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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Extreme Water Uptake of Hygroscopic Hydrogels through Maximized Swelling‐Induced Salt Loading

Abstract Hygroscopic hydrogels are emerging as scalable and low‐cost sorbents for atmospheric water harvesting, dehumidification, passive cooling, and thermal energy storage. However, devices using these materials still exhibit insufficient performance, partly due to the limited water vapor uptake of the hydrogels. Here, the swelling dynamics of hydrogels in aqueous lithiumchloride solutions, the implications on hydrogel salt loading, and the resulting vapor uptake of the synthesized hydrogel–salt composites are characterized. By tuning the salt concentration of the swelling solutions and the cross‐linking properties of the gels, hygroscopic hydrogels with extremely high salt loadings are synthesized, which enable unprecedented water uptakes of 1.79 and 3.86 gg −1 at relative humidity (RH) of 30% and 70%, respectively. At 30% RH, this exceeds previously reported water uptakes of metal–organic frameworks by over 100% and of hydrogels by 15%, bringing the uptake within 93% of the fundamental limit of hygroscopic salts while avoiding leakage problems common in salt solutions. By modeling the salt‐vapor equilibria, the maximum leakage‐free RH is elucidated as a function of hydrogel uptake and swelling ratio. These insights guide the design of hydrogels with exceptional hygroscopicity that enable sorption‐based devices to tackle water scarcity and the global energy crisis.

Graeber, Gustav↗
DOE OSTI2022

Comparative uptake, translocation, and plant mediated transport of Tc-99, Cs-133, Np-237, and U-238 in Savannah River Site soil columns for the grass species Andropogon virginicus

Here, this study examines the ability of the grass species Andropogon virginicus to alter the subsurface transport and redistribution of a suite of radionuclides ( 99 Tc, 133 Cs (stable analog for 135 Cs and 137 Cs), 237 Np, 238 U) with varying chemical behaviors in a Savannah River Site soil via the use of vegetated and unvegetated soil columns. After an acclimation period, a small volume of solution containing all radionuclides was introduced into the columns via Rhizon© pore water sampling tubes. Plants were grown for an additional 4 weeks before shoots were harvested, and columns were prepared for sampling. Plant presence led to decreased radionuclide release from the columns, mainly due to radionuclide specific combinations of system hydrology differences resulting from plant transpiration as well as plant uptake. For the most mobile radionuclides, 99 Tc followed by 237 Np, plant presence resulted in significantly different soil concentration profiles between vegetated and unvegetated columns, including notable upward migration for 237 Np in columns with plants. Additionally, plant uptake of 99 Tc was the greatest of all the radionuclides, with plant tissues containing an average of 44 % of the 99 Tc, while plant uptake only accounted for <2 % of 237 Np and <0.5 % of 133 Cs and 238 U in the system. Although overall plant uptake of 133 Cs and 238 U were similar, the majority of 133 Cs taken up by plants was associated with 133 Cs already available in the aqueous phase while 238 U uptake was mainly associated with the solid phase, meaning that plant activity resulted in a fraction of the native 238 U being mobilized and thus, made available for plant uptake. Overall, this study quantified the influence of several plant-mediated physical and biogeochemical factors that have significant influence on radionuclide mobility and transport in this complex system which can be further utilized in future system or site-specific environmental transport and risk assessment models.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Opportunistic Short‐Term Water Uptake Dynamics by Subalpine Trees Observed via In Situ Water Isotope Measurements

