Water movement within a fringing reef flat,Orpheus Island,North Queensland,Australia

A technique to examine through reef water movement by direct tracing using fluorescent dyes is described. Results from an experiment conducted on the sand dominated fringing reef flat at Pioneer Bay, Orpheus Island, North Queensland, indicate net seaward water movement velocities in the order of 40 m day^-1, and considerable vertical mixing. A conceptual model of water movement is proposed in which dispersive type water movement is predominant when the reef flat is submerged, with advection being more significant when the reef flat is exposed. The application of the method to the study of the mechanisms of diagenesis is discussed and water quality rather than water agitation is suggested as being the principal reason for most rapid lithification being reported as occurring near the sediment water interface.     

Foliar water uptake: Processes,pathways, and integration into plant water budgets

Nearly all plant families, represented across most major biomes, absorb water directly through their leaves. This phenomenon is commonly referred to as foliar water uptake. Recent studies have suggested that foliar water uptake provides a significant water subsidy that can influence both plant water and carbon balance across multiple spatial and temporal scales. Despite this, our mechanistic understanding of when, where, how, and to what end water is absorbed through leaf surfaces remains limited. We first review the evidence for the biophysical conditions necessary for foliar water uptake to occur, focusing on the plant and atmospheric water potentials necessary to create a gradient for water flow. We then consider the different pathways for uptake, as well as the potential fates of the water once inside the leaf. Given that one fate of water from foliar uptake is to increase leaf water potentials and contribute to the demands of transpiration, we also provide a quantitative synthesis of observed rates of change in leaf water potential and total fluxes of water into the leaf. Finally, we identify critical research themes that should be addressed to effectively incorporate foliar water uptake into traditional frameworks of plant water movement.     

Water stress effects on leaf elongation,leaf water potential,transpiration, and nutrient uptake of rice,maize, and soybean

A pot experiment was conducted in the greenhouse to determine and compare the responses of rice (Oryza sativa L. var, IR 36), maize (Zea mays L. var. DMR-2), and soybean (Glycine max [L.] Merr. var. Clark 63) to soil water stress. Leaf elongation, dawn leaf water potential, transpiration rate, and nutrient uptake in stressed rice declined earlier than in maize and soybean. Maize and soybean, compared with rice, maintained high dawn leaf water potential for a longer period of water stress before leaf water potential. Nutrient uptake under water stress conditions was influenced more by the capacity of the roots to absorb nutrients than by transpiration. Transport of nutrients to the shoots may occur even at reduced transpiration rate It is concluded that the ability of maize and soybean to grow better than rice under water stress conditions may be due to their ability to maintain turgor as a result of the slow decline in leaf water potential brought about by low, transpiration rate and continued uptake of nutrient, especially K, which must have allowed osmotic adjustment to occur.     

Microwave dielectric studies on proteins,tissues, and heterogeneous suspensions

We summarize the results of several of our recent studies on the dielectric properties of protein solutions, tissues, and nonionic microemulsions at microwave frequencies extending to 18 GHz. The data in all cases are analyzed using the Maxwell mixture theory to determine the dielectric properties of the suspending water and the amount and dielectric properties of the water of hydration associated with the suspended phase. The dielectric data from the protein solutions and tissues are broadly consistent with the results of previous studies at UHF frequencies; they indicate hydration values in the range of 0.4–0.6 g water/g protein. There is evidence of a dielectric relaxation process occurring at low-GHz frequencies that can be attributed in part to dielectric relaxation of the “bound” water in the system. The remaining solvent water appears to have dielectric properties close to, if not precisely the same as, those of pure water. The average relaxation frequency of the suspending water in the microemulsions is reduced from that of pure water, evidently reflecting an average of that of the water of hydration (～5–6 GHz) and that of pure water. This reduced average relaxation frequency implies an increased average viscosity of the water and (by Walden's rule) accounts for the unexpectedly low ionic conductivity of the preparations.     

