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At least 739 records · Page 41Linked to original sources

USGS2016

Influence of vertical and lateral heat transfer on permafrost thaw, peatland landscape transition, and groundwater flow

Recent climate change has reduced the spatial extent and thickness of permafrost in many discontinuous permafrost regions. Rapid permafrost thaw is producing distinct landscape changes in the Taiga Plains of the Northwest Territories, Canada. As permafrost bodies underlying forested peat plateaus shrink, the landscape slowly transitions into unforested wetlands. The expansion of wetlands has enhanced the hydrologic connectivity of many watersheds via new surface and near-surface flow paths, and increased streamflow has been observed. Furthermore, the decrease in forested peat plateaus results in a net loss of boreal forest and associated ecosystems. This study investigates fundamental processes that contribute to permafrost thaw by comparing observed and simulated thaw development and landscape transition of a peat plateau-wetland complex in the Northwest Territories, Canada from 1970 to 2012. Measured climate data are first used to drive surface energy balance simulations for the wetland and peat plateau. Near-surface soil temperatures simulated in the surface energy balance model are then applied as the upper boundary condition to a three-dimensional model of subsurface water flow and coupled energy transport with freeze-thaw. Simulation results demonstrate that lateral heat transfer, which is not considered in many permafrost models, can influence permafrost thaw rates. Furthermore, the simulations indicate that landscape evolution arising from permafrost thaw acts as a positive feedback mechanism that increases the energy absorbed at the land surface and produces additional permafrost thaw. The modeling results also demonstrate that flow rates in local groundwater flow systems may be enhanced by the degradation of isolated permafrost bodies.

Northwest Territories↗

USGS2023

Patterns, drivers, and a predictive model of dam removal cost in the United States

Given the burgeoning dam removal movement and the large number of dams approaching obsolescence in the United States, cost estimating data and tools are needed for dam removal prioritization, planning, and execution. We used the list of removed dams compiled by American Rivers to search for publicly available reported costs for dam removal projects. Total cost information could include component costs related to project planning, dam deconstruction, monitoring, and several categories of mitigation activities. We compiled reported costs from 455 unique sources for 668 dams removed in the United States from 1965 to 2020. The dam removals occurred within 571 unique projects involving 1–18 dams. When adjusted for inflation into 2020 USD, cost of these projects totaled \$1.522 billion, with per-dam costs ranging from $1 thousand (k) to \$268.8 million (M). The median cost for dam removals was \$157k, \$823k, and \$6.2M for dams that were< 5 m, between 5–10 m, and > 10 m in height, respectively. Geographic differences in total costs showed that northern states in general, and the Pacific Northwest in particular, spent the most on dam removal. The Midwest and the Northeast spent proportionally more on removal of dams less than 5 m in height, whereas the Northwest and Southwest spent the most on larger dam removals > 10 m tall. We used stochastic gradient boosting with quantile regression to model dam removal cost against potential predictor variables including dam characteristics (dam height and material), hydrography (average annual discharge and drainage area), project complexity (inferred from construction and sediment management, mitigation, and post-removal cost drivers), and geographic region. Dam height, annual average discharge at the dam site, and project complexity were the predominant drivers of removal cost. The final model had an R 2 of 57% and when applied to a test dataset model predictions had a root mean squared error of $5.09M and a mean absolute error of \$1.45M, indicating its potential utility to predict estimated costs of dam removal. We developed a R shiny application for estimating dam removal costs using customized model inputs for exploratory analyses and potential dam removal planning.

Frontiers in Ecology and Evolution↗

USGS2008

Coastal Louisiana ecosystem assessment and restoration program: The role of ecosystem forecasting in evaluating restoration planning in the Mississippi River Deltaic Plain

