Now showing items 3103-3122 of 3320

• #### Transient electromagnetics for permafrost

Transient electromagnetic (TEM) soundings were carried out with a Geonics EM-37 instrument at more than forty sites in Alaska, primarily along a line from Reindeer Island to Glennallen, to investigate its application to the study of permafrost. Procedures were developed for correcting TEM sounding data for the effects of transmitter turnoff time. Best fit geoelectric models of horizontally layered earth were derived by computer inverse modeling, using program NLSTCI (Anderson, 1982), and used to interpret the soundings in terms of the thickness of permafrost at each site. The interpretations indicate permafrost thicknesses vary substantially between sounding sites on land, although the general trend of thicker permafrost at more northern latitudes is evident. Under favorable circumstances, the depth to the base of ice-bearing permafrost may be resolved within $\pm$10%. Soundings taken over sea ice indicate that the thickness of the thawed sediments overlying ice-bearing permafrost can be determined, the subsea permafrost is multilayered beyond about 3 km offshore, but that the TEM system used may not resolve the base of ice-bearing subsea permafrost in this warm, high-salinity, and multilayered environment. An anomalous, double-sign reversal was obtained at a site in the Kuparuk region which was successfully modeled using a complex resistivity of the Cole-Cole type. The model parameters indicate that this unusual signature may be related to the known deposits of gas hydrates beneath the site suggesting that deep deposits of gas hydrates may be detectable from the ground surface using the TEM method. Finally, it is noted that TEM soundings for permafrost are most productively performed in a line or grid tied to sites with known subsurface lithology so that modeling parameters may be constrained to physically reasonable values.
• #### Transient spatiotemporal chaos in a diffusively and synaptically coupled Morris-Lecar neuronal network

Transient spatiotemporal chaos was reported in models for chemical reactions and in experiments for turbulence in shear flow. This study shows that transient spatiotemporal chaos also exists in a diffusively coupled Morris-Lecar (ML) neuronal network, with a collapse to either a global rest state or to a state of pulse propagation. Adding synaptic coupling to this network reduces the average lifetime of spatiotemporal chaos for small to intermediate coupling strengths and almost all numbers of synapses. For large coupling strengths, close to the threshold of excitation, the average lifetime increases beyond the value for only diffusive coupling, and the collapse to the rest state dominates over the collapse to a traveling pulse state. The regime of spatiotemporal chaos is characterized by a slightly increasing Lyapunov exponent and degree of phase coherence as the number of synaptic links increases. In contrast to the diffusive network, the pulse solution must not be asymptotic in the presence of synapses. The fact that chaos could be transient in higher dimensional systems, such as the one being explored in this study, point to its presence in every day life. Transient spatiotemporal chaos in a network of coupled neurons and the associated chaotic saddle provide a possibility for switching between metastable states observed in information processing and brain function. Such transient dynamics have been observed experimentally by Mazor, when stimulating projection neurons in the locust antennal lobe with different odors.
• #### Transient spatiotemporal chaos on complex networks

Some of today's most important questions regard complex dynamical systems with many interacting components. Network models provide a means to gain insight into such systems. This thesis focuses on a network model based upon the Gray-Scott cubic autocatalytic reaction-diffusion system that manifests transient spatiotemporal chaos. Motivated by recent studies on the small-world topology discovered by Watts and Strogatz, the network's original regular ring topology was modified by the addition of a few irregular connections. The effects of these added connections on the system's transience as well on the dynamics local to the added connections were examined. It was found that the addition of a single connection can significantly effect the transient time of spatiotemporal chaos and that the addition of two connections can transform the system's spatiotemporal chaos from transient to asymptotic. These findings suggest that small modifications to a network's topology can greatly affect its behavior.
• #### Translanguaging in linguistically diverse classrooms: theory to practice