Water Balance in Cucumis Plants, Measured by Nuclear Magnetic Resonance, II

Nuclear magnetic resonance (NMR) was used to investigate theeffects of changes in root temperature, of changes in the areaof root in contact with culture solution and of day/night rhythmon the water balance of a cucumber and a gherkin plant. Resultsare discussed in terms of water potential, flow rate and resistanceusing a previously presented model of water balance. As longas water uptake alone is varied, flow rate and water content(or potential) will change in the same direction. In contrast,from that model it is predicted that changes in transpirationwill affect flow rate and water content in opposite ways. Anexperimental verification of this prediction was given in theprevious paper. Results obtained by the NMR method are comparedto those determined using a dendrometer. The results demonstratethat the NMR method is a valuable tool to study plant waterbalance and that it can serve as a technique for discriminatingbetween changes in plant water balance that are due to changesin water uptake by roots and those due to changes in transpiration. Key words: Water balance model, Cucumis satious L., flow, water content, NMR, water balance measurement     

Growth, Turgor, Water Potential, and Young's Modulus in Pea Internodes

The relations between longitudinal growth, Young's modulus, turgor, water potential, and tissue tensions have been studied on growing internodes of etiolated pea seedlings in an attempt to apply some physical concepts to the growth of a well-known plant material. The modulus has been determined by the resonance frequency method and expressed as E_tissue It increases nearly proportional to the turgor pressure and is at water saturation more than 50 times higher than at plasmolysis. E_tissue is higher in the epidermis than in the ground parenchyma. Indoleacetic acid causes a decrease in Etissue Other properties have been studied on intact and split segments of internodes in solutions of graded mannitol additions. — The following tentative picture of the normal course of the growth has been obtained. Auxin induces growth both in the periphery (epidermis) and in the central core (parenchyma) under a decrease in E_tissue This is followed by an increase of E_tissue which is independent of auxin but depending upon the turgor pressure. It is assumed to involve internal structural changes of the cell walls of the type of creep. The rapid growth takes place in a dynamic system with a low water potential despite favourable water conditions. Epidermis and parenchyma grow equally rapid without tissue tensions. — Such can be produced artificially by splitting of segments and water uptake. The parenchyma thereby loses its sensitivity to auxin. This is the background of the split stem test for auxin. — E_tissue increases when growth is slowing down, probably owing to both synthesis of wall substance and structural changes within the wall. The cells attain a more static condition with E_tissue higher in epidermis than in parenchyma. This leads to the normal tissue tensions. — The result agrees with growth according to the multi-net-principle. The cause of the low water potential and low turgor is discussed with reference to the dynamic nature of both growth and water transport and a probably low matric potential of the streaming water. The decrease in E_tissue following auxin addition is small but is the net difference between an auxin-induced decrease and an increase through the assumed creep.     

Plasticization, antiplasticization, and molecular packing in amorphous carbohydrate-glycerol matrices

The molecular packing of amorphous maltodextrin-glycerol matrices is systematically explored by combining positron annihilation lifetime spectroscopy (PALS) with thermodynamic measurements and dilatometry. Maltodextrin-glycerol matrices are equilibrated at a range of water activities between 0 and 0.54 at T = 25 °C to analyze the effect of both water and glycerol on the average molecular hole size and the specific volume of the matrices. In the glassy state, glycerol results in a systematic reduction of the average molecular hole size. In contrast, water interacts with the carbohydrate matrix in a complex way. Thermodynamic clustering theory shows that, at very low water contents the water molecules are well dispersed and are closely associated with the carbohydrate chains. In this regime water acts as an antiplasticizer, whereby it reduces the size of the molecular holes. Conversely, at higher water contents, while still in the glassy state, water acts as a plasticizer by increasing the average hole volume of the carbohydrate matrices. This plasticization-dominated mechanism is likely to be due to the interplay between the ability of water to form hydrogen bonds with the hydroxyl residues on the carbohydrate chains and its mobility, which is significantly decoupled from the bulk mobility of the matrix. Our findings are of key importance for the understanding of the effect of glycerol on the biostabilization performance of these carbohydrate matrices, as it provides a first insight on how molecular packing can relate to the dynamics in such matrices.     

