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At least 829 records · Page 46Linked to original sources
USGS2007

Geology and complex collapse mechanisms of the 3.72 Ma Hannegan caldera, North Cascades, Washington, USA

Contiguous ring faults of the 8 × 3.5 km Hannegan caldera enclose the Hannegan volcanics in the Cascade arc of northern Washington. The caldera collapsed in two phases, which each erupted rhyolitic ignimbrite (72.3%–75.2% SiO 2 ). The first collapse phase, probably trap-door style, erupted the ≥900-m-thick ignimbrite of Hannegan Peak at 3.722 ± 0.020 Ma. This single cooling unit, generally welded, has an uppermost facies of nonwelded ignimbrite and fine ash. A short period of localized sedimentation followed. Eruption of the ignimbrite of Ruth Mountain then led to a second trap-door collapse as the first-phase partial ring fault propagated to the south to completely enclose the caldera. Wall-rock breccias are intercalated as lenses and megabreccia blocks in both ignimbrites. The minimum intracaldera volume is 55–60 km 3 . No base is exposed, nor are outflow sheets preserved. Caldera collapse and glacial erosion have removed precaldera volcanic rocks, which survive only as intracaldera breccias. Rhyolite dikes and pods, one of which yielded a 40 Ar/ 39 Ar age of 3.72 ± 0.34 Ma, intrude the ring fault and caldera fill. Daciteandesite domes, dikes, and lava flows were emplaced subsequently; one lava flow gives a 40 Ar/ 39 Ar age of 2.96 ± 0.20 Ma. The quartz diorite of Icy Peak and the granite of Nooksack Cirque (plutons with 206 Pb/ 238 U zircon ages of 3.42 ± 0.10 Ma and 3.36 ± 0.20 Ma, respectively) intrude caldera fill and basement rocks on the southwest margin of the caldera. Both plutons are now exceptionally well exposed on high, glacially sculpted peaks within the caldera, indicating erosion of at least 1 km of intracaldera fill. Hannegan caldera anchors the northeast end of a linear NE-SW age-progressive migration of magmatic focus from the Chilliwack batholith to the active Mount Baker volcano.

Washington↗
USGS2010

Age, genesis, and paleoclimatic interpretation of the Sangamon/Loveland complex in the Lower Mississippi Valley, USA

For more than a century, the Sangamon paleosol (the Sangamon) has been an integral part of geologic and pedologic investigations in the central United States, including the Upper Mississippi and Lower Missouri River Valleys. Compositional, pedologic, micromorphologic, stratigraphic, and age data indicate that the prominent reddish paleosol developed in silt-rich deposits of the Lower Mississippi Valley, from southernmost Illinois to northwestern Mississippi, represents multiple periods of soil formation, and is wholly or in part time equivalent to the Sangamon of the central United States. Thermoluminescence data, for localities where the Sangamon developed in loess, indicate that the primary period of loess deposition was from 190 to 130 ka (oxygen isotope stage, OIS6), that loess deposition continued intermittently from 130 to 74 ka (OIS5), and that deposition was wholly or in part coeval with Loveland loess deposition in the central United States. Beryllium-10, chemical, and pedologic data indicate that in the Lower Mississippi Valley: (1) the Sangamon represents a minimum time period of 60-80 k.y.; (2) there were at least two periods of soil formation, ca. 130-90 ka and 74-58 ka (OIS4); and (3) rates of weathering and pedogenesis equaled or exceeded the net loess-accumulation rate until at least 46 ka (OIS3) and resulted in development of a paleosol in the overlying basal Roxana Silt. Along a N-S transect from southern Illinois to western Mississippi, Sangamon macroscopic characteristics as well asthe micro-morphology, chemistry, and mineralogy, suggest a regional paleoclimate during periods of soil formation that: (1) was warm to hot, with a wider range in temperature, precipitation, and evapotranspiration than present; (2) had seasonal to decadal or longer periods of drought; and (3) had down-valley (southward) trends of increasing temperature and precipitation and decreasing seasonality and variation in annualto decadal precipitation. ?? 2011 Geological Society of America.

