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A new approach for measuring fluxes across surface water—groundwater interfaces was recently proposed. The Automatic Seepage Meter (ASM) is equipped with a precise water level sensor and digital memory that analyzes water level time series in a vertical tube inserted into a streambed (Solomon et al., 2020, https://doi.org/10.1029/2019WR026983). The ability to infer flux values with high temporal resolution relies on an accurate interpretation of water level dynamics inside the tube. Here, we reduce the three‐dimensional hydrodynamic problem that describes the ASM water level in a variety of field conditions to a single ordinary differential equation. This novel general analytical solution for estimating ASM responses is more comprehensive and flexible than previous approaches and is applicable to the entire range of field conditions, including steady or transient stream stages, evaporation, rainfall, and noise. For example, our analysis determines the timing of the nonmonotonic ASM response to a monotonic linear stream stage variation and explains previously used empirical parabolic approximation for estimating fluxes. We present algorithms for simultaneous inference of vertical interface flux and hydraulic conductivity values together with an example code. We quantify how the accuracy of parameter estimation depends on test duration and noise amplitude and propose how our analysis can be used to optimize field test protocols. On this basis, changing the ASM geometry by increasing the radius and decreasing tube insertion depth may enable ASM field test protocols that estimate interface flux and hydraulic conductivity faster while maintaining desired accuracy. Potential applications of joint parameter estimation are suggested. Key Points: A generalized equation of water level dynamics in the Automatic Seepage Meter valid for a variety of field conditionsThe theory considers surface water level fluctuations, evaporation, rainfall, and ambient noiseWater flux and vertical hydraulic conductivity estimation accuracy is analyzed with examples and recommendations [ABSTRACT FROM AUTHOR]

Groundwater transit time distributions (TTDs) describe the spectrum of flow‐weighted apparent ages of groundwater from aquifer recharge to discharge. Regional‐scale TTDs in stream baseflow are often estimated from numerical models with limited calibration from groundwater sampling and suggest much younger groundwater discharge than has been observed by discrete age‐dating techniques. We investigate both local and regional‐scale groundwater TTDs in the Upper Middle Loup watershed (5,440 km2) overlying the High Plains Aquifer in the Nebraska Sand Hills, USA. We determined flow‐weighted apparent ages of groundwater discharging through the streambed at 88 discrete points along a 99 km groundwater‐dominated stream segment using 3H, noble gases, 14C, and groundwater flux measurements at the point‐scale (<7.6 cm diameter). Points were organized in transects across the stream width (3–10 points per transect) and transects were clustered in five sampling areas (10–610 m in stream length) located at increasing distances along the stream. Groundwater apparent ages ranged from 0 to 8,200 years and the mean groundwater transit time along the 99 km stream is >3,000 years. TTDs from upstream sampling areas were best fit by distributions with a narrow range of apparent ages, but when older groundwater from downstream sampling areas is included, the regional TTD is scale dependent and the distribution is better described by a gamma model (α ≈ 0.4) which accommodates large fractions of millennial‐aged groundwater. Observations indicate: (a) TTDs can exhibit spatial variability within a watershed and (b) watersheds can discharge larger fractions of old groundwater (>1,000 years) than commonly assumed. Plain Language Summary: The transit time distribution (TTD) of an aquifer describes the complete spectrum of groundwater transit times from the water table to discharge at an outlet such as a stream. TTDs indicate how susceptible aquifers may be to contamination, drought, or pumping. Despite their importance, TTDs are difficult to quantify and many approaches either overestimate the relative fraction of young groundwater discharge or have been conducted in small systems (areas <1,000 km2 or stream lengths <10 km). We measured the flow‐weighted transit time of groundwater through the streambed at 88 points along a 99 km stream in the Upper Middle Loup watershed (5,440 km2) in Nebraska, USA to estimate TTDs of the underlying High Plains Aquifer at various spatial scales. Transit times ranged from 0 to 8,200 years and the mean transit time is >3,000 years along the entire study stream with substantially older groundwater discharge downstream. Upstream TTDs were well‐fit by distributions with larger fractions of young groundwater (<15 years), but TTDs for the entire study stream were better fit by distributions that accommodate large fractions of millennial‐aged groundwater. Our findings suggest that TTDs can vary within a watershed and ancient groundwater may be a significant component of modern streamflow. Key Points: Groundwater age and flux along a 99 km stream overlying the High Plains Aquifer, USA yield transit time distributions (TTD) and meanGroundwater ages ranged from 0 to 8,200 years with mean age >3,000 years and increasing apparent age of baseflow downstreamTTD evolution with stream distance suggests streams overlying regional systems may intersect large fractions of millennial‐aged groundwater [ABSTRACT FROM AUTHOR]

The recent surge in the availability of sensor data and computational resources has fostered the development of technologies for optimization, control, and monitoring of large infrastructures, integrating data and numerical modeling. The major bottleneck in this type of technologies is the model response time, since repetitive solutions are typically required. To reduce the computational time, reduced order models (ROMs) are used as surrogates for expensive finite element (FE) simulations enabling the use of complex models in this type of applications. In this work, ROMs are explored for the solution of the fully coupled hydro‐mechanical system of equations that governs the water flow through partially saturated soil. The POD‐based Reduced Basis Method and the Discrete Empirical Interpolation Method (DEIM), as well as its localized version (LDEIM), are examined in solving a parametrized problem simulating the mechanical loading of an embankment dam. Hydraulic and mechanical soil properties are considered as parameters. It is shown that the combination of these methods results in simulations that require 1/10 to 1/100 of the FE response time. Moreover, the method is shown to yield scaling efficiency gains with increasing problem size. [ABSTRACT FROM AUTHOR]

Objective: Bariatric surgeries involve manipulation of the viscera and are associated with significant postoperative pain. Paracetamol is a nonopioid analgesic with a rapid onset, and it is effective and safe. The study compared the effects of pre‐ and postincisional intravenous paracetamol administration for optimal postoperative pain management in patients undergoing bariatric surgeries. Methods: This is a prospective, double‐blinded, placebo‐controlled randomized clinical trial of adult patients, admitted electively for laparoscopic bariatric surgery. The patients were randomly divided into two groups. One group of patients was given paracetamol at the beginning of the operation, prior to the surgical incision, the other group of patients received the same treatment at the end of the operation. Results: Patients who were given preincisional intravenous paracetamol presented significantly lower visual analog scale (VAS) scores following the surgery compared with patients who were given intravenous paracetamol in the last 30 minutes of the operation (VAS, median [IQR] = 2 [2‐3] vs. 5 [3‐6]; p < 0.001). They also required fewer postoperative opioids and tramadol (in milligrams, respectively, 1 [0‐5] vs. 7.5 [5‐10] and 300 [100‐400] vs. 400 [200‐500]) compared with later analgesia administration (p < 0.001 and p = 0.03). The levels of inflammatory markers measured at fixed intervals from paracetamol administration were not statistically different between the study groups. Conclusion: Early analgesia with intravenous paracetamol, given before the surgical incision, may result in lower VAS scores postoperatively compared with the same treatment administered toward the end of the operation. [ABSTRACT FROM AUTHOR]