Water Flows in Higher Plants: Physiology,Evolution, and System Analysis

Water movement in higher plants is treated as a symplastic fluid flow incorporated into a unified hydrodynamic system comprising the apoplast and vessels (or tracheids). Since water flow is of vital necessity for algae (phylogenetic ancestors of higher plants), it can be stated that higher plants colonized land, still keeping connections with their former water habitat. It is argued that colonization of terrestrial areas by plants became possible due to the appearance and maintenance of a gradient of water chemical potential between the rhizosphere and atmosphere, which drives water flows. Autonomization of flows in the symplast is considered as a vector of evolution, whereas the gradient of water activity is a factor of evolution. The osmotic models of water uptake by roots are analyzed; the role of potassium circulation in water-transporting system is determined; and a mechanism of automatic coupling between CO₂ uptake through stomata and water evaporation from leaves is presented. An inherent property of the systems to explicitly or implicitly duplicate its structural or functional elements substantiates possible interactions between the mechanisms underlying opposite water flows in plants.     

Aquaporin Membrane Channels: Biophysics, Classification, Functions, and Possible Biotechnological Applications

Water represents the major component of all living organisms. To make the cell to adapt to the surrounding environment and carry out its biological functions, water has to move into and out of the cell interior driven by osmotic forces. For over a century, scientists studying the movement of fluid into and out of the cell struggled with a difficult biophysical question: how does water pass through the cell? Movement of water across the membrane was indicated almost as soon as the lipid bilayer was recognized as being the plasma membrane of cells, back in the 1920s. Simple diffusion of water across the lipid bilayer occurs through all biological membranes. However, its low velocity and finite extent soon became apparent, suggesting the existence of additional pathways for water moving through the membrane. In spite of the enormous amount of work carried out in this area, the precise and complete answer only came relatively recently with the discovery of aquaporins, transmembrane channel proteins making the membrane tenfold to 100-fold more permeable to water than membranes lacking such pores. The water conductance featured by the aquaporins is astonishing: in fact, each single aquaporin pore can conduct billions of water molecules per second. A branch of the aquaporin family, the aquaglyceroporins, features conductance to small neutral solutes in addition to water. This review summarizes recent updates on the molecular structure, regulation, biophysics, and biological functions of aquaporins. Possible biotechnological applications of aquaporins are also described.     

Na, Cl, and Water Transport by Rat Ileum in Vitro

Interrelationships between metabolism, NaCl transport, and water transport have been studied in an in vitro preparation of rat ileum. When glucose is present in the mucosal solution, Na and Cl both appear to be actively transported from mucosa to serosa while water absorption is passive and dependent on net solute transport. Removal of glucose from the mucosal solution or treatment with dinitrophenol, monoiodoacetate, or anoxia inhibits active salt transport and as a result, water absorption is also inhibited. The dependence of water absorption on metabolism can be explained as a secondary effect due to its dependence on active salt transport. The relationship between salt and water transport has been discussed in terms of a model system.     

The Relationship between Transpiration, Root Water Uptake, and Leaf Water Potential

The effect of changing the transpiration rate on leaf waterpotential and water balance has been examined to show if permeabilityof the plant (predominantly the roots) is constant or varieswith the transpiration rate. Measurements of leaf effectivethickness, water potential, transpiration, and uptake of waterby roots were made on sunflower, barley, and maize plants grownin solution culture and subjected to a range of atmosphericconditions and root treatments: cooling, low osmotic potential,and removal of part of the root system. Leaf water potential changed little under a wide range of atmosphericconditions and rates of water flux in the three species, sothat the root permeability to water increases as the rate oftranspiration, and therefore flow across the root surface, increases.Equality between uptake and loss of water and thereby maintenanceof constant leaf water potential is assisted by stomatal changes,which appear to be in response to conditions at or in the rootrather than a direct response to changes in bulk leaf waterpotential.     

Water stress, ammonium, and leaf senescence in detached rice leaves

Ammonium accumulation in relation to water stress-promoted senescence of detached rice leaves was investigated. The effect of water stress on the senescence of detached rice leaves is associated with the accumulation of ammonium. The accumulation of ammonium in detached rice leaves by water stress is attributed to a decrease in glutamine synthetase activity. Ammonium accumulation in detached rice leaves, induced by water stress, was accompanied by an increase in tissue sensitivity to ethylene which, in turn, accelerated leaf senescence.     

