• Basal shear strength inversions for ice sheets with an application to Jakobshavn Isbræ, Greenland

      Habermann, Marijke; Truffer, Martin; Maxwell, David; Freymueller, Jeff; Pettit, Erin; Tape, Carl (2013-12)
      Satellite and in situ observations of ice sheet outlet glaciers around the turn of the 21st century showed that rapid changes in ice dynamics are possible and important for the evolution of ice sheets. When attempting to model these dynamic changes the conditions at the ice-bed interface are crucial. Inverse methods can be used to infer basal properties, such as the basal yield stress, from abundant surface velocity observations by using a physical model of ice flow. Inverse methods are very powerful, but they need to be applied with care, otherwise errors can dominate the solution. In this study we investigate the potentials and caveats of inverse methods. Synthetic experiments can be designed where basal conditions are assumed and an ice flow model is used to produce a set of 'synthetic' surface velocities. These can then be used to examine and evaluate inverse methods. We find that in iterative inverse methods it is essential to use a stopping criterion that will prevent overfitting the data. We introduce a new and rapidly-converging iterative inverse method called Incomplete Gauss Newton method, where the linearized problem is partly minimized in each step.In a practical application of inverse methods to the terminus region of Jakobshavn Isbræ, Greenland we investigate changes in basal conditions over time by performing inversions for different years of available surface velocity data. We find a decrease in basal yield stress in the lower areas of the glacier that agrees with effective pressure changes due to the changes in ice geometry. This supports an ocean and terminus driven system. The difference between the modeled and observed velocity fields, called residual, contains information about the ability to reproduce the velocities when only adjustment of the basal condition is allowed. With a properly regularized inversion the residual patterns can be used to investigate sources of error in the system. We find that the ice geometry and the model simplifications influence the ability to reproduce observed velocity fields more than the error in observed velocity does. This indicates that further progress must come from model improvements and improved capabilities to measure bedrock geometry.
    • Baseline data of bird populations in the Sierra Gorda Biosphere Reserve, Mexico: a citizen science approach

      Anderson, Teresa S.; Fix, Peter J.; Carsten-Conner, Laura D.; Dalle-Molle, Lois K. (2017-12)
      This project tested the viability of converting a local environmental education group, "Eco Chavos" into a team of citizen scientists. In rural biosphere reserves in Mexico, with few resources and large resident populations, community-based biological inventory and monitoring has the potential to increase the impact of Mexican biosphere reserves by generating scientific information and engaging local residents in hands-on environmental education. To test this, I formed a citizen science birding group and trained them in bird identification, survey techniques, data collection, and data management. The project began in January 2016 and in December 2016 I stopped mentoring the program and let it continue under its own leadership. Our team was composed of an Eco Chavos group and a resident ornithologist who conducted land and water-based surveys multiple times a month. As of August 2017, 160 bird species have been registered, including three species endemic to Mexico; the Crimson-collared Grosbeak (Rhodothraupis celaeno), Blue Mockingbird (Melanotis caerulescens), and Spotted Wren (Campylorhynchus gularis). The survey provided an inventory of bird diversity in the reservoir, and could serve as a starting point to measure occurrence and abundance over time. The data were published in the updated management plan of the Sierra Gorda Biosphere Reserve as well as in a new bird book, Guía de Aves de la Presa Jalpan. A new community group, "Aves de la Presa Jalpan" was formed and contributed information via an online public database. The database may be used by the international network of bird monitors to analyze population trends in both local Mexican bird populations and in international bird migrations. In addition, participants showed increased bird identification skills, leadership, increased interest in birds, and engagement in project tasks and planning. Infrastructure was built to encourage birdwatching tourism in the Biosphere Reserve and the foundation was set to continue this research in the future.
    • Bathymetric and spatial distribution of echinoderms on seamounts in the Gulf of Alaska

