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At least 1,477 records · Page 82Linked to original sources

USGS2022

Spatial models can improve the experimental design of field-based transplant gardens by preventing bias due to neighborhood crowding

Field-based transplant gardens, including common and reciprocal garden experiments, are a powerful tool for studying genetic variation and gene-by-environment interactions. These experiments assume that individuals within the garden represent independent replicates growing in a homogenous environment. Plant neighborhood interactions are pervasive across plant populations and could violate assumptions of transplant garden experiments. We demonstrate how spatially explicit models for plant–plant interactions can provide novel insights on genotypes' performance in field-transplant garden designs. We used individual-based models, based on data from a sagebrush ( Artemisia spp.) common garden, to simulate the impact of spatial plant–plant interactions on between-group differences in plant growth. We found that planting densities within the range of those used in many common gardens can bias experimental outcomes. Our results demonstrate that higher planting densities can lead to inflated group differences and may confound genotypes' competitive ability and genetically underpinned variation. Synthesis. We propose that spatially explicit models can help avoid biased results by informing the design and analysis of field-based transplant garden experiments. Alternately, including neighborhood effects in post hoc analyses of transplant garden experiments is likely to provide novel insights into the roles of biotic factors and density dependence in genetic differentiation.

Ecology and Evolution↗

USGS2022

Calibration of an evapotranspiration algorithm in a semiarid sagebrush steppe using a 3-ha lysimeter and Landsat normalized difference vegetation index data

In arid and semiarid environments, evapotranspiration (ET) is the primary discharge component in the water balance, with potential ET exceeding precipitation. For this reason, reliable estimates of ET are needed to construct accurate water budgets in these environments. Remote sensing affords the ability to provide fast, accurate, field-scale ET estimates, but these methods have largely been restricted to deep rooted (phreatophytic) plant communities underlain by shallow groundwater. We used 13 years of data from a 3-ha drainage lysimeter in a semiarid sagebrush steppe and Landsat normalized difference vegetation index (NDVI) data to calibrate a generalized least squares model capable of predicting vadose zone ET in a high elevation upland ecosystem. Annual precipitation was the best predictor of annual ET, as they were nearly balanced every year analysed (mean difference = 3 mm). We incorporated reference crop ET and a linear combination of NDVI and precipitation to capably predict ET on a subannual, lag-determined interval of 48 days, with a mean error of only 9.92% across all observations. To our knowledge, this is the first vegetation index-ET algorithm calibrated in a semiarid upland plant community using field-scale lysimetry. Vadose zone ET is particularly important at waste disposal sites in the Desert Southwest, where accurate and spatially explicit ET estimates are needed for monitoring potential mobilization and transport of contaminants past the root zone into local aquifers and for monitoring and modelling effects of recharge on flow and transport of contaminants in underlying aquifers.

Utah↗

USGS2025

Ecological thresholds and transformations due to climate change: The role of abiotic stress

An ecological threshold is the point at which a comparatively small environmental change triggers an abrupt and disproportionately large ecological response. In the face of accelerating climate change, there is concern that abrupt ecosystem transformations will become more widespread as critical ecological thresholds are crossed. There has been ongoing debate, however, regarding the prevalence of ecological thresholds across the natural world. While ecological thresholds are ubiquitous in some ecosystems, thresholds have been difficult to detect in others. Some studies have even concluded that threshold responses are uncommon in the natural world and overly emphasized in the ecological literature. As ecologists who work in ecosystems chronically exposed to high abiotic stress, we consider ecological thresholds and ecosystem transformations to be critical concepts that can greatly advance understanding of ecological responses to climate change and inform ecosystem management. But quantifying ecological thresholds can be challenging, if not impossible, without data that are strategically collected for that purpose. Here, we present a conceptual framework built upon linkages between abiotic stress, climate-driven ecological threshold responses, and the risk of ecosystem transformation. We also present a simple approach for quantifying ecological thresholds across abiotic stress gradients. We hypothesize that climate-driven threshold responses are especially influential in ecosystems chronically exposed to high abiotic stress, where autotroph diversity is low and foundation species play a prominent ecological role. Abiotic conditions in these environments are often near physiological tolerance limits of foundation species, which means that small abiotic changes can trigger landscape-level ecological transformations. Conversely, the alleviation of stress near thresholds can allow foundation species to thrive and spread into previously inhospitable locations. We provide examples of this climate-driven threshold behavior from four high-stress environments: coastal wetlands, coral reefs, drylands, and alpine ecosystems. Our overarching aim in this review is to clarify the strong relationships between abiotic stress, climate-driven ecological thresholds, and the risk of ecosystem transformation under climate change.