The development of ecosystem management plans to restore and rehabilitate natural resources requires an understanding of how specific ecological mechanisms regulate the structure and function of ecosystems. To achieve restoration goals, comprehensive plans and engineering designs must effectively change environmental drivers at the regional level to reduce stress conditions at the local environment that are responsible for ecosystem degradation. This document focuses on the Coastal Louisiana Ecosystem Assessment and Restoration (CLEAR) ecosystem forecasting framework and how it can be used to support the analysis of Louisiana’s coastal restoration plans. Specifically, the framework is designed to (1) develop and incorporate conceptual ecological models that can be used to integrate ecological needs and opportunities with engineering designs, (2) utilize wetland loss rates to describe the most likely “future without” scenario for a variety of ecosystem attributes, (3) estimate broad ecosystem responses to restoration alternatives based on processes associated with succession of geomorphic and ecological systems, and (4) calculate ecological benefits for incorporation into decision support tools associated with large-scale geomorphic and hydrologic processes. This paper provides a brief overview of the spatial framework and modular design of the CLEAR ecosystem forecasting framework and describes in greater detail the evolution of the landscape change module, concepts for its refinement, and how it was utilized in evaluating a coastal restoration alternative proposed in the Coastal Protection and Restoration Authority Preliminary Draft Master Plan. Such projections by the CLEAR forecasting framework can evaluate processes and conditions that result in sustainable coastal ecosystems with habitat functions that support higher trophic levels.

Louisiana↗

USGS2026

Statewide surficial geologic map of Nebraska underscores Quaternary landscape evolution from the High Plains to the Central Lowland

Surficial geologic mapping in Nebraska has been conducted primarily at the 1:24,000 scale since the mid-1990s, although there have also been limited efforts to map generalized Quaternary and surficial geology within the state and the region. We compiled and evaluated disparate maps (1:24,000–1:1,000,000) and datasets—including geologic, soil and soil parent material, and geomorphic maps as well as LiDAR derivatives—to produce a single 1:500,000 scale surficial geologic map of Nebraska that is the first of its kind. This new map provides a coarse-scale surficial geologic map that will be incorporated into a nationwide U.S. Geological Survey Quaternary geologic map. It also reflects the variation and uniqueness of physical landscapes in the state, where the Great Plains and Central Lowland physiographic provinces meet, further developing a richer interdisciplinary understanding of regional geomorphology in the heart of North America.

Nebraska↗

USGS2007

Geology and Mineral Resources of the East Mojave National Scenic Area, San Bernardino County, California

From our evaluations that largely used model-based criteria, we conclude that much of the East Mojave National Scenic Area (EMNSA) contains significant indications of epigenetic mineralization of various types. Economically significant concentrations of many metals may possibly remain to be discovered in many parts of the EMNSA (see also Wetzel and others, 1992). We have discussed specific types of metallic deposits that are known to be present in the EMNSA. Some mountain ranges that have widespread occurrences are the Providence Mountains, Clark Mountain Range, Ivanpah Mountains, and New York Mountains; the area of Hackberry Mountain is included in a tract that is judged to be favorable for the discovery of epithermal, volcanic-hosted gold deposits (pl. 2). These ranges make up a broad, roughly north-south-trending region in the central part of the EMNSA. Much less endowed with known occurrences of all of the various types of deposits considered above are the Granite Mountains, the central parts of the Piute Range, the Fenner Valley area, the general area of Cima Dome, the Cima volcanic field, and areas west to Soda Lake. We have attempted to make some judgments concerning the gravel-covered areas in the EMNSA (pl. 3), including the areal extent of bedrock apparently covered only by thin veneers of gravel. But few data are available to us for the overwhelming bulk of the covered areas. The presence of any mineralization, the type of mineralization, and the extent and intensity of mineralization in the covered areas is essentially unknown. The likelihood is high, however, that those areas in the EMNSA covered only by a thin cap of gravels could host mineralization similar to that known in the adjoining mountain ranges. Most buried epigenetic-mineral deposits do not respond to standard geophysical methods, particularly at the coarse spacing of the data-collection points available for our evaluation. Restricting judgments concerning the presence of undiscovered metal resources in the EMNSA only to currently known types of deposits and to regionally representative tonnages for such deposits would undoubtedly yield small estimates for volumes of many metals that might be exploited. Metals from most newly discovered, base- and ferrous-metal deposits of the types presently known in the EMNSA probably would be insignificant from the standpoint of national needs. For example, copper from a newly discovered skarn deposit in the EMNSA would have roughly a 25 percent chance of being in excess of approximately 10,000 tonnes contained Cu, if the grade-and-tonnage distribution curves of Jones and Menzie (1986b) for copper skarns are applicable to copper skarn in the EMNSA. Most copper in the United States is produced in the Southwest from much larger open-pit operations than those associated with the typical copper skarn; the former operations exploit large-tonnage porphyry-type systems. Historically, the EMNSA has been the site of minor production of many metals from a large number of sites. Since 1985, however, a small number of sites in the EMNSA whose gold production and reserves are much greater than that of the preceding discoveries have been developed (see U.S. Bureau of Mines, 1990a). Nonetheless, widespread distribution of numerous types of deposits (including copper skarn, lead-zinc skarn, tin-tungsten skarn, polymetallic vein, gold-silver quartz-pyrite vein, low-fluorine porphyry molybdenum, gold breccia pipe, and volcanic-hosted gold) that are petrogenetically associated with igneous rock in many parts of the EMNSA is indicative of a metallogenic environment that may be the site of future discoveries of mineral-deposit types that are not now recognized by the exploration community. The science, art, and, yes, even luck of exploration procedures continually evolve, and this evolution is one of the most important aspects of currently employed methods of exploration (Bailly, 1981; Hutchinson and Grauch, 1991).

