps into an effective positive velocity gradient with depth. The results of both analytical and numerical evaluation of this integral can be summarized as follows for body waves in the crust and upper mantle: (1) In the special case of a critical velocity gradient (a gradient equal and opposite to the effective curvature gradient), waves interacting with the boundary at the critical angle of incidence have the same form as the classical head wave for flat, homogeneous layers. (2) For gradients more negative than critical, the amplitude of waves incident at the critical angle decay more rapidly with distance than the classical head wave. (3) For gradients that are positive, null, and less negative than critical, the amplitude of waves near the critical angle decays less rapidly with distance than the classical head wave, and at sufficiently large distances, the refracted wave field can be adequately described in terms of ray-theoretical diving waves. At intermediate distances from the critical point, the spectral amplitude of the refracted wave is scalloped due to multiple diving wave interference.

Geophysical Journal of the Royal Astronomical Soci↗
USGS2024

Efficacy of non-lead ammunition distribution programs to offset fatalities of golden eagles in southeast Wyoming

Golden eagles ( Aquila chrysaetos ) face many anthropogenic risks including illegal shooting, electrocution, collision with wind turbines and vehicles, and lead poisoning. Minimizing or offsetting eagle deaths resulting from human-caused sources is often viewed as an important management objective. Despite understanding the leading anthropogenic sources of eagle fatalities, existing scientific research supports few practical solutions to mitigate these causes of death. We implemented a non-lead ammunition distribution program in southeast Wyoming, USA, and evaluated its effectiveness as a compensatory mitigation action to offset incidental take (i.e., fatalities) of golden eagles at wind energy facilities. In 2020 and 2022, we distributed non-lead ammunition to 699 hunters with big-game tags specific to our >400,000-ha study area. These hunters harvested 296 pronghorn ( Antilocapra americana ), 14 deer ( Odocoileus spp.), and 33 elk ( Cervus canadensis ) in the study area, which accounted for 6.9% and 6.5% of the harvest in these hunt units in 2020 and 2022, respectively. We used road surveys in 2020 to estimate a density of 0.036 (95% CI = 0.018–0.058) golden eagles/km 2 during the big game hunting season in our study area. Model output suggests that our non-lead ammunition distribution program offset the fatality of 3.84 (95% CI = 1.06–23.72) eagles over the course of these 2 hunting seasons. Our work illustrates the potential usefulness of non-lead ammunition distribution programs as an action to mitigate eagle fatalities caused by wind facilities or other anthropogenic causes of death.

Wyoming↗
USGS2017

Analysis of a GRACE global mascon solution for Gulf of Alaska glaciers

We present a high-resolution Gravity Recovery and Climate Experiment (GRACE) mascon solution for Gulf of Alaska (GOA) glaciers and compare this with in situ glaciological, climate and other remote-sensing observations. Our GRACE solution yields a GOA glacier mass balance of –65 ± 11 Gt a –1 for the period December 2003 to December 2010, with summer balances driving the interannual variability. Between October/November 2003 and October 2009 we obtain a mass balance of –61 ± 11 Gt a –1 from GRACE, which compares well with –65 ± 12 Gt a –1 from ICESat based on hypsometric extrapolation of glacier elevation changes. We find that mean summer (June–August) air temperatures derived from both ground and lower-troposphere temperature records were good predictors of GRACE-derived summer mass balances, capturing 59% and 72% of the summer balance variability respectively. Large mass losses during 2009 were likely due to low early melt season surface albedos, measured by the Moderate Resolution Imaging Spectroradiometer (MODIS) and likely associated with the 31 March 2009 eruption of Mount Redoubt, southwestern Alaska. GRACE data compared well with in situ measurements at Wolverine Glacier (maritime Alaska), but poorly with those at Gulkana Glacier (interior Alaska). We conclude that, although GOA mass estimates from GRACE are robust over the entire domain, further constraints on subregional and seasonal estimates are necessary to improve fidelity to ground observations.

