Geology topics

Research about Idaho, Wyoming

Source-linked reports with geographic coverage including Idaho, Wyoming.

At least 19 recordsLinked to original sources

USGS2025

Heterogeneity of locked‐pasture snow conditions modulate habitat and movement choices of a facultative migrant

Habitat selection and movement are key mechanisms by which animals can respond to and potentially cope with highly variable environmental conditions. Optimal responses likely vary, however, depending on the severity and scope of conditions. We tested this hypothesis using a facultative migrant species, the Great Gray Owl ( Strix nebulosa ), which exhibits high inter- and intra-individual variation in the timing, direction, and distance of winter movements. Specifically, we evaluated whether episodic, spatiotemporally variable “locked-pasture” snow conditions, which restrict access to subnivean food, prompted shifts in habitat selection or long-distance movements by owls. We quantified the movement of 42 owls using global positioning system (GPS) data within the Greater Yellowstone Ecosystem, USA, during 2017–2022. We used a novel ecological application of SnowModel, a snow evolution modeling system, to estimate fine-scale, physical snow properties likely to influence access to prey. Variables included snow depth, snow crusts produced by wind, and ice crusts produced by melt-freeze and rain-on-snow events. Owls avoided heterogeneously distributed wind crusts via local shifts in habitat selection. More homogenous ice crusts elicited long-distance movements away from affected home ranges. Finally, owls employed both proximate shifts in habitat selection and long-distance movements to avoid deeper snow. Ultimately, owls exhibited behavioral flexibility in response to limiting snow conditions that can vary in terms of severity, spatial extent, and duration. Such behavioral responses determine species distribution, with implications for population and community dynamics in spatiotemporally variable systems. Understanding the effects of, and responses to, environmental controls is increasingly important given the scope of on-going global change.

Idaho, Wyoming↗

USGS2024

Estimating ungulate migration corridors from sparse movement data

Many ungulates migrate between distinct summer and winter ranges, and identifying, mapping, and conserving these migration corridors have become a focus of local, regional, and global conservation efforts. Brownian bridge movement models (BBMMs) are commonly used to empirically identify these seasonal migration corridors; however, they require location data sampled at relatively frequent intervals to obtain a robust estimate of an animal’s movement path. Fitting BBMMs to sparse location data violates the assumption of conditional random movement between successive locations, overestimating the area (and width) of a migration corridor when creating individual and population-level occurrence distributions, and precluding the use of low-frequency, or sparse, data in mapping migration corridors. In an effort to expand the utility of BBMMs to include sparse global positioning system (GPS) data, we propose an alternative approach to model migration corridors from sparse GPS data. We demonstrate this method using GPS data collected every 2 hours from four mule deer (Odocoileus hemionus) and four elk (Cervus canadensis) herds within Wyoming and Idaho. First, we used BBMMs to estimate a baseline corridor for the 2-hour data. We then subsampled the 2-hour data to one location every 12 hours (a proxy for sparse data) and fitted BBMMs to the 12-hour data using a fixed motion variance (FMV) value, instead of estimating the Brownian motion variance empirically. A range of FMV values was tested to identify the value that best approximated the baseline migration corridor. FMV values within a species-specific range (mule deer: 400–1,200 m2; elk: 600–1,600 m2) successfully delineated migration corridors similar to the 2-hour baseline corridors; overall, lower values delineated narrower corridors and higher values delineated wider corridors. Optimal FMV values of 800 m2 (mule deer) and 1,000 m2 (elk) decreased the inflation of the 12-hour corridors relative to the 2-hour corridors from traditional BBMMs. This FMV approach thus enables using sparse movement data to approximate realistic migration corridor dimensions, providing an important alternative when movement data are collected infrequently. This approach greatly expands the number of datasets that can be used for migration corridor mapping—a useful tool for management and conservation across the globe.

