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At least 37 records · Page 2Linked to original sources
USGS2011

Collection, processing, and interpretation of ground-penetrating radar data to determine sediment thickness at selected locations in Deep Creek Lake, Garrett County, Maryland, 2007

The U.S. Geological Survey collected geophysical data in Deep Creek Lake in Garrett County, Maryland, between September 17 through October 4, 2007 to assist the Maryland Department of Natural Resources to better manage resources of the Lake. The objectives of the geophysical surveys were to provide estimates of sediment thickness in shallow areas around the Lake and to test the usefulness of three geophysical methods in this setting. Ground-penetrating radar (GPR), continuous seismic-reflection profiling (CSP), and continuous resistivity profiling (CRP) were attempted. Nearly 90 miles of GPR radar data and over 70 miles of CSP data were collected throughout the study area. During field deployment and testing, CRP was determined not to be practical and was not used on a large scale. Sediment accumulation generally could be observed in the radar profiles in the shallow coves. In some seismic profiles, a thin layer of sediment could be observed at the water bottom. The radar profiles appeared to be better than the seismic profiles for the determination of sediment thickness. Although only selected data profiles were processed, all data were archived for future interpretation. This investigation focused on selected regions of the study area, particularly in the coves where sediment accumulations were presumed to be thickest. GPR was the most useful tool for interpreting sediment thickness, especially in these shallow coves. The radar profiles were interpreted for two surfaces of interest-the water bottom, which was defined as the "2007 horizon," and the interface between Lake sediments and the original Lake bottom, which was defined as the "1925 horizon"-corresponding to the year the Lake was impounded. The ground-penetrating radar data were interpreted on the basis of characteristics of the reflectors. The sediments that had accumulated in the impounded Lake were characterized by laminated, parallel reflections, whereas the subsurface below the original Lake bottom was characterized by more discontinuous and chaotic reflections, often with diffractions indicating cobbles or boulders. The reflectors were picked manually along the water bottom and along the interface between the Lake sediments and the pre-Lake sediments. A simple graphic approach was used to convert traveltimes to depth through water and depth through saturated sediments using velocities of the soundwaves through the water and the saturated sediments. Nineteen cross sections were processed and interpreted in 9 coves around Deep Creek Lake, and the difference between the 2007 horizon and the 1925 horizon was examined. In most areas, GPR data indicate a layer of sediment between 1 and 7 feet thick. When multiple cross sections from a single cove were compared, the cross sections indicated that sediment thickness decreased toward the center of the Lake.

Maryland↗
USGS2020

Interpretation of hydrogeologic data to support groundwater management, Bazile Groundwater Management Area, northeast Nebraska, 2019—A case demonstration of the Nebraska Geocloud

Nitrate, age tracer, and continuous groundwater-level data were interpreted in conjunction with airborne electromagnetic (AEM) survey data to understand the movement of nitrate within the Bazile Groundwater Management Area (BGMA) in northeastern Nebraska. Previously published age tracer data and nitrate data indicated vertical stratification of groundwater quality. Younger groundwater sampled within shallow parts of the aquifer had higher concentrations of nitrate, with 70 percent exceeding the U.S. Environmental Protection Agency maximum contaminant level of 10 milligrams per liter. In contrast, groundwater sampled from deeper parts of the aquifer indicated that nitrate concentrations were less than 2 milligrams per liter and that groundwater likely recharged prior to widespread use of commercial fertilizer. The hydrostratigraphic interpretation of AEM profiles indicated that shallow and deep monitoring wells were often screened within the same homogenous zone of aquifer material. In contrast, test-hole logs indicated that there often are fine-grained layers within these homogenous zones that separate the shallow and deep monitoring well screens, but these fine-grained layers are not detected by the AEM technique because of decreased resolution of the AEM technique with depth. The stratification of groundwater ages and nitrate concentrations likely was caused by groundwater-flow paths of different length, location and time of recharge, and denitrification. Within paleochannels interpreted from AEM and test-hole data, pesticides detected in groundwater generally coincide with elevated nitrate concentrations. Continuous groundwater-level data from four monitoring well nests indicated that groundwater pumping can impose or increase downward hydraulic gradients and facilitate the downward movement of nitrate into deeper parts of the High Plains aquifer. Given the density of irrigation wells within the BGMA, this effect on the hydraulic gradient is likely prevalent in other areas of the BGMA. Understanding seasonal water-level changes can allow water managers to better predict and assess the hydraulic gradient and the vulnerability of groundwater in deeper parts of the High Plains aquifer. Nitrate, age tracer, and continuous groundwater-level data within the BGMA were interpreted in conjunction with AEM data as a case demonstration of the Nebraska Geocloud. The Nebraska Geocloud was initiated to protect taxpayer investments in AEM data collection and realize maximum benefit of these data by creating a publicly available, online digital database for long-term data storage. The Lower Platte North, Lower Platte South, Papio-Missouri River, Nemaha, Lower Loup, Central Platte, Upper Elkhorn, Lower Elkhorn, Lower Niobrara, and Lewis and Clark Natural Resources Districts; the University of Nebraska-Lincoln Conservation and Survey Division, Nebraska Natural Resources Commission, Nebraska Department of Natural Resources; and the U.S. Geological Survey entered a cooperative agreement to begin a program of data management and research aimed at understanding the best use of AEM for groundwater sustainability and management. Resulting case-study interpretations are provided to guide use of the Nebraska Geocloud to assess water-quality conditions and can be used by water managers and staff to address applicable water resource problems.

