SEARCH · USGS Science

Results for “Experimental Results”

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

SourceResearch connectionFrom yearThrough year

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

At least 613 records · Page 34Linked to original sources

USGS1996

Compensating for estimation smoothing in kriging

Smoothing is a characteristic inherent to all minimum mean-square-error spatial estimators such as kriging. Cross-validation can be used to detect and model such smoothing. Inversion of the model produces a new estimator-compensated kriging. A numerical comparison based on an exhaustive permeability sampling of a 4-fr2 slab of Berea Sandstone shows that the estimation surface generated by compensated kriging has properties intermediate between those generated by ordinary kriging and stochastic realizations resulting from simulated annealing and sequential Gaussian simulation. The frequency distribution is well reproduced by the compensated kriging surface, which also approximates the experimental semivariogram well - better than ordinary kriging, but not as well as stochastic realizations. Compensated kriging produces surfaces that are more accurate than stochastic realizations, but not as accurate as ordinary kriging. ?? 1996 International Association for Mathematical Geology.

Mathematical Geology↗

USGS2018

Research frontiers for improving our understanding of drought‐induced tree and forest mortality

Accumulating evidence highlights increased mortality risks for trees during severe drought, particularly under warmer temperatures and increasing vapour pressure deficit (VPD). Resulting forest die‐off events have severe consequences for ecosystem services, biophysical and biogeochemical land–atmosphere processes. Despite advances in monitoring, modelling and experimental studies of the causes and consequences of tree death from individual tree to ecosystem and global scale, a general mechanistic understanding and realistic predictions of drought mortality under future climate conditions are still lacking. We update a global tree mortality map and present a roadmap to a more holistic understanding of forest mortality across scales. We highlight priority research frontiers that promote: (1) new avenues for research on key tree ecophysiological responses to drought; (2) scaling from the tree/plot level to the ecosystem and region; (3) improvements of mortality risk predictions based on both empirical and mechanistic insights; and (4) a global monitoring network of forest mortality. In light of recent and anticipated large forest die‐off events such a research agenda is timely and needed to achieve scientific understanding for realistic predictions of drought‐induced tree mortality. The implementation of a sustainable network will require support by stakeholders and political authorities at the international level.

New Phytologist↗

USGS1999

Effects of environmental change on plant species density: Comparing predictions with experiments

Ideally, general ecological relationships may be used to predict responses of natural communities to environmental change, but few attempts have been made to determine the reliability of predictions based on descriptive data. Using a previously published structural equation model (SEM) of descriptive data from a coastal marsh landscape, we compared these predictions against observed changes in plant species density resulting from field experiments (manipulations of soil fertility, flooding, salinity, and mammalian herbivory) in two areas within the same marsh. In general, observed experimental responses were fairly consistent with predictions. The largest discrepancy occurred when sods were transplanted from high- to low-salinity sites and herbivores selectively consumed a particularly palatable plant species in the transplanted sods. Individual plot responses to some treatments were predicted more accurately than others. Individual fertilized plot responses were not consistent with predictions (P > 0.05), nor were fenced plots (herbivore exclosures; R2 = 0.15) compared to unfenced plots (R2 = 0.53). For the remaining treatments, predictions reasonably matched responses (R2 = 0.63). We constructed an SEM for the experimental data; it explained 60% of the variance in species density and showed that fencing and fertilization led to decreases in species density that were not predicted from treatment effects on community biomass or observed disturbance levels. These treatments may have affected the ratio of live to dead biomass, and competitive exclusion likely decreased species density in fenced and fertilized plots. We conclude that experimental validation is required to determine the predictive value of comparative relationships derived from descriptive data.