Toxic cyanobacteria and drinking water: Impacts,detection, and treatment

Blooms of toxic cyanobacteria in water supply systems are a global issue affecting water supplies on every major continent except Antarctica. The occurrence of toxic cyanobacteria in freshwater is increasing in both frequency and distribution. The protection of water supplies has therefore become increasingly more challenging. To reduce the risk from toxic cyanobacterial blooms in drinking water, a multi-barrier approach is needed, consisting of prevention, source control, treatment optimization, and monitoring. In this paper, current research on some of the critical elements of this multi-barrier approach are reviewed and synthesized, with an emphasis on the effectiveness of water treatment technologies for removing cyanobacteria and related toxic compounds. This paper synthesizes and updates a number of previous review articles on various aspects of this multi-barrier approach in order to provide a holistic resource for researchers, water managers and engineers, as well as water treatment plant operators.     

Comment on “Assessing water quality of five typical reservoirs in lower reaches of Yellow River,China: Using a water quality index method” by Wei Hou,Shaohua Sun,Mingquan Wang,Xiang Li,Nuo Zhang,Xiaodong Xin,Li Sun,Wei Li,and Ruibao Jia (2016) [Ecological Indicators, 61, 309–316]

Hou et al. (2016) recently developed a water quality index (WQI) for assessing water quality of five typical reservoirs. Despite all the merits of the practical WQI, it suffers from lack of uncertainty consideration; a fact that motivated the present discussion focusing on mitigation of uncertainty in water quality assessment. In this regard, superiority of employing fuzzy WQI (FWQI) rather than crisp WQI is emphasized. Due to robustness of FWQI in handling uncertainties surrounding data acquisition, employment of fuzzy concept can improve water quality assessment and monitoring to generate results which are more consistent with real world conditions.     

Water Balance in Cucumis Plants, Measured by Nuclear Magnetic Resonance, I

In this paper we demonstrate the study of plant water balanceby the non-invasive measurement of tissue water content andwater flow using proton nuclear magnetic resonance (NMR). Sapvelocity and flux were measured independently in the presenceof an excess of stationary tissue water. The instrumentationdescribed allows automated and unattended measurement of flow-and water content-variables in a well-defined region of theplant over periods of several days, with a time resolution betweensuccessive measurements of c. 5 s. Using this apparatus theeffect of changes in light intensity (day/night rhythm) andrelative humidity on stem tissue water content as well as onthe velocity and flux of xylem sap in the stem were investigatedin a cucumber plant. The results are in agreement with predictionsfrom a simple model for plant water balance, which is basedon water potential, flow rate and resistance to flow. As longas only transpiration is varied, flow rate and water content(or potential) are affected in opposite ways as demonstratedin this paper. In contrast, the model predicts that changesin uptake (resulting from changes in, for example, root resistance)will induce changes in water content and flow in the same direction.An experimental verification of this prediction is given ina subsequent paper, where, in addition, the NMR results arecompared to those obtained with a dendrometer. Key words: Water balance model, Cucumis sativus L., flow, water content, NMR, water balance measurement     

Groundwater quality monitoring around Bass Lake,Betty's Bay,South Africa

The study involves the analysis of groundwater around Bass Lake, part of a fragile black water lake system situated along a narrow coastal plain in the southern Cape, in order to establish the quality of the water and to identify the sources of pollution. The study was conducted in 1998 during the winter season in which water samples were taken from Bass Lake and from eight wellpoints surrounding the lake. The samples were analysed for traces of faecal pollution, nutrient concentrations, pH and conductivity. The results of these tests showed that the water is relatively uncontaminated during the winter season. Only slight contamination was found at one sampling site. However there was enough secondary evidence to suggest that the lake had being reasonably polluted at various times of the year. This evidence was in the form of medical reports, changes in the natural vegetation and incidences of algal blooms. It is expected that significant contamination only occurs during the summer time, when the visitor occupancy rate in the surrounding houses is high and consequently ther is an increase in the volume of waste water and sewage received by domestic sewage systems. The study suggests that water monitoring methodology used in this study should yield better results during the drier summer period when there is decrease in the rate of groundwater flow and a lower water table. Monitoring throughout the year is recommended.     