Miscellaneous Field Studies Map↗

USGS2023

Movement behavior, habitat selection, and functional responses to habitat availability among four species of wintering waterfowl in California

Habitat selection analyses provide a window into the perceived value of habitats by animals and how those perceptions compare with other animals, change across time, or change in relation to availability (termed functional responses). Habitat selection analysis and functional responses can be used to develop strategies to avoid habitat limitations, guide habitat management, and set attainable conservation goals. GPS relocations of marked animals are the principal data used in habitat selection analysis. The accuracy and frequency with which tracking devices collect data are increasing and may result in non-stationary point processes that result from latent behaviors previously unidentifiable in sparse data.

California↗

USGS1996

Geology and structural evolution of the Muruntau gold deposit, Kyzylkum desert, Uzbekistan

The Muruntau gold deposit in the Kyzylkum desert of Uzbekistan is the largest single deposit (??? 1100 tonnes of gold) of the class of low-sulfide syndeformation/synigenous gold deposits formed in the brittle/ductile transition zone of the crust within transpressional shear zones. Hosted by the Cambrian to Ordovician Besopan Suite, the ores were deposited in pre-existing thrust-fault- and metamorphism-related permeabilities and in synmineralization dilational zones created in a large fault-related fold. The Besopan Suite is a 5,000-m-thick sequence of turbiditic siltstones, shales and sandstones. The ore is primarily localized at the base of the Besopan-3 unit, which is a 2,000-m-thick series of carbonaceous shales, siltstones, sandstones and cherts. Initial gold deposition took place within the Sangruntau-Tamdytau shear zone, which was developed along the stratigraphic contact between the Besopan-3 and Besopan-4 units. During the mineralization process, folding of the Besopan Suite and a left-step adjustment in the Sangruntau-Tamdytau shear zone were caused by two concurrent events: (1) the activation of the left-lateral Muruntau-Daugyztau shear zone that developed at nearly a 90?? angle to the preceding shear zone and (2) the intrusion of granitoid plutons. These structural events also resulted in the refocusing of hydrothermal fluid flow into new zones of permeability.

Ore Geology Reviews↗

USGS1979

Maps showing late Pleistocene and Holocene evolution of the South Texas continental shelf

Interpretation of acoustical profiles has provided insight into the late Quaternary geologic history of the Continental Shelf off South Texas. (See the geographic index map on sheet 1 for location of the area studied.) The profiles reveal the interplay of tectonism, sedimentation, and cyclic fluctuations of sea level in the building and geologic evolution of the continental terrace. The sequence of sediments studied extends to about 200 meters (m) beneath the sea-floor surface. Four seismic-stratigraphic units underlain by four prominent sound reflectors were identified and mapped. This geologic synthesis, for which the research was funded by the U.S. Bureau of Land Management (BLM), is but one aspect of a coordinated, multidisciplinary environmental study of the South Texas Outer Continental Shelf sponsored by BLM (Berryhill, 1976, 1977). The environmental studies are keyed to the leasing of Federal Outer Continental Shelf (OCS) lands for petroleum exploration and production. Their purpose is to provide the data development of petroleum resources on the OCS, as well as to provide the basis for predicting the impact of oil and gas exploration and production on the marine environment. Of primary concern is the recognition of geologic conditions that might be hazardous to structures placed on the sea floor. Geologic hazards relate directly to the potential for significant movement of the sea floor in the future. Judging sea-floor stability and recognizing geologic features that are potentially hazardous require an understanding of the recent geologic history of the area, which, in turn, entails determining the relative rates and interactions of sedimentation and tectonism through time. In addition to the primary objective, the synthesis provides knowledge about the magnitude and extent of sea-level fluctuations in the western Gulf of Mexico, and it provides a depositional facies model of possible use in appraising the resource potential of the more deeply buried sediments.

