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At least 559 records · Page 31Linked to original sources

USGS1977

Geochemical and petrological studies of a uraniferous granite from the Granite Mountains, Wyoming

Granite rocks from the Granite Mountains, Wyo. have been proposed as the source of uranium deposits in the Crooks Gap, Gas Hills and Shirley Basin uranium districts, Wyoming. We have divided these granitic rocks into four units: (1) a biotitic phase which forms the dominant unit at the western end of the Granite Mountains, (2) a leucocratic phase which was found from 215 to 405 metres in drill hole GM-1, (3) silicified zones which crosscut the granitic rocks and form topographic highs, and (4) fractured zones, in drill hole GM-1, which seem to have been hydrothermally altered. The biotitic phase is hypidiomorphic-granular to xenomorphic-granular alkali granite with anomalously high contents of U (10 parts per million), Th (50 ppm), and Pb (50 ppm). Fission-track studies show that uranium is located in zircon, sphene, apatite, monzite, xenotime, biotite, chlorite, epidote, and magnetite; no intergranular uranium was found. The leucocratic phase is mineralogically similar to the biotitic phase, but contains less than half as much iron. It is xenomorphic granular and commonly contains rounded and retrograded garnets, which suggests that this phase is either metamorphic or contaminated with metamorphic materials. The leucocratic phase has anomalously high contents of U (8 ppm) and Pb (55 ppm), but has a low Th content (10 ppm). The silicified phase and fracture zones exhibit cataclastic and crystalloblastic textures and are highly variable in mineralogy. Potassium-bearing minerals are generally absent. Microcline is replaced by albite and (or) quartz, and biotite is replaced by clinozoisite. Uranium values may be anomalously high in the fracture zones. One sample contains 1100 ppm radium-equivalent uranium. In this and other uranium-rich samples from the fracture zones, the uranium is associated with iron oxides which commonly fill microfractures. According to our model and currently available data, an alkali granite is the best crystalline source rock for uranium, especially if it is unmetamorphosed and rapidly exposed to near-surface conditions for the first time when a favorable basin existed nearby.

Wyoming↗

USGS2014

Statistical analysis of the water-quality monitoring program, Upper Klamath Lake, Oregon, and optimization of the program for 2013 and beyond

Upper Klamath Lake in south-central Oregon has become increasingly eutrophic over the past century and now experiences seasonal cyanobacteria-dominated and potentially toxic phytoplankton blooms. Growth and decline of these blooms create poor water-quality conditions that can be detrimental to fish, including two resident endangered sucker species. Upper Klamath Lake is the primary water supply to agricultural areas within the upper Klamath Basin. Water from the lake is also used to generate power and to enhance and sustain downstream flows in the Klamath River. Water quality in Upper Klamath Lake has been monitored by the Klamath Tribes since the early 1990s and by the U.S. Geological Survey (USGS) since 2002. Management agencies and other stakeholders have determined that a re-evaluation of the goals for water-quality monitoring is warranted to assess whether current data-collection activities will continue to adequately provide data for researchers to address questions of interest and to facilitate future natural resource management decisions. The purpose of this study was to (1) compile an updated list of the goals and objectives for long-term water-quality monitoring in Upper Klamath Lake with input from upper Klamath Basin stakeholders, (2) assess the current water-quality monitoring programs in Upper Klamath Lake to determine whether existing data-collection strategies can fulfill the updated goals and objectives for monitoring, and (3) identify potential modifications to future monitoring plans in accordance with the updated monitoring objectives and improve stakeholder cooperation and data-collection efficiency. Data collected by the Klamath Tribes and the USGS were evaluated to determine whether consistent long-term trends in water-quality variables can be described by the dataset and whether the number and distribution of currently monitored sites captures the full range of environmental conditions and the multi-scale variability of water-quality parameters in the lake. Also, current monitoring strategies were scrutinized for unnecessary redundancy within the overall network.