Idaho, Wyoming↗

USGS2023

Spatio-temporal clustering of post-caldera eruptions at Yellowstone caldera: Implications for volcanic hazards and pre-eruptive magma reservoir configuration

At least 28 rhyolitic lava flows, domes, and tuffs erupted within Yellowstone caldera following its formation 631 ka. Understanding the timing of intracaldera eruptions is essential for characterizing natural hazards posed by Yellowstone volcano. We present 40 Ar/ 39 Ar eruption ages for the Mallard Lake Member and Central Plateau Member of the Plateau Rhyolite, which comprise products from 22 eruptions spanning ~160 to ~70 ka. These eruptions occurred along two linear vent zones within Yellowstone caldera that appear to be extensions of major extracaldera normal faults. Eruptions took place in five brief clusters with group mean ages of 160.3±1.0 ka (2σ), 149.8±4.0 ka, 111.4±0.9 ka, 104.1±0.8 ka, and 70.8±0.7 ka. All mapped products within each informal group have indistinguishable 40 Ar/ 39 Ar eruption ages implying brief eruption durations. Eruption products of each group are spatially clustered, with only one of the two linear vent zones being active during an eruption group. Using the oldest group (160 ka), we apply paleomagnetic and geochemical analyses to investigate the duration of these eruption groups and their pre-eruptive magma reservoir configuration. Paleomagnetic analyses suggest that the nine rhyolite eruptions ~160 ka spanned 400 years or less. Glass and sanidine compositions of each rhyolite are nearly identical, which is consistent with pre-eruptive storage of a large (~130 km 3 ), interconnected melt body within Yellowstone volcano’s crystal-rich magma reservoir. These characteristics differ from intracaldera eruptions that vented near the caldera’s inner ring fracture system, which tend to be compositionally disparate with less temporal clustering. These insights inform hazard mitigation scenarios.

Idaho, Wyoming↗

USGS2023

Experimental manipulation of soil-surface albedo alters phenology and growth of Bromus tectorum (cheatgrass)

Purpose The sensitivity of wildland plants to temperature can be directly measured using experimental manipulations of temperature in situ. We show that soil surface temperature and plant density (per square meter) have a significant impact on the germination, growth, and phenology of Bromus tectorum L., cheatgrass, a short-statured invasive winter-annual grass, and assess a new experimental temperature manipulation method: the application of black and white gravel to warm and cool the soil surface. Methods We monitored height, seed production, and phenological responses of cheatgrass, seeded into colored gravel at low and high densities at two sites in the western USA: Boise, ID and Cheyenne, WY. Soil surface temperature and volumetric water content were measured to assess treatment effects on soil surface microclimate. Results Black gravel increased mean temperatures of the surface soil by 1.6 and 2.6 °C compared to white gravel in Cheyenne and Boise, respectively, causing 21–24 more days with soil temperatures > 0 °C, earlier cheatgrass germination, and up to 2.8-fold increases in cheatgrass height. Higher seeding density of cheatgrass led to 1.4-fold taller plants on black gravel plots at both sites, but not white gravel at the Boise site, indicating a possible thermal benefit or reduction of water demand due to plant clustering in warmer treatments. Conclusions Manipulating soil-surface albedo altered the soil microclimate and thus growth and phenology of cheatgrass, whose life history and growth form confer a strong dependency on soil-surface conditions.