Texas↗

USGS2021

Soil organic carbon development and turnover in natural and disturbed salt marsh environments

Salt marsh survival with sea‐level rise (SLR) increasingly relies on soil organic carbon (SOC) accumulation and preservation. Using a novel combination of geochemical approaches, we characterized fine SOC (≤1 mm) supporting marsh elevation maintenance. Overlaying thermal reactivity, source (δ 13 C), and age (F 14 C) information demonstrates several processes contributing to soil development: marsh grass production, redeposition of eroded material, and microbial reworking. Redeposition of old carbon, likely from creekbanks, represented ∼9‐17% of shallow SOC (≤26 cm), indicating that this process may become increasingly important with SLR. Soils stored marsh grass‐derived compounds with a range of reactivities that were reworked over centuries‐to‐millennia. Decomposition decreases SOC thermal reactivity throughout the soil column while the decades‐long disturbance of ponding accelerated this shift in surface horizons. Empirically derived estimates of SOC turnover based on geochemical composition spanned a wide range (640–9,951 years) and have the potential to inform future predictions of marsh ecosystem evolution.

Massachusetts↗

USGS2007

Coupling alongshore variations in wave energy to beach morphologic change using the SWAN wave model at Ocean Beach, San Francisco, CA

Coastal managers have faced increasing pressure to manage their resources wisely over the last century as a result of heightened development and changing environmental forcing. It is crucial to understand seasonal changes in beach volume and shape in order to identify areas vulnerable to accelerated erosion. Shepard (1950) was among the first to quantify seasonal beach cycles. Sonu and Van Beek (1971) and Wright et al. (1985) described commonly occurring beach states. Most studies utilize widest spaced 2-D cross shore profiles or shorelines extracted from aerial photographs (e.g. Winant et al. 1975; Aubrey, 1979, Aubrey and Ross, 1985; Larson and Kraus, 1994; Jimenez et al., 1977; Lacey and Peck, 1998; Guillen et al., 1999; Norcorss et al., 2002) to analyzed systematic changes in beach evolution. But with the exception of established field stations, such as Duck, NC (Birkemeier and Mason, 1984), ans Hazaki Oceanographical Research Station (HORS) in Japan (Katoh, 1997), there are very few beach change data sets with high temporal and spatial resolutions (e.g. Dail et al., 2000; Ruggiero et al., 2005; Yates et al., in press). Comprehensive sets of nearshore morphological data and local in situ measurements outside of these field stations are very rare and virtually non-existent high-energy coasts. Studied that have attempted to relate wave statistics to beach morphology change require some knowledge of the nearshore wave climate, and have had limited success using offshore measurement (Sonu and Van Beek, 1971; Dail et al., 2000). The primary objective of this study is to qualitatively compare spatially variable nearshore wave predictions to beach change measurements in order to understand the processes responsible for a persistent erosion 'hotspot' at Ocean Beach, San Francisco, CA. Local wave measurements are used to calibrate and validate a wave model that provides nearshore wave prediction along the beach. The model is run for thousands of binned offshore wave conditions to help isolate the effects of offshore wave direction and period on nearshore wave predictions. Alongshore varying average beach change statistics are computed at specific profile locations from topographic beach surveys and lidar data. The study area is located in the San Francisco Bight in central California. Ocean Beach is a seven kilometer long north-south trending sandy coastline located just south of the entrance to the San Francisco Bay Estuary (Figure 1). It contains an erosion hotspot in the southern part of the beach which has resulted in damage to local infrastructure and is the cause of continued concern. A wide range of field data collection and numerical modeling efforts have been focused here as part of the United States Geological Survey's (USGS) San Francisco Bight Coastal Processes Study, which began in October 2003 and represents the first comprehensive study of coastal processes at the mouth of San Francisco Bay. Ocean Beach is exposed to very strong tidal flows, with measured currents often in excess of 1 m/s at the north end of the beach. Current profiler measurements indicate that current magnitudes are greater in the northern portion of the beach, while wave energy is greater in the southern portion where erosion problems are greatest (Barnard et al., 2007). The sub-aerial beach volume fluctuates seasonally over a maximum envelope of 400,000 m 3 for the seven kilometer stretch (Barnard et al, 2007). The wave climate in the region is dominated by an abundance of low frequency energy (greater than 20 s period) and prevailing northwest incident wave angles. The application of a wave model to the region is further complicated by the presence of the Farallon Islands 40 kilometers west, and a massive ebb tidal delta at the mouth of San Francisco Bay (~150 km 2 ), which creates complicated refraction patterns as wave energy moves from offshore Ocean Beach; however the cost and threat of the energetic nearshore environment have limited the temporal and spatial resolution of these measurements. Applying numerical models to predict wave and current patterns along the beach can help supplement the filed data that exists and provide opportunities to make prediction about the impacts of changing environmental forcing.

