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Coastal shoreline forests are vulnerable to seawater exposure, the impacts of which will increase due to sea-level rise, but the longterm adaption strategies and vulnerability of coastal forests are not well understood. We used whole-tree transpiration, leaf water potential, tree-ring width, and tree-ring d13C (a proxy for intrinsic water use efficiency, iWUE) to examine the long-term adaption strategies of red maple (Acer rubrum) trees at the coastal interface (i.e., shoreline) and nearby upland in Maryland, USA. Red maple trees that grew along the shoreline and were exposed to slightly saline water (up to two PSU) had higher transpiration rates than those growing in the nearby upland forest during a wet year, but these differences disappeared during a normal precipitation year. Shoreline trees grew more slowly than upland trees over the last four decades, but these growth differences have disappeared in the last six years. Shoreline and upland trees had similar variation in iWUE, indicating that higher transpiration rates of the seawater exposed trees did not translate into differences in water use efficiency. There were no differences in predawn and midday water potential between upland and shoreline trees, suggesting no water stress occurs in shoreline trees. These findings indicate that urrent soil salinity is below the threshold to constrain coastal red maple physiological activities.
Quantitative simulation of trivalent ƒ-block chelates in water remains challenging because bonded and non-bonded force-field models make different approximations for coordination structure, exchange dynamics, and ion–ligand interactions in highly charged systems. Here, we develop a hybrid machine-learning/molecular-mechanics (ML/MM) framework for Ac 3+ –DOTA in explicit solvent by training an E(3)-equivariant neural network potential (MACELES) on mechanically embedded QM/MM data for Ac aquo and Ac–DOTA species and coupling it to NAMD 2.14 with particle-mesh Ewald electrostatics. Nanosecond ML/MM trajectories remain numerically stable and preserve chelate integrity, yielding a compact DOTA inner shell with an inner-sphere water coordination number of CN Ac,O w ≈ 1.7 arising from a dynamic equilibrium between one- and two-water states (37.5% and 59.9% of frames; three waters 2.5%). A 5 ns potential of mean force shows two low-lying basins at CN Ac,O w ≈ 1 and CN Ac,O w ≈ 2. DFT end-state free energies are consistent with the ML/MM profile, and DFT minimum-energy paths provide a qualitative electronic-structure reference for the observed basin connectivity. State-resolved kinetics reveal picosecond water-exchange pathways that couple hydration changes to transient DOTA arm fluctuations, and training-set comparisons show that temperature-matched Ac–DOTA data optimize energy/force accuracy while more diverse solvated data improve charge prediction. Overall, the present hybrid ML/MM model provides a practical description of Ac 3+ –DOTA hydration thermodynamics and short-time exchange behavior in explicit water at MD-like cost.
Water-in-salt electrolytes (WiSE) are attractive for electrochemical energy storage applications owing to their wide electrochemical stability windows and inherent safety. The high concentration of salts is widely known to suppress the decomposition of water, which otherwise limits the stability of conventional aqueous salt-in-water electrolytes (SiWE). Nevertheless, the microstructural features of WiSE that lead to this enhanced stability have not yet been fully elucidated. In this work, ab initio molecular dynamics simulations were performed to study the energetic, structural, and spectroscopic properties of LiTFSI SiWE and WiSE solutions. A detailed mapping of water-water and water-anion hydrogen bonding and cation–anion electrostatic interactions is reported for both electrolytes. Structural features are presented in terms of both radial and spatial distribution functions. Analysis of IR and vibrational power spectra reveal key differences in the intermolecular interactions in SiWE and WiSE that arise from modified solvation shell structures. Finally, the results obtained herein reveal the most important structural and spectroscopic differences between the electrolytes in normal and superconcentrated concentrations.
The solvent-composition dependence of quenching triplet states of benzophenone (3 BP) by anisole in acetonitrile-water (ACN-H2O) mixtures was investigated by laser flash photolysis over the water mole fraction (xw) increasing from 0 to 0.92. Single exponential decay of 3 BP was observed over the whole composition range. The quenching rate constant consistently increased with the water content but increased far more rapidly with xw > 0.7. The water-triggered electron-transfer (ET) mechanism was confirmed by a steeply growing quantum yield of the benzophenone ketyl radical anion, escaping back-ET when the partial water volume exceeded the acetonitrile one. The water-content influence on the 3 BP quenching rate was described by a kinetic model accounting for the microheterogeneous structure of the ACN-H2O mixtures and the very different solubility of the reactants in the solvent components. According to the model, the ET mechanism occurs at a rate constant of 1.46 × 109 M-1 s -1 and is presumably assisted by the ACN-H2O hydrogen-bonding interaction.
