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At least 1,783 records · Page 99Linked to original sources
USGS2025

An empirical test of maximum depositional age through paired LA-ICP-MS and CA-ID-TIMS detrital zircon analysis with implications for the “Nevadan orogeny” in the Sierra Nevada foothills, California, U.S.A.

The interpretation of maximum depositional age (MDA) from U-Pb detrital zircon data acquired via laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) or secondary ion mass spectrometry (SIMS) is now routine; however, to date only a few studies have presented tests of such MDAs by subsequently analyzing a subset of the same detrital zircon grains with the more accurate and precise chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) method. We first generated LA-ICP-MS dates and MDAs from three turbidite sandstone samples of the Late Jurassic Mariposa Formation (Sierra Nevada foothills, California) containing large proportions of young detrital zircon grains (at the time of sediment deposition). We then removed 4–5 of the apparent youngest grains from the epoxy mount and analyzed them with CA-ID-TIMS. Despite a lack of low Th/U or high U (ppm) characteristics that might indicate U-Pb system disturbance, all LA-ICP-MS dates are younger than corresponding CA-ID-TIMS dates, on the same grain, by up to 11.8 m.y. when considered as point estimates. Only two out of 13 paired analyses overlap within error at 95% confidence. We interpret MDAs from our CA-ID-TIMS dates to be the youngest CA-ID-TIMS dates (YTDs). LA-ICP-MS MDAs based on fewer dates from the young tail of the youngest date distribution perform the worst (i.e., furthest from CA-ID-TIMS MDAs), whereas LA-ICP-MS MDA methods that incorporate more dates from the youngest date distribution perform better; the best performing method in all cases is the maximum likelihood algorithm–minimum. The performance of tested LA-ICP-MS MDA methods is improved by removing statistical outlier dates and by removing visually young “outlier” dates that drift away from the primary distribution of young dates. Our paired LA-ICP-MS/CA-ID-TIMS MDA workflow shows that the accuracy of MDA can be significantly improved by conducting CA-ID-TIMS on as few as four grains from a sample. The combination of our new CA-ID-TIMS MDAs with published CA-ID-TIMS analyses and petrochronology on the nearby Guadalupe igneous complex provides sub-million-year resolution of contemporaneous igneous and sedimentary systems during deformation and clarifies the timing of regional deformation that defines the local “Nevadan orogeny.” Rocks in the upper plate of the Bear Mountains fault zone have a CA-ID-TIMS YTD MDA of 151.71 ± 0.23 Ma, and rocks of the lower plate have a CA-ID-TIMS YTD MDA of 149.92 ± 0.11 Ma. These new MDAs, in conjunction with the observation of fabric-bearing Mariposa Formation xenoliths in the ca. 149.65 ± 0.10 Ma Guadalupe igneous complex, suggest that rocks in the upper plate of the Bear Mountains fault zone represent a slightly older (~2 m.y.) section of Mariposa Formation that was deformed and intruded prior to being juxtaposed against, and further deformed with, a slightly younger lower-plate section of Mariposa Formation in actively deforming, fault-bounded basins. Our observations are not consistent with traditional models that require that sedimentation of the Mariposa Formation ended by ca. 155 Ma. Instead, we interpret our data to be consistent with other evidence for a continuum of deformation in Late Jurassic to Early Cretaceous time and document that the regional “slatey cleavage” observed in the greater Mariposa Formation and used to define the “Nevadan orogeny” in our study area is largely younger than 149.92 ± 0.11 Ma.

California↗
USGS2025

Spatial distribution and relative biomass of bigheaded carps in Lake Balaton, Hungary estimated from an environmental DNA survey

