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At least 1,081 records · Page 60Linked to original sources
USGS2008

Experimental approaches to assessing the impact of a cesium chloride radiological dispersal device

The US EPA, as a part of the Chemical, Biological, Radiological-Nuclear, and Explosives (CBRNE) Research and Technology Initiative (CRTI) project team, is currently working to assess the impacts of an urban radiological dispersion device (RDD) and to develop containment and decontamination strategies. Three efforts in this area are currently underway: development of a laboratory-scale cesium chloride deposition method to mimic a RDD; assessment of cesium (Cs) penetration depth and pathways in urban materials using two dimensional (2-D) mapping laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS); and experimental determination of distribution coefficients (kd) for Cs in water-building material systems. It is critical that, when performing laboratory-scale experiments to assess the fate of Cs from an RDD, the Cs particle deposition method mimics the RDD deposition. Once Cs particles are deposited onto urban surfaces, 2-D mapping of Cs concentrations using LA-ICP-MS is a critical tool for determining Cs transport pathways through these materials. Lastly, distribution coefficients are critical for understanding the transport of Cs in urban settings when direct measurements of its penetration depth are unavailable. An assessment of the newly developed deposition method along with preliminary results from the penetration experiments are presented in this paper.

Conference Paper↗
USGS1995

Effect of increased water depth on growth of a common perennial freshwater-intermediate marsh species in Coastal Louisiana

The response of Sagittaria lancifolia to increased water depths of 7.5 and 15 cm was examined in this field study. Water-depth treatments were achieved by digging sods containing one or two individual plants or ramets of S. lancifolia from the marsh, removing sediment from the resulting hole, and replacing the sods in their original location at the appropriate lower elevation. Plants subjected to increased water depth of 15 cm had higher mean and maximum leaf heights than disturbed control plants. Aboveground biomass was not affected by water-depth treatment; however, 15-cm treatment plants had reduced root biomass and lowered leaf tissue concentrations of Ca, Cu, Fe, Mg, and Zn. Marsh sods at 15 cm below the marsh surface had the lowest redox potential and highest interstitial water sulfide concentration, indicating that this treatment created the most stressful belowground environment. Sagittaria lancifolia plants responded to the level of stress imposed by the experimental conditions with an altered growth form of increased leaf height.

Louisiana↗
USGS2001

Plant community composition and biomass in Gulf Coast Chenier Plain marshes: Responses to winter burning and structural marsh management

Many marshes in the Gulf Coast Chenier Plain, USA, are managed through a combination of fall or winter burning and structural marsh management (i.e., levees and water control structures; hereafter SMM). The goals of winter burning and SMM include improvement of waterfowl and furbearer habitat, maintenance of historic isohaline lines, and creation and maintenance of emergent wetlands. Although management practices are intended to influence the plant community, effects of these practices on primary productivity have not been investigated. Marsh processes, such as vertical accretion and nutrient cycles, which depend on primary productivity may be affected directly or indirectly by winter burning or SMM. We compared Chenier Plain plant community characteristics (species composition and above- and belowground biomass) in experimentally burned and unburned control plots within impounded and unimpounded marshes at 7 months (1996), 19 months (1997), and 31 months (1998) after burning. Burning and SMM did not affect number of plant species or species composition in our experiment. For all three years combined, burned plots had higher live above-ground biomass than did unburned plots. Total above-ground and dead above-ground biomasses were reduced in burned plots for two and three years, respectively, compared to those in unburned control plots. During all three years, belowground biomass was lower in impounded than in unimpounded marshes but did not differ between burn treatments. Our results clearly indicate that current marsh management practices influence marsh primary productivity and may impact other marsh processes, such as vertical accretion, that are dependent on organic matter accumulation and decay.