Water absorption plays a key role in the performance of polymeric anion exchange membranes. It influences important properties such as ionic conductivity and mechanical strength and alters their performance as solid electrolytes in hydrogen electrochemical devices for energy conversion. However, computational approaches that address the relationship between the polymer design and the absorption process are scarce. In this work, we introduce a simple thermodynamic model to predict the water absorption isotherms of polyelectrolyte membranes in contact with a water vapor reservoir that incorporates the specific chemical design of the polymers. The model accurately predicts the water content and macrostructural properties of polynorbornene membranes as a function of the water activity and successfully captures the effect of various polymer design parameters. The energy of pairwise attractive interactions predicted by our model provides a means to interpret the absorption process at the molecular level. The model also reveals the most significant favorable and unfavorable contributions to the free energy and indicates that their balance is solely governed by the water volume fraction, regardless of the polymer design. This universal behavior leads to important implications in the search for better ion exchange membranes.
The mechanistic roles of free hydronium ions, surface hydrides, and interfacial protons during guaiacol hydrodeoxygenation (HDO) on ruthenium nanoparticles are established. As guaiacol adsorbs on Ru, it loses its strong aromaticity and undergoes a rapid H-shift from its hydroxyl to meta carbons (in relation to its hydroxyl group), leading enol and keto surface isomers to exist in chemical equilibrium. HDO occurs via a hydridic H-adatom (H*) attack to the enol, followed by a kinetically relevant C-O bond rupture step, during which water shuttles the hydroxyl proton, enabling its intramolecular attack to the methoxy, evolving a high charged [Ru(s)-(C6H5O-)…(H+)…OCH3]† transition state. The competing HYD begins with a rapid H* attack to the keto, before a second, kinetically relevant H* attack, without proton involvement. Water, despite shifting the thermodynamics towards the more polar surface keto, promotes HDO to a much greater extent than HYD, because of its dual catalytic roles—it mobilizes hydroxyl proton (Brønsted acid) to cleave the strong C-O bond, synchronizing with the Ru metal surface (base) function that stabilizes the resulting [Ru(s)-(C6H5O-)…(H+)…OCH3]† transition state, and the water layers solvate this charged transition state, further reducing its free energy. Free hydronium ions do catalyze a separate homogeneous enol-keto isomerization, but this reaction is kinetically unrelated to HDO catalysis. This mechanistic picture explains the strong effects of polar protic solvent in hydrodeoxygenation, highlighting (i) the requirements of surface hydrides and interfacial protons acting in tandem to complete a HDO turnover and (ii) the cooperative role of protic solvent and metal surface in breaking the aromaticity and stabilizing charged reactive precursors and transition states.
The nature of electron transfer across metal oxide–water interfaces depends significantly on the band gap of the oxide and its band edge energies relative to the potentials of relevant aqueous redox couples. Here we focus on the water interface with MgO, a prototypical wide band gap oxide whose conduction band edge is close in energy to that of water. We investigate the behavior of an excess electron at and out of equilibrium near the interface using ab initio molecular dynamics based on hybrid density functional theory. Our simulations show that under equilibrium conditions the excess electron (donated by an Al impurity in MgO) localizes to a midgap defect state comparable in energy and shape to a hydrated electron in bulk water. To characterize the electron transfer from the conduction band of MgO to interfacial product states, we dope near-equilibrium configurations of the pristine MgO–water system with Al and run short trajectories of these instantaneously out-of-equilibrium systems. Here we observe two distinct products associated with the excess electron: a surface-localized electron (e surf –) and an aqueous hydrogen radical (H • ). The H • pathway exhibits a much higher activation barrier despite being more exoergic, making e surf – the kinetic product. Our characterization of the pathways on the basis of Marcus theory is consistent with the poor observed utility of MgO for water radiolysis. Moreover, we anticipate that the computational framework employed here will be broadly applicable to assessing electron transfer mechanisms at aqueous, photocatalytic interfaces.