Oregon↗

USGS2010

Seasonal and spatial distribution patterns of finfish and selected invertebrates in coastal lagoons of northeastern Florida, 2002-2004

The U.S. Geological Survey conducted a survey of juvenile fisheries resources, in cooperation with the St. Johns River Water Management District and Volusia County, to establish baseline data on spatial and temporal distribution patterns of estuarine fish. The survey was conducted from November 2001 to March 2005 and the baseline data established for the survey in the Northern Coastal Basins were collected from January 2002 to December 2004. The study area included the bar-built estuaries ranging from just north of St. Augustine, Florida, south to Ponce de Leon Inlet. Sampling protocols developed by the Florida Fish and Wildlife Research Institute for their statewide Fisheries Independent Monitoring (FIM) program were replicated to allow for comparability with FIM program results. Samples were collected monthly from randomly selected stations based on a geographically stratified design. Finfish and selected invertebrates were collected using a 21.3-meter center-bag seine with a 3-millimeter mesh, and a 6.1-meter otter trawl with a 3-millimeter mesh liner. Total estimated fish and selected invertebrate densities were similar to estimates from FIM projects in adjacent areas and were characterized by similar dominant species. Preliminary analysis indicates that observed species distribution patterns were mainly a function of proximity to the three inlets within the study area. The two regions encompassing the northern Tolomato River and the Tomoka River and Basin are farthest from inlets and appear to function as oligohaline nursery areas. Those two areas had the greatest estimated densities of shellfish and juvenile sciaenid (drum) species associated with oligohaline waters (for example, Micropogonias undulatus, Sciaenops ocellatus and Cynoscion nebulosus). Samples near inlets, and between the two northern inlets, had greater estimated densities of species limited to euhaline waters, including juvenile clupeids collected at relatively high abundance and species of marine strays collected in low abundance. Based on correspondence analysis, seasonal variation dominated the ordination of seine samples and spatial variation dominated the ordination of trawl samples; this was due to differences in the number and timing of taxa found near inlets versus oligohaline regions. The absence of seagrass habitat in the Northern Coastal Basins is reflected by the absence of a seagrass-fish assemblage.

Scientific Investigations Report↗

USGS2016

Midcontinent Prairie-Pothole wetlands and climate change: An Introduction to the Supplemental Issue

The multitude of wetlands in the Prairie Pothole Region of North America forms one of Earth’s largest wetland complexes. The midcontinent location exposes this ecologically and economically important wetland system to a highly variable climate, markedly influencing ponded-water levels, hydroperiods, chemical characteristics, and biota of individual basins. Given their dominance on the landscape and recognized value, great interest in how projected future changes in climate will affect prairie-pothole wetlands has developed and spawned much scientific research. On June 2, 2015, a special symposium, “Midcontinent Prairie-Pothole Wetlands: Influence of a Changed Climate,” was held at the annual meeting of the Society of Wetland Scientists in Providence, Rhode Island, USA. The symposium’s twelve presenters covered a wide range of relevant topics delivered to a standing-room-only audience. Following the symposium, the presenters recognized the need to publish their presented papers as a combined product to facilitate widespread distribution. The need for additional papers to more fully cover the topic of prairie-pothole wetlands and climate change was also identified. This supplemental issue of Wetlands is the realization of that vision.

Prairie Pothole Region↗

USGS2025

Bridging theory and practice to inform seed selection for restoration

Introduction Land managers often face the critical decision of what plant materials to select for ecological restoration. Selection depends on factors that span ecological conditions and human interventions in the restoration process, which can strongly influence the recovery of a degraded ecosystem. Objectives To improve the seed selection process, we compared scientific literature and guidance from five federal agencies to bridge seed selection “theory” and “practice” in the interior western and central United States. Methods We extracted recurring themes and keywords associated with abiotic, biotic, land management, and producer practices that influence seed selection and analyzed their proportional use between agency guidance and scientific literature. Results We identified significant overlap between key concepts in guidance and literature, highlighting the interconnectedness between science and management. However, nuanced patterns emerged across seed selection themes, including more focus in the literature on local adaptation and genetic structure, ramifications of introducing gene flow and artificial selection during plant production, and provenancing strategies to address changing climatic conditions. In contrast, agency guidance focused on genetically appropriate and environmentally suitable seed selection and practical concerns, including seed cost, availability, and diversity. Seed selection studies in the literature were concentrated in the Great Basin and Colorado Plateau, scattered in the Great Plains, and were largely experimental. Conclusions Our review suggests new opportunities for co-production of science and decision-making frameworks among researchers, land managers, and seed producers to inform seed selection guidance for restoration.

