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2361. [Article] Coastal sand dunes of Oregon and Washington
In Part I the environment of the coastal dunes of Oregon and Washington is analyzed. Most of the substratum is a narrow foreland or terrace, in part submerged, that borders the mountain front. Temperature ...Citation Citation
- Title:
- Coastal sand dunes of Oregon and Washington
- Author:
- Cooper, William Skinner, 1884-
In Part I the environment of the coastal dunes of Oregon and Washington is analyzed. Most of the substratum is a narrow foreland or terrace, in part submerged, that borders the mountain front. Temperature is relatively low in summer and rarely reaches the freezing point in winter. Winter precipitation is heavy, and there is almost no snow; there is a pronounced deficiency in precipitation in summer. The summer wind is a very constant afternoon sea breeze from north to northwest; winter winds are variable but include frequent southwest gales. Longshore currents are governed by the seasonal winds, moving southward in summer and northward in winter. The regional vegetation is dense, tall conifer forest. The influence of man has been comparatively slight: in prehistoric times the starting of forest fires; in historic time moderate disturbance due to grazing and recent efforts to control the movement of the sand. Part II deals with forms and processes. The simplest combination of elements comprises sand, wind, and water. Interaction of these produces two patterns. In the transverse-ridge pattern the individual unit is a ridge essentially normal to the summer wind and moving with it; it is asymmetric in profile with gentle windward slope and steep leeward slope (slipface). Origin and maintenance of this profile are explained in accordance with principles developed in the field of aerodynamics, and conclusions arrived at deductively are confirmed by slow-motion photography of smoke streams on the dunes. The oblique-ridge pattern occurs only where there is full exposure to both seasonal winds, plenty of space, and plenty of sand. These conditions are met only in Region III (Coos Bay dune sheet). The units are much more massive than the transverse ridges and are essentially stationary. Their trend lies between the means of summer and winter winds. A theoretical explanation of their origin and maintenance is presented, and the oblique ridges and the "longitudinal dunes" of certain desert regions are compared. Neither transverse nor oblique ridge is found in stabilized condition. The factor vegetation added to the other three-sand, wind, and water-promotes stabilization. On a prograding shore, successive beach ridges are quickly captured and fixed, and retain their initial form indefinitely. On a retrograding shore the processes are exceedingly complex and involve repeated stabilization and rejuvenation. Two cases are presented: flat shore, with and without abundant sand supply; stabilized dune masses undergoing erosion. In the latter case, the commoner, development involves the following phases: trough blowout, merging of troughs, reduction to deflation base, and precipitation ridge, which may in time become completely stabilized while still retaining its characteristic form. In places sheltered from one or the other of the seasonal winds, usually the summer wind, giant parabola dunes, which may likewise become fixed by vegetation, develop. Part III is a description of the dune localities of the Oregon-Washington coast and an account of their history. Forty per cent of this coast bears dunes of greater or lesser magnitude. Thirty dune localities are grouped in four regions. Region I includes four localities north of Tillamook Head, Oregon, making a continuous strip 53 km long, that bears the parallel beach-dune-ridge pattern associated with progradation. The forms in Regions II, III, and IV, heterogeneous and complex, are those characteristic of retrograding shores. The two principal stabilized forms are the precipitation ridge and the parabola dune. In Regions II, III, and IV the existing features came into being mainly during the last grand period of sea-level rise, and the seaward portions of massive parabola complexes have been sliced away in varying degree by the advancing sea. The beach-ridge dunes of Region I were formed during the period of comparatively stable sea level, with a probable small net lowering, which followed the maximum of sea advance and has extended to the present. Progradation here during this period, in contrast with almost none south of Tillamook Head, has been possible because of the ample bed load carried to the coast by the Columbia River. South of Tillamook Head there is, in a number of well-distributed localities, evidence of three episodes of advance. The first is represented by the strip of thoroughly stabilized dunes that nearly everywhere forms the inner marginal part of the dune complexes. This episode reached its culmination before the sea had attained its maximum of advance-attested by the slicing away of portions of completely stabilized masses. The second advance for the most part fell short of the first, though in a few places it overpassed the limits of the latter; present condition ranges from complete stabilization to vigorous activity. The third episode is represented by active dunes with open access to the shore. In certain localities there are only an inner strip of stabilized dunes and an outer zone of active dunes. It is assumed that in these the visible effects of the second and third episodes have merged. An earlier cycle of dune development, similar to the modern one in character and extent, is proved by eolian sediments containing altered podzolic soils, which make a minor part of the mantle of unconsolidated materials that lies upon the rock platform of the 30-m terrace. The dunes of which these masses are remnants were formed during the next-to-the-last grand period of submergence. Development of the dunes of Regions II, III, and IV, associated with the grand period of submergence, is assigned to the period of deglaciation that followed the Wisconsin maximum, and mainly to the period of rapid deglaciation that began after the Valders-Mankato advance. The beach-ridge dunes of Region I, on the other hand, have developed in their entirety in the time since sea-level rise was succeeded by stability. By analogy, the earlier cycle of dune development was associated with the waning phase of Illinoian glaciation, and it may be assumed that similar dune cycles were associated with the earlier glaciations of the Pleistocene.
