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At least 307 records · Page 17Linked to original sources

USGS2015

Enhanced microbial coalbed methane generation: A review of research, commercial activity, and remaining challenges

Coalbed methane (CBM) makes up a significant portion of the world’s natural gas resources. The discovery that approximately 20% of natural gas is microbial in origin has led to interest in microbially enhanced CBM (MECoM), which involves stimulating microorganisms to produce additional CBM from existing production wells. This paper reviews current laboratory and field research on understanding processes and reservoir conditions which are essential for microbial CBM generation, the progress of efforts to stimulate microbial methane generation in coal beds, and key remaining knowledge gaps. Research has been primarily focused on identifying microbial communities present in areas of CBM generation and attempting to determine their function, in-situ reservoir conditions that are most favorable for microbial CBM generation, and geochemical indicators of metabolic pathways of methanogenesis (i.e., acetoclastic or hydrogenotrophic methanogenesis). Meanwhile, researchers at universities, government agencies, and companies have focused on four primary MECoM strategies: 1) microbial stimulation (i.e., addition of nutrients to stimulate native microbes); 2) microbial augmentation (i.e., addition of microbes not native to or abundant in the reservoir of interest); 3) physically increasing microbial access to coal and distribution of amendments; and 4) chemically increasing the bioavailability of coal organics. Most companies interested in MECoM have pursued microbial stimulation: Luca Technologies, Inc., successfully completed a pilot scale field test of their stimulation strategy, while two others, Ciris Energy and Next Fuel, Inc., have undertaken smaller scale field tests. Several key knowledge gaps remain that need to be addressed before MECoM strategies can be implemented commercially. Little is known about the bacterial community responsible for coal biodegradation and how these microorganisms may be stimulated to enhance microbial methanogenesis. In addition, research is needed to understand what fraction of coal is available for biodegradation, and methods need to be developed to determine the extent of in-situ coal biodegradation by MECoM processes for monitoring changes to coal quality. Questions also remain about how well field-scale pilot tests will scale to commercial production, how often amendments will need to be added to maintain new methane generation, and how well MECoM strategies transfer between coal basins with different formation water geochemistries and coal ranks. Addressing these knowledge gaps will be key in determining the feasibility and commercial viability of MECoM technology.

International Journal of Coal Geology↗

USGS2025

Navigating the possibilities and pitfalls of biocrust recovery in a changing climate

Biological soil crusts are complex communities composed of lichens, mosses, bacteria, and cyanobacteria that create a living skin on the soil surface across drylands worldwide. Although small in size, the vast area that biocrusts cover and the critical functions they provide make them a cornerstone of dryland health and resiliency. In addition to being important, biocrusts are exceptionally vulnerable to certain types of disturbance. Although they can withstand a wide range of temperatures and long periods without precipitation, biocrusts are highly sensitive to land-use change and are vulnerable to physical and compressional disturbance (i.e., trampling, vehicles, cattle, heavy machinery). In the face of these disturbances, a critical, long-standing question of interest to dryland ecologists is: Can biocrusts recover following disturbance without active intervention. If so, how long does it take? Early estimates of biocrust recovery suggested recovery can be incredibly slow (on the order of thousands of years), with more modern studies finding potential for faster recovery, especially with intervention. Multiple lines of evidence agree that recovery is context dependent, differing across climates, soils, and with the types of disturbance and biocrust. Additionally, active restoration of biocrusts is becoming more common as tractable strategies are developed for facilitating the establishment of biocrusts after disturbance. Here, we add to the body of knowledge about biocrust recovery following disturbances by reviewing recovery patterns, their connection to climate change, considerations for recovery in changing climates, and the role of restoration.