Abstract Variations in tree water sources are important to understand in semi‐arid ecosystems because climatic shifts towards lower snowpack and increased drought affect water availability in subalpine forests of the western US. Here, we use daily in situ measurements of stable isotopes ( 2 H & 18 O) in soil and tree stem water, soil matric potential and sap flow to study tree water uptake dynamics. We instrumented three soil profiles down to 90 cm, as well as three aspen and engelmann spruce trees near Gothic, Colorado, in the East River watershed. We observed the fate of natural isotopic variations in rainfall, soil, and plants from June to October 2022, and in August 2023 we conducted a 2 H labeled irrigation experiment. Our observations showed that all studied aspen trees compensated for water scarcity in the shallow soil by shifting the dominant water source at 60(±20) cm to ⅔ of uptake from 90 cm within a few days of a dry period. Both species relied on snowmelt stored in the subsoil to sustain transpiration. Intense rainfall caused the plant water uptake to shift partially to top soil layers within 2 days. Spruce transpiration was lower and relied more on snowmelt, because rainfall infiltration was low in the spruce stand due to high canopy interception. Our findings highlight the important role of snowmelt stored in the deep soil layers for subalpine forest drought response and the dominant fate of monsoonal rainfall to become transpiration rather than recharging groundwater and streams in the Upper Colorado River. Plain Language Summary There is a need to understand how trees in mountainous regions respond to dry conditions that lead to water scarcity, because climate projections suggest that such conditions will become more frequent in the future. Here we present a novel data set of measurements of daily stable isotopes of water across soil profiles and in tree stems of aspen and spruce. Our data show that when the upper soil dried out, aspen trees shifted to using water from deeper layers (beneath 60 cm) to keep transpiring. For spruce trees the uptake pattern is less clear, but both types of trees mainly used snowmelt stored in the deeper soil layers to survive the dry summer. After heavy rain, aspen and spruce trees switched to using water from the top 20 cm of soil. However, for spruce, only some rain reached the soil because the dense tree canopy intercepted it, so spruce trees stayed more dependent on snowmelt and used less water overall. This study shows how important deep snowmelt water is for helping forests survive dry periods and suggests that most summer rain is quickly used by trees rather than replenishing streams and groundwater in the headwaters of the Colorado River. Key Points Tree water resources changed within a few days from snow dominated to higher share of rainfall as soils wetted up after a dry period Compensatory plant water uptake by aspen from the deep layer (90 cm), while uptake from soil depths that became drier (60 cm) declined Strong differences between water sources and availability beneath aspen and spruce, respectively

Sprenger, Matthias↗
NASA NTRS1972

Maximal Oxygen Uptake, Sweating and Tolerance to Exercise in the Heat

The physiological mechanisms that facilitate acute acclimation to heat have not been fully elucidated, but the result is the establishment of a more efficient cardiovascular system to increase heat dissipation via increased sweating that allows the acclimated man to function with a cooler internal environment and to extend his performance. Men in good physical condition with high maximal oxygen uptakes generally acclimate to heat more rapidly and retain it longer than men in poorer condition. Also, upon first exposure trained men tolerate exercise in the heat better than untrained men. Both resting in heat and physical training in a cool environment confer only partial acclimation when first exposed to work in the heat. These observations suggest separate additive stimuli of metabolic heat from exercise and environmental heat to increase sweating during the acclimation process. However, the necessity of utilizing physical exercise during acclimation has been questioned. Bradbury et al. (1964) have concluded exercise has no effect on the course of heat acclimation since increased sweating can be induced by merely heating resting subjects. Preliminary evidence suggests there is a direct relationship between the maximal oxygen uptake and the capacity to maintain thermal regulation, particularly through the control of sweating. Since increased sweating is an important mechanism for the development of heat acclimation, and fit men have high sweat rates, it follows that upon initial exposure to exercise in the heat, men with high maximal oxygen uptakes should exhibit less strain than men with lower maximal oxygen uptakes. The purpose of this study was: (1) to determine if men with higher maximal oxygen uptakes exhibit greater tolerance than men with lower oxygen uptakes during early exposure to exercise in the heat, and (2) to investigate further the mechanism of the relationship between sweating and maximal work capacity.