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2362. [Article] What's romance got to do with it? Sexual health outcomes of relationship dynamics among urban African American adolescents
Urban African American adolescents exhibit high levels of risk behavior, disproportionately high rates of sexually transmitted infections (STIs), and are at risk for acquiring Human Immunodefiency Virus ...Citation Citation
- Title:
- What's romance got to do with it? Sexual health outcomes of relationship dynamics among urban African American adolescents
- Author:
- Towner, Senna Lee
Urban African American adolescents exhibit high levels of risk behavior, disproportionately high rates of sexually transmitted infections (STIs), and are at risk for acquiring Human Immunodefiency Virus (HIV). To date, interventions that address the high rates of STIs in this population demonstrate only moderate efficacy. As researchers strive to develop more effective interventions, social-ecological factors and developmental and gender issues are being considered. This study aimed to provide insight into the gendered characteristics of heterosexual urban African American adolescents' romantic relationships, and how these characteristics impact condom use. From a developmental standpoint, sexuality and romance are a normal part of adolescence. Thus, STI/HIV prevention targeted at urban African American youth can be improved if it considers romantic relationship dynamics, and how they influence sexual health behaviors including condom use. To this end, the current study examined the interconnection among interpersonal relationship factors including monogamy, commitment, trust, and respect, as well as intrapersonal relationship factors including gender and relationship history. Furthermore, this study examined how these inter- and intrapersonal factors impact youths' condom use behaviors. This research was guided by the existing literature, theoretical frameworks (i.e., the ecological perspective on health, Rusbult and Buunk's commitment theory, and Rotenberg and colleagues' trust framework), and the "directed perspective" (i.e., lens theory). A qualitative methodological approach was employed to collect data from 52 heterosexual, sexually experienced, African American adolescents (20 females; 32 males) ranging from 15-17 years in age at the time of enrollment. These youth resided in low-income neighborhoods of two large cities in the United States. Data from semi-structured interviews were analyzed using a phenomenological approach. Data analysis took place in four primary stages including: (a) development of case summaries; (b) development and refinement of codes and a codebook, and organization of data using matrices; (c) content analysis and reliability checks; and (d) reviews and critiques by, and discussions with, other research team members. Numerous themes and subthemes that provide insight into the multifaceted characteristics of urban African American adolescents' romantic relationships emerged. Findings show that study participants' romantic relationships were indeed characterized by gender-specific beliefs and behaviors, but that some beliefs and behaviors were similar across gender. For instance, males and females alike acknowledged positive feelings towards monogamy, trust, and respect, and they considered these dynamics as closely linked. That is, males and females viewed monogamy as indicative of commitment, and monogamous and committed relationships were those that were trusting and respectful. Youths' relationship experiences, however, contradicted their ideals to a great extent. For instance, despite the finding that males held positive perceptions of monogamy, they often engaged in multiple partnerships. This finding that shows young African American males’ often engage in multiple partnerships corroborates other research. Furthermore, these data provide insight into the social pressures experienced by urban African American males that encourage them to engage in multiple partnerships and remain uncommitted. According to the current findings, males' multiple partnerships set in motion a breakdown in relationship dynamics (i.e., lack of commitment, mistrust, disrespect), and thus youth experienced less-than ideal romantic relationships. Adolescents' less-than ideal experiences subsequently impacted their current and future romantic relationship beliefs and expectations. For instance, because males were frequently non-monogamous, females did not commonly express commitment to or trust in males. Despite this, only a few females talked about breaking up with a partner whom they mistrusted. Males, on the other hand, considered being monogamous and committed when they had negative experiences with being in multiple, uncommitted sexual partnerships. In addition, relationship dynamics, most noticeably trust (although trust was intricately linked to monogamy, commitment, and respect), impacted condom use. Although adolescents considered condom use important, males and females considered not using condoms when they were with a partner whom they trusted was monogamous and free from STIs. Furthermore, some male respondents talked about the need to balance the protection that condoms provided with the pleasure experienced when not using them. With casual and mistrusted partners, safety tended to take precedence; with more serious and trusted partners, pleasure tended to take precedence. Finally, these data elicited gender similarities and differences related to romantic respect perceptions. Across gender, respect was thought to be an important dynamic in romantic relationships, and one closely related to monogamy, commitment, and trust. Because beliefs about respect were interrelated with beliefs about other relationship dynamics that impacted condom use, respect may also impact condom use. The findings of this study suggest that youth have an understanding about how to develop healthy romantic relationships in adolescence and, in turn, healthy romantic relationships in adulthood. That said, respondents had little to no experience with being in healthy relationships. These study findings can help guide future research, and inform sexual health interventions. For example, investigators should explore further males' belief that monogamy is positive, as this belief frequently contradicted their related behavior (i.e., males often had multiple sexual partners). Finally, future interventions, including dyadic-level interventions, should focus on the dynamics of relationships. In doing so, the efficacy of STI/HIV prevention efforts targeted at African American youth may be enhanced.
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2363. [Article] Mixed-conifer forests of central Oregon : structure, composition, history of establishment, and growth
The structure and composition of mixed-conifer forest (MCF) in central Oregon has been altered by fire exclusion and logging. The resulting increased density, spatial contagion, and loss of fire resistant ...Citation Citation
- Title:
- Mixed-conifer forests of central Oregon : structure, composition, history of establishment, and growth
- Author:
- Merschel, Andrew G.
The structure and composition of mixed-conifer forest (MCF) in central Oregon has been altered by fire exclusion and logging. The resulting increased density, spatial contagion, and loss of fire resistant trees decrease the resiliency of this ecosystem to fire, drought, and insects. The historical and current composition and structure of MCF are characterized by steep environmental gradients and a complex mixed-severity fire regime. This inherent variation makes it difficult to determine the magnitude of anthropogenic effects and set objectives for restoration and management. As a result, there is a lack of consensus regarding how MCF should be managed and restored across the landscape. My primary research objectives were to: (1) Characterize the current structure and composition of MCF and how these vary with environmental setting; and (2) Characterize establishment and tree growth patterns in MCF in different environmental settings. To address these objectives, I collected field data on structure and composition and increment cores across a range of environmental conditions in MCF of the eastern Cascades and Ochoco Mountains. I used cluster analysis to identify four stand types based on structure and composition in the eastern Cascades study area and four analogous types in the Ochoco Mountains study area. Variation in understory composition and the presence of large diameter shade tolerant species distinguish each type. Stand types occupied distinct environmental settings along a climatic gradient of increasing precipitation and elevation. At relatively dry PIPO sites understories were dominated by ponderosa pine. At wetter PIPO/PSME and PIPO ABGC sites understories were dominated by shade tolerant species, but ponderosa pine was dominant in the overstory. At the coolest and wettest PIPO/PSME/ABGC sites understories were dominated by grand fir and shade tolerant species were common in the overstory. In the eastern Cascades current density of all live trees and snags was 432, 461, 570, 372 trees per hectare (TPH) for the four stand types identified. Stand types in the drier Ochoco Mountains were currently less dense at 279, 304, 212, and 307 TPH. Current MCF densities in both areas are 2-3 times higher than densities estimated for the late 19th and early 20th centuries from other studies in those two areas. Reconstruction of cuts in each stand type indicates that the density of large diameter ponderosa pine has been reduced by approximately 50% in all stand types in both study regions. Age histograms demonstrate that current density and composition of MCF stand types is a product of abrupt increases in tree establishment following fire exclusion in the late 19th century. The number of trees established increased after 1900 in all stand types, but the timing and composition of changes in establishment varied with climate. At dry PIPO sites increases in establishment were delayed until the 1920s and 1930s and were composed of ponderosa pine. At PIPO/PSME and PIPO/ABGC sites with intermediate precipitation, establishment was dominated by ponderosa pine prior to 1900, but after 1900 establishment was dominated by a large pulse of Douglas-fir and grand fir. At the wettest PIPO/PSME/ABGC there was less evidence of changes in structure and composition over time. My results indicate that compared to dry pine and dry-mixed conifer sites, relatively productive moist mixed-conifer sites were characterized by large changes in structure and composition. Such sites could be considered more ecologically altered by lack of fire than drier forest types that had high fire frequencies but slower rates of stand development and less plant community change. Radial growth patterns of cored ponderosa pines differed between the eastern Cascades and Ochoco Mountains. In the eastern Cascades mean growth rates and variance decreased during favorable climatic periods after 1900. This is likely related to increased competition, and provides evidence that current stand density lacks a temporal analog in the 18th and 19th centuries. Sensitivity of growth to climate and harvest suggest competition for water in the denser forest of the eastern Cascades, and indicates thinning will increase the diameter growth rate of large old pines. In the Ochoco Mountains, ponderosa pine tree growth was less responsive to climate prior to fire exclusion in the late 1800s, and growth did not respond to fire events. This suggests competition among trees was historically low in this region. After fire exclusion growth became more responsive to wet and dry climatic cycles, which may indicate that increased density and competition made trees more responsive to climate variability. Patterns of slow and fast growth appeared to differ between study regions and likely differ at the sub-regional scale. Further analysis of the relationship between growth and climate in different environmental settings is needed to distinguish where stand development has been modified by disruption of fire regimes.