Geological Society of America Bulletin↗
USGS2014

Chemical complexity and source of the White River Ash, Alaska and Yukon

The White River Ash, a prominent stratigraphic marker bed in Alaska (USA) and Yukon (Canada), consists of multiple compositional units belonging to two geochemical groups. The compositional units are characterized using multiple criteria, with combined glass and ilmenite compositions being the best discriminators. Two compositional units compose the northern group (WRA-Na and WRA-Nb), and two units are present in the eastern group (WRA-Ea and the younger, WRA-Eb). In the proximal area, the ca. 1900 yr B.P. (Lerbekmo et al., 1975) WRA-Na displays reverse zoning in the glass phase and systematic changes in ilmenite composition and estimated oxygen fugacity from the base to the top of the unit. The eruption probably tapped different magma batches or bodies within the magma reservoir with limited mixing or mingling between them. The 1147 cal yr B.P. (calibrated years, approximately equivalent to calendric years) (Clague et al., 1995) WRA-Ea eruption is only weakly zoned, but pumices with different glass compositions are present, along with gray and white intermingled glass in individual pumice clasts, indicating the presence of multiple magmatic bodies or layers. All White River Ash products are high-silica adakites and are sourced from the Mount Churchill magmatic system.

Alaska, Yukon↗
USGS2013

Reconsidering residency: Characterization and conservation implications of complex migratory patterns of shortnose sturgeon ( Acispenser brevirostrum )

Efforts to conserve endangered species usually involve attempts to define and manage threats at the appropriate scale of population processes. In some species that scale is localized; in others, dispersal and migration link demic units within larger metapopulations. Current conservation strategies for endangered shortnose sturgeon ( Acipenser brevirostrum ) assume the species is river resident, with little to no movement between rivers. However we have found that shortnose sturgeon travel more than 130 km through coastal waters between the largest rivers in Maine. Indeed, acoustic telemetry shows that shortnose sturgeon enter six out of the seven acoustically monitored rivers we have monitored, with over 70% of tagged individuals undertaking coastal migrations between river systems. Four migration patterns were identified for shortnose sturgeon inhabiting the Penobscot River, Maine: river resident (28%), spring coastal emigrant (24%), fall coastal emigrant (33%), and summer coastal emigrant (15%). No shortnose sturgeon classified as maturing female exhibited a resident pattern, indicating differential migration. Traditional river-specific assessment and management of shortnose sturgeon could be better characterized using a broader metapopulation scale, at least in the Gulf of Maine, that accounts for diverse migratory strategies and the importance of migratory corridors as critical habitat.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2018

Flow-mediated effects on travel time, routing, and survival of juvenile Chinook salmon in a spatially complex, tidally forced river delta

We evaluated the interacting influences of river flows and tides on travel time, routing, and survival of juvenile late-fall Chinook salmon ( Oncorhynchus tshawytscha ) migrating through the Sacramento–San Joaquin River Delta. To quantify these effects, we jointly modeled the travel time, survival, and migration routing in relation to individual time-varying covariates of acoustic-tagged salmon within a Bayesian framework. We used observed arrival times for detected individuals and imputed arrival times for undetected individuals to assign covariate values in each reach. We found travel time was inversely related to river inflow in all reaches, yet survival was positively related to inflow only in reaches that transitioned from bidirectional tidal flows to unidirectional flow with increasing inflows. We also found that the probability of fish entering the interior Delta, a low-survival reach, declined as inflow increased. Our study illustrates how river inflows interact with tides to influence fish survival during the critical transition between freshwater and ocean environments. Furthermore, our analytical framework introduces new techniques to integrate formally over missing covariate values to quantify effects of time-varying covariates.

California↗
USGS2024

Complex interactions of deer herbivory, soil chemistry, and competing vegetation explain oak–hickory forest tree regeneration in central Pennsylvania, USA

The root causes of forest tree regeneration failure are difficult to resolve, although numerous studies show ungulate herbivory, soil conditions, and competition from undesirable vegetation as likely contributors. To better understand the relative importance of each issue, we conducted a 7-year manipulative experiment to assess the interactive effects of white-tailed deer ( Odocoileus virginianus ) herbivory, soil acidity, and competing vegetation on tree regeneration in oak–hickory forests of central Pennsylvania, USA. Outcomes depended on initial tree seedling abundance, and all three factors had significant interactions. At low initial seedling abundance, fencing resulted in the greatest increase, but all treatments had a positive effect on seedling growth and abundance. At higher initial seedling abundance, abundance failed to recover 7 years after herbicide treatment and soil pH was an important predictor. When soil pH was >4.6 from lime application, seedling growth and abundance in unfenced controls with high initial abundance was comparable to the fenced-only treatment. Competing vegetation, assumed to be a symptom of excessive, long-term deer herbivory, does not seem to be the primary factor limiting tree regeneration in our study area. Ameliorating acid deposition warrants greater consideration as a management action because it could provide long-lasting benefits compared to short-term fence installations.