American Journal of Botany↗

USGS2017

Crotalus oreganus lutosus (Great Basin Rattlesnake). Defensive behavior/head hiding and tongue display

A variety of snake species employ head hiding as defensive behavior (Greene 1973. J. Herpetol. 7:143–161), but such behavior seems to be rarely observed in rattlesnakes. A recent report (Medica 2009. Herpetol. Rev. 40:95–97) presented observations on Crotalus scutulatus scutulatus and cited cases of similar behavior involving C. atrox , C. ruber , and C. viridis viridis . Here we report an encounter on 28 May 2016 with a C. oreganus lutosus (total length ca. 900 mm) observed 16 km S of Fallon, Churchill County, Nevada, USA. At 0925 h this snake was spotted by AKJ near the edge of the pavement on U.S. Hwy. 95. When approached, the snake presented typical active defensive behavior, with the rattle elevated (although not rattling), striking occasionally, and frequently flicking its conspicuous lavender and black tongue. As AKJ continued to take pictures the snake coiled more tightly (Fig. 1A), maintaining its rattle concealed and finally hiding its head beneath its coils (Fig. 1B). After photographing this pose AKJ made his first physical contact with the snake by scooping it up with a small shovel and placing it off the road. At this point the snake recovered its feisty attitude and would not retreat despite attempts to move it further away from the road. The snake did not rattle during the entire encounter (which lasted less than 5 min). Head hiding as a “last resort” in response to a persistent unavoidable threat may be more widespread within the family Crotalidae than previously documented.

Nevada↗

USGS2024

Measuring and interpreting the surface and shallow subsurface process influences on coastal wetland elevation: A review

A century ago, measuring elevation in tidal wetlands proved difficult, as survey leveling of soft marsh soils relative to a fixed datum was error prone. For 60 years, vertical accretion measures from marker horizons were used as analogs of elevation change. But without a direct measure of elevation, it was not possible to measure the total influence of surface and subsurface processes on elevation. In the 1990s, the surface elevation table (SET) method, which measures the movement of the wetland surface relative to a fixed point beneath the surface (i.e., the SET benchmark base), was combined with the marker horizon method (SET-MH), providing direct, independent, and simultaneous measures of surface accretion and elevation and quantification of surface and shallow subsurface process influences on elevation. SET-MH measures have revealed several fundamental findings about tidal wetland dynamics. First, accretion [ A ] is often a poor analog for elevation change [ E ]. From 50–66% of wetlands experience shallow subsidence ( A > E ), 7–10% shallow expansion ( A < E ), 7% shrink-swell, and for 24–36% A is an analog for E ( A = E ). Second, biological processes within the root zone and physical processes within and below the root zone influence elevation change in addition to surface processes. Third, vegetation plays a key role in wetland vertical dynamics. Plants trap sediment and increase resistance to erosion and compaction. Soil organic matter accumulation can lead to shallow expansion, but reduced plant growth can lead to subsidence, and plant death to soil collapse. Fourth, elevation rates are a better indicator of wetland response to sea-level rise than accretion rates because they incorporate subsurface influences on elevation occurring beneath the marker horizon. Fifth, combining elevation trends with relative sea-level rise (RSLR) trends improves estimates of RSLR at the wetland surface (i.e., RSLR wet ). Lastly, subsurface process influences are fundamental to a wetland’s response to RSLR and plant community dynamics related to wetland transgression, making the SET-MH method an invaluable tool for understanding coastal wetland elevation dynamics.

Estuaries and Coasts↗

USGS1989

Subsurface-water flow and solute transport: federal glossary of selected terms

The purpose of this report is to provide a glossary of selected terms for saturated and unsaturated flow and related processes involved in transport of contaminants in the subsurface. The glossary contains five tables. Table 1 is a list of parameters with associated symbols and units. Tables 2 to 5 are conversion charts. The original manuscript was prepared by Thomas J. Nicholson, U.S. Nuclear Regulatory Commission. It was subsequently examined by the Ground-Water Glossary Working Group and experts within and outside the Federal Government, whose recommendations were accommodated where appropriate in the glossary. It is hoped that the glossary will aid in the communications between soil scientists, hydrologists, and hydrogeologists. The terms defined in the glossary were selected after an extensive survey of glossaries and reports in the areas of (1) ground-water geology, hydraulics, and chemistry, (2) soil-water physics and chemistry, (3) contaminant transport, (4) unsaturated-zone hydrology, (5) chemistry and transport of solutes, and (6) ground-water quality. Some of the definitions have been modified for clarity from a variety of technical sources. Where more than one definition appears for the selected term, the first one was determined by the working group to be the most appropriate general definition, followed by other, more specialized, definitions. Some terms and definitions are not currently in use by all agencies; however, they are included in the glossary because they can be found in the literature. The reader is encouraged to consult with the original source cited for more explanatory comments. Additional regulatory definitions, which are underlined and are taken directly from the Code of Federal Regulations (CFR) and Federal laws (USC), were added following review by the various Federal agencies in May 1986. The definitions and conversion charts are from two principal sources provided herein. The first is the 11Glossary11 compiled by A. I. Johnson in the 1981 report by the American Society of Testing and Materials titled Permeability and Groundwater Contaminant Transport. The second is Manu a 1 40, 11Ground-water Management, 11 produced by the American Society of Civil Engineers in 1985.