Idaho, Wyoming↗

USGS2022

A statistical framework for modelling migration corridors

1. Management of animal populations requires spatially explicit knowledge of movement corridors, such as those used during seasonal migrations. GPS tracking data allows for mapping of corridors from directly observed movements, providing important insights, but tracking data is absent for many populations. 2. We developed a novel statistical corridor modeling approach that predicts movement corridors from cost-distance movement models fit directly to migration tracking data. Unlike existing predictive approaches, this does not require the ad-hoc transformation of habitat suitability surfaces into resistance surfaces. We tested the ability of the approach to recover parameters used to generate simulated movements. We then used GPS data from three migrating mule deer (Odocoileus hemionus) herds in Idaho and Wyoming to model corridors as a function of elevation, slope, aspect, percent shrub, date of peak green-up, snow-off date, and human footprint. We assessed the predictive ability of the fitted models using validation tracks from the same herd as well as from the other herds. 3. The approach reproduced parameters used to generate the simulated movements, predicted the corridors used by migratory populations, and described the direction, magnitude, and confidence levels of the effects of environmental variables on corridors. The effects environmental variables had on corridors differed depending on the herd. Within-herd validation indicated that fitted corridor models are more accurate at predicting migration corridors than null models, and cross-herd validation indicated that fitted models for some herds accurately predicted the observed migrations of other herds. 4. In addition to the practical benefit of mapping corridors for management, our statistical corridor modeling framework sets the stage for evaluating fundamental questions about the fitness tradeoffs, navigation, learning, fidelity, and movement constraints that influence migratory and other corridor-generating behavior. Models of predictive corridors can inform management and planning for the conservation of migrations across taxa, including the potential restoration of corridors. Our corridor modeling approach is also readily applied to non-migratory animal movements.

Idaho, Wyoming↗

USGS2022

Geophysical imaging of the Yellowstone hydrothermal plumbing system

The nature of Yellowstone National Park’s plumbing system linking deep thermal fluids to its legendary thermal features is virtually unknown. The prevailing concepts of Yellowstone hydrology and chemistry are that fluids reside in reservoirs with unknown geometries, flow laterally from distal sources and emerge at the edges of lava flows . Here we present a high-resolution synoptic view of pathways of the Yellowstone hydrothermal system derived from electrical resistivity and magnetic susceptibility models of airborne geophysical data . Groundwater and thermal fluids containing appreciable total dissolved solids significantly reduce resistivities of porous volcanic rocks and are differentiated by their resistivity signatures . Clay sequences mapped in thermal areas and boreholes typically form at depths of less than 1,000 metres over fault-controlled thermal fluid and/or gas conduits . We show that most thermal features are located above high-flux conduits along buried faults capped with clay that has low resistivity and low susceptibility. Shallow subhorizontal pathways feed groundwater into basins that mixes with thermal fluids from vertical conduits. These mixed fluids emerge at the surface, controlled by surficial permeability, and flow outwards along deeper brecciated layers. These outflows, continuing between the geyser basins, mix with local groundwater and thermal fluids to produce the observed geochemical signatures. Our high-fidelity images inform geochemical and groundwater models for hydrothermal systems worldwide.

Idaho, Wyoming↗

USGS2021

The interactive effects of stream temperature, stream size, and non-native species on Yellowstone cutthroat trout

Climate change and non-native species are considered two of the biggest threats to native salmonids in North America. We evaluated how non-native salmonids and stream temperature and discharge were associated with Yellowstone cutthroat trout ( Oncorhynchus clarkii bouvieri ) distribution, abundance, and body size to gain a more complete understanding of the existing threats to native populations. Allopatric Yellowstone cutthroat trout were distributed across a wide range of average August temperatures (3.2 to 17.7 °C), but occurrence significantly declined at colder temperatures (<10 °C) with increasing numbers of non-natives. At warmer temperatures, occurrence remained high, despite sympatry with non-natives. Yellowstone cutthroat trout relative abundance was significantly reduced with increasing abundance of non-natives, with the greatest impacts at colder temperatures. Body sizes of large Yellowstone cutthroat trout (90th percentile) significantly increased with warming temperatures and larger stream size, highlighting the importance of access to these more productive stream segments. Considering multiple population-level attributes demonstrates the complexities of how native salmonids (such as Yellowstone cutthroat trout) are likely to be affected by shifting climates.

