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At least 73 records · Page 4Linked to original sources
USGS2026

CrustCheck: A conceptual framework for interpreting biocrust trait–function relationships in drylands

Introduction Biocrusts are increasingly recognized for their contribution to soil stability, hydrology, nutrient cycling, and energy balance in drylands, yet practical field methods for assessing functional roles are limited. Existing approaches typically rely on cover estimates, taxonomic identification, or laboratory analyses, providing little insight into functional variation among biocrust types. To address this gap, we developed CrustCheck, a literature-derived conceptual framework that synthesizes potential relationships between easily observable biocrust traits and key ecological functions. The framework provides a foundation for future empirical validation of these relationships. Objectives We aimed to: (1) identify visual characteristics of biocrusts potentially associated with key ecological functions, and (2) synthesize these relationships into a literature-derived conceptual framework for comparative interpretation of potential biocrust contributions to landscape function. Methods We conducted a structured review of global literature on biocrusts' contribution to landscape function, drawing on multiple databases, targeted journals, and identifying relevant scientific publications from reference lists. We screened sources for information on relationships between visual traits and metrics of landscape function, synthesized relationships thematically, and used them to develop a multi-trait, function-oriented conceptual framework to inform further testing of these hypotheses in the field. Results Our review revealed that visual traits such as thickness/height, patchiness, cover, and surface roughness emerged as potential indicators of surface stability, hydrological function, and nutrient accumulation. Community composition was also frequently associated with these functions, while color reflected energy balance and carbon fixation potential. Conclusions Literature reveals that visual traits of biocrusts may serve as proxies for landscape function. CrustCheck is presented here as a conceptual synthesis framework intended to support interpretation of potential trait–function relationships rather than as a quantitatively validated predictive tool.

Restoration Ecology↗
USGS1977

Clay-mineral variability in the suspended sediments of the San Francisco Bay system, California

Semiquantitative determinations of the clay-mineral composition have been made on nearly synoptic samples of surface suspended sediments collected seasonally throughout the San Francisco Bay system. The relative amounts of chlorite + kaolinite are generally highest in the northern reach of the system, whereas illite is dominant in the southern reach. The proportion of montmorillonite is low throughout the bay. Time-series and replicate samples collected at individual stations show that the difference in clay-mineral content between reaches is real and reflects a change in the source of clay-mineral particles within the bay. The Sacramento-San Joaquin river system supplies the northern reach, whereas most clay-mineral particles come from resuspension by waves and tidal currents in the southern reach. Analyses of bottom sediments and the spatial variability in the northern reach suggest that the relationship between the abundance and sources of clay minerals may, in turn, be a function of particle size. This study demonstrates the utility of suspended clay minerals in the interpretation of sediment-dispersal patterns in estuaries.

California↗
USGS2012

Tools for quantifying isotopic niche space and dietary variation at the individual and population level.

Ecologists are increasingly using stable isotope analysis to inform questions about variation in resource and habitat use from the individual to community level. In this study we investigate data sets from 2 California sea otter ( Enhydra lutris nereis ) populations to illustrate the advantages and potential pitfalls of applying various statistical and quantitative approaches to isotopic data. We have subdivided these tools, or metrics, into 3 categories: IsoSpace metrics, stable isotope mixing models, and DietSpace metrics. IsoSpace metrics are used to quantify the spatial attributes of isotopic data that are typically presented in bivariate (e.g., δ 13 C versus δ 15 N) 2-dimensional space. We review IsoSpace metrics currently in use and present a technique by which uncertainty can be included to calculate the convex hull area of consumers or prey, or both. We then apply a Bayesian-based mixing model to quantify the proportion of potential dietary sources to the diet of each sea otter population and compare this to observational foraging data. Finally, we assess individual dietary specialization by comparing a previously published technique, variance components analysis, to 2 novel DietSpace metrics that are based on mixing model output. As the use of stable isotope analysis in ecology continues to grow, the field will need a set of quantitative tools for assessing isotopic variance at the individual to community level. Along with recent advances in Bayesian-based mixing models, we hope that the IsoSpace and DietSpace metrics described here will provide another set of interpretive tools for ecologists.