Report↗

USGS2024

Plan to coordinate post-earthquake investigations supported by the National Earthquake Hazards Reduction Program (NEHRP)

Introduction This report presents a plan supported by the National Earthquake Hazards Reduction Program (NEHRP) to coordinate domestic and international post-earthquake investigations (herein called “the Plan”). Post-earthquake scientific and engineering investigations are undertaken to capture critical information to understand the causes and impacts of the event, lessons from which can substantially improve the Nation’s resilience after future earthquakes. NEHRP is the Federal Government’s coordinated nationwide program to reduce risks to life and property from earthquakes. The Plan describes the activation and coordination of the four designated NEHRP Agencies in the Federal Government: Federal Emergency Management Agency, National Institute of Standards and Technology, U.S. National Science Foundation, and U.S. Geological Survey (USGS). The Plan also describes coordination between NEHRP Agencies and other organizations that may participate in pre-event and post-earthquake investigations, including non-NEHRP Federal agencies; State, regional, local, Tribal, and territorial agencies; domestic nongovernmental organizations; academic institutions and affiliated organizations; private companies; foreign governmental agencies and nongovernmental organizations; and international organizations. The Plan delineates the coordination of NEHRP post-earthquake scientific and engineering investigations to document the direct, indirect, and cascading physical and societal impacts from fault rupture and ground shaking hazards and from secondary hazards such as landslides, liquefaction, and tsunamis. In addition, the Plan identifies pre-event activities necessary to ensure that post-earthquake investigations are executed effectively. The USGS is the lead NEHRP Agency for activating and coordinating NEHRP post-earthquake investigations and for implementing this Plan. The USGS also leads coordination of the NEHRP Agencies in completing the pre-event activities identified in the Plan. The Plan has new information and supersedes USGS Circular 1242, “The Plan to Coordinate NEHRP Post-Earthquake Investigations,” which was published in 2003. This second-generation Plan was developed with the assistance of the Applied Technology Council (ATC) of Redwood City, California, under USGS contract 140G0121P0309, ATC-155. A 17-member Project Review Panel provided guidance on plan development, and input was solicited from subject matter experts representing key stakeholder groups and from participants at a public workshop.

Circular↗

USGS2005

Native fishes of the Sacramento-San Joaquin drainage, California: A history of decline

In this paper, we review information regarding the status of the native fishes of the combined Sacramento River and San Joaquin River drainages (hereinafter the "Sacramento-San Joaquin drainage") and the factors associated with their declines. The Sacramento-San Joaquin drainage is the center of fish evolution in California, giving rise to 17 endemic species of a total native fish fauna of 28 species. Rapid changes in land use and water use beginning with the Gold Rush in the 1850s and continuing to the present have resulted in the extinction, extirpation, and reduction in range and abundance of the native fishes. Multiple factors are associated with the declines of native fishes, including habitat alteration and loss, water storage and diversion, flow alteration, water quality, and invasions of alien species. Although native fishes can be quite tolerant of stressful physical conditions, in some rivers of the drainage the physical habitat has been altered to the extent that it is now more suited for alien species. This interaction of environmental changes and invasions of alien species makes it difficult to predict the benefits of restoration efforts to native fishes. Possible effects of climate change on California's aquatic habitats add additional complexity to restoration of native fishes. Unless protection and restoration of native fishes is explicitly considered in future water management decisions, declines are likely to continue.