Restoration Ecology↗

USGS2006

USGS Abandoned Mine Lands Research Presented at the NAAMLP Meeting in Billings, Mont., Sept. 25, 2006

The following talk was an invited presentation given at the National Association of Abandoned Mine Lands Programs meeting in Billings, Montana on Sept. 25, 2006. The objective of the talk was to outline the scope of the U.S. Geological Survey research, past, present and future, in the area of abandoned mine research. Two large Professional Papers have come out of our AML studies: Nimick, D.A., Church, S.E., and Finger, S.E., eds., 2004, Integrated investigations of environmental effects of historical mining in the Basin and Boulder mining districts, Boulder River watershed, Jefferson County, Montana: U.S. Geological Survey Professional Paper 1652, 524 p., 2 plates, 1 DVD, URL: http://pubs.er.usgs.gov/usgspubs/pp/pp1652 Church, S.E., von Guerard, Paul, and Finger, S.E., eds., 2006, Integrated Investigations of Environmental Effects of Historical Mining in the Animas River Watershed, San Juan County, Colorado: U.S. Geological Survey Professional Paper 1651, 1,096 p., 6 plates, 1 DVD (in press). Additional publications and links can be found on the USGS AML website at URL: http://amli.usgs.gov/ or are accessible from the USGS Mineral Resource Program website at URL: http://minerals.usgs.gov/.

Open-File Report↗

USGS2017

Synthesis of downstream fish passage information at projects owned by the U.S. Army Corps of Engineers in the Willamette River Basin, Oregon

The U.S. Army Corps of Engineers (USACE) operates the Willamette Valley Project (Project) in northwestern Oregon, which includes a series of dams, reservoirs, revetments, and fish hatcheries. Project dams were constructed during the 1950s and 1960s on rivers that supported populations of spring Chinook salmon ( Oncorhynchus tshawytscha ), winter steelhead ( O. mykiss ), and other anadromous fish species in the Willamette River Basin. These dams, and the reservoirs they created, negatively affected anadromous fish populations. Efforts are currently underway to improve passage conditions within the Project and enhance populations of anadromous fish species. Research on downstream fish passage within the Project has occurred since 1960 and these efforts are documented in numerous reports and publications. These studies are important resources to managers in the Project, so the USACE requested a synthesis of existing literature that could serve as a resource for future decision-making processes. In 2016, the U.S. Geological Survey conducted an extensive literature review on downstream fish passage studies within the Project. We identified 116 documents that described studies conducted during 1960–2016. Each of these documents were obtained, reviewed, and organized by their content to describe the state-of-knowledge within four subbasins in the Project, which include the North Santiam, South Santiam, McKenzie, and Middle Fork Willamette Rivers. In this document, we summarize key findings from various studies on downstream fish passage in the Willamette Project. Readers are advised to review specific reports of interest to insure that study methods, results, and additional considerations are fully understood.

Oregon↗

USGS2008

Climate simulation and flood risk analysis for 2008-40 for Devils Lake, North Dakota

Devils Lake and Stump Lake in northeastern North Dakota receive surface runoff from a 3,810-square-mile drainage basin, and evaporation provides the only major water loss unless the lakes are above their natural spill elevation to the Sheyenne River. In September 2007, flow from Devils Lake to Stump Lake had filled Stump Lake and the two lakes consisted of essentially one water body with an elevation of 1,447.1 feet, about 3 feet below the existing base flood elevation (1,450 feet) and about 12 feet below the natural outlet elevation to the Sheyenne River (1,459 feet). Devils Lake could continue to rise, causing extensive additional flood damages in the basin and, in the event of an uncontrolled natural spill, downstream in the Red River of the North Basin. This report describes the results of a study conducted by the U.S. Geological Survey, in cooperation with the Federal Emergency Management Agency, to evaluate future flood risk for Devils Lake and provide information for developing updated flood-insurance rate maps and planning flood-mitigation activities such as raising levees or roads. In about 1980, a large, abrupt, and highly significant increase in precipitation occurred in the Devils Lake Basin and elsewhere in the Northern Great Plains, and wetter-than-normal conditions have persisted through the present (2007). Although future precipitation is impossible to predict, paleoclimatic evidence and recent research on climate dynamics indicate the current wet conditions are not likely to end anytime soon. For example, there is about a 72-percent chance wet conditions will last at least 10 more years and about a 37-percent chance wet conditions will last at least 30 more years. A stochastic simulation model for Devils Lake and Stump Lake developed in a previous study was updated and used to generate 10,000 potential future realizations, or traces, of precipitation, evaporation, inflow, and lake levels given existing conditions on September 30, 2007, and randomly generated future duration of the current wet period. On the basis of the simulations, and assuming ice-free conditions and calm wind, the Devils Lake flood elevation for an annualized flood risk of 1 percent (analogous to a “100-year” riverine flood) was estimated to be 1,454.6 feet for a 10-year time horizon (2008–17). Therefore, without adjusting for wind or ice, a residence near Devils Lake at elevation 1,454.6 feet has the same chance of being flooded sometime during the next 10 years as a residence at the edge of the 100-year flood plain along a river. Adjusting for the effects of wind or ice, which will increase the flood elevations for many locations near the lakes, was not within the scope of this study.