California↗

USGS2020

Capturing, preserving and digitizing legacy seismic data from the Montserrat Volcano Observatory analog seismic network, July 1995 – December 2004

An eruption of the Soufrière Hills Volcano (SHV) on the eastern Caribbean island of Montserrat began on 18 July 1995 and continued until February 2010. Within nine days of the eruption onset, an existing four‐station analog seismic network (ASN) was expanded to 10 sites. Telemetered data from this network were recorded, processed, and archived locally using a system developed by scientists from the U.S. Geological Survey (USGS) Volcano Disaster Assistance Program (VDAP). In October 1996, a digital seismic network (DSN) was deployed with the ability to capture larger amplitude signals across a broader frequency range. These two networks operated in parallel until December 2004, with separate telemetry and acquisition systems (analysis systems were merged in March 2001). Although the DSN provided better quality data for research, the ASN featured superior real‐time monitoring tools and captured valuable data including the only seismic data from the first 15 months of the eruption. These successes of the ASN have been rather overlooked. This article documents the evolution of the ASN, the VDAP system, the original data captured, and the recovery and conversion of more than 230,000 seismic events from legacy SUDS, Hypo71, and Seislog formats into Seisan database with waveform data in miniSEED format. No digital catalog existed for these events, but students at the University of South Florida have classified two-thirds of the 40,000 events that were captured between July 1995 and October 1996. Locations and magnitudes were recovered for ~10,000 of these events. Real-time seismic amplitude measurement, seismic spectral amplitude measurement, and tiltmeter data were also captured. The result is that the ASN seismic dataset is now more discoverable, accessible, and reusable, in accordance with FAIR data principles. These efforts could catalyze new research on the 1995–2010 SHV eruption. Furthermore, many observatories have data in these same legacy data formats and might benefit from procedures and codes documented here.

Soufrière Hills Volcano↗

USGS2018

Sea‐level rise, habitat loss, and potential extirpation of a salt marsh specialist bird in urbanized landscapes

Sea‐level rise (SLR) impacts on intertidal habitat depend on coastal topology, accretion, and constraints from surrounding development. Such habitat changes might affect species like Belding's savannah sparrows ( Passerculus sandwichensis beldingi ; BSSP), which live in high‐elevation salt marsh in the Southern California Bight. To predict how BSSP habitat might change under various SLR scenarios, we first constructed a suitability model by matching bird observations with elevation. We then mapped current BSSP breeding and foraging habitat at six estuarine sites by applying the elevation‐suitability model to digital elevation models. To estimate changes in digital elevation models under different SLR scenarios, we used a site‐specific, one‐dimensional elevation model (wetland accretion rate model of ecosystem resilience). We then applied our elevation‐suitability model to the projected digital elevation models. The resulting maps suggest that suitable breeding and foraging habitat could decline as increased inundation converts middle‐ and high‐elevation suitable habitat to mudflat and subtidal zones. As a result, the highest SLR scenario predicted that no suitable breeding or foraging habitat would remain at any site by 2100 and 2110. Removing development constraints to facilitate landward migration of high salt marsh, or redistributing dredge spoils to replace submerged habitat, might create future high salt marsh habitat, thereby reducing extirpation risk for BSSP in southern California.