Nebraska↗
USGS2021

Techniques to improve ecological interpretability of black box machine learning models

Statistical modeling of ecological data is often faced with a large number of variables as well as possible nonlinear relationships and higher-order interaction effects. Gradient boosted trees (GBT) have been successful in addressing these issues and have shown a good predictive performance in modeling nonlinear relationships, in particular in classification settings with a categorical response variable. They also tend to be robust against outliers. However, their black-box nature makes it difficult to interpret these models. We introduce several recently developed statistical tools to the environmental research community in order to advance interpretation of these black-box models. To analyze the properties of the tools, we applied gradient boosted trees to investigate biological health of streams within the contiguous USA, as measured by a benthic macroinvertebrate biotic index. Based on these data and a simulation study, we demonstrate the advantages and limitations of partial dependence plots (PDP), individual conditional expectation (ICE) curves and accumulated local effects (ALE) in their ability to identify covariate–response relationships. Additionally, interaction effects were quantified according to interaction strength (IAS) and Friedman’s H 2 "> H 2 statistic. Interpretable machine learning techniques are useful tools to open the black-box of gradient boosted trees in the environmental sciences. This finding is supported by our case study on the effect of impervious surface on the benthic condition, which agrees with previous results in the literature. Overall, the most important variables were ecoregion, bed stability, watershed area, riparian vegetation and catchment slope. These variables were also present in most identified interaction effects. In conclusion, graphical tools (PDP, ICE, ALE) enable visualization and easier interpretation of GBT but should be supported by analytical statistical measures. Future methodological research is needed to investigate the properties of interaction tests. Supplementary materials accompanying this paper appear on-line.

Journal of Agricultural, Biological, and Environme↗
USGS2005

Interpretation of the Last Chance thrust, Death Valley region, California, as an Early Permian décollement in a previously undeformed shale basin

The Last Chance thrust, discontinuously exposed over an area of at least 2500 km 2 near the south end of the Cordilleran foreland thrust belt in the Death Valley region of east-central California, is controversial because of its poorly constrained age and its uncertain original geometry and extent. We interpret this thrust to be Early Permian in age, to extend throughout a sedimentary basin in which deep-water Mississippian shale overlain by Pennsylvanian and earliest Permian limestone turbidites accumulated, to represent about 30 km of eastward displacement, and to be related to convergence on a northeast-trending segment of the Early Permian continental margin. Last Chance deformation occurred between the times of the Antler and Sonoma orogenies of Late Devonian–Early Mississippian and Late Permian ages, respectively, and followed Early to Middle Pennsylvanian truncation of the continental margin by transform faulting. In the western part of the Mississippian shale basin in east-central California, the originally recognized exposures of the Last Chance thrust show Neoproterozoic and early Paleozoic strata above lower-plate Mississippian shale. Farther east, faults subparallel to bedding above, below, and within the Mississippian shale are interpreted to mark the thrust zone and to represent a regional décollement. At the eastern margin of the basin, upper-plate thrust slices of deep-water, late Paleozoic strata are interpreted to have piled up against the margin of the Mississippian carbonate shelf to form a large antiformal stack above the Lee Flat thrust, which we regard as the easternmost exposure of the Last Chance thrust. Thrust loading depressed the western part of the shelf, creating a new sedimentary basin in which about 3.5 km of younger Early Permian deep-water strata were deposited against the antiformal stack. Later, probably in the Late Permian, other thrusts, including the Inyo Crest thrust, which was subsequently overlapped by Early to Middle(?) Triassic marine strata, cut across the Last Chance thrust. We interpret the Last Chance thrust as similar in many ways to Appalachian-type décollements in which the zone of thrusting is localized along a shale interval. The Last Chance thrust, however, has been dismembered during later geologic events so that its original geometry has been obscured. Our model may have unrecognized analogs in other structurally complex shale basins in which the initial deformation was along a major shale unit.