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Supervolcanic eruptions are among the most catastrophic phenomena on Earth, erupting 100s-1000s of cubic kilometers of magma, and producing devastating local effects and global climate perturbations. The ...
Citation Citation
- Title:
- Insights into the Geochemical Evolution of the Youngest Toba Tuff (Sumatra, Indonesia) Magma Chamber Through the Lens of Zircon-hosted Melt Inclusions
- Author:
- Lerner, Allan (Allan Henry)
Supervolcanic eruptions are among the most catastrophic phenomena on Earth, erupting 100s-1000s of cubic kilometers of magma, and producing devastating local effects and global climate perturbations. The largest supervolcanic eruption of the last 28 Ma was the 74 ka Youngest Toba Tuff (YTT) eruption from Sumatra, Indonesia, which erupted 2,800 – 5,300 km³ of magma and may have pushed the human species to the brink of extinction. Despite the global significance of such events, the magmatic evolution that builds to super-eruptions remains poorly understood. The mineral zircon provides a unique potential to gain multidimensional insights into the pre-eruptive evolution of magma chambers by combining mineral and melt inclusion chemistry with U-series mineral dating. We combine zircon U-Th dating and trace element chemistry with zircon-hosted melt inclusion chemistries and volatile abundances to investigate the magmatic evolution preceding the YTT eruption To begin, we present the first detailed study of the susceptibility of zircon-hosted inclusions to syn- or post-entrapment modification of melt compositions. We conclude that boundary layer effects are negligible in even very small zircon-hosted inclusions owing to the slow growth rate of zircon crystals. Post-entrapment crystallization (PEC) of the zircon host phase is also a trivial concern, owing to the low Zr content of most melts. PEC of other daughter phases is recognized (< ~2% amphibole and sanidine), but these effects are also minor relative to melt inclusions in many major-phase minerals. The diffusive exchange of water from zircon-hosted melt inclusions is modeled to occur in less than 10 ka, and requilibration may occur within decades-centuries. Therefore, water contents of zircon-hosted inclusions represent late-stage storage conditions rather than long-term records of magmatic water. Zircon-hosted inclusions should remain diffusively sealed to all melt species, apart from H⁺, He, and Li⁺, over typical magmatic system timescales (104-105 yrs). Therefore, we conclude that zircon is a robust, albeit small, melt inclusion host and entrapped inclusions will be largely representative of the melt environments in which they formed. We then apply the multidimensional utility of zircon to gain insights into the pre-eruptive evolution of the YTT magmatic system. YTT zircon grains have U-Th crystallization ages spanning from the ~74 ka eruption age to > 375 ka, reinforcing earlier findings that the YTT system was long-lived. A progressive increase of U in zircon growth zones from < 500 to ~1,500 ppm indicates that the YTT system, or a portion of it, became highly fractionated between 130-200 ka. A lull in zircon formation between ~110-130 ka is contemporaneous with a previously recognized increase in chemical diversity of allanite, possibly reflecting a period of enhanced thermal input into the system. We identify two main populations of zircon-hosted melt inclusions. A low-MgO type is chemically evolved (> 280 ppm Rb, ~125 ppm Ba, 25-30 ppm Sr, < 0.03 wt% MgO) and has high water contents (3.8-5.7 wt% H₂O), consistent with formation and storage in a highly fractionated crystal mush ~4-9 km deep. A high-MgO type (250-260 ppm Rb, 160-450 ppm Ba, 35-55 ppm Sr, 0.04-0.07 wt% MgO) has compositions similar to matrix glasses, and is typically less hydrous (0.5-3.5 wt% H₂O), suggesting shallow (< 3 km) formation, storage, and syn-eruptive degassing in a less evolved melt. Melt inclusions dated via U-Th measurements of their entrapping zircon zones show no clear temporal differences between the two MgO populations. Rather, melt inclusions entrapped throughout the entire YTT history have relatively invariant major element compositions, and also have no discernible temporal trends in volatile abundances. We largely attribute these findings to the narrow stability field in which zircon crystallize, which inherently limits the compositional range of zircon-hosted inclusions. Zircon-hosted melt inclusions (particularly the high-MgO type) of many ages occur within sealed reentrant melt-channels. This suggests that melt inclusions in YTT zircon grains commonly formed as the system re-established zircon saturation following periods of zircon dissolution during thermal recharge events. A number of zircon grains have melt channels actively open to the grain exterior, which are rimmed with 1-3 μm of cathodoluminescence-bright (low-U) zircon growth. These dissolution/regrowth features are texturally similar to dissolution zones and high-temperature overgrowths described previously in YTT quartz; collectively, these textures provide evidence of a major thermal perturbation(s) 10s-100s of years before the YTT eruption. We conclude that high-T, mafic recharge events occurred throughout the pre-eruptive YTT evolution, and suggest that one or more large recharge events triggered the cataclysmic 74 ka YTT eruption.
