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At least 1,351 records · Page 75Linked to original sources
USGS2020

Karst geology of the Upper Midwest, USA

Karst in the Upper Midwest occurs within a thick sequence of mixed carbonate and siliciclastic Cambrian through Pennsylvanian sedimentary rocks, with a minor occurrence of karst in Proterozoic sandstone. Deposition of the sediments occurred on a marine epeiric ramp that spanned much of the North American continent through most of the Paleozoic. The Upper Midwest region experienced dramatic changes in sea level over geologic time, resulting in the observed sequence of interbedded carbonate and clastic rocks. The greatest degree of karst development occurs within (1) the Lower Ordovician Prairie du Chien Group below the Sauk-Tippecanoe (Knox) unconformity, (2) the Upper Ordovician Galena Group, (3) the Middle and Upper Devonian Wapsipinicon and Cedar Valley Groups, and (4) the Middle Mississippian Mammoth Cave Group and correlative formations. Uplift and exposure of the rocks likely occurred in the Permian, with some later deposition of Cretaceous terrestrial sediments atop the marine strata. Nearly all the Cenozoic sedimentary units were removed by ice sheets during the Pleistocene; however, pockets of Cretaceous sediments persist on the margins of the Driftless Area, a region of the Upper Mississippi River Valley that remained largely free of ice during the last ice age.

Book chapter↗
USGS2021

The 4th paradigm in multiscale data representation: Modernizing the National Geospatial Data Infrastructure

The need of citizens in any nation to access geospatial data in readily usable form is critical to societal well-being, and in the United States (US), demands for information by scientists, students, professionals and citizens continue to grow. Areas such as public health, urbanization, resource management, economic development and environmental management require a variety of data collected from many sources to identify problems, monitor trends and propose solutions. Such information needs and demands have driven the coordination of federal and regional government agencies with respective private sector participation to develop national geospatial data infrastructures in many countries.

Book chapter↗
USGS2021

Spatial data reduction through element -of-interest (EOI) extraction

Any large, multifaceted data collection that is challenging to handle with traditional management practices can be branded ‘Big Data.’ Any big data containing geo-referenced attributes can be considered big geospatial data. The increased proliferation of big geospatial data is currently reforming the geospatial industry into a data-driven enterprise. Challenges in the big spatial data domain can be summarized as the ‘Big Vs’ – variety, volume, velocity, veracity and value. Big spatial data sources can be considered in two broad classes, active and passive, as each is impacted to varying degrees. Some of these challenges may be alleviated by reducing unprocessed, or minimally processed, (raw) data to features, which we refer to as the extraction of Elements of Interest (EOI). In fact, many applications require EOI extraction from raw data to enable their basic employment. This chapter presents current state-of-the-art methods to create EOI from some types of georeferenced big data. We classify the data types into two realms: active and passive. Active data are those collected specifically for the purpose to which they are applied. Passive data are those collected for purposes other than those for which they are utilized, included those ‘collected’ for no particular purpose at all. The chapter then presents use cases from both the active and passive spatial realms, including the active applications of terrain feature extraction from digital elevation models and vegetation mapping from remotely-sensed imagery and passive applications like building identification from VGI and point-of-interest data mining from social networks for land use classification. Finally, the chapter concludes with future research needs.

Book chapter↗
USGS2020

Terrestrial wildlife in the post-mined Appalachian landscape: Status and opportunities

Coal mining is an anthropogenic stressor that has impacted terrestrial and semi-aquatic wildlife in the Appalachian Plateau since European settlement. Creation of grassland and early-successional habitats resulting from mining in a forested landscape has resulted in novel, non-analog habitat conditions. Depending on the taxa, the extent of mining on the landscape, and reclamation practices, effects have ranged across a gradient of negative to positive. Forest-obligate species such as woodland salamanders and forest-interior birds or those that depend on aquatic systems in their life cycle have been most impacted. Others, such as grassland and early-successional bird species have responded favorably. Some bat species, as an unintended consequence, use legacy deep mines as winter hibernacula in a region with limited karst geology. Recolonization of impacted wildlife often depends on life strategies and species’ vagility, but also on altered or arrested successional processes on the post-surface mine landscape. Many wildlife species will benefit from Forest Reclamation Approach practices going forward. In the future, managers will be faced with decisions about reforestation versus maintaining open habitats depending on the conservation need of species. Lastly, the post-mined landscape currently is the focal point for a regional effort to restore elk ( Cervus canadensis ) in the Appalachians.