Earth-Science Reviews↗
USGS2019

The effects of topographic surveying technique and data resolution on the detection and interpretation of geomorphic change

Change detection of high resolution topographic data is commonly used in river valleys to quantify reach- and site-scale sediment budgets by estimating the erosion/deposition volume, and to interpret the geomorphic processes driving erosion and deposition. Field survey data are typically collected as point clouds that are often converted to gridded raster datasets and the ultimate choice of grid resolution is left to the user. This choice may have important implications for both the quantification and interpretation of geomorphic change. Here we used concurrent topographic data collected by terrestrial laser scanning (TLS) and structure-from-motion (SfM) photogrammetry to quantify the influence of grid resolution and sampling technique on (a) the sediment budget and (b) the presence and role of geomorphic processes (i.e., alluvial, colluvial, aeolian, and fluvial transport) driving topographic change at four sites along the Colorado River in Grand Canyon, Arizona, USA. We found that while both techniques produced similar estimates for site-scale sediment budgets, the magnitude of detected topographic change was dampened at coarser pixel resolutions. An overall decrease in the areal extent of erosion and deposition were observed, respectively, when coarsening pixel size from 5 cm to 1 m among all sites. Coarser resolution data tended to affect interpretation of landscape change along the margins of river valleys. For example, when changing from 5 cm to 1 m pixel resolution, the inferred contribution of aeolian changes to total site-scale geomorphic change increased in area by 7.9%, whereas the inferred contribution of alluvial and colluvial processes decreased in area by 97.9% and 88.2%, respectively. More generally, we found that coarsening pixel sizes disproportionately attributed geomorphic change to one or more of the most common processes operating at a site. We also found that coarsening pixel resolution amplified the net sediment imbalance at the site scale, driving the imbalance at erosional sites further into erosion and vice versa for depositional sites. Our results have implications both for point cloud data collection and for raster dataset processing. We argue that selecting the finest obtainable resolution is not always warranted to accurately quantify and interpret geomorphic change, because remote sensing technique, topographic data resolution, and analysis procedure can be optimized to capture the spatial scale of those processes driving landscape change. However, in landscapes at or near sediment equilibrium (i.e., equal amounts of erosion and deposition), the finest obtainable topographic data resolution is warranted to avoid amplifying sediment imbalance and erroneously inferring that sites are trending toward erosion or deposition.

Arizona↗
USGS2014

Interpretations of evidence for large Pleistocene paleolakes in the Bonneville basin, western North America: COMMENT on: Bonneville basin shoreline records of large lake intervals during marine isotope stage 3 and the last glacial maximum, by Nishizawa et al. (2013)

Nishizawa et al. (2013) argue in support of three large paleolakes in the Bonneville basin during Marine Oxygen Isotope Stage 3 (MIS 3). If true, that would be an important contribution to paleoclimate investigations. However, the key evidence in support of their argument consists of four radiocarbon ages that are out of stratigraphic order and near the practical and theoretical limit of the dating method. The interpretation of three large MIS 3 lakes conflicts with some of their own data, as well as with independently derived stratigraphic information from the basin. Nishizawa et al. (2013) also interpret a series of radiocarbon ages of mollusk samples as indicating previously undocumented lake transgressions a few thousand years older than basal radiocarbon ages of wood samples. We believe that these interpretations are in error, and arise largely from reliance on radiocarbon ages from carbonate material. Lake records constrained by ages of non-carbonate organic materials, along with compelling stratigraphic information from unconformities and buried soils, argue for not changing interpretations of Lake Bonneville history until more supporting information for older lakes at relatively high altitudes is found.