Ecology and Evolution↗

USGS2021

Multiple climate change-driven tipping points for coastal systems

As the climate evolves over the next century, the interaction of accelerating sea level rise (SLR) and storms, combined with confining development and infrastructure, will place greater stresses on physical, ecological, and human systems along the ocean-land margin. Many of these valued coastal systems could reach “tipping points,” at which hazard exposure substantially increases and threatens the present-day form, function, and viability of communities, infrastructure, and ecosystems. Determining the timing and nature of these tipping points is essential for effective climate adaptation planning. Here we present a multidisciplinary case study from Santa Barbara, California (USA), to identify potential climate change-related tipping points for various coastal systems. This study integrates numerical and statistical models of the climate, ocean water levels, beach and cliff evolution, and two soft sediment ecosystems, sandy beaches and tidal wetlands. We find that tipping points for beaches and wetlands could be reached with just 0.25 m or less of SLR (~ 2050), with > 50% subsequent habitat loss that would degrade overall biodiversity and ecosystem function. In contrast, the largest projected changes in socioeconomic exposure to flooding for five communities in this region are not anticipated until SLR exceeds 0.75 m for daily flooding and 1.5 m for storm-driven flooding (~ 2100 or later). These changes are less acute relative to community totals and do not qualify as tipping points given the adaptive capacity of communities. Nonetheless, the natural and human built systems are interconnected such that the loss of natural system function could negatively impact the quality of life of residents and disrupt the local economy, resulting in indirect socioeconomic impacts long before built infrastructure is directly impacted by flooding.

California↗

USGS2026

From understanding to action: Integrating new and old methodologies to manage marine infectious disease

Marine diseases can have far-reaching effects on population, community and ecosystem health; however, our ability to track, predict and manage these diseases has, historically, been poor. As a result, the fields of disease ecology and epidemiology have developed at a slower pace for marine than terrestrial systems [ 1 ]. New methodologies, including genomic tools for diagnostics [ 2 , 3 ], transcriptomic tools for measuring host and pathogen responses to infection (e.g. [ 4 , 5 ]), regional oceanic modelling systems that estimate environmental conditions influencing pathogen dispersal and disease progression [ 6 ], artificial intelligence methods for quantifying pathology from images (e.g. [ 7 ]) and advanced disease modelling techniques [ 8 , 9 ] are precipitating a rapid increase in our understanding of marine pathosystems. In 2016, these efforts led to the first special issue of Philosophical Transactions of the Royal Society B ( Marine diseases, volume 371, issue 1689) focused entirely on marine disease ecology and evolution, and in 2020, the first book, Marine disease ecology, was devoted to this topic [ 10 ]. This special issue, focused on marine disease management , is being published a decade after the first Philosophical Transactions special issue on marine diseases. The shift to a management focus reflects an urgent need for management strategies to address high-impact diseases and the rapid methodological advances that have resulted. The papers included in this issue demonstrate the value of combining classical approaches (e.g. routine disease surveillance, reductionistic pathogen challenge trials, rapid throughput diagnostics) with cutting-edge technologies (e.g. high-resolution oceanographic models, Bayesian models, replicated transcriptomic studies) to identify drivers of disease, quantify impacts and suggest management strategies.

Philosophical Transactions of the Royal Society, S↗

USGS2023

Climatic drivers of estuarine sediment dynamics

Estuarine sediment dynamics are controlled by myriad physical processes that operate across broad spatiotemporal scales. On the smallest scales, interactions between turbulence and individual particles control mobilization and settling, while interactions across larger scales between freshwater and marine inflow can control decadal timescale geomorphic change. Climate change, through the combined effects of sea-level rise, precipitation intensity, atmospheric variability, and anthropogenic intervention will affect sediment dynamics, geomorphology, and ultimately estuarine function. Therefore, it is imperative to understand the influence of these effects on sediment dynamics to assess the future evolution of estuaries. In this chapter we address the basic tidal, non-tidal, and geologic timescale concepts of estuarine sediment transport, then we illustrate how these concepts may be affected by future climate change. While sea-level rise alone will tend to favor sediment trapping and landward movement of estuaries, human influences within the watershed and estuary, including shoreline stabilization and dredging, may be of similar magnitude. The overarching goal of this chapter is to provide the reader with a basic framework of estuarine sediment transport so they can apply these general concepts to a specific system, under a predicted future state of climate, and develop testable hypotheses on future estuarine geomorphology and function.

