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At least 1,189 records · Page 66Linked to original sources

USGS1997

Influence of basin-scale physical variables on life history characteristics of cutthroat trout in Yellowstone Lake

Individual spawning populations of Yellowstone cutthroat trout Oncorhynchus clarki bouvieri differ in life history characteristics associated with broad spatial and temporal environmental patterns, but relationships between specific life history characteristics of Yellowstone cutthroat trout and physical aspects of the environment are poorly understood. We examined basin-scale physical characteristics of tributary drainages and subbasins of Yellowstone Lake in relation to timing (peak and duration) of lacustrine–adfluvial Yellowstone cutthroat trout spawning migrations and mean length of cutthroat trout spawners in 27 tributaries to the lake. Stream drainages varied along gradients that can be described by mean aspect, mean elevation, and drainage and stream size. Approximately two-thirds of the variation in the timing of the peak of the annual cutthroat trout spawning migrations and average length of spawners was explained by third-order polynomial regressions with mean aspect and basin area as predictor variables. Because most cutthroat trout ascend tributaries soon after peak runoff, it appears that the influence of basin-scale physical variables on the date of the migration peak is manifested by the pattern of stream discharge. Spawner length does not seem to be a direct function of stream size in the Yellowstone Lake watershed, and aspect of the tributary basin seems to have a greater influence on the body length of cutthroat trout spawners than does stream size. Mechanisms that explain how the interaction of basin-scale physical variables influence spawner length were not investigated directly; however, we found evidence of distinct aggregations of cutthroat trout that are related to physical and limnological characteristics of the lake subbasins, and there is some indication that lake residence may be related to tributary location.

Wyoming↗

USGS2010

The quality of our nation's waters: Nutrients in the nation's streams and groundwater, 1992-2004

National Findings and Their Implications Although the use of artificial fertilizer has supported increasing food production to meet the needs of a growing population, increases in nutrient loadings from agricultural and, to a lesser extent, urban sources have resulted in nutrient concentrations in many streams and parts of aquifers that exceed standards for protection of human health and (or) aquatic life, often by large margins. Do NAWQA findings substantiate national concerns for aquatic and human health? National Water-Quality Assessment (NAWQA) findings indicate that nutrient concentrations in streams and groundwater in basins with significant agricultural or urban development are substantially greater than naturally occurring or “background” levels. For example, median concentrations of total nitrogen and phosphorus in agricultural streams are about 6 times greater than background levels. Findings also indicate that concentrations in streams routinely were 2 to 10 times greater than regional nutrient criteria recommended by the U.S. Environmental Protection Agency (USEPA) to protect aquatic life. Such large differences in magnitude suggest that significant reductions in sources of nutrients, as well as greater use of land management strategies to reduce the transport of nutrients to streams, are needed to meet recommended criteria for streams draining areas with significant agricultural and urban development. Nitrate concentrations above the Federal drinking-water standard—or Maximum Contaminant Level (MCL)—of 10 milligrams per liter (mg/L, as nitrogen) are relatively uncommon in samples from streams used for drinking water or from relatively deep aquifers; the MCL is exceeded, however, in more than 20 percent of shallow (less than 100 feet below the water table) domestic wells in agricultural areas. This finding raises concerns for human health in rural agricultural areas where shallow groundwater is used for domestic supply and may warn of future contamination of deeper groundwater pumped from public‑supply wells. Are levels of nutrients in water increasing or decreasing? A decadal assessment of trends in concentrations of nitrogen and phosphorus from about 1993 to 2003 shows minimal changes in those concentrations in the majority of studied streams across the Nation, and more upward than downward trends in concentrations at sites with changes. These findings underscore the need for reductions in nutrient inputs or management strategies that would reduce transport of nutrients to streams. Upward trends were evident among all land uses, including those only minimally affected by agricultural and (or) urban development, which suggests that additional protection of some of our Nation’s most pristine streams warrants consideration. The median of nitrate concentrations in groundwater from 495 wells also increased significantly from 3.2 to 3.4 mg/L (6 percent) during about the same period, and the proportion of wells with concentrations of nitrate greater than the MCL increased from 16 to 21 percent. Nitrate concentrations in water in deep aquifers are likely to increase during the next decade as shallow groundwater with elevated concentrations moves downward. The potential for future contamination of the deep aquifers requires attention because these aquifers commonly are used for public water supply, and because restoration of groundwater is costly and difficult. Long-term and consistent monitoring of nutrients, improved accounting of nutrient sources, and improved tracking and modeling of climatic and landscape changes will be essential for distinguishing trends in nutrient concentrations, understanding the causes of those trends, and accurately tracking the effectiveness of strategies implemented to manage nutrients.

