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At least 235 records · Page 13Linked to original sources

Comments on 'Remarks on the secular change in the energy density spectrum of the geomagnetic field' by Joachim Meyer.

Meyer has discussed only the Rn aspect of the Alldredge (1984) paper he is criticising. He has ignored the pictorial demonstration of the need for higher harmonics to properly describe the secular variation field than the main field as demonstrated. This more or less independent demonstration supports the general conclusion of that paper.

Journal of Geomagnetism & Geoelectricity

Trends in long-period seismicity related to magmatic fluid compositions

Sound speeds and densities are calculated for three different types of fluids: gas-gas mixture; ash-gas mixture; and bubbly liquid. These fluid properties are used to calculate the impedance contrast (Z) and crack stiffness (C) in the fluid-driven crack model (Chouet: J. Geophys. Res., 91 (1986) 13,967; 101 (1988) 4375; A seismic model for the source of long-period events and harmonic tremor. In: Gasparini, P., Scarpa, R., Aki, K. (Eds.), Volcanic Seismology, IAVCEI Proceedings in Volcanology, Springer, Berlin, 3133). The fluid-driven crack model describes the far-field spectra of long-period (LP) events as modes of resonance of the crack. Results from our calculations demonstrate that ash-laden gas mixtures have fluid to solid density ratios comparable to, and fluid to solid velocity ratios lower than bubbly liquids (gas-volume fractions <10%). This difference results in synthetic far-field spectra with higher impedance contrasts and narrower spectral bandwidths for ash-laden gas mixture than spectra for bubbly liquids. Spectral characteristics are described in terms of the quality factor Q-1. Q-1 is measured by the ratio of the frequency of the dominant spectral peak to the bandwidth of the peak measured at one half of its amplitude. This factor expresses the losses of energy due to elastic radiation Q-1r and other dissipative mechanisms Q-1i at the source, Q-1 = Q-1r + Q-1i. Spectra for LP events recorded at active volcanoes such as Galeras in Colombia and Kilauea in Hawaii, have Q-1 factors in the range of 0.1-0.002. The Q-1r factors due to radiation loss calculated for a sphere filled with a H2O-CO2 or H2O-SO2 gas mixture, vary between 0.0015 and 0.0040 with a change in wt% H2O at 800-1600 K and 10-50 MPa. For gas-rich mixtures, Q-1r has a strong dependence on resonator geometry (spherical versus rectangular). The spectra from a resonating sphere filled with gas-rich mixture yields values of Q-1r an order of magnitude smaller than those from a rectangular crack. For a resonating crack filled with an ash-gas mixture (or pseudogas), Q-1r varies parabolically from ???0.006 for an ash-rich mixture, to 0.0015 or 0.0023 for a H2O-rich or CO2-rich mixture at 800 K and 25 MPa. For low (<20%) gas-volume fraction fluids (foams, bubbly fluids and ash-rich pseudogases), the magnitudes for Q-1r are independent of crack geometry. Spectra associated with a foam (gas-volume fractions 10-90%) or bubbly basalt (gas-volume fractions <10%) may have a dominant spectral peak with values of Q-1r on the order of 0.01 and 0.1, respectively. The spectra from a resonating sphere filled with a foam containing >20% gas-volume fraction yields values of Q-1r similar to those for a rectangular crack. As with gas-gas and ash-gas mixtures, an increase in mass fraction narrows the bandwidth of the dominant mode and shifts the spectra to lower frequencies. Including energy losses due to dissipative processes in a bubbly liquid increases attenuation. Attenuation may also be higher in ash-gas mixtures and foams if the effects of momentum and mass transfer between the phases were considered in the calculations. ?? 2001 Elsevier Science B. V. All rights reserved.

