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At least 1,081 records · Page 60Linked to original sources
USGS2017

2.3. Global-scale atmospheric dispersion of microorganisms

This chapter addresses long-range dispersion and the survival of microorganisms across a wide range of altitudes in Earth's atmosphere. Topics include mechanisms of dispersion, survivability of microorganisms known to be associated with long-range transport, natural and artificial sources of bioaerosols, residence time estimation through the use of proxy aerosols, transport and emission models, and monitoring assays (both culture and molecular based). We conclude with a discussion of the known limits for Earth's biosphere boundary, relating aerobiology studies to planetary exploration given the large degree of overlapping requirements for in situ studies (including low biomass life detection and contamination control).

Book chapter↗
USGS2017

Earthquake source properties from instrumented laboratory stick-slip

Stick-slip experiments were performed to determine the influence of the testing apparatus on source properties, develop methods to relate stick-slip to natural earthquakes and examine the hypothesis of McGarr [2012] that the product of stiffness, k , and slip duration, Δ t , is scale-independent and the same order as for earthquakes. The experiments use the double-direct shear geometry, Sierra White granite at 2 MPa normal stress and a remote slip rate of 0.2 µm/sec. To determine apparatus effects, disc springs were added to the loading column to vary k . Duration, slip, slip rate, and stress drop decrease with increasing k , consistent with a spring-block slider model. However, neither for the data nor model is k Δ t constant; this results from varying stiffness at fixed scale. In contrast, additional analysis of laboratory stick-slip studies from a range of standard testing apparatuses is consistent with McGarr's hypothesis. k Δ t is scale-independent, similar to that of earthquakes, equivalent to the ratio of static stress drop to average slip velocity, and similar to the ratio of shear modulus to wavespeed of rock. These properties result from conducting experiments over a range of sample sizes, using rock samples with the same elastic properties as the Earth, and scale-independent design practices.

Book chapter↗
USGS2016

Dynamics of permeability evolution in stimulated geothermal reservoirs

Spatially and temporally evolving permeability fields are fundamentally associated with the operation of enhanced geothermal systems. This chapter explores the resulting magnitude and patterns of permeability alteration as well as the coupled physical processes that control the evolution of permeability during shear stimulation and long-term evolution of a geothermal reservoir. It also explores mechanisms involved in the enhancement of fracture permeability, targeting injection pressures that encourage self-propping shear stimulation alongside elastic pressure and thermal dilatation of fracture sets. Simulation of a short-term, high-injection-rate enhanced geothermal system stimulation explored the importance of hydraulic versus thermal effects and the impact of a temperature differential between fluid in the fractures and the adjoining rock matrix. The effects of variations in fracture spacing on the evolution of permeability is at least as important as the magnitude of initial permeability, and quantifying the driving mechanisms is critical to understanding reservoir response.

Book chapter↗
USGS2017

Brown trout as an invader: A synthesis of problems and perspectives in western North America

Brown trout are one of the most pervasive and successful invaders worldwide and are ubiquitous across the Intermountain West, USA (IMW). This species is the foundation of extremely popular and economically significant sport fisheries despite well-established negative effects on native fishes and ecosystems, resulting in very challenging, and often opposing, conservation and management goals. Herein, we review the direct (e.g., competition and predation) and indirect (e.g., disease vectors) pathways through which brown trout across the IMW have posed a threat to native species. We discuss the importance of brown trout as economically and culturally important fisheries, especially in novel tailwater ecosystems created by damming. To this end, we surveyed 24 experts from eight states across the IMW to document the relevance of novel brown trout fisheries in 51 tailwaters and found brown trout are thriving in these novel ecosystems, which are often unsuitable for native fishes. We discuss the challenging interplay between protecting native species and managing novel brown trout fisheries. Notably, the future of exotic brown trout in the IMW is shifting as the prestige of native fisheries is growing and many non-native eradication efforts have occurred. The future of exotic brown trout in the IMW, will depend on the nexus of public sentiment and policy, the effectiveness of eradication efforts, and the effect of climate change on both the native fishes and exotic brown trout. Regardless, because brown trout are pervasive and have a broad distribution through the IMW, populations of this species will likely persist at least in some locations into the future.

