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At least 1,765 records · Page 98Linked to original sources

USGS2025

Detection of deer at remote camera sites in relation to snow conditions

In the rain-snow transition zone of the Pacific Northwest, climate change is expected to alter the incidence of rain-on-snow and freeze-thaw events, which will change snow density and hardness dynamics. In winter, the ability of economically and ecologically important wildlife species, such as deer ( Odocoileus spp.), to efficiently move through the landscape and access forage is mediated by snow conditions. Therefore, snow properties such as density and hardness can directly affect how energetically costly it is for these animals to survive. However, little is known about whether and how ungulates use habitats based on snow density and hardness. We deployed a stratified network of remote camera stations in complex forested terrain in Latah County, Idaho, USA, to remotely measure snow depth and detect deer. We also collected snow density and hardness measurements throughout the winter. We used these data to determine the degree to which the probability of deer presence at cameras could be explained by snow conditions and air temperature. Snow depth and density had negative relationships with the probability of deer presence, while ram resistance (a proxy for snow hardness) had a marginal positive effect. We were able to estimate snow conditions important to deer in winter 2020–2021 primarily using data obtained from cameras. This provides an important proof-of-concept that can be applied at different sites and climate conditions to gain a deeper understanding of how deer are affected by snowpack properties. These methods can be used by managers to determine how ungulates are affected by snow depth, density, and hardness collectively and subsequently inform ungulate management in a changing climate.

Idaho↗

USGS2025

Evaluation of the acute toxicity of the piscicide TFM to Burbot

Non-target animal sensitivity remains a concern when treating Laurentian Great Lakes streams with 4-nitro-3-(trifluoromethyl)phenol (TFM), the main pesticide used to control Sea Lamprey Petromyzon marinus as part of the bi-national Great Lakes Fishery Commission's Sea Lamprey Control Program. Populations of Burbot Lota lota , a historically and culturally important fish, inhabit some of the streams that are treated with TFM. While many species of fish inhabiting the Great Lakes streams have been assessed for sensitivity to TFM, we are not aware of previous research to assess the risk to Burbot. We assessed the sensitivity of Burbot to TFM using replicate 12-hour flow-through diluter toxicity tests. We found Burbot to have a median lethal concentration (LC 50 ) of 9.74 mg/L, while the minimum lethal concentration (LC 99.9 ) for Sea Lamprey was predicted to be 2.5 mg/L in similar waters. The resulting toxicity ratio (LC 50 of non-target organism/LC 99.9 of Sea Lamprey) of Burbot was 3.90, well above the toxicity ratios for known sensitive species. Our results suggest Burbot are not expected to be adversely affected during a typical TFM stream treatment.

Great Lakes↗

USGS2014

A test of the compensatory mortality hypothesis in mountain lions: a management experiment in West-Central Montana

Mountain lions ( Puma concolor ) are widely hunted for recreation, population control, and to reduce conflict with humans, but much is still unknown regarding the effects of harvest on mountain lion population dynamics. Whether human hunting mortality on mountain lions is additive or compensatory is debated. Our primary objective was to investigate population effects of harvest on mountain lions. We addressed this objective with a management experiment of 3 years of intensive harvest followed by a 6-year recovery period. In December 2000, after 3 years of hunting, approximately 66% of a single game management unit within the Blackfoot River watershed in Montana was closed to lion hunting, effectively creating a refuge representing approximately 12% (915 km 2 ) of the total study area (7,908 km 2 ). Hunting continued in the remainder of the study area, but harvest levels declined from approximately 9/1,000 km 2 in 2001 to 2/1,000 km 2 in 2006 as a result of the protected area and reduced quotas outside. We radiocollared 117 mountain lions from 1998 to 2006. We recorded known fates for 63 animals, and right-censored the remainder. Although hunting directly reduced survival, parameters such as litter size, birth interval, maternity, age at dispersal, and age of first reproduction were not significantly affected. Sensitivity analysis showed that female survival and maternity were most influential on population growth. Life-stage simulation analysis (LSA) demonstrated the effect of hunting on the population dynamics of mountain lions. In our non-hunted population, reproduction (kitten survival and maternity) accounted for approximately 62% of the variation in growth rate, whereas adult female survival accounted for 30%. Hunting reversed this, increasing the reliance of population growth on adult female survival (45% of the variation in population growth), and away from reproduction (12%). Our research showed that harvest at the levels implemented in this study did not affect population productivity (i.e., maternity), but had an additive effect on mountain lion mortality, and therefore population growth. Through harvest, wildlife managers have the ability to control mountain lion populations.