Ecosphere↗

USGS2025

Expression and mechanisms of behavioral plasticity in large mammals

Behavioral plasticity, the alteration of behavior in response to stimuli, is becoming increasingly important in the context of human-induced rapid environmental change. Theoretical and empirical studies suggest that the expression and magnitude of behavioral plasticity are likely facilitated or constrained primarily by two factors: environmental variation and endogenous traits such as body size. The contextual role of these factors on behavioral plasticity, however, is poorly understood; there are relatively few studies that have compared the magnitude and potential drivers of behavioral plasticity at different levels (i.e., population and individual) across species, especially in free-ranging animals with diverse behavioral traits such as large mammals. Here, we quantify and test potential hypotheses for the mechanisms underpinning behavioral plasticity at the individual and population level in response to variation in summer temperatures for 1068 animal-years in 17 populations across nine species of large mammals. All populations displayed behavioral plasticity in response to increased temperatures, modifying their relative selection for heat-relieving habitat attributes (e.g., elevation) and heat-generating behavior (i.e., movement speed). We found strong support for the hypothesis that the variability of the physical environment is an important driver of behavioral plasticity—both mean population behavioral plasticity and variation among individuals within each population in plasticity were lower with increased heterogeneity of habitat attributes such as tree cover. Yet, the variability in environmental conditions (i.e., the magnitude of the temperature increase) had no effect on behavioral plasticity within and among populations. We did not detect an effect of endogenous traits on the expression of behavioral plasticity; however, we note that data availability limited our tests of this hypothesis to a select few endogenous traits (body size, feeding guild, and sex of the tracked individuals) that predominantly vary at the species level, for which we had one to three replicate populations per species. Our results provide an integrative and generalizable understanding of the expression of behavioral plasticity among populations of large mammals in temperate environments and emphasize the important but nuanced role of environmental variation in determining the scope of behavioral plasticity in these populations.

Wyoming↗

USGS2025

Land use and soil characteristics are associated with increased risk of treponeme-associated hoof disease in elk

Environments can shape the occurrence and extent of disease outbreaks in wildlife. We studied the effects of environmental features on the occurrence of treponeme-associated hoof disease (TAHD), an emerging infectious disease of free-ranging elk ( Cervus canadensis ), in southwestern Washington, USA. During the 2016–2022 harvest seasons, successful elk hunters returned mandatory harvest reports and noted the presence or absence of hoof abnormalities indicative of TAHD. We used generalized linear models and an information-theoretic approach to model selection to relate (1) the spatial distribution of hoof abnormalities to features of landscapes (land cover, topography, and soil characteristics) and (2) the temporal distribution of hoof abnormalities to precipitation during the year preceding the harvest season. The probability of hoof disease increased with soil clay content and proportion of agricultural land (88% of model weight). We found no conclusive evidence for an effect of precipitation on the occurrence of TAHD, but this could relate to relatively high annual precipitation (>140 cm) in the study area. Nevertheless, disease cases may have been negatively associated with precipitation during February–June (55% of model weight). Soils and land management practices may increase the risk of hoof disease by promoting the survival of pathogens that cause TAHD, the susceptibility of elk to infection, or the intensity of pathogen transmission among elk when congregated. Focusing on areas where the risk of disease is greatest may facilitate the detection of TAHD during surveillance. Likewise, removing infected elk and dispersing uninfected elk from areas with the greatest risk of disease may enhance the effectiveness of efforts to reduce transmission. Basing this work on the knowledge that disease risk is modified by factors of hosts, pathogens, and environments, this study serves as an application of the epidemiological triad framework to better understand the ecology and epidemiology of an emerging infectious disease in wildlife.