North Dakota↗

USGS2006

Submarine landslides in the Santa Barbara Channel as potential tsunami sources

Recent investigations using the Monterey Bay Aquarium Research Institutes (MBARI) Remotely Operated Vehicles (ROVs) "Ventana" and "Tiburon" and interpretation of MBARI's EM 300 30 kHz multibeam bathymetric data show that the northern flank of the Santa Barbara Basin has experienced massive slope failures. Of particular concern is the large (130 km2) Goleta landslide complex located off Coal Oil Point near the town of Goleta, that measures 14.6-km long extending from a depth of 90 m to nearly 574 m deep and is 10.5 km wide. We estimate that approximately 1.75 km3 has been displaced by this slide during the Holocene. This feature is a complex compound submarine landslide that contains both surfical slump blocks and mud flows in three distinct segments. Each segment is composed of a distinct head scarp, down-dropped head block and a slide debris lobe. The debris lobes exhibit hummocky topography in the central areas that appear to result from compression during down slope movement. The toes of the western and eastern lobes are well defined in the multibeam image, whereas the toe of the central lobe is less distinct. Continuous seismic reflection profiles show that many buried slide debris lobes exist and comparison of the deformed reflectors with ODP Drill Site 149, Hole 893 suggest that at least 200 000 years of failure have occurred in the area (Fisher et al., 2005a). Based on our interpretation of the multibeam bathymetry and seismic reflection profiles we modeled the potential tsunami that may have been produced from one of the three surfical lobes of the Goleta slide. This model shows that a 10 m high wave could have run ashore along the cliffs of the Goleta shoreline. Several other smaller (2 km2 and 4 km2) slides are located on the northern flank of the Santa Barbara Basin, both to the west and east of Goleta slide and on the Concepcion fan along the western flank of the basin. One slide, named the Gaviota slide, is 3.8 km2, 2.6 km long and 1.7 km wide. A distinct narrow scar extends from near the eastern head wall of this slide for over 2 km eastward toward the Goleta slide and may represent either an incipient failure or a remnant of a previous failure. Push cores collected within the main head scar of this slide consisted of hydrogen sulfide bearing mud, possibly suggesting active fluid seepage and a vibra-core penetrated ???50 cm of recent sediment overlying colluvium or landslide debris confirming the age of ???300 years as proposed by Lee et al. (2004). However, no seeps or indications of recent movement were observed during our ROV investigation within this narrow head scar indicating that seafloor in the scar is draped with mud. ?? 2006 Author(s). This work is licensed under a Creative Commons License.

Natural Hazards and Earth System Sciences↗

USGS2022

A geophysical characterization of structure and geology of the Northern Granite Springs Valley Geothermal System, Northwestern Nevada