Arsenic Concentrations in the Surface,Well, and Drinking Waters of the Hisarcik,Turkey, Area

Arsenic is one of the most important water pollutants because of its carcinogenicity. The association between arsenical poisoning and the development of internal malignancies and skin cancer is well known. The U.S. Environmental Protection Agency (USEPA) sets maximum contaminant level goals at zero for carcinogens. In this study are presented groundwater arsenic concentrations in the area of naturally rich boron sources of Turkey. Water samples were collected from the Hisarcik, Turkey, area, which has a large boron mine. An inductively coupled plasma/mass spectrometry method was used to analyze arsenic concentrations in water samples. The arsenic levels in water ranged from no detectable amounts to 3.00 mg As/L (mean: 0.46 ± 0.07SD). This mean As level exceeds by a factor of 10 the USEPA's current Maximum Contaminant Level of 0.05 mgAs/L. Some possible health problems associated with consumption of arsenic-contaminated water are discussed and public health interventions proposed.     

Water, water everywhere, and its remarkable chemistry

Photosystem II (PSII), the multisubunit pigment-protein complex localised in the thylakoid membranes of oxygenic photosynthetic organisms, uses light energy to drive a series of remarkable reactions leading to the oxidation of water. The products of this oxidation are dioxygen, which is released to the atmosphere, and reducing equivalents destined to reduce carbon dioxide to organic molecules. The water oxidation occurs at catalytic sites composed of four manganese atoms (Mn(4)-cluster) and powered by the redox potential of an oxidised chlorophyll a molecule (P680(*+)). Gerald T (Jerry) Babcock and colleagues showed that electron/proton transfer processes from substrate water to P680(*+) involved a tyrosine residue (Y(Z)) and proposed an attractive reaction mechanism for the direct involvement of Y(Z) in the chemistry of water oxidation. The 'hydrogen-atom abstract/metalloradical' mechanism he formulated is an expression of his genius and a highlight of his many other outstanding contributions to photosynthesis research. A structural basis for Jerry's model is now being revealed by X-ray crystallography.     

The interaction of salts, amides, and water.

Infrared and Raman spectra are presented for salt solutions in N-methyl formamide and N,N'-dimethylformamide. Viscosities are reported for many of these solutions. Spectroscopic and viscosity data are also given for amide-salt solutions containing water. The three-component systems exhibit a hydrogen-bonding strength of water proton greater than amide proton, and an acceptor strength of Cl- greater than amide carbonyl oxygen greater than water oxygen. The salt cation is deduced by means of viscosity measurements to interact strongly with the amide carbonyl oxygen, even in the presence of appreciable quantities of water. Association of amides by hydrogen bonding through halide ions is also indicated.     

Influence of fresh water discharge on nutrient distribution in a macrotidal lagoon,West Sussex,UK

Results of nitrate and phosphate concentrations measured using hand-held ‘Hach’ monitors are presented, both over individual tidal cycles and over longer term deployments at Pagham Harbour, West Sussex, UK. This macrotidal lagoon (offshore tidal range 3.0 m neaps–6.5 m springs) is a site of key importance as a nature reserve and a home for several rare species of plants and animals. In particular, the effects of fresh water-salt water stratification over 4 tidal cycles at two tidal-fresh water boundaries is presented. It is shown that obtaining periodic vertical profile measurements during individual tidal cycles helps to quantify the transport mechanisms of nutrients from the tidal limits into the main body of the lagoon. Of key interest is the interaction between sediment-bound nutrients with the surrounding water in which the sediment is suspended during parts of the tidal cycle. Synthesis of these results with existing knowledge about sediment-water-nutrient interactions reveals how it is possible for nutrients to become trapped at the muddy tidal limits of the lagoon. In certain cases it is shown that nutrient-rich water from fresh water streams only gradually mixes with the denser, salt water of the incoming tide. Whilst a degree of salinity-induced stratification may be expected during the flood tide, these observations suggest that the water column is stratified with respect to both N and P, even well into the ebb tide. Thus at sites where stratification is important, there is a tendency for nutrients to remain preferentially near the water surface, and thus come into contact with fine, less mobile sediments near the surface of inter-tidal zones, which are themselves, in general, accreting. Since the overlying water is generally slow-moving during high water, it is postulated that saline-induced vertical stratification of estuarine water is an important mechanism in promoting nutrient build-up in muddy inter-tidal areas of this kind.