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2365. [Article] Genesis of some soils in the central western Cascades of Oregon
Soils representative of several landscape units in the H. J. Andrews Experimental Forest, Western Cascade Range, were sampled, analyzed, and tentatively classified. Genetic inferences were drawn relating ...Citation Citation
- Title:
- Genesis of some soils in the central western Cascades of Oregon
- Author:
- Brown, R. B.
Soils representative of several landscape units in the H. J. Andrews Experimental Forest, Western Cascade Range, were sampled, analyzed, and tentatively classified. Genetic inferences were drawn relating soils to landscape position and other factors of soil formation. Descriptive information and nutrient capital data were provided to support ecosystem modelling efforts by the Coniferous Forest Biome study group of the U. S./International Biological Program (IBP). To meet the "nutrient capital" requirements of IBP, and to gain insight particularly into the effects of coarse fragments on soil genesis, a volumetric approach was used. Soil organic matter, total N, extractable P, exchangeable cations, free Fe oxides, and cation exchange capacity were expressed in terms of weight or equivalents per unit volume of "whole soil," defined as organic and mineral fine earth components plus pore space plus coarse fragments. The various entities, in grams or equivalents per liter of whole soil, were observed as to their variation with depth. Additional calculations showed levels of the various entities per surface meter ³ of whole soil. Soil temperature data from several sites within the Andrews Forest showed the mesic-frigid soil temperature regime boundary to fall at about the 600 m (2, 000 ft) elevation on south slopes and at about the 450 m (1, 500 ft) elevation on north slopes. The frigidcryic boundary apparently was above the 1, 500 m (4,900 ft) elevation in the Andrews Forest. A sequence of three fluvial and two colluvial soils ranging in elevation from 440 to 460 m was studied in conjunction with concurrent IBP investigations into the geomorphic history of the area The soil on a floodplain adjacent to Lookout Creek, in the sandy-skeletal, mixed, mesic family of Fluventic Hapludolls, was between 500 and 7, 000 yrs in age. The adjacent stream terrace soil, in the loamyskeletal, mixed, mesic family of Fluventic Dystrochrepts, was > 7, 000 yrs old as evidenced Mazama pumice erposi tE-; on or near the surface of the terrace. Volumetric analysis suggested that the floodplain soil had a mollic epipedon largely by virtue of its high content of coarse fragments. The coarse fragments caused a concentration of soil organic matter and recycled cations into a smaller volume of fine earth as compared with the terrace soil, which was lower in coarse fragments. An alluvial-colluvial fan emanated from an adjacent slope and lapped onto the terrace. The soil in this fan was a member of the Fluventic Eutrochrepts, loamy-skeletal, mixed, mesic. It was high in base status and moderately high in clay content, apparently because the southeast-facing source area for parent material here had experienced only shallow weathering and minimal leaching. Across Lookout Creek from these landscape units was a remnant of a high colluvial terrace emanating from a northwest-facing watershed. At the crest of this fan remnant the soil was a member of the loamy-skeletal, mixed, mesic family of Fluventic Dystrochrepts with a distinct layer of Mazama pumice at the 75 to 85 cm depth. This terrace is cut by the watershed stream, which has deposited a comparatively well sorted fan. Soils are in the coarseloamy, mixed, mesic family of Fluventic Dystrochrepts, Eight landscape units in longitudinal and transverse crosssections of upper McRae Creek valley, ranging in elevation from 800 to 1, 200 m, were chosen to study upland soil genesis. Proceeding up the valley, stage of profile development appeared to decrease, indicating a series of depositional events. Soils varied from Eutric Glossoboralfs, fine, mixed on the lowermost surface to Fluventic Dystrochrepts, fine-loamy, mixed, frigid on the next higher surface, to Fluventic Dystrochrepts, loamy-skeletal, mixed, frigid on the next higher surface, to Typic Haplumbrepts, loamy-skeletal, mixed, frigid on the backslope at the valley headwall. The two lowermost soils contrasted markedly with the two uppermost soils, being lower in content of organic matter and N, and higher in base status and clay content. The upper two soils, typical of upper valley bottom and sideslope soils in the region, were extremely low in exchangeable bases and base saturation as measured at pH 7. Compared with the two lower soils, however, these upper soils had relatively high soil: water pH values and relatively small drops in pH from soil:water to soil :KCI measurement. This may be an indication that the upper soils were higher in amorphous content. Greater pH-dependent-CEC would have caused the upper soils to exhibit unrealistically high CEO s--and thus low base saturations--when measured at pH 7. A topoclimosequence of soils on north, east (saddle), and south-facing landscape units with a single parent rock lithology was studied in the transverse valley transect. All three soils were placed tentatively in the Andic Dystrochrepts. The north-facing soil was in a medial - skeletal, frigid family, was the deepest to bedrock ( > 1 1/2 m), aria had the freshest coarse fragments of the three soils. The saddle and south-facing soils were in medial-skeletal, frigid and medial, frigid families, respectively. They were shallow ( <1 m) to saprolite bedrock, with well weathered coarse fragments in the regolith, demonstrating shallower, but apparently more intense weathering on the more exposed sites. These more exposed soils were darker in color than the north-facing soil. Soil organic matter levels were not strikingly different among the three soils. Soil N levels were significantly higher in the south-facing soil than in the east and north-facing soils. Levels of exchangeable bases, while low, were not as low in these three soils as in the upper valley bottom and backslope soils. Saprolite horizons had higher base saturations than overlying horizons.
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Streamflow patterns are a result of the interaction of many factors, including climate, vegetation, geology, and topography. Analyses indicate that streamflow patterns have changed around the United States ...
Citation Citation
- Title:
- Interacting effects of climate, forest dynamics, landforms, and river regulation on streamflow trends since 1950 : examples from the Willamette Basin and forested headwater sites in the US
- Author:
- Hatcher, Kendra L.
