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At least 1,495 records · Page 83Linked to original sources

USGS2019

Patterns of primary production and ecological drought in Yellowstone

Introduction: Photosynthesis converts sunlight into stored energy in millions of leaves, flowers and seeds that maintain the web of life in Yellowstone. This transformation of energy fixes carbon, supplies organic matter to soils, and can become fuel for wildfire. As the first link of the food chain, new plant biomass is called primary production and provides energy to consumers, including wildlife. While Yellowstone is a mountain environment with deep winter snowpack, the park can get very dry in some years as evidenced by massive wildfires in 1988 and 2016. Droughts like these not only contribute to fire potential, but they affect primary production, the food chain and likely will play an increasingly important role in transforming vegetation structure and composition in the future. Meteorological, agricultural, and hydrological drought have been assessed quantitatively for many years, but key indicators of drought in wildland ecosystems have not been formally defined until recently (Crausbay et al., 2017). One promising new method to do this is by measuring how vegetation responds to negative effects of drought, and positive effects of favorable conditions that offset negative effects of drought. The balance of drought stress and growth has important implications for future vegetation condition as the climate of Yellowstone changes. Monitoring primary production, and predicting future vegetation changes are needed to provide a comprehensive view of park health and anticipate future ecosystem changes (Crabtree et al. 2009, Nemani et al. 2009). Although an important indicator of ecosystem condition, primary production can be time and resource-intensive to monitor in wildland settings using traditional ground-based methods such as clipping and weighing. Fortunately, ground-based methods can be complemented and enhanced by monitoring primary production with satellite imagery. Measurements of solar radiation reflectance in visible and near infra-red wavelengths can indicate primary production at frequent weekly intervals from the Moderate Resolution Imaging Spectrometer (MODIS) on satellites operated by NASA. The Greater Yellowstone Inventory and Monitoring Network (GRYN) uses this information to track changes in primary production across Yellowstone over time. They link these measurements to vegetation types, soils, and climate to understand where and when changes in production have occurred and may occur in the future.

Yellowstone National Park↗

USGS2023

Subsurface porewater flow accelerates talik development under the Alaska Highway, Yukon: A prelude to road collapse and permafrost thaw?

The presence of taliks (perennially unfrozen zones in permafrost areas) adversely affects the thermal stability of infrastructure in cold regions, including roads. The role of heat advection on talik development and feedback on permafrost degradation has not been quantified methodically in this context. We incorporate a surface energy balance model into a coupled groundwater flow and energy transport numerical model (SUTRA-ice). The model, calibrated with long-term observations (1997–2018 on the Alaska Highway), is used to investigate and quantify the role of heat advection on talik initiation and development under a road embankment. Over the 25-year simulation period, the new model is driven by reconstructed meteorological data and has a good agreement with near surface soil temperatures. The model successfully reproduces the increasing depth to the permafrost table (mean absolute error <0.2 m), and talik development. The results demonstrate that heat advection provides an additional energy source that expedites the rate of permafrost thaw and roughly doubles the rate of permafrost table deepening, compared to purely conductive thawing. Talik initially formed and grew over time under the combined effect of water flow, snow insulation, road construction and climate warming. Talik formation creates a new thermal state under the road embankment, resulting in acceleration of underlying permafrost degradation, due to the positive feedback of heat accumulation created by trapped unfrozen water. In a changing climate, mobile water flow will play a more important role in permafrost thaw and talik development under road embankments, and is likely to significantly increase maintenance costs and reduce the long-term stability of the infrastructure.