Silver carp ( Hypophthalmichthys nobilis ), bighead carp ( H. molitrix ) and their hybrids, collectively known as bigheaded carps, have been introduced to Lake Balaton, Hungary. The current stock sizes are difficult to assess. We investigated environmental DNA (eDNA) techniques targeted for bigheaded carps, assessed the spatial distribution of eDNA in Lake Balaton, compared eDNA concentrations to environmental variables to assess potential habitat selection based on those variables, and provided an estimate of biomass of bigheaded carps relative to eDNA shedding rates per unit biomass observed in controlled experiments. Water samples were collected from 70 sites in an array across the lake. Biomass estimation was calculated using mean eDNA concentration obtained by quantitative PCR of the samples and previously determined eDNA shedding rates of bigheaded carps under controlled conditions in a laboratory. Concentration of eDNA was highly variable between sites, resulting in wide confidence intervals. Basins did not significantly differ in eDNA concentration, and there were no strong relationships between environmental variables and eDNA concentration, indications that bigheaded carps use the entire lake. The model provided an estimate of 4,830 metric tonnes (2,750–8,030 tonnes) of bigheaded carps in Lake Balaton, or 81.0 kg/ha. The eDNA method produced a value close to previous estimates by traditional means of total biomass of bigheaded carps in the lake, and like traditional methods, there was a broad confidence interval on the estimate of the mean. The results of the present study support the utility of aquatic eDNA analysis, and the need for further comparisons with fisheries methods and supporting data from laboratory studies.

Lake Balaton↗
USGS2025

Development of genomic markers for monitoring and research on plethodontid salamanders

Despite the importance of plethodontid salamanders and their vulnerability to ongoing environmental change, they are inherently difficult to monitor due to their cryptic nature. Recent advances in genomics have created new opportunities for monitoring of populations and their responses to environmental perturbations. In this study, we developed a new target capture-based genomic panel for the purposes of genetic monitoring in plethodontid salamanders. We demonstrate its utility in several distantly related species and present an example application in two representative species with co-occurring distributions but different ecological attributes and expected patterns of population structure: Plethodon jordani and Desmognathus wrighti . Although the number of successfully assembled loci declined with phylogenetic distance from the original reference species ( Desmognathus spp), we obtained high-quality data from thousands of loci from species in all four genera tested ( Desmognathus , Plethodon , Eurycea , and Gyrinophilus ), which span the deepest split in Plethodontidae. Landscape genetic analyses detected weak but statistically significant geographic structure in P. jordani , and much stronger geographic structure in D. wrighti , as expected based on the lower population density and likely lower dispersal ability of D. wrighti . Our target capture panel is broadly applicable across salamanders in Plethodontidae and has the potential to provide data for a wide range of phylogenetic, biogeographic, and population genetics research questions.

North Carolina, Tennessee↗
USGS2025

Missing data in ecology: Syntheses, clarifications, and considerations

In ecology and related sciences, missing data are common and occur in a variety of different contexts. When missing data are not handled properly, subsequent statistical estimates tend to be biased, inefficient, and lack proper confidence interval coverage. Missing data are often grouped into three categories: missing completely at random (MCAR), missing at random (MAR), and missing not at random (MNAR). We review each category and compare their benefits and drawbacks. We review several approaches to handling missing data including complete case analysis, imputation, inverse probability weighting, and data augmentation. We clarify what types of variables should accompany imputation methods and how those variables are influenced by the analysis methods. Additionally, we discuss missing data that lack a formal basis for measurement and hence are fundamentally different from MCAR, MAR, and MNAR missing data. Throughout, we introduce concepts and numeric examples using both simulated data and data from the United States Environmental Protection Agency's 2016 National Wetland Condition Assessment. We conclude by providing five considerations for ecologists and other scientists handling missing data.

Ecological Monographs↗
USGS2025

Imaging hyporheic exchange by integrating deep learning and physics-informed inversion of time-lapse self-potential data

Self-potential (SP) monitoring is increasingly used for subsurface flow characterization due to its sensitivity to hydrogeological and geochemical processes. However, SP inversion remains challenging due to its ill-posed nature, sparse data coverage, and strong transient noise. This study proposes a hybrid framework to image hyporheic exchange using a time-lapse SP data set monitored from a streamflow site in Oak Ridge, Tennessee. Dipole moment tomography grids generated from the physics-informed numerical inversion is first used to train a Vision Transformer (ViT) model that maps surface SP sequences to 2D source distributions. While the numerical method is more responsive to transient signals, the ViT model better captures persistent spatial structures. Their complementary outputs are jointly analyzed in the spatiotemporal domain to isolate dynamic hyporheic exchange zones and distinguish transient from steady state subsurface flow features. This approach integrates physical inversion and deep learning to enhance interpretability, generalization, and temporal awareness in SP analysis.

