ALBERT

Description: Current physically based overland flow erosion models for rangeland application do not separate disturbed and undisturbed conditions in modeling concentrated flow erosion. In this study, concentrated flow simulations on disturbed and undisturbed rangelands were used to estimate the erodibility and to evaluate the performance of linear and power law equations that describe the relationship between erosion rate and several hydraulic parameters. None of the hydraulic parameters consistently predicted the detachment capacity well for all sites, however, stream power performed better than most of other hydraulic parameters. Using power law functions did not improve the detachment relation with respect to that of the linear function. Concentrated flow erodibility increased significantly when a site was exposed to a disturbance such as fire or tree encroachment into sagebrush steppe. This study showed that burning increases erosion by amplifying the erosive power of overland flow through removing obstacles and by changing the soil properties affecting erodibility itself. However, the magnitude of fire impact varied among sites due to inherent differences in site characteristics and variability in burn severity. In most cases we observed concentrated flow erodibility had a high value at overland flow initiation and then started to decline with time due to reduction of sediment availability. Thus we developed an empirical function to predict erodibility variation within a runoff event as a function of cumulative unit discharge. Empirical equations were also developed to predict erodibility variation with time postdisturbance as a function of readily available vegetation cover and surface soil texture data.

Description: Abstract Borates and borosilicates are potential candidates for the design and development of glass formulations with important industrial and technological applications. A major challenge that retards the pace of development of borate/borosilicate based glasses using predictive modeling is the lack of reliable computational models to predict the structure‐property relationships in these glasses over a wide compositional space. A major hindrance in this pursuit has been the complexity of boron‐oxygen bonding due to which it has been difficult to develop adequate B–O interatomic potentials. In this article, we have evaluated the performance of three B–O interatomic potential models recently developed by Bauchy et al [J. Non‐Cryst. Solids, 2018, 498, 294–304], Du et al [J. Am. Ceram. Soc. https://doi.org/10.1111/jace.16082] and Edèn et al [Phys. Chem. Chem. Phys., 2018, 20, 8192–8209] aiming to reproduce the short‐to‐medium range structures of sodium borosilicate glasses in the system 25 Na2O x B2O3 (75 − x) SiO2 (x = 0‐75 mol%). To evaluate the different force fields, we have computed at the density functional theory level the NMR parameters of 11B, 23Na, and 29Si of the models generated with the three potentials and the simulated MAS NMR spectra compared with the experimental counterparts. It was observed that the rigid ionic models proposed by Bauchy and Du can both reliably reproduce the partitioning between BO3 and BO4 species of the investigated glasses, along with the local environment around sodium in the glass structure. However, they do not accurately reproduce the second coordination sphere of silicon ions and the Si–O–T (T = Si, B) and B‐O‐T distribution angles in the investigated compositional space which strongly affect the NMR parameters and final spectral shape. On the other hand, the core‐shell parameterization model proposed by Edén underestimates the fraction of BO4 species of the glass with composition 25Na2O 18.4B2O3 56.6SiO2 but can accurately reproduce the shape of the 11B and 29Si MAS‐NMR spectra of the glasses investigations due to the narrower B–O–T and Si‐O‐T bond angle distributions. Finally, the effect of the number of boron atoms (also distinguishing the BO3 and BO4 units) in the second coordination sphere of the network former cations on the NMR parameters have been evaluated.

Description: We describe an approach for calibrating a two-dimensional (2-D) flow model of hyporheic exchange using observations of temperature and pressure to estimate hydraulic and thermal properties. A longitudinal 2-D heat and flow model was constructed for a riffle-pool sequence to simulate flow paths and flux rates for variable discharge conditions. A uniform random sampling approach was used to examine the solution space and identify optimal values at local and regional scales. We used a regional sensitivity analysis to examine the effects of parameter correlation and nonuniqueness commonly encountered in multidimensional modeling. The results from this study demonstrate the ability to estimate hydraulic and thermal parameters using measurements of temperature and pressure to simulate exchange and flow paths. Examination of the local parameter space provides the potential for refinement of zones that are used to represent sediment heterogeneity within the model. The results indicate vertical hydraulic conductivity was not identifiable solely using pressure observations; however, a distinct minimum was identified using temperature observations. The measured temperature and pressure and estimated vertical hydraulic conductivity values indicate the presence of a discontinuous low-permeability deposit that limits the vertical penetration of seepage beneath the riffle, whereas there is a much greater exchange where the low-permeability deposit is absent. Using both temperature and pressure to constrain the parameter estimation process provides the lowest overall root-mean-square error as compared to using solely temperature or pressure observations. This study demonstrates the benefits of combining continuous temperature and pressure for simulating hyporheic exchange and flow in a riffle-pool sequence.