Two aggregated regularized systems of equations for a multicomponent homogeneous gas mixture are considered. An entropy balance equation with a non‐negative entropy production is derived for them in the presence of diffusion fluxes. The existence, uniqueness and L2‐dissipativity of weak solutions to an initial‐boundary value problem for the systems linearized on a constant solution are established. The Petrovskii parabolicity and the local in time classical unique solvability of the Cauchy problem are also proved for the aggregated systems themselves. [ABSTRACT FROM AUTHOR]

On many Navajo Sandstone outcrops in southern Utah, steep, decimetre‐high scarps (downslope‐facing margins of rock sheets) interrupt smooth slopes covered by crustose lichens. Scarps form where sheeting joints and water emerge at the land surface. Weathering at scarp faces causes upslope backwasting of rock sheets and leaves behind smooth, unweathered rock surfaces that become stabilized by lichens. We hypothesize that subsurface, low‐angle, open fractures in porous and permeable rocks are barriers to downward flux of water through the vadose zone. Runoff and lateral flow through the uppermost rock sheets deliver water to scarps, inducing backwasting. Monitoring of temperature and water/ice content within two surficial rock sheets revealed that, in the winter of 2020–2021, snowmelt that entered lichen‐covered surfaces persisted for 64 days and underwent 46 freeze/thaw cycles. Water gained from summer rains remained for a maximum of 11 days. Flaking rock and dangling lichen crusts that overhang scarps indicate backwasting is now active. We conclude that freeze/thaw cycles (rather than salt precipitation) drive backwasting at our study sites, all of which are located more than 1400 m above sea level where the climate is relatively cool, and snowfalls are frequent. Backwasting would likely be more rapid and extensive under a cooler, wetter (periglacial) climate. Although broad, gently sloping, lichen‐covered rock sheets dominate the land surface, they are not downwasting; weathering is instead restricted to the near‐vertical, lichen‐free, backwasting scarps. [ABSTRACT FROM AUTHOR]

We utilized 251 measurements from a recently developed automated seepage meter (ASM) in streambeds in the Nebraska Sand Hills, USA to investigate the small‐scale spatial variability of groundwater seepage flux (q) and the ability of the ASM to estimate mean q at larger scales. Small‐scale spatial variability of q was analyzed in five dense arrays, each covering an area of 13.5–28.0 m2 (169 total point measurements). Streambed vertical hydraulic conductivity (K) was also measured. Results provided: (a) high‐resolution contour plots of q and K, (b) anisotropic semi‐variograms demonstrating greater correlation scales of q and K along the stream length than across the stream width, and (c) the number of rows of points (perpendicular to streamflow) needed to represent the groundwater flux of areas up to 28.0 m2. The findings suggest that representative streambed measurements are best conducted perpendicular to streamflow to accommodate larger seepage flux heterogeneity in this direction and minimize sampling redundancy. To investigate the ASM's ability to produce accurate mean q at larger scales, seepage meters were deployed in four stream reaches (170–890 m), arranged in three to six transects (three to eight points each) per reach across the channel. In each reach, the mean seepage flux from ASMs was compared to the seepage flux from bromide tracer dilution. Agreement between the two methods indicates the viability of a modest number of seepage meter measurements to determine the overall groundwater flux to the stream and can guide sampling for solutes and environmental tracers. Plain Language Summary: Surface waters can be windows into groundwater aquifers. When conditions are right, groundwater is pushed up through the streambed and into the stream bringing with it natural and artificial solutes that are used as tracers for aquifer evaluation. Therefore, measurements of groundwater seepage fluxes are important. Utilizing a new tool (Solomon et al., 2020, https://doi.org/10.1029/2019WR026983) for point measurements of groundwater flux (over an area of about 10 cm2), this study makes an unprecedented number of direct discharge measurements in the Sand Hills, Nebraska, USA in both (a) small areas (13.5–28.0 m2) of streambed and (b) along a much larger (170–890 m) stream segments. The results indicate that a modest number of discharge measurements in transects perpendicular to streamflow may accurately represent the groundwater flux in both small sections of stream and even in larger stream sections up to 890 m long. This means that if groundwater is discharging into the stream, the average seepage flux from the groundwater aquifer over the entire stream segment can be obtained through sampling a relatively small number of streambed locations. This potentially provides water resource managers valuable information on fluxes of both groundwater contaminants and age‐dating tracers without installing resource‐demanding wells. Key Points: A recently developed seepage meter produced high‐resolution maps of groundwater flux through streambeds in the Nebraska Sand Hills, USAAnisotropic semi‐variograms suggest representative point sampling is best conducted in rows of evenly spaced points across the stream widthGroundwater flux measured at 3–6 channel transects of seepage meters (3–8 points each) estimated total flux in reaches up to 890 m long [ABSTRACT FROM AUTHOR]

Open‐bottom permeameters (OBP) are commonly used for estimating the hydraulic properties of sediment beds under water bodies and fluxes across the sediment‐water interface. The specific shape factor for an OBP flow situation is necessary for data interpretation. It is determined by the ratio of the permeameter tube radius to the tube's penetration depth within the sediment. Previous permeameter designs favored small radii which allowed for deeper penetration and stability of the tube. The shape factor is provided here for large footprint OBPs that allows for shallow penetration and greater radius. Through a numerical and analytical modeling study of the OBP hydrodynamics, previous knowledge on the OBP shape factor is generalized to the entire range of radius‐to‐penetration ratios that might be practically applied. The results reveal the advantages of the large footprint design, including better sensitivity due to the ability to impose larger discharge over a shorter test duration. Plain Language Summary: Various instruments use open‐bottom permeameters (OBP) for investigation of characteristics of the surface water‐groundwater interfaces, for example by slug tests, seepage meter tests, and piezo‐seep meter tests. Previously, typical designs favored small tube radii which allowed for deeper penetration and stability of the tubes. It is shown that large footprint instruments (with large tube radius‐to‐penetration ratios) may provide better sensitivity and practical advantages in various tests. A numerical and analytical modeling of the OBP hydrodynamics generalized the OBP shape factor necessary for data interpretation in the entire practical range of radius‐to‐penetration ratios. Key Points: Open‐bottom permeameters are used for studies of fluxes and sediment properties of surface water‐groundwater interfacesTraits and advantages of large radii and shallow penetrations of permeameters are demonstrated using hydrodynamic analysisFor applications, shape factor values are calculated and documented in the entire range of practically necessary parameters [ABSTRACT FROM AUTHOR]