Environmental Management↗
USGS2014

Spatial distribution of loggerhead turtle ( Caretta caretta ) emergences along a highly dynamic beach in the northern Gulf of Mexico

As coastlines change due to sea level rise and an increasing human presence, understanding how species, such as marine turtles, respond to alterations in habitat is necessary for proper management and conservation. Survey data from a major nesting beach in the northern Gulf of Mexico, where a revetment was installed, was used to assess spatial distribution of loggerhead emergences. Through use of Quadrat analysis and piecewise linear regression with breakpoint, we present evidence to suggest that nest site selection in loggerheads is determined in the nearshore environment, and by characteristics such as wave height, alongshore currents, depth and patterns of erosion and accretion. Areas of relatively dense nesting were found in areas with relatively strong alongshore currents, relatively small waves, a steep offshore slope and the largest historical rates of erosion. Areas of relatively dense nesting also corresponded to areas of low nesting success. Both nesting and non-nesting emergences were clustered immediately adjacent to the revetment and at other eroding sites along the beach. These results suggest that alterations to the nearshore environment from activities such as construction of a jetty, dredging or installation of pilings, may impact sea turtle nest distribution alongshore. We also show that piecewise linear regression with breakpoint is a technique that can be used with geomorphological and oceanographic data to predict locations of nest clumping and may be useful for managers at other nesting beaches.

Florida↗
USGS2011

Ecosystem ecology meets adaptive management: food web response to a controlled flood on the Colorado River, Glen Canyon

Large dams have been constructed on rivers to meet human demands for water, electricity, navigation, and recreation. As a consequence, flow and temperature regimes have been altered, strongly affecting river food webs and ecosystem processes. Experimental high‐flow dam releases, i.e., controlled floods, have been implemented on the Colorado River, USA, in an effort to reestablish pulsed flood events, redistribute sediments, improve conditions for native fishes, and increase understanding of how dam operations affect physical and biological processes. We quantified secondary production and organic matter flows in the food web below Glen Canyon dam for two years prior and one year after an experimental controlled flood in March 2008. Invertebrate biomass and secondary production declined significantly following the flood (total biomass, 55% decline; total production, 56% decline), with most of the decline driven by reductions in two nonnative invertebrate taxa, Potamopyrgus antipodarum and Gammarus lacustris . Diatoms dominated the trophic basis of invertebrate production before and after the controlled flood, and the largest organic matter flows were from diatoms to the three most productive invertebrate taxa ( P. antipodarum , G. lacustris , and Tubificida). In contrast to invertebrates, production of rainbow trout ( Oncorhynchus mykiss ) increased substantially (194%) following the flood, despite the large decline in total secondary production of the invertebrate assemblage. This counterintuitive result is reconciled by a post‐flood increase in production and drift concentrations of select invertebrate prey (i.e., Chironomidae and Simuliidae) that supported a large proportion of trout production but had relatively low secondary production. In addition, interaction strengths, measured as species impact values, were strongest between rainbow trout and these two taxa before and after the flood, demonstrating that the dominant consumer–resource interactions were not necessarily congruent with the dominant organic matter flows. Our study illustrates the value of detailed food web analysis for elucidating pathways by which dam management may alter production and strengths of species interactions in river food webs. We suggest that controlled floods may increase production of nonnative rainbow trout, and this information can be used to help guide future dam management decisions.

Arizona↗
USGS2009

Holocene core logs and site statistics for modern patch-reef cores: Biscayne National Park, Florida

