Total Water Flux Research Articles

Effects of frozen soil and snow cover on cold‐season soil water dynamics in Tokachi, Japan

AbstractDespite the potential impact of winter soil water movements in cold regions, relatively few field studies have investigated cold‐season hydrological processes that occur before spring‐onset of snowmelt infiltration. The contribution of soil water fluxes in winter to the annual water balance was evaluated over 5 years of field observations at an agricultural field in Tokachi, Hokkaido, Japan. In two of the winters, soil frost reached a maximum depth of 0·2 m (‘frozen’ winters), whereas soil frost was mostly absent during the remaining three winters (‘unfrozen’ winters). Significant infiltration of winter snowmelt water, to a depth exceeding 1·0 m, occurred during both frozen and unfrozen winters. Such infiltration ranged between 126 and 255 mm, representing 28–51% of total annual soil water fluxes. During frozen winters, a substantial quantity of water (ca 40 mm) was drawn from deeper layers into the 0–0·2 m topsoil layer when this froze. Under such conditions, the progression and regression of the freezing front, regulated by the thickness of snow cover, controlled the quantity of soil water flux below the frozen layer. During unfrozen winters, 13–62 mm of water infiltrated to a depth of 0·2 m, before the spring snowmelt. These results indicate the importance of correctly evaluating winter soil water movement in cold regions. Copyright © 2010 John Wiley & Sons, Ltd.

Seasonal Losses of Dissolved Organic Carbon and Total Dissolved Solids from Rice Production Systems in Northern California

Water quality concerns have arisen related to rice (Oryza sativa L.) field drain water, which has the potential to contribute large amounts of dissolved organic carbon (DOC) and total dissolved solids (TDS) to the Sacramento River. Field-scale losses of DOC or TDS have yet to be quantified. The objectives of this study were to evaluate the seasonal concentrations of DOC and TDS in rice field drain water and irrigation canals, quantify seasonal fluxes and flow-weighted (FW) concentrations of DOC and TDS, and determine the main drivers of DOC and TDS fluxes. Two rice fields with different straw management practices (incorporation vs. burning) were monitored at each of four locations in the Sacramento Valley. Fluxes of DOC ranged from 3.7 to 34.6 kg ha(-1) during the growing season (GS) and from 0 to 202 kg ha(-1) during the winter season (WS). Straw management had a significant interaction effect with season, as the greatest DOC concentrations were observed during winter flooding of straw incorporated fields. Fluxes and concentrations of TDS were not significantly affected by either straw management or season. Total seasonal water flux accounted for 90 and 88% of the variability in DOC flux during the GS and WS, respectively. Peak DOC concentrations occurred at the onset of drainflow; therefore, changes in irrigation management may reduce peak DOC concentrations and thereby DOC losses. However, the timing of peak DOC concentrations from rice fields suggest that rice field drainage water is not the cause of peak DOC concentrations in the Sacramento River.

Water uptake, transport and structure characterization in poly(ethylene glycol) diacrylate hydrogels

Crosslinked poly(ethylene glycol) (PEG) free-standing films were prepared by UV-induced photopolymerization of poly(ethylene glycol) diacrylate (PEGDA) crosslinker in the presence of varying amounts of water or monofunctional poly(ethylene glycol) acrylate (PEGA). The crosslinked PEGDA films exhibited polymerization induced phase separation (PIPS) when the water content of the prepolymerization mixture was greater than 60 wt%. These phase separated films contain pores that scatter visible light, rendering them translucent or opaque. Visible light absorbance measurements, water uptake, water permeability, and salt kinetic desorption experiments were used to characterize the structure of these phase separated, crosslinked hydrogels. The films with PIPS exhibited a porous morphology in CryoSEM studies. Dead-end filtration experiments using deionized water and 1 g/l bovine serum albumin (BSA) solutions were performed to explore the fundamental transport and fouling properties of these materials. The total flux of pure water through the films after prior exposure to BSA solution was nearly equal to that measured for the as-prepared material, indicating that these PEGDA films resist fouling by BSA under the conditions studied.