Journal of Volcanology and Geothermal Research

Behavioral responses of sea lamprey (Petromyzon marinus) and white sucker (Catostomus commersonii) to turbulent flow during fishway passage attempts

An understanding of how undesirable and desirable fish species respond behaviorally to turbulent flow in fishways would guide development of selective fish passage techniques. We applied high-resolution computational fluid dynamics modeling and competing risks analysis towards the development of predictive selective passage models. Sea lamprey ( Petromyzon marinus ; an invasive fish in the Great Lakes Basin, North America) upstream passage probability declined from 0.73 to 0.03 as flow conditions became increasingly turbulent, while declines in white sucker ( Catostomus commersonii , a native fish in the region) upstream passage probability were less substantial (0.53 to 0.44). Deploying a sea lamprey trap in the fishway did not effectively reduce sea lamprey upstream passage probability, though capture rate increased during trials with cooler water temperature and low total kinetic energy. Bifurcated fishways that maintain low turbulent flow in the entrapment route and high turbulent flow in the upstream passage route could increase the effectiveness of trapping sea lamprey in fishways as a means to advance selective passage goals.

Wisconsin

Comparative ability of northern pintails, gadwalls, and northern shovelers to metabolize foods

Feeding trials were used to compare the ability of northern pintails ( Anas acuta ), gadwalls ( A. strepera ), and northern shovelers ( A. clypeata ) to metabolize energy from a turkey starter ration, alfalfa pellets, and common barnyardgrass ( Echinochloa crusgalli ) seeds. No differences (P > 0.05) were detected among the three species for any of the three foods (kg body weight/day basis), for dry matter intake (DMI), body weight gain (BWG), apparent metabolizable energy (AME), or metabolized energy (MEE) on any given diet consumed in quantities large enough to promote body weight gain. The AME content of alfalfa was 57% less than the value for turkey starter and 50% less than for barnyardgrass seeds. All three species metabolized more energy and gained weight faster when fed turkey starter. Energy modeling may be facilitated if additional research verifies that all species of dabbling ducks have equal ability to obtain energy from foods available to them in the wild. Behavioral and morphological factors may be more important in defining feeding niches than digestive physiology, at least for the three duck species tested, at the time of year of the experiments, and within the limits of the quality of foods used.

Journal of Wildlife Management

Activity patterns of bats during the fall and spring along ridgelines in the central Appalachians

Many central Appalachian ridges offer high wind potential, making them attractive to future wind-energy development. Understanding seasonal and hourly activity patterns of migratory bat species may help to reduce fatalities at wind-energy facilities and provide guidance for the development of best management practices for bats. To examine hourly migratory bat activity patterns in the fall and spring in Virginia in an exploratory fashion with a suite of general temporal, environmental, and weather variables, we acoustically monitored bat activity on five ridgelines and side slopes from early September through mid-November 2015 and 2016 and from early March through late April 2016 and 2017. On ridges, bat activity decreased through the autumn sample period, but was more variable through the spring sample period. In autumn, migratory bat activity had largely ceased by mid-November. Activity patterns were species specific in both autumn and spring sample periods. Generally, migratory bat activity was negatively associated with hourly wind speeds but positively associated with ambient temperatures. These data provide further evidence that operational mitigation strategies at wind-energy facilities could help protect migratory bat species in the Appalachians; substantially slowing or locking wind turbine blade spin during periods of low wind speeds, often below where electricity is generated, and warm ambient temperatures may minimize mortality during periods of high bat activity.

Virginia, West Virginia

Depositional environments as a guide to uranium mineralization in the Chinle Formation, San Rafael Swell, Utah

Uranium deposits in the San Rafael Swell are related to sedimentary depositional environments in the Upper Triassic Chinle Formation. The sedimentary textures resulting from depositional processes operating in low-energy environments appear to have influenced uranium mineralization. The Ohinle consists of three fining-upward, fluvial-lacustrine sequences. Uranium minerals are concentrated in the lower part of the lowest sequence in areas where sediments of low-energy environments are complexly interbedded with sediments of other environments. Areas favorable for uranium exploration exist in the subsurface to the north, west, and south of the Chinle outcrop in the Swell. This determination is based on the spatial distribution of depositional environments and the pattern of Chinle deposition through time.