Louisiana↗

USGS2011

Feeding ecology and energetics

Successful management of walleye and sauger populations often requires a detailed knowledge of prey resources. As with many fishes, diets of juvenile Sander spp. are often different than those of adult fish and can have important implications for growth and survival. Similarly, spatial and temporal variation in diet composition can contribute to variation in growth and production of Sander populations. Thus, management efforts (e.g., stocking) aimed at enhancing walleye and sauger populations benefit from the knowledge and tools to effectively quantify feeding patterns. Today, fisheries managers face a myriad of challenges posed by nonnative species, eutrophication, climate change, and water availability, to name just a few. As a result, knowledge about prey use, energetics, and effects of Sander populations on food web structure has increased dramatically in the last 30 years. Experimental work with larval and juvenile walleyes has provided new insights into factors affecting growth and survival during early life stages (see Chapter 7) that has benefitted management and propagation efforts. Similarly, contemporary analytical approaches, such as bioenergetics modeling and stable isotope analysis, have improved our understanding of walleye foraging behavior and provided new tools for exploring trophic interactions. In this chapter, we review the general feeding ecology of walleye and sauger and highlight contemporary approaches for quantifying energy acquisition and trophic interactions.

Book chapter↗

USGS2006

Keystone predators (eastern newts, Notophthalmus viridescens) reduce the impacts of an aquatic invasive species

Predation, competition, and their interaction are known to be important factors that influence the structure of ecological communities. In particular, in those cases where a competitive hierarchy exists among prey species, the presence of certain keystone predators can result in enhanced diversity in the prey community. However, little is known regarding the influence of keystone predator presence on invaded prey communities. Given the widespread occurrence of invasive species and substantial concern regarding their ecological impacts, studies on this topic are needed. In this study I used naturalistic replications of an experimental tadpole assemblage to assess the influence of predatory eastern newts, Notophthalmus viridescens , on the outcome of interspecific competition among native and nonindigenous tadpoles. When newts were absent, the presence of the tadpoles of one invasive species, the Cuban treefrog, Osteopilus septentrionalis , resulted in decreased survival and growth rate of the dominant native species, Bufo terrestris , and dominance of the tadpole assemblage by O. septentrionalis . However, the presence of one adult newt generally reduced or eliminated the negative impacts of O. septentrionalis tadpoles, resulting in comparable survival and performance of native species in invaded and noninvaded treatments. Differential mortality among the tadpole species suggests that newts preyed selectively on O. septentrionalis tadpoles, supporting the hypothesis that newts acted as keystone predators in the invaded assemblage. The presence of nonindigenous larval cane toads, Bufo marinus , did not significantly affect native species, and this species was not negatively affected by the presence of newts. Collectively, these results suggest that eastern newts significantly modified the competitive hierarchy of the invaded tadpole assemblage and reduced the impacts of a competitively superior invasive species. If general, these results suggest that the presence of certain species may be an essential factor regulating the ecological impacts of biological invasions.

Oecologia↗

USGS1993

Experimental dynamic metamorphism of mineral single crystals

This paper is a review of some of the rich and varied interactions between non-hydrostatic stress and phase transformations or mineral reactions, drawn mainly from results of experiments done on mineral single crystals in our laboratory or our co-authors. The state of stress and inelastic deformation can enter explicitly into the equilibrium phase relations and kinetics of mineral reactions. Alternatively, phase transformations can have prominent effects on theology and on the nature of inelastic deformation. Our examples represent five types of structural phase changes, each of which is distinguished by particular mechanical effects. In increasing structural complexity, these include: (1) displacive phase transformations involving no bond-breaking, which may produce anomalous brittle behavior. A primary example is the a - β quartz transition which shows anomalously low fracture strength and tertiary creep behavior near the transition temperature; (2) martensitic-like transformations involving transformation strains dominated by shear deformation. Examples include the orthoenstatite → clinoenstatite and w u ̈ rtzite → sphalerite "> würtzite→sphalerite transformations; (3) coherent exsolution or precipitation of a mineral solute from a supersaturated solid-solution, with anisotropy of precipitation and creep rates produced under nonhydrostatic stress. Examples include exsolution of corundum from MgO · n Al 2 O 3 spinels and Ca-clinopyroxene from orthopyroxene; (4) order-disorder transformations that are believed to cause anomalous plastic yield strengthening, such as MgO - nAl 2 O 3 spinels; and (5) near-surface devolatilization of hydrous silicate single-crystals that produces a fundamental brittleness thought to be connected with dehydration at microcracks at temperatures well below nominal macroscopic dehydration temperatures.