Pennsylvania↗
USGS2019

Tools to understand seasonality in health: quantification of microbe loads and analyses of compositional ecoimmunological data reveal complex patterns in Mojave Desert Tortoise (Gopherus agassizii) populations

Using data from six wild Mojave Desert Tortoise ( Gopherus agassizii (Cooper, 1861)) populations, we quantified seasonal differences in immune system measurements and microbial load in the respiratory tract, pertinent to this species’ susceptibility to upper respiratory tract disease. We quantified bacteria-killing activity of blood plasma and differential leukocyte counts to detect trends in temporal variation in immune function. We used centered log-ratio (clr) transformations of leukocyte counts and stress that such transformations are necessary for compositional data. We tested animals for the potential pathogen Pasteurella testudinis Snipes and Biberstein, 1982 with a newly created quantitative polymerase chain reaction (qPCR) assay, as well as for the known respiratory pathogens Mycoplasma agassizii Brown et al., 2001 and Mycoplasma testudineum Brown et al., 2004. We found very little disease and suggest that P. testudinis is a prevalent, commensal microbe in these Mojave Desert Tortoise populations, and its quantification may be a tool to study natural fluctuations in microbe levels in Mojave Desert Tortoise respiratory tracts. Our analyses showed that both the potential for inflammatory responses and microbe levels are highest in the spring for healthy Mojave Desert Tortoises, when lymphocyte levels are lowest. The genetic and statistical tools that we used are easily applicable to other wildlife systems and provide the necessary data to quantify species-wide trends in health and test hypotheses pertinent to host–microbe dynamics.

Canadian Journal of Zoology↗
USGS1993

Complex interactions of multiple aquatic consumers: an experimental mesocosm manipulation

In 7-m 3 outdoor tanks filled with lake water, the presence/absence of omnivorous young-of-the- year Micropterus salmoides), zooplanktivorous Menidia beryllina , and herbivorous larval Hyla chrysocelis was experimentally manipulated. A cross-classified design was used to assess the interactive effects of these vertebrate consumers on the experimental food webs. The primary effects of the experimental manipulations on food web components were two- and three-way interactions in which the effect of a given treatment was dependent on the presence of another treatment. Results suggest that the addition or removal of consumers may not cause linear, additive changes in food webs.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2017

The fascinating and complex dynamics of geyser eruptions

Geysers episodically erupt liquid and vapor. Despite two centuries of scientific study, basic questions persist—why do geysers exist? What determines eruption intervals, durations, and heights? What initiates eruptions? Through monitoring eruption intervals, analyzing geophysical data, taking measurements within geyser conduits, performing numerical simulations, and constructing laboratory models, some of these questions have been addressed. Geysers are uncommon because they require a combination of abundant water recharge, magmatism, and rhyolite flows to supply heat and silica, and large fractures and cavities overlain by low-permeability materials to trap rising multiphase and multicomponent fluids. Eruptions are driven by the conversion of thermal to kinetic energy during decompression. Larger and deeper cavities permit larger eruptions and promote regularity by isolating water from weather variations. The ejection velocity may be limited by the speed of sound of the liquid + vapor mixture.

Annual Review of Earth and Planetary Sciences↗
USGS2014

Photographic evidence of interspecies mating in geckos of the Lepidodactylus lugubris unisexual-bisexual complex (Squamata: Gekkonidae)

An interspecies mating between unisexual Lepidodactylus lugubris and a male of the bisexual Lepidodactylus moestus was photographed by Carlos Cianchini on Kosrae [Island], FSM, at 18:15 h on 22 August 2013 (Figure 1). The mating pair was on a window frame inside a house at Pukusruk Wan village (05°21'01" N, 163°00'41" E, elev. 28 m a.s.l.) on the northeastern side of the island. This is the first direct evidence of mating between these two species.

Phyllomedusa↗
USGS2009

Symbiotic lifestyle expression by fungal endophytes and the adaptation of plants to stress: unraveling the complexities of intimacy