Washington↗

USGS2020

Upwelling buffers climate change impacts on coral reefs of the eastern tropical Pacific

Corals of the eastern tropical Pacific live in a marginal and oceanographically dynamic environment. Along the Pacific coast of Panamá, stronger seasonal upwelling in the Gulf of Panamá in the east transitions to weaker upwelling in the Gulf of Chiriquí in the west, resulting in complex regional oceanographic conditions that drive differential coral-reef growth. Over millennial timescales, reefs in the Gulf of Chiriquí recovered more quickly from climatic disturbances compared with reefs in the Gulf of Panamá. In recent decades, corals in the Gulf of Chiriquí have also had higher growth rates than in the Gulf of Panamá. As the ocean continues to warm, however, conditions could shift to favor the growth of corals in the Gulf of Panamá, where upwelling may confer protection from high-temperature anomalies. Here we describe the recent spatial and temporal variability in surface oceanography of nearshore environments in Pacific Panamá and compare those conditions with the dynamics of contemporary coral-reef communities during and after the 2016 coral-bleaching event. Although both gulfs have warmed significantly over the last 150 yr, the annual thermal maximum in the Gulf of Chiriquí is increasing faster, and ocean temperatures there are becoming more variable than in the recent past. In contrast to historical trends, we found that coral cover, coral survival, and coral growth rates were all significantly higher in the Gulf of Panamá. Corals bleached extensively in the Gulf of Chiriquí following the 2015–2016 El Niño event, whereas upwelling in the Gulf of Panamá moderated the high temperatures caused by El Niño, allowing the corals largely to escape thermal stress. As the climate continues to warm, upwelling zones may offer a temporary and localized refuge from the thermal impacts of climate change, while reef growth in the rest of the eastern tropical Pacific continues to decline.

Gulf of Chiriqui, Gulf of Panama↗

USGS2023

A nitrifier-enriched microbial community contributes to the degradation of environmental DNA

Environmental DNA (eDNA) surveys are a promising alternative to traditional monitoring of invasive species, rare species, and biodiversity. Detecting organism-specific eDNA reduces the need to collect physical specimens for population estimates, and the high sensitivity of eDNA assays may improve detection of rare or cryptic species. However, correlating estimated concentrations of eDNA with species abundance can be difficult due to the many abiotic and biotic factors that influence eDNA persistence and degradation. Here, we assessed the impact of a nitrifier-enriched microbial (NEM) community on the persistence and degradation of Hypophthalmichthys molitrix (silver carp) milt eDNA using experimental aquatic mesocosms and a quantitative PCR approach. The NEM community was cultured from combined sediment and water samples collected from a golf course pond in Columbia, Missouri (USA), and experiments were conducted in the dark at 22°C. We found that the NEM community transformed organic nitrogen from silver carp milt to measurable amounts of nitrate, both in the presence and absence of ammonia nitrogen. Additionally, regardless of ammonia availability, milt eDNA followed a one-phase exponential decay pattern after an initial 24-h plateau in the presence of the NEM community. However, milt eDNA had a shorter half-life (12.5 h) in the absence of exogenous ammonia compared to when ammonia was present (15 h). In sterile mesocosms, eDNA was stable during the 72-h experiment. Together, these results suggest that the presence of microorganisms is necessary for short-term degradation of eDNA. Furthermore, nitrifying microbial communities, which are ubiquitous in most soil and water environments, could limit eDNA persistence in the environment. Understanding the contributions of environmental microbial communities will allow more confidence in sampling design and eDNA result interpretations for biodiversity management applications.