Montana↗

USGS2014

Book review: Spatial capture-recapture

Understanding how animals use space is a vital aspect of conservation planning and wildlife management. Technological developments (e.g., increased computer power and desktop geographic information system [GIS] applications) are bringing the ability to analyze spatial data sets to the individual biologist. Therefore, it is not surprising that methodologies have been developed to incorporate space into capture-recapture models, which are some of the most fundamental models in the field of wildlife ecology. Spatial Capture-Recapture (hereafter SCR) is a timely and informative contribution that summarizes the history and motivation behind SCR models, in addition to providing details of the methodological framework that allows the reader to develop and customize SCR models to address their own ecological questions. Review info: Spatial Capture-Recapture. By J. Andrew Royle, Richard B. Chandler, Rahel Sollmann, and Beth Gardner, 2014. ISBN: 978-0124059399, 577 pp.

Journal of Wildlife Management↗

USGS2014

Effect of hunter selectivity on harvest rates of radio-collared white-tailed deer in Pennsylvania

Radio transmitters are a commonly used tool for monitoring the fates of harvested species, although little research has been devoted to whether a visible radio transmitter changes a hunters' willingness to harvest that animal. We initially surveyed deer hunters to assess their willingness to harvest radio-collared deer and predicted radio collars were unlikely to affect the harvest of antlerless deer, but hunters may be less willing to harvest small-antlered males with radio collars compared to large-antlered males. We fitted white-tailed deer ( Odocoileus virginianus ) with radio collars that were visible to hunters or with ear-tag transmitters or ear-tags that were difficult to detect visually and estimated if harvest rates differed among marking methods. For females, the best model failed to detect an effect of radio collars on harvest rates. Also, we failed to detect a difference between male deer fitted with radio collars and ear-tag transmitters. When we compared males fitted with radio collars versus ear tags, we found harvest rate patterns were opposite to our predictions, with lower harvest rates for adult males fitted with radio collars and higher harvest rates for yearling males fitted with radio collars. Our study suggests that harvest rate estimates generated from a sample of deer fitted with visible radio collars can be representative of the population of inference.

Pennsylvania↗

USGS2015

Species richness and distributions of boreal waterbirds in relation to nesting and brood-rearing habitats

Identification of ecological factors that drive animal distributions allows us to understand why distributions vary temporally and spatially, and to develop models to predict future changes to populations–vital tools for effective wildlife management and conservation. For waterbird broods in the boreal forest, distributions are likely driven by factors affecting quality of nesting and brood-rearing habitats, and the influence of these factors may extend beyond singles species, affecting the entire waterbird community. We used occupancy models to assess factors influencing species richness of waterbird broods on 72 boreal lakes, along with brood distributions of 3 species of conservation concern: lesser scaup ( Aythya affinis ), white-winged scoters ( Melanitta fusca ), and horned grebe ( Podiceps auritus ). Factors examined included abundance of invertebrate foods (Amphipoda, Diptera, Gastropoda, Hemiptera, Odonata), physical lake attributes (lake area, emergent vegetation), water chemistry (nitrogen, phosphorus, chlorophyll a concentrations), and nesting habitats (water edge, non-forest cover). Of the 5 invertebrates, only amphipod density was related to richness and occupancy, consistently having a large and positive relationship. Despite this importance to waterbirds, amphipods were the most patchily distributed invertebrate, with 17% of the study lakes containing 70% of collected amphipods. Lake area was the only other covariate that strongly and positively influenced species richness and occupancy of scaup, scoters, and grebes. All 3 water chemistry covariates, which provided alternative measures of lake productivity, were positively related to species richness but had little effect on scaup, scoter, and grebe occupancy. Conversely, emergent vegetation was negatively related to richness, reflecting avoidance of overgrown lakes by broods. Finally, nesting habitats had no influence on richness and occupancy, indicating that, at a broad spatial scale, brood distributions are largely driven by the presence of quality brood-rearing lakes, not nesting habitats. Our findings are relevant to generating conservation plans or management goals; specifically, boreal lakes with abundant amphipods and surface areas >25 ha are important habitat for waterbird broods and merit conservation, especially given the patchy distribution of amphipods. Moreover, these high quality brood-rearing lakes are much rarer, and thus more constraining, than are quality nesting habitats, which are likely abundant in the boreal.