      Underwood, Danielle Parker (2006-12)
      The bathymetric and spatial distribution of echinoderms was examined on five seamounts in the Kodiak-Bowie seamount chain in the northern Gulf of Alaska from video transects of 200 or 500 m length, conducted at approximately 700, 1700 and 2700 m depths with the DSV Alvin in August, 2004. Temperature and salinity varied significantly with depth, but not between seamounts; an oxygen minimum zone encompassed the shallowest depth sampled. Holothuroid (Pannychia and Psolus) and asteroid density for the shallower depth category was 19.94·100 m⁻² and 2.07·100 m⁻², significantly higher than at the deeper depths. Asteroid density generally decreased northwesterly along the seamount chain. Density of three ophiuroid genera (Asteronyx, Amphigyptis, and Ophiomoeris) was 139.6·100 m⁻² on Dickens Seamount, and was significantly less on the other three seamounts to a low of 31.19·100 m⁻² on Pratt Seamount. Ophiuroid density was significantly higher at the intermediate depth (141.07·100 m⁻²), and lower at the other two depths. Density of Pentametrocrinus and Guillecrinus crinoids was not significantly affected by seamount or depth, but was highest (3.15·100 mm⁻²) at the deepest depths. No echinoids were found on transects, but were observed on three of the seamounts. Many brittle stars and asteroids were found associated with paragorgid and primnoid corals.
    • Bathymetry of Alaskan arctic lakes: a key to resource inventory with remote-sensing methods

      Mellor, Jack C. (1982-05)
      Water depth is a major factor in predicting resources associated with tens-of-thousands of uninventoried Alaskan arctic lakes. Lakes were studied for physical, chemical, and biological resources related to water depth in 3 specific areas along a north/south transect extending from Pt. Barrow on the Arctic Ocean to the foothills of the Brooks Range. Side-Looking Airborne Radar (SLAR) imagery was acquired over the same study transect to investigate its application for determining lake depth. Ice thicknesses, necessary for the interpretation of depth contours from SLAR imagery, were measured along with other parameters in the study lakes throughout the winter 1978-79. This ice-thickness data and sequential SLAR images are used to illustrate a method of contouring water depths in arctic lakes. This is based on changes in intensity of SLAR signal return which define the zone at which ice cover contacts the bottom. This intensity is a function of physical and dielectric properties of the snow, ice, water, bottom substrates, and ice inclusions within these lakes. A computer program was developed to manipulate Landsat satellite digital data and compile a master file of lakes and their computer-calculated surface features (i.e. area, perimeter, crenulation, and centroid). The master file uniquely identifies each computer catalogued lake by latitude and longitude and stores the calculated features in a data base that can be retrieved for a specified geographic ABSTRACT area. Each lake record also provides storage space for resource data collected outside the computer generated data. The application of these remote-sensing tools and the knowledge of aquatic resources associated with bathymetry add to our ability for regional inventory, classification, and management of arctic lake resources.
    • Bayesian methods in glaciology

      Brinkerhoff, Douglas; Truffer, Martin; Aschwanden, Andy; Tape, Carl; Bueler, Ed (2017-12)
      The problem of inferring the value of unobservable model parameters given a set of observations is ubiquitous in glaciology, as are large measurement errors. Bayes' theorem provides a unified framework for addressing such problems in a rigorous and robust way through Monte Carlo sampling of posterior distributions, which provides not only the optimal solution for a given inverse problem, but also the uncertainty. We apply these methods to three glaciological problems. First, we use Markov Chain Monte Carlo sampling to infer the importance of different glacier hydrological processes from observations of terminus water flux and surface speed. We find that the opening of sub-glacial cavities due to sliding over asperities at the glacier bed is of a similar magnitude to the opening of channels due to turbulent melt during periods of large input flux, but also that the processes of turbulent melting is the greatest source of uncertainty in hydrological modelling. Storage of water in both englacial void spaces and exchange of water between the englacial and subglacial systems are both necessary to explain observations. We next use Markov Chain Monte Carlo sampling to determine distributed glacier thickness from dense observations of surface velocity and mass balance coupled with sparse direct observations of thickness. These three variables are related through the principle of mass conservation. We develop a new framework for modelling observational uncertainty, then apply the method to three test cases. We find a strong relationship between measurement uncertainty, measurement spacing, and the resulting uncertainty in thickness estimates. We also find that in order to minimize uncertainty, measurement spacing should be 1-2 times the characteristic length scale of variations in subglacial topography. Finally, we apply the method of particle filtering to compute robust estimates of ice surface velocity and uncertainty from oblique time-lapse photos for the rapidly retreating Columbia Glacier. The resulting velocity fields, when averaged over suitable time scales, agree well with velocity measurements derived from satellites. At higher temporal resolution, our results suggest that seasonal evolution of the subglacial drainage system is responsible for observed changes in ice velocity at seasonal scales, and that this changing configuration produces varying degrees of glacier flow sensitivity to changes in external water input.
    • Bayesian predictive process models for historical precipitation data of Alaska and southwestern Canada