Book chapter↗

USGS2008

Acetylene as fast food: Implications for development of life on anoxic primordial earth and in the outer solar system

Acetylene occurs, by photolysis of methane, in the atmospheres of jovian planets and Titan. In contrast, acetylene is only a trace component of Earth's current atmosphere. Nonetheless, a methane-rich atmosphere has been hypothesized for early Earth; this atmosphere would also have been rich in acetylene. This poses a paradox, because acetylene is a potent inhibitor of many key anaerobic microbial processes, including methanogenesis, anaerobic methane oxidation, nitrogen fixation, and hydrogen oxidation. Fermentation of acetylene was discovered ∼25 years ago, and Pelobacter acetylenicus was shown to grow on acetylene by virtue of acetylene hydratase, which results in the formation of acetaldehyde. Acetaldehyde subsequently dismutates to ethanol and acetate (plus some hydrogen). However, acetylene hydratase is specific for acetylene and does not react with any analogous compounds. We hypothesize that microbes with acetylene hydratase played a key role in the evolution of Earth's early biosphere by exploiting an available source of carbon from the atmosphere and in so doing formed protective niches that allowed for other microbial processes to flourish. Furthermore, the presence of acetylene in the atmosphere of a planet or planetoid could possibly represent evidence for an extraterrestrial anaerobic ecosystem. Astrobiology 8, 45–58.

Astrobiology↗

USGS2006

Does the Great Valley Group contain Jurassic strata? Reevaluation of the age and early evolution of a classic forearc basin

The presence of Cretaceous detrital zircon in Upper Jurassic strata of the Great Valley Group may require revision of the lower Great Valley Group chronostratigraphy, with significant implications for the Late Jurassic-Cretaceous evolution of the continental margin. Samples (n = 7) collected from 100 km along strike in the purported Tithonian strata of the Great Valley Group contain 20 Cretaceous detrital zircon grains, based on sensitive high-resolution ion microprobe age determinations. These results suggest that Great Valley Group deposition was largely Cretaceous, creating a discrepancy between biostratigraphy based on Buchia zones and chronostratigraphy based on radiometric age dates. These results extend the duration of the Great Valley Group basal unconformity, providing temporal separation between Great Valley forearc deposition and creation of the Coast Range Ophiolite. If Great Valley forearc deposition began in Cretaceous time, then sediment by passed the developing forearc in the Late Jurassic, or the Franciscan subduction system did not fully develop until Cretaceous time. In addition to these constraints on the timing of deposition, pre-Mesozoic detrital zircon age signatures indicate that the Great Valley Group was linked to North America from its inception. ?? 2006 Geological Society of America.

Geology↗

USGS2013

Hydraulic and Geomorphic Assessment of the Merced River and Historic Bridges in Eastern Yosemite Valley, Yosemite National Park, California: Sacramento, California

