Airborne electromagnetic imaging of discontinuous permafrost

The evolution of permafrost in cold regions is inextricably connected to hydrogeologic processes, climate, and ecosystems. Permafrost thawing has been linked to changes in wetland and lake areas, alteration of the groundwater contribution to stream flow, carbon release, and increased fire frequency. But detailed knowledge about the dynamic state of permafrost in relation to surface and groundwater systems remains an enigma. Here, we present the results of a pioneering ~1,800 line-kilometer airborne electromagnetic survey that shows sediments deposited over the past ~4 million years and the configuration of permafrost to depths of ~100 meters in the Yukon Flats area near Fort Yukon, Alaska. The Yukon Flats is near the boundary between continuous permafrost to the north and discontinuous permafrost to the south, making it an important location for examining permafrost dynamics. Our results not only provide a detailed snapshot of the present-day configuration of permafrost, but they also expose previously unseen details about potential surface – groundwater connections and the thermal legacy of surface water features that has been recorded in the permafrost over the past 1,000 years. This work will be a critical baseline for future permafrost studies aimed at exploring the connections between hydrogeologic, climatic, and ecological processes, and has significant implications for the stewardship of Arctic environments

Constraining fault-zone hydrogeology through integrated hydrological and geoelectrical analysis

International audienceThe hydrogeologic influence of the Elkhorn fault in South Park, Colorado, USA, is examined through hydrologic data supplemented by electrical resistivity tomography and self-potential measurements. Water-level data indicate that groundwater flow is impeded by the fault on the spatial scale of tens of meters, but the lack of outcrop prevents interpretation of why the fault creates this hydrologic heterogeneity. By supplementing hydrologic and geologic data with geoelectrical measurements, further hydrogeologic interpretation is possible. Resistivity profiles and self-potential data are consistent with the interpretation of increased fracturing within 70 m of the fault. Further interpretation of the fault zone includes the possibility of a vertical groundwater flow component in a fractured and relatively high permeability damage zone and one or more relatively low permeability fault cores resulting in a conduit-barrier behavior of the fault zone at the meter to tens-of-meters scale. Calculated hydraulic heads from the self-potential data reveal additional complexity in permeability structure, including a steeper hydraulic gradient immediately west of the interpreted fault trace than suggested by the well data alone

Data Series 902 Digital Geospatial Presentation of Geoelectrical and Geotechnical Data for the Lower American River and Flood Plain, East Sacramento, California Digital Geospatial Presentation of Geoelectrical and Geotechnical Data for the Lower American

For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS. For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod To order this and other USGS information products, visit http://store.usgs.gov Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Abstract To characterize the extent and thickness of lithologic units that may have differing scour potential, the U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, has performed several geoelectrical surveys of the lower American River channel and flood plain between Cal Expo and the Rio Americano High School in east Sacramento, California. Additional geotechnical data have been collected by the U.S. Army Corps of Engineers and its contractors. Data resulting from these surveys have been compiled into similar database formats and converted to uniform geospatial datums and projections. These data have been visualized in a digital three-dimensional framework project that can be viewed using freely available software. These data facilitate a comprehensive analysis of the resistivity structure underlying the lower American River corridor and assist in levee system management

Quantifying salinity in the layered coastal aquifers underlying and adjacent to Delaware Bay USA using AEM-derived resistivity

<p>Airborne electromagnetic (AEM) methods are particularly well suited to coastal aquifer salinity studies, yet the quantitative translation from bulk resistivity to fluid salinity carries uncertainty that can impact mapped salinity distributions and interpretations of the freshwater-saline interface and hydrostratigraphic layers. A recent AEM survey of the region near the Delaware Bay, USA highlights several challenges common to coastal hydrogeologic settings that may influence both qualitative and quantitative interpretation. We use a Bayesian inversion to estimate geophysical parameter uncertainty, and results are integrated with hydrogeologic measurements to develop quantitative interpretations of salinity across the freshwater-saline interface in stacked aquifers.</p>Open-Access Online Publication: October 30, 202

Novel Textbook Outcomes following emergency laparotomy:Delphi exercise

Background: Textbook outcomes are composite outcome measures that reflect the ideal overall experience for patients. There are many of these in the elective surgery literature but no textbook outcomes have been proposed for patients following emergency laparotomy. The aim was to achieve international consensus amongst experts and patients for the best Textbook Outcomes for non-trauma and trauma emergency laparotomy. Methods: A modified Delphi exercise was undertaken with three planned rounds to achieve consensus regarding the best Textbook Outcomes based on the category, number and importance (Likert scale of 1–5) of individual outcome measures. There were separate questions for non-trauma and trauma. A patient engagement exercise was undertaken after round 2 to inform the final round. Results: A total of 337 participants from 53 countries participated in all three rounds of the exercise. The final Textbook Outcomes were divided into ‘early’ and ‘longer-term’. For non-trauma patients the proposed early Textbook Outcome was ‘Discharged from hospital without serious postoperative complications (Clavien–Dindo ≥ grade III; including intra-abdominal sepsis, organ failure, unplanned re-operation or death). For trauma patients it was ‘Discharged from hospital without unexpected transfusion after haemostasis, and no serious postoperative complications (adapted Clavien–Dindo for trauma ≥ grade III; including intra-abdominal sepsis, organ failure, unplanned re-operation on or death)’. The longer-term Textbook Outcome for both non-trauma and trauma was ‘Achieved the early Textbook Outcome, and restoration of baseline quality of life at 1 year’. Conclusion: Early and longer-term Textbook Outcomes have been agreed by an international consensus of experts for non-trauma and trauma emergency laparotomy. These now require clinical validation with patient data.</p