Atmospheric humidity and soil moisture in the Amazon forest are tightly coupled to the region’s water balance, or the difference between two moisture fluxes, evapotranspiration minus precipitation (ET-P). However, large and poorly characterized uncertainties in both fluxes, and in their difference, make it challenging to evaluate spatiotemporal variations of water balance and its dependence on ET or P. Here, we show that satellite observations of the HDO/H 2 O ratio of water vapor are sensitive to spatiotemporal variations of ET-P over the Amazon. When calibrated by basin-scale and mass-balance estimates of ET-P derived from terrestrial water storage and river discharge measurements, the isotopic data demonstrate that rainfall controls wet Amazon water balance variability, but ET becomes important in regulating water balance and its variability in the dry Amazon. Changes in the drivers of ET, such as above ground biomass, could therefore have a larger impact on soil moisture and humidity in the dry (southern and eastern) Amazon relative to the wet Amazon.
In this study, we present direct evidence for neutrons causing nucleation of supercooled water. Highly purified water (20 nm filtration) is cooled to well below freezing (as low as −20 °C) with a radioactive calibration source of neutrons/gamma-rays either present or removed during each of many control cooling runs for the same volume of water. When it is primarily neutrons irradiating the sample bulk, the non-equilibrium freezing point (also known as the “supercooling point”) is, on average, +0.7 °C warmer than the control equivalent, with a statistical significance of greater than 5 Sigma, with systematic uncertainty included. This effect is not observed with water in the presence of gamma-rays instead of neutrons. While these neutrons should have theoretically had sufficient energy to mount the energy barrier, corroborating our results, their raising of supercooling temperature has never been reported experimentally to the best of our knowledge. The potential to use deeply supercooled solutions, not only water, as metastable detectors for radiation and perhaps dark matter or neutrino physics presents now a new avenue for exploration.
Water (H 2 O), in all forms, is an important constituent in planetary bodies, controlling habitability and influencing geological activity. Under conditions found in the interior of many planets, as the pressure increases, the H-bonds in water gradually weaken and are replaced by ionic bonds. Recent experimental measurements of the water equation of state (EOS) showed both a new phase of H-bonded water ice, ice-VIIt, and a relatively low transition pressure just above 30 GPa to ionic bonded ice-X, which has a bulk modulus 2.5 times larger. The higher bulk modulus of ice-X produces larger planets for a given mass, thereby either reducing the atmospheric contribution to the volume of many exoplanets or limiting their water content. We investigate the impact of the new EOS measurements on the planetary mass–radius relation and interior structure for water-rich planets. We find that the change in the planet mass–radius relation caused by the systematic differences between previous and new experimental EOS measurements is comparable to the observational uncertainties in some planet sizes – an issue that will become more important as observations continue to improve.
The expansion of sugarcane (cane), a high-yielding perennial crop, will likely reshape the bioenergy landscape in the Southeastern US. However, its ecohydrological implications, particularly following conversion from grazed pastures, a dominant land use in the region, remain highly uncertain. We investigated the impact of cane expansion on evapotranspiration (ET) and its partitioning, and the mechanisms influencing both ET components and water use efficiency (WUE) across multiple scales and growth cycles in subtropical Florida. We combined eddy covariance, biometric measurements, and process-based stomatal conductance (g s ) models. ET was 1.7% lower in cane than in improved pasture (IMP) but exceeded that in semi-native pasture (SN) by 21%. Transpiration (T) followed a similar pattern, consistent with lower g s in cane relative to IMP. Cane had more conservative water use and greater sensitivity of g s to vapor pressure deficit (VPD) compared to IMP pasture, suggesting cane may be more tolerant of increasing atmospheric water demand. In contrast, SN showed lower g s and weaker stomatal sensitivity to VPD compared to cane, resulting in lower T. In cane, stomatal regulation and T varied across growth cycles, with stomata becoming less water conservative as stands matured, highlighting the importance of incorporating stand age-dependent stomatal regulation into hydrological models. Evaporation (E) was higher in cane than pastures (19%–26%), partially offsetting WUE gains. Cane exhibited higher intrinsic WUE (GPP/g s ; Gross Primary Productivity), ecosystem WUE (GPP/ET), and harvest WUE (harvest/ET) than both pasture types. Large-scale pasture-to-cane conversion could produce widely contrasting hydrological outcomes. The net regional impact will depend on the proportion of each pasture type converted and on cane's high g s sensitivity to VPD, which triggers tight stomatal regulation and conservative water use, both of which will become increasingly consequential under intensifying atmospheric water demand.