      Vanney, Peter; Short, Margaret; Goddard, Scott; Barry, Ronald (2016-05)
      In this paper we apply hierarchical Bayesian predictive process models to historical precipitation data using the spBayes R package. Classical and hierarchical Bayesian techniques for spatial analysis and modeling require large matrix inversions and decompositions, which can take prohibitive amounts of time to run (n observations take time on the order of n3). Bayesian predictive process models have the same spatial framework as hierarchical Bayesian models but fit a subset of points (called knots) to the sample which allows for large scale dimension reduction and results in much smaller matrix inversions and faster computing times. These computationally less expensive models allow average desktop computers to analyze spatially related datasets in excess of 20,000 observations in an acceptable amount of time.
    • Beach ridge geomorphology of Kotzebue Sound: Implications for paleoclimatology and archaeology

      Mason, Owen Kenneth (1990)
      Beach ridges occur on all continents and record the horizontal addition of shoreface beyond the reach of storms. Improved cartographic methods in the nineteenth century allowed British historians to link shoreline changes with abandoned villages. This scientific trajectory was paralleled in the Bering Strait region from the 1880's to the 1930's. In the 1950's J. L. Giddings formalized "beach ridge archaeology" as a survey strategem using relative position to infer relative cultural chronology in northwest Alaska. Modern researchers use archaeological dates and data to document past climates or environments. At Cape Espenberg, on Seward Peninsula, my use of archaeological, stratigraphic, pedological, granulometric and photogrammetric data allows the delineation of 4000 years of coastal evolution. Four chronostratigraphic units are distinguished, using archaeological dates as minimum age assignments. Dune ridges formed in discrete intervals: 3300 to 2000 BP and from 1200 BP to the present; while low, berm ridges are predominant 4000-3300 and from 2000-1200 BP. The two different types of ridges correspond to variable climatic conditions: dune ridges formed after higher storm surges and winter winds while the lower berm ridges are related to less intense storm surges. Coastal dunes at Cape Espenberg are soon altered by plant succession processes with distance from the beach. As primary dunes are eroded, a complex blowout topography results. Erosional processes in blowouts were monitored during 1987-1989, revealing substantial vertical changes, up to 10 cm of erosion per yr. These rapid changes have considerable influence on archaeological site stability. Studies of the gravel ridge systems confirm the proxy storm record apparent in the coastal dunes atop the beach ridges on the Seward Peninsula. The geoarchaeological methodology allows correlations between depositional units within nine of the principal beach ridge and chenier complexes of northwest Alaska. The onset of deposition was at 4000-3500 BP. The complexes at Cape Espenberg and Choris Peninsula contain elevated, broader transgressive ridge sets 3300-2000 BP and from 1100-200 BP, connected with increased storm activity in the North Pacific. Erosional disconformities between successive sets of beach ridges occur at Cape Krusenstern at ca. 3000 BP and before 2000 BP. Between 2000-1000 BP extensive progradation occurred at nearly all complexes, indicating that less stormy conditions predominated.
    • Beaver population ecology in interior Alaska

