Condensation onto the skin as a means for water gain by tree frogs in tropical Australia

Green tree frogs, Litoria caerulea, in the wet-dry tropics of northern Australia remain active during the dry season with apparently no available water and temperatures that approach their lower critical temperature. We hypothesized that this surprising activity might be because frogs that are cooled during nighttime activity gain water from condensation by returning to a warm, humid tree hollow. We measured the mass gained when a cool frog moved into either a natural or an artificial hollow. In both hollows, water condensed on cool L. caerulea, resulting in water gains of up to 0.93% of body mass. We estimated that the water gained was more than the water that would be lost to evaporation during activity. The use of condensation as a means for water gain may be a significant source of water uptake for species like L. caerulea that occur in areas where free water is unavailable over extended periods.     

Water structure changes induced by ceramics can be detected by increased permeability through aquaporin

Aquporins are intrinsic membrane proteins that function as water channel to transport water and/or mineral nutrients across biological membranes. In this study, we aimed to clarify whether water structure can be changed by the presence of ceramics and whether such a change can be determined by aquaporin. First, we confirmed that ceramics could transform tap water into active tap water by increasing water permeability through aquaporin. We also found that this change in water permeability by treatment with ceramics occurred in distilled water. The distilled water was determined to exhibit the same aquaporin permeability as the original tap water. Our data indicate that the aquaporin permeability of water can be changed by severe physical shocks, such as slapping and sonication, which is consistent with the implication that the aquaporin permeability is closely related to the structure of the water. In this study, using aquaporins, we first reported that the treatment of water with ceramics can affect the structure of water, and the water can retain the structure for a given period under certain condition     

Electromyographic analysis of walking in water in healthy humans

This study was designed to describe and clarify muscle activities which occur while walking in water. Surface electromyography (EMG) was used to evaluate muscle activities in six healthy subjects (mean age, 23.3 +/- 1.4 years) while they walked on a treadmill in water (with or without a water current) immersed to the level of the xiphoid process, and while they walked on a treadmill on dry land. The trials in water utilized the Flowmill which has a treadmill at the base of a water flume. Integrated EMG analysis was conducted for the quantification of muscle activities. In order to calculate the %MVC, the measurement of maximal voluntary contraction (MVC) of each muscle was made before the gait analysis, thus facilitating a comparison of muscle activities while walking in water with those on dry land. The %MVCs obtained from each of the tested muscles while walking in water, both with and without a water current, were all found to be lower than those obtained while walking on dry land at a level of heart rate response similar to that used when walking on dry land. Furthermore, the %MVCs while walking in water with a water current tended to be greater when compared to those while walking in water without a water current. In conclusion, the present study demonstrated that muscle activities while walking in water were significantly decreased when compared to muscle activities while walking on dry land, that muscle activities while walking in water tended to be greater with a water current than without, and that the magnitude of the muscle activity in water was relatively small in healthy humans. This information is important to design water-based exercise programs that can be safely applied for rehabilitative and recreational purposes.     

Inferring foliar water uptake using stable isotopes of water

A growing number of studies have described the direct absorption of water into leaves, a phenomenon known as foliar water uptake. The resultant increase in the amount of water in the leaf can be important for plant function. Exposing leaves to isotopically enriched or depleted water sources has become a common method for establishing whether or not a plant is capable of carrying out foliar water uptake. However, a careful inspection of our understanding of the fluxes of water isotopes between leaves and the atmosphere under high humidity conditions shows that there can clearly be isotopic exchange between the two pools even in the absence of a change in the mass of water in the leaf. We provide experimental evidence that while leaf water isotope ratios may change following exposure to a fog event using water with a depleted oxygen isotope ratio, leaf mass only changes when leaves are experiencing a water deficit that creates a driving gradient for the uptake of water by the leaf. Studies that rely on stable isotopes of water as a means of studying plant water use, particularly with respect to foliar water uptake, must consider the effects of these isotopic exchange processes.     

The molecular basis of water transport in the brain

Brain function is inextricably coupled to water homeostasis. The fact that most of the volume between neurons is occupied by glial cells, leaving only a narrow extracellular space, represents an important challenge, as even small extracellular volume changes will affect ion concentrations and therefore neuronal excitability. Further, the ionic transmembrane shifts that are required to maintain ion homeostasis during neuronal activity must be accompanied by water. It follows that the mechanisms for water transport across plasma membranes must have a central part in brain physiology. These mechanisms are also likely to be of pathophysiological importance in brain oedema, which represents a net accumulation of water in brain tissue. Recent studies have shed light on the molecular basis for brain water transport and have identified a class of specialized water channels in the brain that might be crucial to the physiological and pathophysiological handling of water.     