The bedrock in Biscayne National Park (BNP), a 1,730-square kilometer (km2) region off southeast Florida, consists of Pleistocene (1.8 million years ago (Ma) to 10,000 years ago (ka)) and Holocene (10 ka to present) carbonate rocks (Enos and Perkins, 1977; Halley and others, 1997; Multer and others, 2002). Most of the surficial limestone in BNP, including the islands of the Florida Keys, was formed at ~125 ka during the highstand of marine oxygen-isotope substage 5e, when sea level was approximately 6 meters (m) higher than today (Chappell and Shackleton, 1986; Multer and others, 2002; Lidz and others, 2003; Siddall and others, 2003; Balsillie and Donoghue, 2004). During the substage-5e regression, the entire Florida Platform became exposed. Subaerial exposure lasted for approximately 115,000 years (kyr), which resulted in erosion and enhancement of karst-like features (Lidz and others, 2006). As the Holocene transgression began to flood the Florida shelf ~7 to 6 ka, the bedrock depression under Biscayne Bay began to flood, and Holocene coral and reef debris laid the foundation for the present reef system (Enos and Perkins, 1977; Lighty and others, 1982; Toscano and Macintyre, 2003; Lidz and others, 2006). More than 3,000 patch reefs exist within the BNP boundary. Most contain hermatypic corals of various species such as those belonging to Montastrea, Diploria, Siderastrea, Porites, Acropora, and Agaricia. Patch reefs within BNP have two morphologies: pinnacle and flat top. Experimental Advanced Airborne Research Lidar (EAARL) data collected along the offshore BNP coral reef tract show that these two morphologies are clearly defined both in the high-resolution bathymetry maps produced by the Lidar data and by statistical analyses of the Lidar dataset (Brock and others, 2008). Brock and others (2008) also show that the pinnacle patch reefs are deeper than the more shallow, broad, and flat patch reefs. The control for these two patch-reef morphologies is unclear; however, their shapes may be due to a slightly lowered sea level or a stillstand in the middle-Holocene around 4 ka that caused erosion of the shallower reefs and allowed the deeper reefs to remain unaffected. Lidz and others (2006) have suggested a stillstand around 4 ka that carved a 2.5-kilometer (km)-wide nearshore rock ledge into the seaward side of every island in the Florida Keys. The objectives of this study were to sample living corals to understand the more recent (<200 years) changes in climate and environmental conditions of the area and to investigate the Holocene (in this case, <8,000 years in the Florida Keys) depositional history at progressively deeper patch-reef sites. This report provides statistics for the cores and core sites and a basic lithologic description of these Holocene cores.

Florida↗
USGS2006

Applicability of terrestrial LIDAR scanning for scientific studies in Grand Canyon National Park, Arizona

In November 2004, an experimental high flow release of water from Glen Canyon Dam into the Colorado River through Grand Canyon National Park in Arizona was conducted. The goal of the experiment was to evaluate the use of high flow events as a management tool for the preservation and restoration of natural resources in the Colorado River below Glen Canyon Dam. The U.S. Geological Survey (USGS), Grand Canyon Monitoring and Research Center (GCMRC) located in Flagstaff, Arizona performed oversight of all aspects of scientific data collection including suspended sediment transport studies, biological population variations, effects on archaeological resources, and morphological studies of river sand bars. As part of the experimental high flow studies, the USGS Coastal and Marine Geology (CMG) team was invited to participate to test the effectiveness of utilizing terrestrial LIDAR technology for gathering morphological data on sand bars, biological habitats, and archaeological sites. The CMG is equipped with a terrestrial LIDAR unit and has used the technique in a variety of terrains to gather high-resolution morphological data. A three-member team from CMG participated in the experiment, joining a GCMRC team on a river trip from November 18 to November 21, 2004. This report begins with a brief description of the LIDAR technique and then outlines the data collected, processing required, and results for three study areas located within the Grand Canyon. Specifically, studies were performed at the Mile 30 Sand Bar, at Vaseys Paradise (Mile 32), and at the Mile 66 Palisades Archaeological Site. Conclusions and recommendations for utilizing terrestrial LIDAR for future studies at each of these sites are also included.

Arizona↗
USGS1995

Effects of selective forest clearing fertilization, and liming on the hydrology and water quality of a small tributary to the Quabbin Reservoir, central Massachusetts

