Drying of tundra landscapes will limit subsidence-induced acceleration of permafrost thaw.

We used a model for permafrost hydrology informed by detailed measurements of soil ice content to better understand the potential risk of abrupt permafrost thaw triggered by melting ground ice, a key open question associated with permafrost response to a warming Arctic. Our spatially resolved simulations of a well-characterized site in polygonal tundra near Utqiagvik, Alaska, agree well with multiple types of observations in the current climate. Projections indicate 63 cm of bulk subsidence from 2006 to 2100 in the strong-warming Representative Concentration Pathway 8.5 climate. Permafrost thaw as measured by the increase in active layer thickness (ALT)-the thickness of the soil layer that thaws each summer-is accelerated by subsidence, but the effect is relatively small. The ALT increases from the current-day value of approximately 50 cm to approximately 180 cm by 2100 when subsidence is included compared to about 160 cm when it is neglected. In these simulations, previously identified positive feedbacks between subsidence and thaw are self-limiting on decadal time frames because landscape runoff and increasing evapotranspiration result in drier tundra with weaker surface/atmosphere coupling. These results for a tundra site that is representative of large swathes of the Alaska North Slope suggest that subsidence is unlikely to lead to abrupt thaw over large areas. However, subsidence does have significant effects on the hydrology of polygonal tundra. Specifically, subsidence increases landscape runoff, which helps maintain streamflow in the face of increased evapotranspiration but also causes drier tundra conditions that could have deleterious effects on sensitive Arctic wetland ecosystems.

Incorporating concentration-dependent sediment microbial activity into methylmercury production kinetics modeling.

In anoxic environments, anaerobic microorganisms carrying the hgcAB gene cluster can mediate the transformation of inorganic mercury (Hg(II)) to monomethylmercury (MMHg). The kinetics of Hg(II) transformation to MMHg in periphyton from East Fork Poplar Creek (EFPC) in Oak Ridge, TN have previously been modeled using a transient availability model (TAM). The TAM for Hg(II) methylation combines methylation/demethylation kinetics with kinetic expressions for processes that decrease Hg(II) and MMHg availability for methylation and demethylation (multisite sorption of Hg(II) and MMHg, Hg(II) reduction/Hg(0) oxidation). In this study, the TAM is used for the first time to describe MMHg production in sediment. We assessed MMHg production in sediment microcosms using two different sediment types from EFPC: a relatively anoxic, carbon-rich sediment with higher microbial activity (higher CO2 production from sediment) and a relatively oxic, sandy, carbon-poor sediment with lower microbial activity (lower CO2 production from sediment). Based on 16s rRNA sequencing, the overall microbial community structure in the two sediments was retained during the incubations. However, the hgcA containing methanogenic Euryarchaeota communities differed between sediment types and their growth followed different trajectories over the course of incubations, potentially contributing to the distinct patterns of MMHg production observed. The general TAM paradigm performed well in describing MMHg production in the sediments. However, the MMHg production and ancillary data suggested the need to revise the model structure to incorporate terms for concentration-dependent microbial activity over the course of the incubations. We modified the TAM to include Monod-type kinetics for methylation and demethylation and observed an improved fit for the carbon-rich, microbially active sediment. Overall our work shows that the TAM can be applied to describe Hg(II) methylation in sediments and that including expressions accounting for concentration-dependent microbial activity can improve the accuracy of the model description of the data in some cases.

Small team-based medical imaging of human cadavers: an innovative tool for interdisciplinary learning inHuman Gross Anatomy andRadiologic Sciences