California↗

USGS2006

A review of major storm impacts on coastal wetland elevations

Storms have long been recognized as agents of geomorphic change to coastal wetlands. A review of recent data on soil elevation dynamics before and after storms revealed that storms affected wetland elevations by storm surge, high winds, and freshwater flushing of the estuary (inferred). The data also indicate that measures of sediment deposition and erosion can often misrepresent the amount and even direction of elevation change because of storm influences on subsurface processes. Simultaneous influence on both surface and subsurface processes by storms means that soil elevation cannot always be accurately estimated from surface process data alone. Eight processes are identified as potentiatly influencing soil elevation: sediment deposition, sediment erosion, sediment compaction, soil shrinkage, root decomposition (following tree mortality from high winds), root growth (following flushing with freshwater, inferred), soil swelling, and lateral folding of the marsh root mat. Local wetland conditions (e.g., marsh health, tide height, groundwater level) and the physical characteristics of the storm (e.g., angle of approach, proximity, amount of rain, wind speed, and storm surge height) were apparently important factors determining the storm's effect on soil elevation. Storm effects on elevation were both permanent (on an ecological time scale) and short-lived, but even short-term changes have potentially important ecological consequences. Shallow soil subsidence or expansion caused by a storm must be considered when calculating local rates of relative sea level rise and evaluating storm effects on wetland stability.

Estuaries and Coasts↗

USGS2020

Volcanological applications of unoccupied aircraft systems (UAS): Developments, strategies, and future challenges

Unoccupied aircraft systems (UAS) are developing into fundamental tools for tackling the grand challenges in volcanology; here, we review the systems used and their diverse applications. UAS can typically provide image and topographic data at two orders of magnitude better spatial resolution than space-based remote sensing, and close-range observations at temporal resolutions down to those of video frame rates. Responsive deployments facilitate dense time-series measurements, unique opportunities for geophysical surveys, sample collection from hostile environments such as volcanic plumes and crater lakes, and emergency deployment of ground-based sensors (and robots) into hazardous regions. UAS have already been used to support hazard management and decision-makers during eruptive crises. As technologies advance, increased system capabilities, autonomy and availability, supported by more diverse and lighter-weight sensors, will offer unparalleled potential for hazard monitoring. UAS are expected to provide opportunities for pivotal advances in our understanding of complex physical and chemical volcanic processes.

Volcanica↗

USGS2018

Spatial organization of the gastrointestinal microbiota in urban Canada geese

Recent reviews identified the reliance on fecal or cloacal samples as a significant limitation hindering our understanding of the avian gastrointestinal (gut) microbiota and its function. We investigated the microbiota of the esophagus, duodenum, cecum, and colon of a wild urban population of Canada goose ( Branta canadensis ). From a population sample of 30 individuals, we sequenced the V4 region of the 16S SSU rRNA on an Illumina MiSeq and obtained 8,628,751 sequences with a median of 76,529 per sample. These sequences were assigned to 420 bacterial OTUs and a single archaeon. Firmicutes , Proteobacteria , and Bacteroidetes accounted for 90% of all sequences. Microbiotas from the four gut regions differed significantly in their richness, composition, and variability among individuals. Microbial communities of the esophagus were the most distinctive whereas those of the colon were the least distinctive, reflecting the physical downstream mixing of regional microbiotas. The downstream mixing of regional microbiotas was also responsible for the majority of observed co-occurrence patterns among microbial families. Our results indicate that fecal and cloacal samples inadequately represent the complex patterns of richness, composition, and variability of the gut microbiota and obscure patterns of co-occurrence of microbial lineages.

Scientific Reports↗

USGS2020

Practices of biological soil crust rehabilitation in China: Experiences and challenges

Biological soil crusts (biocrusts) are a central component of dryland ecosystems. However, they are highly vulnerable to disturbance and natural recovery may be slow. Therefore, finding ways to enhance the reestablishment of biocrusts after disturbance has been of great interest to researchers. This article provides a review of the laboratory cultivation and field inoculations of biocrust materials in China (mostly published in Chinese). Larger filamentous cyanobacteria (e.g. Microcoleus ) are relatively easy, although slow, to grow in culture compared to other biocrust components. Thus, most researchers have focused their efforts on the cyanobacteria and a few species of mosses that are also easily grown but at smaller scale. For all the studies, a small amount of biocrust material was collected and its biomass enhanced under controlled conditions. However, the enhancement was done using various methods and techniques in different regions. These materials were then applied to disturbed field sites, again with various methods. Results show that keeping the inoculated soil surface wet for some time period after inoculation was crucial for restoration success. Cyanobacterial establishment was improved by installing automatic sprinkling using micro‐irrigation techniques and/or physical structures that reduced sediment moving onto the inoculated area. Experimental applications in China showed that cyanobacteria can be successfully inoculated at a large scale (hundreds of ha). Moss inoculation, on the other hand, was only accomplished at a small scale (several m 2 ). To assess whether biocrust restoration can enhance the establishment of a self‐supporting ecosystem, further research is needed on how inoculation affects vegetation diversity and structure and ecological processes.