Effects of selective forest clearing on water yield and water quality were investigated in a 308-hectare basin that drains to Quabbin Reservoir Watershed in central Massachusetts. The experimental basin and a nearby 280-hectare control basin were studied together for comparison. Streamflow was measured continuously and water-quality samples were collected biweekly in both basins from February 1985 through September 1989. During the same period, measurements of precipitation quantity and ground- water levels were made and samples were collected for determination of precipitation and ground-water quality. After an initial monitoring period to establish baseline hydrology and water quality in both basins, an area of red pine and white pine forest in the experimental basin was cleared. From October 1986 until April 1987, 23.8 percent of the total basal area was removed by clearcutting and thinning. Part of the cleared area was converted to rye and other field grasses, and the remainder was allowed to regrow naturally. Fertilizer and lime were applied to part of the cleared area. An additional 8.3 percent of basal area was cleared in fall 1988. Despite differences in bedrock geology, topography, and amount of wetland area, pre- treatment hydrology and chemistry of the two basins were similar. Biogeochemical reactions of the dilute mixture of sulfuric and nitric acids in precipitation with soils and rocks in the basins resulted in moderately buffered calcium-magnesium bicarbonate-type streamwater. During high flows, sulfate concentrations increased and alkalinity decreased. Selective forest clearing resulted in a slight increase in water yield during the year in which the clearing took place, particularly during the spring high-flow period, but flows returned to normal thereafter. Concurrent increases in solute flux were primarily a function of the increased water flux. No major alterations to biogeochemical processes were induced by the forest clearing, nor were any effects from the fertilizer or liming activity observed. The minimal effect observed from the clearing was attributed primarily to the limited area that was cleared, and the location of the cleared area in the headwaters of the basin (away from the riparian zone).

Massachusetts↗
USGS2016

Potential effects of sea-level rise on plant productivity: Species-specific responses in northeast Pacific tidal marshes

Coastal wetland plants are adapted to varying degrees of inundation. However, functional relationships between inundation and productivity are poorly characterized for most species. Determining species-specific tolerances to inundation is necessary to evaluate sea-level rise (SLR) effects on future marsh plant community composition, quantify organic matter inputs to marsh accretion, and inform predictive modeling of tidal wetland persistence. In 2 macrotidal estuaries in the northeast Pacific we grew 5 common species in experimental mesocosms across a gradient of tidal elevations to assess effects on growth. We also tested whether species abundance distributions along elevation gradients in adjacent marshes matched productivity profiles in the mesocosms. We found parabolic relationships between inundation and total plant biomass and shoot counts in Spartina foliosa and Bolboschoenus maritimus in California, USA, and in Carex lyngbyei in Oregon, USA, with maximum total plant biomass occurring at 38, 28, and 15% time submerged, respectively. However, biomass of Salicornia pacifica and Juncus balticus declined monotonically with increasing inundation. Inundation effects on the ratio of belowground to aboveground biomass varied inconsistently among species. In comparisons of field distributions with mesocosm results, B. maritimus , C. lyngbyei and J. balticus were abundant in marshes at or above elevations corresponding with their maximum productivity; however, S. foliosa and S. pacifica were frequently abundant at lower elevations corresponding with sub-optimal productivity. Our findings show species-level differences in how marsh plant growth may respond to future SLR and highlight the sensitivity of high marsh species such as S. pacifica and J. balticus to increases in flooding.

California, Oregon↗
USGS2013

Differential regulation of sodium-potassium pump isoforms during smolt development and seawater exposure of Atlantic salmon

Freshwater and seawater isoforms of the alpha subunit of Na + /K + -ATPase (NKA) have previously been identified in gill ionocytes of Atlantic salmon ( Salmo salar ). In the present study we examine the abundance and cellular localization of these isoforms during the parr–smolt transformation, a developmental process that is preparatory for seawater entry. The abundance of NKAα1a was lower in smolts than in parr, remained relatively constant during spring and decreased in summer. NKAα1b increased tenfold in smolts during spring, peaking in late April, coincident with downstream migration and increased salinity tolerance. NKAα1b increased a further twofold after seawater exposure of smolts, whereas NKAα1a decreased by 98%. The abundance of NKAα1b-positive, and NKAα1b and NKAα1a co-labeled ionocytes increased during smolt development, whereas the number of NKAα1a cells decreased. After seawater exposure of smolts, NKAα1b-positive ionocytes increased, NKAα1a-positive cells decreased, and co-labeled cells disappeared. Plasma growth hormone and cortisol increased during spring in smolts, but not in parr, peaking just prior to the highest levels of NKAα1b. The results indicate that the increase in the abundance of NKAα1b during smolt development is directly linked to the increase in salinity tolerance that occurs at this stage, but that significant changes also occur after seawater exposure. Spring increases in circulating levels of growth hormone and cortisol indicate that these hormones may be instrumental in upregulating NKAα1b during smolt development.