The purpose of this study was to develop an interdisciplinary activity that merged the disciplines of human gross anatomy and radiology early in the educational process of doctors and radiographers allowing students to use human cadavers to learn anatomy and medical imaging (technique and in-terpretation) through small-group problem-solving sessions. Over 10 years, 734 student doctors and radiographers were divided into small groups and assigned cadavers. Images of cadavers included x-rays, CT and MRI regional and full-body series. Students problem-solved radiographic parameters and interpreted images. Student radiographers completed a semester project labeling anatomical structures in a CT or MRI series. Student doctors used images during dissection and presented radiographic series to demonstrate understanding of anatomy, radiology and skilled use of image analysis software. Participants completed a 100-question LIKERT Scale survey. Data were ana-lyzed based on overall group, cadaver experience, and radiography experience. Students produced high-quality images for use in the laboratory andclassroom, and 95% agreed that this activity helped them to learn anatomy and radiography. Students agreed that x-rays, CT and MRI scans were 92.0%, 91.1% and 90.1% beneficial, respectively, in learning anatomy and radiology, and 90% of participants documented that this program had a positive impact in knowledge and competency development for his or her chosen career. Both radiography and medical students reported that working on interprofessional teams enhanced their knowledge of anatomy and radiology and under-scored the importance of partnerships in healthcare. This program serves as a novel model for interdisciplinary team-based-learning of human anatomy and radiology

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The AQUA-MER databases and aqueous speciation server: A web resource for multiscale modeling of mercury speciation.

To assess the chemical reactivity, toxicity, and mobility of pollutants in the environment, knowledge of their species distributions is critical. Because their direct measurement is often infeasible, speciation modeling is widely adopted. Mercury (Hg) is a representative pollutant for which study of its speciation benefits from modeling. However, Hg speciation modeling is often hindered by a lack of reliable thermodynamic constants. Although computational chemistry (e.g., density functional theory [DFT]) can generate these constants, methods for directly coupling DFT and speciation modeling are not available. Here, we combine computational chemistry and continuum-scale modeling with curated online databases to ameliorate the problem of unreliable inputs to Hg speciation modeling. Our AQUA-MER databases and web server (https://aquamer.ornl.gov) provides direct speciation results by combining web-based interfaces to a speciation calculator, databases of thermodynamic constants, and a computational chemistry toolkit to estimate missing constants. Although Hg is presented as a concrete use case, AQUA-MER can also be readily applied to other elements. © 2019 Wiley Periodicals, Inc.

The conference effect: National surgery meetings are associated with increased mortality at trauma centers without American College of Surgeons verification.

BACKGROUND: Thousands of physicians attend scientific conferences each year. While recent data indicate that variation in staffing during such meetings impacts survival of non-surgical patients, the association between treatment during conferences and outcomes of a surgical population remain unknown. The purpose of this study was to examine mortality resulting from traumatic injuries and the influence of hospital admission during national surgery meetings. STUDY DESIGN: Retrospective analysis of in-hospital mortality using data from the Trauma Quality Improvement Program (2010-2011). Identified patients admitted during four annual meetings and compared their mortality with that of patients admitted during non-conference periods. Analysis included 155 hospitals with 12,256 patients admitted on 42 conference days and 82,399 patients admitted on 270 non-conference days. Multivariate analysis performed separately for hospitals with different levels of trauma center verification by state and American College of Surgeons (ACS) criteria. RESULTS: Patient characteristics were similar between meeting and non-meeting dates. At ACS level I and level II trauma centers during conference versus non-conference dates, adjusted mortality was not significantly different. However, adjusted mortality increased significantly for patients admitted to trauma centers that lacked ACS trauma verification during conferences versus non-conference days (OR 1.2, p = 0.008), particularly for patients with penetrating injuries, whose mortality rose from 11.6% to 15.9% (p = 0.006). CONCLUSIONS: Trauma mortality increased during surgery conferences compared to non-conference dates for patients admitted to hospitals that lacked ACS trauma level verification. The mortality difference at those hospitals was greatest for patients who presented with penetrating injuries.

Kinetics of Methylmercury Production Revisited.