Streamflow patterns are a result of the interaction of many factors, including climate, vegetation, geology, and topography. Analyses indicate that streamflow patterns have changed around the United States over the past century, raising questions about the possible role of climate variability as a driver of water yield. This thesis examines streamflow trends in two separate analyses: a study of streamflow trends and the physical characteristics of large basins in the Willamette River Basin, and a study of streamflow trends in small headwater basins around the United States. In the Willamette River basin, as in much of the western US where summer precipitation is low, declining streamflow will exacerbate the task of water management to meet varying demands for water. Although regional climate warming over the past half-century in the Pacific Northwest is a plausible cause of declining streamflow, climate is only one of several factors that determine the hydrologic regime of the Willamette River basin. This study quantified trends in streamflow from 1950 to 2010 in ten sub-basins of the Willamette, including seven 60-600 km² predominantly forested sub-basins above dams in the Willamette National Forest, and three gages downstream of dams in urban areas of the Willamette valley (Albany, Salem, and Portland). Trends at the annual, seasonal, and daily time scales were estimated using linear regression with appropriate transformation of variables and the Mann-Kendall non-parametric test. Trends in streamflow and runoff ratios in the Willamette Basin were compared to geology, topography, and changes in forest cover above dams. Data on forest cover by age class were obtained from Willamette National Forest. Up to 29% of area in sub-basins above dams was clearcut since the 1930s. From 1 to 51% of basin area above dams is on young (<7 ma) volcanic rocks of the High Cascades, which have longer water residence times than the older (7-25 ma) volcanic rocks of the western Cascades, which make up the remainder of basin area above dams. From 71 to 93% of basin area above dams is above 800 m elevation, where seasonal snowpacks are controlled by winter temperature and precipitation. Over the study period (1950-2010), precipitation in the Willamette River basin did not change significantly at the seasonal or annual time scale. Declining streamflows in spring and summer were found in low elevation basins above dams. These trends may be attributed to climate-warming-induced increases in the rain:snow ratio and earlier snowmelt, or changes in water use by vegetation in response to climate warming, or both. More rapid declines in summer and fall discharge and runoff ratios occurred in basins which experienced relatively rapid conversion of old to young forest in the past half-century and have relatively large proportions of young forest today. Declining flows can be attributed to increasing evapotranspiration in young forests and shallow flow paths in Western Cascades-dominated basins that intersect the rooting zone. High-elevation basins with greater percentages of High Cascades geology are less susceptible to declining discharge, even if they have substantial areas in young forest. In contrast to the trends in streamflow above dams, trends over time in streamflow downstream of dams in the Willamette basin have been largely influenced by management of reservoirs and flow. Flow downstream of the dams has become more homogenized throughout the year, with higher flows in the fall and declines in the later winter/early spring. However, discharge has declined at the annual time scale, and in the spring and summer. These trends may be a result of flow management, decreasing spring streamflow upstream of the dams, or a recent trend of relatively dry years. Although historical water yields may not be representative of future water yields, long term historical climate and discharge records from instrumented sites provide the basis for understanding the effects of climate variability on water yield from headwater systems. This study quantified trends in climate and streamflow data from eight predominantly forested headwater basins in the US to understand the complex relationships between climate change, basin geography, vegetation, history, and hydrology. Data were obtained for up to 70-year periods from the Long Term Ecological Research (LTER) network and US Forest Service system of Experimental Forests and Ranges (EFR). Trends in precipitation, temperature, discharge, and runoff ratios were calculated for annual, seasonal, and daily data using linear regression of appropriately transformed data and Mann-Kendall non-parametric tests. Linear regression with appropriate transformation of variables produced similar results to the Mann-Kendall analysis. The first day of spring (defined as the last day of freezing temperature) has moved earlier by 0.31 to 1.98 days/year at all sites, except the alpine site. Most sites experienced significant increases in spring minimum air temperature, but only a few sites experienced an associated change in spring runoff ratios. Spring runoff ratios decreased in sites with snowpacks and near-zero mean spring air temperature (AND). Fall baseflow increased at the alpine, non-forested site (NWT), apparently as a result of increased permafrost melt. Earlier snowmelt and decreases in spring discharge and runoff ratios are expected to lead to increases in winter streamflow and reductions in summer streamflow. However, despite increases in summer minimum air temperature at most sites, summer runoff ratios did not change at most sites, and some sites (HBR, FER) experienced increases in summer and fall runoff ratios. The expected reduction in summer runoff ratios in response to warmer temperature at these sites may have been mitigated by reductions in leaf area due to disturbance or forest succession after logging in the early 1900s. These findings indicate that both climate change and hydrologic response to climate change varies across the US. The lack of expected streamflow responses apparently is the result of ecosystem processes that produce counteracting trends in vegetation water use in response to climate trends; these processes deserve further study.
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2367. [Article] Hawaiian duck (Anas wyvilliana) behavior and response to wetland habitat management at Hanalei National Wildlife Refuge on Kaua'i
The endangered Hawaiian Duck (koloa maoli; Anas wyvilliana), a non-migratory and island-endemic species, experienced a significant population decline during the twentieth century due to factors such as ...Citation Citation
- Title:
- Hawaiian duck (Anas wyvilliana) behavior and response to wetland habitat management at Hanalei National Wildlife Refuge on Kaua'i
- Author:
- Malachowski, Christopher P.