Book chapter↗
USGS2018

Modeling and simulation of emergent behavior in transportation infrastructure restoration

The objective of this chapter is to create a methodology to model the emergent behavior during a disruption in the transportation system and that calculates economic losses due to such a disruption, and to understand how an extreme event affects the road transportation network. The chapter discusses a system dynamics approach which is used to model the transportation road infrastructure system to evaluate the different factors that render road segments inoperable and calculate economic consequences of such inoperability. System dynamics models have been integrated with business process simulation model to evaluate, design, and optimize the business process. The chapter also explains how different factors affect the road capacity. After identifying the various factors affecting the available road capacity, a causal loop diagram (CLD) is created to visually represent the causes leading to a change in the available road capacity and the effects on travel costs when the available road capacity changes.

Book chapter↗
USGS2019

Empirical estimation of natural geoelectric hazards

Geoelectric field time series can be estimated by convolving estimates of Earth‐surface impedance, such as those obtained from magnetotelluric survey measurements, with historical records of geomagnetic variation obtained at magnetic observatories. This straightforward procedure permits the mapping of geoelectric field variation during magnetic storms. Statistical analysis of the time series allows extrapolation to extreme‐value amplitudes, such as might be realized during an intense magnetic storm in the future. The development of these products is illustrated for the Mid‐Atlantic United States, using impedances obtained from EarthScope survey data and geomagnetic variation records obtained at the Fredericksburg observatory operated by the U.S. Geological Survey. For this region, 100‐year geoelectric exceedance amplitudes have a range of almost three orders of magnitude (from 0.04 V/km at a site in southern Pennsylvania to 24.29 V/km at a site in central Virginia), and they have significant geographic granularity, which is due to site‐to‐site differences in surface impedance (and subsurface electrical conductivity structure). Maps of 100‐year exceedance amplitudes resemble those of geoelectric amplitudes for the March 1989 magnetic storm, and, in that sense, the March 1989 storm resembles what might be loosely called a “100‐year” event.

Book chapter↗
USGS2019

The first 3D conductivity model of the contiguous US: Reflections on geologic structure and application to induction hazards

Estimation of ground level geoelectric fields has been identified by the National Space Weather Action Plan as a key component of assessment and mitigation of space weather impacts on critical infrastructure. Estimates of spatially and temporally variable electric fields are used to generate statistically based hazard maps and show promise toward monitoring and responding to geomagnetic disturbances in near real‐time. One approach to geoelectric field estimation is to employ three‐dimensional (3D) Earth conductivity models. These data‐constrained conductivity models are the results of regional magnetotelluric inversions based primarily on NSF’s Earthscope USArray impedances, which to date cover ~60% of the contiguous United States. Here, we present the first‐ever composite conductivity model of the contiguous United States and describe its compilation from 3D regional conductivity models, a global mantle conductivity model, offshore bathymetry, and sediment thickness data. We discuss structures within the conductivity model and how they relate to the complex geologic tapestry of the continent. Finally, we discuss the utility of this synthesis model for estimation and mitigation of geomagnetically induced currents.

Book chapter↗
USGS2021

Radiometric constraints on the timing, tempo, and effects of large igneous province emplacement