Laboratory measurements of the biologically mediated methylation of mercury (Hg) to the neurotoxin monomethylmercury (MMHg) often exhibit kinetics that are inconsistent with first-order kinetic models. Using time-resolved measurements of filter passing Hg and MMHg during methylation/demethylation assays, a multisite kinetic sorption model, and reanalyses of previous assays, we show that competing kinetic sorption reactions can lead to time-varying availability and apparent non-first-order kinetics in Hg methylation and MMHg demethylation. The new model employing a multisite kinetic sorption model for Hg and MMHg can describe the range of behaviors for time-resolved methylation/demethylation data reported in the literature including those that exhibit non-first-order kinetics. Additionally, we show that neglecting competing sorption processes can confound analyses of methylation/demethylation assays, resulting in rate constant estimates that are systematically biased low. Simulations of MMHg production and transport in a hypothetical periphyton biofilm bed illustrate the implications of our new model and demonstrate that methylmercury production may be significantly different than projected by single-rate first-order models.

The weight of obesity on the human immune response to vaccination.

Despite the high success of protection against several infectious diseases through effective vaccines, some sub-populations have been observed to respond poorly to vaccines, putting them at increased risk for vaccine-preventable diseases. In particular, the limited data concerning the effect of obesity on vaccine immunogenicity and efficacy suggests that obesity is a factor that increases the likelihood of a poor vaccine-induced immune response. Obesity occurs through the deposition of excess lipids into adipose tissue through the production of adipocytes, and is defined as a body-mass index (BMI) ≥ 30 kg/m(2). The immune system is adversely affected by obesity, and these "immune consequences" raise concern for the lack of vaccine-induced immunity in the obese patient requiring discussion of how this sub-population might be better protected.

The impact of immunosenescence on humoral immune response variation after influenza A/H1N1 vaccination in older subjects.

BACKGROUND: Although influenza causes significant morbidity and mortality in the elderly, the factors underlying the reduced vaccine immunogenicity and efficacy in this age group are not completely understood. Age and immunosenescence factors, and their impact on humoral immunity after influenza vaccination, are of growing interest for the development of better vaccines for the elderly. METHODS: We assessed associations between age and immunosenescence markers (T cell receptor rearrangement excision circles - TREC content, peripheral white blood cell telomerase - TERT expression and CD28 expression on T cells) and influenza A/H1N1 vaccine-induced measures of humoral immunity in 106 older subjects at baseline and three timepoints post-vaccination. RESULTS: TERT activity (TERT mRNA expression) was significantly positively correlated with the observed increase in the influenza-specific memory B cell ELISPOT response at Day 28 compared to baseline (p-value=0.025). TREC levels were positively correlated with the baseline and early (Day 3) influenza A/H1N1-specific memory B cell ELISPOT response (p-value=0.042 and p-value=0.035, respectively). The expression and/or expression change of CD28 on CD4+ and/or CD8+ T cells at baseline and Day 3 was positively correlated with the influenza A/H1N1-specific memory B cell ELISPOT response at baseline, Day 28 and Day 75 post-vaccination. In a multivariable analysis, the peak antibody response (HAI and/or VNA at Day 28) was negatively associated with age, the percentage of CD8+CD28 low T cells, IgD+CD27- naïve B cells, and percentage overall CD20- B cells and plasmablasts, measured at Day 3 post-vaccination. The early change in influenza-specific memory B cell ELISPOT response was positively correlated with the observed increase in influenza A/H1N1-specific HAI antibodies at Day 28 and Day 75 relative to baseline (p-value=0.007 and p-value=0.005, respectively). CONCLUSION: Our data suggest that influenza-specific humoral immunity is significantly influenced by age, and that specific markers of immunosenescence (e.g., the baseline/early expression of CD28 on CD4+ and/or CD8+ T cells and T cell immune abnormalities) are correlated with different humoral immune response outcomes observed after vaccination in older individuals, and thus can be potentially used to predict vaccine immunogenicity.

Detection of influenza A/H1N1-specific human IgG-secreting B cells in older adults by ELISPOT assay.