Environmental DNA↗

USGS2019

Seasonal, tidal, and geomorphic controls on sediment export to Amazon River tidal floodplains

Mainstem–floodplain material exchange in the tidal freshwater reach of ma jor rivers may lead to significant sequestration of riverine sediment, but this zone remains understudied compared to adjacent fluvial and marine environ ments. This knowledge gap prompts investigation of floodplain-incising tidalchannels found along the banks of tidal rivers and their role in facilitating water and suspended-sediment fluxes between mainstem and floodplain. To evaluate this role, and how it evolves along the tidal river and with time, we measured water level, flow velocity, temperature, and suspended-sediment concentration (SSC) in four tidal channels along the tidal Amazon River, Brazil. Eleven deployments were made during low, rising, high, and falling seasonal Amazon discharge. Generally, channels export high-SSC water from the mainstem to the tidal floodplain on flood tides and transfer low-SSC water back to the mainstem on ebbs. Along the length of the tidal river, the interaction between tidal and seasonal water-level variations and channel–floodplain morphology is a primary control on tidal-channel sediment dynamics. Close to the river mouth, where tides are large, this interaction produces transient flow features and current induced sediment resuspension, but the importance of these processes decreases with distance upstream. Although the magnitude of the exchange of water and sediment between mainstem and floodplain via tidal channels is a small percentage of the total mainstem discharge in this large tidal-river system, tidal channels are important conduits for material flux between these two environments. This flux is critical to resisting floodplain submergence during times of rising sea level.

Amazon River↗

USGS2017

Acute toxicity of polyacrylamide flocculants to early life stages of freshwater mussels

Polyacrylamide has become an effective tool for reducing construction-related suspended sediment and turbidity, which are considered to have significant adverse impacts on aquatic ecosystems and are a leading cause of the degradation of North American streams and rivers. However, little is known about the effects of polyacrylamide on many freshwater organisms, and prior to the present study, no information existed on the toxicity of polyacrylamide compounds to native freshwater mussels (family Unionidae), one of the most imperiled faunal groups globally. Following standard test guidelines, we exposed juvenile mussels (test duration 96 h) and glochidia larvae (test duration 24 h) to 5 different anionic polyacrylamide compounds and 1 non-ionic compound. Species tested included the yellow lampmussel ( Lampsilis cariosa ), an Atlantic Slope species that is listed as endangered in North Carolina; the Appalachian elktoe ( Alasmidonta raveneliana ), a federally endangered Interior Basin species; and the washboard ( Megalonaias nervosa ), a common Interior Basin species. We found that median lethal concentrations (LC50s) of polyacrylamide ranged from 411.7 to >1000 mg/L for glochidia and from 126.8 to >1000 mg/L for juveniles. All LC50s were orders of magnitude greater (2–3) than concentrations typically recommended for turbidity control (1–5 mg/L), regardless of their molecular weight or charge density. The results demonstrate that the polyacrylamide compounds tested were not acutely toxic to the mussel species and life stages tested, indicating minimal risk of short-term exposure from polyacrylamide applications in the environment. However, other potential uses of polyacrylamide in the environment (e.g., wastewater treatment, paper processing, mining, algae removal) and their chronic or sublethal effects remain uncertain and warrant additional investigation.

Environmental Toxicology and Chemistry↗

USGS2019

Toward sustainable environmental quality: Priority research questions for North America

Anticipating, identifying, and prioritizing strategic needs represent essential activities by research organizations. Decided benefits emerge when these pursuits engage globally important environment and health goals, including the United Nations Sustainable Development Goals. To this end, horizon scanning efforts can facilitate identification of specific research needs to address grand challenges. We report and discuss 40 priority research questions following engagement of scientists and engineers in North America. These timely questions identify the importance of stimulating innovation and developing new methods, tools, and concepts in environmental chemistry and toxicology to improve assessment and management of chemical contaminants and other diverse environmental stressors. Grand challenges to achieving sustainable management of the environment are becoming increasingly complex and structured by global megatrends, which collectively challenge existing sustainable environmental quality efforts. Transdisciplinary, systems‐based approaches will be required to define and avoid adverse biological effects across temporal and spatial gradients. Similarly, coordinated research activities among organizations within and among countries are necessary to address the priority research needs reported here. Acquiring answers to these 40 research questions will not be trivial, but doing so promises to advance sustainable environmental quality in the 21st century.