The endangered Hawaiian Duck (koloa maoli; Anas wyvilliana), a non-migratory and island-endemic species, experienced a significant population decline during the twentieth century due to factors such as habitat loss, overharvest, introduced mammalian predators, and hybridization with introduced feral Mallards (A. platyrhynchos). A key objective for Hawaiian Duck recovery is to establish a protected and managed network of wetland habitats; however, development of effective habitat management plans is stymied by the lack of information on patterns of habitat use in relation to fundamental resource requirements. Furthermore, many generalizations regarding dabbling duck behavior and resource requirements that guide seasonal wetland management objectives in North America may not apply to tropical regions and island systems. In this thesis, I compare the behavioral repertoire of the Hawaiian Duck with closely related island-endemic waterfowl and migratory North American Anas, I investigate the behavioral response of Hawaiian Ducks to wetland habitat management and taro cultivation, and I examine the effects of environmental, climatic, temporal, and social factors on the activity budgets of Hawaiian Ducks. I conducted instantaneous focal sampling (n = 984 observation sessions; 328.8 hr) throughout the annual cycle from September 2010 to August 2011 at managed wetlands and taro lo'i within Hanalei National Wildlife Refuge (NWR), Kaua'i. I documented 73 specific Hawaiian Duck behaviors in eight broad behavior categories including foraging, maintenance, resting, locomotion, alert, courtship, and intraspecific and interspecific agonistic interactions. I found that the behavioral repertoire of the Hawaiian Duck was similar to that of the Mallard; however, subtle variations in the form and linkage of certain courtship displays, such as nod-swimming, were observed. Additionally, male Hawaiian Ducks were occasionally associated with brood-rearing females (11% of brood observations), and this behavior appeared to be a male strategy whereby females received little perceived benefit , but males may have potentially garnered additional breeding attempts or maintained pair-bonds for subsequent breeding seasons. After accounting for sex, pair status, month, and time of day, the diurnal behavioral activities of Hawaiian Ducks differed between managed wetlands and taro habitats (F₆,₉₆₀ = 30.3, P < 0.001). Hawaiian Ducks utilized taro predominantly for resting (44%), maintenance (21%), and foraging (15%), while birds used managed wetlands for a variety of activities, including foraging (11%), maintenance (28%), resting (27%), and locomotion (22%). Social activities, particularly courtship, occurred more frequently in managed wetlands than in taro (H₁ = 11.9, P < 0.001). In managed wetlands, birds foraged slightly more with increasing cover of Cyperus spp. (r = 0.18, P < 0.001) and Fimbristylis littoralis (r = 0.17, P < 0.01) and decreasing cover of Urochloa mutica (r = -0.15, P < 0.01) and wetland vegetation height (r = -0.22, P < 0.001). Within taro habitat, the behavioral activities of Hawaiian Ducks differed significantly between birds in lo'i and on dikes (F₆,₄₆₈ = 142.8, P < 0.001); birds utilized lo‘i dikes for resting (60%) and maintenance activities (21%), whereas birds entered lo‘i primarily to forage (45%). The activity budget of Hawaiian Ducks was strongly influenced by time of day (F₁₈,₂₇₁₅.₇₈ = 6.4, P < 0.001), and birds spent more time engaged in active behaviors (i.e., foraging, locomotion, and alert) and less time resting during early morning and evening than during late morning and afternoon. While strong seasonal shifts in most behavioral patterns were not detected, males allocated more time to courting (1.1 vs. 0.3%; H1 = 6.92, P = 0.009) and mate-guarding (0.5 vs. <0.1%; H₁ = 9.83, P = 0.002) in managed wetlands between November and March than the remainder of the year. The effects of sex (F₆,₉₆₀ = 6.06, P < 0.001) and social status (F₆,₆₈₂ = 6.69, P < 0.001) on activity budgets were also significant. Females spent more time foraging (18 vs. 12%) and less time in alert, locomotor, and social behaviors than males. Paired birds allocated more time to aggression towards conspecifics, mate-guarding, and courtship, and within taro lo‘i, paired birds foraged more and rested less than unpaired birds. Overall, Hawaiian Duck allocated diurnal activity budgets differently in managed and cultivated wetland habitat at Hanalei NWR, suggesting that both systems may play an important role in fulfilling fundamental daily and seasonal resource requirements. The increased range of activities and foraging tactics used in managed wetlands may indicate the greater habitat diversity (e.g., vegetation structure, patchiness, plant species richness, range of water depths) provided by seasonal wetlands. In general, Hawaiian Duck allocated less time to diurnal foraging than North American Anas, such Mallard and Mottled Duck (A. fulvigula), suggesting that Hawaiian Duck may have lower daily and seasonal energy demands, have access to higher quality diet, or allot more time to nocturnal foraging activities. Also, unlike many North American migratory waterfowl that demonstrate significant behavioral plasticity in adjusting activity budgets to meet seasonal energy demands associated with breeding, molting, wintering, and migration, Hawaiian Duck did not exhibit a strong seasonal shift in most behaviors which may reflect their non-migratory nature and asynchronous life history cycle.
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2368. [Article] Factors that influence risk behavior in HIV infected women receiving antiretroviral therapy in Kampala and Masaka, Uganda
Women living in sub-Saharan Africa are more affected by HIV/AIDS than any other population in the world. Two-thirds of all new HIV infections worldwide occur in sub-Saharan Africa and over 60% of these ...Citation Citation
- Title:
- Factors that influence risk behavior in HIV infected women receiving antiretroviral therapy in Kampala and Masaka, Uganda
- Author:
- MacLachlan, Ellen W.
Women living in sub-Saharan Africa are more affected by HIV/AIDS than any other population in the world. Two-thirds of all new HIV infections worldwide occur in sub-Saharan Africa and over 60% of these infections are in women. Indeed, 70% of all women globally who are infected with HIV reside in this region (UNAIDS, 2006). If women are already infected with HIV, unprotected sex puts them at risk of transmitting the virus to a partner or to an unborn child. It also puts them at risk of becoming superinfected with different HIV strains, including HIV strains that are already resistant to HIV drugs (Little et al., 1999; Hecht et al., 1998; Flaks, Burman, Gourley, Rietmeijer, Cohn, 2003; Kozal et al., 2006). HIV infected women also need to be concerned with adherence to their antiretroviral therapy (ART) regimen. Lack of adherence to drug regimens puts women at risk of poor HIV treatment outcomes such as drug resistance (Chesney, 2003). When used consistently and correctly, male condoms are the most effective method of protection against HIV for sexually active persons (Stone, Timyan, Thomas,1999). Women, however, may be unable to negotiate the use of a male condom because strong gender-based power differentials and conservative social and cultural norms often make this decision completely up to a man (Gupta, 2002; Cohen, 2004). The constraints on a woman’s ability to reduce her risk have led to concerns about the use of individual based models for HIV/AIDS behavior in women. These models often fail to acknowledge the relationship factors and the social, cultural and economic contexts that influence women’s behavior. These concerns with inadequate models of HIV risk reduction for women have resulted in the publication of numerous articles proposing social-structural, also referred to as structural and environmental, models of HIV/AIDS risk reduction for women (Parker et al., 2002; O’Leary & Martins, 2000; Parker et al., 2000; Sumartojo,2000; Sweat & Denison, 1995; Decosas, 1996; Farmer, 2003; Turshen, 1998; Tawil et al., 1995; Lurie et al., 2004). This study, therefore, sought to use social-structural variables in exploring women’s HIV-related risk behaviors in a sub-Saharan Africa setting, Uganda, in East Africa. Although much is known about structural and environmental approaches to HIV prevention among HIV negative women, little is known about the potential application of this approach to studying sexual risk behaviors and adherence to ART among HIV infected women. The overall aim of the study was to examine associations between social-structural variables (e.g., poverty, gender power dynamics) and two outcome variables: history of unprotected sex and self-reported adherence to ART among HIV infected women enrolled in drug therapy programs. Data were collected using structured interviews with 377 HIV infected women in four different HIV/AIDS treatment programs in Kampala and Masaka, Uganda. A major finding of the study was that few women in the sample were sexually active(34%), partly due to the high proportion of non-sexually active widows (49%). The majority of sexually active women reported condom use at last sex act (75%) and disclosure of their HIV status to a main partner (78%). In multivariate analysis condom use at last sex act was strongly predicted by the need to borrow food to survive (OR=5.440, 95% CI 1.237, 23.923, p<.05), possibly indicating that women engaging in sexual exchange for food are more likely to use condoms. Forced, coercive or survival sex was significantly associated with the number of meals missed per week due to lack of food (OR=1.130, 95% CI 1.125, 1.526, p<.005). In addition, married women compared to unmarried women were three times more likely to have experienced forced, coercive or survival sex (OR=2.911, 95% CI 1.234, 6.87, p<.05). Because married women are considered to be relatively more economically stable, the findings that missing meals due to lack of food and married marital status are both associated with forced, coercive or survival sex, when adjusted for other factors, support the conclusion that both impoverished women and women with access to more resources can be at risk. Alternately, married women may not have as ready access to resources as is usually assumed and could also be engaging in sexual exchange behavior and borrowing food to get by. In either case, married women are probably more likely than their unmarried counterparts to experience large gender power differentials, despite their economic resources, that limit their ability to use condoms. Indeed, for all women in the study, the structural equation modeling (SEM) model fitting analyses indicated that genderbased power may be a more important predictor than economic security of women’s sexual risk behaviors. Neither factor was, however, predictive of ART adherence in this study sample. In summary, findings suggested that sexual exchange for food and other assistance is probably common and likely driven by economic deprivation. On the contrary, results indicated that sexual exchange is not necessarily linked with risky behaviors such as lack of condom use. There is evidence of increased risk for married women in the study, especially the risk of forced, coercive or survival sex. The complex interactions between poverty, hunger, marital status, gender-based power and different HIV/AIDS risk behaviors should be further examined in order to inform the implementation of HIV/AIDS programs designed for women.