Circular↗

USGS2018

Geochemical conditions and nitrogen transport in nearshore groundwater and the subterranean estuary at a Cape Cod embayment, East Falmouth, Massachusetts, 2013–14

Nitrogen transport and transformation were studied during 2013 to 2014 by the U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, in a subterranean estuary beneath onshore locations on the Seacoast Shores peninsula, a residential area in Falmouth, Massachusetts, served by septic systems and cesspools, and adjacent offshore locations in the Eel River, a saltwater embayment connected to the ocean. The field investigation included installation and sampling of clusters of wells and temporary sampling points near a transect extending from about 35 meters (m) onshore to 18 m offshore. The fresh groundwater at the study site formed a lens about 11 m thick at the shoreline that was underlain by saline groundwater. Groundwater flow in the water-table aquifer was oriented northwestward toward the embayment. Nitrate concentrations in the fresh groundwater at a site about 35 m onshore increased in the downward direction from less than 500 micromoles per liter near the water table to about 1,700 micromoles per liter just above the freshwater/saltwater transition zone. Dissolved oxygen was largely absent in the onshore fresh groundwater. Distributions of salinity, dissolved oxygen, and nitrate at the shoreline and offshore generally were similar to those onshore; at some locations, however, shallow saline water was present above the freshwater, and there were scattered occurrences of elevated dissolved oxygen concentrations. Geochemical indicators of nitrate reduction, including concentrations of the reaction product nitrogen gas, stable isotope ratios of nitrate and nitrogen gas, and changes in alkalinity, provided evidence for nitrate reduction in two zones separated vertically by a zone 7–8 m thick with no evidence of nitrate reduction. The shallow nitrate-reduction zone was near the water table in fresh groundwater onshore, where nitrate reduction may be related to particular recharge conditions at nearby sources. The shallow nitrate-reduction zone also may be related to an interval of fine-grained sediments at about the same altitude (−1 to −6 m relative to the National Geodetic Vertical Datum of 1929), where flow is slower and reactive electron donors such as solid organic carbon, iron, or sulfide phases may be present to drive the reduction. The deep nitrate-reduction zone was near the freshwater/saltwater transition zone, where nitrate reduction may be related to mixing of freshwater containing nitrate and saltwater containing dissolved organic carbon and ammonium, or to fine-grained sediments near the transition zone. The maximum amount of nitrate converted to nitrogen gas was estimated to be less than or equal to 300 micromoles per liter in both nitrate-reduction zones. The presence of nitrate and low dissolved oxygen concentrations in the 7–8-meter-thick zone between the shallow and deep nitrate-reduction zones are conditions that could permit nitrate reduction. The absence of evidence of nitrate reduction in the high-nitrate zone may have resulted from the lack of reactive electron donors in that depth interval. The high-nitrate zone dissipated somewhat in the offshore direction, but the current study did not extend far enough to encompass the fresh groundwater discharge area or determine how much of the nitrate was removed prior to discharge. A shallow intertidal saltwater cell was formed during a spring tide by saltwater infiltration during tidal run-up on the beach. Nitrate reduction might have occurred if nitrate-containing fresh groundwater discharging to the estuary mixed with the saltwater containing dissolved organic carbon in this zone, but samples collected from the intertidal saltwater cell during this study were not analyzed for indicators of nitrate reduction. Elevated dissolved oxygen concentrations in fresh groundwater 9 m offshore may indicate that groundwater flow was partly oblique to the sampling transect or that groundwater from a regional flow system was converging under the river near the study area. Flow directions also may have been affected by aquifer heterogeneity such as the shallow fine-grained sediments onshore and at the bottom of the Eel River. Improved understanding of the fate of nitrate in this type of complex setting might be gained by including additional characterization of aquifer heterogeneity and groundwater flow and extending investigations of nitrate reduction to the shallow sediments in the intertidal saltwater cell and adjacent subtidal zone and to locations farther offshore beneath the estuary.

Massachusetts↗

USGS2011

Mercury bioaccumulation and biomagnification in Ozark stream ecosystems

Crayfish ( Orconectes spp.), Asian clam ( Corbicula fluminea ), northern hog sucker (hog sucker; Hypentelium nigricans ), and smallmouth bass (smallmouth; Micropterus dolomieu ) from streams in southeastern Missouri (USA) were analyzed for total mercury (HgT) and for stable isotopes of carbon (δ 13 C), nitrogen (δ 15 N), and sulfur (δ 34 S) to discern Hg transfer pathways. HgT concentrations were generally lowest in crayfish (0.005–0.112 μg/g dw) and highest in smallmouth (0.093–4.041 μg/g dw), as was δ 15 N. HgT was also lower and δ 15 N was higher in all biota from a stream draining a more heavily populated historical lead–zinc mining area than from similar sites with mostly undeveloped forested watersheds. δ 13 C in biota was lowest at spring-influenced sites, reflecting CO 2 inputs and temperature influences, and δ 34 S increased from south to north in all taxa. However, HgT was not strongly correlated with either δ 13 C or δ 34 S in biota. Trophic position (TP) computed from crayfish δ 15 N was lower in hog suckers (mean=2.8) than in smallmouth (mean=3.2), but not at all sites. HgT, δ 13 C, δ 34 S, and TP in hog suckers increased with total length (length) at some sites, indicating site-specific ontogenetic diet shifts. Changes with length were less evident in smallmouth. Length-adjusted HgT site means in both species were strongly correlated with HgT in crayfish ( r 2 =0.97, P <0.01), but not with HgT in Corbicula ( r 2 =0.02, P >0.05). ANCOVA and regression models incorporating only TP and, for hog suckers, length, accurately and precisely predicted HgT concentrations in both fish species from all locations. Although low compared to many areas of the USA, HgT (and therefore methylmercury) concentrations in smallmouth and hog suckers are sufficiently high to represent a threat to human health and wildlife. Our data indicate that in Ozark streams, Hg concentrations in crayfish are at least partly determined by their diet, with concentrations in hog suckers, smallmouth, and possibly other higher-level consumers largely determined by concentrations in crayfish and other primary and secondary consumers, fish growth rates, and TP.