Yukon↗

USGS2011

Feeding ecology and energetics

Successful management of walleye and sauger populations often requires a detailed knowledge of prey resources. As with many fishes, diets of juvenile Sander spp. are often different than those of adult fish and can have important implications for growth and survival. Similarly, spatial and temporal variation in diet composition can contribute to variation in growth and production of Sander populations. Thus, management efforts (e.g., stocking) aimed at enhancing walleye and sauger populations benefit from the knowledge and tools to effectively quantify feeding patterns. Today, fisheries managers face a myriad of challenges posed by nonnative species, eutrophication, climate change, and water availability, to name just a few. As a result, knowledge about prey use, energetics, and effects of Sander populations on food web structure has increased dramatically in the last 30 years. Experimental work with larval and juvenile walleyes has provided new insights into factors affecting growth and survival during early life stages (see Chapter 7) that has benefitted management and propagation efforts. Similarly, contemporary analytical approaches, such as bioenergetics modeling and stable isotope analysis, have improved our understanding of walleye foraging behavior and provided new tools for exploring trophic interactions. In this chapter, we review the general feeding ecology of walleye and sauger and highlight contemporary approaches for quantifying energy acquisition and trophic interactions.

Book chapter↗

USGS2002

The effects of atmospheric nitrogen deposition in the Rocky Mountains of Colorado and southern Wyoming— A synthesis and critical assessment of published results

The Rocky Mountain region of Colorado and southern Wyoming receives as much as 7 kilograms per hectare per year ((kg/ha)/yr) of atmospheric nitrogen (N) deposition, an amount that may have caused changes in aquatic and terrestrial life in otherwise pristine ecosystems. The Rocky Mountain National Park, in its role of protecting air-quality related values under provisions of the Clean Air Act Amendments of 1977, has provided support for this synthesis and critical assessment of published literature on the effects of atmospheric N deposition. Results from published studies indicate a long-term increase in the rate of atmospheric N deposition during the 20th century, but no region-wide increase during the past 2 decades, although the rate of atmospheric N deposition has increased at three sites east of the Continental Divide in the Front Range region since the mid-1980s. Much of the increase in atmospheric N deposition at all three sites has resulted from an increase in the ammonium concentrations of wet deposition; this suggests an increase in contributions from agricultural areas or from vehicle traffic east of the Rocky Mountains. Lakes at two study sites in the Front Range (Loch Vale and Green Lakes Valley) had NO 3 - concentrations of 30 to 40 micromoles per liter (µmol/L) during early spring snowmelt and remained at 5 to 10 µmol/L during summer. Retention of N in atmospheric wet deposition in some sub-catchments of these lakes was less than 50 percent, which reflects an advanced stage of N saturation. Nitrate concentrations in surface waters west of the Continental Divide were lower—often less than 10 µmol/L during snowmelt and less than 2 µmol/L during summer -- than surface waters east of the Divide, except in areas such as the Mt. Zirkel Wilderness that receive elevated amounts of atmospheric N deposition of 4 to 5 (kg/ha)/yr. Atmospheric N deposition in the Front Range east of the Divide may have altered the composition of alpine tundra-plant communities and lake diatoms, but additional studies would be needed to definitively demonstrate the hypothesized cause-and-effect relations. Rates of N-mineralization and nitrification in soils of the Front Range have increased in response to increased atmospheric N deposition. Projected future population growth and energy use in Colorado and the west increase the likelihood that the subtle effects of atmospheric N deposition now evident in the Front Range will become more pronounced and widespread in the future. The likelihood of future increased N emissions along the Front Range warrants a continuation of existing long-term precipitation and surface-water chemistry monitoring programs, and an expansion of the networks into areas that receive large amounts of atmospheric N deposition, but currently lack adequate monitoring. Long-term study and expanded sampling are needed to address uncertainties about the effects of atmospheric N deposition on terrestrial plant communities, nutrient limitation in lake plankton, shifts of dominant species within diatom communities, and on amphibian response to episodic surface-water acidification.