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2369. [Article] All in a DNA's work : conservation genetics and monitoring of the New Zealand endemic Maui's and Hector's dolphins
The critically endangered Maui's dolphin (Cephalorhynchus hectori maui) and the endangered Hector's dolphin (C. h. hectori) are endemic to the coastal waters of New Zealand, where their primary threat ...Citation Citation
- Title:
- All in a DNA's work : conservation genetics and monitoring of the New Zealand endemic Maui's and Hector's dolphins
- Author:
- Hamner, Rebecca Marie
The critically endangered Maui's dolphin (Cephalorhynchus hectori maui) and the endangered Hector's dolphin (C. h. hectori) are endemic to the coastal waters of New Zealand, where their primary threat is fisheries-related mortality. The Maui's dolphin is among the most critically endangered cetaceans in the world, with its remnant population primarily concentrated in approximately 140 km along the central west coast of New Zealand's North Island. Its closely related sister subspecies, the Hector's dolphin, is more abundant and offers a useful comparison for studying the Maui's dolphin. My work used genetic tools to examine demographic and genetic parameters relevant for conservation considerations regarding Maui's and Hector's dolphins, as well as to build upon past genetic baselines for the purpose of long-term genetic monitoring of these subspecies. Three genetic datasets formed the basis for most analyses: (1) Maui's 01-07, including 54 Maui's dolphin individuals sampled between 2001 and 2007 (n = 70 biopsies, 12 beachcast); (2) Maui's 10-11, including 40 Maui's dolphin individuals sampled in 2010 and 2011 (n = 69 biopsies, 1 beachcast); and (3) Hector's CB11-12, including 148 Hector's dolphin individuals sampled in Cloudy Bay in 2011 and 2012 (n = 263 biopsies). Microsatellite genotypes were used to identify individuals for a genotype recapture abundance estimate of individuals age 1⁺ (N₁₊) and for the estimation of effective population size (N[subscript e]). Both populations exhibited a high N[subscript e] relative to N₁₊, consistent with expectations given their life history characteristics and the limited data available for other dolphin species. The abundance of Maui's dolphins was confirmed to be very low, Maui's 10-11 N₁₊ = 55 (95% CL = 48 - 69), and as expected, it had much lower linkage disequilibrium N[subscript e] (61, 95% CL = 29 - 338) than Hector's CB11-12 (N[subscript e] = 207, 95% CL = 127 - 447; N₁₊ = 272, 95% CL = 236 - 323). The slightly higher Ne/N₁₊ ratio of the Maui's dolphin compared to the Hector's dolphin is consistent with a recent decline in the Maui's dolphin. Although the point estimates of both N[subscript e] and N₁₊ decreased between the two Maui's dolphin datasets (Maui's 01-07: N[subscript e] = 74, 95% CL = 37 - 318; N₁₊ = 69, 95% CL = 38 - 125), the confidence intervals widely overlapped. Maui's 10-11 had significantly fewer alleles (average 4 alleles/locus) and lower heterozygosity (H₀ = 0.316, H[subscript e] = 0.319) than Hector's CB11-12 (average 7 alleles/locus, H₀ = 0.500, H[subscript e] = 0.495; all P <0.001). Interestingly, one microsatellite locus (PPHO104) had anomalously high diversity (31 to 63 alleles) in both Hector's and Maui's dolphins and appears to be influenced by diversifying selection. The observed and expected heterozygosity, internal relatedness, and F[subscript IS] of Maui's dolphins all showed patterns consistent with a decline of the subspecies, although none differed significantly over the short time interval between the two datasets collected in 2001-07 and 2010-11. The lack of significant decline in any of the parameters analyzed for Maui's dolphins is not surprising given the low power to detect a low to moderate decline over the short interval (<1 generation) between the two sampling periods. Compared to minimum viable effective population sizes proposed to guide management decisions, the Maui's dolphin has declined below the recommended threshold of N[subscript e] = 50, recently increased to N[subscript e] ≥100, thought to be necessary to avoid inbreeding depression in the short term (5 generations, ~65.2 years for Maui's and Hector's dolphins). Additionally, both the Maui's dolphin and Cloudy Bay Hector's dolphin populations are below the recommended threshold of N[subscript e] = 500, recently increased to N[subscript e] ≥1000, thought to be necessary to preserve long-term evolutionary potential. This is less of a concern for the Cloudy Bay Hector's population, which is thought to maintain gene flow with neighboring populations. However, for the small, isolated Maui's dolphin population, inbreeding depression is likely to be an increasing concern. Furthermore, each Maui's dolphin individual holds a disproportionate amount of the total genetic variation of the subspecies and would represent a disproportionately large demographic and genetic loss if it died before realizing its reproductive potential in the population. There is, however, potential for genetic restoration by interbreeding with Hector's dolphins, as genetic monitoring of Maui's dolphins revealed the first contemporary dispersal of four (two living females, one dead female, one dead male) Hector's dolphins into the Maui's dolphin distribution. Two Hector's dolphins (one dead female neonate, one living male) were also sampled along the North Island's southwest coast, outside the presumed range of either subspecies. Together, these records provide evidence of long-distance dispersal by Hector's dolphins (≥400 km) and the possibility of an unsampled Hector's dolphin population along the southwest coast of the North Island or northern South Island. These results highlight the value of genetic monitoring for subspecies lacking distinctive physical appearances, as such discoveries are not detected by other means but have important conservation implications. Although the Maui's dolphin is critically endangered, it is not necessarily doomed to extinction. The subspecies appears to be maintaining an equal sex ratio and connectivity within its remnant range, and the highly diverse locus PPHO104 could potentially offer clues to an inbreeding avoidance mechanism. If Maui's dolphins interbreed with the recently identified Hector's dolphin immigrants, it could provide genetic restoration, enhancing chances of long-term survival of the Maui's dolphin. Continued genetic monitoring and examination of recovered carcasses for phenotypic signs of inbreeding are important for gauging genetic threats to the survival of Maui's dolphins, as well as determining if any Hector's dolphin populations appear to be declining toward the critically endangered state of the Maui's dolphin. The results of this work contributed to the decision by the New Zealand Department of Conservation and Ministry for Primary Industries to conduct an updated risk assessment for Maui's dolphins and accelerate the review of the Maui's Dolphin Threat Management Plan. Consequently, commercial and recreational set net restrictions were extended slightly to reduce entanglement risk to Maui's dolphins utilizing the southern part of their distribution, as well as any Hector's dolphins that disperse north into that area. The results related to the population of Hector's dolphins in Cloudy Bay provide information that will contribute to the upcoming review of the Hector's dolphin component of the Threat Management Plan.