      Boyce, Mark S. (1974-05)
      The ecology of beaver (Castor canadensis Kuhl) populations along two streams in interior Alaska was studied in 1972 and 1973. The two study areas were similar in most respects, except for the history of human trapping intensity. The heavily trapped population exhibited the following contrasts to the essentially unexploited population: (1) higher mortality among adult age classes, (2) higher survivorship of the prereproductives, (3) a sex ratio with a preponderance of females, (4) decreased age at first breeding and consequently, (5) a smaller average size at maturity. Males appear to expend lower effort for parental activities than do females, and consequently exhibit higher survivorship than their mates. Population regulating mechanisms, management implications, and the evolution of an optimal life history strategy are discussed. The distribution and abundance of beaver colonies were related to habitat types and characteristics of the physical environment by multiple linear regression analysis.
    • Becoming adults in a rural Yup'ik community: a longitudinal qualitative study exploring resilience

      Ford, Tara J.; Allen, James; Whipple, Jason; David, Eric John; Henry, David; Rasmus, Stacy M. (2013-08)
      The aim of this study is to explore strategies for navigating challenges in a rural Alaskan Yup'ik community among youth and young adults. This qualitative study captures a longitudinal perspective as youth (N=25; 11 -18 years old) were originally interviewed in January 2010. For the current study, participants were re-interviewed in December 2012. Follow-up interviews addressed life challenges over the past three years and resources that helped them with their hard times. To reinforce the multifaceted nature of growing-up in a rural Yup'ik community, scholarly literature along with observations, conversations with local residents, and local wisdom captured in anthropological work are featured throughout this paper. Fifteen youth (14 years old - 20 years old) agreed to be re-interviewed. Developmental changes were noted regarding challenges and protective resources. Youth emphasized challenges as sources of vulnerabilities around lack of employment and interpersonal relationship strain. Similar to findings from the original study, interpersonal relationship distress was discussed in three distinct contexts including antagonist "girl drama," family discord, and partner relations conflicts. Youth identified personal strengths such as re-framing challenges, seeking personal space, and family support to overcome challenges. Contemporary understanding of emergent young adults' role and responsibilities in a rural Yup'ik setting warrants further study as it was found to be a source of vulnerability. Findings can inform clinical and prevention work in the community. For example, targeted community activities can address reported challenges including job fairs and workshops on healthy relationships with specificity to the experience of becoming an adult in rural Alaska.
    • Becoming Aware As A Parent, Schoolteacher And Community Member

      Angaiak-Bond, Anna (2010)
      The researcher uses autoethnography to understand whether a parent can act to maintain and reinvigorate Yup'ik at home after the child has already become English dominant. The research takes place in the village of Tununak, where the mother/researcher, a fluent Yup'ik speaker, lives with her son. The Tununak school has a Yup'ik First Language Program (YFL). Under this program, the first three years of school are taught in Yup'ik, their children's first language. The fourth year is a transition period in which English is introduced. After exiting the YFL program, English becomes the primary language of instruction. Eventually, the majority of the students become English dominant. The researcher's child attended the YFL program and is now 15 years old. At the beginning of this research he spoke Yup'ik minimally. English was his dominant language He was considered Limited English Proficient when he entered school. He has been designated as fully English proficient since 6 th grade. His Yup'ik proficiency improved during the course of the research as he began to speak more phrases/sentences than he did at the beginning. The researcher seeks to learn if her role as a parent can reinvigorate her child's first language, Yup'ik, after he has already become English dominant. The research provided insights into one parent's attempts to strengthen the usage of Yup'ik at home. Data analysis focused on identifying factors that facilitated and/or hindered the process of speaking Yup'ik dominantly at home.
    • Beetles and spiders as indicators of forest recovery on Prince of Wales Island, Alaska