A new model for second-language learning, translanguaging, is emerging in recent years as an antithesis to the immersion model of language education. Translanguaging views language as a system and encourages the use of all of students' languages and language learning resources in the classroom. Translanguaging stands in stark contrast to the language-separation underpinning of the immersion model of language education. While there exists a growing quantity of research on the theoretical foundations of translanguaging, there is a very limited amount of published application of translanguaging principles to curriculum, especially in the linguistically diverse classroom. This project investigates translanguaging inside these classrooms where multiple different languages are spoken and where the teacher does not speak the same second language as the students. As an application product, eight translanguaging strategies are provided and applied to a pre-established language arts curriculum, with a specific focus on the linguistically diverse classroom. While the strategies are crafted specifically for fifth- and sixth-grade language arts, they are easily adaptable to fit a wide variety of grade levels and content areas.
• #### Transport And Formation Processes For Fine Airborne Ash From Three Recent Volcanic Eruptions In Alaska: Implications For Detection Methods And Tracking Models

Airborne fine volcanic ash was collected during the eruptions of Augustine Volcano in 2006, Pavlof Volcano in 2007, and Redoubt Volcano in 2009 using Davis Rotating Unit for Measurement (DRUM) cascade impactors to observe atmospheric processes acting on ash as an atmospheric particle. During the Redoubt eruption, samples were also collected by Beta Attenuation Mass (BAM-1020) and Environmental Beta Attenuation Mass (EBAM) monitors. BAM-1020s and EBAMs provided real-time mass concentration data; DRUM samplers provided samples for post-eruptive analysis. DRUM samples were retrospectively analyzed for time-resolved mass concentration and chemistry. EBAM and BAM-1020s reported near real-time, time-resolved mass concentrations. Scanning Electron Microscopy with Energy Dispersive Spectroscopy was conducted to determine particle size, shape, and composition. Image processing methods were developed to determine particle size distributions and shape factors. Ash occurred as single grains, ash aggregates, and hybrid aggregates. Ash aggregates occurred in plumes from pyroclastic flows and were found in a discrete aerodynamic size range (2.5-1.15 microm). Hybrid ash was common in all samples and likely formed when downward mixing ash mingled with upward mixing sea salt and non-sea salt sulfate. The mass concentration of sulfate did not vary systematically with ash which indicated that the source of sulfate was not necessarily volcanic. Ash size distributions were log-normal. Size distribution plots of ash collected from the same plume at different transport distances showed that longer atmospheric residence times allowed for more aggregation to occur which led to larger but fewer particles in the plume the longer it was transported. Ash transport and dispersion models forecasted ash fall over a broad area, but ash fall was only observed in areas unaffected by topographic barriers. PM10 (particulates &le; 10 microm in aerodynamic diameter or OA) ash was detected closer to the volcano when no PM2.5 (particulates &le; 2.5 microm O A) ash was observed. Further downwind, PM2.5 ash was collected which indicated that the settling rates of PM10 and PM2.5 influenced their removal rates. Diurnal variations in ash mass concentrations were controlled by air masses rising due to solar heating which transported ash from the sampling site, or descending due to radiative cooling which brought ash to the sampling site. Respirable (PM2.5) ash was collected when there were no satellite ash detections which underscored the importance of ash transport and dispersion models for forecasting the presence of ash when mass concentrations are below satellite detection limits.
• #### The transport of aerosols into Denali National Park and Preserve

Denali National Park and Preserve (DNPP) is a federally protected Class I visibility area in Alaska. The Regional Haze Rule in the U.S. Clean Air Act requires the visibility in all Class I areas to be 'pristine.' According to the EPA DNPP does not have `pristine' air. Therefore, the Alaska Department of Environmental Conservation conducted a 15-month study of particulate matter smaller than 2.5 micrometers (PM2.5) from March, 2008 through June, 2009 to identify the aerosol sources in DNPP. DRUM aerosol impactors collected aerosols at four sites (DNPP Headquarters, Trapper Creek, McGrath, and Lake Minchumina) around DNPP. The aerosol data underwent a series of analyses including: a seasonal analysis of elemental composition, an analysis of potential source regions as identified by the HYbrid Single-Particle Lagrangian Integrated Trajectory ectory (HYSPLIT) model, and Chemical Mass Balance (CMB) analyses to identify specific aerosol sources. These analyses show that the predominant sources of aerosols impacting DNPP during winter and spring lie outside of Alaska and during summer and fall are from outside and local sources. Outside sources include deserts in China and industry in Russia. Because many of the aerosols impacting DNPP are produced internationally, the visibility in DNPP cannot be restored without international collaboration.
• #### Transport of dungeness crab (Cancer magister) megalopae into Glacier Bay, Alaska