Journal of Experimental Biology↗
USGS2013

Physiological responses of adult rainbow trout experimentally released through a unique fish conveyance device

We assessed the physiological stress responses (i.e., plasma levels of cortisol, glucose, and lactate) of adult Rainbow Trout Oncorhynchus mykiss at selected time intervals after they had passed a distance of 15 m through a unique fish conveyance device (treatment fish) or not (controls). This device differs from traditional fish pumps in two important ways: (1) it transports objects in air, rather than pumping them from and with water; and (2) it uses a unique tube for transport that has a series of soft, deformable baffles spaced evenly apart and situated perpendicular within a rigid, but flexible outer shell. Mean concentrations of the plasma constituents never differed (P > 0.05) between control and treatment fish at 0, 1, 4, 8, or 24 h after passage, and only minor differences were apparent between the different time intervals within a group. We observed no obvious injuries on any of our fish. Our results indicate that passage through this device did not severely stress or injure fish and it may allow for the rapid and safe movement of fish at hatcheries, sorting or handling facilities, or passage obstacles.

North American Journal of Fisheries Management↗
USGS1993

Interaction of rising frazil with suspended particles: Tank experiments with applications to nature

Widespread occurrence of sediment-laden (turbid) sea ice and high concentrations of diatoms and foraminifers in ice have recently been reported from both polar regions. Many possible mechanisms of particle entrainment into ice have been postulated, among which scavenging by rising frazil ice and nucleation or adhesion of ice onto suspended particles appear to be the most likely ones. No reliable experimental data on the mechanisms, however, are available. Because of the importance of turbid ice for sediment transport, tanks for laboratory-scale experiments were constructed, in which frazil crystals produced at the base were monitored rising through water column laden with various types of particulate matter, including plankton. Observations made in salt water are reported here. Over a distance of 1.5 m, frazil < 1 mm in diameter grew to crystals or flocs several cm in diameter, rising at average velocities of 2 to 3 cm/s. Rise velocities were a function of frazil size, but varied greatly due to interactions of ice particles of different size and velocity and the resulting turbulence. Sand-size particles could be either trapped permanently by rising frazil, or were temporarily supported and again released. With live plankton, a several-fold enrichment of ice occurred, suggesting that their irregular shapes or appendages were caught by ice flocs. Diatom- and foram tests were also relatively effectively trapped. The concentration of silt- and clay-size terrigenous detritus in frazil tended to increase relative to the water. We found no preferential sorting by ice in this size range. Various kinds of evidence showed that ice does not nucleate onto foreign particles, and has no adhesive properties. Foreign material resided in the interstices of crystal aggregates, and particles denser than water could be released by agitation, suggesting that scavenging is a mechanical process. With rising frazil, the settling of particulate matter therefore is either retarded or reversed, resulting in a net upward sediment flux and a sediment-laden ice cover from this process of suspension freezing.

Cold Regions Science and Technology↗
USGS2021

Plasma metabolite indices are robust to extrinsic variation and useful indicators of foraging habitat quality in Lesser Scaup