Geophysical Research Letters↗
USGS2025

Same view through a different lens: Comparing population trends for North American birds using eBird and the Breeding Bird Survey

Confidently estimating population trends is of vital importance for a wide range of ecological, conservation, and management applications. North America has 2 major data sources for estimating population trends of breeding birds—the North American Breeding Bird Survey (BBS) and the global participatory science project eBird. Because the surveys differ in protocols, coverage, and data analysis, their trend estimates are expected to vary in magnitude, direction, and/or precision for at least some species and regions. Here, we compare independently derived estimates of population change between 2012 and 2022 for every combination of species and bird conservation region (BCR) covered by both surveys ( n = 5,577 combinations) as well as aggregated across entire ranges or within the U.S. or Canada. Uncertainty was substantial for both surveys, though more prevalent for BBS (81% of credibility intervals for estimates included zero) than eBird (34% of confidence intervals overlapped zero). We found agreement of trend directions between the 2 surveys. Only 1.3% of estimated trends were significant in opposite directions between the 2 surveys for all species/BCR combinations, with the median difference in trend magnitude being –0.02% (BBS minus eBird trend). Correlations between the 2 were strongest for estimates that were graded as being high credibility compared to estimates judged to have medium or low credibility. Both surveys were subject to species, taxonomic, and regional effects that influenced agreement. Overall, we show where trend estimates derived from BBS and eBird agree, explore where they diverge, present several comparisons to assist in interpreting results from both surveys, and inform efforts to integrate information from each.

Ornithological Applications↗
USGS2025

Spring weather influences breeding propensity, the most important productivity component for Arctic-nesting lesser snow geese

Animal reproduction is composed of several stages, which collectively determine overall productivity. Yet, it is not fully understood how different productivity components contribute to population change. To bridge this gap, we leveraged integrated population modelling and transient life-table response experiments, together with population-level data on lesser snow geese ( Anser caerulescens caerulescens ) breeding on Wrangel Island, Russia, from 1970 to 2022. We assessed contributions of breeding propensity, clutch size, nest success, egg survival, hatching success and pre-fledging survival to population change, and tested hypotheses about the effects of environmental drivers and density dependence on different components. Breeding propensity contributed the most to variation in population growth, followed by nest success. These two components were negatively affected by the timing of snow melt. We found no overall deleterious effects of climate change on productivity. Density dependence had a positive effect on multiple productivity components, likely through predator swamping. Our results show the importance of breeding propensity to the population dynamics of this long-lived animal, which is notable because this productivity component is often overlooked. Our results also demonstrate that the effects of environmental conditions and density dependence can differ among animal populations of different sizes, locations and life histories.

Wrangel Island↗
USGS2025

Too hot for comfort: Elevated temperatures influence gene expression and exceed thermal tolerance of bigmouth shiners, Ericymba dorsalis

Environmental and associated ecosystem change may affect the persistence of fish species based on their ability to adapt to changing conditions, including decreasing flows and rising water temperatures. Exceeding the thermal tolerances of stream fish will likely result in a loss of ability to maintain metabolic processes. We evaluated the critical thermal maximum (CTmax) of bigmouth shiner ( Ericymba dorsalis ) and analysed the expression of heat shock protein 70 messenger RNA (mRNA) (HSP70) to quantify a thermal stress response over a gradient of temperatures (25°C–31°C). E. dorsalis HSP70 mRNA expression was upregulated in response to temperatures >25°C, indicating a stress response. This study supports the existence of a thermal stress threshold for E. dorsalis . The frequency at which this threshold is exceeded may increase under forecasted future climate scenarios for Nebraska.

Nebraska↗
USGS2025

Refined chronology of late Quaternary eruptions at Harrat Khaybar, Saudi Arabia, with implications for magma dynamics and regional volcanic history