The northern Granite Springs Valley in northwestern Nevada is the focus of recent studies for its potential for hosting undiscovered geothermal resources. Although the area lacks definitive surface manifestations of an active hydrothermal system, previous studies identify this region as having potential for hosting a blind geothermal resource, based on elevated subsurface temperatures and a favorable structural framework of the area. As part of the Nevada Play Fairway Project, we conducted high resolution geophysical surveys to better characterize the valley’s geothermal resources. This included ground magnetic, gravity, magnetotelluric, and rock property studies aimed at mapping and modeling subsurface geology and structure. Various derivative and filtering methods were employed to delineate buried faults and contacts from gravity and magnetic data. A depth to basement gravity inversion reveals that the basin is deepest on the west side of the valley. Flanking the basin to the east is a prominent gravity high interpreted as an intra-basin horst. A new high-resolution ground magnetic survey reveals a prominent elongate NW-trending magnetic high, interpreted as an unexposed subsurface dike swarm situated near the boundary between the basin and horst and confined to basement. Geophysical models help constrain basin fill comprised of Cenozoic sediments and volcanic rocks. These overlie Mesozoic crystalline basement that, in the west, consists of Cretaceous granitic intrusives and, to the east, dominantly Mesozoic metasedimentary rocks. The contact between these basement lithologies is not certain but inferred to coincide with the geophysically mapped dike swarm. This is partly supported by the fact that the dikes, as projected along strike to the northwest, intersect the contact between the Cretaceous intrusions and older Mesozoic basement rocks to the north of the study area. Although the age of the inferred dike swarm is not known, the trend of the anomaly is consistent with some of the Tertiary dikes in the nearby Sahwave Range, suggesting emplacement predated or was coeval with early development of the basin. The coincidence of the geothermal system, horst, dike swarm, and terminating normal fault zone suggests that basin tectonics and hydrothermal activity were influenced by both pre-existing basement structure and recent deformation. This relationship may pertain more generally to other hydrothermal settings throughout the Great Basin. If so, future efforts focused on mapping basement geology and structure may prove important to understanding underlying structural controls on geothermal systems. This work is supporting the next phase of research involving additional 3D geophysical and geologic modeling under the U.S. Department of Energy funded INGENIOUS project. The focus of this new work is on the western flank and structural corners of the horst block, based on evidence from detailed geophysical structural mapping, new shallow temperature data, and detailed 3D geologic and geophysical modeling, all aimed at identifying sites for temperature gradient drilling that may intersect zones with sufficient permeability and temperature to support geothermal development.

Geothermal Resources Council Transactions↗

USGS2011

Defining conservation priorities for freshwater fishes according to taxonomic, functional, and phylogenetic diversity

To date, the predominant use of systematic conservation planning has been to evaluate and conserve areas of high terrestrial biodiversity. Although studies in freshwater ecosystems have received recent attention, research has rarely considered the potential trade-offs between protecting different dimensions of biodiversity and the ecological processes that maintain diversity. We provide the first systematic prioritization for freshwaters (focusing on the highly threatened and globally distinct fish fauna of the Lower Colorado River Basin, USA) simultaneously considering scenarios of: taxonomic, functional, and phylogenetic diversity; contemporary threats to biodiversity (including interactions with nonnative species); and future climate change and human population growth. There was 75% congruence between areas of highest conservation priority for different aspects of biodiversity, suggesting that conservation efforts can concurrently achieve strong complementarity among all types of diversity. However, sizable fractions of the landscape were incongruent across conservation priorities for different diversity scenarios, underscoring the importance of considering multiple dimensions of biodiversity and highlighting catchments that contribute disproportionately to taxonomic, functional, and phylogenetic diversity in the region. Regions of projected human population growth were not concordant with conservation priorities; however, higher human population abundance will likely have indirect effects on native biodiversity by increasing demand for water. This will come in direct conflict with projected reductions in precipitation and warmer temperatures, which have substantial overlap with regions of high contemporary diversity. Native and endemic fishes in arid ecosystems are critically endangered by both current and future threats, but our results highlight the use of systematic conservation planning for the optimal allocation of limited resources that incorporates multiple and complementary conservation values describing taxonomic, functional, and phylogenetic diversity.

Ecological Applications↗

USGS2019

Recruitment dynamics and reproductive ecology of Blue Sucker in Texas, with a focus on the Big Bend region of the Rio Grande

Blue Sucker Cycleptus elongatus is a state-listed threatened species in Texas and is considered vulnerable throughout its range. Once considered a single, wide-ranging species, blue suckers are now recognized as a complex of closely related, but genetically and morphologically distinct species within the genus Cycleptus , including an undescribed species within the Rio Grande Basin. Numerous factors likely are driving the decline of blue suckers in Texas, including flow alteration, water quality, habitat fragmentation, and changing land-use patterns, but it is not clear how these factors interact to influence the abundance and distribution of the species. Our research integrates a variety of methodologies to provide information critical to the conservation and management of Blue Sucker in the Sabine River (Texas and Louisiana) and Colorado River (Texas) and Rio Grande Blue Sucker Cycleptus sp. cf. elongatus in the Rio Grande. The objectives of this report are to 1) determine the habitat associations of the young-of-year (YOY) Rio Grande Blue Sucker; 2) assess the effects of flow regime on growth and recruitment of Blue Sucker in the lower Sabine River; and 3) examine differences in life-history traits of Blue Suckers and flow regime across river basins in Texas. This study is the first to quantitatively address the sequence of YOY blue sucker mesohabitat use and increases our understanding of early life history of blue suckers, and the results of this work will help to develop conservation and management strategies, e.g., prioritizing conservation areas, developing flow recommendation, etc., for blue suckers throughout their geographic distribution.