Journal of Mammalogy↗
USGS1984

Lightning fires in North Dakota grasslands and in pine-savanna lands of South Dakota and Montana

Lightning strike fires which occurred between 1940 and 1981 were studied in mixed-grass prairie grasslands and in pine-savanna lands in the Northern Great Plains region. A majority (73%) of ignitions occurred during July and August, while a lesser number was recorded in April, May, June, and September. The April-September period is also the average time of the freeze-free period and approximates the average distribution period for thunderstorm activity in this region. The area burned by each of 293 lightning fires (most of which were suppressed) ranged from 0.004-1158.3 ha ( X̄ = 10.8 ha). The frequency of lightning fires in mixed-grass prairie grasslands averaged 6.0/yr per 10,000 km 2 in eastern North Dakota, 22.4/yr per 10,000 km 2 in southcentral North Dakota, 24.7/yr per 10,000 km 2 in western North Dakota, and 91.7/yr per 10,000 km 2 in pine-savanna lands in northwestern South Dakota and southeastern Montana. The ecological role of lightning-set fires is discussed relative to the development of resource research and management plans and to the interpretation of historical records of natural fire occurrence in the Northern Great Plains region.

Journal of Range Management↗
USGS2012

A refined index of model performance: a rejoinder

Willmott et al. [Willmott CJ, Robeson SM, Matsuura K. 2012. A refined index of model performance. International Journal of Climatology , forthcoming. DOI:10.1002/joc.2419.] recently suggest a refined index of model performance ( d r ) that they purport to be superior to other methods. Their refined index ranges from − 1.0 to 1.0 to resemble a correlation coefficient, but it is merely a linear rescaling of our modified coefficient of efficiency ( E 1 ) over the positive portion of the domain of d r . We disagree with Willmott et al. ( 2012 ) that d r provides a better interpretation; rather, E 1 is more easily interpreted such that a value of E 1 = 1.0 indicates a perfect model (no errors) while E 1 = 0.0 indicates a model that is no better than the baseline comparison (usually the observed mean). Negative values of E 1 (and, for that matter, d r < 0.5) indicate a substantially flawed model as they simply describe a ‘level of inefficacy’ for a model that is worse than the comparison baseline. Moreover, while d r is piecewise continuous, it is not continuous through the second and higher derivatives. We explain why the coefficient of efficiency ( E or E 2 ) and its modified form ( E 1 ) are superior and preferable to many other statistics, including d r , because of intuitive interpretability and because these indices have a fundamental meaning at zero. We also expand on the discussion begun by Garrick et al. [Garrick M, Cunnane C, Nash JE. 1978. A criterion of efficiency for rainfall-runoff models. Journal of Hydrology 36 : 375-381.] and continued by Legates and McCabe [Legates DR, McCabe GJ. 1999. Evaluating the use of “goodness-of-fit” measures in hydrologic and hydroclimatic model validation. Water Resources Research 35 (1): 233-241.] and Schaefli and Gupta [Schaefli B, Gupta HV. 2007. Do Nash values have value? Hydrological Processes 21 : 2075-2080. DOI: 10.1002/hyp.6825.]. This important discussion focuses on the appropriate baseline comparison to use, and why the observed mean often may be an inadequate choice for model evaluation and development.

International Journal of Climatology↗
USGS2019

The potential role of very high-resolution imagery to characterise lake, wetland and stream systems across the Prairie Pothole Region, United States

Aquatic features critical to watershed hydrology range widely in size from narrow, shallow streams to large, deep lakes. In this study we evaluated wetland, lake, and river systems across the Prairie Pothole Region to explore where pan-sharpened high-resolution (PSHR) imagery, relative to Landsat imagery, could provide additional data on surface water distribution and movement, missed by Landsat. We used the monthly Global Surface Water (GSW) Landsat product as well as surface water derived from Landsat imagery using a matched filtering algorithm (MF Landsat) to help consider how including partially inundated Landsat pixels as water influenced our findings. The PSHR outputs (and MF Landsat) were able to identify ~60–90% more surface water interactions between waterbodies, relative to the GSW Landsat product. However, regardless of Landsat source, by documenting many smaller (<0.2 ha), inundated wetlands, the PSHR outputs modified our interpretation of wetland size distribution across the Prairie Pothole Region.