Determining accurate and precise ages for Quaternary volcanic centers is essential for reconstructing volcanic field histories, understanding magmatic processes, and assessing potential hazards or risk. Harrat Khaybar, western Saudi Arabia, is one of the youngest and potentially most active volcanic fields on the Arabian plate, has been active since ca. 1.7 Ma, and is characterized by a spectrum of rock compositions ranging from predominantly alkalic basalt to trachyte and comendite. Previous work in Harrat Khaybar utilizing 40 Ar/ 39 Ar incremental heating geochronology to constrain morphological preservation and superpositional relationships bracketed the volcanic activity into broad age groups in intervals of ∼150 k.y., and the youngest and most compositionally evolved volcanoes, including Jabal Abyad, Jabal Bayda, and Jabal Qidr, were assigned to the age groups between ca. 300 ka and present. Herein, we establish a detailed chronology of prehistoric silicic and historical basaltic eruptions at central Harrat Khaybar using four independent eruption age determination techniques: zircon double-dating (ZDD), which combines 238 U- 230 Th disequilibrium or U-Pb with (U-Th)/He dating; zircon U-Pb dating; cosmogenic 3 He dating; and cosmogenic 36 Cl geochronology. These were employed to accurately date six volcanic centers, including the comenditic Jabal Abyad, Jabal Bayda, Jabal Ibayl, and Jabal Alhayyirah, the trachytic Jabal Aluthmor, and the basaltic Jabal Qidr. Additionally, our previously published 40 Ar/ 39 Ar ages have been recalculated using isochron intercept (nonatmospheric) 40 Ar/ 36 Ar for the trapped Ar component. Our new results reveal that zircon rims from Jabal Abyad and Jabal Bayda define isochron 238 U- 230 Th crystallization ages of 125 ± 4 ka and 144 ± 6 ka, concordant with ZDD eruption ages of 132 ± 4 ka and 149 ± 5 ka, respectively. Zircon U-Pb crystallization and (U-Th)/He eruption ages from Jabal Alhayyirah are concordant at 471 ± 14 ka and 458 ± 18 ka, respectively. Finally, zircons from the nearby Jabal Ibayl yield a U-Pb weighted mean crystallization age of 566 ± 16 ka concordant with the corresponding (U-Th)/He eruption age of 554 ± 12 ka, both of which are notably older than the previously proposed eruption ages of 300−150 ka. Recalculations of published 40 Ar/ 39 Ar ages for the youngest volcanoes at central Harrat Khaybar are now in excellent agreement with new geochronological data. Our new age data reveal several new insights into the development of Harrat Khaybar. It is now clear that the comenditic eruptions do not belong to the same eruptive phase and indicate an extended history during which comendites have episodically punctuated the basaltic volcanism since at least 600 ka. The data indicate that Jabal Ibayl and Jabal Alhayyirah represent separate older volcanic events, whereas the younger Jabal Abyad and Jabal Bayda volcanoes appear to be coeval, and their spatial proximity implies that they share a magmatic lineage and maybe a common plumbing system. Zircon age spectra of the comendites reveal obvious xenocrysts and antecrysts indicating assimilation of basement and plutonic progenitors, but otherwise they define broad unimodal populations of crystallization ages that overlap within error with the respective eruption ages. We interpret this to indicate that zircon crystallization continued up to the time of eruption. The cosmogenic ages of Jabal Aluthmor and Jabal Qidr reveal that these centers erupted as recently as ca. 2000 and 760 years ago, respectively. Broadly coeval young silicic and basaltic eruptions at northern Harrat Rahat, the harrat immediately south of Harrat Khaybar, may imply a shared geodynamic forcing between the two adjacent volcanic fields.

Harrat Khaybar↗
USGS2025

U.S. Geological Survey geomagnetic variometer data: Capitalizing on seismic infrastructure

The U.S. Geological Survey’s Geomagnetism Program is collaborating with the Earthquake Hazards Program and Global Seismographic Network Program to densify magnetic field observations. This collaboration focuses on the installation of magnetometers, or magnetic variometers, at existing seismic stations. Along with improving the density of space weather observations for hazard monitoring, these data can be used to correct colocated magnetic field induced noise in seismic data. Such corrections are especially useful during time periods of large magnetic storms where the magnetic field‐induced instrument noise can be of similar amplitude to earthquake ground‐motion records.

contiguous United States↗
USGS2025

Assessment of coastal and fluvial morphodynamic changes using Structure-for-Motion: A case study of the Sfȃntu Gheorghe Mouth (Danube Delta, Romania)