There is an apparent temporal correlation between large igneous province (LIP) emplacement and global environmental crises, including mass extinctions. Advances in the precision and accuracy of geochronology in the past decade have significantly improved estimates of the timing and duration of LIP emplacement, mass extinction events, and global climate perturbations, and in general have supported a temporal link between them. In this chapter, we review available geochronology of LIPs and of global extinction or climate events. We begin with an overview of the methodological advances permitting improved precision and accuracy in LIP geochronology. We then review the characteristics and geochronology of 12 LIP/event couplets from the past 700 Ma of Earth history, comparing the relative timing of magmatism and global change, and assessing the chronologic support for LIPs playing a causal role in Earth's climatic and biotic crises. We find that (1) improved geochronology in the last decade has shown that nearly all well-dated LIPs erupted in < 1 Ma, irrespective of tectonic setting; (2) for well-dated LIPs with correspondingly well-dated mass extinctions, the LIPs began several hundred ka prior to a relatively short duration extinction event; and (3) for LIPs with a convincing temporal connection to mass extinctions, there seems to be no single characteristic that makes a LIP deadly. Despite much progress, higher precision geochronology of both eruptive and intrusive LIP events and better chronologies from extinction and climate proxy records will be required to further understand how these catastrophic volcanic events have changed the course of our planet's surface evolution.

Book chapter↗
USGS2024

Rare Earth Elements in coal fly ash and their potential recovery

Coal fly ash is a potential resource of valuable elements, such as rare earth elements (REEs), which are retained and concentrated upon combustion. Understanding REE occurrence within fly ash is vital to developing recovery methods. Some of the highest REE contents occur in fly ash derived from U.S. Appalachian Basin coals, and coals influenced by input volcanic ash are especially enriched. Leaching studies of bulk fly ash show that, as a proportion of the total REEs present, samples from eastern U.S. coals are generally less extractable than fly ash derived from lower REEs western U.S. coals. Aluminosilicate glasses formed during combustion comprise the largest mass fraction of coal fly ash. REE-enriched domains are present locally in fly ash at the nanometer scale. Annual fly ash production, combined with coal ash already in storage, makes up a large resource for potential recovery of rare earths and associated critical elements. Further extraction technology developments are needed to overcome difficulties in REE concentration and purification to produce coal-ash-derived REE materials of saleable purity.

Book chapter↗
USGS2023

Forecasting water levels using machine (deep) learning to complement numerical modelling in the southern Everglades, USA

Water level is an important guide for water resource management and wetland ecosystems, defining one of the most basic processes in hydrology. This research seeks to investigate the possibility of complementing numerical modeling with a Machine Learning (ML) model to forecast daily water levels in the southern Everglades in Florida, USA. An exact analytical solution to water level may not be possible, but using the computational methods afforded by ML, the traditional numerical techniques may be enhanced to generate more robust, scalable predictions. Five locations were chosen for application of the Time-Delayed Neural Network (TDNN) and Long-Short Term Memory Recurrent Neural Network (LSTM-RNN) ML models, which were built to estimate water level with 1, 2, 3, 7 and 10 day forecasts using a simulation step of 1 day. The results showed that rainfall forecasts from weather models could improve water-level forecasts if the accuracy and performance of the weather models can be improved. The ML models presented here improve water-level predictions from a historical hydrologic model for a 24 hour forecast horizon.

Florida↗
USGS2021

Land management strategies influence soil organic carbon stocks of prairie potholes of North America

Soil organic carbon (SOC) stocks of Prairie Pothole Region (PPR) wetlands in the central plains of Canada and the United States are highly variable due to natural variation in biota, soils, climate, hydrology, and topography. Land-use history (cropland, grassland) and land-management practices (drainage, restoration) also affect SOC stocks. We conducted a region-wide assessment of wetland SOC stocks using data from the Canadian and US portions of the PPR under various management types. Natural wetlands with no disturbance history in the wetland basin or surrounding catchment had considerably greater average SOC stocks in the upper (0–15 cm) soil profile than wetlands surrounded by cropland. Hydrologically restored wetlands did not show significantly greater SOC stocks than drained wetlands, but wetlands surrounded by restored grasslands did have greater SOC stocks in the upper soil profile than those surrounded by croplands. Similarities among cropped and restored wetlands likely were due to insufficient time since restoration, as well as high variability attributable to several environmental factors within the region. We conclude that avoided loss of natural wetlands from drainage and avoided loss of native grasslands from cropping have the most benefit for preserving wetland SOC stocks. Robust PPR SOC models that incorporate multiple abiotic, biotic, and land-use factors are required to determine where and when restoration is most effective for SOC sequestration.