Prairie Pothole Region↗
USGS2023

Redd superimposition mediates the accuracy, precision, and significance of redd counts for cutthroat trout

Redd counts are commonly applied to estimate spawning population size for salmonids and allow for broad spatial and temporal coverage in monitoring efforts. However, the utility of redd counts may be compromised by observation error, particularly with respect to superimposition, where later arriving spawners construct redds overlapping existing redds. Here, we provide a mechanistic evaluation of the effects of superimposition on the error structure and biological significance of redd count data for Yellowstone cutthroat trout ( Oncorhynchus clarkii bouvieri ) spawning within tributaries to the Snake River, Wyoming. We used a Bayesian framework to parse observation error into distinct components and found low detection of redd clusters (i.e., areas of superimposition) was offset by overestimates of the number of redds per cluster, such that observed counts accurately reflected census redd abundance. However, a saturating relationship between redd counts and spawner abundance indicated that counts is best interpreted as effective reproductive effort rather than spawner abundance. Our results provide a mechanistic understanding of redd count data that can be used to assess their application and interpretation for monitoring.

Wyoming↗
USGS2005

Juvenile rainbow trout production in New York tributaries of Lake Ontario: implications for Atlantic salmon restoration

Three Pacific salmonid species Onchorynchus spp. have replaced the extirpated Atlantic salmon Salmo salar as the main migratory salmonid in the Lake Ontario drainage. One of those species, the nonnative rainbow trout O. mykiss, has become widely distributed within the historical Atlantic salmon habitat, occupying an ecological niche similar to that of juvenile Atlantic salmon. Consequently, both a tributary's carrying capacity for Atlantic salmon and competition from established nonnative species are important when considering the feasibility of Atlantic salmon restoration. Estimation of juvenile rainbow trout production will help evaluate the capacity of tributaries to produce salmonids that occupy similar niches. Geostatistical methods were applied to standardized and efficiency-corrected electrofishing data from three of New York's best salmonid-producing streams to precisely estimate juvenile rainbow trout populations. Results indicated that each study stream could produce 20,000&ndash;40,000 age-0 and 4,000&ndash;10,000 age-1 and older rainbow trout per year. Statistical interpolation indicated areas of significantly different production potential and points of significant changes in productivity. Closer examination of the niche similarity and competitive potential of these two species is needed to properly interpret these estimates with regard to Atlantic salmon restoration.

New York↗
USGS2012

The early bird gets the shrimp: Confronting assumptions of isotopic equilibrium and homogeneity in a wild bird population

1. Because stable isotope distributions in organic material vary systematically across energy gradients that exist in ecosystems, community and population structures, and in individual physiological systems, isotope values in animal tissues have helped address a broad range of questions in animal ecology. It follows that every tissue sample provides an isotopic profile that can be used to study dietary or movement histories of individual animals. Interpretations of these profiles depend on the assumption that metabolic pools are isotopically well mixed and in equilibrium with dietary resources prior to tissue synthesis, and they extend to the population level by assuming isotope profiles are identically distributed for animals using the same proximal dietary resource. As these assumptions are never fully met, studying structure in the variance of tissue isotope values from wild populations is informative. 2. We studied variation in &delta; 13 C, &delta; 15 N, &delta; 2 H and &delta; 18 O data for feathers from a population of eared grebes (Podiceps nigricollis) that migrate to Great Salt Lake each fall to moult feathers. During this time, they cannot fly and feed almost exclusively on superabundant brine shrimp (Artemia franciscana). The ecological simplicity of this situation minimized the usual spatial and trophic complexities often present in natural studies of feather isotope values. 3. Ranges and variances of isotope values for the feathers were larger than those from previously published studies that report feather isotopic variance, but they were bimodally distributed in all isotope dimensions. Isotope values for proximal dietary resources and local surface water show that some of the feathers we assumed to have been grown locally must have been grown before birds reached isotopic equilibrium with local diet or immediately prior to arrival at Great Salt Lake. 4. Our study provides novel insights about resource use strategies in eared grebes during migration. More generally, it demonstrates the utility of studying variance structures and questioning assumptions implicit in the interpretation of stable isotope data from wild animals.