Reduced‐order models are essential tools to deal with parametric problems in the context of optimization, uncertainty quantification, or control and inverse problems. The set of parametric solutions lies in a low‐dimensional manifold (with dimension equal to the number of independent parameters) embedded in a large‐dimensional space (dimension equal to the number of degrees of freedom of the full‐order discrete model). A posteriori model reduction is based on constructing a basis from a family of snapshots (solutions of the full‐order model computed offline), and then use this new basis to solve the subsequent instances online. Proper orthogonal decomposition (POD) reduces the problem into a linear subspace of lower dimension, eliminating redundancies in the family of snapshots. The strategy proposed here is to use a nonlinear dimensionality reduction technique, namely, the kernel principal component analysis (kPCA), in order to find a nonlinear manifold, with an expected much lower dimension, and to solve the problem in this low‐dimensional manifold. Guided by this paradigm, the methodology devised here introduces different novel ideas, namely, 1) characterizing the nonlinear manifold using local tangent spaces, where the reduced‐order problem is linear and based on the neighboring snapshots, 2) the approximation space is enriched with the cross‐products of the snapshots, introducing a quadratic description, 3) the kernel for kPCA is defined ad hoc, based on physical considerations, and 4) the iterations in the reduced‐dimensional space are performed using an algorithm based on a Delaunay tessellation of the cloud of snapshots in the reduced space. The resulting computational strategy is performing outstandingly in the numerical tests, alleviating many of the problems associated with POD and improving the numerical accuracy. [ABSTRACT FROM AUTHOR]

Joint probabilistic inversions of magnetotelluric (MT) and seismic data have great potential for imaging the thermochemical structure of the lithosphere as well as mapping fluid/melt pathways and regions of mantle metasomatism. In this contribution, we present a novel probabilistic (Bayesian) joint inversion scheme for 3D MT and surface‐wave dispersion data particularly designed for large‐scale lithospheric studies. The approach makes use of a recently developed strategy for fast solutions of the 3D MT forward problem (Manassero et al., 2020, https://doi.org/10.1093/gji/ggaa415) and combines it with adaptive Markov chain Monte Carlo (MCMC) algorithms and parallel‐in‐parallel strategies to achieve extremely efficient simulations. To demonstrate the feasibility, benefits and performance of our joint inversion method for imaging the temperature and conductivity structures of the lithosphere, we apply it to two numerical examples of increasing complexity. The inversion approach presented here is timely and will be useful in the joint analysis of MT and surface wave data that are being collected in many parts of the world. This approach also opens up new avenues for the study of trans‐lithospheric and trans‐crustal magmatic systems, the detection of metasomatized mantle, and the incorporation of MT into multi‐observable inversions for the physical state of the Earth's interior. Plain Language Summary: The joint analysis of two or more geophysical data sets is becoming common practice for imaging the Earth's interior. This approach has great potential when the different data sets offer complementary sensitivities to the properties of interest. Such is the case of combining MT, that is, magnetotelluric (a technique based on observed electric and magnetic fields) and seismic data. In this context, probabilistic methods offer a powerful and general platform for the joint analysis of these data sets and their uncertainties. However, the inclusion of MT data into 3D probabilistic schemes has so far not been possible due to the significant computational cost of the MT problem. In this contribution we present a novel probabilistic joint analysis scheme for MT and surface‐wave data which is based on a recently developed strategy to achieve fast and efficient solutions to the MT problem (Manassero et al., 2020, https://doi.org/10.1093/gji/ggaa415). We demonstrate the feasibility, benefits and performance of our approach for whole‐lithosphere and upper mantle structures up to ∼400 km depth. The approach presented here will be useful in the joint analysis of MT and seismic data that are being collected in many parts of the world. Key Points: We present a novel strategy to invert 3D magnetotelluric (MT) data together with other data sets in a fully probabilistic mannerPerform the first joint probabilistic inversion of 3D MT and surface‐wave data for imaging the conductivity distribution in the lithosphereDemonstrate the applicability of our approach to include 3D MT data into joint probabilistic inversions for imaging the Earth's interior [ABSTRACT FROM AUTHOR]

The Inertia Relief (IR) technique is widely used by industry and produces equilibrated loads allowing to analyze unconstrained systems without resorting to the more expensive full dynamic analysis. The main goal of this work is to develop a computational framework for the solution of unconstrained parametric structural problems with IR and the Proper Generalized Decomposition (PGD) method. First, the IR method is formulated in a parametric setting for both material and geometric parameters. A reduced order model using the encapsulated PGD suite is then developed to solve the parametric IR problem, circumventing the so‐called curse of dimensionality. With just one offline computation, the proposed PGD‐IR scheme provides a computational vademecum that contains all the possible solutions for a predefined range of the parameters. The proposed approach is nonintrusive and it is therefore possible to be integrated with commercial finite element (FE) packages. The applicability and potential of the developed technique is shown using a three‐dimensional test case and a more complex industrial test case. The first example is used to highlight the numerical properties of the scheme, whereas the second example demonstrates the potential in a more complex setting and it shows the possibility to integrate the proposed framework within a commercial FE package. In addition, the last example shows the possibility to use the generalized solution in a multi‐objective optimization setting. [ABSTRACT FROM AUTHOR]

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When subduction initiates along a transform fault, it is often interpreted that the older and therefore denser oceanic lithosphere should evolve into the downgoing plate. However, in the western Pacific, several geological cases are probably characterized by young oceanic plates underthrusting older and denser plates. Using numerical simulations of a transform fault under compression, we propose that subduction polarity depends mainly on the age offset between the two adjacent plates, the strength of the transform fault, and the plasticity of the plates. A small age offset across the plate interface favors the subduction initiation of the younger plate. Furthermore, weak transform faults promote strain localization along the plate boundary and trigger the underthrusting of the older and denser plate. Plastic deformation is prone to localize within the thinner and weaker plates in a location far from the transition zone of the two plates if the rate of strain weakening of plates is fast enough. When plates have a large age offset the younger plate may still underthrust if plasticity plays a role. Our numerical models explore factors controlling the induced subduction polarities and the potential mechanism of young plate subduction and explain certain related subduction geological settings. [ABSTRACT FROM AUTHOR]