Investigation on drying of middle distillate by Pervaporation

The drying of middle distillate (MD), from which diesel fuel is made, by Pervaporation (PV) was experimentally investigated in a laboratory plant applying organic membranes. The work was conducted in cooperation with a refinery in which MD is catalytically desulphurized by hydrogenation. The H2S formed is separated by steam stripping. The resulting water content in the MD is removed by decanting and subsequent vacuum drying. The objective was to investigate whether drying to low ppm water content is technically possible by the process of PV and to find out about the feasibility of replacing the vacuum drying by PV to save energy. The drying to low ppm water content was accomplished successfully. Permeate total and pure water fluxes are reported. Economic estimations compared vacuum drying costs taken from an existing plant with a design for a full scale multi-module PV plant. The run time of a plant for the point, at which energy savings make up for higher investment costs is estimated.

Development of polyelectrolyte complexes of chitosan and phosphotungstic acid as pervaporation membranes for dehydration of isopropanol

Using a solution technique, chitosan-based polyelectrolyte complexes (PECs) were developed as pervaporation membranes by incorporating phosphotungstic acid (PTA). The resulting membranes were characterized by Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Membranes were tested for their ability to separate water–isopropanol mixtures by pervaporation in the temperature range of 30–50 °C. The experimental results demonstrated that both flux and selectivity were increased simultaneously with increasing PTA content in the membrane. The permeation flux of pure chitosan membrane was increased dramatically from 4.13 to 11.70 × 10 −2 kg/m 2 h and correspondingly its separation factor was increased from 4490 to 11,241 and then decreased to 7490 at 30 °C for 10 mass% of water in the feed. The total flux and flux of water were found to be almost overlapping particularly for PECs membranes, suggesting that these could be used effectively to break the azeotropic point of water–isopropanol mixtures. From the temperature dependency of diffusion and permeation values, the Arrhenius activation parameters were estimated and discussed in the context of membranes efficiency. The pure chitosan and a small amount of PTA-incorporated PECs membranes exhibited positive heat of sorption while other PECs membranes exhibited negative heat of sorption, giving exothermic contribution.

Development of novel composite membranes using quaternized chitosan and Na +-MMT clay for the pervaporation dehydration of isopropanol

Novel polymer–clay-based composite membranes were prepared by incorporating sodium montmorillonite (Na +-MMT) clay into quaternized chitosan. The resulting membranes were characterized by Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WXAD), and thermogravimetric analysis (TGA). The effect of membrane swelling was studied by varying the water concentration in the feed. The membranes were employed for the pervaporation dehydration of isopropanol in terms of feed composition and Na +-MMT clay loading. The experimental results demonstrated that membrane containing 10 mass% of Na +-MMT clay showed the highest separation selectivity of 14,992 with a flux of 14.23 × 10 −2 kg/m 2 h at 30 °C for 10 mass% of water in the feed. The total flux and flux of water are found to be overlapping each other particularly for clay-incorporated membranes, signifying that the composite membranes developed in the present study involving quaternized chitosan and Na +-MMT clay are highly selective toward water. From the temperature-dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The resulting activation energy values obtained for water permeation ( E pw ) are much lower than those of isopropanol permeation ( E pIPA ) , suggesting that the developed composite membranes have higher separation efficiency for the water–isopropanol system. The estimated E p and E D values ranged between 8.97 and 11.89, and 7.56 and 9.88 kJ/mol, respectively. The positive heat of sorption ( Δ H s ) values were obtained for all the membranes, suggesting that Henry’s mode of sorption is predominant in the process.