Environmental Toxicology and Chemistry↗

USGS2020

Emerging and historical contaminants detected in desert rodents collected near a low‐level radioactive waste site

In an effort to determine contaminant presence, concentrations, and movement from a low‐level radioactive waste (LLRW) burial disposal site to ecosystems in the surrounding area, a study was developed to assess concentrations of per‐ and polyfluoroalkyl substances (PFAS), polychlorinated biphenyls (PCBs), and tritium. To complete this assessment small mammals, vegetation, soil, and insect samples were collected from areas within and adjacent to the Beatty, Nevada, LLRW site and from a reference area located approximately 3 km south of the LLRW site. Samples underwent analysis via liquid chromatography tandem mass spectrometry, gas chromatography mass spectrometry, or scintillation spectroscopy depending on the analyte of interest. Small mammal tissues showed maximum concentrations of over 1700 ng/g for PFAS, 1600 ng/g for PCBs, and 10 000 Bq/kg for tritium. The primary contaminants found in soil samples were PCBs, with maximum concentrations exceeding 25 ng/g. Trace amounts of PFAS were also detected in soils and insects. Only qualitative data were obtained from vegetation samples because of the complex matrix of the dominant plant species (creosote bush; Larrea tridentata [Sessé & Moc. ex DC.] Coville). Overall, these data indicate the presence of various anthropogenic contaminants in the ecosystem surrounding the LLRW area, but additional analyses are necessary to confirm the sources and migration pathways of PFAS and PCBs in this hyperarid environment. Environ Toxicol Chem 2020;00:1–8. © 2020 SETAC

Nevada↗

USGS2022

Prioritizing pesticides of potential concern and identifying potential mixture effects in Great Lakes tributaries using passive samplers

To help meet the objectives of the Great Lakes Restoration Initiative with regard to increasing knowledge about toxic substances, 223 pesticides and pesticide transformation products were monitored in 15 Great Lakes tributaries using polar organic chemical integrative samplers. A screening-level assessment of their potential for biological effects was conducted by computing toxicity quotients (TQs) for chemicals with available US Environmental Protection Agency (USEPA) Aquatic Life Benchmark values. In addition, exposure activity ratios (EAR) were calculated using information from the USEPA ToxCast database. Between 16 and 81 chemicals were detected per site, with 97 unique compounds detected overall, for which 64 could be assessed using TQs or EARs. Ten chemicals exceeded TQ or EAR levels of concern at two or more sites. Chemicals exceeding thresholds included seven herbicides (2,4-dichlorophenoxyacetic acid, diuron, metolachlor, acetochlor, atrazine, simazine, and sulfentrazone), a transformation product (deisopropylatrazine), and two insecticides (fipronil and imidacloprid). Watersheds draining agricultural and urban areas had more detections and higher concentrations of pesticides compared with other land uses. Chemical mixtures analysis for ToxCast assays associated with common modes of action defined by gene targets and adverse outcome pathways (AOP) indicated potential activity on biological pathways related to a range of cellular processes, including xenobiotic metabolism, extracellular signaling, endocrine function, and protection against oxidative stress. Use of gene ontology databases and the AOP knowledgebase within the R-package ToxMixtures highlighted the utility of ToxCast data for identifying and evaluating potential biological effects and adverse outcomes of chemicals and mixtures. Results have provided a list of high-priority chemicals for future monitoring and potential biological effects warranting further evaluation in laboratory and field environments. Environ Toxicol Chem 2023;42:340–366. Published 2022. This article is a U.S. Government work and is in the public domain in the USA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Great Lakes tributaries↗

USGS1992

Polychlorinated biphenyl residues and egg mortality in double-crested cormorants from the Great Lakes

We evaluated the overall potency of polychlorinated biphenyl (PCB)-containing extracts from double-crested cormorant ( Phalacrocorax auritis ) eggs with an in vitro bioassay system, the H4IIE rat hepatoma cell bioassay. Results from the H4IIE bioassay were strongly correlated with the hatching success of eggs in the colonies, whereas conventional methods of PCB analysis correlated poorly with hatching success of eggs from the same colonies. These observations suggest that even though concentrations of total PCB residues have declined in almost all compartments of the environment, their effects are still being observed. The significance of this observation is that the adverse symptoms presently observed in certain Great Lakes fish-eating waterbird populations do not appear to be caused by some as yet unidentified industrial chemical or chemicals and seem not to be the result of pesticides, but rather to the dioxin-like activity of PCBs. Evidence is presented to suggest that the relative enrichment of the potency of PCBs in the environment may play a role in the persistence of the observed adverse symptoms.