The majority of overland transport needs for crude petroleum and refined petroleum products are met using pipelines. Numerous studies have developed optimization methods for design of these systems in order to minimize construction costs while meeting capacity requirements. Here, we formulate problems to optimize the operations of existing single liquid commodity pipeline systems subject to physical flow and pump engineering constraints. The objectives are to maximize the economic value created for users of the system and to minimize operating costs. We present a general computational method for this class of continuous, non‐convex nonlinear programs, and examine the use of pump operating settings and flow allocations as decision variables. The approach is applied to compute optimal operating regimes and perform engineering economic sensitivity analyses for a case study of a crude oil pipeline developed using publicly available data. [ABSTRACT FROM AUTHOR]

Spinal muscular atrophy (SMA) is the most common genetic cause of infant mortality. SMA is a spectral disorder and is categorised based on symptom onset and severity. The median life expectancy for infants with SMA presenting before 6 months of age is less than 2 years without respiratory support. To date, there is no cure for SMA. In June 2017, nusinersen was approved in Canada as the first disease-modifying drug for SMA because of its demonstrated benefits on motor function and survival in clinical trials. However, with a price tag of almost 1 million dollars for the first year of therapy, careful clinical, treatment-based and ethical consideration of the principles of (i) best interests; (ii) universality; (iii) portability; (iv) public administration; (v) accessibility; and (vi) comprehensiveness are important guideposts to ensure transparent and equitable allocation of health-care resources for nusinersen and all other future orphan drugs. [ABSTRACT FROM AUTHOR]

When designing a structure or engineering a component, it is crucial to use methods that provide fast and reliable solutions, so that a large number of design options can be assessed. In this context, the proper generalized decomposition (PGD) can be a powerful tool, as it provides solutions to parametric problems, without being affected by the "curse of dimensionality." Assessing the accuracy of the solutions obtained with the PGD is still a relevant challenge, particularly when seeking quantities of interest with guaranteed bounds. In this work, we compute compatible and equilibrated PGD solutions and use them in a dual analysis to obtain quantities of interest and their bounds, which are guaranteed. We also use these complementary solutions to compute an error indicator, which is used to drive a mesh adaptivity process, oriented for a quantity of interest. The corresponding solutions have errors that are much lower than those obtained using a uniform refinement or an indicator based on the global error, as the proposed approach focuses on minimizing the error in the quantity of interest. [ABSTRACT FROM AUTHOR]

Summary: The proper generalized decomposition is a well‐established reduced order method, used to efficiently obtain approximate solutions of multi‐dimensional problems in a procedure that controls the effects of the "curse of dimensionality." The question of assessing the quality of the solutions obtained and adapting the approximations assumed, for example, the finite element meshes used, so that the best result is obtained at minimal cost, remains a relevant challenge. This article deals with finite element solutions for solid mechanics problems, using the error obtained from a dual analysis, the difference between complementary solutions, to bound the error in the solutions and to drive an optimal adaptivity process, which obtains meshes with errors significantly lower than those obtained using a uniform refinement. [ABSTRACT FROM AUTHOR]

Summary: The design of a new magnetic resonance imaging (MRI) scanner requires multiple numerical simulations of the same magneto‐mechanical problem for varying model parameters, such as frequency and electric conductivity, in order to ensure that the vibrations, noise, and heat dissipation are minimized. The high computational cost required for these repeated simulations leads to a bottleneck in the design process due to an increased design time and, thus, a higher cost. To alleviate these issues, the application of reduced order modeling techniques, which are able to find a general solution to high‐dimensional parametric problems in a very efficient manner, is considered. Building on the established proper orthogonal decomposition technique available in the literature, the main novelty of this work is an efficient implementation for the solution of 3D magneto‐mechanical problems in the context of challenging MRI configurations. This methodology provides a general solution for varying parameters of interest. The accuracy and efficiency of the method are proven by applying it to challenging MRI configurations and comparing with the full‐order solution. [ABSTRACT FROM AUTHOR]

In this work we study the dynamics of double subduction systems with opposite polarity in adjacent segments. A combined approach of numerical and analog experiments allows us to compare results and exploit the strengths of both methodologies. High‐resolution numerical experiments complement laboratory results by providing quantities difficult to measure in the laboratory such as stress state, flow patterns, and energy dissipation. Results show strong asymmetries in the mantle flow that produce in turn asymmetries in the trench and in the downgoing slab deformation. The mantle flow pattern varies with time; the toroidal cells between the plates evolve until merging into one unique cell when the trenches align. In that moment the maximum upward flow is observed close to the trenches. The interaction between the mantle flow produced by each subducting plate makes the rollback processes slower than in a single subduction case. This is consistent with the observed energy dissipation rate that is smaller in the double subduction system than in two single subductions. Moreover, we provide a detailed analysis on the setup and boundary conditions required to numerically reproduce the analog experiments. Boundary conditions at the bottom of the domain are crucial to reproduce their analog counterparts. Numerical results are compared to natural examples of multi‐slab subduction systems in terms of upper mantle seismic anisotropy, relative trench retreat velocities, and composition of subduction‐related magmatism. Key Points: Numerical models of double subduction have been developed to reproduce laboratory experiments and to understand the dynamics of the systemThe interaction between the induced mantle flows slows down the evolution of the system and generates additional deformation of platesIn the horizontal plane mantle flow forms four toroidal cells with symmetry axes that rotate during trench retreat [ABSTRACT FROM AUTHOR]

We describe a new automatic seepage meter for use in soft bottom streams and lakes. The meter utilizes a thin‐walled tube that is inserted into the streambed or lakebed. A hole in the side of the tube is fitted with an electric valve. Prior to the test, the valve is open and the water level inside the tube is the same as the water level outside the tube. The test starts with closure of the valve, and the water level inside the tube changes as it moves toward the equilibrium hydraulic head that exists at the bottom of the tube. The time rate of change of the water level immediately after the valve closes is a direct measure of the seepage rate (q). The meter utilizes a precision linear actuator and a conductance circuit to sense the water level to a precision of about ±0.1 mm. The meter can also provide an estimate of vertical hydraulic conductivity (Kv) if data are collected for a characteristic time. The detection limit for q depends on the vertical hydraulic head gradient. For Kv = 1 m/day, q of about 2 mm/day can be measured. Results from a laboratory sand tank show excellent agreement between measured and true q, and results from a field site are similar to values from calculations based on independent measurements of Kv and vertical head gradients. The meter can provide rapid (30 min) q measurements for both gaining and losing systems and complements other methods for quantifying surface water groundwater interactions. Key Points: New seepage meter for streams and lakes has been developedRapid seepage rate measurements can be made for several daysThe device can measure water levels to ±0.1 mm [ABSTRACT FROM AUTHOR]