Appalachian Plateau↗
USGS2020

The INI North American Regional Nitrogen Center: 2011–2015 nitrogen activities in North America

The North American Nitrogen Center (NANC) carries out three main charges: (1) conducting assessments on nitrogen (N) flows within North America and the consequences for human health, water resources, biodiversity, and greenhouse gas emissions; (2) facilitating efforts to develop solutions to the problem of excess nitrogen in agricultural, institutional, and natural resource management sectors; and (3) presenting these results to policy makers. There are formidable challenges in reducing N loss from all parts of the North American food production and supply chain, including altering consumer behavior. The NANC is working with producers, trade groups, universities, and supply chains to develop effective practices for minimizing loss of reactive nitrogen (N r ) to the environment. The NANC is also helping public land management and regulatory agencies prepare effective policy approaches toward minimizing ecological damage from atmospheric N r deposition.

Book chapter↗
USGS2020

Global challenges for nitrogen science-policy interactions: Towards the International Nitrogen Management System (INMS) and improved coordination between multi-lateral environmental agreements

Human interference with the nitrogen cycle has doubled reactive nitrogen inputs to the global biosphere over the past century, leading to changes across multiple environmental issues that require urgent action. Nitrogen fertilizers and biological nitrogen fixation have allowed benefits of increased crop harvest and livestock production, while in some areas there is insufficient nitrogen to fertilize crops. Whether in excess or deficit, nitrogen losses from its inefficient use are causing a combination of freshwater and marine pollution, air pollution, alteration of climate balance, stratospheric ozone loss, biodiversity loss and reduction of soil quality. The resulting nitrogen pollution affects human health, well-being and livelihoods. Scientific efforts have begun to bring these issues together. However, there is still a high degree of fragmentation between research on the different benefits and threats of reactive nitrogen and between the respective policy frameworks, especially at the global scale. We argue that a more joined-up approach to managing the global nitrogen cycle is needed to develop the ‘gravity of common cause’ between nitrogen issues and to avoid policy trade-offs. We describe how a coherent system for science evidence provision is being developed to support policy development through the ‘International Nitrogen Management System’ (INMS). There is now a matching challenge to bring together the multiple policy agreements relevant for nitrogen as a foundation to address synergies/trade-offs and to set priorities. Based on review of existing frameworks, we outline the concept for an Interconvention nitrogen coordination mechanism. This could make a major contribution to multiple Sustainable Development Goals by stimulating the next generation of international nitrogen strategies: maximizing the benefits of efficient nitrogen use, while minimizing its many environmental threats.

Book chapter↗
USGS2020

On the use of statistical analysis to understand submarine landslide processes and assess their hazard