Book chapter↗
USGS2021

Winter flooding to conserve agricultural peat soils in a temperate climate: Effect on greenhouse gas emissions and global warming potential

This study investigated the CO 2 and CH 4 emission rates from agricultural operations on peat soils in the Sacramento-San Joaquin Delta, comparing two common soil management treatments: leaving the field fallow in the winter and flooding the field in winter. Winter flooding is intended to reduce the oxidative loss of soil organic matter to CO 2 , as well as other putative benefits. The goal of the study was to assess if winter flooding lowers overall net carbon loss from the field and if it increases the net CH 4 emissions to a degree that results in a net increase in Global Warming Potential (GWP). The two treatments had similar annual carbon emissions (1.7–1.8 g C/m 2 /d) with the measured annual CO 2 flux rates for both among the highest previously reported, indicating that the flooding treatment did not effectively mitigate subsidence and loss of soil carbon. The flooded treatment had among the highest annual CH 4 emissions previously reported (64.1 mg C/m 2 /d), an order of magnitude greater than that measured on the fallow treatment (5.9 mg C/m 2 /d). Despite the much larger flux of CH 4 from the flooded treatment, when the net carbon export associated with grain harvest and hydrologic transport is included, the differences in the carbon balance and GWP (equivalent to CO 2 emissions of ~775 g C/m 2 /yr) between treatments is insignificant. Total greenhouse gas emissions and GWP of both sites are among the largest previously documented from cultivated peat systems, putting their climatic effect on par with freshwater wetlands, but without the concomitant soil conservation and carbon sequestration benefits of continuous flooding.

Book chapter↗
USGS2021

Carbon fluxes and potential soil accumulation within Greater Everglades cypress and pine forested wetlands

In forested wetlands, accumulation of organic matter in soil is partly governed by carbon fluxes where photosynthesis, respiration, lateral advection of waterborne carbon, fire-derived carbon emissions, and methanogenesis are balanced by changes in stored carbon. Stored carbon can eventually accumulate as soil over time if net primary productivity exceeds biomass decomposition. For this study, potential soil accumulation was estimated based on four years of continuous daily carbon cycling data and a one-dimensional mass-balance model of landscape-atmospheric exchange for cypress and pine forested wetlands in the Greater Everglades of south Florida. The mass-balance model was driven by eddy-covariance estimates of vertical net ecosystem exchange of carbon dioxide and methane. Key findings include confirmation of a basic premise of the historic Everglades restoration project; specifically, more water either from rainfall or water management encourages soil carbon accumulation and thus conservation of soils that support biologic activity and ecosystem services. For example, an anomalous wet season for south Florida that flooded the forested wetlands through the traditional dry season was followed by the most productive year for photosynthetic carbon uptake and potential soil accumulation. On the other hand, methane emissions were enhanced by the anomalous wet season and extended flooding – which confirmed a complex tradeoff to consider if wetlands are managed for both soil conservation and reduction of greenhouse gas emissions. Potential soil accumulation rates were about 1.7, 2.8, and 18 millimeters per year at the Dwarf Cypress, Cypress Swamp, and Pine Upland ecosystems, assuming soil C density values of 0.07, 0.09, and 0.02 grams of carbon per cubic centimeter, respectively. For these values of soil C density, the accumulation rates are considered a “best-case” upper limit because the lateral export of carbon in the canals and creeks that drain the study area were assumed negligible.