Energy acquisition and storage are important for survival and fecundity of birds during resource-limited periods such as spring migration. Plasma-lipid metabolites (i.e. triglyceride [TRIG], β-hydroxybutyrate [BOHB]) have been used to index changes in lipid stores and, thus, have utility for assessing foraging habitat quality during migration. However, such an index may be affected by energetic maintenance costs, diet, and other factors, and further validation under experimental conditions is needed to understand potential sources of variation and verify existing indices. We evaluated a plasma-lipid metabolite index using 30 female and 28 male wild Lesser Scaup ( Aythya affinis ; hereafter scaup) held in short-term captivity (~24 hr) during spring migration. Similar to previous observational studies, BOHB was negatively associated and TRIG was positively associated with mass change ( R 2 = 0.68). BOHB estimates were nearly identical to those published on free-living scaup, but TRIG estimates differed from free-living scaup and varied by sex, with females having a greater rate of predicted mass change than captive and free-living males. Our results suggest TRIG may be a better measure of energy income than deposition because lipid deposition likely varies with energetic maintenance costs, stress, and underlying physiological processes while TRIG relates primarily to energy income. In contrast, BOHB was a reliable predictor of negative mass change across sexes. The sex-based differences in apparent lipid deposition rates warrant further research before a generalizable model is advisable for comparing mass change predictions across studies. However, if predictions are standardized, this technique is generally robust to variations in energy income vs. lipid deposition across sexes. Accordingly, our evaluation provides verification for the utility of plasma-lipid metabolites as an indicator of foraging habitat quality during migration.

Illinois↗
USGS2023

Multi-scale relationships in thermal limits within and between two cold-water frog species uncover different trends in physiological vulnerability

1. Critical thermal limits represent an important component of an organism's capacity to cope with future temperature changes. Understanding the drivers of variation in these traits may uncover patterns in physiological vulnerability to climate change. Local temperature extremes have emerged as a major driver of thermal limits, although their effects can be mediated by the exploitation of fine-scale spatial variation in temperature through behavioural thermoregulation. 2. Here, we investigated thermal limits along elevation gradients within and between two cold-water frog species ( Ascaphus spp.), one with a coastal distribution ( A. truei ) and the other with a continental range ( A. montanus ). We quantified thermal limits for over 700 tadpoles, representing multiple populations from each species. We combined local temporal and fine-scale spatial temperature data to quantify local thermal landscapes (i.e., thermalscapes), including the opportunity for behavioural thermoregulation. 3. Lower thermal limits for either species could not be reached experimentally without the water freezing, suggesting that cold tolerance is <0.3°C. By contrast, upper thermal limits varied among populations, but this variation only reflected local temperature extremes in A . montanus , perhaps as a consequence of the greater variation in stream temperatures across its range. Lastly, we found minimal fine-scale spatial variability in temperature, suggesting limited opportunity for behavioural thermoregulation and thus increased vulnerability to warming for all populations. 4. By quantifying local thermalscapes, we uncovered different trends in the relative vulnerability of populations across elevation for each species. In A . truei , physiological vulnerability decreased with elevation, whereas in A . montanus , all populations were equally physiologically vulnerable. These results highlight how similar environments can differentially shape physiological tolerance and patterns of vulnerability of species, and in turn impact their vulnerability to future warming.

Montana↗
USGS1997

Investigation of aggregation in solvent extraction of lanthanides by acidic extractants (organophosphorus and naphthenic acid)

Three acidic extractants (I) di(2-ethylhexyl) phosphoric acid (HDEHP), (II) 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEHPEHE) and (III) naphthenic acid were employed in preparing the samples for the characterization of the coordination structure of lanthanide-extractant complexes and the physicochemica nature of aggregates formed in the organic diluent of the solvent extraction systems. Photo correlation spectroscopy (PCS) results on the aggregates formed by the partially saponified HDEHP in n-heptane showed that the hydrodynamic radius of the aggregates was comparable to the molecular dimensions of HDEHP. The addition of 2-octanol into the diluent, by which the mixed solvent was formed, increased the dimensions of the corresponding aggregates. Aggregates formed from the lanthanide ions and HDEHP in the organic phase of the extraction systems were found very unstable. In the case of naphthenic acid, PCS data showed the formation of w/o microemulsion from the saponified naphthenic acid in the mixed solvent. The extraction of lanthanides by the saponified naphthenic acid in the mixed solvent under the given experimental conditions was a process of destruction of the w/o microemulsion. A possible mechanism of the breakdown of the w/o microemulsion droplets is discussed.