Because of their inaccessibility, submarine landslides are typically studied individually and at great effort and expense to provide knowledge of the specific site conditions where these landslides occur. Statistical analysis of submarine landslide scars can offer generalized perspectives on the processes that initiate submarine landslides and can help toward hazard assessment in areas that have not been studied in detail. The following review discusses more than a decade of development of statistical approaches to studying submarine landslides. Landslides were previously viewed together with other natural hazards, such as earthquakes and fires, as a phenomenon whose size distribution obeys an inverse power law. Inverse power law distributions are the result of self-organized avalanche processes, in which the final hazard size cannot be predicted at the onset of the disturbance. We find that volume and area distributions of submarine landslides along the U.S. Atlantic continental slope and along nine other margins worldwide do not follow an inverse power law. Rigorous statistical tests of several different probability distribution models indicate that the lognormal model is most appropriate for these siliciclastic environments. Lognormal distributions can be simulated by assuming that the area of slope failure depends on earthquake magnitude, in other words, failure occurs simultaneously over the area affected by horizontal ground shaking and does not cascade from nucleating sources. Therefore, the maximum landslide size can be predicted from the earthquake magnitude and the distance from the rupturing fault. Moreover, earthquakes <~M4.5 cannot generate significant submarine landslides. We further demonstrate that empirical, offshore landslide hazard curves can be developed from these lognormal landslide size distributions, if the duration of mapped landslide activity is known. In addition to hazard estimation, scaling relationships can yield insights on the physical processes associated with landslide failure. For example, the log-log relationship between volume and area of landslide scars in siliciclastic margins is observed to be almost linear implying that most landslides are translational. Carbonate margins, in contrast, show a power-law distribution of scar volumes and their volume to area relationship is ~1.3. These results suggest that landslides in carbonate margins are governed by the random distributions of existing fissures, and they act like rock falls on land. Although earthquakes are the principal trigger of submarine landslides, the effects of earthquake frequency on slope stability can be counterintuitive. The average size of landslide scars decreases non-linearly with increasing frequency of earthquakes and increases with increasing sedimentation rate. The effect is interpreted as evidence for densification and shear strength increase of margin sediment, induced by repeated seismic shaking.

Book chapter↗
USGS2020

Progress and lessons learned from responses to landslide disasters

Landslides have the incredible power to transform landscapes and also, tragically, to cause disastrous societal impacts. Whereas the mechanics and effects of many landslide disasters have been analyzed in detail, the means by which landslide experts respond to these events has garnered much less attention. Herein, we evaluate nine landslide response case histories conducted by the U.S. Geological Survey over the past two decades and summarize the event history, the response conducted, and the lessons learned from each event. We group the responses into three categories—providing event context from past events, addressing ongoing hazards, and acquiring data for the future—and present the nine case studies accordingly. We also summarize the progress in landslide response that has been made over the past two decades, including insights and advancements on the preparation for such events, the use of new technologies, and the importance of clear communication between all parties during disasters. We believe that exchanging and sharing experiences such as these will promote more clear and successful approaches for responses to landslide disasters in the future.

Book chapter↗
USGS2021

Reproduction

Lake charr Salvelinus namaycush are typically fall spawners although one ecotype has populations that spawn during spring and fall (siscowets in Lake Superior). Lake charr are iteroparous (reproduce more than once in a lifetime) with group-synchronous ovarian development and typically spawn once per year. However, lake charr may not reproduce every year, a phenomenon known as skipped spawning. Free embryos are active on spawning reefs, make diurnal vertical movements from spawning substrate, and feed exogenously much earlier than previously assumed. The abundance of food and predators strongly affects the rate of development, yolk sac absorption, and duration of residence on spawning sites. The necessity for, and timing of, gas bladder inflation, and mechanisms for inflation without access to the surface, need further study. The low survival of free embryos due to thiamine deficiency has likely contributed to the lack of recruitment of lake charr in the Laurentian Great Lakes for decades. Thiaminase, a thiamine-degrading enzyme, appears to be the causal agent for thiamine deficiency in Great Lakes lake charr.

Great Lakes↗
USGS2021

Distribution

The lake charr Salvelinus namaycush is restricted in its native distribution to oligotrophic fresh waters of northern North America largely within the extent of the Pleistocene glaciations. It is the only freshwater species in northwest North America that does not occur in Siberia. A GIS-based native occurrence map linked to the HydroLAKES database does not extend the lake charr range but provides more comprehensive occurrence data than previous maps. The total waterbody area of lakes occupied by lake charr (451,304 km 2 ) is 40% of the total waterbody area across the range. Lake charr occur from 42.020901 latitude in the south to 74.420800 in the north and from −62.700000 longitude in the east to −161.173090 in the west. Lake charr lakes range in surface area from 3.4 to 8,210,000 ha (mean = 9715 ha; median = 191 ha), maximum depth from 2.7 to 614 m, and elevation from sea level to 2035 m ASL (mean = 381 m; median = 366 m). Glaciation, water temperature, dissolved oxygen, depth, and nutrient content are the main variables associated with lake charr native distribution in lakes. Life history variation, physiology, and ecological opportunity are the most likely drivers of lake charr dispersal and colonization.