The turnover of body water as an indicator of health

Water homeostasis is essential for healthy living. Body water turnover, meaning the replacement of body water that is lost in a given period of time, has been examined in a number of previous studies, and a review of their results has yielded the following findings. Children up to 15 years of age show higher body water turnover than adults, although it is not clear how the aging process influences body water. Among people of similar age, the rate of body water turnover seems to be higher in those who exercise than in those who are sedentary. Therefore we hypothesized that healthy individuals have a higher body water turnover than unhealthy individuals whose metabolic balance, as indicated by water turnover, has broken down, and that a prolonged condition of excessively slow body water turnover may be associated with a lower level of metabolism. If so, body water turnover can be an indicator of human health. However, there is a paucity of information regarding water turnover rates in individuals with various physical characteristics. This study indicates the need for further investigation of body water turnover levels associated with significant changes in physiological condition and metabolic state.     

Enthalpy–entropy compensation phenomena in water solutions of proteins and small molecules: A ubiquitous properly of water

This article presents evidence for the existence of a specific linear relationship between the entropy change and the enthalpy change in a variety of processes of small solutes in water solution. The processes include solvation of ions and nonelectrolytes, hydrolysis, oxidation–reduction, ionization of weak electrolytes, and quenching of indole fluorescence among others. The values of the proportionality constant, called the compensation temperature, lie in a relatively narrow range, from about 250 to 315 °K, for all these processes. Such behavior can be a consequence of experimental errors but for a number of the processes the precision of the data is sufficient to show that the enthalpy–entropy compensation pattern is real. It is tentatively concluded that the pattern is real, very common and a consequence of the properties of liquid water as a solvent regardless of the solutes and the solute processes studied. As such the phenomenon requires that theoretical treatments of solute processes in water be expanded by inclusion of a specific treatment of the characteristic of water responsible for compensation behavior. The possible bases of the effect are proposed to be temperature-independent heat-capacity changes and/or shifts in concentrations of the two phenomenologically significant species of water. The relationship of these alternatives to the two-state process of water suggested by spectroscopic and relaxation studies is examined. The existence of a similar and probably identical relationship between enthalpy and entropy change in a variety of protein reactions suggests that liquid water plays a direct role in many protein processes and may be a common participant in the physiological function of proteins. It is proposed that the linear enthalpy–entropy relationship be used as a diagnostic test for the participation of water in protein processes. On this basis the catalytic processes of chymotrypsin and acetylcholinesterase are dominated by the properties of bulk water. The binding of oxygen by hemoglobin may fall in the same category. Similarities and differences in the behavior of small-solute and protein processes are examined to show how they may be related. No positive conclusions are established, but it is possible that protein processes are coupled to water via expansions and contractions of the protein and that in general the special pattern of enthalpy–entropy compensation is a consequent of the properties of water which require that expansions and contractions of solutes effect changes in the free volume of the nearby liquid water. It is shown that proteins can be expected to respond to changes in nearby water and interfacial free energy by expansions and contractions. Such responses may explain a variety of currently unexplained characteristics of protein solutions. More generally, the enthalpy–entropy compensation pattern appears to be the thermodynamic manifestation of “structure making” and “structure breaking,” operationally defined terms much used in discussions of water solutions. If so, the compensation pattern is ubiquitous and requires re-examination of a large body of molecular interpretations derived from quantitative studies of processes in water. Theories of processes in water may have to be expanded to accommodate this aspect of water behavior.     

Enzymatic Reactions in Non-Conventional Media: Prediction of Solvent Water Content for Optimum Water Activity

Most enzymes provide their optimum performance at a given water activity (aw), which is generally solvent independent. For a given organic liquid solvent at a specific temperature or for a supercritical solvent at a specific temperature and pressure this corresponds to a water concentration in which water has the desired activity. We present here a methodology for predicting this water concentration thus reducing substantially the amount of experimental work needed to find the optimum solvent with respect to equilibrium conversion.