Utah↗
USGS2015

Changes in seismic velocity during the first 14 months of the 2004–2008 eruption of Mount St. Helens, Washington

Mount St. Helens began erupting in late 2004 following an 18&thinsp;year quiescence. Swarms of repeating earthquakes accompanied the extrusion of a mostly solid dacite dome over the next 4&thinsp;years. In some cases the waveforms from these earthquakes evolved slowly, likely reflecting changes in the properties of the volcano that affect seismic wave propagation. We use coda-wave interferometry to quantify small changes in seismic velocity structure (usually <1%) between two similar earthquakes and employed waveforms from several hundred families of repeating earthquakes together to create a continuous function of velocity change observed at permanent stations operated within 20&thinsp;km of the volcano. The high rate of earthquakes allowed tracking of velocity changes on an hourly time scale. Changes in velocity were largest near the newly extruding dome and likely related to shallow deformation as magma first worked its way to the surface. We found strong correlation between velocity changes and the inverse of real-time seismic amplitude measurements during the first 3&thinsp;weeks of activity, suggesting that fluctuations of pressure in the shallow subsurface may have driven both seismicity and velocity changes. Velocity changes during the remainder of the eruption likely result from a complex interplay of multiple effects and are not well explained by any single factor alone, highlighting the need for complementary geophysical data when interpreting velocity changes.

Journal of Geophysical Research B: Solid Earth↗
USGS2015

A broader definition of occupancy: A reply to Hayes and Monofils

Occupancy models are widely used to analyze presence&ndash;absence data for a variety of taxa while accounting for observation error (MacKenzie et al. 2002, 2006; Tyre et al. 2003; Royle and Dorazio 2008). Hayes and Monfils (2015) question their use for analyzing avian point count data based on purported violations of model assumptions incurred by avian mobility. Animal mobility is an important consideration, not just for occupancy models, but for a variety of population and habitat models (Boyce 2006, Royle et al. 2009, Manning and Goldberg 2010, Dormann et al. 2013, Renner et al. 2015). Nevertheless, we believe the ultimate conclusions of Hayes and Monfils are shortsighted mainly due to a narrow interpretation of occupancy. Rather than turn away from the use of occupancy models, we believe they remain an appropriate method for analyzing many data sets collected from avian point count surveys. Further, we suggest that there is value in having a broader and more nuanced interpretation of occupancy that incorporates the potential for animal movement.

Journal of Wildlife Management↗
USGS2012

Spatially telescoping measurements for improved characterization of groundwater-surface water interactions

The suite of measurement methods available to characterize fluxes between groundwater and surface water is rapidly growing. However, there are few studies that examine approaches to design of field investigations that include multiple methods. We propose that performing field measurements in a spatially telescoping sequence improves measurement flexibility and accounts for nested heterogeneities while still allowing for parsimonious experimental design. We applied this spatially telescoping approach in a study of ground water-surface water (GW-SW) interaction during baseflow conditions along Lucile Creek, located near Wasilla, Alaska. Catchment-scale data, including channel geomorphic indices and hydrogeologic transects, were used to screen areas of potentially significant GW-SW exchange. Specifically, these data indicated increasing groundwater contribution from a deeper regional aquifer along the middle to lower reaches of the stream. This initial assessment was tested using reach-scale estimates of groundwater contribution during baseflow conditions, including differential discharge measurements and the use of chemical tracers analyzed in a three-component mixing model. The reach-scale measurements indicated a large increase in discharge along the middle reaches of the stream accompanied by a shift in chemical composition towards a regional groundwater end member. Finally, point measurements of vertical water fluxes -- obtained using seepage meters as well as temperature-based methods -- were used to evaluate spatial and temporal variability of GW-SW exchange within representative reaches. The spatial variability of upward fluxes, estimated using streambed temperature mapping at the sub-reach scale, was observed to vary in relation to both streambed composition and the magnitude of groundwater contribution from differential discharge measurements. The spatially telescoping approach improved the efficiency of this field investigation. Beginning our assessment with catchment-scale data allowed us to identify locations of GW-SW exchange, plan measurements at representative field sites and improve our interpretation of reach-scale and point-scale measurements.