      Stockbridge, Jill M.; Sikes, Derek S.; Wagner, Diane; Kruse, James J. (2014-08)
      Commercial logging is among the most important disturbance factors affecting forest biota. An indirect effect of commercial logging is minimal understory within young even-aged forests, which can decrease forest biodiversity. To improve management of young even-aged forest stands within the Tongass National Forest (TNF), foresters are testing alternative forestry practices under the Tongass-Wide Young-Growth Studies (TWYGS). However, little is known about how the new thinning treatments included in the TWYGS will affect forest biota and the recovery of young even-aged forest stands as they transition back into old growth forests. To investigate the effects of thinned secondary growth on forest biota in the TNF on Prince of Wales Island, Alaska, I compared spider and beetle biodiversity in thinned secondary growth to old growth forest stands, clearcuts, and un-thinned secondary growth. Pitfall traps, Berlese funnels, and Lindgren© funnel traps were used to collect spiders and beetles in each forest type to compare species richness, diversity, and assemblages, as well as to identify possible ecological indicators within each habitat. I hypothesized that thinned secondary growth would have a mix of old growth and clearcut species and be further in the process of recovery than un-thinned secondary growth. I found that (1) spider and beetle species richness and diversity from thinned secondary growth were not significantly different from other forest treatments; (2) spider assemblages in thinned secondary growth were significantly different from other forest treatments, whereas beetle assemblages were not different; (3) spider and beetle assemblage structure was mainly influenced by Leaf Area Index (LAI) and; (4) spider and beetle ecological indicators of clearcuts and old growth stands were found within thinned and un-thinned secondary growth stands. These findings support my hypothesis that thinned secondary growth would have both old growth and clearcut species; however, thinned secondary growth was not found to be further in the process of recovery than unthinned secondary growth at the time of this study. Although thinned secondary growth was not further in the process of recovery, it did not adversely affect the biodiversity of spiders and beetles. My results suggest that logging on Prince of Wales Island can change spider and beetle assemblages, but it doesn't negatively impact species richness or diversity. Thinned secondary growth spider and beetle biodiversity may be in the process of recovery to the biodiversity seen in old growth forests. Therefore, spider and beetle biodiversity may resemble old growth forest biodiversity as LAI values increase with closing canopy in thinned secondary growth forest stands. In addition, a checklist of arthropods collected on Prince of Wales Island, Alaska, as part of this work, combined with records from other projects and publications, are included followed by a description of a new species I discovered, Caurinus tlagu Sikes & Stockbridge 2013 (Mecoptera, Boreidae, Caurininae).
    • Behavior Of Granular Materials Under Cyclic And Repeated Loading

      Minassian, George H.; Raad, Lutfi (2003)
      Granular layers are essential contributors to the structural integrity of the pavement system, their premature deformation radically decrease support of the asphalt concrete surface layer, thus leading to the early deterioration of the overall pavement structure. This research was conducted to better understand the behavior of granular materials when subjected to the complex nature of traffic loading. Long-term triaxial tests were conducted on typical Alaskan base course material using both repeated as well as cyclic loading to also account for the shear reversal effects induced by wheel load. Results show that the shear reversal component of the traffic loads, which have been ignored so far, induces considerable damage to the granular layers. Models were presented to predict the different soil moduli while also accounting the effect of strain hardening or densification due to the repetitive nature of the loads applied. Moreover, a simple yet powerful model was presented to predict accumulated permanent strains as function of the stress state, number of load repetitions and the strength level applied. The results obtained in this study also show a clear indication of the existence of given stress level limit beyond which incremental collapse of the system takes place. Furthermore, regions of instability of granular layers subjected to dynamic loading have been defined using a simple response parameter and monotonic shear strength of the soil. An effort was made to explain the instability zones identified in this research by the shakedown theory.* *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Microsoft Office.
    • The behavior of tellurium during copper ore processing at the American Smelting and Refining Company (Tucson, AZ)