Palaeogeography, Palaeoclimatology, Palaeoecology↗
USGS1998

Successful water quality monitoring: The right combination of intent, measurement, interpretation, and a cooperating ecosystem

Water quality monitoring is invaluable to ensure compliance with regulations, detect trends or patterns, and advance ecological understanding. However, monitoring typically measures only a few characteristics in a small fraction of a large and complex system, and thus the information contained in monitoring data depends upon which features of the ecosystem are actually captured by the measurements. Difficulties arise when these data contain something other than intended, but this can be minimized if the purpose of the sampling is clear, and the sampling design, measurements, and data interpretations are all compatible with this purpose. The monitoring program and data interpretation must also be properly matched to the structure and functioning of the system. Obtaining this match is sometimes an iterative process that demands a close link between research and monitoring. This paper focuses on water quality monitoring that is intended to track trends in aquatic resources and advance ecological understanding. It includes examples from three monitoring programs and a simulation exercise that illustrate problems that arise when the information content of monitoring data differs from expectation. The examples show (1) how inconsistencies among, or lack of information about, the basic elements of a monitoring program (intent, design, measurement, interpretation, and the monitored system) can produce a systematic difference (bias) between monitoring measurements and sampling intent or interpretation, and (2) that bias is not just a statistical consideration, but an insidious problem that can undermine the scientific integrity of a monitoring program. Some general suggestions are provided and hopefully these examples will help those engaged in water quality monitoring to enhance and protect the value of their monitoring investment.

Lake and Reservoir Management↗
USGS2005

Interpreting DNAPL saturations in a laboratory-scale injection using one- and two-dimensional modeling of GPR Data

Ground-penetrating radar (GPR) is used to track a dense non-aqueous phase liquid (DNAPL) injection in a laboratory sand tank. Before modeling, the GPR data provide a qualitative image of DNAPL saturation and movement. One-dimensional (1D) GPR modeling provides a quantitative interpretation of DNAPL volume within a given thickness during and after the injection. DNAPL saturation in sublayers of a specified thickness could not be quantified because calibration of the 1D GPR model is nonunique when both permittivity and depth of multiple layers are unknown. One-dimensional GPR modeling of the sand tank indicates geometric interferences in a small portion of the tank. These influences are removed from the interpretation using an alternate matching target. Two-dimensional (2D) GPR modeling provides a qualitative interpretation of the DNAPL distribution through pattern matching and tests for possible 2D influences that are not accounted for in the 1D GPR modeling. Accurate quantitative interpretation of DNAPL volumes using GPR modeling requires (1) identification of a suitable target that produces a strong reflection and is not subject to any geometric interference; (2) knowledge of the exact depth of that target; and (3) use of two-way radar-wave travel times through the medium to the target to determine the permittivity of the intervening material, which eliminates reliance on signal amplitude. With geologic conditions that are suitable for GPR surveys (i.e., shallow depths, low electrical conductivities, and a known reflective target), the procedures in this laboratory study can be adapted to a field site to delineate shallow DNAPL source zones.

Ground Water Monitoring and Remediation↗
USGS2004

Interpretation of the Seattle Uplift, Washington, as a passive-roof duplex

We interpret seismic lines and a wide variety of other geological and geophysical data to suggest that the Seattle uplift is a passive-roof duplex. A passive-roof duplex is bounded top and bottom by thrust faults with opposite senses of vergence that form a triangle zone at the leading edge of the advancing thrust sheet. In passive-roof duplexes the roof thrust slips only when the floor thrust ruptures. The Seattle fault is a south-dipping reverse fault forming the leading edge of the Seattle uplift, a 40-km-wide fold-and-thrust belt. The recently discovered, north-dipping Tacoma reverse fault is interpreted as a back thrust on the trailing edge of the belt, making the belt doubly vergent. Floor thrusts in the Seattle and Tacoma fault zones, imaged as discontinuous reflections, are interpreted as blind faults that flatten updip into bedding plane thrusts. Shallow monoclines in both the Seattle and Tacoma basins are interpreted to overlie the leading edges of thrust-bounded wedge tips advancing into the basins. Across the Seattle uplift, seismic lines image several shallow, short-wavelength folds exhibiting Quaternary or late Quaternary growth. From reflector truncation, several north-dipping thrust faults (splay thrusts) are inferred to core these shallow folds and to splay upward from a shallow roof thrust. Some of these shallow splay thrusts ruptured to the surface in the late Holocene. Ages from offset soils in trenches across the fault scarps and from abruptly raised shorelines indicate that the splay, roof, and floor thrusts of the Seattle and Tacoma faults ruptured about 1100 years ago.