Greenleaf, J. E.↗
NASA NTRS1988

Nitrogen uptake by wheat seedlings, interactive effects of four nitrogen sources: NO3-, NO2-, NH4+, and urea

The net influx (uptake) rates of NO3-, NH4+, NO2-, and urea into roots of wheat (Triticum aestivum cv Yecora Rojo) seedlings from complete nutrient solutions containing all four compounds were monitored simultaneously. Although urea uptake was too slow to monitor, its presence had major inhibitory effects on the uptake of each of the other compounds. Rates of NO3-, NH4+, and NO2- uptake depended in a complex fashion on the concentration of all four N compounds. Equations were developed which describe the uptake rates of each of the compounds, and of total N, as functions of concentrations of all N sources. Contour plots of the results show the interactions over the range of concentrations employed. The coefficients of these equations provide quantitative values for evaluating primary and interactive effects of each compound on N uptake.

NASA Discipline Number 61-10↗
NASA NTRS1991

Cyclic variations in nitrogen uptake rate of soybean plants: effects of pH and mixed nitrogen sources

To determine if the daily pattern of NO3- and NH4+ uptake is affected by acidity or NO3- : NH4+ ratio of the nutrient solution, non-nodulated soybean plants (Glycine max) were exposed for 21 days to replenished, complete nutrient solutions at pH 6.0, 5.5, 5.0, and 4.5 which contained either 1.0 mM NH4+, 1.0 mM NO3- [correction of NO3+], 0.67 mM NH4+ plus 0.33 mM NO3- (2:1 NH4+ : NO3-) [correction of (2:1 NH3+ : NO4-)], or 0.33 mM NH4+ plus 0.67 mM NO3- (1:2 NH4+ : NO3-). Net uptake rates of NH4+ and NO3- were measured daily by ion chromatography as depletion from the replenished solutions. When NH4+ and NO3- were supplied together, cumulative uptake of total nitrogen was not affected by pH or solution NH4+ : NO3- ratio. The cumulative proportion of nitrogen absorbed as NH4+ decreased with increasing acidity; however, the proportional uptake of NH4+ and NO3- was not constant, but varied day-to-day. This day-to-day variation in relative proportions of NH4+ and NO3- absorbed when NH4+ : NO3- ratio and pH of solution were constant indicates that the regulatory mechanism is not directly competitive. Regardless of the effect of pH on cumulative uptake of NH4+, the specific nitrogen uptake rates from mixed and from individual NH4+ and NO3- sources oscillated between maxima and minima at each pH with average periodicities similar to the expected interval of leaf emergence.

Non-NASA Center↗
NASA NTRS1989

Cyclic variations in nitrogen uptake rate of soybean plants: ammonium as a nitrogen source

When NO3- is the sole nitrogen source in flowing solution culture, the net rate of nitrogen uptake by nonnodulated soybean (Glycine max L. Merr. cv Ransom) plants cycles between maxima and minima with a periodicity of oscillation that corresponds with the interval of leaf emergence. Since soybean plants accumulate similar quantities of nitrogen when either NH4+ or NO3- is the sole source in solution culture controlled at pH 6.0, an experiment was conducted to determine if the oscillations in net rate of nitrogen uptake also occur when NH4+ is the nitrogen source. During a 21-day period of vegetative development, net uptake of NH4+ was measured daily by ion chromatography as depletion of NH4+ from a replenished nutrient solution containing 1.0 millimolar NH4+. The net rate of NH4+ uptake oscillated with a periodicity that was similar to the interval of leaf emergence. Instances of negative net rates of uptake indicate that the transition between maxima and minima involved changes in influx and efflux components of net NH4+ uptake.

NASA Discipline Life Support Systems↗
NASA NTRS1988

Cyclic variations in nitrogen uptake rate of soybean plants: effects of external nitrate concentration

Net uptake of NO3- by non-nodulated soybean plants [Glycine max (L.) Merr. cv. Ransom] growing in flowing hydroponic cultures containing 0.5, 1.0 and 10.0 mol m-3 NO3- was measured daily during a 24-d period of vegetative development to determine if amplitude of maximum and minimum rates of net NO3- uptake are responsive to external concentrations of NO3-. Removal of NO3- from the replenished solutions during each 24-h period was determined by ion chromatography. Neither dry matter accumulation nor the periodicity of oscillations in net uptake rate was altered by the external NO3- concentrations. The maxima of the oscillations in net uptake rate, however, increased nearly 3-fold in response to external NO3- concentrations. The maxima and minima, respectively, changed from 4.0 and 0.6 mmol NO3- per gram root dry weight per day at an external solution level of 0.5 mol m-3 NO3- to 15.2 and -2.7 mmol NO3- per gram root dry weight per day at an external solution level of 10.0 mol m-3 NO3-. The negative values for minimum net uptake rate from 10.0 mol m-3 NO3- solutions show that net efflux was occurring and indicate that the magnitude of the efflux component of net uptake was responsive to external concentration of NO3-.