Description: Bayesian networks (BNs) have become a popular method of assessing environmental impacts of water management. However, spatial attributes that influence ecological processes are rarely included in BN models. We demonstrate the benefits of combining two-dimensional hydrodynamic and BN modeling frameworks to explicitly incorporate the spatial variability within a system. The impacts of two diversion scenarios on riparian vegetation recruitment at the Gila River, New Mexico, USA, were evaluated using a coupled modeling framework. We focused on five individual sites in the Upper Gila Basin. Our BN model incorporated key ecological drivers based on the “recruitment box” conceptual model, including the timing of seed availability, floodplain inundation, river recession rate, and groundwater depths. Results indicated that recruitment potential decreased by more than 20% at some locations within each study site, relative to existing conditions. The largest impacts occurring along dynamic fluvial landforms, such as side channel and sand bars. Reductions in recruitment potential varied depending on the diversion scenario. Our unique approach allowed us to evaluate recruitment consequences of water management scenarios at a fine spatial scale, which not only helped differentiate impacts at distinct channel locations, but was useful for informing stakeholders of possible ecological impacts. Our findings also demonstrate that minor changes to river flow may have large ecological implications.

Description: Shape-forming techniques which may be useful in producing components for body armor are reviewed. The techniques are classified in three general categories, dry, wet, and plastic. The different shaping techniques are compared based on key parameters including shape limitations, rate of production, cost, and safety. The techniques are evaluated as to their suitability to be used to produce different body armor components such as breast plates, deltoid, shin and knee protection, and helmets. Dry-pressing is the current standard for producing “relatively flat” components such as breast plates, but performance is limited by the inherent problem associated with dry-pressing, namely, the difficulty in producing homogeneous green bodies because of agglomerates in the powder. Plastic processing has the potential to be useful to produce more reliable “flat” components with improved performance due to high shear mixing breaking up agglomerates. Wet (colloidal) processing techniques such as gelcasting and freeze casting may be useful to produce components with high curvature and more complex shape such as helmets. Tiles or segments may be combined to produce shaped components with increased flexibility.

Description: Biochemical reactions that occur in the hyporheic zone are highly dependent on the time solutes are in contact with sediments of the riverbed. In this investigation, we developed a two-dimensional longitudinal flow and solute transport model to estimate the spatial distribution of mean residence time in the hyporheic zone. The flow model was calibrated using observations of temperature and pressure and the mean residence times were simulated using the age-mass approach for steady state flow conditions. The approach used in this investigation includes the mixing of different ages and flow paths of water through advection and dispersion. Uncertainty of flow and transport parameters was evaluated using standard Monte-Carlo and the generalized likelihood uncertainty estimation method. Results of parameter estimation support the presence of a low-permeable zone in the riffle area that induced horizontal flow at depth within the riffle area. This establishes shallow and localized flow paths and limits deep vertical exchange. For the optimal model, mean residence times were found to be relatively long (10 - 32 days). The uncertainty of hydraulic conductivity resulted in a mean inter-quartile range of 13 days across all piezometers and was reduced by 24% with the inclusion of temperature and pressure observations. To a lesser extent, uncertainty in streambed porosity and dispersivity resulted in a mean inter-quartile range of 2.2- and 4.7 days, respectively. Alternative conceptual models demonstrate the importance of accounting for the spatial distribution of hydraulic conductivity in simulating mean residence times in a riffle-pool sequence.

Description: The Rangeland Hydrology and Erosion Model (RHEM) is a new process-based model developed by the USDA-ARS. RHEM was initially developed for functionally intact rangelands where concentrated flow erosion is minimal and most soil loss occurs by rain splash and sheet flow erosion processes. Disturbance such as fire or woody plant encroachment can amplify overland flow erosion by increasing the likelihood of concentrated flow formation. In this study, we enhanced RHEM applications on disturbed rangelands by using a new approach for the prediction and parameterization of concentrated flow erosion. The new approach was conceptualized based on observations and results of experimental studies on rangelands disturbed by fire and/or by tree encroachment. The sediment detachment rate for concentrated flow was calculated using soil erodibility and hydraulic (flow width and stream power) parameters. Concentrated flow width was calculated based on flow discharge and slope using an equation developed specifically for disturbed rangelands. Soil detachment was assumed to begin with concentrated flow initiation. A dynamic erodibility concept was applied where concentrated flow erodibility was set to decrease exponentially during a runoff event due to declining sediment availability. Erodibility was estimated using an empirical parameterization equation as a function of vegetation cover and surface soil texture. A dynamic partial differential sediment continuity equation was used to model the total detachment rate of concentrated flow and rain splash and sheet flow. The enhanced version of the model was evaluated against rainfall simulation data for three different sites that exhibit some degree of disturbance by fire and/or by tree encroachment. The coefficient of determination ( R 2 ) and Nash-Sutcliffe efficiency ( NSE ) were 0.78 and 0.71, respectively, which indicates the capability of the model using the new approach for predicting soil loss on disturbed rangeland. By using the new concentrated flow modeling approach, the model was enhanced to be a practical tool which utilizes readily available vegetation and soils data for quantifying erosion and assessing erosion risk following rangeland disturbance. This article is protected by copyright. All rights reserved.