Water and Vapor Movement with Condensation and Evaporation in a Sandy Column

The diffusion of warm, humid air into an initially cold, dry, sandy column was analyzed to study the movement of water vapor and liquid water under nonisothermal and low water content conditions. The analysis was performed using the HYDRUS‐1D code. While the water retention curve of sand was measured experimentally, the unsaturated hydraulic conductivity function was inversely estimated from the observed water content profiles in the column. The estimated unsaturated hydraulic conductivity function displayed a shape that reflected distinct processes of capillary pore water flow and film flow at high and low water contents, respectively. Four components of the total water flux, including thermal and isothermal liquid water and water vapor fluxes, were evaluated using the calibrated soil hydraulic properties. Evaporation and condensation rates were calculated based on water mass balance. Water vapor entered the soil column at the hot surface and condensed at the cold bottom. Subsequently, liquid water moved upward and evaporated at the moisture front in the middle of the column where the relative humidity decreased below unity. Liquid water and water vapor then circulated between the bottom and the moisture front, accompanied by condensation and evaporation processes. The impact of the enhancement factor in the thermal vapor diffusion term could not be clearly identified from available experimental water content profiles. Increases in liquid water flow and the evaporation rate could be compensated for by increases in vapor flow and the condensation rate. Additional data would be needed to fully evaluate the effect of the enhancement factor.

Two-dimensional two-phase mass transport model for methanol and water crossover in air-breathing direct methanol fuel cells

A two-dimensional two-phase mass transport model has been developed to predict methanol and water crossover in a semi-passive direct methanol fuel cell with an air-breathing cathode. The mass transport in the catalyst layer and the discontinuity in liquid saturation at the interface between the diffusion layer and catalyst layer are particularly considered. The modeling results agree well with the experimental data of a home-assembled cell. Further studies on the typical two-phase flow and mass transport distributions including species, pressure and liquid saturation in the membrane electrode assembly are investigated. Finally, the methanol crossover flux, the net water transport coefficient, the water crossover flux, and the total water flux at the cathode as well as their contributors are predicted with the present model. The numerical results indicate that diffusion predominates the methanol crossover at low current densities, while electro-osmosis is the dominator at high current densities. The total water flux at the cathode is originated primarily from the water generated by the oxidation reaction of the permeated methanol at low current densities, while the water crossover flux is the main source of the total water flux at high current densities.

Dehydration of THF‐water mixtures using zeolite‐incorporated polymeric membranes

AbstractUsing a solution technique, polymeric composite membranes were prepared by the incorporation of NaY zeolite into chitosan. The resulting membranes were tested for pervaporation separation of water–tetrahydrofuran mixtures in a temperature range of 30–50°C. The effect of membrane swelling on the separation performance was studied by varying the water composition in the feed from 5 to 30 mass %. Pervaporation data demonstrated that both flux and selectivity increased simultaneously with increasing zeolite content in the membrane. This was explained on the basis of enhancement of hydrophilicity, selective adsorption, and establishment of molecular sieving action. It was found that both total flux and flux of water are close to each other, suggesting that the developed membranes are highly selective toward water. The membrane containing the highest loading of zeolite exhibited the highest separation selectivity of 2140 with a substantial water flux of 16.88 × 10−2 kg/(m2 h) at 30°C for 5 mass % of water in the feed. From the temperature dependency of diffusion and permeation data, the Arrhenius activation parameters were estimated. A significant difference was noticed between Epw and EpTHF, EDw and EDTHF values, signifying that membranes developed with higher loading of zeolite exhibited remarkable separation selectivity toward water. The Ep and ED values ranged between 11.69 and 21.23, and 11.21 and 20.72 kJ/mol, respectively. All the membranes exhibited positive ΔHs values, suggesting that the heat of sorption is still dominated by Henry's mode of sorption. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Effects of Peclet number on pore‐scale mixing and channeling of a tracer and on directional advective porosity