B cells play an important role in humoral immunity and antibody production. Use of a B cell ELISPOT assay to quantify antigen-specific B cells can assist other assays to achieve a more complete profile of the humoral immune response after vaccination. We utilized a B cell ELISPOT assay to measure the number of influenza A/H1N1-specific B cells at key timepoints after seasonal influenza vaccination in 106 older adults (50-74 years of age). Blood was drawn from these subjects on Day 0, Day 3, Day 28, and Day 75 after vaccination to represent baseline, early, peak, and late response, respectively, of influenza A/H1N1-specific B cells. A significant increase in A/H1N1-specific B cells (median 36 spot-forming units/SFUs per 200,000 cells, p<0.0001) was seen on Day 28 compared to baseline and Day 3, and this number decreased (23 SFUs, p<0.0001) by Day 75, but not to baseline level. These data suggest that the B cell ELISPOT can be used to profile and monitor the humoral immune responses in older subjects after influenza vaccination, and serve as an immune signature marker.

Robust representation of dry cells in single-layer MODFLOW models.

Dewatered or "dry" grid cells in the USGS ground water modeling software MODFLOW may cause nonphysical artifacts, trigger convergence failures, or interfere with parameter estimation. These difficulties can be avoided in two dimensions by modifying the spatial differencing scheme and the iterative procedure used to resolve nonlinearities. Specifically, the spatial differencing scheme is modified to use the water level on the upstream side of a pair of adjacent cells to calculate the saturated thickness and hence intercell conductance for the pair. This makes it possible to explicitly constrain the water level in a cell to be at or above the cell bottom elevation without introducing nonphysical artifacts. Thus constrained, all initially active cells will remain active throughout the simulation. It was necessary to replace MODFLOW's Picard iteration method with the Newton-Raphson method to achieve convergence in demanding applications involving many dry cells. Tests using a MODFLOW variant based on the new method produced results nearly identical to conventional MODFLOW in situations where conventional MODFLOW converges. The new method is extremely robust and converged in scenarios where conventional MODFLOW failed to converge, such as when almost all cells dewatered. An example application to the Edwards Aquifer in south-central Texas further demonstrates the utility of the new method.

A robust approach for iterative contaminant source location and release history recovery.

Contamination source identification is a crucial step in environmental remediation. The exact contaminant source locations and release histories are often unknown due to lack of records and therefore must be identified through inversion. Coupled source location and release history identification is a complex nonlinear optimization problem. Existing strategies for contaminant source identification have important practical limitations. In many studies, analytical solutions for point sources are used; the problem is often formulated and solved via nonlinear optimization; and model uncertainty is seldom considered. In practice, model uncertainty can be significant because of the uncertainty in model structure and parameters, and the error in numerical solutions. An inaccurate model can lead to erroneous inversion of contaminant sources. In this work, a constrained robust least squares (CRLS) estimator is combined with a branch-and-bound global optimization solver for iteratively identifying source release histories and source locations. CRLS is used for source release history recovery and the global optimization solver is used for location search. CRLS is a robust estimator that was developed to incorporate directly a modeler's prior knowledge of model uncertainty and measurement error. The robustness of CRLS is essential for systems that are ill-conditioned. Because of this decoupling, the total solution time can be reduced significantly. Our numerical experiments show that the combination of CRLS with the global optimization solver achieved better performance than the combination of a non-robust estimator, i.e., the nonnegative least squares (NNLS) method, with the same solver.

Full-Bayesian inversion of the Edwards Aquifer.

The Bayesian inverse approach proposed by Woodbury and Ulrych (2000) is extended to estimate the transmissivity fields of highly heterogeneous aquifers for steady state ground water flow. Boundary conditions are Dirichlet and Neumann type, and sink and source terms are included. A first-order approximation of Taylor's series for the exponential terms introduced by sinks and sources or the Neumann condition in the governing equation is adopted. Such a treatment leads to a linear finite element formulation between hydraulic head and the logarithm of the transmissivity-denoted as ln(T)-perturbations. An updating procedure similar to that of Woodbury and Ulrych (2000) can be performed. This new algorithm is examined against a generic example. It is found that the linearized solution approximates the true solution with an R2 coefficient = 0.96 for an ln(T) variance of 9 for the test case. The addition of hydraulic head data is shown to improve the ln(T) estimates, in comparison to simply interpolating the sparse ln(T) data alone. The new Bayesian code is also employed to calibrate a high-resolution finite difference MODFLOW model of the Edwards Aquifer in southwest Texas. The posterior ln(T) field from this application yields better head fit when compared to the prior ln(T) field determined from upscaling and cokriging. We believe that traditional MODFLOW grids could be imported into the new Bayes code fairly seamlessly and thereby enhance existing calibration of many aquifers.