Missouri↗

USGS2014

Mercury exposure associated with altered plasma thyroid hormones in the declining western pond turtle (Emys marmorata) from California mountain streams

Mercury (Hg) is a global threat to wildlife health that can impair many physiological processes. Mercury has well-documented endocrine activity; however, little work on the effects of Hg on the thyroid hormones triiodothyronine (T3) and thyroxine (T4) in aquatic wildlife exists despite the fact that it is a sensitive endpoint of contaminant exposure. An emerging body of evidence points to the toxicological susceptibility of aquatic reptiles to Hg exposure. We examined the endocrine disrupting potential of Hg in the western pond turtle (Emys marmorata), a long-lived reptile that is in decline throughout California and the Pacific Northwest. We measured total Hg (THg) concentrations in red blood cells (RBCs) and plasma T3 and T4 of turtles from several locations in California that have been impacted by historic gold mining. Across all turtles from all sites, the geometric mean and standard error THg concentration was 0.805 ± 0.025 μg/g dry weight. Sampling region and mass were the strongest determinants of RBC THg. Relationships between RBC THg and T3 and T4 were consistent with Hg-induced disruption of T4 deiodination, a mechanism of toxicity that may cause excess T4 levels and depressed concentrations of biologically active T3.

California↗

USGS2012

Lake sturgeon population attributes and reproductive structure in the Namakan Reservoir, Minnesota and Ontario

Quantified were the age, growth, mortality and reproductive structure of lake sturgeon ( Acipenser fulvescens ) collected in the US and Canadian waters of the Namakan Reservoir. The hypotheses were tested that (i) age and growth of lake sturgeon in the Namakan Reservoir would differ by sex and reproductive stage of maturity, and (ii) that the relative strength of year-classes of lake sturgeon in the reservoir would be affected by environmental variables. To quantify age, growth and mortality of the population, existing data was used from a multi-agency database containing information on all lake sturgeon sampled in the reservoir from 2004 to 2009. Lake sturgeon were sampled in the Minnesota and Ontario waters of the Namakan Reservoir using multi-filament gillnets 1.8 m high and 30–100 m long and varying in mesh size from 178 to 356 mm stretch. Reproductive structure of the lake sturgeon was assessed only during spring 2008 and 2009 using plasma testosterone and estradiol-17β concentrations. Ages of lake sturgeon >75 cm ranged from 9 to 86 years (n = 533, mean = 36 years). A catch-curve analysis using the 1981–1953 year classes estimated total annual mortality of adults to be 4.8% and annual survival as 95.2%. Using logistic regression analysis, it was found that total annual precipitation was positively associated with lake sturgeon year-class strength in the Namakan Reservoir. A 10 cm increase in total annual precipitation was associated with at least a 39% increase in the odds of occurrence of a strong year class of lake sturgeon in the reservoir. Plasma steroid analysis revealed a sex ratio of 2.4 females: 1 male and, on average, 10% of female and 30% of male lake sturgeon were reproductively mature each year (i.e. potential spawners). Moreover, there was evidence based on re-captured male fish of both periodic and annual spawning, as well as the ability of males to rapidly undergo gonadal maturation prior to spawning. Knowledge of lake sturgeon reproductive structure and factors influencing recruitment success contribute to the widespread conservation efforts for this threatened species.

Minnesota, Ontario↗

USGS2012

Transient effects on groundwater chemical compositions from pumping of supply wells at the Nevada National Security Site, 1951-2008