Areas of high Cancer magister larval recruitment and transport mechanisms were identified in the lower portion of Glacier Bay, Alaska. Megalopae were collected at three sites in 2004 and 2005 using light traps positioned within 1 m of the surface and bottom at 10 m depth. Surface traps captured 96.5 - 99.4 % of megalopae collected. Megalopae abundances were highly pulsed and decreased with increasing distance from the mouth of Glacier Bay. Spatial variation was similar between years with significant differences among all sites in 2005. Half of the total annual megalopae supply occurred over just two nights in September or October, the dates of which varied by location. Megalopae abundance in Bartlett Cove was negatively cross-correlated with tidal amplitude at -3 to + 1 d lags and positively cross-correlated with maximum wind speed at a 0 d lag. Megalopae abundance in the South Beardslee Islands was positively correlated with tidal amplitude and negatively correlated with maximum wind speed at +2 to +3 d lags. Abundance in the North Beardslee Islands was low and not correlated with tides or winds. Spatial variation in megalopae abundance and correlations between abundances and transport processes suggests that Dungeness crab megalopae are transported into Glacier Bay.
• #### Transport of fecal bacteria in a rural Alaskan community

People living without piped water and sewer can be at increased risk for fecal-oral diseases. One Alaskan village that relies on hauled water and honeybuckets was studied to determine the pathways of fecal contamination of drinking water and the human environment so that barriers can be established to protect health. Samples were tested for the fecal indicators Escherichia coli and Enterococcus. Several samples were also tested for the pathogens Giardia lamblia and Cryptosporidium parvum. All terrain vehicle (ATV) use and foot traffic transported bacteria within the village and into the home. Surface water flow transported bacteria within the community during spring thaw, but flow from the dump did not appear to contribute to contamination in town. Within the home, viable fecal bacteria were found on waterdippers, kitchen counters and floors, and in washbasin water. Giardia was found at the dump, but not in water from the river adjacent the community. Exposure to fecal contamination could be reduced by cleaning up after dogs, careful disposal of honey bucket bags and gray water, and by protecting stored drinking water.
• #### Travel Writing Sampler: Thailand

"Travel Writing Sampler: Thailand" is a collection of articles and essays employing three different approaches to travel writing: straightforward overview of a place; information-oriented travel article; and personal essay travel narrative. The thematic focus of this collection is travel experiences in Thailand. Part One examines the evolution of the genre of travel writing. Part Two gives the reader an overview of Thailand. Part Three includes four information-oriented articles. Part Four offers examples of personal essay travel narratives. After a review of the literature in this field, I have concluded that successful travel writers balance elements of the information-oriented article and the personal essay travel narrative. Effective, lively travel writing combines the place being written about and the self--of the writer and traveler. <p>
• #### The treatment of missing data on placement tools for predicting success in college algebra at the University of Alaska