Idaho, Wyoming↗

USGS2018

Proactive Rainbow Trout suppression reduces threat of hybridization in the Upper Snake River Basin

Preserving remaining nonhybridized populations Cutthroat Trout Oncorhynchus clarkii is a conservation priority often requiring management action. Although proactive programs for Rainbow Trout O. mykiss and hybrid suppression offer a flexible tool, particularly in large interconnected river basins, this management approach is used less frequently than alternatives such as barriers and piscicides. We describe the results of a targeted Rainbow Trout hybrid suppression program spanning 15 years in the upper Snake River, Wyoming, a core stronghold for Yellowstone Cutthroat Trout O. clarkii bouvieri . Initially, Rainbow Trout hybrids were relatively common in the Gros Ventre River, a major tributary to the Snake River. Between 2002 and 2016, 926 individuals of Rainbow Trout ancestry were removed from the Gros Ventre River. Relative abundance of Rainbow Trout hybrids decreased over this time, while the Yellowstone Cutthroat Trout population increased. Temporal genetic data collected in 2007–2008 and again in 2014 demonstrate that the overall proportion Rainbow Trout admixture and the proportion of hybrids in a sample both significantly decreased in the Gros Ventre River and did not increase elsewhere in the Snake River basin. In conclusion, proactive Rainbow Trout suppression appears to have reduced the threat of Rainbow Trout hybridization in this river basin and helped protect an interconnected metapopulation that has a highly diverse life history and genetic variation important for long-term persistence.

Idaho, Wyoming↗

USGS2018

The timing and origin of pre- and post-caldera volcanism associated with the Mesa Falls Tuff, Yellowstone Plateau volcanic field

We present new sanidine 40 Ar/ 39 Ar ages and paleomagnetic data for pre- and post-caldera rhyolites from the second volcanic cycle of the Yellowstone Plateau volcanic field, which culminated in the caldera-forming eruption of the Mesa Falls Tuff at ca. 1.3 Ma. These data allow for a detailed reconstruction of the eruptive history of the second volcanic cycle and provide new insights into the petrogenesis of rhyolite domes and flows erupted during this time period. 40 Ar/ 39 Ar age data for the biotite-bearing Bishop Mountain flow demonstrate that it erupted approximately 150 kyr prior to the Mesa Falls Tuff. Integrating 40 Ar/ 39 Ar ages and paleomagnetic data for the post-caldera Island Park rhyolite domes suggests that these five crystal-rich rhyolites erupted over a centuries-long time interval at 1.2905 ± 0.0020 Ma (2σ). The biotite-bearing Moonshine Mountain rhyolite dome was originally thought to be the downfaulted vent dome for the pre-caldera Bishop Mountain flow due to their similar petrographic and oxygen isotope characteristics, but new 40 Ar/ 39 Ar dating suggest that it erupted near contemporaneously with the Island Park rhyolite domes at 1.2931 ± 0.0018 Ma (2σ) and is a post-caldera eruption. Despite their similar eruption ages, the Island Park rhyolite domes and the Moonshine Mountain dome are chemically and petrographically distinct and are not derived from the same source. Integrating these new data with field relations and existing geochemical data, we present a petrogenetic model for the formation of the post-Mesa Falls Tuff rhyolites. Renewed influx of basaltic and/or silicic recharge magma into the crust at 1.2905 ± 0.0020 Ma led to [1] the formation of the Island Park rhyolite domes from the source region that earlier produced the Mesa Falls Tuff and [2] the formation of Moonshine Mountain dome from the source region that earlier produced the biotite-bearing Bishop Mountain flow. These magmas were stored in the crust for less than a few thousand years before being erupted contemporaneously along a 30 km long, structurally controlled vent zone related to extracaldera Basin and Range faults. These data highlight the rapidity with which magma can be generated and erupted over large distances at Yellowstone.