Description: Abstract Permafrost degradation in the peat‐rich southern fringe of the discontinuous permafrost zone is catalyzing substantial changes to land cover with expansion of permafrost‐free wetlands (bogs and fens) and shrinkage of forest‐dominated permafrost peat plateaux. Predicting discharge from headwater basins in this region depends upon understanding and numerically representing the interactions between storage and discharge within and between the major land cover types, and how these interactions are changing. To better understand the implications of advanced permafrost thaw‐induced land cover change on wetland discharge, with all landscape features capable of contributing to drainage networks, the hydrological behaviour of a channel fen sub‐basin in the headwaters of Scotty Creek, Northwest Territories, Canada, dominated by peat plateau‐bog complexes, was modelled using the Cold Regions Hydrological Modelling platform for the period of 2009 to 2015. The model construction was based on field water balance observations and performance was deemed adequate when evaluated against measured water balance components. A sensitivity analysis was conducted to assess the impact of progressive permafrost loss on discharge from the sub‐basin, in which all units of the sub‐basin have the potential to contribute to the drainage network, by incrementally reducing the ratio of wetland to plateau in the modelled sub‐basin. Simulated reductions in permafrost extent decreased total annual discharge from the channel fen by 2.5% for every 10% decrease in permafrost area due to increased surface storage capacity, reduced runoff efficiency and increased landscape evapotranspiration. Runoff ratios for the fen hydrological response unit dropped from 0.54 to 0.48 after the simulated 50% permafrost area loss with a substantial reduction of 0.47 to 0.31 during the snowmelt season. The reduction in peat plateau area resulted in decreased seasonal variability in discharge due to changes in the flow path routing, with amplified low‐flows associated with small increases in subsurface discharge, and decreased peak discharge with large reductions in surface runoff.

Description: Abstract Lateral surface connectivity (LSC), defined here as the surficial component of hydrologic exchange flows perpendicular to longitudinal flow, is vital to biogeochemical, geomorphological, and ecological processes on floodplains. Because rivers throughout much of the world have been subjected to anthropogenic manipulation, LSC has been greatly altered. While qualitative descriptions of LSC exist, only a limited number of studies quantify this process. The objective of this study was to quantify mass and momentum flux as proxies for LSC. This objective was met through the analysis of hydrodynamic model outputs along a 10‐km reach of the Middle Rio Grande near Albuquerque, New Mexico, USA. Mass and momentum fluxes were quantified for two synthetic floods across three spatial scales: geomorphic sub‐units, units, and reaches. In addition, three floodplain surface elevations were defined: inset, restored, and historical. Mass and momentum fluxes displayed distinct hydrodynamic signatures at each floodplain surface elevation. Inset floodplains were subjected to the greatest and most widely distributed flux magnitudes, an indication of the anthropogenic alteration along the reach. Flux heterogeneity on inset surfaces was also greatest, and increased flood magnitude did not result in comparable heterogeneity at higher floodplain elevations. Unsteady results showed that peak flux magnitudes can occur on the rising and falling limbs of a flood hydrograph, providing evidence of hysteresis in channel‐floodplain connections. Ultimately, the results are indicative of complexities associated with LSC processes along geomorphologically altered channel‐floodplain systems. The scalable methods are applicable to a wide variety of river‐floodplain systems and are complementary to empirical flux measurements.

Description: The reactivity of particle surfaces can be used as a criterion to group nanoforms (NFs) based on similar potential hazard. Since NFs may partially or completely dissolve over the duration of the assays, with the ions themselves inducing a response, reactivity assays commonly measure the additive reactivity of the particles and ions combined. Here, we determine the concentration of ions released over the course of particle testing, and determine the relative contributions of the released ions to the total reactivity measured. We differentiate three classes of reactivity, defined as being A) dominated by particles, B) additive of particles and ions, or C) dominated by ions. We provide examples for each class by analyzing the NF reactivity of Fe2O3, ZnO, CuO, Ag using the ferric reduction ability of serum (FRAS) assay. Furthermore, another two reactivity tests were performed: Dichlorodihydrofluorescin diacetate (DCFH2‑DA) assay and electron paramagnetic resonance (EPR) spectroscopy. We compare assays and demonstrate that the dose‑response may be almost entirely assigned to ions in one assay (CuO in DCFH2‑DA), but to particles in others (CuO in EPR and FRAS). When considering this data, we conclude that one cannot specify the contribution of ions to NF toxicity for a certain NF, but only for a certain NF in a specific assay, medium and dose. The extent of dissolution depends on the buffer used, particle concentration applied, and duration of exposure. This culminates in the DCFH2‑DA, EPR, FRAS assays being performed under different ion‑to‑particle ratios, and differing in their sensitivity towards reactions induced by either ions or particles. If applied for grouping, read‑across, or other concepts based on the similarity of partially soluble NFs, results on reactivity should only be compared if measured by the same assay, incubation time, and dose range.