This project investigated the statistical significance of baccalaureate student placement tools such as tests scores and completion of a developmental course on predicting success in a college level algebra course at the University of Alaska (UA). Students included in the study had attempted Math 107 at UA for the first time between fiscal years 2007 and 2012. The student placement information had a high percentage of missing data. A simulation study was conducted to choose the best missing data method between complete case deletion, and multiple imputation for the student data. After the missing data methods were applied, a logistic regression with fitted with explanatory variables consisting of tests scores, developmental course grade, age (category) of scores and grade, and interactions. The relevant tests were SAT math, ACT math, AccuPlacer college level math, and the relevant developmental course was Devm /Math 105. The response variable was success in passing Math 107 with grade of C or above on the first attempt. The simulation study showed that under a high percentage of missing data and correlation, multiple imputation implemented by the R package Multivariate Imputation by Chained Equations (MICE) produced the least biased estimators and better confidence interval coverage compared to complete cases deletion when data are missing at random (MAR) and missing not at random (MNAR). Results from multiple imputation method on the student data showed that Devm /Math 105 grade was a significant predictor of passing Math 107. The age of Devm /Math 105, age of tests, and test scores were not significant predictors of student success in Math 107. Future studies may consider modeling with ALEKS scores, and high school math course information.
• #### A treatment planner for severely emotionally disturbed (SED) youth in residential treatment programs

Writing treatment plans is a necessary but time-consuming step for busy counselors and mental health workers. Treatment plans are an important way of documenting and showing (a) the need for treatment, (b) the goals or objectives of treatment, and (c) how progress in treatment is measured. A well-written plan is critical to successfully treating clients, but must also allow agencies and counselors to document their work. Treatment planners assist counselors and other mental health workers when developing treatment plans, but existing planners are broadly focused to appeal to a wide audience. A review of the literature, and data from a residential treatment program for Severely Emotionally Disturbed (SED) youth was used to create a more narrowly focused treatment planner.
• #### Tribological Comparison of Materials

Approximately 600,000 total joint replacement surgeries are performed each year in the United States. Current artificial joint implants are mainly metal-on-plastic. The synthetic biomaterials undergo degradation through fatigue and corrosive wear from load-bearing and the aqueous ionic environment of the human body. Deposits o f inorganic salts can scratch weight-bearing surfaces, making artificial joints stiff and awkward. The excessive wear debris from polyethylene leads to osteolysis and potential loosening of the prosthesis. The lifetime for well-designed artificial joints is at most 10 to 15 years. A patient can usually have two total joint replacements during her/his lifetime. Durability is limited by the body’s reaction to wear debris of the artificial joints. Wear of the artificial joints should be reduced. A focus of this thesis is the tribological performance of bearing materials for Total Replacement Artificial Joints (TRAJ). An additional focus is the scaffolds for cell growth from both a tissue engineering and tribological perspective. The tribological properties of materials including Diam ond-like Carbon (DLC) coated materials were tested for TRAJ implants. The DLC coatings are chemically inert, impervious to acid and saline media, and are mechanically hard. Carbon-based materials are highly biocompatible. A new alternative to total joints implantation is tissue engineering. Tissue engineering is the replacement of living tissue with tissue that is designed and constructed to meet the needs of the individual patient. Cells were cultured onto the artificial materials, including metals, ceramics, and polymers, and the frictional properties of these materials were investigated to develop a synthetic alternative to orthopedic transplants. Results showed that DLC coated materials had low friction and wear, which are desirable tribological properties for artificial joint material. Cells grew on some of the artificial matrix materials, depending on the surface chemistry, wettability, morphology, microstructure etc. The dry, lubricated, and cell culture friction tests showed that bovine serum albumin solution and culture media performed as lubricants. Frictional properties varied. Glass and TR-2 (PET, polyethylene terephthalate) showed good cell culture results and low friction. Both are suitable materials, both as artificial joint implant coatings and as substrates for preparing total joint implants via tissue engineering.
• #### Trichodectes canis, an invasive ectoparasite of Alaskan wolves: detection methods, current distribution, and ecological correlates of spread