Texas↗

USGS2017

Rates of sediment supply to arroyos from upland erosion determined using in situ produced cosmogenic 10 Be and 26 Al

Using 10 Be and 26 Al measured in sediment and bedrock, we quantify rates of upland erosion and sediment supply to a small basin in northwestern New Mexico. This and many other similar basins in the southwestern United States have been affected by cycles of arroyo incision and backfilling several times in the past few millennia. The sediment generation (275 ± 65 g m −2 yr −1 ) and bedrock equivalent lowering rates (102 ± 24 m myr −1 ) we determine are sufficient to support at least three arroyo cycles in the past 3,000 years, consistent with rates calculated from a physical sediment budget within the basin and regional rates determined using other techniques. Nuclide concentrations measured in different sediment sources and reservoirs suggest that the arroyo is a good spatial and temporal integrator of sediment and associated nuclide concentrations from throughout the basin, that the basin is in steady-state, and that nuclide concentration is independent of sediment grain size. Differences between nuclide concentrations measured in sediment sources and reservoirs reflect sediment residence times and indicate that subcolluvial bedrock weathering on hillslopes supplies more sediment to the basin than erosion of exposed bedrock.

New Mexico↗

USGS2022

Reservoir attributes display cascading spatial patterns along river basins

Considering reservoirs as linear fragments in a basin's river network could improve understanding, predictability, and management efficiency. We looked for general cascading spatial patterns across five categories of reservoir attributes: land cover, morphology and hydrology, fish habitat, fish assemblages, and fisheries. Attributes were pulled from various databases for large reservoirs (>100 ha) located in the United States. 16 widely distributed river basins, each including a minimum of 15 large reservoirs, were selected for analysis. Using analysis of covariance with basin as the class variable, we tested each attribute as a linear function of catchment area, which is an index of reservoir position in the basin. The majority of reservoir attributes displayed log-linear patterns as catchment area increased, indicating that reservoirs act as members of a larger network just as river reaches do. Several patterns were detected including attributes with no apparent lengthwise arrangement along the basin; cascading spatial patterns in which attributes increase or decrease from upstream to downstream within a basin; and attributes that increase with catchment area in some basins, decrease in others, or may simply remain constant throughout the basin. We conclude that each pattern may have different implications for management, and that the effectiveness with which most management activities influence reservoirs is likely to increase or decrease along river basins.

Water Resources Research↗

USGS2020

Ensemble ShakeMaps for magnitude 9 earthquakes on the Cascadia Subduction Zone

We develop ensemble ShakeMaps for various magnitude 9 ( ⁠ M "> M M 9) earthquakes on the Cascadia megathrust. Ground‐shaking estimates are based on 30 M "> M M 9 Cascadia earthquake scenarios, which were selected using a logic‐tree approach that varied the hypocenter location, down‐dip rupture limit, slip distribution, and location of strong‐motion‐generating subevents. In a previous work, Frankel et al. (2018) used a hybrid approach (i.e., 3D deterministic simulations for frequencies < 1    Hz "> < 1 Hz <1 Hz and stochastic synthetics for frequencies > 1    Hz "> > 1 Hz >1 Hz ⁠ ) and uniform site amplification factors to create broadband seismograms from this set of 30 earthquake scenarios. Here, we expand on this work by computing site‐specific amplification factors for the Pacific Northwest and applying these factors to the ground‐motion estimates derived from Frankel et al. (2018) . In addition, we use empirical ground‐motion models (GMMs) to expand the ground‐shaking estimates beyond the original model extent of Frankel et al. (2018) to cover all of Washington State, Oregon, northern California, and southern British Columbia to facilitate the use of these ensemble ShakeMaps in region‐wide risk assessments and scenario planning exercises. Using this updated set of 30 M "> M M 9 Cascadia earthquake scenarios, we present ensemble ShakeMaps for the median, 2nd, 16th, 84th, and 98th percentile ground‐motion intensity measures. Whereas traditional scenario ShakeMaps are based on a single hypothetical earthquake rupture, our ensemble ShakeMaps take advantage of a logic‐tree approach to estimating ground motions from multiple earthquake rupture scenarios. In addition, 3D earthquake simulations capture important features such as strong ground‐motion amplification in the Pacific Northwest’s sedimentary basins, which are not well represented in the empirical GMMs that compose traditional scenario ShakeMaps. Overall, our results highlight the importance of strong‐motion‐generating subevents for coastal sites, as well as the amplification of long‐period ground shaking in deep sedimentary basins, compared with previous scenario ShakeMaps for Cascadia.