Environmental Toxicology and Chemistry↗

USGS2023

Review and development of best practices for toxicity tests with dreissenid mussels

Since their introduction to North America in the 1980s, research to develop effective control tools for invasive mussels ( Dreissena polymorpha and D. rostriformis bugensis ) has been ongoing across various research institutions using a range of testing methods. Inconsistencies in experimental methods and reporting present challenges for comparing data, repeating experiments, and applying results. The Invasive Mussel Collaborative established the Toxicity Testing Work Group (TTWG) in 2019 to identify “best practices” and guide development of a standard framework for dreissenid mussel toxicity testing protocols. We reviewed the literature related to laboratory-based dreissenid mussel toxicity tests and determined the degree to which standard guidelines have been used and their applicability to dreissenid mussel testing. We extracted detailed methodology from 99 studies from the peer-reviewed and gray literature and conducted a separate analysis for studies using presettlement and postsettlement mussels. We identified specific components of methods and approaches that could be refined or standardized for dreissenid mussels. These components included species identification, collection methods, size/age class distinction, maintenance practices, testing criteria, sample size, response measures, reporting parameters, exposure methods, and mortality criteria. We consulted experts in the field of aquatic toxicology and dreissenid mussel biology on our proposed. The final recommendations contained in the present review are based on published standard guidelines, methods reported in the published and gray literature, and the expertise of TTWG members and an external panel. In addition, our review identifies research needs for dreissenid mussel testing including improved methods for early–life stage testing, comparative data on life stages and between dreissenid mussel species, inclusion of a reference toxicant, and additional testing of nontarget species (i.e., other aquatic organisms). Environ Toxicol Chem 2023;42:1649–1666. © 2023 His Majesty the King in Right of Canada. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. Reproduced with the permission of the Minister of Environment and Climate Change Canada. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Environmental Toxicology and Chemistry↗

USGS2011

Simulation of branched serial first-order decay of atrazine and metabolites in adapted and nonadapted soils

In the present study a branched serial first-order decay (BSFOD) model is presented and used to derive transformation rates describing the decay of a common herbicide, atrazine, and its metabolites observed in unsaturated soils adapted to previous atrazine applications and in soils with no history of atrazine applications. Calibration of BSFOD models for soils throughout the country can reduce the uncertainty, relative to that of traditional models, in predicting the fate and transport of pesticides and their metabolites and thus support improved agricultural management schemes for reducing threats to the environment. Results from application of the BSFOD model to better understand the degradation of atrazine supports two previously reported conclusions: atrazine (6-chloro- N -ethyl- N ′-(1-methylethyl)-1,3,5-triazine-2,4-diamine) and its primary metabolites are less persistent in adapted soils than in nonadapted soils; and hydroxyatrazine was the dominant primary metabolite in most of the soils tested. In addition, a method to simulate BSFOD in a one-dimensional solute-transport unsaturated zone model is also presented.

Environmental Toxicology and Chemistry↗

USGS2023

Aging, climate, and invasions threaten reservoirs in the Mississippi basin

Reservoirs in the Mississippi River basin are facing three momentous threats. The first two, aging and climate change, are relatively slow moving and their signal can be hard to discern given their stretched temporal scales. The third, species invasions, is faster paced and discernable within shorter temporal scales and restricted spatial scales. Aging and climate directly affect reservoir environments and indirectly affect their biotic communities. Climate change is expected to interact with aging to speed up and, in some instances, slow down aging. Conversely, invasions primarily imperil biotic communities but can also impact environmental elements. This triple jeopardy is expected to transform reservoir environs and their biotic assemblages in various, often uncertain, ways. I take a broad view of these threats within the Mississippi River basin. A basin-scale perspective, in contrast to a single reservoir or regional scale, may enhance awareness of reservoirs at a larger level and produce understanding less evident at local levels, hence possibly offering a wider range of choices for confronting threats. My aim is to (1) provide a synopsis of the assemblage of reservoirs and their attributes over the Mississippi River basin, (2) describe the issues related to aging, climate change, and invasions, and (3) consider a conservation framework for confronting these pressures. Given the overlapping temporal, spatial, and ecological effects of these threats, it is essential to address their effects simultaneously.