Non-NASA Center↗
NASA NTRS1990

Root-zone acidity affects relative uptake of nitrate and ammonium from mixed nitrogen sources

Soybean plants (Glycine max [L.] Merr. cv Ransom) were grown for 21 days on 4 sources of N (1.0 mM NO3-, 0.67 mM NO3- plus 0.33 mM NH4+, 0.33 mM NO3- plus 0.67 mM NH4+, and 1.0 mM NH4+) in hydroponic culture with the acidity of the nutrient solution controlled at pH 6.0, 5.5, 5.0, and 4.5. Dry matter and total N accumulation of the plants was not significantly affected by N-source at any of the pH levels except for decreases in these parameters in plants supplied solely with NH4+ at pH 4.5. Shoot-to-root ratios increased in plants which had an increased proportion [correction of proporiton] of NH4(+)-N in their nutrient solutions at all levels of root-zone pH. Uptake of NO3- and NH4+ was monitored daily by ion chromatography as depletion of these ions from the replenished hydroponic solutions. At all pH levels the proportion of either ion that was absorbed increased as the ratio of that ion increased in the nutrient solution. In plants which were supplied with sources of NO3- plus NH4+, NH4+ was absorbed at a ratio of 2:1 over NO3- at pH 6.0. As the pH of the root-zone declined, however, NH4+ uptake decreased and NO3- uptake increased. Thus, the NH4+ to NO3- uptake ratio declined with decreases in root-zone pH. The data indicate a negative effect of declining root-zone pH on NH4+ uptake and supports a hypothesis that the inhibition of growth of plants dependent on NH4(+)-N at low pH is due to a decline in NH4+ uptake and a consequential limitation of growth by N stress.

NASA Discipline Life Support Systems↗
NASA NTRS2000

Ten-fold augmentation of endothelial uptake of vascular endothelial growth factor with ultrasound after systemic administration

OBJECTIVES: In this study, the feasibility of delivering and enhancing the uptake of vascular endothelial growth factor (VEGF) into the intact endothelium by using ultrasound (US) facilitation was determined. BACKGROUND: A limitation of tissue-targeted drug delivery is the need for direct arterial cannulation. We postulate a mechanism by which agents injected intravenously may be targeted to a tissue using US and ultrasonic contrast agents. METHODS: We used a rat model to test the ability of US and an ultrasonic contrast agent perflurocarbon exposed sonicated dextrose albumin (PESDA) to increase uptake of VEGF in the myocardium. Continuous wave Doppler US (0.6 W/cm2 at 1 MHz for 15 min) was applied to the chest wall overlying the myocardium during intravenous injection with either VEGF (100 microg/kg) alone or a combination of VEGF and PESDA (0.1%). Control rats had VEGF infused without US or PESDA. The VEGF uptake was measured quantitatively in the heart, lung, liver and kidneys by enzyme-linked immunosorbent assay (ng/g of tissue) and morphologically by fluorescence microscopy. RESULTS: There was an eight-fold increase in VEGF uptake in the heart by US alone (16.86 +/- 1.56 vs. 2.11 +/- 0.953 ng/g of tissue, p < 0.0001) and a 13-fold increase with US + PESDA (26.78 +/- 2.88 vs. 2.11 +/- 0.953 ng/g of tissue, p < 0.0001) compared with control rats. Fluorescence microscopy revealed deposition of VEGF in the endothelium of small intramyocardial arterioles. CONCLUSIONS: These results show a marked increase in endothelial VEGF uptake with US and US + PESDA. Thus, US may be used to augment endothelial VEGF uptake 10-fold to 13-fold.