Markov chain Monte Carlo (MCMC) methods have become standard in Bayesian inference and multi‐observable inversions in almost every discipline of the Earth sciences. In the case of geodynamic and/or coupled geophysical‐geodynamic inverse problems, however, the computational cost associated with the solution of large‐scale 3‐D Stokes forward problems has rendered probabilistic formulations impractical. Here we present a novel and extremely efficient method to produce ultrafast solutions of the 3‐D Stokes problem for MCMC simulations. Our approach combines the individual benefits of Reduced Basis techniques, goal‐oriented error formulations, and MCMC algorithms to produce an accurate and computationally efficient surrogate for the forward problem. Importantly, the surrogate adapts itself during the MCMC simulation according to the history of the chain and the goals of the inversion. This maximizes the efficiency of the forward problem and removes the need for preinversion off‐line computations to build a surrogate. We demonstrate the benefits and limitations of the method with several numerical examples and show that in all cases the computational cost is of the order of <1% compared to a traditional MCMC approach. The method is general enough to be applied to a range of problems, including uncertainty quantification/propagation, adjoint‐based geodynamic inversions, sensitivity analyses in mantle convection problems, and in the creating surrogate models for complex forward problems (e.g., heat transfer, seismic tomography, and magnetotellurics). Key Points: An efficient method for producing ultrafast solutions of the 3‐D Stokes problem for mantle convection is presentedThis method is particularly well suited for joint geodynamic‐geophysical probabilistic inverse problems and studies of dynamic topographyThe method is suitable to tackle a range of probabilistic inverse problems where fast solutions for a complex forward problem are needed [ABSTRACT FROM AUTHOR]

Stream bank storage effects during floods have received limited attention, despite the significant role of such floods in aquifer water budgets. One reason is the complexity of geometry of the problem, which commonly has been treated numerically. Using a simple model in a domain with moving boundary, a semianalytical solution for bank storage effects is proposed to account for stream stage hydrograph, floodplain slope, and aquifer parameters. The results extend classic solutions by Cooper and Rorabaugh (1963, https://doi.org/10.3133/wsp1536J) for idealized vertical streambanks but applied to realistic floodplain cross sections. The accuracy of the semianalytical solution is verified by a one‐dimensional numerical method and compared to a vertical two‐dimensional variably saturated‐flow numerical model. Comparison indicates that a robust solution is valid for diagnostic analyses of modeling bank storage effects on floodplains. The semianalytical solution is applied to laboratory experiments as well. The results indicate that the present solution provides reasonable estimates of peak timing and head of groundwater flow response in the sloping bank during varying stream stage. [ABSTRACT FROM AUTHOR]

We propose a new method for groundwater recharge rate estimation in regions with stream‐aquifer interactions, at a linear scale on the order of 10 km and more. The method is based on visual identification and quantification of classically recognized water table contour patterns. Simple quantitative analysis of these patterns can be done manually from measurements on a map, or from more complex GIS data extraction and curve fitting. Recharge rate is then estimated from the groundwater table contour parameters, streambed gradients, and aquifer transmissivity using an analytical model for groundwater flow between parallel perennial streams. Recharge estimates were obtained in three regions (areas of 1500, 2200, and 3300 km2) using available water table maps produced by different methods at different times in the area of High Plains Aquifer in Nebraska. One region is located in the largely undeveloped Nebraska Sand Hills area, while the other two regions are located at a transition zone from Sand Hills to loess‐covered area and include areas where groundwater is used for irrigation. Obtained recharge rates are consistent with other independent estimates. The approach is useful and robust diagnostic tool for preliminary estimates of recharge rates, evaluation of the quality of groundwater table maps, identification of priority areas for further aquifer characterization and expansion of groundwater monitoring networks prior to using more detailed methods. Article impact statement: A new, simple approach for estimating groundwater recharge from groundwater table contours by recognizing and quantifying their patterns. [ABSTRACT FROM AUTHOR]

Active and fossil subduction systems consisting of two adjacent plates with opposite retreating directions occur in several areas on Earth, as the Mediterranean or Western Pacific. The goal of this work is to better understand the first‐order plate dynamics of these systems using the results of experimental models. The laboratory model is composed of two separate plates made of silicon putty representing the lithosphere, on top of a tank filled with glucose syrup representing the mantle. The set of experiments is designed to test the influence of the width of plates and the initial separation between them on the resulting trench velocities, deformation of plates, and mantle flow. Results show that the mantle flow induced by both plates is asymmetric relative to the axis of each plate causing a progressive merging of the toroidal cells that prevents a steady state phase of the subduction process and generates a net outward drag perpendicular to the plates. Trench velocities increase when trenches approach each other and decrease when they separate after their intersection. The trench curvature of both plates increases linearly with time during the entire evolution of the process regardless their width and initial separation. The interaction between the return flows associated with each retreating plate, particularly in the interplate region, is stronger for near plate configurations and correlates with variations of rollback velocities. We propose that the inferred first‐order dynamics of the presented analog models can provide relevant clues to understand natural complex subduction systems. Key Points: Mantle flow induced by opposed adjacent plates is asymmetrical showing a progressive merging of the toroidal cells when trenches approachTrench retreat velocities are not steady and increase/decrease while trenches approach/separateThe first‐order consequences of the dynamics of double subduction systems are relevant in natural scenarios [ABSTRACT FROM AUTHOR]

Abstract: Heat‐pulse tracers are a promising field method to measure Darcy flux in the hyporheic zone. Interpretation of data collected from such tests typically assumes knowledge of the direction of local Darcy flux (vertical) and relies on simplified heat transport models with one‐dimensional fluid flow and heat transfer. These assumptions are seldom valid due to complex flow geometry, heterogeneity, and the presence of localized heat sources. We derive a set of analytical expressions that obviate the need for these simplifying assumptions, thus substantially improving the capabilities of existing field instruments without requiring additional measurements. These closed‐form solutions account for tensorial nature of heat‐transfer parameters, and are obtained by using Green's functions and rotational coordinate transformations. The approach simplifies data collection, estimates three‐dimensional Darcy flux, relates fluid flow to heat‐transfer properties of the host medium, and can facilitate inverse modeling. Field applications of our solutions and their ramifications for data collection and analysis are discussed. [ABSTRACT FROM AUTHOR]