The hydroxide-exchange-membrane water electrolyzer (HEMWE) is a promising means to store intermittent renewable energy in the form of hydrogen chemical energy. The hydroxide-exchange ionomer (HEI) in the gas-evolving electrodes and the hydroxide-exchange membrane (HEM) are key components of HEMWE. In this work, we simulate the cell and examine explicitly the impact of HEI and HEM properties with a focus on improving HEMWE performance when operated with distilled water ( i.e ., no supporting electrolyte). The tradeoff between the ionic conductivity gain and electrochemically active surface area (ECSA) loss is studied. For a constant catalyst loading, distributing more catalyst next to the HEM or making thinner but denser catalyst layer is beneficial for HEMWE performance. The results demonstrate that a higher water diffusion coefficient is desired for HEM to supply reactant water to the cathode. In contrast, a lower water diffusion coefficient is preferred for the cathode HEI to retain the water in the regions with high reaction rates. Overall, the findings provide important insights to optimizing HEI/HEM materials for improved HEMWE performance.
US coastal and island communities have vulnerable energy infrastructure and high energy costs, which are exacerbated by climate change. A unique opportunity exists to use thermal energy from year-round mild temperature variations to satisfy the broad energy needs of these communities. The US Department of Energy’s Oak Ridge National Laboratory designed a small-scale marine-source integrated heat pump (MS-IHP) that, as a single appliance, combines space conditioning, dehumidification (including fresh water harvesting from humid air), and water heating for home and commercial building applications in remote coastal and island communities. The unique, innovative features of the MS-IHP offer improved efficiency and substantially reduced costs for space conditioning, dehumidification, and water heating by seamlessly integrating a heat pump, heat pump water heater, and dehumidifier by using a single compressor; optimal year-round space cooling and heating, dehumidification, water harvesting, and water heating; and improved thermal comfort and reliable operation without frosting and defrosting because of the ocean’s warm temperatures and high heat capacity. Preliminary testing was conducted by retrofitting a commercial heat pump, demonstrating an outperformed performance compared with traditional air-source heat pumps. The MS-IHP technology can help decarbonize energy systems in remote coastal and island communities.
This paper reports the effect of low-cost immersed condensers on the performance of a heat pump water heater (HPWH) that does not require a water-circulating pump. The proposed design is based on the immersion of an L-style condenser coil through an opening in the top of the water tank. The novel design aims to eliminate the need for the water-circulating pumps, thereby substantially improving efficiency and reducing costs and maintenance of the HPWH system. Comprehensive computational fluid dynamics (CFD) simulations and experimental tests were performed, and the results showed that the CFD simulations were close to the experimental data. Further results confirm that the L-style condenser can introduce buoyancy-driven flow and eliminate temperature stratification in the studied HPWH water tank, thereby improving the heat transfer coefficient and coefficient of performance of the HPWH. The testing results further showed that the L-style condenser enabled more than 53% higher coefficient of performance and 400% higher heat transfer coefficient compared with the straight vertical condenser, and achieved much faster water heating. Furthermore, the effects of immersed condensers with different circuits on the HPWH performance were evaluated and compared. All results indicate that the current energy-saving and inexpensive HPWH technology is technically valid, and the benefits of performance improvement and low cost are attractive in future HPWH design.
The author has identified the following significant results. An objective technique was developed to measure the surface area of water bodies. Nineteen water bodies in the Houston and Galveston, Texas area were selected as a basis for the technique development. The actual surface area of each body was determined from rectified and enlarged NASA aircraft photography. A clustering algorithm was used to produce classification maps of the region from ERTS-1 data. Certain classes were identified as being 100% water. Other classes were identified as being mixtures of water with land or vegetation. The number of picture elements falling on each water body and its boundary were counted. A linear regression analysis was performed to relate the total number of picture elements and boundary elements counted to the actual surface area. The standard error of the estimate was 6.7 acres. The absolute error was not a function of the actual surface area of the water body.