Trichodectes canis, (Ischnocera: Trichodectidae), was first documented on Alaska gray wolves (Canis lupis) in 1981. Two hypotheses may explain why T. canis was not observed in Alaska until the 1980s. Symptomatic wolves could be predisposed to pediculosis, whereas mild infestations outside the observed infestation region are undetected by visual inspection. A second possible explanation is that T. canis is an invasive ectoparasite, and Alaska wolves outside the infestation region do not harbor lice. We examined wolf hides from December 2003 to February 2009, to investigate potential sampling locations, determine T. canis current distribution within Alaska, and investigate potential ecological correlates of spread. We determined that the caudal region of the wolf possessed the highest mean proportion of T. canis and we detected all cases of mild pediculosis. Lice were documented on wolves in a contiguous distribution from Southcentral Alaska to immediately north of the Alaska Range, (estimated area 174,000 km²). Occult infestations were not detected outside of the current infestation zone. That pattern of occurrence suggests that T. canis is a novel parasite within Alaska. Ecological correlates positively associated with T. canis presence include wolf densities greater than eight wolves/1000 km² and mean annual January temperatures warmer than -19°C.
• #### Trophic dynamics and stock characteristics of snow crabs, Chionoecetes opilio, in the Alaskan Arctic

Arctic waters off the coast of Alaska have become increasingly open to human activities via dramatic climatic changes, such as reduced sea ice thickness and extent, warming ocean temperatures, and increased freshwater input. This research advances knowledge of snow crab trophic dynamics and stock characteristics in Arctic waters off the Alaska coast. Here, I provided baseline information regarding snow crab position in Beaufort Sea benthic food webs, its specific dietary habits in the Chukchi and Beaufort seas, and expanded upon previously limited life-history and population dynamic data in the Chukchi and Beaufort seas. I first detailed benthic food webs on the Alaskan Beaufort Sea shelf and snow crab trophic positions within these food webs using stable δ¹³C and δ¹⁵N isotope analysis. Water column and sediment particulate organic matter (POM) were used as primary food web end members. Isotopic niche space (δ¹³C – δ¹⁵N) occupied by benthic taxa provided measures of community-wide trophic redundancy and separation. Water column and sediment POM δ¹³C values generally reflected terrestrial POM inputs in the eastern and central shallow (14-90 m) Beaufort regions, but were indicative of persistent marine influence in the western and central deep (100-220 m) regions. Food web structure, as reflected by consumer trophic levels (TLs), trophic redundancy, and trophic niche space, supported the POM findings. In the eastern and central shallow regions, consumers occupied mainly lower TL (TL= 1-3), whereas consumers in the western regions occupied intermediate and higher TL (TL= 3-4). Overall trophic redundancy and niche space occupied by food webs in these four regions, however, was similar. The central deep Beaufort food web was unique in all metrics evaluated, and the comparatively largest isotopic niche space, with high trophic niche separation but low trophic redundancy, suggests that this region may be most vulnerable to perturbations. Snow crabs occupied food webs in the central deep and western shallow and deep Beaufort regions, where they maintained a consistent TL of 4.0 across regions. I then investigated snow crab dietary habits across the Chukchi, and the Alaskan and Canadian Beaufort seas in the size range of 40 to 130 mm CW using stomach contents and stable isotope analyses. Snow crabs consumed four main prey taxa: polychaetes, decapod crustaceans (crabs, amphipods), echinoderms (mainly ophiuroids), and mollusks (bivalves, gastropods). Crab diets in the southern and northern Chukchi Sea regions were similar to those in the western Beaufort Sea in that bivalve, amphipod, and crustacean consumption was highest. The Canadian Beaufort region was most unique in prey composition and in stable isotope values. Cannibalism on snow crabs was higher in the Chukchi Sea regions relative to the Beaufort Sea regions, suggesting that cannibalism may have an impact on recruitment in the Chukchi Sea via reduction of cohort strength after settlement to the benthos, as known from the Canadian Atlantic. Based on a comparison with southern Chukchi Sea macrofauna data, these results document the non-selective, omnivorous role of snow crabs across the entire Pacific Arctic, as well as providing first evidence for cannibalism in the Chukchi Sea. Finally, I generated new estimates of stock biomass, abundance, and maximum sustainable yield, length-weight relationships, size-at-maturity, and fecundity of snow crab in the Alaskan Arctic. Although snow crabs were more abundant in the Chukchi Sea, no crabs larger than the minimum marketable size (> 100 mm carapace width, based on Bering Sea metric) occurred in this region. Harvestable biomass of snow crabs only occurred in the Beaufort Sea, but was considerably lower than previous estimates in the Arctic FMP. Length-weight relationships were generally similar for male and female snow crabs between the Chukchi and Beaufort seas. Size-at-maturity and female fecundity in the Chukchi Sea were similar to snow crabs occurring in other geographic regions; low sample sizes in the Beaufort prevented size-at-maturity and fecundity analysis. Together these results contribute new understanding of Arctic snow crab population dynamics by utilizing a rich dataset obtained recently from the Chukchi and Beaufort regions.
• #### Trophic dynamics in a changing Arctic: interactions between ptarmigan and willows in Northern Alaska