Restoration Ecology↗

USGS2014

Phytoplankton primary production in the world's estuarine-coastal ecosystems

Estuaries are biogeochemical hot spots because they receive large inputs of nutrients and organic carbon from land and oceans to support high rates of metabolism and primary production. We synthesize published rates of annual phytoplankton primary production (APPP) in marine ecosystems influenced by connectivity to land – estuaries, bays, lagoons, fjords and inland seas. Review of the scientific literature produced a compilation of 1148 values of APPP derived from monthly incubation assays to measure carbon assimilation or oxygen production. The median value of median APPP measurements in 131 ecosystems is 185 and the mean is 252 g C m −2 yr −1 , but the range is large: from −105 (net pelagic production in the Scheldt Estuary) to 1890 g C m −2 yr −1 (net phytoplankton production in Tamagawa Estuary). APPP varies up to 10-fold within ecosystems and 5-fold from year to year (but we only found eight APPP series longer than a decade so our knowledge of decadal-scale variability is limited). We use studies of individual places to build a conceptual model that integrates the mechanisms generating this large variability: nutrient supply, light limitation by turbidity, grazing by consumers, and physical processes (river inflow, ocean exchange, and inputs of heat, light and wind energy). We consider method as another source of variability because the compilation includes values derived from widely differing protocols. A simulation model shows that different methods reported in the literature can yield up to 3-fold variability depending on incubation protocols and methods for integrating measured rates over time and depth. Although attempts have been made to upscale measures of estuarine-coastal APPP, the empirical record is inadequate for yielding reliable global estimates. The record is deficient in three ways. First, it is highly biased by the large number of measurements made in northern Europe (particularly the Baltic region) and North America. Of the 1148 reported values of APPP, 958 come from sites between 30 and 60° N; we found only 36 for sites south of 20° N. Second, of the 131 ecosystems where APPP has been reported, 37% are based on measurements at only one location during 1 year. The accuracy of these values is unknown but probably low, given the large interannual and spatial variability within ecosystems. Finally, global assessments are confounded by measurements that are not intercomparable because they were made with different methods. Phytoplankton primary production along the continental margins is tightly linked to variability of water quality, biogeochemical processes including ocean–atmosphere CO 2 exchange, and production at higher trophic levels including species we harvest as food. The empirical record has deficiencies that preclude reliable global assessment of this key Earth system process. We face two grand challenges to resolve these deficiencies: (1) organize and fund an international effort to use a common method and measure APPP regularly across a network of coastal sites that are globally representative and sustained over time, and (2) integrate data into a unifying model to explain the wide range of variability across ecosystems and to project responses of APPP to regional manifestations of global change as it continues to unfold.

Biogeosciences↗

USGS1977

A crystal-chemical classification of borate structures with emphasis on hydrated borates

The rules governing formation of hydrated borate polyanions that were proposed by C.L. Christ in 1960 are critically reviewed and new rules added on the basis of recent crystal structure determinations. Principles and classifications previously published by others are also critically reviewed briefly. The fundamental building blocks from which borate polyanions can be constructed are defined on the basis of the number n of boron atoms, and the fully hydrated polyanions are illustrated. Known structures are grouped accordingly, and a shorthand notation using n and symbols ?? = triangle, T = tetrahedron is introduced so that the polyanions can be easily characterized. For example, 3:??+2T describes [B3O3(OH)5]2-. Correct structural formulas are assigned borates with known structures whereas borates of unknown structure are grouped separately. ?? 1977 Springer-Verlag.