Spatial and temporal patterns in mercury contamination in sediments of the Laurentian Great Lakes.

Data from recent sediment surveys have been collated and mapped in order to determine the spatial distribution of mercury in sediments across the entire Great Lakes basin. Information from historical surveys has also been collated in order to evaluate temporal trends. Lake Huron (2002) exhibited the lowest mercury concentrations (lakewide average concentration, 0.043 microg/g); Lakes Michigan (1994-1996) and Superior (2000) also exhibited relatively low levels (lakewide averages of 0.088 and 0.078 microg/g, respectively). The western basin of Lake Erie (1997-1998, 0.402 microg/g) and Lake Ontario (0.586 microg/g) exhibited the highest levels. Sources of mercury contamination in Lakes Erie and Ontario are primarily attributed to loadings from historical sources, including chlor-alkali production in the Detroit, St. Clair, and Niagara Rivers. The spatial distributions of mercury in sediments of Lakes Huron and Superior suggest that natural geochemical factors are an influence. Surficial sediment mercury contamination was found to have decreased markedly since the late 1960s and 1970s. Decreases in lakewide average sediment concentrations of mercury over this time period ranged from approximately 25% for Lake Ontario to 80% for Lake Huron.

Application of a sediment quality index to the lower Laurentian Great Lakes.

A sediment quality index (SQI) was developed using an equation incorporating three elements; scope--the % of variables that did not meet guidelines; area frequency--the % of failed tests divided by the total number of tests in a group of sites; and amplitude - the magnitude by which failed variables exceeded guidelines. The SQI calculation produces a numerical score with a maximum value of 100 representing the highest sediment quality. A modified SQI was also developed using only the scope and amplitude elements, which computed a score per site with no grouping. The SQI was applied to assessment of sediment quality in Lakes Erie and Ontario using Canadian Federal and Ontario Provincial guidelines for 34 compounds, Spatial trends in sediment quality in both lakes reflected overall trends for most individual contaminant classes, including mercury and polychlorinated biphenyls. In Lake Erie, there was a trend toward lower SQI values from the eastern basin to the western basin, and from the northern area to the southern area of the central basin. Sediment quality in the eastern basin and the northern area of the central basin was classified as excellent (>95); sediments in other areas of Lake Erie ranged from fair to good. In Lake Ontario, the poorest sediment quality was associated with the three major depositional basins; sediment quality among the three basins was quite consistent. The SQI values based on all three elements (scope, frequency and amplitude) for the Niagara basin. Mississauga Basin and Rochester Basin were 67 (fair), 65 (fair) and 70 (fair), respectively. Comparison of SQI values for all lower lake basins showed generally poorer sediment quality in Lake Ontario, compared to Lake Erie.

Spatial and temporal trends in surface water and sediment contamination in the Laurentian Great Lakes.

Data from recent sediment and surface water surveys have been collated and mapped to illustrate the spatial distribution of contaminants across the entire Great Lakes basin. Information from historical surveys, together with data from surface water monitoring programs in three major connecting channels, has also been collated in order to evaluate temporal trends. In general, Lakes Superior and Michigan exhibited the lowest levels of sediment contamination while Lake Ontario had the highest. Contaminants such as gamma-HCH (lindane) and dieldrin were ubiquitous in surface waters across the entire basin, which was indicative of atmospheric sources. The distribution of other compounds including hexachlorobenzene, octachlorostyrene and mirex indicated the presence of local sources within the watersheds of the connecting channels. Surficial sediment contamination was found to have decreased markedly since the late 1960s and 1970s. Similarly, surface water contamination decreased over the period 1986-1997 with concentrations of dieldrin, hexachlorobenzene, octachlorostyrene and mirex reduced by over 50%. However, the spatial distributions of both sediment and surface water contamination indicate that further effort is warranted in reducing local sources of contaminants, particularly in Lake Ontario.