California, Oregon, Washington↗

USGS2007

Denitrification in the shallow ground water of a tile-drained, agricultural watershed

Nonpoint-source pollution of surface water by N is considered a major cause of hypoxia. Because Corn Belt watersheds have been identified as major sources of N in the Mississippi River basin, the fate and transport of N from midwestern agricultural watersheds have received considerable interest. The fate and transport of N in the shallow ground water of these watersheds still needs additional research. Our purpose was to estimate denitrification in the shallow ground water of a tile-drained, Corn Belt watershed with fine-grained soils. Over a 3-yr period, N was monitored in the surface and ground water of an agricultural watershed in central Illinois. A significant amount of N was transported past the tile drains and into shallow ground water. The ground water nitrate was isotopically heavier than tile drain nitrate, which can be explained by denitrification in the subsurface. Denitrifying bacteria were found at depths to 10 m throughout the watershed. Laboratory and push-pull tests showed that a significant fraction of nitrate could be denitrified rapidly. We estimated that the N denitrified in shallow ground water was equivalent to 0.3 to 6.4% of the applied N or 9 to 27% of N exported via surface water. These estimates varied by water year and peaked in a year of normal precipitation after 2 yr of below average precipitation. Three years of monitoring data indicate that shallow ground water in watersheds with fine-grained soils may be a significant N sink compared with N exported via surface water. ?? ASA, CSSA, SSSA.

Journal of Environmental Quality↗

USGS2023

Establishing big sagebrush seedlings on the Colorado Plateau

Factors such as soil type and precipitation vary across rangeland landscapes, and these factors affect restoration outcomes and ultimately mean that “one size fits all” management strategies are not effective across large, complex landscapes. Big sagebrush (Artemisia tridentata) is a foundational rangeland species that is important to wildlife habitat across the western U.S. On the Colorado Plateau, sagebrush is important browse for ungulates, such as mule deer and pronghorn, which motivates a great deal of restoration effort. However, most scientific knowledge of big sagebrush comes from the Great Basin, and we know much less about how to restore sagebrush on the Colorado Plateau, where soils and precipitation patterns are different and conditions are warmer and drier. This fact sheet describes research about establishing and restoring sagebrush seedlings on the Colorado Plateau.

Utah↗

USGS2020

Calcite precipitation in Lake Powell reduces alkalinity and total salt loading to the Lower Colorado River Basin

Reservoirs can retain and transform carbon, nitrogen, phosphorus, and silica, but less is known about their effects on other biogeochemically relevant solutes. The salinization of freshwater ecosystems is a growing concern in many regions, and the role of reservoirs in salinity transport is an important research frontier. Here, we examine how a large desert southwest reservoir, Lake Powell, has altered the downstream transport of total dissolved solids (TDSs) as well as the dominant cations and anions comprising the TDS pool ( , , and Ca 2+ ). Average downstream TDS concentrations have declined significantly since river impoundment and seasonal fluctuations in TDS concentrations have become more modulated, but year to year variation in TDS concentrations has remained similar. While some of the reductions in TDS concentration can be attributed to watershed management, we find that Lake Powell retains about 10% of the TDS loaded to the system (1991 Mg TDS d −1 ). Much of this retention is occurring in the forms of calcium and bicarbonate, likely via calcite precipitation, and is equivalent to an average burial of 522 mg C m −2 d −1 , thus reducing the alkalinity of downstream water. Flow‐weighted modeling suggests that, in the absence of Lake Powell, downstream salinity limits would be surpassed at the outflow to Lake Powell 41% of the time (vs. 0% of the time currently). Understanding the dominant mechanisms regulating solute transport through the reservoir is important given the relevance for downstream drinking water and irrigation concerns, biogeochemical cycling, and the high potential for reduced flows in the future.

Arizona, Colorado, New Mexico, Utah, Wyoming↗