Nuclear testing and support activities at the Nevada National Security Site have required large amounts of water for construction, public consumption, drilling, fire protection, hydraulic and nuclear testing, and dust control. To supply this demand, approximately 20,000 million gallons of water have been pumped from 23 wells completed in 19 boreholes located across the Nevada National Security Site starting as early as the 1950s. As a consequence of more or less continuous pumping from many of these wells for periods as long as 58 years, transient groundwater flow conditions have been created in the aquifers that supplied the water. To evaluate whether long-term pumping caused changes in water compositions over time, available chemical analyses of water samples from these 19 boreholes were compiled, screened, and evaluated for variability including statistically significant temporal trends that can be compared to records of groundwater pumping. Data used in this report have been extracted from a large database (Geochem08, revision 3.0, released in September 2008) containing geochemical and isotopic information created and maintained by primary contractors to the U.S. Department of Energy, National Nuclear Security Administration, Nevada Site Office. Data extracted from this source were compiled for the entire period of record, converted to uniform reporting units, and screened to eliminate analyses of poor or unknown quality, as well as clearly spurious values. The resulting data are included in accompanying spreadsheets that give values for (1) pH and specific conductance, (2) major ion concentrations, (3) trace element concentrations and environmental isotope ratios, and (4) mean, median, and variance estimates for major ion concentrations. The resulting data vary widely in quality and time-series density. An effort has been made to establish reasonable ranges of analytical uncertainty expected for each analyte and eliminate analyses that are obvious outliers. Analysis of chemical trends in this report primarily rely on specific conductance measurements and major ion concentrations, data considered to be the most accurate and reliable over the entire time span of investigation. The analysis uses parametric and non-parametric evaluations to provide a statistical basis for trend identification. Trace element and isotope data are examined for consistency, but typically are too inaccurate or infrequent to provide a reliable long term basis for trend evaluation. Groundwater withdrawal records compiled in a companion report are included graphically in this report to allow qualitative comparisons between water quality and pumping history. Data for each supply well include (1) a borehole description and summary of pumping history, (2) a description of water-quality parameters, (3) an evaluation of temporal variations of specific conductance and major ion concentrations, and (4) an examination of supporting information from trace element and isotope data. A range of responses are observed for individual supply wells that likely include the effects of both aquifer dynamics and changing borehole conditions. Data from most wells show little or no evidence for temporal variation in water-quality parameters indicating that aquifers at the Nevada National Security Site are capable of producing large volumes of compositionally uniform water over many years of pumping. A smaller number of wells show evidence of transient changes. Wells that have ceased pumping commonly show compositions that shift toward lower concentrations in subsequent bailed samples, which indicates that more dilute water entered the well over time due to either leakage of meteoric water into the well casing or more wide-spread recharge into the shallow phreatic zone. Wells that show systematic changes in water compositions during episodes of pumping commonly have multiple open intervals whose contributions to water in the well may change over time due to hydraulic conditions or well dynamics.

Nevada↗

USGS1983

Anaerobic oxalate degradation: Widespread natural occurrence in aquatic sediments

Significant concentrations of oxalate (dissolved plus particulate) were present in sediments taken from a diversity of aquatic environments, ranging from 0.1 to 0.7 mmol/liter of sediment. These included pelagic and littoral sediments from two freshwater lakes (Searsville Lake, Calif., and Lake Tahoe, Calif.), a hypersaline, meromictic, alkaline lake (Big Soda Lake, Nev.), and a South San Francisco Bay mud flat and salt marsh. The oxalate concentration of several plant species which are potential detrital inputs to these aquatic sediments ranged from 0.1 to 5.0% (wt/wt). In experiments with litter bags, the oxalate content of Myriophyllum sp. samples buried in freshwater littoral sediments decreased to 7% of the original value in 175 days. This suggests that plant detritus is a potential source of the oxalate within these sediments. [ 14 C]oxalic acid was anaerobically degraded to 14 CO 2 in all sediment types tested, with higher rates evident in littoral sediments than in the pelagic sediments of the lakes studied. The turnover time of the added [ 14 C]oxalate was less than 1 day in Searsville Lake littoral sediments. The total sediment oxalate concentration did not vary significantly between littoral and pelagic sediments and therefore did not appear to be controlling the rate of oxalate degradation. However, depth profiles of [ 14 C]oxalate mineralization and dissolved oxalate concentration were closely correlated in freshwater littoral sediments; both were greatest in the surface sediments (0 to 5 cm) and decreased with depth. The dissolved oxalate concentration (9.1 μmol/liter of sediment) was only 3% of the total extractable oxalate (277 μmol/liter of sediment) at the sediment surface. These results suggest that anaerobic oxalate degradation is a widespread phenomenon in aquatic sediments and may be limited by the dissolved oxalate concentration within these sediments.

California, Nevada↗

USGS2019

Trophic plasticity and the invasion of a renowned piscivore: A diet synthesis of northern pike (Esox lucius) from the native and introduced ranges in Alaska, U.S.A.

The invasion of non-native fishes is a leading cause of extinction and imperilment of native freshwater fishes. Evidence suggests that introduced species with generalist diets have the potential for greatest impacts through competition and predation even though populations are often comprised of specialist individuals. The northern pike (Esox lucius), a predatory fish, has been widely introduced outside its native range for recreational fishing purposes, especially in western North America, and it has been implicated in declines and extirpations of native fishes. We synthesized over 2,900 individual northern pike diet records across 31 waterbodies from the native and introduced ranges in Alaska to quantify the extent of diet specialization and generalization relative to freshwater prey communities. To control for effects of ontogenetic diet shifts, we separately analyzed major size classes of northern pike and inferred and visualized trophic plasticity from Prey-Specific Abundance indices and ordination. Diet generalization was common in northern pike among waterbodies and usually consisted of individuals consuming macroinvertebrates. However, when available, individual northern pike diets showed specialization on fishes, amphibians, small mammals, and dragonflies. The reliance on macroinvertebrate prey by northern pike from small, isolated lakes in the native and invasive ranges suggests that dietary plasticity facilitates persistence of these predators in the absence of preferred fish prey. Broadly, this synthesis supports the hypothesis that trophic plasticity and diet generalization widely occur among invasive and native populations of northern pike which is likely to enhance the probability of introduction success, exacerbate their environmental impacts, and complicate management of this potentially invasive freshwater predator.