Idaho, Wyoming↗

USGS2018

Is ungulate migration culturally transmitted? Evidence of social learning from translocated animals

Ungulate migrations are assumed to stem from learning and cultural transmission of information regarding seasonal distribution of forage, but this hypothesis has not been tested empirically. We compared the migratory propensities of bighorn sheep and moose translocated into novel habitats with those of historical populations that had persisted for hundreds of years. Whereas individuals from historical populations were largely migratory, translocated individuals initially were not. After multiple decades, however, translocated populations gained knowledge about surfing green waves of forage (tracking plant phenology) and increased their propensity to migrate. Our findings indicate that learning and cultural transmission are the primary mechanisms by which ungulate migrations evolve. Loss of migration will therefore expunge generations of knowledge about the locations of high-quality forage and likely suppress population abundance.

Idaho, Wyoming↗

USGS2017

Assessment of a strain 19 brucellosis vaccination program in elk

Zoonotic diseases in wildlife present substantial challenges and risks to host populations, susceptible domestic livestock populations, and affected stakeholders. Brucellosis, a disease caused by the bacterium Brucella abortus , is endemic among elk ( Cervus canadensis ) attending winter feedgrounds and adjacent areas of western Wyoming, USA. To minimize transmission of brucellosis from elk to elk and elk to livestock, managers initiated a B. abortus strain 19 ballistic vaccination program in 1985. We used brucellosis prevalence (1971–2015) and reproductive outcome (2006–2015) data collected from female elk attending feedgrounds to assess efficacy of the strain 19 program while controlling for potentially confounding factors such as site and age. From our generalized linear models, we found that seroprevalence of brucellosis was 1) not lower following inception of vaccination; 2) not inversely associated with proportion of juveniles vaccinated over time; 3) not inversely associated with additional yearlings and adults vaccinated over time; and 4) associated more with feeding end-date than proportion of juveniles vaccinated. Using vaginal implant transmitters in adult females that were seropositive for brucellosis, we found little effect of vaccination coverage at reducing reproductive failures (i.e., abortion or stillbirth). Because we found limited support for efficacy of the strain 19 program, we support research to develop an oral vaccine and suggest that continuing other spatio-temporal management actions will be most effective to minimize transmission of brucellosis and reduce dependency of elk on supplemental winter feeding.

Idaho, Wyoming↗

USGS2015

Mechanisms and timescales of generating eruptible rhyolitic magmas at Yellowstone caldera from zircon and sanidine geochronology and geochemistry

We constrain the physical nature of the magma reservoir and the mechanisms of rhyolite generation at Yellowstone caldera via detailed characterization of zircon and sanidine crystals hosted in three rhyolites erupted during the (ca. 170 – 70 ka) Central Plateau Member eruptive episode – the most recent post-caldera magmatism at Yellowstone. We present 238U-230Th crystallization ages and trace-element compositions of the interiors and surfaces (i.e., unpolished rims) of individual zircon crystals from each rhyolite. We compare these zircon data to 238U- 230Th crystallization ages of bulk sanidine separates coupled with chemical and isotopic data from single sanidine crystals. Zircon age and trace-element data demonstrate that the magma reservoir that sourced the Central Plateau Member rhyolites was long-lived (150 – 250 kyr) and genetically related to the preceding episode of magmatism, which occurred ca. 256 ka. The interiors of most zircons in each rhyolite were inherited from unerupted material related to older stages of Central Plateau Member magmatism or the preceding late Upper Basin Member magmatism (i.e., are antecrysts). Conversely, most zircon surfaces crystallized near the time of eruption from their host liquids (i.e., are autocrystic). The repeated recycling of zircon interiors from older stages of magmatism demonstrates that sequentially erupted Central Plateau Member rhyolites are genetically related. Sanidine separates from each rhyolite yield 238U-230Th crystallization ages at or near the eruption age of their host magmas, coeval with the coexisting zircon surfaces, but are younger than the coexisting zircon interiors. Chemical and isotopic data from single sanidine crystals demonstrate that the sanidines in each rhyolite are in equilibrium with their host melts, which considered along with their near-eruption crystallization ages suggests that nearly all CPM sanidines are autocrystic. The paucity of antecrystic sanidine crystals relative to antecrystic zircons require a model where eruptible rhyolites are generated by extracting melt and zircons from a long-lived mush of immobile crystal-rich magma. In this process the larger sanidine crystals remain trapped in the locked crystal network. The extracted melts (plus antecrystic zircon) amalgamate into a liquid dominated (i.e., eruptible) magma body that is maintained as a physically distinct entity relative to the bulk of the long-lived crystal mush. Zircon surfaces and sanidines in each rhyolite crystallize after melt extraction/amalgamation and their ages constrain the residence time of eruptible magmas at Yellowstone. Residence times of the large volume rhyolites (~40 – 70 km3) are ≤ 1 kyr (conservatively < 6 kyr), which suggests that large volumes of rhyolite can be generated rapidly by extracting melt from a crystal mush. Because the lifespan of the crystal mush that sourced the Central Plateau Member rhyolites is two orders of magnitude longer than the residence time of eruptible magma bodies within the reservoir, it is apparent that the Yellowstone magma reservoir spends most of its time in a largely-crystalline (i.e., uneruptible) state, similar to the present-day magma reservoir, and that eruptible magma bodies are ephemeral features.