      Josephson, Amy E.; Hayes, Sarah M.; Newberry, Rainer J.; Trainor, Thomas P. (2016-08)
      Essentially all tellurium (Te), an element used in solar panels and other high technology devices, is recovered as a byproduct of copper mining. Recent increases in demand have sparked questions of long-term supplies of Te (crustal abundance ~3 μg∙kg-1). As part of a larger study investigating Te resources, this project examines the behavior of Te during Cu ore mining, smelting, and refining at the American Smelting and Refining Company (Tucson, AZ) as a first step toward optimizing Te recovery. Mass balance calculations estimate that only 4 ± 1% of the Te in the ore reports to the Cu anodes, while 60 ± 30%, 0.8 ± 0.2% and 5.8 ± 0.4% is lost in the tailings, slag, and dust, respectively. The uncertainties reported are the standard deviation of analytical measurements, but due to heterogeneity of Te distribution in the ore, the actual uncertainty is likely higher. Microprobe data shows that Te in the concentrate is mainly present as telluride minerals, but substitution into sulfides most likely also occurs. X-ray fluorescence (XRF) mapping showed that Te is collocated with S in the raw anode slimes, pressed anode slimes, and doré furnace soda slag. X-ray absorption spectroscopy (XAS) was used to examine Te speciation in anode slimes. It was found that Te oxidizes during the Cu ore smelting process, with 44% Te4+ in the flash furnace SO₂ filter. Te also showed 32% Te4+ in the raw and pressed anode slimes. The doré furnace soda slag and dust filter showed the most oxidation of Te at 57% Te4+ and 60% Te6+ respectively. These results indicate several points in the extraction process that could be examined further to determine if additional Te might be recovered from the overall process.
    • Behavior, physiology, biological age, and cultural role of long-lived Bering Sea seabirds

      Young, Rebecca C.; Kitaysky, Alexander S.; Chapin, F. Stuart; Carothers, Courtney L.; Haussmann, Mark F. (2014-05)
      This dissertation focuses on the intersection of behavior, physiology, and biological age. Biological age is a measure of an organism's progress through life, and it incorporates chronological age as well as the actions of environment and innate quality at the individual level. We estimate biological age using telomere length as a biomarker. Telomere degradation in relation to oxidative stress links it directly to purported proximate mechanisms of aging under the free radical theory of aging. Short telomeres, or telomere loss, have been related to ecological indicators of lowered fitness. Our work focuses on aging in the thick-billed murre (Uria lomvia), a long-lived seabird breeding in the Bering Sea. Seabirds exemplify the "slow-lived" paradigm; they have long lifespans, low reproductive rates, and high adult survival. First we address the relationship between chronological age and telomere length in the thick-billed murre. We found longer telomeres in chicks than in adults, and longer telomeres in adult females than in adult males. Then we examine biological age, telomere length, in relation to physiology and behavior of murres equipped with a recording device to monitor foraging behavior. Chapter two describes the physiological and reproductive investment of these murres in relation to their biological age, while chapter three addresses the habitat and prey choices made by these birds in relation to sex, biological age, and environment. Behaviorally murres remain healthy into their old ages, with physiological diving capacity similar or improved in old birds. Stress patterns demonstrate that when conditions are good, older birds are more stressed, but experience buffers their stress levels under poor conditions. The fourth chapter of this thesis deals with seabirds as part of the larger socio-ecological system that includes the indigenous people living on the Pribilof Islands. The Priblovians value seabirds, but are members of periphery communities troubled by a poor economy and disconnected from a past that was tightly coupled to the natural world. Development requires active management by local stakeholders to reconnect with cultural and economic resources (like seabirds) and to make the communities more sustainable and resilient.
    • Beneath the terrible surface

      Lagergren, Jenny Kristine (2002-05)
      'Beneath the terrible surface' is concerned with connections among people, animals, objects, and land that are important, but subtle and often overlooked. The poems are concrete and find meaning through a moment slowed downed and viewed from a new angle, which ultimately conveys emotion. While moments are described, the goal is not description, but exploration. A point in time becomes important by what happens or does not happen and by what is noticed and felt by the speakers and characters. Though not always positive, they detail an awareness of the intricate, important and sometimes invisible connections between many forms of life. The collection contemplates what it takes to love a landscape, appreciate animals, and notice, react, and care for life that does not lend itself to immediate liking.
    • Beneficiation of rare earth minerals from Bokan Mountain: Dotson Ridge ore