Utah

Dietary restriction causes chronic elevation of corticosterone and enhances stress response in red-legged kittiwake chicks

Release of corticosterone in hungry kittiwake chicks facilitates begging and allows them to restore depleted energy reserves by increasing parental food provisioning. However, in order to avoid detrimental effects of chronic elevation of corticosterone, chicks might suppress adrenocortical activity in response to prolonged food shortages. In this study we examined temporal dynamics of corticosterone release in red-legged kittiwake (Rissa brevirostris) chicks exposed to prolonged restrictions in energy content and/or nutritional quality (low versus high lipid content) of their food. Starting at the age of 15 days, chicks were fed either high- or low-lipid fish at 40%, 65%, and 100% of ad libitum energy intake. Body mass measurements and baseline plasma samples were taken on a weekly basis after beginning of the treatment. After 3 weeks of treatment, chicks were exposed to a standardized acute handling and restraint stress protocol, where in addition to a baseline sample, three plasma samples were taken at intervals up to 50 min. We found that food-restricted chicks had lower body mass, chronically (during 2-3 weeks) elevated baseline and higher acute stress-induced levels of corticosterone compared to chicks fed ad libitum. Low lipid content of food further exacerbated these effects. An increase in baseline levels of corticosterone was observed within a week after energy requirements of food-restricted chicks exceeded their daily energy intake. A tendency for suppression of adrenocortical activity was observed in treatments fed low-lipid diets only at the end of the experiment. We suggest that nest-bound chicks, if food-stressed, might suffer deleterious effects of chronic elevation of corticosterone.

Journal of Comparative Physiology B: Biochemical,

Probabilistic assessment methodology for continuous-type petroleum accumulations

The analytic resource assessment method, called ACCESS (Analytic Cell-based Continuous Energy Spreadsheet System), was developed to calculate estimates of petroleum resources for the geologic assessment model, called FORSPAN, in continuous-type petroleum accumulations. The ACCESS method is based upon mathematical equations derived from probability theory in the form of a computer spreadsheet system. ?? 2003 Elsevier B.V. All rights reserved.

International Journal of Coal Geology

Source mechanism of long-period events at Kusatsu-Shirane Volcano, Japan, inferred from waveform inversion of the effective excitation functions

We investigate the source mechanism of long-period (LP) events observed at Kusatsu-Shirane Volcano, Japan, based on waveform inversions of their effective excitation functions. The effective excitation function, which represents the apparent excitation observed at individual receivers, is estimated by applying an autoregressive filter to the LP waveform. Assuming a point source, we apply this method to seven LP events the waveforms of which are characterized by simple decaying and nearly monochromatic oscillations with frequency in the range 1-3 Hz. The results of the waveform inversions show dominant volumetric change components accompanied by single force components, common to all the events analyzed, and suggesting a repeated activation of a sub-horizontal crack located 300 m beneath the summit crater lakes. Based on these results, we propose a model of the source process of LP seismicity, in which a gradual buildup of steam pressure in a hydrothermal crack in response to magmatic heat causes repeated discharges of steam from the crack. The rapid discharge of fluid causes the collapse of the fluid-filled crack and excites acoustic oscillations of the crack, which produce the characteristic waveforms observed in the LP events. The presence of a single force synchronous with the collapse of the crack is interpreted as the release of gravitational energy that occurs as the slug of steam ejected from the crack ascends toward the surface and is replaced by cooler water flowing downward in a fluid-filled conduit linking the crack and the base of the crater lake. ?? 2003 Elsevier Science B.V. All rights reserved.