Alaska↗
USGS1988

Pumping tests in nonuniform aquifers - The radially symmetric case

Traditionally, pumping-test-analysis methodology has been limited to applications involving aquifers whose properties are assumed uniform in space. This work attempts to assess the applicability of analytical methodology to a broader class of units with spatially varying properties. An examination of flow behavior in a simple configuration consisting of pumping from the center of a circular disk embedded in a matrix of differing properties is the basis for this investigation. A solution describing flow in this configuration is obtained through Laplace-transform techniques using analytical and numerical inversion schemes. Approaches for the calculation of flow properties in conditions that can be roughly represented by this simple configuration are proposed. Possible applications include a wide variety of geologic structures, as well as the case of a well skin resulting from drilling or development. Of more importance than the specifics of these techniques for analysis of water-level responses is the insight into flow behavior during a pumping test that is provided by the large-time form of the derived solution. The solution reveals that drawdown during a pumping test can be considered to consist of two components that are dependent and independent of near-well properties, respectively. Such an interpretation of pumping-test drawdown allows some general conclusions to be drawn concerning the relationship between parameters calculated using analytical approaches based on curve-matching and those calculated using approaches based on the slope of a semilog straight line plot. The infinite-series truncation that underlies the semilog analytical approaches is shown to remove further contributions of near-well material to total drawdown. In addition, the semilog distance-drawdown approach is shown to yield an expression that is equivalent to the Thiem equation. These results allow some general recommendations to be made concerning observation-well placement for pumping tests in nonuniform aquifers. The relative diffusivity of material on either side of a discontinuity is shown to be the major factor in controlling flow behavior during the period in which the front of the cone of depression is moving across the discontinuity. Though resulting from an analysis of flow in an idealized configuration, the insights of this work into flow behavior during a pumping test are applicable to a wide class of nonuniform units.

Journal of Hydrology↗
USGS2004

Transport and time lag of chlorofluorocarbon gases in the unsaturated zone, Rabis Creek, Denmark

Transport of chlorofluorocarbon (CFC) gases through the unsaturated zone to the water table is affected by gas diffusion, air–water exchange (solubility), sorption to the soil matrix, advective–dispersive transport in the water phase, and, in some cases, anaerobic degradation. In deep unsaturated zones, this may lead to a time lag between entry of gases at the land surface and recharge to groundwater. Data from a Danish field site were used to investigate how time lag is affected by variations in water content and to explore the use of simple analytical solutions to calculate time lag. Numerical simulations demonstrate that either degradation or sorption of CFC-11 takes place, whereas CFC-12 and CFC-113 are nonreactive. Water flow did not appreciably affect transport. An analytical solution for the period with a linear increase in atmospheric CFC concentrations (approximately early 1970s to early 1990s) was used to calculate CFC profiles and time lags. We compared the analytical results with numerical simulations. The time lags in the 15-m-deep unsaturated zone increase from 4.2 to between 5.2 and 6.1 yr and from 3.4 to 3.9 yr for CFC-11 and CFC-12, respectively, when simulations change from use of an exponential to a linear increase in atmospheric concentrations. The CFC concentrations at the water table before the early 1990s can be estimated by displacing the atmospheric input function by these fixed time lags. A sensitivity study demonstrates conditions under which a time lag in the unsaturated zone becomes important. The most critical parameter is the tortuosity coefficient. The analytical approach is valid for the low range of tortuosity coefficients (τ = 0.1–0.4) and unsaturated zones greater than approximately 20 m in thickness. In these cases the CFC distribution may still be from either the exponential or linear phase. In other cases, the use of numerical models, as described in our work and elsewhere, is an option.

Rabis Creek↗
USGS1989

Enhanced detection of infectious hematopoietic necrosis virus by pretreatment of cell monolayers with polyethylene glycol

To improve quantification of very low levels of infectious hematopoietic necrosis virus (IHNV) in samples of tissue, ovarian fluid, or natural water supplies, we tested the ability of polyethylene glycol (PEG) to enhance the sensitivity and speed of the plaque assay system. We compared 4, 7, and 10% solutions of PEG of molecular weight 6,000, 8,000, or 20,000 applied at selected volumes and for various durations. When cell monolayers of epithelioma papulosum cyprini (EPC), fathead minnow (FHM), chinook salmon embryo (CHSE-214), and bluegill fry (BF2) were pretreated with 7% PEG-20,000, they produced 4-17-fold increases in plaque assay titers of IHNV. The plaque assay titers of viral hemorrhagic septicemia virus, chum salmon reovirus, and chinook salmon paramyxovirus were also enhanced by exposure of CHSE-214 cells to PEG, but the titers of infectious pancreatic necrosis virus and Oncorhynchus masou virus were not substantially changed. Plaques formed by IHNV on PEG-treated EPC cells incubated at 15°C had a larger mean diameter at 6 d than those on control cells at 8 d; this suggests the assay could be shortened by use of PEG. Pretreatment of EPC cell monolayers with PEG enabled detection of IHNV in some samples that appeared negative with untreated cells. For example, when ovarian fluid samples from chinook salmon Oncorhynchus tshawytscha were inoculated onto untreated monolayers of EPC cells, IHNV was detected in only 11 of 51 samples; 17 of the samples were positive when PEG-treated EPC cells were used. PDF