If the enzyme optimum water activity is known, the methodology predicts the required water content in the solvent to achieve this aw value. If, in addition, the enzyme water activity curve is available, this methodology provides the total water that must be added to the system (enzyme plus solvent) so that a specific water activity can be obtained.

The same methodology can also be applied to predict the effect of the total water content of the system (initial or initial plus produced) on the water activity values. It is shown that: (a) for esterification reactions taking place in hydrophobic organic solvents, the produced water can lead to a substantial change in water activity, but not for less hydrophobic solvents; (b) introduction of dry CO₂ into a system, pre-equilibrated to a certain water activity at atmospheric pressure, can lead to a substantial decrease in the water activity especially at temperatures just above the critical one of the solvent and pressures larger than that.     

Meeting water requirements of an expanding world population

Water availability in the root zone (green water) is a critical component of plant production, but is often deficient in many Third World regions. When deficient, runoff water (blue water) can be added. Focusing on ten physiographic regions in Africa and Asia, characterized by mainly or partly dry climates and rapid population growth, this study analyses whether in a 30-years'' perspective enough blue water could be provided to allow food self-sufficiency. It is assumed that for food self-sufficiency some 900 cubic metres of water per person per year has to be provided. In judging the realism it is assumed that a maximum 25 per cent increase in water mobilization rate would be manageable in a 30-year period. The study suggests that by 2025, water scarcity will make regions populated by some 55 per cent of the world''s population dependent on food imports. For water-wasting regions in Central Asia, water saving might, however, free the water needed. The paper closes by proposing some urgent measures. <br>     

飞来峡水库水质现状及其向广州供水能力的探讨

水库供水(特别是对城市的供水)已成为缓解全球水资源供给不足的重要途径。于2001年至2003年的丰水期和枯水期调查分析了新建河流型水库-飞来峡水库的水质、浮游植物群落特征和营养状态。结果表明飞来峡水库水质良好,多数水质指标为地表水Ⅱ水质标准,其营养盐浓度、浮游植物的密度均较低,属于贫中营养。从近几年的水质变化来看,建库后,水质改善明显。通过对广州市饮用水源水水质现状及存在问题的分析,从水质和水量两方面探讨了飞来峡水水库作为广州优质水源地的优势。由于来水量大,水库水质净化能力强,飞来峡水库水质和水量均有保证,可作为广州市重要水源地之一。但今后,在流域管理和水土保持工作更应重视和加强。     

Volumetric water footprints,applied in a global context,do not provide insight regarding water scarcity or water quality degradation

Many authors have presented estimates of volumetric water footprints in the context of describing and comparing the water requirements of crop production and industrial activities. In recent years, water footprints have been proposed as indicators for use in assessing the sustainability, efficiency, and equity of water allocations in a global context. That perspective is notably ambitious, given that volumetric water footprints contain information pertaining to just one resource, with no consideration of scarcity values, opportunity costs, or the impacts of water use on the environment, livelihoods, or human health. The suggestion that water scarcity must be assessed from a global perspective also is misplaced. Water scarcity and water quality degradation arise in local and regional settings. The impacts and potential remedies must be evaluated at those levels, by scientists and public officials charged with determining the policies and investments needed to ensure wise use of water resources. Efforts to extend access to clean, safe, and affordable water to the millions of households lacking such access also must be designed and implemented locally. Public officials will not gain useful insight by comparing volumetric water footprints in a global context. Water scarcity and water quality degradation cannot be resolved by reorganizing production activities across river basins and continents.     

Multinuclear NMR study of enzyme hydration in an organic solvent

Multinuclear NMR spectroscopy has been used to study water bound to subtilisin Carlsberg suspended in tetrahydrofuran (THF), with the water itself employed as a probe of the hydration layer's physicochemical and dynamic characteristics. The presence of the enzyme did not affect the intensity, chemical shift or linewidth of water (up to 8% v/v) added to THF, as measured by 17O- and 2H-NMR. This finding suggests that hydration of subtilisin can be described by a three-state model that includes tightly bound, loosely bound, and free water. Solid-state 2H-NMR spectra of enzyme-bound D2O support the existence of a non-exchanging population of tightly bound water. An important implication is that the loosely-bound water is the same as free water from an NMR viewpoint. This loosely bound water must also be the water responsible for the large increase in catalytic activity observed in previous hydration studies.     