Alaska↗

USGS2015

Rapid growth and genetic diversity retention in an isolated reintroduced black bear population in the central appalachians

Animal reintroductions are important tools of wildlife management to restore species to their historical range, and they can also create unique opportunities to study population dynamics and genetics from founder events. We used non-invasive hair sampling in a systematic, closed-population capture-mark-recapture (CMR) study design at the Big South Fork (BSF) area in Kentucky during 2010 and Tennessee during 2012 to estimate the demographic and genetic characteristics of the black bear ( Ursus americanus ) population that resulted from a reintroduced founding population of 18 bears in 1998. We estimated 38 (95% CI: 31–66) and 190 (95% CI: 170–219) bears on the Kentucky and Tennessee study areas, respectively. Based on the Tennessee abundance estimate alone, the mean annual growth rate was 18.3% (95% CI: 17.4–19.5%) from 1998 to 2012. We also compared the genetic characteristics of bears sampled during 2010–2012 to bears in the population during 2000–2002, 2–4 years following reintroduction, and to the source population. We found that the level of genetic diversity since reintroduction as indicated by expected heterozygosity ( H E ) remained relatively constant ( H E(source, 2004)  = 0.763, H E(BSF, 2000–2002)  = 0.729, H E(BSF, 2010–2012)  = 0.712) and the effective number of breeders ( N B ) remained low but had increased since reintroduction in the absence of sufficient immigration ( N B(BSF, 2000–2002)  = 12, N B(BSF, 2010–2012)   = 35). This bear population appears to be genetically isolated, but contrary to our expectations, we did not find evidence of genetic diversity loss or other deleterious genetic effects typically observed from small founder groups. We attribute that to high initial genetic diversity in the founder group combined with overlapping generations and rapid population growth. Although the population remains relatively small, the reintroduction using a small founder group appears to be demographically and genetically sustainable.

Kentucky, Tennessee↗

USGS2015

Spatially explicit modeling of blackbird abundance in the Prairie Pothole Region

Knowledge of factors influencing animal abundance is important to wildlife biologists developing management plans. This is especially true for economically important species such as blackbirds (Icteridae), which cause more than $100 million in crop damages annually in the United States. Using data from the North American Breeding Bird Survey, the National Land Cover Dataset, and the National Climatic Data Center, we modeled effects of regional environmental variables on relative abundance of 3 blackbird species (red-winged blackbird, Agelaius phoeniceus ; yellow-headed blackbird, Xanthocephalus xanthocephalus ; common grackle, Quiscalus quiscula ) in the Prairie Pothole Region of the central United States. We evaluated landscape covariates at 3 logarithmically related spatial scales (1,000 ha, 10,000 ha, and 100,000 ha) and modeled weather variables at the 100,000-ha scale. We constructed models a priori using information from published habitat associations. We fit models with WinBUGS using Markov chain Monte Carlo techniques. Both landscape and weather variables contributed strongly to predicting blackbird relative abundance (95% credibility interval did not overlap 0). Variables with the strongest associations with blackbird relative abundance were the percentage of wetland area and precipitation amount from the year before bird surveys were conducted. The influence of spatial scale appeared small—models with the same variables expressed at different scales were often in the best model subset. This large-scale study elucidated regional effects of weather and landscape variables, suggesting that management strategies aimed at reducing damages caused by these species should consider the broader landscape, including weather effects, because such factors may outweigh the influence of localized conditions or site-specific management actions. The regional species distributional models we developed for blackbirds provide a tool for understanding these broader landscape effects and guiding wildlife management practices to areas that are optimally beneficial. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Iowa, Minnesotta, Montana, Nebraska, North Dakota↗