Colorado, Wyoming↗

USGS2017

Distribution, nesting activities, and age-class of territorial pairs of golden eagles at the Altamont Pass Wind Resource Area, California, 2014–16

The substantial numbers of golden eagles ( Aquila chrysaetos ) killed by collisions with oldgeneration wind turbines each year at the Altamont Pass Wind Resource Area (APWRA) in California has been well documented from previous studies. Few eagle nests have been documented in the APWRA, however, and adults and subadults 3+ years of age killed by turbines were generally not associated with nearby territories. We searched a subset of randomly selected survey plots for territorial pairs of golden eagles and associated nesting attempts within the APWRA as part of a broader investigation of population dynamics in the surrounding northern Diablo Range. In contrast to limited historical observations from 1988 to 2013, our surveys documented up to 15 territorial pairs within 3.2 kilometers (km) of wind turbines at the APWRA annually, 9 of which were not previously documented or only observed intermittently during historical surveys. We found evidence of nesting activity by adult pairs at least once during our study at six of these territories. We also determined that 23–36 percent of territories identified within 3.2 km of the APWRA had a subadult pair member, but that no pairs with a subadult member attempted to nest. These data will be useful to developers, wildlife managers, and future raptor studies in the area to evaluate and minimize the potential effects of wind energy or other development activities on previously unknown territorial pairs in the area.

California↗

USGS2014

Analytical solutions for benchmarking cold regions subsurface water flow and energy transport models: one-dimensional soil thaw with conduction and advection

Numerous cold regions water flow and energy transport models have emerged in recent years. Dissimilarities often exist in their mathematical formulations and/or numerical solution techniques, but few analytical solutions exist for benchmarking flow and energy transport models that include pore water phase change. This paper presents a detailed derivation of the Lunardini solution, an approximate analytical solution for predicting soil thawing subject to conduction, advection, and phase change. Fifteen thawing scenarios are examined by considering differences in porosity, surface temperature, Darcy velocity, and initial temperature. The accuracy of the Lunardini solution is shown to be proportional to the Stefan number. The analytical solution results obtained for soil thawing scenarios with water flow and advection are compared to those obtained from the finite element model SUTRA. Three problems, two involving the Lunardini solution and one involving the classic Neumann solution, are recommended as standard benchmarks for future model development and testing.

Advances in Water Resources↗

USGS2019

Adaptive management of flows from R.L. Harris Dam (Tallapoosa River, Alabama)—Stakeholder process and use of biological monitoring data for decision making

Adaptive management has been applied to problems with multiple conflicting objectives in various natural resources settings to learn how management actions affect divergent values regarding system response. Hydropower applications have only recently begun to emerge in the field, yet in the specific example reported herein, stakeholders invested in determining the best management alternatives for attainment of a suite of objectives outlined in a long-term adaptive management program below R.L. Harris Dam, a large, privately owned dam in Alabama. Stakeholders convened an objective-setting workshop to engage a governance structure and developed a decision support model to determine appropriate actions that optimized stakeholder values. The process led to implemented change in dam operation inclusive of incorporating hypothetical responses in system parameters to management. To account for the iterative loop of adaptive management, yearly monitoring of state variables that approximated many stakeholder objectives was performed from 2005 to 2016 and data collected were incorporated into the decision model. Specific analysis of fish and macroinvertebrate population responses indicated a less than satisfactory response for some stakeholders to the flow-management changes at the dam. Uncertainty regarding the best management to provide adequate hydrologic and thermal habitats for fauna and boatable days for recreationists still exists. The project led to a Federal Energy Regulatory Commission process for renewing the license to operate the dam (beginning in 2018); adaptive management could be a viable path forward to ensure stakeholder satisfaction related to new management options.

Alabama↗

USGS2003

The effect of chamber mixing velocity on bias in measurement of sediment oxygen demand rates in the Tualatin River basin, Oregon