The ability to accurately map erosion, flooding, and habitat loss in coastal environments is crucial for formulating national strategies aimed at preventing and mitigating the impacts of natural disasters. A fundamental component of this process is the implementation of coastal morphodynamics monitoring through Structure-from-Motion (SfM) techniques, utilizing high-resolution 2D/3D data obtained from aerial photogrammetry. To assess morphodynamic changes over a three-year period (2022 – 2024), several SfM-based photogrammetric studies were conducted, each year, in the Romanian sector of the Danube-Black Sea coastal zone, specifically at the mouth of one of the Danube River distributaries (Sf Gheorghe branch) into the Black Sea, and along the left bank, near Sf Gheorghe locality, located within the Danube Delta Biosphere Reserve (DDBR). The essential equipment for aerial photogrammetry comprises Unmanned Aerial Vehicles (UAVs) and Global Navigation Satellite Systems (GNSS). In this study, the UAV used was a DJI Mavic 3T (Enterprise/Thermal) drone, complemented by two Trimble R12i and R4 GNSS systems, as well as approximately 10 Ground Control Points (GCPs). Data acquisition and processing were carried out using specialized photogrammetric software (Agisoft Metashape) along with various GIS tools (e.g., Blue Marble Geographics Global Mapper and ESRI ArcMap). The photogrammetric products generated for the study, as detailed in this paper, include Digital Elevation Models (DEMs), Digital Terrain Models (DTMs), orthomosaics (orthophotos), and others. At Sfântu Gheorghe beach, a comparison between 2023 and 2024 photogrammetric surveys revealed that the left bank of the Sf. Gheorghe Arm, at the river mouth into the Black Sea, suffered from a twist (erosion) of up to 64 metres. Additionally, on the selected perimetre (total area of 31,910 square meters ) from the beach and dune zone of Sf. Gheorghe, an area of up to 16,202 square meters was eroded between 2023 and 2024. This contrasts with the period between 2022 and 2023, during which deposition predominated. Erosion at the Danube mouths and the adjacent Black Sea coastline is driven by a complex interaction of natural and anthropogenic factors. Natural processes, including subsidence, sea-level rise, and episodic extreme storm events, contribute significantly to coastal dynamics. Meanwhile, human-induced factors, such as upstream hydrotechnical works that limits sediment transport, cutting of navigation canals, as well as the exacerbating effects of climate change, further accelerate erosion. The recent Structure-from-Motion (SfM) surveys provide essential quantitative data, enabling a detailed analysis of both short-term and long-term morphodynamic changes influenced by seasonal variations and extreme hydrometeorological events in this highly dynamic coastal system.

Sfȃntu Gheorghe Mouth (Danube Delta)↗
USGS2025

Predicting secretive species distribution using Bayesian networks with and without expert elicitation: A case study incorporating double-blind peer review

1. Species that are secretive, imperilled and consequently data deficient often re-quire conservation action despite limited available information. In such scenarios, Bayesian networks (BNs) offer a versatile and intuitive approach for utilizing various information sources, including literature reviews, community science data sets and expert knowledge. Although it has been suggested that peer review be incorporated during expert elicitations in a BN modelling context, little information exists about how to implement this approach or about how models constructed using this approach perform. 2. We documented a double-blind peer review approach for expert elicitation in a BN modelling context. Further, we compared BN models that were generated by experts who engaged in this peer-review process (PRBNs) to those that were generated by a single expert whose knowledge was supplemented only by a literature review (LRBNs). These comparisons were based on the ability to predict the occurrence (via community science and satellite telemetry data) of a secretive and data deficient species, the King Rail ( Rallus elegans ), throughout a large region. 3. We found that the LRBNs tended to predict King Rail occurrence as well as, or better than, the PRBNs. The LRBNs that we evaluated provided more consistent predictions across our study area. However, preliminary data suggest that the PRBNs may better distinguish between locations of focal and non-focal species within smaller regions. 4. Practical implication. Our framework for utilizing double-blind peer review could serve as a useful guide and have practical implications for incorporating expert knowledge in BN models. Further, our model comparison case study suggests that, in some contexts, a single expert who uses a literature review to inform the creation of BN models may be able to accurately predict the occurrence of a secretive and data-deficient focal species. Taken together, this information could help ecologists decide when a double-blind peer review approach to expert elicitation is necessary and how to implement this approach in a BN modelling context.