Washington↗
USGS1997

Seismic interpretation of the deep structure of the Wabash Valley Fault System

Interpretations of newly available seismic reflection profiles near the center of the Illinois Basin indicate that the Wabash Valley Fault System is rooted in a series of basement-penetrating faults. The fault system is composed predominantly of north-northeast-trending high-angle normal faults. The largest faults in the system bound the 22-km wide 40-km long Grayville Graben. Structure contour maps drawn on the base of the Mount Simon Sandstone (Cambrian System) and a deeper pre-Mount Simon horizon show dip-slip displacements totaling at least 600 meters across the New Harmony fault. In contrast to previous interpretations, the N-S extent of significant fault offsets is restricted to a region north of 38° latitude and south of 38.35° latitude. This suggests that the graben is not a NE extension of the structural complex composed of the Rough Creek Fault System and the Reelfoot Rift as previously interpreted. Structural complexity on the graben floor also decreases to the south. Structural trends north of 38° latitude are offset laterally across several large faults, indicating strike-slip motions of 2 to 4 km. Some of the major faults are interpreted to penetrate to depths of 7 km or more. Correlation of these faults with steep potential field gradients suggests that the fault positions are controlled by major lithologic contacts within the basement and that the faults may extend into the depth range where earthquakes are generated, revealing a potential link between specific faults and recently observed low-level seismicity in the area.

Illinois, Indiana, Kentucky↗
USGS1979

Geologic interpretation of the gravity anomaly map of the Seward and Blying Sound quadrangles, Alaska

For more than 20 years, gravity surveys have been conducted in the vicinity of Prince William Sound, the epicentral region of the great Alaska earthquake of March 27, 1964. Some of the major regional gravity anomalies were outlined by Thiel, Ostenso, Bonini (1960), and additional anomalies were defined by pre- and post-earthquake gravity studies reported by Barnes and Allen (1965) and Case, Barnes, Plafker, and Robbins (1966). Another gravity anomaly map was prepared by personnel of the U.S. Coast and Geodetic Survey (now the National Oceanic and Atmospheric Administration) (Wood, 1966, p. 131; Rice, 1969, p. 5-20). Anomalies shown by Rice (1969) are broadly similar to those shown by Case, Barnes, Plafker, and Robbins (1966); Rice's interpretations concerned mainly gravity changed related to the earthquake, and the data were not interpreted in terms of regional geology. New gravity stations were established in 1976 as part of the mineral resource appraisal of the Seward and Blying Sound quadrangles. This report incorporates the new data obtained in 1976, reinterprets some anomalies previously discussed by Case, Barnes, Plafker, and Robbins (1966), and interprets other anomalies not previously discussed. Descriptions of the major rock units and structural features are found in the companion report by Tysdal and Case (in press). An interpretation of the aeromagnetic map of the region has been prepared by Case, Tysdal, Hillhouse, and Gromme (1979).

Alaska↗
USGS2007

Geologic interpretation and multibeam bathymetry of the sea floor in the vicinity of the Race, eastern Long Island Sound