The fossil record indicates that fungal symbionts have been associated with plants since the Ordovician period (approximately 400 million years ago), when plants first became established on land (Pirozynski and Malloch, 1975; Redecker et al., 2000; Remy et al., 1994; Simon et al., 1993). Transitioning from aquatic to terrestrial habitats likely presented plants with new stresses, including periods of desiccation. Since symbiotic fungi are known to confer drought tolerance to plants (Bacon, 1993; Read and Camp, 1986), it has been suggested that fungal symbiosis was involved with or responsible for the establishment of land plants (Pirozynski and Malloch, 1975). Symbiosis was first defined by De Bary in 1879, and since that time, all plants in natural ecosystems have been found to be colonized with fungal and bacterial symbionts. It is clear that individual plants represent symbiotic communities with microorganisms associated in or on tissues below- and aboveground. There are two major classes of fungal symbionts associated with internal plant tissues: fungal endophytes that reside entirely within plants and may be associated with roots, stems leaves, or flowers; and mycorrhizal fungi that reside only in roots but extend out into the rhizosphere. In addition, fungal endophytes may be divided into two classes: (1) a relatively small number of fastidious species that are limited to a few monocot hosts (Clay and Schardl, 2002), and (2) a large number of tractable species with broad host ranges, including both monocots and eudicots (Stone et al., 2000). While significant resources and research have been invested in mycorrhizae and class 1 endophytes, comparatively little is known about class 2 endophytes, which may represent the largest group of fungal symbionts. This is partially because the symbiotic functionalities of class 2 endophytes have only recently been elucidated and shown to be responsible for the adaptation of some plants to high-stress environments (Redman et al., 1999, 2001, 2002a; Arnold et al., 2003; Dingle and McGee, 2003; Ernst et al., 2003). In this chapter, we focus on symbiotic interactions between class 2 endophytes and a variety of monocot and eudicot host species. Specifically, we will discuss the ability of endophytes to express more than one symbiotic lifestyle, fungal taxonomy vs. lifestyle expression, the adaptive nature of symbioses, mechanisms of symbiotically conferred stress tolerance, and the evolutionary implications of adaptive symbiosis. We will refer to class 2 endophytes as fungal endophytes throughout the text.

Book chapter↗
USGS2011

Estimating temporal trend in the presence of spatial complexity: A Bayesian hierarchical model for a wetland plant population undergoing restoration

Monitoring programs that evaluate restoration and inform adaptive management are important for addressing environmental degradation. These efforts may be well served by spatially explicit hierarchical approaches to modeling because of unavoidable spatial structure inherited from past land use patterns and other factors. We developed Bayesian hierarchical models to estimate trends from annual density counts observed in a spatially structured wetland forb (Camassia quamash [camas]) population following the cessation of grazing and mowing on the study area, and in a separate reference population of camas. The restoration site was bisected by roads and drainage ditches, resulting in distinct subpopulations ("zones") with different land use histories. We modeled this spatial structure by fitting zone-specific intercepts and slopes. We allowed spatial covariance parameters in the model to vary by zone, as in stratified kriging, accommodating anisotropy and improving computation and biological interpretation. Trend estimates provided evidence of a positive effect of passive restoration, and the strength of evidence was influenced by the amount of spatial structure in the model. Allowing trends to vary among zones and accounting for topographic heterogeneity increased precision of trend estimates. Accounting for spatial autocorrelation shifted parameter coefficients in ways that varied among zones depending on strength of statistical shrinkage, autocorrelation and topographic heterogeneity-a phenomenon not widely described. Spatially explicit estimates of trend from hierarchical models will generally be more useful to land managers than pooled regional estimates and provide more realistic assessments of uncertainty. The ability to grapple with historical contingency is an appealing benefit of this approach.

PLoS ONE↗
USGS2015

Modeling the complex impacts of timber harvests to find optimal management regimes for Amazon tidal floodplain forests

At the Amazon estuary, the oldest logging frontier in the Amazon, no studies have comprehensively explored the potential long-term population and yield consequences of multiple timber harvests over time. Matrix population modeling is one way to simulate long-term impacts of tree harvests, but this approach has often ignored common impacts of tree harvests including incidental damage, changes in post-harvest demography, shifts in the distribution of merchantable trees, and shifts in stand composition. We designed a matrix-based forest management model that incorporates these harvest-related impacts so resulting simulations reflect forest stand dynamics under repeated timber harvests as well as the realities of local smallholder timber management systems. Using a wide range of values for management criteria (e.g., length of cutting cycle, minimum cut diameter), we projected the long-term population dynamics and yields of hundreds of timber management regimes in the Amazon estuary, where small-scale, unmechanized logging is an important economic activity. These results were then compared to find optimal stand-level and species-specific sustainable timber management (STM) regimes using a set of timber yield and population growth indicators. Prospects for STM in Amazonian tidal floodplain forests are better than for many other tropical forests. However, generally high stock recovery rates between harvests are due to the comparatively high projected mean annualized yields from fast-growing species that effectively counterbalance the projected yield declines from other species. For Amazonian tidal floodplain forests, national management guidelines provide neither the highest yields nor the highest sustained population growth for species under management. Our research shows that management guidelines specific to a region’s ecological settings can be further refined to consider differences in species demographic responses to repeated harvests. In principle, such fine-tuned management guidelines could make management more attractive, thus bridging the currently prevalent gap between tropical timber management practice and regulation.