Arkansas, Louisiana, Mississippi, Missouri, Tennes↗
USGS2025

The influence of postfire root strength decay on shallow landslide susceptibility in western Oregon

Severe wildfires can increase the potential for postfire landslides, partly due to the loss of vegetation and root reinforcement. This study investigates the multi-year dynamics of root strength following wildfire in coniferous forests of western Oregon and evaluates implications for postfire slope stability. Root tensile strength was measured through laboratory testing of 969 roots collected from 26 test pits over four postfire timeframes: unburned conditions, 4–12 months postfire (Cedar Creek, 2022), 24–35 months postfire (Holiday Farm, 2020), and 59–67 months postfire (Eagle Creek, 2017). Variables analyzed include root diameter, tensile thread strength, stiffness, progressive tensile strength with displacement, time-dependent strength and ductility, root area ratio, and cohesion. Results indicate a 50% reduction in root strength after wildfire, with the lowest values occurring around 4 years postfire. Projections indicate it could take 10–22 years following fire for root strength to recover to 70% and 90% of the prefire original root strength, respectively. This timeline indicates a multi-year window of vulnerability for shallow landslides that reaches a maximum approximately 4 years following fire. Brittle failure behavior was observed in burned root systems compared to unburned root systems, signaling a more abrupt loss of strength at yield. Simple slope stability analyses show that reduced root strength can lead to instability on more gentle slopes and under less saturation in comparison to unburned conditions. These findings highlight the critical role of root reinforcement in postfire slope stability and the long-term implications of wildfire disturbance on landslide susceptibility.

Oregon↗
USGS2025

Reconciliation of geochronology and paleozoogeography for Quaternary marine terraces, San Luis Obispo Bay area, California, USA

In the San Luis Obispo Bay area of central California, interpretations of marine terrace ages have been hampered by inconsistent results from geochronological indicators (U-series ages of corals and correlations using amino acid racemization of mollusks) and seemingly contradictory paleozoogeographic aspects of fossil faunal assemblages. New U-series ages of corals, amino acid data from mollusks, and detailed analyses of fossil mollusk assemblages are presented that reconcile many of the apparently discordant results from previous studies. The two lowest-elevation terraces are Q1 (lower) and Q2 (upper); both are thought to date from high-sea stands of marine isotope stage (MIS) 5, the last interglacial complex. A combination of U-series dating and amino acid racemization results indicates that the Q1 terrace probably dates to the ∼80 ka high-sea stand of MIS 5a. U-series analyses of corals from the Q2 terrace show open-system histories, but consideration of two alternative open-system histories indicates that this terrace likely hosts corals dating to the high-sea stands of MIS 5c (∼105–95 ka) and MIS 5e (∼130–115 ka). Amino acid ratios in the fossil bivalve Leukoma staminea (Conrad, 1837) support the age differences between the two terraces and the open-system models suggested by the U-series data. Alkenone studies along much of the coast of California have shown that sea surface temperatures (SSTs) of the eastern Pacific Ocean were warmer than present during MIS 5e. During MIS 5c, on the other hand, SSTs were either similar to the present or cooler, but in either case, much cooler than during MIS 5e. The paleozoogeographic aspects of the molluscan faunas from the Q2 terrace support an interpretation that these deposits contain a mixture of fossils from both the MIS 5c and 5e high-sea stands. Fossils from the Q2 terrace include southern or southward-ranging species (likely dating to MIS 5e) and northern or northward-ranging species (likely dating to MIS 5c). A mixture of MIS 5e and MIS 5c fossils on the Q2 terrace is consistent with similar data reported for other localities in California. This phenomenon is explained by glacial isostatic adjustment (GIA) processes, which brought about a higher-than-present sea level during MIS 5c. GIA processes, combined with a low uplift rate, allowed mixing of MIS 5e fossils during the MIS 5c high-sea stand through capture of an MIS 5e terrace that had experienced minimal uplift in ∼20,000 years. Terrace reoccupation and fossil mixing such as that in the San Luis Obispo Bay area can be expected along any part of the Pacific Coast of North America that was affected by GIA processes and where uplift rates are low.

California↗
USGS2025

Quantifying depuration of methylmercury from fish consumption by travelers

During a two-week field sampling expedition in Gabon, two American scientists consumed fish daily from the Ogooué River watershed. We sampled their scalp and facial hair periodically to evaluate hair as a biomarker to track shifts in methylmercury (MeHg) exposure from diet. Each individual differed in the onset and extent of MeHg accumulation but showed similar depuration rates. Pretrip baseline Hg isotope values between participants were distinct from Gabonese fishes allowing us to detect shifts in MeHg sources in the hair of both individuals. δ 202 Hg values tracked the mass-dependent fractionation of MeHg depuration stemming from in vivo metabolism, leading to δ 202 Hg increases of 0.014 ± 0.001 per mille and total Hg losses of 8.3 ± 1.1 ng g –1 daily. While limited in scope due to minimal participants, our findings reveal a complex interaction between prior MeHg burdens, contemporary MeHg intakes, and sources of consumed fishes (locally caught versus market-sourced) in determining the dynamics of MeHg concentrations and δ 202 Hg in human hair. We also suggest that the offset in δ 202 Hg values used in literature between fish and human hair (1.75 ± 0.25‰) may overlook a time domain that increases starting fish-hair δ 202 Hg offsets (0.94‰), through time.