Book chapter↗
USGS2021

Life history and population dynamics

Lake charr Salvelinus namaycush life history and population dynamics metrics were reviewed to evaluate populations inside ( n = 462) and outside ( n = 24) the native range. Our goals were to create a database of metrics useful for evaluating population status and to test for large-scale patterns between metrics and latitude and lake size. An average lake charr grew from a 69-mm length at age-0 ( L 0 ) at 89 mm/year early growth rate ( ω ) to 50% maturity at 420 mm ( L 50 ) at age 8 ( t 50 ), and then continued to grow toward a 717-mm asymptotic length ( L ∞ ). L 50 was positively correlated to ω , whereas t 50 was inversely correlated to ω . Lake charr grew slower toward larger size and older age in northern latitudes and larger lakes than in southern latitudes and smaller lakes. Population density (number/ha) and yield density (kg/ha) decreased with lake size, and yield and total annual mortality ( A ) decreased with latitude. Native populations grew slower ( ω ), were heavier at 500 mm ( W 500 ), matured at shorter L 50 , grew to a shorter L ∞ , and suffered lower annual mortality A than non-native populations. Our review and database should be useful to managers and researchers for quantifying lake charr population status across the species range.

Book chapter↗
USGS2021

Trophic ecology

The trophic ecology of lake charr Salvelinus namaycush morphotypes from small and large lakes within their native and introduced ranges is reviewed over the past 50 years. The lake charr is an apex predator in most habitats it occupies, where it plays a significant role in defining food webs. While often considered piscivores, lake charr feed on a range of aquatic prey throughout their life history, including zooplankton, benthic invertebrates, and fish, as well as terrestrial insects, mammals, birds, amphibians, and reptiles. Lake charr diets that vary within morphotypes among lakes and among sympatric morphotypes reflect differences in habitat use, prey availability, and individual preferences. Temporal variability in diet can result from seasonal prey pulses, thermal barriers, and long-term prey dynamics. Lake charr adapt quickly to consume invasive prey fishes, and often decimate native prey fishes and other piscivores in lakes into which they are introduced. Salient research topics in lake charr trophic ecology include: (1) how best to quantify spatial and temporal trophic niche space; and, (2) how changing environmental conditions, such as invasive species and lake warming, will influence lake charr feeding and broader lake food-web dynamics.

Book chapter↗
USGS2021

The concept of evanescent microbial ecosystems in Earth's atmosphere

This essay presents the hypothesis that short-lived or evanescent microbial ecosystems exist in Earth’s lower troposphere (~ < 4 km). This hypothesis is supported by culture- and molecular-based studies that have shown diverse, viable, and metabolically active microbial communities within Earth’s atmospheric boundary layer. Surprisingly, microorganisms are routinely recovered in samples collected at extreme altitudes including those within the stratosphere (> 18 km). Volcanic eruptions, dust storms, fires, and sea spray are known to seed the atmosphere with microorganisms and to serve as potential nutrient sources while in the atmosphere and upon deposition. Recent research has demonstrated that microorganisms are metabolically active in clouds; for example, archaea capable of utilizing gases such as methane and hydrogen-nitrogen have been identified in clouds and in the atmosphere over natural and anthropogenic gas seeps. The only difference between this hypothesized ecosystem to more traditionally defined ecosystems is its evanescent characteristics where clouds or gas plumes eventually dissipate as they reside over and traverse Earth’s terrestrial and/or aquatic environments. The life cycle of these hypothesized evanescent airborne ecosystems would be short-lived relative to the classically defined biomes or ecosystems.