Idaho, Wyoming↗

USGS2015

Detection probabilities of electrofishing, hoop nets, and benthic trawls for fishes in two western North American rivers

Research comparing different sampling techniques helps improve the efficiency and efficacy of sampling efforts. We compared the effectiveness of three sampling techniques (small-mesh hoop nets, benthic trawls, boat-mounted electrofishing) for 30 species in the Green (WY, USA) and Kootenai (ID, USA) rivers by estimating conditional detection probabilities (probability of detecting a species given its presence at a site). Electrofishing had the highest detection probabilities (generally greater than 0.60) for most species (88%), but hoop nets also had high detectability for several taxa (e.g., adult burbot Lota lota , juvenile northern pikeminnow Ptychocheilus oregonensis ). Benthic trawls had low detection probabilities (<0.05) for most taxa (84%). Gear-specific effects were present for most species indicating large differences in gear effectiveness among techniques. In addition to gear effects, habitat characteristics also influenced detectability of fishes. Most species-specific habitat relationships were idiosyncratic and reflected the ecology of the species. Overall findings of our study indicate that boat-mounted electrofishing and hoop nets are the most effective techniques for sampling fish assemblages in large, coldwater rivers.

Idaho, Wyoming↗

USGS2008

Track of the Yellowstone hotspot: Young and ongoing geologic processes from the Snake River Plain to the Yellowstone Plateau and Tetons

This field trip highlights various stages in the evolution of the Snake River Plain–Yellowstone Plateau bimodal volcanic province, and associated faulting and uplift, also known as the track of the Yellowstone hotspot. The 16 Ma Yellowstone hotspot track is one of the few places on Earth where time-transgressive processes on continental crust can be observed in the volcanic and tectonic (faulting and uplift) record at the rate and direction predicted by plate motion. Recent interest in young and possible renewed volcanism at Yellowstone along with new discoveries and synthesis of previous studies, i.e., tomographic, deformation, bathymetric, and seismic surveys, provide a framework of evidence of plate motion over a mantle plume. This 3-day trip is organized to present an overview into volcanism and tectonism in this dynamically active region. Field trip stops will include the young basaltic Craters of the Moon, exposures of 12–4 Ma rhyolites and edges of their associated collapsed calderas on the Snake River Plain, and exposures of faults which show an age progression similar to the volcanic fields. An essential stop is Yellowstone National Park, where the last major caldera-forming event occurred 640,000 years ago and now is host to the world's largest concentration of hydrothermal features (>10,000 hot springs and geysers). This trip presents a quick, intensive overview into volcanism and tectonism in this dynamically active region. Field stops are directly linked to conceptual models related to hotspot passage through this volcano-tectonic province. Features that may reflect a tilted thermal mantle plume suggested in recent tomographic studies will be examined. The drive home will pass through Grand Teton National Park, where the Teton Range is currently rising in response to the passage of the North American plate over the Yellowstone hotspot.