      Narantsetseg, Purevbaatar; Наранцэцэг, Пүрэвбаатар; Ganguli, Rajive; Ghosh, Tathagata; Akdogan, Guven (2014-12)
      The purpose of this research work was to study the beneficiation of rare earth ore of the Bokan Mountain -- Dotson Ridge deposit, located near Ketchikan, Alaska. Rare earth element (REE) composite ore samples from the Bokan Mountain -- Dotson Ridge deposit were tested using gravity concentration, magnetic separation, flotation, and leaching techniques to separate the REE. The composite ore sample was a product of a preliminary x-ray sorting process. Qualitative electron microprobe analysis of the ore showed that most of the REE minerals in the ore were silicate minerals. Since the electron microprobe analysis samples were coated with carbon during sample preparation, the carbon element was inactivated for analysis. Because of this, carbonate compounds of minerals' particles could not be detected. 95% of the REE mineral particles appear to be smaller than about 10 μm in size (about 100 μm² in area). For the gravity concentration, light rare earth elements (LREE) and heavy rare earth elements' (HREE) individual elemental recovery values were in the ranges of 49.6-52.8% and 46.3-48.8%, respectively, at 25% of mass yield. In order to separate a larger amount of the REE, a wet high intensity magnetic separation (WHIMS) test was carried out on tailings of the gravity concentration tests. The HREE individual elemental recovery values ranged from 56.3-63.1% at 37% mass yield, while LREE individual elemental recovery values were in the 57.9% - 59.1% range. For the combined gravity and magnetic separation processes, the net individual elemental recovery values of the LREE and the HREE were in the range of 79.6-80.5% and 76.5-80.9%, respectively. The combined mass yield of the gravity and magnetic separation processes was 3%. Direct leaching tests conducted on the composite ground ore feed yielded high individual elemental recovery values of 90-92% of the LREE. The HREE individual elemental recovery values ranged from 56.5-87.3%. In the leaching, 20% HCl was used in the 1st and 2nd stages with a duration of 2 hrs in each stage at 90°C. The solid percentage of the leach slurry was 20% w/w. The composite ground ore sample was tested in conventional flotation using a 2.0 L capacity Denver cell. In the flotation, 0.05 kg/tonne of Cytec Aero 6493 collector, 0.05 kg/tonne of Cytec Aero Froth 88, and 0.1 kg/tonne of sodium metasilicate as a depressant were used. Pulp pH was set around 9. Results showed individual elemental recovery values in the range of 44.6-50.4% or the LREE. The HREE individual elemental recovery values ranged from 27.9-44.5%. The mass yield of the flotation was 23%. The flotation recoveries reported here are significantly lower than what was achieved previously. For the Leach after flotation process, leaching was conducted on the first concentrate of flotation. Individual elemental recovery values of the LREE and HREE were 94.7-96.5% and 61.1-90.5%, respectively. The concentrate was leached using 20% HCl in both the 1st and 2nd stages, with a duration of 2 hrs in each stage at 90°C. Flotation/Leach process net recoveries of LREE by individual elemental values ranged from 42.2-48.5%. HREE net recoveries by individual elemental values ranged from 17.1-41.4%.
    • Benthic community development in Boca de Quadra, Alaska

      Winiecki, Carol Irene (1986-05)
      The purpose of this experiment was to find ways of evaluating the community development in Boca de Quadra, a fjord in southeast Alaska, after a severe physical disturbance. Containers of defaunated sediment were used near the head of the fjord to simulate the benthic habitat after such a disturbance. Important features of community development were described, potential indicator taxa were selected, and the extent of community development was examined. Seasonal variations tended to mask the developmental trends. However, samples collected during the same season, but representing various lengths of colonization, allowed developmental trends to be observed in faunal composition, numbers of taxa, density, biomass, and diversity. Maldanidae, Nematoda, Lumbrineris luti. Leitoscoloplos pugettensis, Pholoe minuta. and Spionidae are potential indicators of community maturity.