Science in China, Series B: Chemistry↗
USGS2012

Food availability and offspring sex in a monogamous seabird: insights from an experimental approach

Sex allocation theory predicts that parents should favor offspring of the sex that provides the greatest fitness return. Despite growing evidence suggesting that vertebrates are able to overcome the constraint of chromosomal sex determination, the general pattern remains equivocal, indicating a need for experimental investigations. We used an experimental feeding design to study sex allocation during 3 years in black-legged kittiwakes ( Rissa tridactyla ). Intense male–male competition for securing a breeding site is common in this species in which males are heavier and larger than females. Hence, we hypothesized that parents producing fledglings in better than average condition, as supplementarily fed pairs do, would increase their fitness return by producing sons. Conversely, producing daughters would be a better tactic for Unfed parents. Hence, we predicted that Fed parents produce more sons than Unfed parents. This prediction is particularly expected if sexual dimorphism arises as early as during chick rearing, suggesting strong selective pressures for optimal male development. Our results showed that 1) males were heavier and larger than females prior to fledging and that 2) Fed parents produced relatively more male hatchlings than Unfed parents. We interpret this result in terms of a Trivers–Willard-type process. Furthermore, our data revealed that Unfed parents significantly overproduced female hatchlings, whereas offspring sex ratio was balanced among Fed parents. Because the 3 reproductive seasons we considered were particularly poor food years, Unfed parents may have overproduced daughters to avoid the apparent higher reproductive costs of raising sons.

Behavioral Ecology↗
USGS1999

Utility of EXAFS in characterization and speciation of mercury-bearing mine wastes

Extensive mining of large mercury deposits located in the California Coast Range has resulted in mercury contamination of both the local environment and water supplies. The solubility, dispersal, and ultimate fate of mercury are all affected by its chemical speciation, which can be most readily determined in a direct fashion using EXAFS spectroscopy. EXAFS spectra of mine wastes collected from several mercury mines in the California Coast Range with mercury concentrations ranging from 230 to 1060 mg/kg (ppm) have been analyzed using a spectral database of mercury minerals and sorbed mercury complexes. While some calcines have been found to consist almost exclusively of mercuric sulfide, HgS, others contain additional, more soluble mercury phases, indicating a greater potential for the release of mercury into solution. This experimental approach can provide a quantitative measurement of the mercury compounds present and may serve as an indicator of the bioavailability and toxicity levels of mercury mine wastes.

Journal of Synchrotron Radiation↗
USGS2012

A terrestrial lidar-based workflow for determining three-dimensional slip vectors and associated uncertainties

Three-dimensional (3D) slip vectors recorded by displaced landforms are difficult to constrain across complex fault zones, and the uncertainties associated with such measurements become increasingly challenging to assess as landforms degrade over time. We approach this problem from a remote sensing perspective by using terrestrial laser scanning (TLS) and 3D structural analysis. We have developed an integrated TLS data collection and point-based analysis workflow that incorporates accurate assessments of aleatoric and epistemic uncertainties using experimental surveys, Monte Carlo simulations, and iterative site reconstructions. Our scanning workflow and equipment requirements are optimized for single-operator surveying, and our data analysis process is largely completed using new point-based computing tools in an immersive 3D virtual reality environment. In a case study, we measured slip vector orientations at two sites along the rupture trace of the 1954 Dixie Valley earthquake (central Nevada, United States), yielding measurements that are the first direct constraints on the 3D slip vector for this event. These observations are consistent with a previous approximation of net extension direction for this event. We find that errors introduced by variables in our survey method result in <2.5 cm of variability in components of displacement, and are eclipsed by the 10–60 cm epistemic errors introduced by reconstructing the field sites to their pre-erosion geometries. Although the higher resolution TLS data sets enabled visualization and data interactivity critical for reconstructing the 3D slip vector and for assessing uncertainties, dense topographic constraints alone were not sufficient to significantly narrow the wide (<26°) range of allowable slip vector orientations that resulted from accounting for epistemic uncertainties.

Geosphere↗