Field tracer tests indicate that advective porosity, the quantity relating advective velocity to Darcy flux, may exhibit directional dependence. Theory (S. P. Neuman, 2005) suggests that directional variations in advective porosity could arise from incomplete mixing of an inert tracer between directional flow channels within a sampling volume of soil or rock that may be hydraulically isotropic or anisotropic, rendering advective porosity a function of Peclet number. Whereas Neuman was able to quantify the process for idealized intersecting fracture sets, his theory is too abstract to allow doing so for more complex systems of fractures or pores. We use Smoothed Particle Hydrodynamics (e.g., A. M. Tartakovsky and P. Meakin, 2005, 2006) to simulate advective‐diffusive transport of a passive tracer in the interior of an idealized pore space between impermeable circular or elliptical solid grains of random size, arranged randomly within a square domain. Our numerical experiments reveal a transition from complete mixing of tracer at small Peclet numbers to the gradual evolution of pore‐scale channels of tracer which allow less and less mixing as Peclet numbers grow. Advective porosity, computed as the ratio between total water flux across the domain boundaries and migration rate of the tracer center of mass, is found to diminish asymptotically from a value close to the total porosity at small Peclet numbers to a constant dominated entirely by advection at large Peclet numbers. When total porosity is kept constant, channeling is less pronounced and mixing more prominent when flow takes place parallel to the longer axes of elliptical grains as compared to when the grains are circular. On the other hand, channeling is more pronounced and mixing less so when flow takes place perpendicular to the longer elliptical grain axes. Correspondingly, the rate at which advective porosity diminishes with increasing Peclet number is slower and the asymptote is larger when flow takes place parallel to the longer axes of elliptical grains than when the grains are circular. However, the rate is faster and the asymptote smaller when flow takes place perpendicular to the longer elliptical grain axes.

Carbon Dioxide Transport through Membranes

Several membrane channels, like aquaporin-1 (AQP1) and the RhAG protein of the rhesus complex, were hypothesized to be of physiological relevance for CO(2) transport. However, the underlying assumption that the lipid matrix imposes a significant barrier to CO(2) diffusion was never confirmed experimentally. Here we have monitored transmembrane CO(2) flux (J(CO2)) by imposing a CO(2) concentration gradient across planar lipid bilayers and detecting the resulting small pH shift in the immediate membrane vicinity. An analytical model, which accounts for the presence of both carbonic anhydrase and buffer molecules, was fitted to the experimental pH profiles using inverse problems techniques. At pH 7.4, the model revealed that J(CO2) was entirely rate-limited by near-membrane unstirred layers (USL), which act as diffusional barriers in series with the membrane. Membrane tightening by sphingomyelin and cholesterol did not alter J(CO2) confirming that membrane resistance was comparatively small. In contrast, a pH-induced shift of the CO(2) hydration-dehydration equilibrium resulted in a relative membrane contribution of about 15% to the total resistance (pH 9.6). Under these conditions, a membrane CO(2) permeability (3.2 +/- 1.6 cm/s) was estimated. It indicates that cellular CO(2) uptake (pH 7.4) is always USL-limited, because the USL size always exceeds 1 mum. Consequently, facilitation of CO(2) transport by AQP1, RhAG, or any other protein is highly unlikely. The conclusion was confirmed by the observation that CO(2) permeability of epithelial cell monolayers was always the same whether AQP1 was overexpressed in both the apical and basolateral membranes or not.

Water Vapor Diffusion Through Soil as Affected by Temperature and Aggregate Size

Water vapor diffusion through the soil is an important part in the total water flux in the unsaturated zone of arid or semiarid regions and has several significant agricultural and engineering applications because soil moisture contents near the surface are relatively low. Water vapor diffusing through dry soil is absorbed for both long and short terms. Long-term absorption allows more water to enter than exit the soil, as reflected in the concentration gradient. Short-term absorption leads to an apparent reduction in the diffusion rate, as reflected in the diffusion coefficient. This investigation studied the effects of soil temperature and porosity on the isothermal diffusion of water vapor through soil. The diffusion model consisted of 25.4 cm × 8.9 cm × 20.3 cm Plexiglas box divided into two compartments by a partition holding a soil reservoir. Water vapor moved from a container suspended by a spring in one compartment, through the porous medium in the center of the model, to calcium chloride in a container suspended by a spring in the other compartment. The porous materials consisted of aggregates of varying size (2–2.8, 1–2, and 0.5–1 mm) of a Fayatte silty clay loam (a fine-silty, mixed mesic Typic Hapludalf). The flow rates of water vapor were measured at temperatures of 10, 20, 30, and 40°C. Warmer temperatures increased the rate of diffusion through dry soil while reduced the amount of water absorbed by that soil. Reducing porosity slowed the rate of diffusion and increased the amount of water absorbed. The dry soil in this study absorbed from 1/8 to 2/3 of the diffusing water. Maximum absorption rates occurred with the most compact soil samples at the highest temperature, though the maximum absorption as a percentage of the diffusing water was in the compact samples at the lowest temperature. The diffusivity equation D/D 0 = [(S – 0.1)/0.9]2 fit the D/D 0 values obtained from these data if a coefficient of 1/3 or 1/3.5 is added to correct for the time delays caused by temporary sorption of the diffusing water vapor. The data, influenced by the interaction of water vapor and soil materials, represent a diffusion rate lower than the diffusion rate that would have resulted without this interaction.