Journal of Volcanology and Geothermal Research

The 1909 Taipei earthquake: implication for seismic hazard in Taipei

The 1909 April 14 Taiwan earthquake caused significant damage in Taipei. Most of the information on this earthquake available until now is from the written reports on its macro-seismic effects and from seismic station bulletins. In view of the importance of this event for assessing the shaking hazard in the present-day Taipei, we collected historical seismograms and station bulletins of this event and investigated them in conjunction with other seismological data. We compared the observed seismograms with those from recent earthquakes in similar tectonic environments to characterize the 1909 earthquake. Despite the inevitably large uncertainties associated with old data, we conclude that the 1909 Taipei earthquake is a relatively deep (50–100 km) intraplate earthquake that occurred within the subducting Philippine Sea Plate beneath Taipei with an estimated M_W of 7 ± 0.3. Some intraplate events elsewhere in the world are enriched in high-frequency energy and the resulting ground motions can be very strong. Thus, despite its relatively large depth and a moderately large magnitude, it would be prudent to review the safety of the existing structures in Taipei against large intraplate earthquakes like the 1909 Taipei earthquake.

Taipei

Breeding ecology of Horned Puffins ( Fratercula corniculata ) in Alaska: annual variation and effects of El Niño

Both within and among seabird species, different aspects of breeding biology may respond to changes in prey availability in distinct ways, and the identification of species-specific breeding parameters that are sensitive to food availability is useful for monitoring purposes. We present data from a 5-year study (1995–1999) of the breeding ecology of Horned Puffins ( Fratercula corniculata ) in Alaska. The El Ni&ntilde;o – Southern Oscillation event of 1997–1998 provided an opportunity to examine the sensitivity of various breeding parameters to a reduction in prey availability caused by the anomalous oceanographic conditions of 1998. Horned Puffins were able to maintain high fledging success (83–97%) over the 5 years of the study, despite the poor local feeding conditions in 1998. The rate of increase in chick mass was lowest in 1998, and evidence suggests that chicks also fledged at the youngest ages in that year. The impacts of reduced food availability on growth varied among body structures, suggesting differential allocation of energy and nutrients. There was no variation among years in either chick diet or the mass of food loads delivered by adults. We suggest that rates of chick growth, specifically mass increase, may be a good parameter to measure for use in monitoring Horned Puffins.

Canadian Journal of Zoology

Measuring basal force fluctuations of debris flows using seismic recordings and empirical green's functions

We present a novel method for measuring the fluctuating basal normal and shear stresses of debris flows by using along‐channel seismic recordings. Our method couples a simple parameterization of a debris flow as a seismic source with direct measurements of seismic path effects using empirical Green's functions generated with a force hammer. We test this method using two large‐scale (8 and 10 m 3 ) experimental flows at the U.S. Geological Survey debris‐flow flume that were recorded by dozens of three‐component seismic sensors. The seismically derived basal stress fluctuations compare well in amplitude and timing to independent force plate measurements within the valid frequency range (15–50 Hz). We show that although the high‐frequency seismic signals provide band‐limited forcing information, there are systematic relations between the fluctuating stresses and independently measured flow properties, especially mean basal shear stress and flow thickness. However, none of the relationships are simple, and since the flow properties also correlate with one another, we cannot isolate a single factor that relates in a simple way to the fluctuating forces. Nevertheless, our observations, most notably the gradually declining ratio of fluctuating to mean basal stresses during flow passage and the distinctive behavior of the coarse, unsaturated flow front, imply that flow style may be a primary control on the conversion of translational to vibrational kinetic energy. This conversion ultimately controls the radiation of high‐frequency seismic waves. Thus, flow style may provide the key to revealing the nature of the relationship between fluctuating forces and other flow properties.