Journal of Structural Geology↗

USGS2002

Impacts of off-road vehicles on nitrogen cycles in biological soil crusts: Resistance in different U.S. deserts

Biological soil crusts are an important component of desert ecosystems, as they influence soil stability and fertility. This study examined and compared the short-term vehicular impacts on lichen cover and nitrogenase activity (NA) of biological soil crusts. Experimental disturbance was applied to different types of soil in regions throughout the western U.S. (Great Basin, Colorado Plateau, Sonoran, Chihuahuan, and Mojave deserts). Results show that pre-disturbance cover of soil lichens is significantly correlated with the silt content of soils, and negatively correlated with sand and clay. While disturbance appeared to reduce NA at all sites, differences were statistically significant at only 12 of the 26 sites. Cool desert sites showed a greater decline than hot desert sites, which may indicate non-heterocystic cyanobacterial species are more susceptible to disturbance than non-heterocystic species. Sandy soils showed greater reduction of NA as sand content increased, while fine-textured soils showed a greater decline as sand content increased. At all sites, higher NA before the disturbance resulted in less impact to NA post-disturbance. These results may be useful in predicting the impacts of off-road vehicles in different regions and different soils.

Journal of Arid Environments↗

USGS1974

An experimental study of the partitioning of a rare earth element (Gd) in the system diopside—Aqueous vapour

The partitioning of Gd in the experimental system diopside-aqueous vapor as a function of temperature, pressure, composition of the phases, time, grain size, solid-liquid ratio and Gd concentration has been investigated. A radioactive tracer measurement was used to determine Gd concentration in the separated phases. Diposides were reacted with aqueous vapor containing tracer Gd and reversibility was tested by reacting Gd-doped diopsides with pure aqueous vapor. Equilibration of Gd between the bulk of the diopside and the liquid was found to be limited by the slow rate of Gd diffusion in diopside, maximum value of D = 2 × 10 −15 cm 2 sec −1 at 800°C and 1 kb. Depending on whether the diopside was previously synthesized or synthesized from an oxide mix during the experiment, Gd concentrations were zoned in the crystal such that higher concentrations existed at the edges or center, respectively. Equilibrium is difficult to achieve in these experiments, but at the optimum experimental conditions for equilibration, the Gd diopside-aqueous vapor distribution coefficient is 20 ± 6 (800°C, 1 kb) in approximate agreement with previous results of 55 ± 23. Changing the composition of the aqueous vapor indicated that possible mechanisms for Gd substitution included coupling of Gd 3+ with H + or Na + replacing 2Ca 2+ , or substitution of 2Gd 3+ for 3Ca 2+ with formation of a cation vacancy.

Geochimica et Cosmochimica Acta↗

USGS2007

Study of a prehistoric landslide using seismic reflection methods integrated with geological data in the Wasatch Mountains, Utah, USA

An integration of geological and geophysical techniques characterizes the internal and basal structure of a landslide along the western margin of the Wasatch Mountains in northern Utah, USA. The study area is within a region of planned and continuing residential development. The Little Valley Landslide is a prehistoric landslide as old as 13??ka B.P. Drilling and trenching at the site indicate that the landslide consists of chaotic and disturbed weathered volcanic material derived from Tertiary age volcanic rocks that comprise a great portion of the Wasatch Range. Five short high-resolution common mid-point seismic reflection profiles over selected portions of the site examine the feasibility of using seismic reflection to study prehistoric landslides in the Wasatch Mountain region. Due to the expected complexity of the near-surface geology, we have pursued an experimental approach in the data processing, examining the effects of muting first arrivals, frequency filtering, model-based static corrections, and seismic migration. The results provide a framework for understanding the overall configuration of the landslide, its basal (failure) surface, and the structure immediately underlying this surface. A glide surface or de??collement is interpreted to underlie the landslide suggesting a large mass movement. The interpretation of a glide surface is based on the onset of coherent reflectivity, calibrated by information from a borehole located along one of the seismic profiles. The glide surface is deepest in the center portion of the landslide and shallows up slope, suggesting a trough-like feature. This study shows that seismic reflection techniques can be successfully used in complex alpine landslide regions to (1) provide a framework in which to link geological data and (2) reduce the need for an extensive trenching and drilling program. ?? 2007 Elsevier B.V. All rights reserved.