Journal of Aquatic Animal Health↗
USGS1978

Pressure gradients and boiling as mechanisms for localizing ore in porphyry systems

Fluid inclusions in ore zones of porphyry systems indicate that extensive boiling of hydrothermal fluids accompanies deposition of ore and gangue minerals. The boiling commonly accompanied a change from a lithostatic to a hydrostatic environment during evolution of an epizonal stock. Pressure gradients near the margin of the stock can determine whether ore or only a diffuse zone of mineralization is formed. A sharp drop in pressure in an epizonal environment is more likely to cause extensive boiling than a comparable change in a deeper environment, as the slope of the boiling curve steepens with an increase 'in pressure. The drop in pressure causes the hydrothermal fluids to boil and creates a crackle (stockwork) breccia, which hosts the veinlets of gangue quartz and ore minerals. The boiling selectively partitions CO 2 , H 2 S, and HCl into the vapor phase, changing the pH, composition, ionic strength, and thus the solubility product of metal complexes in the remaining liquid and causing the ore and gangue to come out of solution. Fluid inclusions trapped from boiling solutions can exhibit several forms, depending on the physical and chemical conditions of the hydrothermal fluid from which they were trapped. In one case, inclusions when heated can homogenize to either liquid or vapor at the same temperature, which is the true boiling temperature. In another case, homogenization of various inclusions can occur through a range of temperatures. The latter case results from the trapping of mixture of liquid and vapor. Variations in salinity can result from boiling of the hydrothermal fluid, or intermittent incorporation of high-salinity fluids from the magma, or trapping of fluids of varying densities at pressure-temperature conditions above the critical point of the fluid. In places, paleopressure-temperature transition zones can be recognized by fluid-inclusion homogenization temperatures and phase relationships and by the presence of anhydrite daughter minerals. Boiling of a hydrothermal fluid in the porphyry environment affects light stable isotopes. Hydrogen is preferentially fractionated into the vapor phase from water boiling below 223°C; above this temperature deuterium is selectively enriched in the vapor phase. In certain environments boiling creates a vapor-dominated system in which the condensate is swept away by meteoric waters and the H/D in the residual fluids is progressively increased through time.

Utah↗
USGS2000

Water movement through a thick unsaturated zone underlying an intermittent stream in the western Mojave Desert, southern California, USA

Previous studies indicated that small amounts of recharge occur as infiltration of intermittent streamflow in washes in the upper Mojave River basin , in the western Mojave Desert , near Victorville, California. These washes flow only a few days each year after large storms . To reach the water table , water must pass through an unsaturated zone that is more than 130 m thick. Results of this study, done in 1994–1998, show that infiltration to depths below the root zone did not occur at control sites away from the wash. At these sites, volumetric water contents were as low as 0.01 and water potentials (measured as the combination of solute and matric potentials using a water activity meter) were as negative as −14,000 kPa. Water-vapor movement was controlled by highly negative solute potentials associated with the accumulation of soluble salts in the unsaturated zone. Highly negative matric potentials above and below the zone of maximum solute accumulation result from movement of water vapor toward the highly negative solute potentials at that depth. The δ 18 O and δ D (delta oxygen-18 and delta deuterium) isotopic composition of water in coarse-grained deposits plots along a Rayleigh distillation line consistent with removal of water in coarse-grained layers by vapor transport. Beneath Oro Grande Wash, water moved to depths below the root zone and, presumably, to the water table about 130 m below land surface. Underneath Oro Grande Wash, volumetric water contents were as high as 0.27 and water potentials (measured as matric potential using tensiometers) were between −1.8 and −50 kPa. On the basis of tritium data, water requires at least 180–260 years to infiltrate to the water table. Clay layers impede the downward movement of water. Seasonal changes in water vapor composition underneath the wash are consistent with the rapid infiltration of a small quantity of water to great depths and subsequent equilibration of vapor with water in the surrounding material. It may be possible to supplement natural recharge from the wash with imported water. Recharge to the wash may be advantageous because the unsaturated zone is not as dry as most areas in the desert and concentrations of soluble salts are generally lower underneath the wash.

Journal of Hydrology↗