Alaska↗

USGS2015

Health and condition of endangered juvenile Lost River and shortnose suckers relative to water quality and fish assemblages in Upper Klamath Lake, Oregon, and Clear Lake Reservoir, California

Executive Summary Most mortality of endangered Lost River ( Deltistes luxatus ) and shortnose ( Chasmistes brevirostris ) suckers in Upper Klamath Lake, Oregon, appears to occur within the first year of life. However, juvenile suckers in Clear Lake Reservoir, California, appear to survive longer and may even recruit to the spawning populations. Our goal in this study was to develop productive lines of inquiry into the causes of mortality of juvenile suckers, especially in Upper Klamath Lake, through comparison of sucker health and environmental conditions in both lakes. The health of juvenile suckers was associated with physical, biological, and chemical characteristics in each lake from July to September 2013 and 2014. Water-quality dynamics differed substantially between lakes. Diel fluctuations were greater for dissolved-oxygen concentrations and pH in Upper Klamath Lake than in Clear Lake Reservoir, but diel temperature fluctuations were greater in Clear Lake Reservoir. Minimum dissolved-oxygen concentrations were as low as 1.0 milligram per liter (mg/L) in Upper Klamath Lake, but were no lower than 5.7 mg/L in Clear Lake Reservoir. Unionized ammonia (NH 3 ) concentrations were near or less than the minimum reporting limit of 0.002 mg/L NH 3 in Clear Lake Reservoir and generally were less than the concentration known to cause cellular changes to the gills or mortality of suckers in Upper Klamath Lake. Concentrations of microcystins were less than the detection limit (≤0.10 microgram per liter [μg/L]) in both dissolved (<63 micrometers [μm]) and particulate (≥63 μm) fractions of water samples collected from Clear Lake Reservoir in both years. In Upper Klamath Lake, concentrations of microcystins were relatively low in the 2013 particulate fractions and dissolved fractions of samples in both years, but as high as 44.30 μg/L, more than 44 times the World Health Organization recommended levels for drinking water (1 μg/L), in the 2014 particulate fraction. However, there was little histological evidence and no chemical evidence that these concentrations in water were harmful to suckers that we captured. The species and age compositions of juvenile sucker populations differed between lakes. A total of 98 percent of all juvenile suckers captured in Upper Klamath Lake were age-0. In contrast, as many as six age classes of suckers were represented in Clear Lake Reservoir, indicating much better juvenile survival than in Upper Klamath Lake. Based on genetic species identification, 98 percent of juvenile suckers collected from Clear Lake Reservoir were shortnose or Klamath largescale suckers ( Catostomus snyderi ). In contrast, there was a high degree of apparent genetic hybridization in juvenile suckers collected from Upper Klamath Lake, and both Lost River and non-Lost River juvenile suckers were nearly equally represented in samples. Neither gross nor histological examination revealed a high prevalence of abnormalities in suckers that might indicate a mechanism for juvenile mortality in Upper Klamath Lake. Therefore, high mortality primarily may have occurred outside our study period (for example, in spring or over winter), or was owing to a factor that could not be detected with our methods (for example, predation). Alternatively, abnormalities in a small percentage of passively captured suckers in Upper Klamath Lake may indicate health-related issues that were more prevalent in populations than in our samples. Some apparent symptoms of stress or exposure to irritants, such as peribiliary cuffing in hepatocytes and mild inflammation and necrosis in gill tissues, were present in suckers from both lakes and do not appear to be clues to the cause of differential mortality between lakes. Seasonal trends in energy storage as glycogen and triglycerides were similar between lakes, indicating prey availability was not a factor in differential mortality. Differences in sucker health and condition between lakes were considered the most promising clues to the causes of differential juvenile sucker morality between lakes. A low prevalence of petechial hemorrhaging of the skin (16 percent) and deformed opercula (8 percent) in Upper Klamath Lake suckers may indicate exposure to a toxin other than microcystin. Suckers grew slower in their first year of life, but had similar or greater triglyceride and glycogen levels in Upper Klamath Lake compared to Clear Lake Reservoir. These findings do not suggest a lack of prey quantity but may indicate lower prey quality in Upper Klamath Lake.