Non-NASA Center↗
DOE OSTI2021

Root lateral interactions drive water uptake patterns under water limitation

The plasticity of root water uptake determines the maintenance of transpiration during periods of water limitation and drought. However, the mechanistic basis of plant water uptake, as well as the implications of water uptake strategies at the individual and ecosystem scale remain elusive. We model three-dimensional root water uptake under variably saturated conditions for a one-hectare temperate forest plot for a growing season with a pronounced mid-season dry period. Variations in root architecture, hydraulic properties, and degree of lateral interaction between root systems produce divergent local responses to water limitation and provide insights on individual and community response to meteorological conditions. Results demonstrate the plasticity of ecosystem-scale responses to surface drying, where interacting roots shift regions of active uptake to deeper soil layers with less abundant root biomass. These shifts, a product of both root system and soil hydraulic properties, illustrate intimate links between root and soil hydraulics in determining plant water sourcing. Furthermore, we demonstrate that root lateral interactions are beneficial at the ecosystem-scale, even when trees compete for water. Specifically, a more spatially extensive root system facilitates access to a larger soil water reservoir, often ameliorating water limitation and reducing sharp water potential gradients. While the reduction of water stress is a benefit, it can be offset by increased root construction and maintenance costs associated with the larger rooting system. A plausible “viability” region of root communal co-existence is therefore implied where competitive pressures and root production costs are balanced by a potential water benefit.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2014

Spring Hydrology Determines Summer Net Carbon Uptake in Northern Ecosystems

Increased photosynthetic activity and enhanced seasonal CO2 exchange of northern ecosystems have been observed from a variety of sources including satellite vegetation indices (such as the Normalized Difference Vegetation Index; NDVI) and atmospheric CO2 measurements. Most of these changes have been attributed to strong warming trends in the northern high latitudes (greater than or equal to 50N). Here we analyze the interannual variation of summer net carbon uptake derived from atmospheric CO2 measurements and satellite NDVI in relation to surface meteorology from regional observational records. We find that increases in spring precipitation and snow pack promote summer net carbon uptake of northern ecosystems independent of air temperature effects. However, satellite NDVI measurements still show an overall benefit of summer photosynthetic activity from regional warming and limited impact of spring precipitation. This discrepancy is attributed to a similar response of photosynthesis and respiration to warming and thus reduced sensitivity of net ecosystem carbon uptake to temperature. Further analysis of boreal tower eddy covariance CO2 flux measurements indicates that summer net carbon uptake is positively correlated with early growing-season surface soil moisture, which is also strongly affected by spring precipitation and snow pack based on analysis of satellite soil moisture retrievals. This is attributed to strong regulation of spring hydrology on soil respiration in relatively wet boreal and arctic ecosystems. These results document the important role of spring hydrology in determining summer net carbon uptake and contrast with prevailing assumptions of dominant cold temperature limitations to high-latitude ecosystems. Our results indicate potentially stronger coupling of boreal/arctic water and carbon cycles with continued regional warming trends.

Carbon Uptake↗
DOE OSTI2021

Coupled uptake and conversion of C 12 H 26 and NO on Pd/SSZ-13: Experiments and modeling

The uptake of NO in the presence of C 12 H 26 (dodecane) and H 2 O over a Pd/SSZ-13 washcoated Passive NOx Adsorber (PNA) monolith is reported. When a co-feed containing C 12 H 26 and NO is supplied to an unsaturated (with C 12 H 26 ) sample, the NO uptake is unaffected but during the subsequent temperature ramp the release of trapped NO is delayed from 175°C to over 220°C. The release delay is beneficial for PNA performance as the primary NO x aftertreatment technology, Selective Catalytic Reduction (SCR), is not operated below 200°C. However, pre-saturation of C 12 H 26 followed by the same NO and C 12 H 26 co-feed results in a decrease in the NO uptake compared to the NO-only feed. We conjecture that C 12 H 26 pre-adsorbed on the exterior surface of the sample blocks NO access to the pores, decreasing the number of available sites for NO uptake. Oxidation of C 12 H 26 leads to the generation of partial oxidation product CO at lower temperatures (<250°C) and deep oxidation product CO 2 at higher temperatures. Carbon monoxide binds strongly to Pd sites with NO and can delay NO release. A Pd/SSZ-13 washcoated monolith model developed in an earlier study [Ambast et al., Appl. Catal. B. Environmental (2021)] is upgraded to include C 12 H 26 storage, release, and conversion. Through a systematic combination of judicious experiments, model tuning, and validation, we provide evidence for the underlying NO uptake and release mechanisms in the presence of C 12 H 26 .