Journal of Geophysical Research Earth Surface

Trace fossils and sedimentary facies from a Late Cambrian‐Early Ordovician tide‐dominated shelf (Santa Rosita Formation, northwest Argentina): Implications for ichnofacies models of shallow marine successions

The Santa Rosita Formation is one the most widely distributed lower Paleozoic units of northwest Argentina. At the Quebrada del Salto Alto section, east of Purmamarca, Jujuy Province, it is represented by four sedimentary facies: thick‐bedded planar cross‐stratified quartzose sandstones (A), thin‐bedded planar cross‐stratified quartzose sandstones and mudstones (B), wave‐rippled sandstones and bioturbated mudstones (C), and black and greenish gray shales (D). Paleocurrent data, sandstone architecture, and sedimentary structures from faciès A and B indicate bipolar/bimodal paleoflows, suggesting the action of tidal currents. The succession is interpreted as that of a tide‐dominated shelf, with only secondary influence of wave processes. Trace fossils are restricted to facies B and C. The Cruziana ichnocoenosis is preserved on the soles of thin‐bedded planar cross‐stratified quartzose sandstones (faciès B). This ichnocoenosis consists of Conostichus isp., Cruziana omanica, C. semiplicata, C. cf. tortworthi, Cruziana isp. Helminthopsis abeli, Monomorphichnus bilinearis, M. multilineatus, Palaeophycus tubularis, Rusophycus carbonarias, R. latus , and R. isp. The occurrence of Cruziana semiplicata , C. omanica, C. cf. tortworthi , and Rusophycus latus supports a Late Cambrian‐Tremadoc age. Slabbing of Cruziana shows complex interactions between biologic and sedimentologic processes, and suggests a predominance of exhumed traces, washed out and recast by tractive sand deposition. Sandstone soles are densely packed with biogenic structures and exhibit distinctive clusters of Rusophycus isp. that most likely represent trilobite nesting burrows. The Cruziana ichnocoenosis records the resident fauna of a protected, lower intertidal to subtidal interbar setting. The Skolithos ichnocoenosis is represented by high to low density vertical burrows of Skolithos linearis , which extend downwards to the quartzose sandstone soles of faciès B and cross the Cruziana ichnocoenosis. The Skolithos ichnocoenosis represents colonization by suspension‐feeding organisms following a major change in environmental conditions, related to the migration of lower intertidal to subtidal sandwaves. The Planolites ichnocoenosis consists exclusively of Planolites montanus within mudstones overlying wave‐rippled sandstones (facies C). The Planolites ichnocoenosis records opportunistic colonization by inf aunal deposit feeders that mined the organic‐rich fine‐grained sediment during the waning phase of storms that scoured organic detritus from the sea bottom. The section records, from base to top, a Cruziana‐Skolithos ichnofacies zone, a Skolithos ichnofacies zone and an unbioturbated zone typified by the thick‐bedded cross‐stratified quartzose sandstone (fades A). This trend reflects progressively higher energy conditions linked to the establishment of a large sand wave complex. The presence of a mixed Cruziana‐Skolithos ichnofacies in the lower interval reflects changes in substrate and energy levels, rather than water depth. Accordingly, contrasting ichnocoenoses from interbars (Cruziana) and sandwaves (Skolithos) must be considered an example of ichnofacies controlled by local parameters instead of general bathymétrie trends. Conversely, the vertical replacement of the Cruziana ichnofacies by the Skolithos ichnofacies towards the middle interval of the section reflects the environmental changes associated with the transition between the intertidal and subtidal zones. As overall tidal energy increases from supratidal to subtidal settings, the Skolithos ichnofacies tends to occur seaward of the Cruziana ichnofacies in tide‐dominated shallow marine environments. Therefore, onshore‐offshore ichnofacies replacement in tide‐dominated shallow seas is opposite to that in wave‐dominated marine settings.