Nuclear Magnetic Resonance Transverse Relaxation Times of Water Protons in Skeletal Muscle

The observation of the spin-echo decay in a long time domain has revealed that there exist at least three different fractions of non- (or slowly) exchanging water in the rat gastrocnemius muscle. These fractions of water are characterized with different nuclear magnetic resonance (NMR) relaxation times and are identified with the different parts of tissue water. The water associated with the macromolecules was found to be approximately 8% of the total tissue water and not to exchange rapidly with the rest of the intracellular water. The transverse relaxation time (T₂) of the myoplasm is 45 ms which is roughly a 40-fold reduction from that of a dilute electrolyte solution. This fraction of water accounts for 82% of the tissue water. The reduced relaxation time is shown neither to be caused by fast exchange between the hydration and myoplasmic water nor by the diffusion of water across the local magnetic field gradients which arise from the heterogeneity in the sample. About 10% of the tissue water was resolved to be associated with the extracellular space, the relaxation time of which is approximately four times that of the myoplasm. Mathematical treatments of the proposed mechanisms which may be responsible for the reduction of tissue water relaxation times are given in this paper. The results of our study are consistent with the notion that the structure and/or motions of all or part of the cellular water are affected by the macromolecular interface and this causes a change in the NMR relaxation rates.     

区域水安全格局构建:研究进展及概念框架

随着全球变化背景下生态安全问题的日益严峻,生态安全格局研究成为宏观生态学关注的热点领域;水作为重要的自然生态要素,其安全格局的构建也是区域生态安全格局优化的重要组成部分,但目前其基本内涵、构建理论与方法、指标体系等尚未受到足够重视,缺乏系统梳理。在对比分析资源、环境与灾害等多学科视角下水安全概念异同的基础上,明晰了区域水安全格局的概念内涵,将其定义为保障区域水安全目标的土地利用空间格局;系统探讨了水安全格局构建历程与方法研究进展,指出水安全研究正由定量评价向空间管控转型,水环境安全格局构建严重滞后,缺乏水安全格局与自然生态过程、社会经济过程的耦合关联分析;最后,基于景观生态学格局-过程互馈理论和地理学区域综合视角,以GIS空间分析、In VEST模型等为技术支撑,构建了水资源安全、水环境安全和水灾害规避安全3个单一维度的水安全格局,并提出基于空间多准则分析模型的区域综合水安全格局构建概念框架,以期有效提升中国城市化进程的水安全格局保障。     

Anesthetic Gases and Water Structure : The effect of xenon on tritiated water flux across the gut

Pauling and Miller have independently proposed that the presence of an anesthetic gas in tissue induces a cage-like arrangement of hydrogen-bonded water molecules. The theories recognize that most gas-hydrate crystals would not form at the temperature and pressure that exist during anesthesia and propose that other components of tissue such as protein should have a stabilizing effect. Measurements of the behavior of water, rather than the anesthetic agent, would provide alternative information about the likelihood of hydrate crystal formation and this information could be such as to be applicable to body temperature and to pressures used for anesthesia. If the number of hydrogen-bonded water molecules in tissue is increased, then the movement of an average water molecule should be hindered. Movement of water through the tissue may be measured by tagging it with tritium and the anesthetic gas should then slow the movement of tritiated water through the tissue. The flux of tritiated water through rat cecum is indeed slowed when the cecum is exposed to the anesthetic gas, xenon, which can participate biochemically only by virtue of its van der Waals interaction. The decrement in water flux is in reasonable agreement with what could be expected theoretically from calculations based on the activation energy for the self-diffusion of water and the degree of hypothermia necessary to produce narcosis.     

Metabolic processes account for the majority of the intracellular water in log-phase Escherichia coli cells as revealed by hydrogen isotopes