Three sediment oxygen demand (SOD) measurement chambers were deployed in the Tualatin River near Tigard, Oregon, at river mile 10 in August 2000. SOD rates were calculated for three different circulation velocities during each chamber deployment. The SOD rate at each velocity was calculated from a graph of dissolved oxygen concentration versus elapsed time. An acoustic doppler current profiler (ADCP) was used to measure stream discharge and near-bottom water velocities in the Tualatin at river mile 10 and at two upstream locations. Measured river and chamber velocities were similar, indicating that results from the chambers were representative of instream effects. At low to moderate chamber circulation velocities (less than about 7.5 centimeters per second), the measured SOD rate appeared to be only slightly affected by the circulation velocity, indicating that the measured rates reflect the rate of oxygen utilization by chemical and biological reactions in the sediment rather than the rate of physical transport of oxygen to the sediment-water interface. Above about 7.5 centimeters per second, however, the measured oxygen depletion rate was affected by the circulation velocity, as sufficient energy was generated within the chamber to resuspend bottom sediment, as evidenced by increased turbidity. The resuspended sediment particles contributed to the measured oxygen loss rate by increasing the surface area of decomposing material in contact with the water column, resulting in a measured SOD rate that was anomalously high. Two different alignments of the chamber circulation diffusers were tested. With both diffuser alignments, SOD rates were similar at circulation velocities low enough to avoid sediment resuspension. The same resuspension effect probably exists in the Tualatin River during storm-runoff events following prolonged periods of low flow, when increased stream velocity may result in the resuspension of bottom sediments. The resuspension causes increased turbidity and increased oxygen demand, resulting in lower instream dissolved oxygen concentrations.

Water-Resources Investigations Report↗

USGS2019

Rare earth element mineral deposits in the United States

Because of their unique special chemical properties, many of the metals in the group of rare earth elements (REEs) have essential applications in 21st century technologies. Examples of products that use REEs are cell phones, computers, fluorescent and light-emitting-diode lights, flat-screen television and computer monitors, and in high-strength magnets used by clean energy technologies such as the generators of wind turbines and batteries of hybrid and electric vehicles. REEs are used in many defense applications, such as in components of jet engines, missile guidance systems, antimissile defense systems, satellites, and communication systems. The rare earth elements have become vital to manufacturing numerous high-tech products, which has been accompanied by a large increase in their demand. At the same time, there has been concern by the United States and many other Nations about the near-monopoly of mining, processing, and supply of REEs from one Nation, China. Between 2011 and 2017, China produced approximately 84 percent of the world’s REEs, and during this time the United States only produced REEs between 2012 and 2015. The U.S. production came entirely from the Mountain Pass mine in California, providing only about 4 percent of the world REE supply. Because REEs are essential for technological applications and are primarily supplied by one Nation, there has been an increased concern in identifying new sources of REEs, including economic REE deposits. In response to these concerns, since 2009, the U.S. Geological Survey (USGS) has conducted numerous studies focused on the distribution, geology, and potential resources for the REE-bearing mineral deposits in the United States. The basic characteristics of mineral deposit types that host REE enrichments in the United Sates are summarized in this report, with selected examples. Several types of REE-enriched mineral deposits are reviewed, including deposits in carbonatites, alkaline igneous rocks, sedimentary phosphate-rich rocks (phosphorite), regions containing REE-rich veins, iron oxide deposits containing REE-bearing apatite, monazite-xenotime-bearing placer deposits (heavy-mineral sands), and ion-adsorption clay deposits (REE in granite-derived regolith). A better understanding of these mineral deposits will assist in identifying domestic resources to help alleviate the dependence on imported REEs. The economic development of REE mineral deposits is affected by many factors beyond mining, such as commodity prices and mineral processing costs. Most of the REEs are hosted by minerals that have complex chemical formulas; this presents more challenges to process and extract the REEs. Continued advancements and refinements in mineral processing techniques may allow REE deposits with complex mineralogy to be economically developed in the future.