USGS2015

Feather isotope analysis reveals differential patterns of habitat and resource use in populations of white-winged doves

The white-winged dove ( Zenaida asiatica ) serves an important ecological role as a diurnal pollinator of the saguaro cactus in the Sonoran desert and an economic role as a highly sought after game bird in North America. White-winged doves are intimately linked to anthropogenic changes on the landscape and because of this, have experienced dramatic population fluctuations over the last 75 years in response, both positively and negatively, to anthropogenic changes on the landscape. To understand the factors driving population growth and decline of migratory species like the white-winged dove, it is imperative we study resource use on both their breeding and wintering grounds. To understand how populations are distributed on the wintering grounds, we tested an alternative to band recovery approaches by using stable isotope analysis. Before we could use isotope analysis to link breeding and wintering locations for this species, we first needed to determine if hydrogen (δ 2 H) and carbon (δ 13 C) stable isotopes in feather tissue (δ 2 H f and δ 13 C f , respectively) could differentiate among populations of white-winged doves across their breeding range in Texas, New Mexico, and Arizona. δ 2 H f and δ 13 C f not only differentiated between populations of white-winged doves that breed in the United States, but δ 2 H f also provided further differentiation in white-winged doves that breed in native Sonoran Desert and agricultural habitats in the western portion of their range. Ecological processes associated with desert resources and anthropogenic influences, specifically saguaro cacti and irrigated crops, largely determined δ 2 H f in some white-winged doves in Arizona whereas δ 2 H of precipitation (δ 2 H p ) largely determined δ 2 H f of doves in New Mexico and Texas. This study highlights the usefulness of stable isotope analysis to differentiate populations of animals across the landscape and the insight isotopes can provide into habitat and resource use. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Arizona, California, New Mexico, Texas↗

USGS2015

Connectivity among subpopulations of Louisiana black bears as estimated by a step selection function

Habitat fragmentation is a fundamental cause of population decline and increased risk of extinction for many wildlife species; animals with large home ranges and small population sizes are particularly sensitive. The Louisiana black bear ( Ursus americanus luteolus ) exists only in small, isolated subpopulations as a result of land clearing for agriculture, but the relative potential for inter-subpopulation movement by Louisiana black bears has not been quantified, nor have characteristics of effective travel routes between habitat fragments been identified. We placed and monitored global positioning system (GPS) radio collars on 8 female and 23 male bears located in 4 subpopulations in Louisiana, which included a reintroduced subpopulation located between 2 of the remnant subpopulations. We compared characteristics of sequential radiolocations of bears (i.e., steps) with steps that were possible but not chosen by the bears to develop step selection function models based on conditional logistic regression. The probability of a step being selected by a bear increased as the distance to natural land cover and agriculture at the end of the step decreased and as distance from roads at the end of a step increased. To characterize connectivity among subpopulations, we used the step selection models to create 4,000 hypothetical correlated random walks for each subpopulation representing potential dispersal events to estimate the proportion that intersected adjacent subpopulations (hereafter referred to as successful dispersals). Based on the models, movement paths for males intersected all adjacent subpopulations but paths for females intersected only the most proximate subpopulations. Cross-validation and genetic and independent observation data supported our findings. Our models also revealed that successful dispersals were facilitated by a reintroduced population located between 2 distant subpopulations. Successful dispersals for males were dependent on natural land cover in private ownership. The addition of hypothetical 1,000-m- or 3,000-m-wide corridors between the 4 study areas had minimal effects on connectivity among subpopulations. For females, our model suggested that habitat between subpopulations would probably have to be permanently occupied for demographic rescue to occur. Thus, the establishment of stepping-stone populations, such as the reintroduced population that we studied, may be a more effective conservation measure than long corridors without a population presence in between.