42 ENGINEERING↗
DOE OSTI2022

A Kinetic Model for Predicting Trace Gas Uptake and Reaction

A model is developed to describe trace gas uptake and reaction with applications to aerosols and microdroplets. Gas uptake by the liquid is formulated as a coupled equilibria that links gas, surface, and bulk regions of the droplet or solution. Previously, this framework was used in explicit stochastic reaction-diffusion simulations to predict the reactive uptake kinetics of ozone with droplets containing aqueous aconitic acid, maleic acid, and sodium nitrite. With the use of prior data and simulation results, a new equation for the uptake coefficient is derived, which accounts for both surface and bulk reactions. Lambert W functions are used to obtain closed form solutions to the integrated rate laws for the multiphase kinetics; similar to previous expressions that describe Michaelis-Menten enzyme kinetics. Together these equations couple interface and bulk processes over a wide range of conditions and do not require many of the limiting assumptions needed to apply resistor model formulations to explain trace gas uptake and reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Uranyl uptake into metal–organic frameworks: a detailed X-ray structural analysis

Metal–organic frameworks (MOF) are a subclass of porous framework materials that have been used for a wide variety of applications in sensing, catalysis, and remediation. Among these myriad applications is their remarkable ability to capture substances in a variety of environments ranging from benign to extreme. Among the most common and problematic substances found throughout the world's oceans and water supplies is [UO 2 ] 2+ , a common mobile ion of uranium, which is found both naturally and as a result of anthropogenic activities, leading to problematic environmental contamination. While some MOFs possess high capability for the uptake of [UO 2 ] 2+ , many more of the thousands of MOFs and their modifications that have been produced over the years have yet to be studied for their ability to uptake [UO 2 ] 2+ . However, studying the thousands of MOFs and their modifications presents an incredibly difficult task. As such, a way to narrow down the numbers seems imperative. In this work, we evaluate the binding behaviors as well as identify the specific binding sites of [UO 2 ] 2+ incorporated into six different Zr MOFs to elucidate specific features that improve [UO 2 ] 2+ uptake. In doing so, we also present a method for the determination and verification of these binding sites by Anomalous wide-angle X-ray scattering, X-ray fluorescence, and X-ray absorption spectroscopy. This research not only presents a way for future research into the uptake of [UO 2 ] 2+ into MOFs to be conducted but also a means to evaluate MOFs more generally for the uptake of other compounds to be applied for environmental remediation and improvement of ecosystems globally.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Uptake of polystyrene nanospheres by wheat and Arabidopsis roots in agar, hydroponics, and soil