Idaho, Wyoming↗

USGS2005

Calibration of the DRASTIC ground water vulnerability mapping method

Ground water vulnerability maps developed using the DRASTIC method have been produced in many parts of the world. Comparisons of those maps with actual ground water quality data have shown that the DRASTIC method is typically a poor predictor of ground water contamination. This study significantly improved the effectiveness of a modified DRASTIC ground water vulnerability map by calibrating the point rating schemes to actual ground water quality data by using nonparametric statistical techniques and a geographic information system. Calibration was performed by comparing data on nitrite plus nitrate as nitrogen (NO 2 + NO 3 -N) concentrations in ground water to land-use, soils, and depth to first-encountered ground water data. These comparisons showed clear statistical differences between NO 2 + NO 3 -N concentrations and the various categories. Ground water probability point ratings for NO 2 + NO 3 -N contamination were developed from the results of these comparisons, and a probability map was produced. This ground water probability map was then correlated with an independent set of NO 2 + NO 3 -N data to demonstrate its effectiveness in predicting elevated NO 2 + NO 3 -N concentrations in ground water. This correlation demonstrated that the probability map was effective, but a vulnerability map produced with the uncalibrated DRASTIC method in the same area and using the same data layers was not effective. Considerable time and expense have been outlaid to develop ground water vulnerability maps with the DRASTIC method. This study demonstrates a cost-effective method to improve and verify the effectiveness of ground water vulnerability maps.

Idaho, Wyoming↗

USGS1997

Nitrate (NO2+NO3–N) in ground water of the Upper Snake River basin, Idaho and western Wyoming, 1991–95

Factors related to contamination of ground water by dissolved nitrite plus nitrate as nitrogen (NO 2 +NO 3 -N) in parts of the upper Snake River Basin were evaluated at regional and local scales. Regional-scale relations between NO 2 +NO 3 -N concentrations and depth to first-encountered ground water, land use, precipitation, and soils were evaluated using a geographic information system. Local-scale relations between NO 2 +NO 3 -N concentrations and other nutrients, major ions, nitrogen isotopes, stable isotopes, and tritium in five areas with different hydrogeologic settings, land use, and sources of irrigation water were evaluated to determine the factors causing differences in NO 2 +NO 3 -N. Data were collected and analyzed as part of the U.S. Geological Survey's National Water-Quality Assessment Program, which began in 1991.

Idaho, Wyoming↗

USGS1995

Water-quality assessment of the upper Snake River Basin, Idaho and western Wyoming — Environmental setting, 1980-92