Engineering Geology↗

USGS1996

Air pollutant intrusion into the Wieliczka Salt Mine

The Wieliczka Salt Mine World Cultural Heritage Site contains many rock salt sculptures that are threatened by water vapor condensation from the mine ventilation air. Gaseous and particulate air pollutant concentrations have been measured both outdoors and within the Wieliczka Salt Mine, along with pollutant deposition fluxes to surfaces within the mine. One purpose of these measurements was to determine whether or not low deliquescence point ionic materials (e.g., NH4NO3) are accumulating on surfaces to an extent that would exacerbate the water vapor condensation problems in the mine. It was found that pollutant gases including SO2 and HNO3 present in outdoor air are removed rapidly and almost completely from the air within the mine by deposition to surfaces. Sulfur isotope analyses confirm the accumulation of air pollutant-derived sulfur in liquid dripping from surfaces within the mine. Particle deposition onto interior surfaces in the mine is apparent, with resulting soiling of some of those sculptures that have been carved from translucent rock salt. Water accumulation by salt sculpture surfaces was studied both experimentally and by approximate thermodynamic calculations. Both approaches suggest that the pollutant deposits on the sculpture surfaces lower the relative humidity (RH) at which a substantial amount of liquid water will accumulate by 1% to several percent. The extraordinarily low SO2 concentrations within the mine may explain the apparent success of a respiratory sanatorium located deep within the mine.

Environmental Science & Technology↗

USGS2002

Mercury loading and methylmercury production and cycling in high-altitude lakes from the Western United States

Studies worldwide have shown that mercury (Hg) is a ubiquitous contaminant, reaching even the most remote environments such as high-altitude lakes via atmospheric pathways. However, very few studies have been conducted to assess Hg contamination levels of these systems. We sampled 90 mid-latitude, high-altitude lakes from seven national parks in the western United States during a four-week period in September 1999. In addition to the synoptic survey, routine monitoring and experimental studies were conducted at one of the lakes (Mills Lake) to quantify MeHg fluxrates and important process rates such as photo-demethylation. Results show that overall, high-altitude lakes have low total mercury (HgT) and methylmercury (MeHg) levels (1.07 and 0.05 ng L -1 , respectively), but a very good correlation of Hg to MeHg (r 2 = 0.82) suggests inorganic Hg(II) loading is a primary controlling factor of MeHg levels in dilute mountain lakes. Positive correlations were also observed for dissolved organic carbon (DOC) and both Hg and MeHg, although to a much lesser degree. Levels of MeHg were similar among the seven national parks, with the exception of Glacier National Park where lowerconcentrations were observed (0.02 ng L -1 ), and appear to be related to naturally elevated pH values there. Measured rates ofMeHg photo-degradation at Mills Lake were quite fast, and this process was of equal importance to sedimentation and stream flow for removing MeHg. Enhanced rates of photo-demethylation are likely an important reason why high-altitude lakes, with typically high water clarity and sunlight exposure, are low in MeHg.