Digital terrain models (DTMs) produced from multibeam bathymetric data provide valuable base maps for marine geological interpretations (Todd and others, 1999; Mosher and Thomson, 2002; ten Brink and others, 2004; Poppe and others, 2006a, b, c, d). These maps help define the geological variability of the sea floor (one of the primary controls of benthic habitat diversity), improve our understanding of the processes that control the distribution and transport of bottom sediments and the distribution of benthic habitats and associated infaunal community structures, and provide a detailed framework for future research, monitoring, and management activities. The bathymetric survey interpreted herein (National Oceanic and Atmospheric Administration (NOAA) survey H11250) covers roughly 94 km² of sea floor in an area where a depression along the Orient Point-Fishers Island segment of the Harbor Hill-Roanoke Point-Charlestown Moraine forms the Race, the eastern opening to Long Island Sound. The Race also divides easternmost Long Island Sound from northwestern Block Island Sound (fig. 1). This bathymetry has been examined in relation to seismic reflection data collected concurrently, as well as archived seismic profiles acquired as part of a long-standing geologic mapping partnership between the State of Connecticut and the U.S. Geological Survey (USGS). The objective of this work was to use these acoustic data sets to interpret geomorphological attributes of the sea floor, and to use these interpretations to better understand the Quaternary geologic history and modern sedimentary processes.

Connecticut;New York↗
USGS2009

Results and Interpretations of U.S. Geological Survey Data Collected In and Around the Tuba City Open Dump, Arizona

This Open-File Report was originally an Administrative Report presentation to the Bureau of Indian Affairs based on U.S. Geological Survey data that has been collected and presented in four previous reports (Open-File Reports 2009-1020, 2008-1380, and 2008-1374, and an Administrative Report on geophysical data). This presentation was given at a technical meeting requested by the BIA on March 3 and 4, 2009, in Phoenix, Arizona. The idea for this meeting was for all the technical people working on issues related to the Tuba City Open Dump site to come together and share their data collection procedures, results, interpretations, and working hypotheses. The meeting goal was to have a clear record of each party's interpretations and a summary of additional data that would be needed to solve differences of opinion. The intention of this presentation is not to provide an exhaustive summary of U.S. Geological Survey efforts at the Tuba City Open Dump site given in the four previously published Open-File Reports listed above, since these reports have already been made available. This presentation briefly summarizes the data collected for those reports and provides results, interpretations, and working hypotheses relating to the data available in these reports. The major questions about the Tuba City Open Dump addressed by the U.S. Geological Survey are (1) what are the sources for uranium and other constituents found in the ground water in and around the Tuba City Open Dump, (2) what is the current distribution of ground water contaminants away from the Tuba City Open Dump (can plume limits be delineated), and (3) what controls the mobility of uranium and other constituents in and around the Tuba City Open Dump? Data collection, results, and interpretations by the U.S. Geological Survey that address these questions are presented herein.

Open-File Report↗
USGS2011

Quantifying viruses and bacteria in wastewater—Results, interpretation methods, and quality control