Louisiana↗

USGS2017

Associations between cyanobacteria and indices of secondary production in the western basin of Lake Erie

Large lakes provide a variety of ecological services to surrounding cities and communities. Many of these services are supported by ecological processes that are threatened by the increasing prevalence of cyanobacterial blooms which occur as aquatic ecosystems experience cultural eutrophication. Over the past 10 yr, Lake Erie experienced cyanobacterial blooms of increasing severity and frequency, which have resulted in impaired drinking water for the surrounding communities. Cyanobacterial blooms may impact ecological processes that support other services, but many of these impacts have not been documented. Secondary production (production of primary consumers) is an important process that supports economically important higher trophic levels. Cyanobacterial blooms may influence secondary production because cyanobacteria are a poor‐quality food resource and cyanotoxins may be harmful to consumers. Over 3 yr at 34 sites across the western basin of Lake Erie, we measured three indices of secondary production that focus on the dominant bivalve taxa: (1) growth of a native unionid mussel, (2) the size of young‐of‐year dreissenid mussels, and (3) the mass of colonizing animals on a Hester‐Dendy sampler. Associations between these indices and cyanobacterial data were estimated to assess whether cyanobacteria are associated with variation in secondary production in the western basin of Lake Erie. The results suggest cyanobacterial abundance alone is only weakly associated with secondary production, but that cyanotoxins have a larger effect on secondary production. Given recurring late‐summer cyanobacterial blooms, this impact on secondary production has the potential to undermine Lake Erie's ability to sustain important ecosystem services.

Lake Erie↗

USGS2019

Light exposure along particle flowpaths in large rivers

Sunlight is a critical resource in aquatic systems driving photosynthesis, photodegradation of organic matter and contaminants, animal behavior, and the activity of human pathogens. In rivers, solutes, materials, and organisms are turbulently mixed across the water column during downstream transport and exposed to highly variable sunlight. However, there are no measurements of suspended particles' sunlight exposure during downstream transport to characterize this variability, and it is unclear if current measurement approaches and optical theory capture the light exposure of suspended particles. We deployed neutrally buoyant drifters and stationary buoys in the Upper Mississippi (WI, U.S.A.) and Neuse Rivers (NC, U.S.A.) to measure underwater sunlight from the perspective of suspended particles. In our study sites, underwater sunlight varied more along flowpaths measured by drifters than over time measured by fixed‐site buoys; sunlight exposure along flowpaths was dominated by bursts of light (sunflecks) that accounted for 62–99% of the cumulative sunlight exposure; and modeled sunlight exposure using optical theory was consistently 56–1700% higher than measured sunlight exposure along flowpaths. Our results suggested that suspended particles in the study reaches experienced darker conditions than predicted and have important implications for how to quantify underwater sunlight in rivers.

North Carolina, Wisconsin↗

USGS2022

Phenological variation in spring migration timing of adult alewife (Alosa pseudoharengus) in coastal Massachusetts

The timing of biological events in plants and animals, such as migration and reproduction, is shifting due to climate change. Anadromous fishes are particularly susceptible to these shifts as they are subject to strong seasonal cycles when transitioning between marine and freshwater habitats to spawn. We used linear models to determine the extent of phenological shifts in adult Alewife Alosa pseudoharengus as they migrated from ocean to freshwater environments during spring to spawn at 12 sites along the northeastern USA. We also evaluated broadscale oceanic and atmospheric drivers that trigger their movements from offshore to inland habitats, including sea surface temperature, North Atlantic Oscillation index, and Gulf Stream index. Run timing metrics of initiation, median (an indicator of peak run timing), end, and duration were found to vary among sites. Although most sites showed negligible shifts towards earlier timing, statistically significant changes were detected in three systems. Overall, winter sea surface temperature, spring and fall transition dates, and annual run size were the strongest predictors of run initiation and median dates, while a combination of within-season and seasonal-lag effects influenced run end and duration timing. Disparate results observed across the 12 spawning runs suggest that regional environmental processes were not consistent drivers of phenology and local environmental and ecological conditions may be more important. Additional years of data to extend time series and monitoring of Alewife timing and movements in nearshore habitats may provide important information about staging behaviors just before adults transition between ocean and freshwater habitats.