The Merced River in the popular and picturesque eastern-most part of Yosemite Valley in Yosemite National Park, California, USA, has been extensively altered since the park was first conceived in 1864. Historical human trampling of streambanks has been suggested as the cause of substantial increases in stream width, and the construction of undersized stone bridges in the 1920s has been suggested as the major factor leading to an increase in overbank flooding due to deposition of bars and islands between the bridges. In response, the National Park Service at Yosemite National Park (YNP) requested a study of the hydraulic and geomorphic conditions affecting the most-heavily influenced part of the river, a 2.4-km reach in eastern Yosemite Valley extending from above the Tenaya Creek and Merced River confluence to below Housekeeping Bridge. As part of the study, present-day conditions were compared to historical conditions and several possible planning scenarios were investigated, including the removal of an elevated road berm and the removal of three undersized historic stone bridges identified by YNP as potential problems: Sugar Pine, Ahwahnee and Stoneman Bridges. This Open-File Report will be superseded at a later date by a Scientific Investigations Report. A two-dimensional hydrodynamic model, the USGS FaSTMECH (Flow and Sediment Transport with Morphological Evolution of Channels) model, within the USGS International River Interface Cooperative (iRIC) model framework, was used to compare the scenarios over a range of discharges with annual exceedance probabilities of 50-, 20-, 10-, and 5- percent. A variety of topographic and hydraulic data sources were used to create the input conditions to the hydrodynamic model, including aerial LiDAR (Light Detection And Ranging), ground-based LiDAR, total station survey data, and grain size data from pebble counts. A digitized version of a historical topographic map created by the USGS in 1919, combined with estimates of grain size, was used to simulate historical conditions, and the planning scenarios were developed by altering the present-day topography. Roughness was estimated independently of measured water-surface elevations by using the mapped grain-size data and the Keulegan relation of grain size to drag coefficient. The FaSTMECH hydrodynamic model was evaluated against measured water levels by using a 130.9 m 3 s -1 flow (approximately a 33-percent annual exceedance probability flood) with 36 water-surface elevations measured by YNP personnel on June 8, 2010. This evaluation run had a root mean square error of 0.21 m between the simulated- and observed water-surface elevations (less than 10 percent of depth), though the observed water-surface elevations had relatively high variation due to the strong diurnal stage changes over the course of the 4.4-hour collection period, during which discharge varied by about 15 percent. There are presently no velocity data with which to test the model. A geomorphic assessment was performed that consisted of an estimate of the magnitude and frequency of bedload and suspended-sediment transport at “Tenaya Bar”, an important gravel-cobble bar located near the upstream end of the study site that determines the amount of flow across the floodplain at the Sugar Pine – Ahwahnee bend. An analysis of select repeat cross-sections collected by YNP since the late 1980s was done to investigate changes in channel cross-sectional area near the Tenaya Bar site. The results of the FaSTMECH models indicate that the maximum velocities in the present-day channel within the study reach are associated with Stoneman and Sugar Pine Bridges, at close to 3.0 m s -1 for the 5-percent annual exceedance probability flood. The modeled maximum velocities at Ahwahnee Bridge are comparatively low, at between 1.5 and 2.0 m s -1 , most likely due to the bridge's orientation parallel to down-valley floodplain flows. The results of the FaSTMECH models for the bridge removal scenarios indicate a reduction in average velocity at the bridge sites for the range of flows by approximately 23-38 percent (Sugar Pine Bridge), 32-42 percent (Ahwahnee Bridge), and 33-39 percent (Stoneman Bridge), though a side channel of concern to YNP management did not appear to be substantially affected by the removal scenarios. In comparison to the historical data, the FaSTMECH results suggest that flows for present-day conditions do not inundate the floodplain until between the 50- and 20-percent annual exceedance probability flood, whereas historically, a large portion of the floodplain was inundated during the 50-percent annual exceedance probability flood. Modeled maximum velocities in the present-day channel commonly exceed 2.0 m s -1 , whereas with the historical scenario, modeled maximum in-channel velocities rarely exceeded 2.0 m s -1 . The geomorphic analysis of the magnitude-frequency of bedload and suspended-sediment transport suggests that at the important Tenaya Bar site, the majority of bed sediment is mobile during most snowmelt-dominated floods. In contrast to sediment transport capacity, the analysis of repeat cross-sections suggests that bedload sediment supply into the eastern Yosemite Valley may be quite different between rain-on-snow floods and snowmelt-dominated floods, potentially with most sediment supply occurring during rain-on-snow floods, such as the 1997 flood. In contrast, the magnitude-frequency analysis of bedload and suspended-sediment transport suggests that long-term bedload sediment transport is likely dominated by snowmelt floods, and suspended-sediment transport is relatively low compared to bedload transport. Obtaining measured velocity data throughout the study reach would aid in model calibration, and thus would improve confidence in model results. Improved confidence in the model velocity results would allow additional substantial analyses of reach-scale effects of the planning scenarios and would enable the development of geomorphic models to evaluate the long-term geomorphic responses of the site. In addition, the collection of watershed sediment-supply data, about which little is presently known, would give planners helpful tools to plan restoration scenarios for this nationally important river.

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