Membrane bioreactors (MBR), used for wastewater treatment in Ohio and elsewhere in the United States, have pore sizes small enough to theoretically reduce concentrations of protozoa and bacteria, but not viruses. Sampling for viruses in wastewater is seldom done and not required. Instead, the bacterial indicators Escherichia coli (E. coli) and fecal coliforms are the required microbial measures of effluents for wastewater-discharge permits. Information is needed on the effectiveness of MBRs in removing human enteric viruses from wastewaters, particularly as compared to conventional wastewater treatment before and after disinfection. A total of 73 regular and 28 quality-control (QC) samples were collected at three MBR and two conventional wastewater plants in Ohio during 23 regular and 3 QC sampling trips in 2008-10. Samples were collected at various stages in the treatment processes and analyzed for bacterial indicators E. coli, fecal coliforms, and enterococci by membrane filtration; somatic and F-specific coliphage by the single agar layer (SAL) method; adenovirus, enterovirus, norovirus GI and GII, rotavirus, and hepatitis A virus by molecular methods; and viruses by cell culture. While addressing the main objective of the study-comparing removal of viruses and bacterial indicators in MBR and conventional plants-it was realized that work was needed to identify data analysis and quantification methods for interpreting enteric virus and QC data. Therefore, methods for quantifying viruses, qualifying results, and applying QC data to interpretations are described in this report. During each regular sampling trip, samples were collected (1) before conventional or MBR treatment (post-preliminary), (2) after secondary or MBR treatment (post-secondary or post-MBR), (3) after tertiary treatment (one conventional plant only), and (4) after disinfection (post-disinfection). Glass-wool fiber filtration was used to concentrate enteric viruses from large volumes, and small volume grab samples were collected for direct-plating analyses for bacterial indicators and coliphage. After filtration, the viruses were eluted from the filter and further concentrated. The final concentrated sample volume (FCSV) was used for enteric virus analysis by use of two methods-cell culture and a molecular method, polymerase chain reaction (PCR). Quantitative PCR (qPCR) for DNA viruses and quantitative reverse-transcriptase PCR (qRT-PCR) for RNA viruses were used in this study. To support data interpretations, the assay limit of detection (ALOD) was set for each virus assay and used to determine sample reporting limits (SRLs). For qPCR and qRT-PCR the ALOD was an estimated value because it was not established according to established method detection limit procedures. The SRLs were different for each sample because effective sample volumes (the volume of the original sample that was actually used in each analysis) were different for each sample. Effective sample volumes were much less than the original sample volumes because of reductions from processing steps and (or) from when dilutions were made to minimize the effects from PCR-inhibiting substances. Codes were used to further qualify the virus data and indicate the level of uncertainty associated with each measurement. Quality-control samples were used to support data interpretations. Field and laboratory blanks for bacteria, coliphage, and enteric viruses were all below detection, indicating that it was unlikely that samples were contaminated from equipment or processing procedures. The absolute value log differences (AVLDs) between concurrent replicate pairs were calculated to identify the variability associated with each measurement. For bacterial indicators and coliphage, the AVLD results indicated that concentrations <10 colony-forming units or plaque-forming units per 100 mL can differ between replicates by as much as 1 log, whereas higher concentrations can differ by as much as 0.3 log. The AVLD results for viruses indicated that differences between replicates can be as great as 1.2 log genomic copies per liter, regardless of the concentration of virus. Relatively large differences in molecular results for viruses between replicate pairs were likely due to lack of precision for samples with small effective volumes. Concentrations of E. coli, fecal coliforms, enterococci, and somatic and F-specific coliphage in post-secondary and post-tertiary samples in conventional plants were higher than those in post-MBR samples. In post-MBR and post-secondary samples, concentrations of somatic coliphage were higher than F-specific coliphage. In post-disinfection samples from two MBR plants (the third MBR plant had operational issues) and the ultraviolet conventional plant, concentrations for all bacterial indicators and coliphage were near or below detection; from the chlorine conventional plant, concentrations in post-disinfection samples were in the single or double digits. All of the plants met the National Pollutant Discharge Elimination System required effluent limits established for fecal coliforms. Norovirus GII and hepatitis A virus were not detected in any samples, and rotavirus was detected in one sample but could not be quantified. Adenovirus was found in 100 percent, enterovirus in over one-half, and norovirus GI in about one-half of post-preliminary wastewater samples. Adenovirus and enterovirus were detected throughout the treatment processes, and norovirus GI was detected less often than the other two enteric viruses. Culturable viruses were detected in post-preliminary samples and in only two post-treatment samples from the plant with operational issues.

Scientific Investigations Report↗
USGS1977

Cauldron subsidence of Oligocene age at Mount Lewis, Shoshone Range, Nevada: A reasonable interpretation

James Gilluly has rejected the interpretation of Wrucke and Silberman (U.S. Geol. Survey Prof. Paper 876, 1975) that a thrust fault and tear fault mapped by Gilluly and Gates (U.S. Geol. Survey Prof. Paper 465, 1965) as structures bounding the upper plate of the Roberts Mountains thrust at Mount Lewis are parts of a ring fracture around an area that underwent volcanic collapse. In his discussion (this volume) of our paper, Gilluly fails to consider important questions that we presented in support of the subsidence hypothesis. Instead of answering these critical questions, Gilluly merely recapitulates the interpretations that he and Gates gave in Professional Paper 465. We presented new information, including a map of one critical area along the cauldron boundary where, among other significant differences in geologic interpretation, we found the ring fault where previously no steep fault was shown. Gilluly believes that the paucity of dikes along the ring fracture at Mount Lewis is highly anomalous for cauldrons. However, the amount of dike rock is comparable to that in known cauldrons (some cauldrons have none) and is what might be expected at high levels in subsidence structures that have undergone relatively little resurgent igneous activity after collapse. Gilluly concludes that in formulating our interpretation of volcanic collapse, we have ignored much evidence that he and Gates have presented on thrust faulting; in the Shoshone Range. On the contrary, we have considered their ideas and have reinterpreted them using new evidence that strongly supports the concept of cauldron subsidence at Mount Lewis.