Florida↗
USGS2021

Modeling the impacts of hydrology and management on carbon balance at the Great Dismal Swamp, Virginia and North Carolina, USA

The impact of drainage on the stability of peatland carbon sinks is well known; however, much less is understood regarding the way active management of the water-table affects carbon balance. In this study, we determined the carbon balance in the Great Dismal Swamp, a large, forested peatland in the southeastern USA, which has been drained for over two hundred years and is now being restored through hydrologic management. We modeled future net ecosystem carbon balance over 100 years (2012 to 2112) using in situ field observations paired with simulations of water-table depth. The three scenarios used in the model were baseline conditions, flooded/wet conditions, and drained/dry conditions, which represent a range of potential management actions and climate conditions at the Great Dismal Swamp. In the Baseline scenario, results show a carbon sink of 0.7 Tg, or an average annual rate of 0.23 Mg C/ha/yr. The Flooded/Wet scenario produced a net ecosystem carbon balance of 4.6 Tg C or an average annual rate of 1.06 Mg C/ha/yr. For the Drained/Dry scenario, under which no management was conducted, and typically dry conditions were assumed, the Great Dismal Swamp becomes a net carbon source at –2.07 Tg C or an average annual rate of –0.38 Mg C/ha/yr.

North Carolina, Virginia↗
USGS2021

Ecosystem service co-benefits provided through wetland carbon management

What is the role of wetland carbon management in providing ecosystem services? Ecosystem services are the benefits that nature provides to people, and they are often categorized as: provisioning (e.g., food and water), regulating (e.g., climate mitigation and flood protection), cultural (e.g., cultural and recreational), and supporting (e.g., nutrient cycling) services ( www.millenniumassessment.org/ ). Ecosystem services are a function of the quantity and quality of the ecosystem. External factors such as land development, pollution, fragmentation, resource overuse, and climate change can negatively influence an ecosystem's capacity to provide ecosystem services; conversely, management actions to conserve and restore systems can increase ecosystem services (Pindilli, 2019). Wetland carbon management is a set of preservation, conservation, or restoration actions used to preserve ecosystem function that protects or enhances stored carbon or biologic carbon sequestration, with the intent to regulate climate (see Moomaw et al., 2018). By managing for wetland carbon resources, there is often a co-benefit of the preservation or enhancement of other ecosystem services; it may also increase ecosystem disservices (such as mosquito production). This chapter provides an overview of the types of ecosystem service co-benefits provided by wetland carbon management, with specific examples from the literature.

Book chapter↗
USGS2021

The importance of wetland carbon dynamics to society: Insight from the Second State of the Carbon Cycle Science Report

The Second State of the Carbon Cycle Report (SOCCR2) culminated in 19 chapters that spanned all North American sectors – from Energy Systems to Agriculture and Land Use – known to be important for understanding carbon (C) cycling and accounting. Wetlands, both inland and coastal, were found to be significant components of C fluxes along the terrestrial to aquatic hydrologic continuum. In this chapter, we synthesize the role of wetlands in the overall C footprint of North America (from Canada to Mexico) as one metric of the societal values placed on these terrestrial-aquatic interfaces. We also summarize the effects of management activities and climate change on the wetland C cycle and give some perspectives on the current and future importance of wetlands to society.

Geophysical Monograph Series↗
USGS2021

Carbon flux, storage, and wildlife co-benefits in a restoring estuary

Tidal marsh restorations may result in transitional mudflat habitats depending on hydrological and geomorphological conditions. Compared to tidal marsh, mudflats are thought to have limited value for carbon sequestration, carbon storage, and foraging benefits for salmon. We evaluated greenhouse gas exchange, sediment carbon storage, and invertebrate production at restoration and reference tidal marsh sites within the Nisqually River Delta, Puget Sound, Washington. Within the first seven years, the restoration site was a sparsely vegetated mudflat that didn't sequester atmospheric CO2; but, had sediment carbon accumulation rates similar to the reference site due to allochthonous carbon subsidies from nearby mature marshes. Compared to other estuarine habitat types, the tidal marsh supported the greatest production of energy-rich insect prey for juvenile salmon; yet, the restoration site produced similar, and at times elevated, invertebrate prey resources and prey energy compared to the reference site. As a result, salmon that foraged within the restoration site gained measurable benefits as indicated by their bioenergetic growth potential. The restoration site received carbon subsidies from the broader estuarine landscape for both sediment carbon accumulation and invertebrate prey production. These findings demonstrate the importance of habitat connectivity and show how blue carbon and wildlife co-benefits are closely intertwined.

Washington↗