Amazon River, Mazagão watershed↗
USGS2018

Evaluating time-removal models for estimating availability of boreal birds during point count surveys: Sample size requirements and model complexity

We used conventional and finite mixture removal models with and without time-varying covariates to evaluate availability given presence for 152 bird species using data from point counts in boreal North America. We found that the choice of model had an impact on the estimability of unknown model parameters and affected the bias and variance of corrected counts. Finite mixture models provided better fit than conventional removal models and better adjusted for count duration. However, reliably estimating parameters and minimizing variance using mixture models required at least 200–1,000 detections. Mixture models with time-varying proportions of infrequent singers were best supported across species, indicating that accounting for date- and time-related heterogeneity is important when combining data across studies over large spatial scales, multiple sampling time frames, or variable survey protocols. Our flexible and continuous time-removal modeling framework can be used to account for such heterogeneity through the incorporation of easily obtainable covariates, such as methods, date, time, and location. Accounting for availability bias in bird surveys allows for better integration of disparate studies at large spatial scales and better adjustment of local, regional, and continental population size estimates.

Condor↗
USGS2018

Variation in soil carbon dioxide efflux at two spatial scales in a topographically complex boreal forest

Carbon dynamics of high-latitude regions are an important and highly uncertain component of global carbon budgets, and efforts to constrain estimates of soil-atmosphere carbon exchange in these regions are contingent on accurate representations of spatial and temporal variability in carbon fluxes. This study explores spatial and temporal variability in soilatmosphere carbon dynamics at both fine and coarse spatial scales in a high-elevation, permafrost-dominated boreal black spruce forest. We evaluate the importance of landscape-level investigations of soil-atmosphere carbon dynamics by characterizing seasonal trends in soil-atmosphere carbon exchange, describing soil temperature-moisture-respiration relations, and quantifying temporal and spatial variability at two spatial scales: the plot scale (0–5 m) and the landscape scale (500–1000 m). Plot-scale spatial variability (average variation on a given measurement day) in soil CO 2 efflux ranged from a coefficient of variation (CV) of 0.25 to 0.69, and plot-scale temporal variability (average variation of plots across measurement days) in efflux ranged from a CV of 0.19 to 0.36. Landscape-scale spatial and temporal variability in efflux was represented by a CV of 0.40 and 0.31, respectively, indicating that plot-scale spatial variability in soil respiration is as great as landscape-scale spatial variability at this site. While soil respiration was related to soil temperature at both the plot- and landscape scale, landscape-level descriptions of soil moisture were necessary to define soil respiration-moisture relations. Soil moisture variability was also integral to explaining temporal variability in soil respiration. Our results have important implications for research efforts in high-latitude regions where remote study sites make landscape-scale field campaigns challenging.

Arctic, Antarctic, and Alpine Research↗
USGS2023

Thirteen years of turtle capture–mark–recapture in a small urban pond complex in Louisiana, USA

Turtles are one of the most imperiled vertebrate groups in the world. With habitat destruction unabated in many places, urban and suburban greenspaces may serve as refugia for turtles, at least those species able to tolerate heavily altered landscapes. In south-central Louisiana, we have conducted a turtle capture–mark–recapture effort in two ponds in an urban greenspace for 13 yr to understand species composition, survival, and individual growth rates. We had 574 total captures of 251 individuals of five species from 2009–2021, with Trachemys scripta elegans (Red-Eared Sliders) and Sternotherus odoratus (Eastern Musk Turtles) being the most common. Apparent annual survival for T. scripta (0.79) was similar to estimates reported in other studies in altered habitats, whereas apparent annual survival for S. odoratus (0.89) was slightly or much higher than other published studies. Growth rates of T. scripta were comparable to other studies and showed both sexes have similar rates of growth until maturity, which is earlier and at a smaller size in males. The two ponds showed marked differences in captures by size, with significantly more juvenile T. scripta captured in the pond with more vegetation, depth, and a softer bottom. Most T. scripta (78.5%) that were recaptured came from the same pond from which they were originally captured. The basic demographic data gained in this study can serve as a starting point for broader questions on urbanization effects and as a comparison to more natural populations.

Louisiana↗