Design of managed aquifer recharge ( MAR) for augmentation of groundwater resources often lacks detailed data, and simple diagnostic tools for evaluation of the water table in a broad range of parameters are needed. In many large-scale MAR projects, the effect of a regional aquifer base dip cannot be ignored due to the scale of recharge sources (e.g., wadis, streams, reservoirs). However, Hantush's (1967) solution for a horizontal aquifer base is commonly used. To address sloping aquifers, a new closed-form analytical solution for water table mound accounts for the geometry and orientation of recharge sources at the land surface with respect to the aquifer base dip. The solution, based on the Dupiuit-Forchheimer approximation, Green's function method, and coordinate transformations is convenient for computing. This solution reveals important MAR traits in variance with Hantush's solution: mounding is limited in time and space; elevation of the mound is strongly affected by the dip angle; and the peak of the mound moves over time. These findings have important practical implications for assessment of various MAR scenarios, including waterlogging potential and determining proper rates of recharge. Computations are illustrated for several characteristic MAR settings. [ABSTRACT FROM AUTHOR]

Tetraspanins are a family of transmembrane proteins that form membrane microdomains. They play important roles in migration, adhesion and other cellular processes. TspanC8, a subfamily of tetraspanins, was found to associate and promote ADAM10 trafficking and cell surface localization. One of its members, Tspan33, is expressed in activated B cells. Using RT- PCR and flow cytometry, we analysed the pattern of expression of Tspan33 in B cells from healthy donors. We found Tspan33 expression in early and late stages of B cell development. However, Tspan33 expression did not correlate with ADAM10 surface expression. We also found expression of Tspan33 early in the activation process. Given its predominant expression in activated B cells and in several lymphomas, but not in naive B cells, we hypothesize that Tspan33 could be a potential target for therapeutic purposes. [ABSTRACT FROM AUTHOR]

The identification of the geological structure from seismic data is formulated as an inverse problem. The properties and the shape of the rock formations in the subsoil are described by material and geometric parameters, which are taken as input data for a predictive model. Here, the model is based on the Helmholtz equation, describing the acoustic response of the system for a given wave length. Thus, the inverse problem consists in identifying the values of these parameters such that the output of the model agrees the best with observations. This optimization algorithm requires multiple queries to the model with different values of the parameters. Reduced order models are especially well suited to significantly reduce the computational overhead of the multiple evaluations of the model. In particular, the proper generalized decomposition produces a solution explicitly stating the parametric dependence, where the parameters play the same role as the physical coordinates. A proper generalized decomposition solver is devised to inexpensively explore the parametric space along the iterative process. This exploration of the parametric space is in fact seen as a post-process of the generalized solution. The approach adopted demonstrates its viability when tested in two illustrative examples. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The solution of a steady thermal multiphase problem is assumed to be dependent on a set of parameters describing the geometry of the domain, the internal interfaces and the material properties. These parameters are considered as new independent variables. The problem is therefore stated in a multidimensional setup. The proper generalized decomposition (PGD) provides an approximation scheme especially well suited to preclude dramatically increasing the computational complexity with the number of dimensions. The PGD strategy is reviewed for the standard case dealing only with material parameters. Then, the ideas presented in [Ammar et al., 'Parametric solutions involving geometry: A step towards efficient shape optimization.' Comput. Methods Appl. Mech. Eng., 2014; 268:178-193] to deal with parameters describing the domain geometry are adapted to a more general case including parametrization of the location of internal interfaces. Finally, the formulation is extended to combine the two types of parameters. The proposed strategy is used to solve a problem in applied geophysics studying the temperature field in a cross section of the Earth crust subsurface. The resulting problem is in a 10-dimensional space, but the PGD solution provides a fairly accurate approximation (error ≤1 %) using less that 150 terms in the PGD expansion. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Background The introduction of pegylated interferon (PEG- IFN)-α in the treatment of chronic hepatitis C has led to an increase in sustained virological response. Despite reduced immunogenicity of the pegylated form in comparison with native interferon ( IFN)-α, a high frequency of adverse cutaneous reactions has been reported with pegylated IFN-α. Here, we aimed to investigate the immunological mechanisms underlying pegylated IFN-α-induced drug eruptions. Methods Hepatitis C patients suffering from drug eruptions in association with administration of pegylated interferons were enrolled in the study ( n = 22). Subjects were tested for sensitivity to pegylated IFN-α2a, pegylated IFN-α2b, or ribavirin using intradermal, scratch, and/or patch tests, as well as lymphocyte activation tests ( LATs). Skin biopsies obtained from pegylated IFN-α-associated exanthemas, as well as from localized inflammatory skin reactions at pegylated IFN-α injection sites, were analyzed for the expression of relevant chemokines by quantitative real-time PCR and immunohistochemistry. Results A subset of patients suffering from pegylated IFN-α-associated exanthemas displayed positive intradermal tests to PEG- IFNs but not to conventional IFN (11/22). In selected patients, this observation correlated with the presence of pegylated IFN-specific T cells (3/11). Chemokine profiles of inflammatory skin reactions at the injection sites reflected an IFN-α-signature, whereas lesional skin of exanthemas showed induction of TH2-associated chemokines. Conclusions Our results indicate that specific sensitizations are one cause of exanthemas under therapy with PEG- IFNs. Clinical proof-of-concept analyses demonstrate that affected patients may benefit from a switch to conventional, nonpegylated drugs, enabling IFN-α therapy continuation without drug-associated skin eruptions. [ABSTRACT FROM AUTHOR]

The publication of the ACMG recommendations has reignited the debate over predictive testing for adult-onset disorders in minors. Response has been polarized. With this in mind, we review and critically analyze this debate. First, we identify long-standing inconsistencies between consensus guidelines and clinical practice regarding risk assessment for adult-onset genetic disorders in children using family history and molecular analysis. Second, we discuss the disparate assumptions regarding the nature of whole genome and exome sequencing underlying arguments of both supporters and critics, and the role these assumptions play in the arguments for and against reporting. Third, we suggest that implicit differences regarding the definition of best interests of the child underlie disparate conclusions as to the best interests of children in this context. We conclude by calling for clarity and consensus concerning the central foci of this debate. [ABSTRACT FROM AUTHOR]