Circular↗

USGS2025

Evaluating the potential to quantify salmon habitat via UAS-based particle image velocimetry

Continuous, high-resolution data for characterizing freshwater habitat conditions can support successful management of endangered salmonids. Uncrewed aircraft systems (UAS) make acquiring such fine-scale data along river channels more feasible, but workflows for quantifying reach-scale salmon habitats are lacking. We evaluated the potential for UAS-based mapping of hydraulic habitats using spectrally based depth retrieval and particle image velocimetry (PIV) by comparing these methods to a more well-established flow modeling approach. Our results indicated that estimates of water depth, depth-averaged velocity, and flow direction derived via remote sensing and modeling techniques were comparable and in good agreement with field measurements. Predictions of spring-run Chinook salmon ( Oncorhynchus tshawytscha ) juvenile rearing habitat produced from PIV and model output were similar, with small errors relative to direct field observations. Estimates of hydraulic heterogeneity based on kinetic energy gradients in the flow field were generally consistent between PIV and flow modeling, but errors relative to field measurements were larger. PIV results were sensitive to the velocity index ( α ) used to convert surface velocities to depth-averaged velocities. Sun glint precluded PIV analysis along the margins of some images and a large degree of overlap between frames was thus required to obtain continuous coverage of the reach. Similarly, shadows cast by riparian vegetation caused gaps in spectrally based bathymetric maps. Despite these limitations, our results suggest that for sites with sufficient water surface texture, UAS-based PIV can provide detailed hydraulic habitat information at the reach scale, with accuracies comparable to traditional field methods and multidimensional flow modeling.

Oregon↗

USGS1985

Simulated effects of increased recharge on the ground-water flow system of Yucca Mountain and vicinity, Nevada-California

A study was performed to assess the potential effects of changes in future climatic conditions on the groundwater system in the vicinity of Yucca Mountain, the site of a potential mined geologic repository for high-level nuclear wastes. These changes probably would result in greater rates of precipitation and, consequently, greater rates of recharge. The study was performed by simulating the groundwater system, using a two-dimensional, finite-element, groundwater flow model. The simulated position of the water table rose as much as 130 meters near the U.S. Department of Energy 's preferred repository area at Yucca Mountain for a simulation involving a 100-percent increase in precipitation compared to modern-day conditions. Despite the water table rise, no flooding of the potential repository would occur at its current proposed location. According to the simulation, springs would discharge south and west of Timber Mountain, along Fortymile Canyon, in the Amargosa Desert near Lathrop Wells and Franklin Lake playa, and near Furnace Creek Ranch in Death Valley, where they presently discharge. Simulated directions of groundwater flow paths near the potential repository area generally would be the same for the baseline (modern-day climate) and the increased-recharge simulations, but the magnitude of flow would increase by 2 to 4 times that of the baseline-simulation flow. (USGS)

California, Nevada↗

USGS2020

Shale gas development has limited effects on stream biology and geochemistry in a gradient-based, multiparameter study in Pennsylvania

The number of horizontally drilled shale oil and gas wells in the United States has increased from nearly 28,000 in 2007 to nearly 127,000 in 2017, and research has suggested the potential for the development of shale resources to affect nearby stream ecosystems. However, the ability to generalize current studies is limited by the small geographic scope as well as limited breadth and integration of measured chemical and biological indicators parameters. This study tested the hypothesis that a quantifiable, significant relationship exists between the density of oil and gas (OG) development, increasing streamwater concentrations of known geochemical tracers of OG extraction, and the composition of benthic macroinvertebrate and microbial communities. 25 headwater streams that drain lands across a gradient of shale gas development intensity were sampled. Our strategy included comprehensive measurements across multiple seasons of sampling to account for temporal variability of geochemical parameters, including known shale OG geochemical tracers, and microbial and benthic macroinvertebrate communities. No significant relationships were found between the intensity of OG development, shale OG geochemical tracers, or benthic macroinvertebrate or microbial community composition, whereas significant seasonal differences in stream chemistry were observed. These results highlight the importance of considering spatial and temporal variability in stream chemistry and biota and not only the presence of anthropogenic activities in a watershed. This comprehensive, integrated study of geochemical and biological variability of headwater streams in watersheds undergoing OG development provides a robust framework for examining the effects of energy development at a regional scale.