California, Oregon↗

USGS2009

Iodine-129 in the Snake River Plain Aquifer at and Near the Idaho National Laboratory, Idaho, 2003 and 2007

From 1953 to 1988, wastewater containing approximately 0.94 curies of iodine-129 (129I) was generated at the Idaho National Laboratory (INL) in southeastern Idaho. Almost all of this wastewater was discharged at or near the Idaho Nuclear Technology and Engineering Center (INTEC) on the INL site. Most of the wastewater was discharged directly into the eastern Snake River Plain aquifer through a deep disposal well until 1984; however, some wastewater also was discharged into unlined infiltration ponds or leaked from distribution systems below the INTEC. In 2003, the U.S. Geological Survey (USGS), in cooperation with the U.S. Department of Energy, collected samples for 129I from 36 wells used to monitor the Snake River Plain aquifer, and from one well used to monitor a perched zone at the INTEC. Concentrations of 129I in the aquifer ranged from 0.0000066 +- 0.0000002 to 0.72 +- 0.051 picocuries per liter (pCi/L). Many wells within a 3-mile radius of the INTEC showed decreases of as much as one order of magnitude in concentration from samples collected during 1990-91, and all of the samples had concentrations less than the Environmental Protection Agency's Maximum Contaminant Level (MCL) of 1 pCi/L. The average concentration of 129I in 19 wells sampled during both collection periods decreased from 0.975 pCi/L in 1990-91 to 0.249 pCi/L in 2003. These decreases are attributed to the discontinuation of disposal of 129I in wastewater after 1988 and to dilution and dispersion in the aquifer. Although water from wells sampled in 2003 near the INTEC showed decreases in concentrations of 129I compared with data collected in 1990-91, some wells south and east of the Central Facilities Area, near the site boundary, and south of the INL showed slight increases. These slight increases may be related to variable discharge rates of wastewater that eventually moved to these well locations as a mass of water from a particular disposal period. In 2007, the USGS collected samples for 129I from 36 wells that are used to monitor the aquifer south of INTEC and from 2 wells that are used to monitor perched zones at INTEC. Concentrations of 129I in the eastern Snake River Plain aquifer ranged from 0.000026 +- 0.000002 to 1.16 +- 0.04 pCi/L, and the concentration at one well exceeded the maximum contaminant level (1 pCi/L) for public drinking water supplies. The average concentration of 19 wells sampled in 2003 and 2007 did not differ; however, slight increases and decreases of concentrations in several areas around the INTEC were evident in the aquifer. The decreases are attributed to the discontinued disposal and to dilution and dispersion in the aquifer. The increases may be due to the movement into the aquifer of remnant perched water below the INTEC. In 2007, the USGS also collected samples from 31 zones in 6 wells equipped with multi-level WestbayTM packer sampling systems to help define the vertical distribution of 129I in the aquifer. Concentrations ranged from 0.000011 +- 0.0000005 to 0.0167 +- 0.0007 pCi/L. For three wells, concentrations of 129I between zones varied one to two orders of magnitude. For two wells, concentrations varied for one zone by more than an order of magnitude from the wells' other zones. Similar concentrations were measured from all five zones sampled in one well. All of the 31 zones had concentrations two or more magnitudes below the maximum contaminant level.

Scientific Investigations Report↗

USGS2024

Models no not provide proof: An example of model ambiguity and application of isotopic data in a mine pit lake

Geochemical and hydrologic models of pit lakes are commonly used in environmental regulatory decisions to predict future water quality and hydrologic conditions and to understand existing pit lakes. Models may be used to quantify sulfide oxidation, predict thermal/chemical stratification and mixing, and better understand connections between pit lakes and aquifers. One concern related to the hydrologic character of pit lakes is if they are terminal (a groundwater sink with no outflow) or flowthrough (both receiving groundwater inflow and discharging to groundwater). This question was pertinent to the Liberty pit lake, a small acidic pit lake formed in a former Cu deposit in south-central Nevada where potentiometric and geochemical data potentially indicate pit-lake outflow. Potential discharge to groundwater from the pit lake was evaluated using a water-balance model, but uncertainty in hydraulic parameters led to ambiguity in the hydrologic character. Stable isotopes of water were then sampled from the pit lake and adjacent groundwater wells, which unambiguously indicated the lack of an evaporative signature in downgradient groundwater because the groundwater did not plot on a hypothetical mixing line between evaporated pit lake water and observed meteoric recharge. This methodology provided a more effective and more data-driven approach for understanding pit-lake hydrology. Although predictive models are required to quantify reasonable bounds on future conditions, many models contain substantial uncertainty and are not well suited in some environments. Datasets that provide more clear lines of evidence could be collected from existing pit lakes whenever possible to inform water-rock interaction, limnological behavior, and connectivity to adjacent groundwater.

Nevada↗

USGS2020

Millennial-scale climate and human drivers of environmental change and fire activity in a dry, mixed-conifer forest of northwestern Montana