Alaska↗
USGS2006

Influence of deflection on a fold-to-fault progression: field evidence from near Marietta, South Carolina

Four periods of deformation (D1-D4) are recognized in the Lion Park Road borrow pit near Marietta, South Carolina. Although each period is characterized by distinct structures, D3 produced two structural styles (D3a, D3b) resulting from layer-parallel shortening. D3a is characterized by detachment folding at the tip of an underlying thrust. D3b is a fold-to-fault progression that was localized by east-dipping, quartz-filled gash fractures. The fold-to-fault progression demonstrates the influence of a mechanical anisotropy on ramp development. The early stages of D3b were formed by deflection of northwest-directed, layer-parallel shortening and active, down-section propagation of folds and thrusts. Following connection with a splay of basal detachment, later D3b stages resulted from up-section movement that produced kink folding and a throughgoing thrust. This up-section movement deformed and modified the geometries of older, down-section structures. Detailed mesoscopic field observations, integrated with a combination of current thrust fault models, are used to interpret the D3b fold-to-fault progression. ?? 2006 Elsevier Ltd. All rights reserved.

Journal of Structural Geology↗
USGS2019

Lithospheric signature of late Cenozoic extension in electrical resistivity structure of the Rio Grande rift, New Mexico, USA

We present electrical resistivity models of the crust and upper mantle from two‐dimensional (2‐D) inversion of magnetotelluric (MT) data collected in the Rio Grande rift, New Mexico, USA. Previous geophysical studies of the lithosphere beneath the rift identified a low‐velocity zone several hundred kilometers wide, suggesting that the upper mantle is characterized by a very broad zone of modified lithosphere. In contrast, the surface expression of the rift (e.g., high‐angle normal faults and synrift sedimentary units) is confined to a narrow region a few tens of kilometers wide about the rift axis. MT data are uniquely suited to probing the depths of the lithosphere that fill the gap between surface geology and body wave seismic tomography, namely the middle to lower crust and uppermost mantle. We model the electrical resistivity structure of the lithosphere along two east‐west trending profiles straddling the rift axis at the latitudes of 36.2 and 32.0°N. We present results from both isotropic and anisotropic 2‐D inversions of MT data along these profiles, with a strong preference for the latter in our interpretation. A key feature of the anisotropic resistivity modeling is a broad (~200‐km wide) zone of enhanced conductivity (<20 Ωm) in the middle to lower crust imaged beneath both profiles. We attribute this lower crustal conductor to the accumulation of free saline fluids and partial melt, a direct result of magmatic activity along the rift. High‐conductivity anomalies in the midcrust and upper mantle are interpreted as fault zone alteration and partial melt, respectively.