Alkali niobates and tantalates are currently important lead-free functional oxides. The formation and decomposition energetics of potassium tantalum oxide compounds (K2OTa2O5) were measured by high-temperature oxide melt solution calorimetry. The enthalpies of formation from oxides of KTaO3 perovskite and defect pyrochlores with K/Ta ratio of less than 1 stoichiometry-K0.873Ta2.226O6, K1.128Ta2.175O6, and K1.291Ta2.142O6-were experimentally determined, and the values are (−203.63±2.92) kJ mol−1 for KTaO3 perovskite, and (−339.54±5.03) kJ mol−1, (−369.71±4.84) kJ mol−1, and (−364.78±4.24) kJ mol−1, respectively, for non-stoichiometric pyrochlores. That of stoichiometric defect K2Ta2O6 pyrochlore, by extrapolation, is (−409.87±6.89) kJ mol−1. Thus, the enthalpy of the stoichiometric pyrochlore and perovskite at K/Ta=1 stoichiometry are equal in energy within experimental error. By providing data on the thermodynamic stability of each phase, this work supplies knowledge on the phase-formation process and phase stability within the K2OTa2O5 system, thus assisting in the synthesis of materials with reproducible properties based on controlled processing. Additionally, the relation of stoichiometric and non-stoichiometric pyrochlore with perovskite structure in potassium tantalum oxide system is discussed. [ABSTRACT FROM AUTHOR]

Analytical models of groundwater flow with a spatially varying elevation of a top boundary are widely used. However, a vast majority of previous analytical studies truncated the irregularly shaped top section with little to no analyses of the shortcomings of the approximate solutions for the resulting rectangles or parallelepipeds. We present an analytical approach based on a perturbation technique that treats complete domains. It is especially accurate near the top boundary, where fluid circulation is most pronounced and higher accuracy is typically needed, such as in regional or hyporheic systems flow. The approach is illustrated by analyzing flow for a Tóthian unit basin. [ABSTRACT FROM AUTHOR]

Background/Aim This article explores the development of a unique, culturally sensitive, designated academic occupational therapy programme for the Ultra- Orthodox ( Haredi) minority in Israel. This normative university environment did not provide the opportunity for Haredi participation due to the lack of consideration of the strong commitment to a modest way of life of this community. This prevented their participation in academia and resultant employment that are necessary for economic advancement of the community. Method A follow-up survey that tracked the programme's graduates' participation in the workforce was used to determine the success of the initial goal of the establishment of the designated programme. Results Slightly above 97% of the respondents worked as occupational therapists during the first year after completing their bachelor's degree. The employment data obtained from the graduates showed that the central goal of the Council of Higher Education has been achieved. The designated culturally adapted occupational therapy programme has provided varied employment opportunities for its graduates in diverse professional environments. Conclusion With the implementation of this programme, the occupational therapy department of the University of Haifa has created greater accessibility of the profession to both the occupational therapy providers and the recipients of occupational therapy intervention as well as serve as a model for other communities. [ABSTRACT FROM AUTHOR]

An analysis method for slug tests performed in a partially penetrating well within a vertical cutoff wall is presented. A steady-state shape factor for evaluating hydraulic conductivity of the material within the wall was derived by applying the method of images to the previously developed analytical solution of Zlotnik et al. (2010) for an infinite aquifer. Two distinct boundary conditions were considered: constant-head boundary for the case of direct contact between the wall and the aquifer, and no-flux boundary representing an impermeable filter cake on the sides of the wall. The constant-head and no-flux boundary conditions yield significantly higher and lower shape factors, respectively, than those for the infinite aquifer. Consequently the conventional line-fitting method for slug test analysis would yield an inaccurate estimate of the hydraulic conductivity of a vertical cutoff wall. [ABSTRACT FROM AUTHOR]

One-km resolution MODIS-based mean annual evapotranspiration (ET) estimates in combination with PRISM precipitation rates were correlated with depth to groundwater ( d) values in the wide alluvial valley of the Platte River in Nebraska for obtaining a net recharge ( Rn) vs. d relationship. MODIS cells with irrigation were excluded, yielding a mixture of predominantly range, pasture, grass, and riparian forest covers on sandy soils with a shallow groundwater table. The transition depth ( dt) between negative and positive values of the net groundwater recharge was found to be at about 2 (±1) m. Within 1 (±1) m of the surface and at a depth larger than about 7 to 8 (±1) m, the mean annual net recharge became independent of d at a level of about −4 (±12)% and 13 (±10)%, respectively, of the mean annual precipitation rate. The obtained Rn( d) relationship is based on a calibration-free ET estimation method and may help in obtaining the net recharge in shallow groundwater areas of negligible surface runoff where sufficient groundwater-depth data exist. [ABSTRACT FROM AUTHOR]

SUMMARY When applied to diffusion problems in a multi-phase setup, the popular extended finite element method (XFEM) strategy suffers from an inaccurate representation of the local fluxes in the vicinity of the interface. The XFEM enrichment improves the global quality of the solution but it is not enforcing any local feature to the fluxes. Thus, the resulting numerical fluxes in the vicinity of the interface are not realistic, in particular when conductivity ratios between the different phases are very high. This paper introduces an additional restriction to the XFEM formulation aiming at properly reproducing the features of the local fluxes in the transition zone. This restriction is implemented through Lagrange multipliers, and the stability of the resulting mixed formulation is tested satisfactorily through the Chapelle-Bathe numerical procedure. Several examples are presented, and the solutions obtained show a spectacular improvement with respect to the standard XFEM. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT Several motor-function scales have been developed to assess neurological function in animal models of stroke, subarachnoid hemorrhage and closed head injury. We hypothesize that the location of arterial and venous catheters, even in the absence of brain injury, may impact rats' motor performance. Our study examined the effect of catheter location, rate of infection and the time required for catheter placement. We further describe an original technique of tail artery cannulation without exposure of the artery. Sixty-one rats were anesthetized and randomly assigned to one of seven groups, including no catheter, tail artery or artery + vein catheters, or femoral artery or artery + vein catheters. A neurological severity score (NSS) was determined at 1 h, 24 h and 48 h after surgical preparation or catheter placement. NSS at 1 h after placement of unilateral and bilateral femoral catheters was higher than the NSS observed at 1 h after placement of tail arterial and venous catheters ( P < 0.01). The NSS also was higher at 24 h in the bilateral femoral catheter groups as compared with the tail catheter groups ( P < 0.05). There were no differences in the NSS observed between the groups that had tail catheters and the sham group at 1 h, 24 h or 48 h. Infection rate at the site of catheter placement and the time required for catheter placement was also higher in the femoral catheter groups ( P < 0.001). Thus, we propose that the line location may bias a study's results and lead to deceptive interpretations of neurological assessment following rat head injury. Compared to femoral vessels, tail blood vessels are preferable locations for lines placement. [ABSTRACT FROM AUTHOR]