Book chapter↗
USGS2021

Middle Holocene hydrologic changes catalyzed by river avulsion in Big Soda Lake, Nevada, USA

Big Soda Lake is a 63 m deep, 1.6 km 2 maar lake in the Great Basin of Nevada, USA. Water level in the lake is controlled by groundwater inputs from the surrounding aquifer and the only surface water input is rainfall, which is negligible. A core taken in 2010 records an 8.75 m depositional history of the lake. A radiocarbon date on fossil pollen from 8.4 m below the sediment water interface (BSWI) of 14,740 (+1120/−825) cal yr BP suggests that the core may cover the latest Pleistocene and Holocene depositional history of the lake. Stable isotope values of oxygen and carbon (δ 18 O and δ 13 C) on authigenic calcite, diatom assemblages, and sedimentary structures all show consistent hydrological change from initially saline water at the bottom of the core to fresh/brackish water at about 6 m BWSI, back to saline water at 4.3 m. At 4.3 m depth, the bedding and color of the core change abruptly, and the stable- isotope and diatom assemblages indicate a consistently hypersaline lake until near the top of the core, when fresh water entered the lake due to irrigation and canal building in the twentieth century. The stable isotopes of the calcite abruptly change from inversely varying isotopic compositions below 4.3 m depth to covarying above. This break between relatively fresh and saline conditions in the lake occurs during the middle Holocene, although the exact timing of the transition is unknown due to variability in the 14 C age determinations. The cause for such an abrupt change is difficult to explain through climate shifts, as evidence suggests climate in the Great Basin was different from what the Big Soda Lake record indicates in the Early Holocene. It is hypothesized that the Walker River flowed to the Carson River basin before 5600 cal yr BP, with water either flowing directly into the lake or raising the groundwater table sufficiently to freshen Big Soda Lake. The initial increase in salinity likely was caused by decreased flow of the Walker River due to Middle Holocene aridity. The lake level lowered slowly, and more saline conditions prevailed until 4.3 m depth when water from the Walker River stopped flowing into the Carson River basin. Above 4.3 m depth, diatom and isotopic evidence indicates that the lake became consistently saline. The isotopic and diatom assemblage transitions observed in Big Soda Lake sediment are not consistent with climate reconstructions and demonstrate that hydrologic shifts in a basin can be an important driver of change regardless of climatic conditions. However, climate shifts may also play a role in the hydrologic changes by supplying more or less water to river courses that may induce river avulsion.

Nevada↗
USGS2021

History of Great Salt Lake, Utah, USA: Since the termination of Lake Bonneville

During the past half century or so diverse histories of Great Salt Lake have been written from differing perspectives and all of them have contributed ideas and essential data. The published literature, however, can be confusing and misleading. In this chapter, we review and provide context for a number of those publications. This chapter is intended as a summary of what is known, what is not known, and what cannot be known with precision about the history of the lake. Great Salt Lake is the largest hydrographically closed lake in the Bonneville basin of northwestern Utah. It responds to both short-term weather and long-term climate. In the Lake Bonneville/Great Salt Lake lacustrine system, the end of Lake Bonneville at 13,000 yr BP marks the beginning of Great Salt Lake. The much larger and deeper lakes of the Bonneville lake cycle responded to the pluvial climate of oxygen isotope stage 2, but the warmer, drier climate of oxygen isotope stage 1 led to rapid fluctuations within a relatively narrow, well-documented elevation range, 5 m above and 9 m below the historical mean elevation of ~1280 m. Two exceptional but short-lived rises of Great Salt Lake to elevations higher than 5 m above ~1280 m have been documented —one during the Gilbert episode, which peaked about 11,600 yr BP near an elevation of 1295 m, and one to about 1289 m sometime after about 11,000 yr BP. The historical Great Salt Lake hydrograph (the past 150 years) shows its labile behavior. Smooth-curve hydrographs based on estimates of lake level at time scales of decades, centuries, or millennia, such as those presented in previous publications, do not accurately portray the way lake level rises and falls, and a precise plot of post-Bonneville changes in level of Great Salt Lake would resemble the “jagged” historical record. The available sedimentary and geomorphic data are not conducive at this time to the production of a highly precise hydrograph, so we suggest that post-Bonneville lake-level history be portrayed, imprecisely but accurately, as confined generally between the elevation limits of 1285 and 1271 m, with an indication of the exceptional spikes in the lake level.