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2370. [Article] The Responses of Slope-spawning Flatfish to Environmental Variability in the Eastern Bering Sea
When adult spawning and juvenile settling locations of marine fishes are geographically separated, their early life history stages must rely on transport and their own behavior to move them toward suitable ...Citation Citation
- Title:
- The Responses of Slope-spawning Flatfish to Environmental Variability in the Eastern Bering Sea
- Author:
- Vestfals, Cathleen D.
When adult spawning and juvenile settling locations of marine fishes are geographically separated, their early life history stages must rely on transport and their own behavior to move them toward suitable habitats for successful recruitment to the juvenile phase. Variations in climate may reduce the availability of spawning and juvenile nursery habitats and alter ocean circulation patterns, which can disrupt dispersal pathways and affect life cycle closure. This research focused on two commercially- and ecologically-important flatfish species in the eastern Bering Sea (EBS), Greenland halibut (Reinhardtius hippoglossoides) and Pacific halibut (Hippoglossus stenolepis), which may be especially sensitive to climate variability due to strong seasonally and ontogenetically variable distributions and extended pelagic larval phases. Data from fishery-dependent and fishery-independent sources were analyzed to determine the influence of environmental variability on adult habitat use, thus gaining a uniquely comprehensive range of seasonal and geographic coverage of each species' distribution. Transport along and across the Bering Slope was characterized from 23 years (1982 - 2004) of simulations from a Regional Ocean Modeling System (ROMS) ocean circulation model, with the expectation that changes in the strength and position of the Bering Slope Current (BSC) would affect recruitment, and that circulation features along and across the shelf edge would be strongly influenced by atmospheric forcing. To understand the physical mechanisms of larval delivery to shelf nursery areas, Greenland and Pacific halibut dispersal pathways were simulated from their source (e.g., spawning areas over the continental slope) to settlement locations (e.g., juvenile nursery areas on the continental shelf) using DisMELS (Dispersal Model for Early Life Stages), an individual-based particle-tracking model. Spatial patterns of dispersal were characterized for each species and for years with contrasting settlement success to understand the influence of local oceanographic and atmospheric conditions on dispersal corridor use. Adult Greenland and Pacific halibut exhibited strong and contrasting responses to changes in temperature on the shelf, with catches decreasing and increasing, respectively, at approximately 1°C. The effect of temperature was not as prominent along the slope, suggesting that slope habitats may provide some insulation from shelf-associated environmental variability, particularly for Greenland halibut. With warming, Greenland halibut exhibited more of a bathymetric shift in distribution, while the shift was more latitudinal for Pacific halibut. Habitat partitioning may, in part, explain differences in Greenland and Pacific halibut adult distributions. Analysis of modeled circulation revealed strong variations in the strength and position of the BSC, with changes in along-shelf and cross-shelf flow associated with changes in recruitment. Greenland halibut benefitted from decreased along-shelf and on-shelf flow, while Pacific halibut benefitted from on-shelf flows through Bering and Pribilof canyons. Variability in transport and the BSC position was strongly influenced by winds, ice cover, and large-scale climatic drivers. Greenland and Pacific halibut dispersal pathways varied between years, with distinct differences in dispersal characteristics found between the two species. In general, Greenland halibut connected to shelf nursery areas via more northern corridors, while Pacific halibut connected through more southern ones. In years with poor settlement success, the reverse pattern was observed. Greenland halibut dispersal metrics were strongly correlated with along- and cross-shelf transport, as well as NW along-shelf winds and ice, while Pacific halibut had strong associations with SW onshelf winds. Spawning time and location, along with climate-induced changes in circulation, appear to differentially affect Greenland and Pacific halibut dispersal pathways, which can lead to variations in their recruitment. Overall, Greenland and Pacific halibut had contrasting responses to similar environmental forcing, and predicted climate change is expected to impact these species in different ways. With increasing warming on the EBS shelf, they will likely further partition their habitats, with Greenland halibut finding colder refuges along the slope and Pacific halibut inhabiting larger portions of the shelf. Climate-induced changes in circulation were found to affect the transport of halibut eggs and larvae and their recruitment to the juvenile phase, which suggests an important role in their slope-shelf connectivity. Results of this study suggest that Greenland and Pacific halibut use different mechanisms to move from their spawning locations along the slope to their settlement areas on the shelf, and that environmental conditions that increase slope-shelf connectivity for one species will likely result in reduced connectivity for the other. This research improves our understanding of how slopespawning flatfish respond to a changing ocean environment, which is important for effective management of their populations, as predicted climate change will likely alter their habitat use and population dynamics.