2,2‐Bis[4‐(3,4‐dicarboxyphenoxy) phenyl]propane dianhydride (BPADA)‐based polyimide membranes for pervaporation dehydration of isopropanol: Characterization and comparison with 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA)‐based polyimide membranes

AbstractPolyimides were synthesized from one‐step polycondensation of BPADA and various diamines and were characterized with GPC, FTIR, NMR, DSC, and TGA. Polyimide membranes were prepared, and their hydrophilicity was estimated by contact angles and the free energies of interfacial interactions. Pervaporation properties were investigated for the dehydration of isopropanol, and comparisons were made between BPADA‐based membranes and 6FDA‐based membranes. The concentration coefficients of BPADA‐based membranes were calculated from the linear moiety contribution method based on the results from 6FDA‐based membranes, and they were compared to understand the effects of the feed concentration on pervaporation properties. The effects of temperature on permeation flux were studied with permeation activation energies for total flux and water flux in permeates. Moiety contribution factors for activation energies were used to correlate permeation flux and monomer moieties in the polymers, and reasonable results were obtained for BPADA. It is revealed that steric effects of monomers may change the diffusion properties, while functional groups are favorable to the changes in sorption properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Pervaporation dehydration of isopropyl alcohol with NaY zeolite incorporated hybrid membranes

AbstractWith a solution technique, NaY zeolite incorporated, tetraethylorthosilicate‐crosslinked poly(vinyl alcohol) membranes were prepared. The resulting membranes were tested for their ability to separate isopropyl alcohol/water mixtures by pervaporation in the temperature range of 30–50°C. The effects of the zeolite content and feed composition on the pervaporation performance of the membranes were investigated. The experimental results demonstrated that both flux and selectivity increased simultaneously with increasing zeolite content in the membranes. This was explained on the basis of the enhancement of hydrophilicity, selective adsorption, and establishment of a molecular sieving action attributed to the creation of pores in the membrane matrix. The membrane containing 15 mass % zeolite exhibited the highest separation selectivity of 3991 with a flux of 5.39 × 10−2 kg/m2 h with 10 mass % water in the feed at 30°C. The total flux and flux of water were close to each other for almost all the studied membranes, and this suggested that the membranes could be used effectively to break the azeotropic point of water/isopropyl alcohol mixtures to remove a small amount of water from isopropyl alcohol. From the temperature‐dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The activation energy values obtained for water were significantly lower than those for isopropyl alcohol, and this suggested that the developed membranes had a higher separation efficiency for water/isopropyl alcohol systems. The activation energy values for total permeation and water permeation were found to be almost the same for all the membranes, and this signified that coupled transport was minimal because of the highly selective nature of the membranes. Positive heat of sorption values were observed in all the membranes, and this suggested that Henry's mode of sorption was predominant. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Nutrient Input Through Occult and Wet Deposition into a Subtropical Montane Cloud Forest