Shrubs have been expanding in the Arctic over the past century, with important consequences for ecosystem functioning, plant community composition, and wildlife habitat. Herbivores have the capacity to strongly moderate the growth and biomass of shrubs, and therefore need to be considered when attempting to understand and project future changes to Arctic ecosystems. Ptarmigan (Lagopus lagopus, L. muta) are common and widespread in many tundra regions, and feed on shrubs throughout their life cycle. Ptarmigan are likely to be an important herbivore in northern Alaska where shrub expansion is rapidly occurring; however, little is known about their spatial and temporal distribution in the Arctic, or the effect of their browsing on shrubs. This dissertation provides novel information on ptarmigan population ecology and herbivory in northern Alaska. Ptarmigan occupancy in northeastern Alaska increased from March through May, lending support to the idea that they undergo a spring migration from southern wintering grounds to breeding grounds north of the Brooks Range. Ptarmigan distributions were strongly linked to the presence of shrubs; occupancy was greatest in dense patches of riparian willows that grew tall enough to exceed snow depth. The frequency and intensity of ptarmigan browsing in feltleaf willow (Salix alaxensis) stands in northeastern and northwestern Alaska was high, such that ptarmigan browsed 82-89% of willows and removed 30-39% of buds. Browsed willow branches produced fewer catkins than un-browsed branches, but doubled the volume of current annual growth produced the following summer. These longer, larger-diameter shoots bore 40-60% more buds than shoots on unbrowsed branches. The removal of distal buds stimulated dormant buds at the base of the branch to produce shoots, resulting in a "broomed" architecture. Despite their tendency to produce longer shoots when browsed, highly broomed willows with a history of browsing were shorter than un-broomed willows. Broomed willows were more likely to be re-browsed by ptarmigan. Moose browsing was not as prevalent (17-44% of willows browsed) as ptarmigan browsing and resulted in reduced catkin production and increased shoot volume. Simulated ptarmigan browsing of feltleaf willows caused a similar response to that observed in the wild. Browsed willows produced fewer catkins and more buds per shoot, although buds were smaller than on un-browsed willows. Browsing altered the architecture and bud production of willows such that the biomass of easily accessible buds (within 50 cm of snow level) was greater (129 ± 30 mg) on browsed willows than un-browsed willows (113 ± 50 mg). Browsing did not affect nitrogen concentrations, but slightly reduced carbon concentrations and protein precipitation capacity (tannins) in buds produced the following winter. In a feeding preference study, when broomed and un-broomed willow branches were placed in the snow at equal heights, wild ptarmigan showed no preference for either type but obtained more buds from broomed willows. A synthesis of original and published research showed that browsing by vertebrate herbivores in the Arctic is not uniform, and that certain shrubs (such as willows) are more heavily browsed than others (such as evergreen ericoids, resin birches, and Siberian alder (Alnus viridis fruticosa)). These differences in preference translate to variation in the degree to which herbivores regulate Arctic shrub growth and community structure. As shrubs expand in the Arctic, unpalatable, fast-growing species such as alder may have an advantage over more palatable species such as willows. Collectively, this research fills critical gaps in our knowledge of ptarmigan population ecology in Alaska, provides novel insights into how ptarmigan regulate their food source for their own benefit, and enhances our understanding of how herbivores influence shrub expansion in the Arctic.
• #### Trophic Dynamics In Marine Nearshore Systems Of The Alaskan High Arctic (Kelp, Laminaria, Carbon Isotope, Productivity)