Plant uptake of micro- and nanoplastics can lead to contamination of food with plastic particles and subsequent human consumption of plastics. There is evidence that plant roots can take up micro and nanoplastics; however, most of this evidence stems from experiments conducted with plants grown in hydroponics or agar systems where uptake of nanoparticles by roots is more favorable than when plants were grown in soil. Here, we discern the root uptake and accumulation of polystyrene nanospheres in plants grown in different growth media: agar, hydroponics, and soil. In addition, we tested the impacts of nanospheres on plant biomass and plant stress. Wheat and Arabidopsis thaliana were grown in agar, hydroponics, and soil media and exposed to polystyrene nanospheres. Three different nanospheres were used (40 nm and 200 nm carboxylate-modified and 200 nm amino-modified polystyrene) and uniformly mixed into the growth media. Plants were grown for 7 to 10 days and the roots were then examined for the presence of nanospheres by confocal laser scanning microscopy and scanning electron microscopy. Plant stress was evaluated by measuring reactive oxygen species (ROS). We observed the 40 nm nanospheres inside the plant roots, but the 200 nm nanospheres only adhered to the root cap cells showing no uptake into the roots. Furthermore, confocal images indicated that root uptake of nanospheres was favored in hydroponic solutions as compared to agar and soil media. Plant biomass was generally not affected by the nanospheres, except for hydroponically grown Arabidopsis thaliana, where biomass was significantly reduced. Small sized (40 nm) and positively charged (200 nm amino-modified) nanospheres showed higher ROS accumulation in plants than negatively charged 200 nm carboxylate-modified nanospheres. In conclusion, this study provides evidence that polystyrene nanospheres can be taken up into the interior of plant roots and cause plant stress, but these impacts are less pronounced in media where the plastic particles are less mobile, like in agar and soil media as compared to hydroponic systems.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Anomalously enhanced ion transport and uptake in functionalized angstrom-scale two-dimensional channels

Emulating angstrom-scale dynamics of the highly selective biological ion channels is a challenging task. Recent work on angstrom-scale artificial channels has expanded our understanding of ion transport and uptake mechanisms under confinement. However, the role of chemical environment in such channels is still not well understood. Here, we report the anomalously enhanced transport and uptake of ions under confined MoS2-based channels that are ~five angstroms in size. The ion uptake preference in the MoS2-based channels can be changed by the selection of surface functional groups and ion uptake sequence due to the interplay between kinetic and thermodynamic factors that depend on whether the ions are mixed or not prior to uptake. Our work offers a holistic picture of ion transport in 2D confinement and highlights ion interplay in this regime.

2D channels↗
DOE OSTI2021

Warm-season net CO 2 uptake outweighs cold-season emissions over Alaskan North Slope tundra under current and RCP8.5 climate

Abstract Arctic warming has increased vegetation growth and soil respiration during recent decades. The rate of Arctic warming will likely amplify over the 21st century. Previous studies have revealed that the most severe Arctic warming occurred during the cold season (September to May). The cold-season warming has posited significant CO 2 emissions to the atmosphere via respiration, possibly offsetting warm-season (June to August) net CO 2 uptake. However, prevailing Earth system land models poorly represent cold-season CO 2 emissions, making estimates of Arctic tundra annual CO 2 budgets highly uncertain. Here, we demonstrate that an improved version of the energy exascale Earth system model (E3SM) land model (ELMv1-ECA) captures the large amount of cold-season CO 2 emissions over Alaskan Arctic tundra as reported by two independent, observationally-constrained datasets. We found that the recent seven-decades warming trend of cold-season soil temperature is three times that of the warm-season. The climate sensitivity of warm-season net CO 2 uptake, however, is threefold higher than for the cold-season net CO 2 loss, mainly due to stronger plant resilience than microbial resilience to hydroclimatic extremes. Consequently, the modeled warm-season net CO 2 uptake has a larger positive trend (0.74 ± 0.14 gC m −2 yr −1 ) than that of cold-season CO 2 emissions (0.64 ± 0.11 gC m −2 yr −1 ) from 1950 to 2017, supported by enhanced plant nutrient uptake and increased light- and water-use efficiency. With continued warming and elevated CO 2 concentrations under the representative concentration pathway (RCP) 8.5 scenario, the increasing rate of warm-season net CO 2 uptake is more than twice the rate of cold-season emissions (1.33 ± 0.32 gC m −2 yr −1 vs 0.50 ± 0.12 gC m −2 yr −1 ), making the modeled Alaskan Arctic tundra ecosystem a net CO 2 sink by 2100. However, other geomorphological and ecological disturbances (e.g. abrupt permafrost thaw, thermokarst development, landscape-scale hydrological changes, wildfire, and insects) that are not considered here might alter our conclusion.

54 ENVIRONMENTAL SCIENCES↗