California, Colorado, Montana, Wyoming↗

USGS2005

Measuring rates of biodegradation in a contaminated aquifer using field and laboratory methods

Rates of biodegradation were measured in a petroleum hydrocarbon-contaminated aquifer using a combination of field and laboratory methods. These methods are based on tracking concentration changes of substrates (both electron donors and acceptors) or final products of microbial metabolism over time. Ground water at the study site (Hanahan, South Carolina) is anoxic, and sulfate reduction is the predominant terminal electron accepting process. Laboratory studies conducted with sediment cored from the site showed that 14 C-toluene was mineralized to 14 CO 2 with a first-order degradation rate constant (k tol ) of -0.01 d −1 under sulfate-reducing conditions. Under nitrate-amended, Fe(III)-amended, or nonamended (methanogenic) conditions, toluene was not significantly mineralized. 14 C-Benzene was degraded at low but measurable rates (k ben = -0.003 d −1 ) under sulfate-reducing conditions whereas degradation under methanogenic conditions was negligible. These results illustrate the extreme sensitivity of laboratory-measured biodegradation rates to terminal electron-accepting conditions, and show the necessity of carefully matching experimental conditions to in situ conditions. Concentration decreases of toluene along aquifer flowpaths, when the uncertainty of ground-water flow velocities was considered, indicated k tol values ranging from -0.0075 to -0.03 d −1 . Concentration decreases of sulfate and concentration increases of dissolved inorganic carbon (DIC), when normalized for assumed stoichiometric oxidation of toluene coupled to sulfate reduction, yielded a k so4 range of -0.005 to -0.02 d −1 , and a k DIC value range of +0.00075 to +0.003 d −1 . Because both laboratory and field methods have numerous sources of uncertainty, a combination of these methods is the most appropriate procedure for evaluating biodegradation rate constants in contaminated ground-water systems.

Groundwater↗

USGS2014

Nutritional stress affects corticosterone deposition in feathers of Caspian tern chicks

Stressful environmental conditions affect the adrenocortical function of developing animals, which can have consequences for their fitness. Discovery of the avian stress hormone corticosterone (CORT) in feathers has the potential to broaden the application of endocrine research in ecological and evolutionary studies of wild birds by providing a long-term measure of CORT secretion. Mechanisms of CORT deposition in feathers are not well known and few studies have related feather CORT to circulating plasma CORT during feather growth. Our objective was to experimentally test the validity of using feather CORT as a measure of CORT secretion in developing birds experiencing nutritional stress. Caspian tern Hydroprogne caspia chicks were fed ad libitum or restricted (35% less than ad libitum) diets for four weeks. We measured CORT in feathers from these chicks to examine the relationship between feather CORT concentrations and nutritional limitation, circulating plasma CORT, and feather development. We found that feather CORT was higher in controls fed ad libitum than in restricted individuals, despite higher levels of plasma CORT in restricted chicks compared to controls. Feather mass and growth rates were strongly and positively related to feather CORT concentrations in both treatments. This is the first experimental study to show that feather CORT concentrations can be lower in response to nutritional stress, even when plasma CORT concentrations are elevated. Our results indicate that CORT deposition in feathers may be confounded when feather mass and growth rates are compromised by nutritional stress. We conclude that feather CORT can be used for assessing nutritional stress in growing birds, but the direction of response depends on how strongly stress affects feather development.

Journal of Avian Biology↗

USGS1992

Synchronism of the Siberian Traps and the Permian-Triassic boundary

Uranium-lead ages from an ion probe were taken for zircons from the ore-bearing Noril'sk I intrusion that is comagmatic with, and intrusive to, the Siberian Traps. These values match, within an experimental error of ±4 million years, the dates for zircons extracted from a tuff at the Permian-Triassic (P-Tr) boundary. The results are consistent with the hypothesis that the P-Tr extinction was caused by the Siberian basaltic flood volcanism. It is likely that the eruption of these magmas was accompanied by the injection of large amounts of sulfur dioxide into the upper atmosphere, which may have led to global cooling and to expansion of the polar ice cap. The P-Tr extinction event may have been caused by a combination of acid rain and global cooling as well as rapid and extreme changes in sea level resulting from expansion of the polar ice cap.