Trends in spatial and temporal levels of persistent organic pollutants in Lake Erie sediments.

A Lake Erie sediment survey was conducted in 1997 to characterize spatial trends in contamination, and for comparison with a 1971 survey to assess any changes in environmental quality since the advent of measures to reduce contaminant sources. Contaminant data for some contaminant classes in 1971 was based on analysis of frozen archived samples, thereby allowing a direct comparison between surficial sediment contamination in 1971 and 1997 based on modern analytical methods. Lake-wide contaminant concentrations of polychlorinated biphenyls (PCBs) and organochlorine compounds including hexachlorobenzene and the DDT compounds in 1997 were substantially lower, compared to levels in samples collected in 1971. Lake-wide average sediment PCB levels were found to have decreased roughly 70% from 136 ng/g in 1971 to 43 ng/g in 1997. Similarly, reductions in other compound classes ranged from 40% to 80%. In 1997, some individual contaminants classes including PCBs exhibited a spatial trend toward increasing sediment contamination from the eastern basin to the western basin, and from the north-central basin to the south-central basin. Levels of organic contaminants in sediments in some areas of Lake Erie still exceeded the strictest Canadian Federal and Ontario Provincial guidelines. However, exceedances of guidelines describing contaminated environments in 1997 were predominantly restricted to the western basin and near-shore sites in the southern part of the central basin.

Using temperature to test models of flow near Yucca Mountain, Nevada.

Ground water temperatures in the fractured volcanic aquifer near Yucca Mountain, Nevada, have previously been shown to have significant spatial variability with regions of elevated temperatures coinciding roughly with near-vertical north-south trending faults. Using insights gained from one-dimensional models, previous investigators have suggested upwelling along faults from an underlying aquifer as a likely explanation for this ground water temperature pattern. Using a three-dimensional coupled flow and heat-transport model, we show that the thermal high coinciding with the Paintbrush fault zone can be explained without significant upwelling from the underlying aquifer. Instead, the thermal anomaly is consistent with thermal conduction enhanced slightly by vertical ground water movement within the volcanic aquifer sequence. If more than approximately 400 m3/day of water enters the volcanic aquifer from below along a 10 km fault zone, the calculated temperatures at the water table are significantly greater than the measured temperatures. These results illustrate the potential limitations in using one-dimensional models to interpret ground water temperature data, and underscore the value in combining temperature data with fully coupled three-dimensional simulations.

Persistent organic pollutants in Detroit River suspended sediments: polychlorinated dibenzo-p-dioxins and dibenzofurans, dioxin-like polychlorinated biphenyls and polychlorinated naphthalenes.

Suspended sediments from the Detroit River were collected in 1999 and 2000 using sediment traps at sites ranging from western Lake Erie to southern Lake St. Clair and analyzed to determine the spatial distributions of contaminants including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs), dioxin-like PCBs (DLPCBs) and polychlorinated naphthalenes (PCNs). Concentrations of all three contaminant classes were clearly elevated at sites in the lower reaches of the river in the Trenton Channel. The potential influence of the Trenton Channel as a source of contamination to western Lake Erie was further evidenced by PCDD/PCDF homologue profiles, which indicated a contribution from chemical manufacturing in addition to the normal background combustion profile. Toxic equivalents (TEQs) for PCDDs/PCDFs generally exceeded those for DLPCBs; combined total TEQs in July 2000 for these two compound classes ranged from 2.30 pg/g in southern Lake St. Clair to 306 pg/g at a station just downstream of the outflow of Monguagon Creek in the Trenton Channel. The spatial distribution of PCN contamination was similar to that of PCDDs/PCDFs and DLPCBs, with the highest level of total PCNs (8200 ng/g) detected at a site in the Trenton Channel near Elizabeth Park; TEQs for PCNs in the Trenton Channel ranged from 73 to 3300 pg/g. The data indicate that PCNs represent a significant contribution to dioxin-like biological activity in Detroit River suspended sediments.