Pennsylvania↗

USGS1976

High-resolution seismic reflection profiling for mapping shallow aquifers in Lee County, Florida

High-resolution continuous seismic reflection profiling equipment was utilized to define the configuration of sedimentary layers underlying part of Lee County, Florida. About 45 miles (72 kilometers) of profile were made on the Caloosahatchee River Estuary and San Carlos Bay. Two different acoustic energy sources, a high resolution boomer and a 45-electrode high resolution sparker, both having a power input of 300 joules, were used to obtain both adequate penetration and good resolution. The seismic profiles show that much of the strata of middle Miocene to Holocene age apparently are extensively folded but not faulted. Initial interpretations indicate that: (1) the top of the Hawthorn Formation (which contains the upper Hawthorn aquifer) has much relief due chiefly to apparent folding; (2) the limestone, sandstone, and unconsolidated sand and phosphorite, which together compose the sandstone aquifer, appear to be discontinuous; (3) the green clay unit of the Tamiami Formation contains large scale angular beds dipping eastward; and (4) numerous deeply cut alluvium-filled paleochannels underlie the Caloosahatchee River. (Woodard-USGS)

Florida↗

USGS2018

Featured collection introduction: Connectivity of streams and wetlands to downstream waters

Connectivity is a fundamental but highly dynamic property of watersheds. Variability in the types and degrees of aquatic ecosystem connectivity presents challenges for researchers and managers seeking to accurately quantify its effects on critical hydrologic, biogeochemical, and biological processes. However, protecting natural gradients of connectivity is key to protecting the range of ecosystem services that aquatic ecosystems provide. In this featured collection, we review the available evidence on connections and functions by which streams and wetlands affect the integrity of downstream waters such as large rivers, lakes, reservoirs, and estuaries. The reviews in this collection focus on the types of waters whose protections under the U.S. Clean Water Act have been called into question by U.S. Supreme Court cases. We synthesize 40+ years of research on longitudinal, lateral, and vertical fluxes of energy, material, and biota between aquatic ecosystems included within the Act's frame of reference. Many questions about the roles of streams and wetlands in sustaining downstream water integrity can be answered from currently available literature, and emerging research is rapidly closing data gaps with exciting new insights into aquatic connectivity and function at local, watershed, and regional scales. Synthesis of foundational and emerging research is needed to support science‐based efforts to provide safe, reliable sources of fresh water for present and future generations.

Journal of the American Water Resources Associatio↗

USGS2018

Downstream impacts of dams: shifts in benthic invertivorous fish assemblages

Impoundments alter connectivity, sediment transport and water discharge in rivers and floodplains, affecting recruitment, habitat and resource availability for fish including benthic invertivorous fish, which represent an important link between primary producers and higher trophic levels in tropical aquatic ecosystems. We investigated long-term changes to water regime, water quality, and invertivorous fish assemblages pre and post impoundment in three rivers downstream of Porto Primavera Reservoir in south Brazil: Paraná, Baía and Ivinhema rivers. Impacts were distinct in the Paraná River, which is fully obstructed by the dam, less evident in the Baía River which is partially obstructed by the dam, but absent in the unimpounded Ivinhema River. Changes in water regime were reflected mainly as changes in water-level fluctuation with little effect on timing. Water transparency increased in the Paraná River post impoundment but did not change in the Baía and Ivinhema rivers. Changes in fish assemblages included a decrease in benthic invertivorous fish in the Paraná River and a shift in invertivorous fish assemblage structure in the Baía and Paraná rivers but not in the unimpounded Ivinhema River. Changes in water regime and water transparency, caused by impoundment, directly or indirectly impacted invertivorous fish assemblages. Alterations of fish assemblages following environmental changes have consequences over the entire ecosystem, including a potential decrease in the diversity of mechanisms for energy flow. We suggest that keeping existing unimpounded tributaries free of dams, engineering artificial floods, and intensive management of fish habitat within the floodplain may preserve native fish assemblages and help maintain functionality and ecosystem services in highly impounded rivers.