Groundwater beneath the former Nebraska Ordnance Plant (NOP) is contaminated with the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and trichloroethene (TCE). Previous treatability experiments confirmed that permanganate could mineralize RDX in NOP aquifer material. The objective of this study was to determine the efficacy of permanganate to transform RDX in the field by monitoring a pilot-scale in situ chemical oxidation (ISCO) demonstration. In this demonstration, electrical resistivity imaging (ERI) was used to create two-dimensional (2-D) images of the test site prior to, during, and after injecting sodium permanganate. The ISCO was performed by using an extraction-injection well configuration to create a curtain of permanganate. Monitoring wells were positioned downgradient of the injection zone with the intent of capturing the permanganate-RDX plume. Differencing between ERI taken preinjection and postinjection determined the initial distribution of the injected permanganate. ERI also quantitatively corroborated the hydraulic conductivity distribution across the site. Groundwater samples from 12 downgradient wells and 8 direct-push profiles did not provide enough data to quantify the distribution and flow of the injected permanganate. ERI, however, showed that the permanganate injection flowed against the regional groundwater gradient and migrated below monitoring well screens. ERI combined with monitoring well samples helped explain the permanganate dynamics in downgradient wells and support the use of ERI as a means of monitoring ISCO injections. [ABSTRACT FROM AUTHOR]

In previous studies, we have shown that by increasing the brain-to-blood glutamate efflux upon scavenging blood glutamate with either oxaloacetate or pyruvate, one achieves highly significant neuroprotection particularly in the context of traumatic brain injury. The current study examines, for the first time, how the blood glutamate scavenging properties of glutamate-pyruvate transaminase (GPT), alone or in combination with pyruvate, may contribute to the spectrum of its neuroprotective mechanisms and improve the outcome of rats exposed to brain ischemia, as they do after head trauma. Rats that were exposed to permanent middle cerebral artery occlusion (MCAO) and treated with intravenous 250 mg/kg pyruvate had a smaller volume of infarction and reduced brain edema, resulting in an improved neurological outcome and reduced mortality compared to control rats treated with saline. Intravenous pyruvate at the low dose of 31.3 mg/kg did not demonstrate any neuroprotection. However, when combined with 0.6 mg/kg of GPT there was a similar neuroprotection observed as seen with pyruvate at 250 mg/kg. Animals treated with 1.69 g/kg glutamate had a worse neurological outcome and a larger extent of brain edema. The decrease in mortality, infarcted brain volume and edema, as well as the improved neurological outcome following MCAO, was correlated with a decrease in blood glutamate levels. We therefore suggest that the blood glutamate scavenging activity of GPT and pyruvate contributes to the spectrum of their neuroprotective mechanisms and may serve as a new neuroprotective strategy for the treatment of ischemic stroke. [ABSTRACT FROM AUTHOR]

Various subsurface flow systems exhibit a combination of small-scale to large-scale anisotropy in hydraulic conductivity ( K). The large-scale anisotropy results from systematic trends (e.g., exponential decrease or increase) of K with depth. We present a general two-dimensional solution for calculation of topography-driven groundwater flow considering both small- and large-scale anisotropy in K. This solution can be applied to diverse systems with arbitrary head distribution and geometry of the water table boundary, such as basin or hyporheic flow. In a special case, this solution reduces to the well-known Tóth model of uniform isotropic basin. We introduce an integral measure of flushing intensity that quantifies flushing at different depths. Using this solution, we simulate heads and streamlines and provide analyses of flow structure in the flow domain, relevant to basin analyses or hyporheic flow. It is shown that interactions between small-scale anisotropy and large-scale anisotropy strongly control the flow structure. In the classic Tóth flow model, the flushing intensity curves exhibit quasi-exponential decrease with depth. The new measure is capable of capturing subtle changes in the flow structure. Our study shows that both small- and large-scale anisotropy characteristics have substantial effects that need to be integrated into analysis of topography-driven flow. [ABSTRACT FROM AUTHOR]

Potentiomanometers (PMs) are commonly used to determine flux directions across interfaces between surface waters and aquifers. We describe a complementary function: estimating small-scale hydraulic conductivity ( K) in a lakebed, using the constant-head injection test (CHIT) by Cardenas and Zlotnik (2003) with the PM designed by Winter et al. (1988). A piezometer with a small screen is inserted into the lakebed. Local head potential is obtained by measuring the head difference between the test point and the aquifer interface. The piezometer is then used for water injection. This technique is illustrated by measurements taken from Alkali Lake in the Sand Hills, Nebraska, United States. Lakebed K and seepage fluxes ranged from 0.037 to 0.090 m/d and Darcy velocities ranged from 0.004 to 0.027 m/d. Results were consistent with the supplementary data gathered using a modified CHIT and a cone penetrometer. The compact size of the device and the small volumes used for injection enable this method to estimate lakebed K values as low as 0.01 to 0.1 m/d, a range seldom explored in lake-aquifer interface systems. [ABSTRACT FROM AUTHOR]

Lakes of varying salinity are ubiquitous in dune environments with semiarid climates. Often these lakes become solute traps due to specific groundwater flow conditions. Over geological time after emergence of such lakes, the groundwater flow and mass transport processes lead to accumulation of solutes. This salinity increase can result in mineral deposition and free convection from lakes. However, high solute concentrations in these lakes are often not observed. We propose a conceptual model that estimates the lake salinity dynamics and yields concentration profiles beneath the lakes over centennial and millennial scales. Unlike previous approaches, a simple mathematical model is proposed based on coupling the lake solute mass balance with the advection-dispersion equation. We discuss limitations of the model and apply it to conditions of the Nebraska Sand Hills, USA. We show that the lake salinity concentration is consistent with the regional paleoclimate data. The proposed model can be used to constrain hydrologic paleoclimate reconstructions, which is a significant challenge for lakes in dune environments. [ABSTRACT FROM AUTHOR]