Massachusetts↗

USGS2019

A brief introduction to integrated pest management for aquatic systems

Aquatic invasive plants and animals are increasingly becoming a problem, causing severe economic and ecological damage to critical freshwater systems. The best strategy for controlling an invasive pest employs an integrated pest management (IPM) approach using a combination of biological, physical, chemical, and social/cultural control methods. Here, we examine the history and development of IPM and provide a discussion of the components of an IPM program involving development, evaluation, and management. Control approaches will be reviewed and the application of this technique to aquatic systems will be discussed. A discussion of the Great Lakes Fishery Commission's (GLFC) Integrated Management of Sea Lamprey Petromyzon marinus Control Program will be provided to illustrate the application of IPM to an aquatic system.

North American Journal of Fisheries Management↗

USGS2023

Tagger effects in aquatic telemetry: Short-term and delayed impacts of surgery in Atlantic salmon smolts

Objective An assumption of biotelemetry is that animal performance is unaffected by the tagging process and tag burden, yet this assumption is often untested or not thoroughly explored. Our objective was to explore how transmitter implantation procedures influenced Atlantic Salmon Salmo salar smolt survival and migratory performance. Methods We monitored radio-tagged smolts, first in the hatchery and then in a river with a receiver array. We assessed survival and in-river performance in relation to surgeon, surgery duration, processing order, and fish size. Results Mortality was 13.3% during an 8-day hatchery-observation but was higher for fish processed by one of two experienced surgeons (25% vs. 2%). Mortality peaked three days post-surgery and was higher for smaller fish and fish tagged during morning tagging sessions (compared to afternoons). The size effect changed over time, being greatest during the first two days post-surgery, and continuing thereafter at a diminished level. Fish performance once released into a river also differed between surgeons (migration initiation 66% vs. 82%; and to-lake migration success 22% vs 43%), and consistent with hatchery observations, fish tagged in the morning by one surgeon performed poorly once released. Conclusion We highlight immediate and lingering effects of surgical procedures on smolt survival that, if not accounted for, could bias inferences about the study population. Researchers should anticipate tagger effects during study design to ensure potential tagger effects (i.e., surgeon, order tagged, conditions during tagging) are balanced across study groups of interest. Testing for a fixed tagger effect in analyses may not always be adequate because a tagger effect may covary with processing order and fish size and may change over time.

North American Journal of Fisheries Management↗

USGS2025

Hosts, pathogens and hot ponds: Thermal mean and variability contribute to spatial patterns of chytrid infection

Temperature is a primary driver of heterogeneity in host–pathogen dynamics and understanding how patch-scale temperature affects landscape-scale patterns of pathogen infection is key to effective monitoring and management. In field studies, both temperature variability and mean temperature are often related to infection of ectothermic animals by fungal pathogens, and although these factors vary spatiotemporally, their contributions to infection outcomes are rarely decomposed into spatial and temporal components. We studied how patch-scale thermal conditions (mean and variability) affect infection of eastern newts Notophthalmus viridescens by Batrachochytrium dendrobatidis ( Bd ), with a special focus on disentangling spatial versus temporal contributions of thermal conditions to infection outcomes. We measured in situtemperature and Bd infection across 20 ponds in two years in southeastern Wisconsin, USA to 1) understand thermal mediation of infection and 2) quantify whether seasonal and/or among-site variation in thermal conditions drive heterogeneity in host–pathogen interactions. In our system, thermal mean and variability covaried tightly, necessitating the creation of a single index to capture both components. We found that 1) this index of thermal mean and variability was strongly and nonlinearly related to Bd infection and 2) differences among patches in thermal conditions drove this relationship, highlighting that variation in patch-level conditions can drive heterogenous host–pathogen outcomes across landscapes. Our research collectively reveals insights about the importance of local, patch-level conditions for mediating disease risk at broader scales.