Warm summer temperatures and longer fire seasons are promoting larger, and in some cases, more fires that are severe in low- and mid-elevation, dry mixed-conifer forests of the Northern Rocky Mountains (NRM). Long-term historical fire conditions and human influence on past fire activity are not well understood for these topographically and biophysically heterogeneous forests. We developed reconstructions of millennial-scale fire activity, vegetation change, and human presence at Black Lake, a small closed-basin lake on the Flathead Indian Reservation in the Mission Valley, Northwestern Montana, United States. Fossil pollen, charcoal, and biomarkers associated with human presence were used to evaluate the interaction between climate variability, fire activity, vegetation change and human activity for the past 7000 years. Comparisons among multiple proxies suggest climate variability acted as the primary control on fire activity and vegetation change from the early Holocene until the late Holocene when records suggest fire activity and climate variability decoupled. Specific biomarkers (5β-stanols including coprostanol and epi-coprostanol) associated with human presence indicate humans were present within the Black Lake watershed for thousands of years, although the inferred intensity of human presence is highly variable. A strong relationship between climate variability and fire activity during the early and mid-Holocene weakens during the last few thousand years, suggesting possible increased influence of humans in mediating fire activity in recent millennia, and/or a shift in the interaction between the distribution and abundance of woody fuel and fire severity. Human-set fires during the cooler and wetter late Holocene may have been aimed at maintaining important cultural resources associated with the heterogeneous mosaic of mixed conifer forests within the Black Lake watershed. The paleoenvironmental reconstruction at Black Lake corroborates archeological records that show humans were present within the Black Lake watershed for over 7000 years. Further research is needed to evaluate the evidence for this continuous presence and the possible role that people played in shaping fire regimes and vegetation within low- to mid-elevation mixed-conifer ecosystems of the NRM.

Montana↗

USGS2026

Alternative future vegetation pathways reveal potential transformations of western US ecosystems

Managing ecosystems in an era of rapid change is inherently challenging not only because of uncertainty in future climate but also due to diverse responses of ecosystems to climate. Projections of ecological transformation alongside information about plausible vegetation trajectories can help land managers explore divergent scenarios and consider how modeled outcomes match their observations. Climate-analog impact models (AIMs) compare environmental information (e.g., vegetation types) between sets of climatically similar locations to infer change and can be used to identify multiple outcomes. We used AIMs to project changes in vegetation across the western United States under a mid-21st century climate scenario, characterize ecological transformation vulnerability based on projection divergence, and demonstrate how AIMs can inform decision-making. We projected high or very high vulnerability to ecological transformation across 29% of the western US, nearly 1 M km 2 . Vulnerability varied among vegetation groups; 75% of alpine vegetation had high or very high vulnerability vs. 6% of desert scrub. We estimate that 9% of the study area faces a high likelihood of transformation based on combined measures of vulnerability and projection agreement. Transformation at the vegetation type ( n = 50) level is projected for 40% (1.4 M km 2 ) of the study area, based on primary projections. As vegetation shifts towards types supported by a more arid climate, forested area is expected to contract by 9% and subalpine forests specifically by 54%. Elsewhere, vulnerability is low or trajectories are uncertain, implying opportunities for managers to intervene. Dry forests, for example, could be stabilized through vegetation management and intentional fire use. Our findings suggest likely ecological transformations with significant downstream consequences for ecosystem services and natural resources. They are best used within decision-making frameworks that draw on multiple lines of evidence including local expertise and complementary knowledge systems.

Arizona, California, Colorado, Idaho, Montana, Nev↗

USGS2019

Monitoring protocol development and assessment for narrowly endemic toads in Nevada, 2018

Several species and subspecies of toads are endemic to small spring systems in the Great Basin, and their restricted ranges and habitat extent make them vulnerable to environmental perturbations. Very little is known about several of these toad populations, so a group of stakeholders including the U.S. Geological Survey, U.S. Fish and Wildlife Service, Bureau of Land Management, Nevada Department of Wildlife, the U.S. Navy, U.S. Forest Service, and Oregon State University met to discuss information needs on these populations and to develop a monitoring protocol that would detect population changes over time. In cooperation with the U.S. Fish and Wildlife Service, the U.S. Geological Survey implemented the proposed survey protocol, a multi-state occupancy design, for three sites: Dixie Valley, Railroad Valley, and Hot Creek, to evaluate its ease of implementation and effectiveness. We found that the multi-state occupancy protocol worked well in the Dixie Valley and, with some refinement, would likely work well in the Railroad Valley. We suggest that capture-mark-recapture of adults might be a more effective approach at Hot Creek. For most life stages of most populations, detection probabilities were positively related to survey duration up to 20 minutes, and the best time of day to conduct surveys varied by life stage and population. We make population-specific suggestions for the number of surveys and their timing and duration. Annual surveys using the suggested survey protocols will likely allow estimation of trends in the proportion of area of each population existing in different population states (occupied, occupied with evidence of reproduction, and unoccupied) and in most cases can be readily implemented with minimal training or handling of toads.

California, Idaho, Nevada, Oregon, Utah↗

USGS2014

Diverse coral communities in mangrove habitats suggest a novel refuge from climate change