This dissertation describes two ecological studies in the arctic Alaskan nearshore zone: the productivity and growth strategies of arctic kelp and the use of natural carbon isotope abundances to examine food web structure and energy flow in the marine ecosystem. Linear growth of the kelp, Laminaria solidungula is greatest in winter and early spring when nutrients are available for new tissue growth. Since over 90% of this growth occurs in complete darkness beneath a turbid ice canopy, the plant draws on stored food reserves and is in a carbon deficit during the ice covered period. Annual productivity of L. solidungula under these conditions is about 6 g C m('-2) compared to about 10 g C m('-2) if light penetrates the ice canopy. Carbon isotope abundances were used to assess food web structure and energy flow in the Boulder Patch, an isolated kelp bed community, and in the Alaskan Beaufort Sea fauna. Isotopic analyses of the resident fauna of the Boulder Patch revealed that kelp carbon contributes significantly to the diet of many benthic animals, including suspension feeders. Some crustaceans, such as mysids and euphausiids (which are key prey species for fishes, birds and marine mammals), also incorporate large amounts of kelp carbon into their tissues when resident in the Boulder Patch. Across the shelf of the Alaskan Beaufort Sea, a distinct gradient in the isotopic composition of marine zooplankton and benthic fauna was related to the intrusion of the Bering Sea water and upwelling in the eastern Beaufort Sea near Barter Island. The ('13)C depletion in fauna of the eastern Beaufort Sea is presumed due to the cycling of ('13)C depleted inorganic carbon into the euphotic zone.
• #### Trophic dynamics of boreal lakes in a changing northern landscape: impacts of lake drying and forest fires

The abundant lakes of northern latitudes are the primary breeding grounds for many waterbird species. In recent decades, temperatures in the north have increased by twice the global average. This substantial warming has caused lake drying and increased wildfires, both of which may impact waterbird habitats. Fires release nutrients locked in terrestrial resources, making them available for transport to lakes, while lake drying concentrates nutrients and other solutes into smaller water volumes. Increased nutrients may fundamentally alter ecosystem processes of lakes by changing the timing and abundance of phytoplankton blooms, which in turn affects the abundance of aquatic invertebrates - the primary food source for breeding waterbirds and their broods. I examined effects of forest fires and lake drying on ecosystems of Subarctic boreal lakes in the Yukon Flats, Alaska, documenting changes to (1) aquatic nutrient and chlorophyll concentrations, (2) aquatic invertebrate densities, and (3) abundance and occupancy of waterbirds. Nutrient, chlorophyll, and invertebrate levels were largely unaffected by a recent forest fire. This ecosystem stability transferred upward to waterbirds, as brood abundance was also unaffected by the fire. On drying lakes, nitrogen and phosphorus concentrations increased >200% and >100%, respectively, from the 1980s to present. At the same time, concentrations of 4 major ions increased, including increases of >500% for chloride and >100% for sodium. Nonetheless, chlorophyll levels, aquatic invertebrate abundance, and occupancy of waterbird broods were largely unaffected by these chemical changes on drying lakes. Overall, ecosystems of Yukon Flats were largely resilient to short-term effects of forest fires and rising chemical concentrations associated with lake drying. Moreover, this resilience spanned multiple trophic levels, from phytoplankton to aquatic invertebrates to waterbirds.
• #### Trophic dynamics of pinniped populations in Alaska using stable carbon and nitrogen isotope ratios