New Mexico↗
USGS2013

2D IR spectra of cyanide in water investigated by molecular dynamics simulations

Using classical molecular dynamics simulations, the 2D infrared (IR) spectroscopy of CN − solvated in D 2 O is investigated. Depending on the force field parametrizations, most of which are based on multipolar interactions for the CN − molecule, the frequency-frequency correlation function and observables computed from it differ. Most notably, models based on multipoles for CN − and TIP3P for water yield quantitatively correct results when compared with experiments. Furthermore, the recent finding that T 1 times are sensitive to the van der Waals ranges on the CN − is confirmed in the present study. For the linear IR spectrum, the best model reproduces the full widths at half maximum almost quantitatively (13.0 cm −1 vs. 14.9 cm −1 ) if the rotational contribution to the linewidth is included. Without the rotational contribution, the lines are too narrow by about a factor of two, which agrees with Raman and IR experiments. The computed and experimental tilt angles (or nodal slopes) α as a function of the 2D IR waiting time compare favorably with the measured ones and the frequency fluctuation correlation function is invariably found to contain three time scales: a sub-ps, 1 ps, and one on the 10-ps time scale. These time scales are discussed in terms of the structural dynamics of the surrounding solvent and it is found that the longest time scale (≈10 ps) most likely corresponds to solvent exchange between the first and second solvation shell, in agreement with interpretations from nuclear magnetic resonance measurements.

Journal of Chemical Physics↗
USGS2024

Insights on arc magmatic systems drawn from natural melt inclusions and crystallization experiments at P H2O =800 MPa under oxidizing conditions

Whole rock compositions at Buldir Volcano, western Aleutian arc, record a strong, continuous trend of iron depletion with decreasing MgO, classically interpreted as a calc-alkaline liquid line of descent. In contrast, olivine-hosted melt inclusions have higher total iron (FeO * ) than whole rocks and show little change in FeO* with decreasing MgO. To investigate this discrepancy and determine the conditions required for strong iron depletion, we conducted oxygen fugacity (ƒO 2 ) buffered, water-saturated crystallization experiments at 800 MPa and ƒO 2 = QFM + 1.6 ± 0.4 (1σ⁠) (where QFM refers to the quartz-fayalite-magnetite buffer) on a high-Al, basaltic starting material modeled after a Buldir lava. Experimental conditions were informed by olivine-hosted melt inclusions that record minimum entrapment pressures as high as 570 MPa, >6 wt % H2O, and ƒO 2 of QFM + 1.4 (±0.2), making Buldir one of the most oxidized and wettest arc volcanoes documented globally. The experiments produce melts with Si-enrichment and Fe-depletion signatures characteristic of evolved, calc-alkaline magmas at the lowest MgO, although FeO * remains roughly constant over most of the experimental temperature range. Experiments saturate CrAl-spinel and olivine at 1160°C, followed by clinopyroxene and Al-spinel at 1085°C, hornblende at 1060°C, and, finally, plagioclase and magnetite between 1040°C and 960°C. Hornblende crystallization, not magnetite, generates the largest increase in SiO2 and largest decrease in FeO * in coexisting melts. Compositions of melt inclusions are consistent with experimental melts and reflect crystallization of a basaltic parent magma at high P H2O . In contrast, the whole rock compositional trends are influenced by magma mixing and phenocryst redistribution and accumulation. The crystallization experiments and natural liquids (melt inclusions and groundmass glass) from Buldir suggest that for an oxidized, hydrous primary basalt starting composition, significant Fe depletion from the melt will not occur until intermediate to late stages of magma crystallization (< ~4.5 wt % MgO). We conclude that the Buldir whole rock trend cannot be reproduced by crystallization at arc-relevant oxygen fugacities and is not a true liquid line of descent, warranting caution when interpreting volcanic trends globally.

Journal of Petrology↗
USGS2008

40Ar/39Ar data for white mica, biotite, and K-feldspar samples from low-grade metamorphic rocks in the Westminster Terrane and adjacent rocks, Maryland

This report contains reduced 40 Ar/ 39 Ar data of white mica and K-feldspar mineral separates and matrix of a whole rock phyllite, all from low-grade metamorphic rocks of the Westminster terrane and adjacent strata in central Maryland. This report presents these data in a preliminary form, but in more detail than can be accommodated in todays professional journals. Also included in this report is information on the location of the samples and a brief description of the samples. The data contained herein are not interpreted in a geological context, and care should be taken by readers unfamiliar with argon isotopic data in the use of these results; many of the individual apparent ages are not geologically meaningful. This report is primarily a detailed source document for subsequent publications that will integrate these data into a geological context.

Maryland↗