Utah↗
USGS2021

Polar bear foraging behavior

Polar bears forage in the marine environment, primarily on the sea ice over the shallow waters of the continental shelf. They are solitary, ambush hunters that catch ringed and bearded seals when they surface to breathe in ice holes or haul out on the ice to rest and molt. In most parts of their range, polar bears experience dramatic seasonal variability in their ability to catch seals, with foraging success peaking in late spring and early summer when seal pups are weaned. During this time, the body mass of polar bears can nearly double, especially in pregnant females, such that body composition may reach 49% body fat. The accumulation of body fat is vital for these bears to survive through the autumn and winter when seals are less accessible or when pregnant adult female bears enter dens and fast. When the sea ice retreats in summer, some bears exhibit a temporary switch to omnivory, feeding on a variety of terrestrial food. However, the energetic benefit of most terrestrial food is small relative to their marine mammal prey and, in some regions, increased land use has been associated with declines in body condition. Reduced accessibility of seal prey to polar bears as a result of global climate change threatens the long-term sustainability of this Arctic predator.

Book chapter↗
USGS2021

Sea otter foraging behavior

Sea otters are marine specialists but diet generalists, which feed primarily on benthic mega-invertebrates (i.e., body dimension >1 cm). They locate and capture epibenthic and infaunal prey with their forepaws by relying on vision and tactile sensitivity during short-duration dives (generally <2 min) in shallow waters (routine dives <30 m and maximum dive depth ~100 m) of the littoral zone. Sea otters have an elevated resting metabolic rate and small or no energy reserves in the form of blubber, so they feed every 3–4 h. Foraging dives often occur in bouts (i.e., two or more consecutive dives), which may last several hours with 1–2 min between dives, depending on the type of prey. Sea otters consume small or soft prey entirely or use their teeth or stone tools to access the flesh of mega-invertebrates with a shell, test, or exoskeleton. The daily percentage of time that sea otters devote to foraging depends on age, sex, presence of a pup, time of year, and prey abundance, which varies geographically, seasonally, and episodically. In areas occupied by sea otters for many years, epifaunal prey generally decline first followed by infaunal species, and this may result in greater foraging effort and diet specialization associated with density-dependent competition for food. Although prey availability strongly influences sea otter carrying capacity, both intrinsic and extrinsic factors influence population equilibrium density, resulting in spatiotemporal variations in foraging behavior.

Book chapter↗
USGS2021

Sea otter predator avoidance behavior

Predators directly affect their prey as a source of mortality, and prey respond by employing antipredator strategies. Sea otters are a keystone predator within the nearshore community, but higher trophic level avian, terrestrial, and pelagic predators (e.g., bald eagles, brown bears, wolves, white sharks, and killer whales) prey on them. Three antipredator strategies used by sea otters are vigilance (group or sentinel detection of danger), avoidance (seeking a location that is inaccessible to predators), and crypsis (the ability to avoid observation or detection). Vigilant behavior allowed sea otters to escape total extinction during the Maritime Fur Trade of the eighteenth and nineteenth centuries. Female otters with pups practice vigilance when they reduce their foraging time and move along meandering paths. Sea otters usually rest at sea, and when they rest on shore, they usually haul out on offshore rocks, reefs, and small islands—possibly a behavioral response to terrestrial predators (brown bears and wolves can kill non-vigilant sea otters on shore). In areas where many sea otters haul out together, group vigilance may be important in detecting an approaching threat. Along the coast of central California, white sharks are a significant source of sea otter mortality, and the only antipredator strategy is avoidance or crypsis by resting in kelp beds. Despite the threat, sea otters still forage in open water, so the perception of risk may be low. In the western Aleutian Islands, killer whale predation is believed to be the cause of a > 90% decline in sea otters. As a result, sea otters perceive killer whales as a threat and limit their movements to shallow, complex habitats where the risk of attack is low. This behavioral response is so strong in the western Aleutian Islands that it may it limit sea otter dispersal among islands, with implications for the connectivity and genetic health of the small, isolated populations that remain.

Book chapter↗