Physics and Chemistry of Minerals↗

USGS1991

Rockslides on the Terminus of "Jokulsargilsjokull", Southern Iceland

On 10 November 1976, a 1.5 km × 0.5 km rockslide deposit on the surface of an unnamed outlet glacier of Mýrdalsjökull ice cap, southern Iceland, was observed from an aircraft. Deposits from two different rockslides, including the larger one observed on 10 November 1976, were visible on a 10 September 1978 aerial photograph of the unnamed outlet glacier. An analysis of vertical and oblique aerial photographs, Landsat images, and seismological records was used to establish the time of occurrence of the larger rockslide to a 30-day period between 9 September 1972 and 9 October 1972. The trigger mechanisms for the rockslide activity appear to have been heavy precipitation prior to the event and the decrease of buttressing mass at the base of the valley wall resulting from recession of the glacier (decrease in width and thickness). The recession led to instability of highly altered hyaloclastite bedrock, talus, and morainal materials on an oversteepened slope. An earthquake as a trigger mechanism was considered to be unlikely from a thorough review of seismic records. Measurements of the downglacier movement of the larger rockslide deposit give an average speed of the glacier as 30±3 m a-1 between September/October 1972 and 10 September 1978. From measurements of aerial photographs taken on 10 September 1978 and 4 September 1984, the average speed of the glacier increased to 45 m a-1 during this 6-year interval. Although the terminus of the unnamed outlet glacier had not yet begun to advance in 1986, it had undergone thickening since 1978.

Geografiska Annaler, Series A: Physical Geography↗

USGS1980

Chemical and physical characteristics of precipitation at selected sites in Florida

Infrequent sampling of precipitation in Florida has been conducted by the U.S. Geological Survey since 1965. A summary of the historical data from 24 sites throughout Florida indicate that the principal ionic composition of atmospheric precipitation samples is calcium-sodium and bicarbonate-chloride with an average specific conductance of 32 micromhos per centimeter at 25 C. Historically, much of the sampling focused on primary nutrients and selected trace elements. Historical data indicate that nitrogen and phosphorus concentrations averaged 1.1 and 0.1 milligrams per liter, respectively. The limited trace metal data indicate that motor-vehicle activity may have a significant impact on local precipitation quality. Lead, for example, was measured in concentrations of as much as 2,400 micrograms per liter in samples collected in a highly populated, commerical area in south Florida. Statistical testing indicated that most major inorganic constituents, primary nutrients, and trace metals were significantly differnet among the sampling sites. The pH data indicated a range of about 5.0 to 7.0, but only limited pH data were collected and analyzed at the historical sites in such a timely manner as to represent pH conditions of the atmospheric precipitation during active rainfall. A critical review of the historical data suggested that while they may reflect local atmospheric quality conditions they likely do not define baseline conditions from a regional perspective. The application of these data were generally limited regarding regional extrapolation due to lack of standardization of sampling techniques, variable methods of sample preservation, nonuniform sampling intervals, variable sample sizes, and different periods of record. (USGS)

Water-Resources Investigations Report↗

USGS2017

Economics, helium, and the U.S. Federal Helium Reserve: Summary and outlook

In 2017, disruptions in the global supply of helium reminded consumers, distributors, and policy makers that the global helium supply chain lacks flexibility, and that attempts to increase production from the U.S. Federal Helium Reserve (the FHR) may not be able to compensate for the loss of one of the few major producers in the world. Issues with U.S. and global markets for helium include inelastic demand, economic availability of helium only as a byproduct, only 4–5 major producers, helium’s propensity to escape earth’s crust, an ongoing absence of storage facilities comparable to the FHR, and a lack of consequences for the venting of helium. The complex combination of these economic, physical, and regulatory issues is unique to helium, and determining helium’s practical availability goes far beyond estimating the technically accessible volume of underground resources. Although most of these issues have been analyzed since helium was recognized to be a valuable mineral commodity in the early 1900s, very few economic models have been developed that adequately consider the unique characteristics of helium and helium markets. In particular, there is a notable lack of recent empirical work to estimate the responsiveness of helium demand, supply, prices, and trade patterns to the ongoing drawdown and sale of helium reserves stored in the FHR. In general, existing models of helium either do not account for an oligopoly controlling supply, or they do not evaluate potential helium extraction and storage programs based on an intertemporal maximization of the value of the resource. Such models could be of very limited use to decision makers. This review found only one working paper with a helium market model that has incorporated both of these vital considerations. That and other economic studies along similar lines could be very useful in helping inform current helium policy discussions and decisions.