Ichnos: An International Journal for Plant and Ani

Eagle fatalities are reduced by automated curtailment of wind turbines

Collision‐caused fatalities of animals at wind power facilities create a ‘green versus green’ conflict between wildlife conservation and renewable energy. These fatalities can be mitigated via informed curtailment whereby turbines are slowed or stopped when wildlife are considered at increased risk of collision. Automated monitoring systems could improve efficacy of informed curtailment, yet such technology is undertested. We test the efficacy of an automated curtailment system—a camera system that detects flying objects, classifies them and decides whether to curtail individual turbines to avoid potential collision—in reducing counts of fatalities of eagles, at Top of the World Windpower Facility (hereafter, the treatment site) in Wyoming, USA. We perform a before–after–control–impact study, comparing the number of eagle fatalities observed at the treatment site with those at a nearby (15 km) control site without automated curtailment, both before and after the implementation of automated curtailment at the treatment site. After correcting for carcass detection probability and scaling fatality estimates to turbine‐years, we estimate that the number of fatalities at the treatment site declined by 63% (95% CI = 59%–66%) between before and after periods while increasing at the control site by 113% (51%–218%). In total, there was an 82% (75%–89%) reduction in the fatality rate at the treatment site relative to the control site. Synthesis and applications . Automated curtailment of wind turbine operation substantially reduced eagle fatalities. This technology therefore has the potential to lessen the conflict between wind energy and raptor conservation. Although automated curtailment reduced fatalities, they were not fully eliminated. Therefore, automated curtailment, as implemented here, is not a panacea and its efficacy could be improved if considered in conjunction with other mitigation actions.

Wyoming

Environmental variation, vegetation distribution, carbon dynamics and water/energy exchange at high latitudes

The responses of high latitude ecosystems to global change involve complex interactions among environmental variables, vegetation distribution, carbon dynamics, and water and energy exchange. These responses may have important consequences for the earth system. In this study, we evaluated how vegetation distribution, carbon stocks and turnover, and water and energy exchange are related to environmental variation spanned by the network of the IGBP high latitude transects. While the most notable feature of the high latitude transects is that they generally span temperature gradients from southern to northern latitudes, there are substantial differences in temperature among the transects. Also, along each transect temperature co-varies with precipitation and photosynthetically active radiation, which are also variable among the transects. Both climate and disturbance interact to influence latitudinal patterns of vegetation and soil carbon storage among the transects, and vegetation distribution appears to interact with climate to determine exchanges of heat and moisture in high latitudes. Despite limitations imposed by the data we assembled, the analyses in this study have taken an important step toward clarifying the complexity of interactions among environmental variables, vegetation distribution, carbon stocks and turnover, and water and energy exchange in high latitude regions. This study reveals the need to conduct coordinated global change studies in high latitudes to further elucidate how interactions among climate, disturbance, and vegetation distribution influence carbon dynamics and water and energy exchange in high latitudes.

Journal of Vegetation Science

Annotated bibliography of scientific research relevant to oil and gas reclamation best management practices in the western United States, published from 1969 through 2020