Nevada↗
USGS2026

Communicating darkness: Visitor preferences for dark sky interpretation

Utah parks are attracting an increasing number of visitors due to the quality dark sky viewing opportunities. Despite increasing engagement in nighttime recreation, limited research exists on visitor interest in interpretation for dark skies in state and national parks. Nighttime visitors at nine Utah state and national park units certified as dark sky parks were surveyed to evaluate their preferences for dark sky-related interpretive topics and communication methods. Visitors expressed the strongest interest in astronomy and improving dark sky viewing, with ranger-led programs emerging as the most favored delivery method. National park visitors showed greater interest than state park visitors in self-guided learning formats such as interpretive displays and mobile apps for topics such as dark sky viewing/astronomy and viewing wildlife at night. These findings highlight the benefits of diverse, yet targeted communication strategies to improve visitor experiences of dark skies and foster stewardship of natural darkness in parks.

Utah↗
USGS2020

Integrated geophysical analysis provides an alternate interpretation of the northern margin of the North American Midcontinent Rift System, Central Lake Superior

The Midcontinent Rift System (MRS) is a 1.1 Ga sequence of voluminous basaltic eruptions and multiple intrusions followed by widespread sedimentation that extends across the Midcontinent and northern Great Lakes region of North America. Previous workers have commonly used seismic-reflection data (Great Lakes International Multidisciplinary Program on Crustal Evolution [GLIMPCE] line A) to demonstrate that the northern rift margin in central Lake Superior developed as a normal growth fault that was structurally inverted to a reverse fault during a compressional event after rifting had ended. A prominent, curvilinear aeromagnetic anomaly that extends from Isle Royale, Michigan, to Superior Shoal in central Lake Superior, Ontario (the IR-SS anomaly), is commonly presented as a manifestation of this reverse fault. We have integrated multidisciplinary geophysical analyses (seismic-reflection, seismic-refraction, aeromagnetic, and gravity), physical-property information (density, magnetic susceptibility and remanence, and compressional-wave velocity), and geologic concepts to develop an alternate interpretation of the rift margin along GLIMPCE line A, where it intersects the IR-SS anomaly. Our new model indicates that a normal fault is the dominant structure at the northern rift margin along line A, contrary to the original rift-margin paradigm, which asserts that compressional structures are the dominant features preserved today. Integral to this alternate model is a newly interpreted, prerift sedimentary basin intruded by sills in northern Lake Superior. Our alternate model of the northern rift margin has implications for interpreting the style, scale, and timing of extension, rift-related intrusion, and compression during development of the MRS.

Lake Superior↗
USGS1998

Study design and interpretation of mammalian carnivore density estimates

Ecological theory and wildlife management often depend on reliable comparison and interpretation of population density estimates. A synthesis of 1,772 mammalian carnivore population estimates (713 unique to reference, species, site, and size of study area) from 74 species revealed global patterns among aspects of study and interpretive design that undermine the reliability and usefulness of density comparisons. The spatial extent of the study area could explain most of the variation in density, probably because study areas are typically delineated around population clusters. We related the scale-defined density estimates (regression residuals) to 28 other variables measured from the published literature, but none provided convincing biological explanation of the variation in density. Many aspects of study and interpretive design were possibly ill-suited to identifying the factor(s) influencing density. Study attributes and findings were reported inconsistently, and were subject to ideological motivations. Descriptions of vegetation were most difficult to relate to density. More intensive sampling and estimation methods produced above-average density estimates, but the differences were slight and the evidence lacking for concluding whether these more intensive methods were also more accurate. The first underlying factor extracted from principle-components analysis described the growing recognition of population declines and range reductions among large-bodied carnivores, which has also influenced study design. Another factor described an increasing trend for density to be compared and extrapolated to larger areas, but without adjusting for the effect of scale. To understand the factors influencing carnivore distribution and abundance, sampling and reporting methods (e.g., site description with maps) will need to represent the available pool of species, locations, and ecological conditions at larger-than-conventional spatial and temporal scales.

Oecologia↗