Trophic changes in populations of Stellar sea lions (Eumetorias jubatus), northern fur seals (Callorhinus ursinus) and harbor seals (Phoca vitulina) in the eastern Bering Sea and Gulf of Alaska were studied using stable isotope analysis. Declining populations of all three species of pinnipeds prompted this study to determine if changes in diet, likely resulting from food limitation, contributed to the declines. Stable carbon and nitrogen isotope ratios were analyzed in the vibrissae (whiskers) and body tissues of pinnipeds from 1993-1998 and compared with muscle tissue from prey species during the same time period to determine pinniped trophic dynamics. Vibrissae growth rate studies revealed harbor seal vibrissae are only retained for one year and then replaced, while Steller sea lions maintain their vibrissae for several years. Isotopic data from all three species are consistent with diets composed of walleye pollock (Theragra chalcogramma) at various times and locations throughout the year. Steller sea lion and northern fur seal vibrissae revealed regular oscillations along their lengths in both carbon and nitrogen isotope ratios that likely corresponded to regional isotopic differences. As these animals moved or migrated from one region to another during the year, they metabolically incorporated the different regional isotope ratios through their prey. Because these animals return to their rookery to pup, breed and molt each year, the isotope ratios in the vibrissae showed a regular pattern of enrichment and deplection. Harbor seals, which tend to stay in one geographic location, have relatively static isotope ratios in their vibrissae, while seals that moved into offshore waters had fluctuating isotope ratios that corresponded to regional difference. No trophic shifts, as evidenced by major changes in nitrogen isotope ratios, were present in any tissues from the three species over the period 1975-1998. Stable isotope ratios of bone collagen for all three species from 1950-1997 indicated no change in trophic level but did reveal that the seasonal primary production in the North Pacific Ocean has declined and may have contributed to a decreased carrying capacity impacting these top trophic organisms
• #### Trophic ecology of nearshore fishes in glacially-influenced estuaries of Southeast Alaska

Estuaries in Southeast Alaska (SEAK) are linked to terrestrial ecosystems by the flow of freshwater from plentiful precipitation and glacial runoff. This thesis examined the trophic ecology of nearshore fishes in SEAK estuaries to advance our understanding of how deglaciation and resulting shifts in the timing and magnitude of freshwater runoff will affect estuarine food webs. The goals of this work were to characterize seasonal variation in the feeding ecology of an abundant estuarine predator across three glacially-influenced sites and to examine the relative contribution of organic matter (OM) from terrestrial-riverine sources to the diets of estuarine consumers. In chapter one, stomach contents of Pacific staghorn sculpin (Leptocottus armatus) were analyzed to test the hypothesis that diets would differ across sampling sites and months, reflecting variation in freshwater runoff and the phenology of estuarine organisms. Stomach contents of staghorn sculpins were collected monthly between April and September 2014, from intertidal sites at mouths of rivers that differ in their headwater hydrology. Staghorn sculpins consumed a variety of prey, including gammarids, mysids, isopods, polychaetes, and other freshwater-tolerant prey, as well as juvenile fish. Weak to moderate differences observed in diet composition across sites and months likely reflected spatial and seasonal shifts in the occurrence of freshwater-tolerant invertebrates and young-of-the-year fishes. Overall, the ability of staghorn sculpins to take advantage of a variety of prey across variable conditions may make them resilient to environmental change. In chapter two, I examined trophic linkages between terrestrial and marine food webs by using stable isotope analysis to evaluate the relative contribution of terrestrial-riverine OM to the diets of estuarine consumers. Analyses showed limited use of terrestrial-riverine OM by marine fishes (Leptocottus armatus and Platichthys stellatus) and more variable use by anadromous fishes (Salvelinus malma and Oncorhynchus kisutch). Intertidal invertebrates used more terrestrial-riverine OM than fish, with greater use of allochthonous OM earlier in the summer. Despite the documented availability of terrestrial-riverine OM, estuarine consumers showed limited use of this resource. These findings inform our baseline understanding of trophic linkages in glacially-influenced estuaries, a critical first step in evaluating future climate driven changes to coastal ecosystems.