Chemical composition of fog and rain water was studied during a 47-day experimental period. The differences between the fog and rain water were found to be significantly for most analyzed ions. H+, NH4+, NO3−, and SO42− made up 85% of the total median ion concentration in fog and 84% in rain water. The total mean equivalent concentration was 15 times higher in the fog than in the rain water. The fog water samples were classified according to their air mass history. The analysis of the 120 h backward trajectory led to the identification of three advection regimes. Significant differences of ion concentrations between the respective classes were found. Air masses of class I travelled exclusively over the Pacific Ocean, class II were carried over the Philippines, and class III were advected from mainland China. The turbulent fog water deposition was determined by the means of the eddy covariance method. The total (turbulent plus gravitational) fog water fluxes ranged between +31.7 mg m−2 s−1 and −56.6 mg m−2 s−1. Fog water droplets with mean diameters between 15 μm and 25 μm contributed most to the liquid water flux. The sample based nutrient input was calculated on the basis of the occult and wet deposition, and the concentrations of the simultaneously collected fog and rainwater samples, respectively. The nutrient input through wet deposition was about 13 times higher than through occult deposition.

Development of novel blocked diisocyanate crosslinked chitosan membranes for pervaporation separation of water–isopropanol mixtures

Using a solution technique, novel polymeric membranes were prepared by incorporating water-soluble blocked diisocyanate into chitosan. The resulting crosslinked membranes were characterized by Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction (WAXD). After measuring the swelling data at different mass% of water, membranes were subjected for the pervaporation separation of water–isopropanol mixtures in a temperature range of 30–60 °C. The experimental results demonstrated that membrane containing 40 mass% of blocked diisocyanate showed the highest separation selectivity of 5918 with a flux of 2.20 × 10 −2 kg/m 2 h at 30 °C for 5 mass% of water. The total flux and flux of water were found to be overlapping particularly for higher crosslinked membranes, suggesting that the membranes developed with higher amount of blocked diisocyanate could be used effectively to break the azeotropic point of water–isopropanol mixture, so as to remove a small amount of water from isopropanol. From the temperature dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The activation energy values obtained for water permeation ( E pw) were more than three times lower than those of isopropanol permeation ( E pIPA), particularly for crosslinked membranes, suggesting that the developed membranes have higher separation efficiency for water–isopropanol system. The activation energy values for total permeation ( E p) and water permeation ( E pw) were almost close to each other, signifying that coupled-transport of both water and isopropanol molecules is minimal due to a higher selective nature of membranes. The estimated E p and E D values ranged between 22.68 and 30.78, and 21.19 and 29.22 kJ/mol, respectively. The positive heat of sorption (Δ H s) observed in all the membranes suggests the Henry's mode of sorption.

Preparation of novel composite membranes for the pervaporation separation of water–acetic acid mixtures

Novel composite membranes were prepared involving “class I” and “class II” hybrid materials. The membranes obtained were characterized by Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Membranes exhibited a remarkable increase in degree of swelling with increasing zeolite loading in “class II” hybrid material. The pervaporation performance of these membranes for the separation of water–acetic acid mixtures was investigated in terms of feed composition and zeolite loading. Both the permeation flux and selectivity increased simultaneously with increasing zeolite content in the membrane matrix. This was explained on the basis of enhancement of hydrophilicity, selective adsorption and the establishment of molecular sieving action. While assessing the membranes’ efficiency, it was noticed that both total flux and flux of water are overlapping each other, signifying that the membranes developed in the present study involving “class I” and “class II” are highly selective towards water. Among the membranes developed, the membrane containing 15 mass% of zeolite exhibited the highest separation selectivity of 2423 with a flux of 8.35 × 10 −2 kg/m 2 h for 10 mass% of water in the feed at 30 °C. Comparison was also made to justify the efficiency of the developed membranes with respect to efficiency of the membranes reported in the literature. From the temperature dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The resulting activation energy values obtained for water diffusion being lower than those of acetic acid diffusion values, suggest that the composite membranes exhibit higher separation efficiency. The negative heat of sorption values (Δ H s) obtained for all the membranes, suggesting that Langmuir's type of sorption is predominant in the process.