Science↗

USGS2009

A Review and Synthesis of the Scientific Information Related to the Biology and Management of Species of Special Concern at Cape Hatteras National Seashore, North Carolina

The U.S. Geological Survey's Patuxent Wildlife Research Center (PWRC) conducted a study for the National Park Service (NPS) Southeast Region, Atlanta, GA, and Cape Hatteras National Seashore (CAHA) in North Carolina to review, evaluate, and summarize the available scientific information for selected species of concern at CAHA (piping plovers, sea turtles, seabeach amaranth, American oystercatchers, and colonial waterbirds). This work consisted of reviewing the scientific literature and evaluating the results of studies that examined critical life history stages of each species, and focused on the scientific findings reported that are relevant to the management of these species and their habitats at CAHA. The chapters that follow provide the results of that review separately for each species and present scientifically based options for resource management at CAHA. Although no new original research or experimental work was conducted, this synthesis of the existing information was peer reviewed by over 15 experts with familiarity with these species. This report does not establish NPS management protocols but does highlight scientific information on the biology of these species to be considered by NPS managers who make resource management decisions at CAHA. To ensure that the best available information is considered when assessing each species of interest at CAHA, this review included published research as well as practical experience of scientists and wildlife managers who were consulted in 2005. PWRC scientists evaluated the literature, consulted wildlife managers, and produced an initial draft that was sent to experts for scientific review. Revisions based on those comments were incorporated into the document. The final draft of the document was reviewed by NPS personnel to ensure that the description of the recent status and management of these species at CAHA was accurately represented and that the report was consistent with our work agreement. The following section summarizes the biological information relevant to resource management for the species of concern at CAHA.

Open-File Report↗

USGS2015

Understanding ocean acidification impacts on organismal to ecological scales

Ocean acidification (OA) research seeks to understand how marine ecosystems and global elemental cycles will respond to changes in seawater carbonate chemistry in combination with other environmental perturbations such as warming, eutrophication, and deoxygenation. Here, we discuss the effectiveness and limitations of current research approaches used to address this goal. A diverse combination of approaches is essential to decipher the consequences of OA to marine organisms, communities, and ecosystems. Consequently, the benefits and limitations of each approach must be considered carefully. Major research challenges involve experimentally addressing the effects of OA in the context of large natural variability in seawater carbonate system parameters and other interactive variables, integrating the results from different research approaches, and scaling results across different temporal and spatial scales.

Oceanography↗

USGS1956

Biology of the sea lamprey in its parasitic phase

The investigations conducted on sea lampreys in aquariums were concerned with the duration of the parasitic phase of life, feeding, growth, and the interrelations between predator and host fish. Observations on lampreys reared from metamorphosis to maturity were made at the Fish and Wildlife Service Laboratory at Hammond Bay, Michigan. Most of the experimental lampreys were mature and ripe after 14 to 18 months of parasitic life. They exhibited signs of irreversible physical degeneration which precedes death. Three specimens were immature after 14, 18, and 26 months in aquariums, thus indicating that under certain conditions, lampreys may extend their parasitic phase. The feeding activity, growth, and shrinkage in size of aquarium specimens were considered typical of lampreys in the Great Lakes, although the wild lampreys achieve greater average size. Female lampreys made more attacks, fed more, killed more fish, and grew larger than males. They also shrank proportionately more in length and weight as they approached sexual maturity, but their terminal average size was slightly larger than that of males. It is estimated that the average fish-kill by a wild lamprey exceeds, and could be approximately double, the 18.5 pounds of fish killed by a laboratory lamprey. The rate and extent of fish destruction depended on the size, sex, and stage in the parasitic phase of the lampreys, and on the species and size of the fish. There was an increase in the number of fish killed as the lampreys grew, and the fish were killed more quickly. Attacks made by experimental lampreys at any stage of their parasitic phase up to full maturity, and on any part of a prey fish except fins, usually resulted in death to the host. Some fish which survived lamprey attacks succumbed to fungus infections of the wounds. A small number of trout recovered from attacks, and their wounds healed.

Research Report↗

USGS1955

Survival and spawning of gill-net-marked red salmon

Research Report↗