Wisconsin↗

USGS2003

Two new organic reference materials for δ13C and δ15N measurements and a new value for the δ13C of NBS 22 oil

Analytical grade L-glutamic acid is chemically stable and has a C/N mole ratio of 5, which is close to that of many of natural biological materials, such as blood and animal tissue. Two L-glutamic acid reference materials with substantially different 13 C and 15 N abundances have been prepared for use as organic reference materials for C and N isotopic measurements. USGS40 is analytical grade L-glutamic acid and has a δ 13 C value of −26.24‰ relative to VPDB and a δ 15 N value of −4.52‰ relative to N 2 in air. USGS41 was prepared by dissolving analytical grade L-glutamic acid with L-glutamic acid enriched in 13 C and 15 N. USGS41 has a δ 13 C value of +37.76‰ and a δ 15 N value of +47.57‰. The δ 13 C and δ 15 N values of both materials were measured against the international reference materials NBS 19 calcium carbonate ( δ 13 C = +1.95‰), L-SVEC lithium carbonate ( δ 13 C = −46.48‰), IAEA-N-1 ammonium sulfate ( δ 15 N = 0.43‰), and USGS32 potassium nitrate ( δ 15 N = 180‰) by on-line combustion continuous-flow and off-line dual-inlet isotope-ratio mass spectrometry. Both USGS40 and USGS41 are isotopically homogeneous; reproducibility of δ 13 C is better than 0.13‰, and that of δ 15 N is better than 0.13‰ in 100-μg amounts. These two isotopic reference materials can be used for (i) calibrating local laboratory reference materials, and (ii) quantifying drift with time, mass-dependent fractionations, and isotope-ratio-scale contraction in the isotopic analysis of various biological materials. Isotopic results presented in this paper yield a δ 13 C value for NBS 22 oil of −29.91‰, in contrast to the commonly accepted value of −29.78‰ for which off-line blank corrections probably have not been quantified satisfactorily.

Rapid Communications in Mass Spectrometry↗

USGS2010

A counter-intuitive approach to calculating non-exchangeable 2 H isotopic composition of hair: treating the molar exchange fraction f E as a process-related rather than compound-specific variable

Hair is a keratinous tissue that incorporates hydrogen from material that an animal consumes but it is metabolically inert following synthesis. The stable hydrogen isotope composition of hair has been used in ecological studies to track migrations of mammals as well as for forensic and archaeological purposes to determine the provenance of human remains or the recent geographic life trajectory of living people. Measurement of the total hydrogen isotopic composition of a hair sample yields a composite value comprised of both metabolically informative, non-exchangeable hydrogen and exchangeable hydrogen, with the latter reflecting ambient or sample preparation conditions. Neither of these attributes is directly measurable, and the non-exchangeable hydrogen composition is obtained by estimation using a commonly applied mathematical expression incorporating sample measurements obtained from two distinct equilibration procedures. This commonly used approach treats the fraction of exchangeable hydrogen as a mixing ratio, with a minimal procedural fractionation factor assumed to be close or equal to 1. Instead, we propose to use full molar ratios to derive an expression for the non-exchangeable hydrogen composition explicitly as a function of both the procedural fractionation factor α and the molar hydrogen exchange fraction f E . We apply these derivations in a longitudinal study of a hair sample and demonstrate that the molar hydrogen exchange fraction f E should, like the procedural fractionation factor α, be treated as a process-dependent parameter, i.e. a reaction-specific constant. This is a counter-intuitive notion given that maximum theoretical values for the molar hydrogen exchange fraction f E can be calculated that are arguably protein-type specific and, as such, f E could be regarded as a compound-specific constant. We also make some additional suggestions for future approaches to determine the non-exchangeable hydrogen composition of hair and the use of standards.

Rapid Communications in Mass Spectrometry↗