Mississippi River basin↗

USGS2007

Geoarchaeology of stratified paleoindian deposits at the Big Eddy site, Southwest Missouri, U.S.A

The Big Eddy site (23CE426) in the Sac River valley of southwest Missouri is a rare recorded example of distinctly stratified Early through Late Paleoindian cultural deposits. Early point types recovered from the site include Gainey, Sedgwick, Dalton (fluted and unfluted), San Patrice, Wilson, and Packard. The Paleoindian record at Big Eddy represents only a fraction of the site's prehistoric cultural record; stratified cultural deposits in alluvium above the Paleoindian components span the entire known prehistoric sequence, and terminal Pleistocene alluvium may contain pre-Early Paleoindian cultural deposits. This study focused on the paleogeomorphic setting, stratigraphy, depositional environments, pedology, geochronology, and history of landscape evolution of the late Pleistocene and early Holocene alluvium at the site. The Paleoindian sequence is associated with a complex buried soil 2.85 m below the modern surface (T1a) of the first terrace of the Sac River valley in the site vicinity. This soil formed at the top of the early submember of the Rodgers Shelter Member (underlying the T1c paleogeomorphic surface) and contains at least 70 cm of stratified Paleoindian cultural deposits, all in floodplain and upper point-bar facies. A suite of 36 radiocarbon ages indicates that the alluvium hosting the Paleoindian sequence aggraded between ca. 13,250 and 11,870 cal yr B.P. (11,380 and 10,180 14C yr B.P.). Underlying deposits accumulated between ca. 15,300 and 13,250 cal yr B.P. (12,950 and 11,380 14C yr B.P.). By ca. 11,250 cal yr B.P. (9,840 14C yr B.P.) the T1c paleogeomorphic surface was buried by the earliest increment of a thick sequence of overbank sheetflood facies, ultimately resulting in deep burial and preservation of the Paleoindian record. The landform-sediment assemblage that hosts the Paleoindian and possibly earlier cultural deposits at Big Eddy is both widespread and well preserved in the lower Sac River valley. Moreover, the terminal Pleistocene and early Holocene depositional environments were favorable for the preservation of the archaeological record. ?? 2007 Wiley Periodicals, Inc.

Geoarchaeology↗

USGS2017

Heat as a groundwater tracer in shallow and deep heterogeneous media: Analytical solution, spreadsheet tool, and field applications

Groundwater flow advects heat, and thus, the deviation of subsurface temperatures from an expected conduction‐dominated regime can be analysed to estimate vertical water fluxes. A number of analytical approaches have been proposed for using heat as a groundwater tracer, and these have typically assumed a homogeneous medium. However, heterogeneous thermal properties are ubiquitous in subsurface environments, both at the scale of geologic strata and at finer scales in streambeds. Herein, we apply the analytical solution of Shan and Bodvarsson (2004), developed for estimating vertical water fluxes in layered systems, in 2 new environments distinct from previous vadose zone applications. The utility of the solution for studying groundwater‐surface water exchange is demonstrated using temperature data collected from an upwelling streambed with sediment layers, and a simple sensitivity analysis using these data indicates the solution is relatively robust. Also, a deeper temperature profile recorded in a borehole in South Australia is analysed to estimate deeper water fluxes. The analytical solution is able to match observed thermal gradients, including the change in slope at sediment interfaces. Results indicate that not accounting for layering can yield errors in the magnitude and even direction of the inferred Darcy fluxes. A simple automated spreadsheet tool (Flux‐LM) is presented to allow users to input temperature and layer data and solve the inverse problem to estimate groundwater flux rates from shallow (e.g., <1 m) or deep (e.g., up to 100 m) profiles. The solution is not transient, and thus, it should be cautiously applied where diel signals propagate or in deeper zones where multi‐decadal surface signals have disturbed subsurface thermal regimes.

Hydrological Processes↗