It is generally believed that water transport across biological membranes is essentially a near-instantaneous process, with water molecules diffusing directly across the membrane as well as through pores such as aquaporins. As a result of these processes by which water can equilibrate across a membrane, a common assumption is that intracellular water is isotopically indistinguishable from extracellular water. To test this assumption directly, we measured the hydrogen isotope ratio of intracellular water in Escherichia coli cells. Our results demonstrate that more than 50% of the intracellular water hydrogen atoms in log-phase E. coli cells are isotopically distinct from the growth medium water and that these isotopically distinct hydrogen atoms are derived from metabolic processes. As expected, the (2)H/(1)H isotope ratio of intracellular water from log-phase cells showed an appreciably larger contribution from metabolic water than did intracellular water from stationary-phase cells (53 +/- 12 and 23 +/- 5%, respectively). The (2)H/(1)H isotope ratio of intracellular water was also monitored indirectly by measuring the isotope ratio of fatty acids, metabolites that are known to incorporate hydrogen atoms from water during biosynthesis. Significantly, the difference in the isotopic composition of intracellular water from log- to stationary-phase E. coli cells was reflected in the hydrogen isotope ratio of individual fatty acids harvested at the two different times, indicating that the isotope ratio of metabolites can be used as an indirect probe of metabolic activity. Together, these results demonstrate that contrary to the common assumption that intracellular water is isotopically identical to extracellular water, these two pools of water can actually be quite distinct.     

Managing water resources for crop production

Increasing crop production to meet the food requirements of the world''s growing population will put great pressure on global water resources. Given that the vast freshwater resources that are available in the world are far from fully exploited, globally there should be sufficient water for future agricultural requirements. However, there are large areas where low water supply and high human demand may lead to regional shortages of water for future food production. In these arid and semi-arid areas, where water is a major constraint on production, improving water resource management is crucial if Malthusian disasters are to be avoided. There is considerable scope for improvement, since in both dryland and irrigated agriculture only about one-third of the available water (as rainfall, surface, or groundwater) is used to grow useful plants. This paper illustrates a range of techniques that could lead to increased crop production by improving agricultural water use efficiency. This may be achieved by increasing the total amount of water available to plants or by increasing the efficiency with which that water is used to produce biomass. Although the crash from the Malthusian precipice may ultimately be inevitable if population growth is not addressed, the time taken to reach the edge of the precipice could be lengthened by more efficient use of existing water resources. <br>     

Counterion effects on the physical properties and the A to B transition of calf-thymus DNA films

We report measurements of the water content and swelling of wet-spun films of Na-, K-, Rb-, and Cs-DNA as a function of relative humidity (rh). The water contents (number of water molecules per base pair of DNA) of these films are found to be quite similar, indicating that the identity of the counterion species is unimportant for the water content. Since the A to B transition for these DNAs occurs at different rhs, the corresponding water contents of the A to B transition are found to be quite different. These films swell as a function of rh in a very similar manner, implying that the changes in the intermolecular bonds in the different DNAs are similar. Dramatic changes are observed in the dimensions of the films above 84% rh for all types of DNA. Combining the water content and swelling measurements yields the dependence of the volume per base pair on water content. The volume per base pair is observed to be a nonlinear function of water content, indicating nonideal mixing of the water with the DNA.     

Combined transport of water and ions through membrane channels

The coupling of ion and water flow through membrane channels is under dispute. Among all human aquaporins only aquaporin-6 exhibits ion channel activity. Whether aquaporin-6 functions also as a water channel cannot yet be determined with confidence. Similarly, a comparison of single-channel water permeabilities from ion channels and aquaporins suggests that ion channels may play a secondary role as water channels. However, the fraction of absorbed fluid that crosses epithelial ion channels still remains to be determined.     

A membrane model describing the effect of temperature on the water conductivity of erythrocyte membranes at subzero temperatures

Thermodynamic models show that the loss of intracellular water from human erythrocytes during freezing depends heavily upon the water conductivity of the erythrocyte membrane. These calculations, which are based on the simple extrapolation of ambient conductivity data to subzero temperatures, show that more than 95% of cell water is transferable during freezing, whereas experiments show that at least 20% of cell water is retained. A study of the effects of different published values for the membrane water conductivity on cell water retained during freezing shows that this discrepancy may be a consequence of the simple extrapolation procedure.For a homogeneous membrane system, absolute reaction rate theory was used to develop a surface-limited permeation model that includes the resistance to the flow of water not only through the interior region of the membrane but also across possible rate-limiting barriers at the solution-membrane interfaces. The model shows that it is unlikely that a single ratelimiting process dominates water transport in the red cell as it is being cooled from ambient to subzero temperatures. The effective membrane conductivity at subzero temperatures could possibly be much lower than a simple extrapolation of existing data would predict. With the aid of this model analytical predictions of intracellular water during freezing are more consistent with experimental observations.