Numerical Analysis of Coupled Water, Vapor, and Heat Transport in the Vadose Zone

Vapor movement is often an important part in the total water flux in the vadose zone of arid or semiarid regions because the soil moisture is relatively low. The two major objectives of this study were to develop a numerical model in the HYDRUS‐1D code that (i) solves the coupled equations governing liquid water, water vapor, and heat transport, together with the surface water and energy balance, and (ii) provides flexibility in accommodating various types of meteorological information to solve the surface energy balance. The code considers the movement of liquid water and water vapor in the subsurface to be driven by both pressure head and temperature gradients. The heat transport module considers movement of soil heat by conduction, convection of sensible heat by liquid water flow, transfer of latent heat by diffusion of water vapor, and transfer of sensible heat by diffusion of water vapor. The modifications allow a very flexible way of using various types of meteorological information at the soil–atmosphere interface for evaluating the surface water and energy balance. The coupled model was evaluated using field soil temperature and water content data collected at a field site. We demonstrate the use of standard daily meteorological variables in generating diurnal changes in these variables and their subsequent use for calculating continuous changes in water contents and temperatures in the soil profile. Simulated temperatures and water contents were in good agreement with measured values. Analyses of the distributions of the liquid and vapor fluxes vs. depth showed that soil water dynamics are strongly associated with the soil temperature regime.

Seasonal metabolism of juvenile green turtles (Chelonia mydas) at Heron Island, Australia

We investigated seasonal changes in the energetics of juvenile green turtles (Chelonia mydas (L., 1758)) (9.8–23.8 kg) from a resident population on the southern Great Barrier Reef. Doubly labeled water was used to determine water flux and field metabolic rate (FMR) of green turtles during summer (mean water temperature (TW) = 25.8 °C) and winter (mean TW = 21.4 °C), and muscle tissue was collected for analysis of thermal sensitivity of metabolic enzyme activity. There was no significant seasonal difference in total body water (TBW) content (73.7% and 75.1% of body mass in summer and winter, respectively) or water flux (7.5% and 6.1% of TBW per day in summer and winter, respectively). The mean FMR during winter (81 ± 15 kJ·kg–1·d–1) was 43% lower than that during summer (142 ± 33 kJ·kg–1·d–1), but the seasonal difference in FMR marginally failed to reach statistical significance (P = 0.17). Thermal dependence of citrate synthase, lactate dehydrogenase, and pyruvate kinase activity was relatively low (Q10 = 1.20–1.68) over the range of temperatures experienced by turtles during summer and winter, and there were no significant seasonal differences in enzyme activity. In summary, juvenile green turtles experience only moderate changes in metabolism within the temperature range and environmental conditions experienced seasonally at this subtropical site.

Modification of tetraethylorthosilicate crosslinked poly(vinyl alcohol) membrane using chitosan and its application to the pervaporation separation of water–isopropanol mixtures

AbstractTetraethylorthosilicate crosslinked poly(vinyl alcohol) membrane was modified by varying the amounts of chitosan. The resulting membranes were characterized by Fourier transform infrared spectroscopy and differential scanning calorimetry. The effects of chitosan content and feed composition on the pervaporation performance of the membranes were analyzed. The modified membranes exhibit simultaneous increase of both flux and selectivity. The membrane containing 15 mass % of chitosan shows the highest separation selectivity of 2991, with a flux of 2.39 × 10−2 kg/(m2 h) at 30°C for 10 mass % of water in the feed. The total flux and flux of water are almost overlapping each other, manifesting that the membranes could be used effectively to break the azeotropic point of water–isopropanol mixture, so as to remove water from the isopropanol. From the temperature dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The activation energy values obtained for water permeation (Epw) are significantly lower than those of isopropanol permeation (EpIPA), suggesting that the membranes developed here have higher separation ability for water–isopropanol system. In addition, difference was negligibly small between the activation energy values of total permeation (Ep) and water permeation (Epw), indicating that coupled transport is minimal because of a higher selective nature of membranes. The Ep and ED values ranged between 40.92 and 52.60, and 39.58 and 52.47 kJ/mol, respectively. The positive heat of sorption (ΔHs) values observed in all the membranes suggests that Henry's mode of sorption is predominant. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1380–1389, 2006