Natural Resources Research↗

USGS2014

Identifying sources of aeolian mineral dust: Present and past

Aeolian mineral dust is an important component of the Earth’s environmental systems, playing roles in the planetary radiation balance, as a source of fertilizer for biota in both terrestrial and marine realms and as an archive for understanding atmospheric circulation and paleoclimate in the geologic past. Crucial to understanding all of these roles of dust is the identification of dust sources. Here we review the methods used to identify dust sources active at present and in the past. Contemporary dust sources, produced by both glaciogenic and non-glaciogenic processes, can be readily identified by the use of Earth-orbiting satellites. These data show that present dust sources are concentrated in a global dust belt that encompasses large topographic basins in low-latitude arid and semiarid regions. Geomorphic studies indicate that specific point sources for dust in this zone include dry or ephemeral lakes, intermittent stream courses, dune fields, and some bedrock surfaces. Back-trajectory analyses are also used to identify dust sources, through modeling of wind fields and the movement of air parcels over periods of several days. Identification of dust sources from the past requires novel approaches that are part of the geologic toolbox of provenance studies. Identification of most dust sources of the past requires the use of physical, mineralogical, geochemical, and isotopic analyses of dust deposits. Physical properties include systematic spatial changes in dust deposit thickness and particle size away from a source. Mineralogy and geochemistry can pinpoint dust sources by clay mineral ratios and Sc-Th-La abundances, respectively. The most commonly used isotopic methods utilize isotopes of Nd, Sr, and Pb and have been applied extensively in dust archives of deep-sea cores, ice cores, and loess. All these methods have shown that dust sources have changed over time, with far more abundant dust supplies existing during glacial periods. Greater dust supplies in glacial periods are likely due to greater production of glaciogenic dust particles from expanded ice sheets and mountain glaciers, but could also include dust inputs from exposed continental and insular shelves now submerged. Future dust sources are difficult to assess, but will likely differ from those of the present because of global warming. Global warming could bring about shifts in dust sources by changes in degree or type of vegetation cover, changes in wind strength, and increases or decreases in the size of water bodies. A major uncertainty in assessing dust sources of the future is related to changes inhuman land use, which could affect land surface cover, particularly due to increased agricultural endeavors and water usage.

Book chapter↗

USGS2019

Hydraulic, geochemical, and thermal monitoring of an aquifer system in the vicinity of Mammoth Lakes, Mono County, California, 2015–17

Since 2014, the U.S. Geological Survey has been working in cooperation with the Bureau of Land Management, Mono County, Ormat Technologies, Inc., and the Mammoth Community Water District to design and implement a groundwater-monitoring program for the proposed Casa Diablo IV Geothermal Power Project in Long Valley Caldera, California, to characterize baseline groundwater-level, water-temperature, and water-chemistry conditions at dedicated monitoring wells and municipal supply wells. The publicly available data and the analyses provided here represent quality-assured and peer-reviewed information to help with the management of the thermal and non-thermal water resources beneath and in the vicinity of the town of Mammoth Lakes, California. The methods of data collection for continuous water levels and quarterly water-temperature profiles for two 600-foot-deep monitoring wells during 2016 through 2017 are discussed. Also discussed are the methods of water-sample collection and characterizations of the water chemistry in numerous wells in the multilayered aquifer system beneath Mammoth Lakes. Additionally, the methodology used to develop digital (mathematical) filters to remove or reduce the effects of barometric pressure and solid Earth tides on the continuous water-level records is discussed. Digitally filtered water levels for a 2017 flow test of a deep geothermal production well are described, and various aquifer responses observed during the flow test are discussed. These are further considered in a companion evaluation of potential physical and chemical influences on the water-level data collected during the flow test. The digitally filtered water-level data indicated that some hydraulic communication exists between the deep geothermal aquifer and shallow groundwater aquifer at the location of the flow test, northeast of Mammoth Lakes. Groundwater-chemistry data from three wells indicated that shallow groundwater naturally mixes with a small component of geothermal water along the northern periphery of the shallow aquifer system at Mammoth Lakes.

California↗