The 35,800-square-mile upper Snake River Basin is one of 20 areas studied as part of the National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey. Objectives of NAWQA are to study ground- and surface-water quality, biology, and their relations to land-use activities. Major land and water uses that affect water quality in the basin are irrigated agriculture, grazing, aquaculture, food processing, and wastewater treatment. Data summarized in this report are used in companion reports to help define the relations among land use, water use, water quality, and biological conditions. The upper Snake River Basin is located in southeastern Idaho and northwestern Wyoming and includes small parts of Nevada and Utah. Total population in the basin was about 425,000 in 1990. Major urban areas are Idaho Falls, Pocatello, Rexburg, and Twin Falls, Idaho, which make up 10, 11,3, and 6 percent of the total population, respectively. Climate in the basin is mostly semiarid and mean annual precipitation ranges from 8 to more than 60 inches. The eastern Snake River Plain is the major geologic feature in the basin and is delineated mostly by Quaternary and Tertiary basalt flows. It is about 55 to 62 miles wide and 320 miles long and bisects the basin in a northeast-southwest direction. The Snake River is the dominant surface-water feature and flows about 453 miles from the southern border of Yellowstone National Park in Wyoming to King Hill, Idaho, where it leaves the basin. The Snake River flows through five reservoirs that provide a total storage capacity of more than 4 million acre-feet. Gravity-flow diversions are predominant in the upper part of the basin and totaled 8.8 million.acre-feet in 1980. Pumped diversions occur mainly in the lower part of the basin and totaled 408,500 acre-feet in 1980. The Snake River Plain aquifer is the predominant ground-water feature in the upper Snake River Basin and underlies the eastern Snake River Plain. The upper 500 feet of the aquifer may store 200 to 300 million acre-feet of water. Ground-water resources that supply agricultural lands are sustained by recharge from surface-water irrigation, precipitation, and tributary inflow. Major ground-water discharges are at springs and seeps or from ground-water pumpage for irrigation. Water use in the basin is dominated by irrigated agriculture, which is the largest consumptive water use in the basin. Major crops in the basin include potatoes, wheat, sugar beets, hay, and barley. Most irrigation needs are supplied from surface-water sources through a series of canals and laterals. In 1990, about 2.5 million acres were irrigated with more than 14.2 million acre-feet of surface and ground water. About 21 percent of the basin is agricultural land and 50 percent is rangeland. Idaho leads the Nation in trout production for commercial sale. Combined mean annual discharges from 12 aquacultural facilities in the basin (1985-90) were about 787,000 acre-feet. These facilities are clustered in a reach of the Snake River between Milner Dam and King Hill where ground-water discharge is from many seeps and springs that provide sufficient quantities of good-quality water. Other facilities that release effluent to the Snake River include 13 municipal wastewater treatment plants and 3 industrial facilities.

Idaho, Wyoming↗

USGS1995

Water-quality assessment of the upper Snake River Basin, Idaho and western Wyoming — Summary of aquatic biological data for surface water through 1992

The 35,800-square-mile upper Snake River Basin in eastern Idaho and western Wyoming was one of 20 areas selected for water-quality study under the National Water-Quality Assessment Program. As part of the initial phase of the study, data were compiled to describe the current (1992) and historical aquatic biological conditions of surface water in the basin. This description of natural and human environmental factors that affect aquatic life provides the framework for evaluating the status and trends of aquatic biological conditions in streams of the basins. Water resource development and stream alterations, irrigated agriculture, grazing, aquaculture, and species introductions have affected stream biota in the upper Snake River Basin. Cumulative effects of these activities have greatly altered cold-water habitat and aquatic life in the middle Snake River reach (Milner Dam to King Hill). Most of the aquatic Species of Special Concern in the basin , consisting of eight native mollusks and three native fish species, are in this reach of the Snake River. Selected long-term studies, including comprehensive monitoring on Rock Creek, have shown reduced pollutant loadings as a result of implementing practice on cropland; however, aquatic life remains affected by agricultural land use. Community level biological data are lacking for most of the streams in the basin, especially for large river. Aquatic life used to assess water quality of the basin includes primarily macroinvertebrate and fish communities. At least 26 different macroinvertebrate and fish community metrics have been utilized to assess water quality of the basin. Eight species of macroinvertebrates and fish are recognized as Species of Special Concern. The native fish faunas of the basin are composed primarily of cold-water species representing 5 families and 26 species. An additional 13 fish species have been introduced to the basin. Concentrations of synthetic organic compounds and trace-element contaminants in whole fish collected in the basin during 1970-90 generally did not exceed National Academy of Sciences and National Academy of Engineering concentration guidelines or the 1980-81 geometric mean concentrations from samples collected as part of the U.S. Fish and Wildlife Service National Contaminant Biomonitoring Program. Currently, there are no State fish consumption advisories on any streams in the basin, The organochlorine compounds DDT and PCB's were the most frequently detected fish tissue contaminant. Selected long-term data on DDT, its metabolites, and PCB's indicate decreasing concentrations of these compounds. Arsenic, mercury, and selenium were slightly elevated compared with nationwide baseline concentrations and may indicate bioaccumularion in the food chain. Concentrations of most other trace elements in fish tissue were below levels of concerns for the protection of humans and wildlife.

Idaho, Wyoming↗