Agence Nationale des Parcs Nationaux↗
USGS2025

Exploring the use of non-invasive drone-based Ground Penetrating Radar (GPR) to characterize biogenic gas dynamics in subtropical peat soils

Peat soils are a critical component of the global carbon cycle as natural producers of biogenic greenhouse gases (e.g., methane and carbon dioxide) that accumulate within the soil matrix and are episodically released to the atmosphere. Previous studies have showed the unique ability of ground-based minimally-invasive geophysical methods like ground-penetrating radar (GPR) to characterize carbon dynamics in peat soils. However, the GPR methods are still limited by the scale of measurements and soil disturbance potentially altering biogenic gas releases during deployment. Here we explore the potential of drone-based GPR for identification of hot spots and hot moments of gas accumulation and release in subtropical peat soils. We collected drone-based GPR datasets across two grids (~ 17,500 m2) in the Florida Everglades during January, September, and November of 2023 to characterize peat thickness and seasonal variability of gas content. Results show that drone-based GPR is effective and efficient for: 1) capturing the temporal variation of in-situ biogenic gas content in peat soils with changes between 1-25% volumetric gas content over repeatable grids; 2) inferring peat thickness from discrete measurements ranging between 0.8-1.2 m; and 3) estimating methane flux releases of 63 and 135 mg CH4 m-2 day-1 for specific locations and time periods that are strikingly consistent with our coincident gas trap measurements. This work also indicates that (1) spatial distribution of gas content in the Everglades is strongly controlled by landscape morphology such as ridges and sloughs and (2) the temporal variation of gas content is seasonal with increased gas production during the wet season.

Florida↗
USGS2025

High-precision earthquake catalog for Minto Flats fault zone, central Alaska, reveals complex and conjugate faulting

The Minto Flats fault zone (MFFZ) in central Alaska is a left‐lateral strike‐slip fault system situated between the continental‐scale right‐lateral Denali and Kaltag‐Tintina faults. The MFFZ has the potential to generate magnitude 7 earthquakes, and it hosted a magnitude 6 earthquake in 1995. It has also produced exotic events, such as very‐low‐frequency earthquakes and nucleation signals. We use network‐matched filtering and relative earthquake relocation techniques to derive a detailed catalog of earthquake locations for the MFFZ. The catalog spans from August 2014 to December 2019, a time period including 13 temporary seismic stations in the region. Our results provide the most complete catalog for the MFFZ and include deeper events, clusters of shallow seismicity, and a complex and segmented fault structure not observed in the original regional catalog. We document right‐lateral strike‐slip faulting, conjugate to the main northeast‐striking left‐lateral faults of the MFFZ. Below Nenana basin, the relocated seismicity reveals northwest‐dipping left‐lateral faults, supporting the inference that deep crustal active faulting is associated with recent basin deformation.

Alaska↗
USGS2025

Achieving interpretable machine learning by functional decomposition of black-box models into explainable predictor effects

Machine learning (ML) models are often based on complex black-box architectures that are difficult to interpret. This interpretability problem can hinder the use of ML in fields like medicine, ecology, and insurance, and has boosted research in interpretable machine learning (IML). Here, we propose a novel approach for the functional decomposition of black-box predictions, which is a core concept of IML. This approach replaces the prediction function with a surrogate model consisting of simpler subfunctions, providing insights into the direction and strength of the main feature contributions and their interactions. Our method is based on a concept termed “stacked orthogonality”, which ensures that the main effects capture as much functional behavior as possible. To compute the subfunctions, we combine neural additive modeling with an efficient post-hoc orthogonalization procedure. Our method yielded plausible results in an analysis of stream biological condition in the Chesapeake Bay watershed (United States).

Chesapeake Bay watershed↗