Integrating recent scientific knowledge into management decisions supports effective natural resource management and can lead to better resource outcomes. However, finding and accessing scientific knowledge can be time consuming and costly. To assist in this process, the U.S. Geological Survey has created a series of annotated bibliographies on topics of management concern for lands in the western United States (U.S.). Oil and gas development on public lands is a long-standing and substantial component of local and regional economies and has expanded in recent decades, particularly on public lands in the western U.S. This development is associated with extensive networks of pipelines, roads, and processing facilities, across which reclamation is Federally mandated following initial well pad development (“interim” reclamation) and once resource extraction is complete (“final” reclamation). Reclamation is critical for recovering ecological services to energy-affected lands, including vegetation productivity, wildlife habitat, water and air quality, and soil stability (for example, resistance to wind and water erosion). However, reclamation of oil and gas affected lands in the western U.S. has proved challenging due to an array of regulatory and environmental factors, such as minimally developed soils, short growing seasons, herbivory, high winds, invasive species, rugged terrain, and in particular, arid climates associated with low total precipitation, high evapotranspiration rates, and highly variable precipitation patterns. We compiled and summarized journal articles, government reports, technical reports, proceedings, and theses and dissertations relevant to oil and gas reclamation. We constrained our search to products published on or before December 31, 2020 but did not limit our search by a starting date; the earliest product resulting from this effort was published in March 1969. Second, we manually scanned the last 15 years (2005-2020) of tables of contents in journals, bibliographies, and proceedings of which we were aware would contain articles highly relevant to this bibliography. We carried out the search for these products through multiple means: (1) performing a structured search of two reference databases, (2) examining articles published since 2005 in highly relevant scientific journals and conference proceedings, and (3) reviewing additional material suggested by authors of products identified in steps 1 and 2. Our search was intentionally broad in order to identify as much relevant work as possible, much of which is professionally applied and tested within the industry of oil and gas reclamation, but which remains unpublished in scientific journals. We refined the initial list of products by removing: (1) duplicates, (2) products not written in English, (3) products that were not relevant to the arid ecosystems of western North America, (4) products that were not released as research, data products, or review articles in journals or as formal scientific reports, and (5) products with data which were not relevant to reclamation of oil and gas-affected lands, or for which the study did not present new data, findings, or syntheses relevant to reclamation of oil and gas-affected lands. We summarized each product using a consistent structure (background, objectives, methods, location, findings, and implications) and assigned standardized management topics to each. Management topics are intended to aid online searching within the bibliography and are described in more detail in the Methods Section of this report; they include what type of disturbance the product addresses (well pads, mining, pipelines), what aspect of oil and gas reclamation they pertain to (practices, standards, monitoring), what type of data are present in the product (for instance soil or vegetation recovery data), and an indication if the product were from a source other than a published, peer-reviewed outlet (such as dissertations or unpublished professional reports – these are identified as grey literature). The review process for this annotated bibliography included an initial internal colleague review of each summary, requesting input on each summary from an author of the original product, and a formal peer-review. Our initial searches resulted in 3,197 total products, of which 290 met our criteria for inclusion. “Reclamation Practices” is by far the management topic most addressed, followed by “Reclamation Monitoring,” for example, products assessing what and how monitoring methods are used to track and measure reclamation outcome. This document may be accessed at https://doi.org/10.3133/ofr20231068 or from the U.S. Geological Survey Publication Warehouse ( https://pubs.usgs.gov/ ). The 1-page product summaries herein will also be used to create a bibliography at https://apps.usgs.gov/science-for-resource-managers that includes links to each original product, where available, and in which subject matter will be searchable by topic, location, and year. The studies compiled and summarized here may inform planning and management actions that seek to reclaim landscapes across the western U.S. which have been affected by oil and gas development.

Open-File Report

Fourier power spectra of the geomagnetic field for circular paths on the Earth's surface.

The Fourier power spectra of geomagnetic component values, synthesized from spherical harmonic models, have been computed for circular paths on the Earth's surface. They are not found to be more useful than is the spectrum of magnetic energy outside the Earth for the purpose of separating core and crustal sources of the geomagnetic field. The Fourier power spectra of N and E geomagnetic components along nearly polar great circle paths exhibit some unusual characteristics that are explained by the geometric perspective of Fourier series on spheres developed by Yee.

Journal of Geomagnetism & Geoelectricity

Keeping pace: Migrating sea lampreys adjust swim speed in response to shifting water velocity to maintain a constant ground speed

Upstream migrating fish must balance energetic costs with environmental and ecological constraints. Theoretical models predict that fish can conserve energy by adjusting swim speed in response to changing water velocity, but detailed field tests of these predictions remain rare. We used fine-scale acoustic telemetry and hydrodynamic modeling to track adult sea lamprey (Petromyzon marinus) migrating through a river and evaluated how movement speeds varied with environmental conditions and individual traits. Swim speed increased with faster water velocities, while ground speed remained constant, supporting the hypothesis that lampreys regulate swim effort to maintain a fixed migration pace. The average ground speed aligned with a predicted optimum of ∼1 body length per second. Both swim and ground speeds declined slightly in deeper water, suggesting a trade-off between movement efficiency and predator avoidance. These findings provide field-based support for a theoretical model of energy optimization and underscore how migratory fish adaptively adjust behavior to local hydrodynamic conditions. Our results highlight the value of using high-resolution tracking and environmental modeling to reveal behavioral tactics that underlie efficient migration strategies.

Michigan