Risk analyses indicate that more than 90% of the world's reefs will be threatened by climate change and local anthropogenic impacts by the year 2030 under "business-as-usual" climate scenarios. Increasing temperatures and solar radiation cause coral bleaching that has resulted in extensive coral mortality. Increasing carbon dioxide reduces seawater pH, slows coral growth, and may cause loss of reef structure. Management strategies include establishment of marine protected areas with environmental conditions that promote reef resiliency. However, few resilient reefs have been identified, and resiliency factors are poorly defined. Here we characterize the first natural, non-reef coral refuge from thermal stress and ocean acidification and identify resiliency factors for mangrove–coral habitats. We measured diurnal and seasonal variations in temperature, salinity, photosynthetically active radiation (PAR), and seawater chemistry; characterized substrate parameters; and examined water circulation patterns in mangrove communities where scleractinian corals are growing attached to and under mangrove prop roots in Hurricane Hole, St. John, US Virgin Islands. Additionally, we inventoried the coral species and quantified incidences of coral bleaching, mortality, and recovery for two major reef-building corals, Colpophyllia natans and Diploria labyrinthiformis , growing in mangrove-shaded and exposed (unshaded) areas. Over 30 species of scleractinian corals were growing in association with mangroves. Corals were thriving in low-light (more than 70% attenuation of incident PAR) from mangrove shading and at higher temperatures than nearby reef tract corals. A higher percentage of C. natans colonies were living shaded by mangroves, and no shaded colonies were bleached. Fewer D. labyrinthiformis colonies were shaded by mangroves, however more unshaded colonies were bleached. A combination of substrate and habitat heterogeneity, proximity of different habitat types, hydrographic conditions, and biological influences on seawater chemistry generate chemical conditions that buffer against ocean acidification. This previously undocumented refuge for corals provides evidence for adaptation of coastal organisms and ecosystem transition due to recent climate change. Identifying and protecting other natural, non-reef coral refuges is critical for sustaining corals and other reef species into the future.

Biogeosciences↗

USGS2012

Rebuilding after collapse: evidence for long-term cohort dynamics in the native Hawaiian rain forest

Questions: Do long-term observations in permanent plots confirm the conceptual model of Metrosideros polymorpha cohort dynamics as postulated in 1987? Do regeneration patterns occur independently of substrate age, i.e. of direct volcanic disturbance impact? Location: The windward mountain slopes of the younger Mauna Loa and the older Mauna Kea volcanoes (island of Hawaii, USA). Methods: After widespread forest decline (dieback), permanent plots were established in 1976 in 13 dieback and 13 non-dieback patches to monitor the population structure of M. polymorpha at ca. 5-yr intervals. Within each plot of 20 × 20 m, all trees with DBH >2.5 cm were individually tagged, measured and tree vigour assessed; regeneration was quantified in 16 systematically placed subplots of 3 × 5 m. Data collected in the subplots included the total number of M. polymorpha seedlings and saplings (five stem height classes). Here we analyse monitoring data from six time steps from 1976 to 2003 using repeated measures ANOVA to test specific predictions derived from the 1987 conceptual model. Results: Regeneration was significantly different between dieback and non-dieback plots. In dieback plots, the collapse in the 1970s was followed by a ‘sapling wave’ that by 2003 led to new cohort stands of M. polymorpha. In non-dieback stands, seedling emergence did not result in sapling waves over the same period. Instead, a ‘sapling gap’ (i.e. very few or no M. polymorpha saplings) prevailed as typical for mature stands. Canopy dieback in 1976, degree of recovery by 2003 and the number of living trees in 2003 were unrelated to substrate age. Conclusions: Population development of M. polymorpha supports the cohort dynamics model, which predicts rebuilding of the forest with the same canopy species after dieback. The lack of association with substrate age suggests that the long-term maintenance of cohort structure in M. polymorpha does not depend on volcanic disturbance but may be related to other environmental mechanisms, such as climate anomalies.

Hawai'i↗

USGS2008

Seabed mapping and characterization of sediment variability using the usSEABED data base

We present a methodology for statistical analysis of randomly located marine sediment point data, and apply it to the US continental shelf portions of usSEABED mean grain size records. The usSEABED database, like many modern, large environmental datasets, is heterogeneous and interdisciplinary. We statistically test the database as a source of mean grain size data, and from it provide a first examination of regional seafloor sediment variability across the entire US continental shelf. Data derived from laboratory analyses ("extracted") and from word-based descriptions ("parsed") are treated separately, and they are compared statistically and deterministically. Data records are selected for spatial analysis by their location within sample regions: polygonal areas defined in ArcGIS chosen by geography, water depth, and data sufficiency. We derive isotropic, binned semivariograms from the data, and invert these for estimates of noise variance, field variance, and decorrelation distance. The highly erratic nature of the semivariograms is a result both of the random locations of the data and of the high level of data uncertainty (noise). This decorrelates the data covariance matrix for the inversion, and largely prevents robust estimation of the fractal dimension. Our comparison of the extracted and parsed mean grain size data demonstrates important differences between the two. In particular, extracted measurements generally produce finer mean grain sizes, lower noise variance, and lower field variance than parsed values. Such relationships can be used to derive a regionally dependent conversion factor between the two. Our analysis of sample regions on the US continental shelf revealed considerable geographic variability in the estimated statistical parameters of field variance and decorrelation distance. Some regional relationships are evident, and overall there is a tendency for field variance to be higher where the average mean grain size is finer grained. Surprisingly, parsed and extracted noise magnitudes correlate with each other, which may indicate that some portion of the data variability that we identify as "noise" is caused by real grain size variability at very short scales. Our analyses demonstrate that by applying a bias-correction proxy, usSEABED data can be used to generate reliable interpolated maps of regional mean grain size and sediment character.

Continental Shelf Research↗