Baía River; Ivinhema River; Paraná River↗

USGS2003

Geologic framework and hydrogeologic characteristics of the Edwards aquifer, Uvalde County, Texas

The Edwards aquifer in Uvalde County is composed of Lower Cretaceous carbonate (mostly dolomitic limestone) strata of the Devils River Formation in the Devils River trend and of the West Nueces, McKnight, and Salmon Peak Formations in the Maverick basin. Rocks in the Devils River trend are divided at the bottom of the Devils River Formation into the (informal) basal nodular unit. Maverick basin rocks are divided (informally) into the basal nodular unit of the West Nueces Formation; into lower, middle, and upper units of the McKnight Formation; and into lower and upper units of the Salmon Peak Formation. The Edwards aquifer overlies the (Lower Cretaceous) Glen Rose Limestone, which composes the lower confining unit of the Edwards aquifer. The Edwards aquifer is overlain by the (Upper Cretaceous) Del Rio Clay, the basal formation of the upper confining unit. Upper Cretaceous and (or) Lower Tertiary igneous rocks intrude all stratigraphic units that compose the Edwards aquifer, particularly in the southern part of the study area. The Balcones fault zone and the Uvalde salient are the principal structural features in the study area. The fault zone comprises mostly en echelon, high-angle, and down-to-the-southeast normal faults that trend mostly from southwest to northeast. The Uvalde salient—resulting apparently from a combination of crustal uplift, diverse faulting, and igneous activity—elevates the Edwards aquifer to the surface across the central part of Uvalde County. Downfaulted blocks associated with six primary faults—Cooks, Black Mountain, Blue Mountain, Uvalde, Agape, and Connor—juxtapose the Salmon Peak Formation (Lower Cretaceous) in central parts of the study area against Upper Cretaceous strata in the southeastern part. The carbonate rocks of the Devils River trend and the Maverick basin are products of assorted tectonic and depositional conditions that affected the depth and circulation of the Cretaceous seas. The Devils River Formation formed in a fringing carbonate bank—the Devils River trend— in mostly open shallow marine environments of relatively high wave and current energy. The West Nueces, McKnight, and Salmon Peak Formations resulted mostly from partly restricted to open marine, tidal-flat, and restricted deep-basinal environments in the Maverick basin. The porosity of the Edwards aquifer results from depositional and diagenetic effects along specific lithostratigraphic horizons (fabric selective) and from structural and solutional features that can occur in any lithostratigraphic horizon (non-fabric selective). In addition to porosity depending upon the effects of fracturing and the dissolution of chemically unstable (soluble) minerals and fossils, the resultant permeability depends on the size, shape, and distribution of the porosity as well as the interconnection among the pores. Upper parts of the Devils River Formation and the upper unit of the Salmon Peak Formation compose some of the most porous and permeable rocks in Uvalde County.

Texas↗

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↗

USGS2011

Long-term post-fire effects on spatial ecology and reproductive output of female Agassiz’s desert tortoises ( Gopherus agassizii ) at a wind energy facility near Palm Springs, California, USA

We studied the long-term response of a cohort of eight female Agassiz’s desert tortoises ( Gopherus agassizii ) during the first 15 years following a large fire at a wind energy generation facility near Palm Springs, California, USA. The fire burned a significant portion of the study site in 1995. Tortoise activity areas were mapped using minimum convex polygons for a proximate post-fire interval from 1997 to 2000, and a long-term post-fire interval from 2009 to 2010. In addition, we measured the annual reproductive output of eggs each year and monitored the body condition of tortoises over time. One adult female tortoise was killed by the fire and five tortoises bore exposure scars that were not fatal. Despite predictions that tortoises would make the short-distance movements from burned to nearby unburned habitats, most activity areas and their centroids remained in burned areas for the duration of the study. The percentage of activity area burned did not differ significantly between the two monitoring periods. Annual reproductive output and measures of body condition remained statistically similar throughout the monitoring period. Despite changes in plant composition, conditions at this site appeared to be suitable for survival of tortoises following a major fire. High productivity at the site may have buffered tortoises from the adverse impacts of fire if they were not killed outright. Tortoise populations at less productive desert sites may not have adequate resources to sustain normal activity areas, reproductive output, and body conditions following fire.

California↗