Effects Of Water Balance Research Articles

Analysis of the influence of the water balance process on the change of landscape patterns in the upper reaches of the Yangtze River

Abstract Based on hydrometeorological data and land-use data (from 1980 to 2015), the effects of water balance on landscape patterns in the upper reaches of the Yangtze River were studied using water balance analysis, the landscape index method, and other methods. Eight appropriate landscape indices (NP, COHESION, LPI, AI, SHDI, CONTAG, SPLIT, and LS) were selected to explore the spatial and temporal characteristics of landscape patterns. From 1980 to 2015, the precipitation in the study area decreased by 6.97%, and the annual precipitation of farmland was maintained at about 1,050 mm. The evapotranspiration (ET) had little change in general, but it varies greatly under different land-use types. Soil water storage variables showed a downward trend, and soil water storage variables of various land-use types changed dramatically during the study period. The total number of patches increased and the patch shape became more complex. At the level of landscape structure, SHDI and SPLIT increased, while CONTAG and COHESION decreased, and the degree of patch fragmentation and landscape heterogeneity improved. Correlation analysis showed that from a time perspective, LSI, SPLIT, and SHDI were significantly negatively correlated with ET, and CONTAG was significantly positively correlated with ET. There was a significant negative correlation between SPLIT and soil water (SW), and a significant positive correlation between COHESION and SW. These results indicated that with the decrease of ET and soil water storage variables, patches became more dispersed and landscape patterns became more fragmented. From the perspective of spatial distribution, the increase of SW increased landscape diversity and decreased landscape connectivity and contagion. The correlation coefficients between SW and the three groups of landscape pattern indexes (SHDI, CONTAG, and COHESION) were higher than those between ET and the three groups of landscape pattern indexes, which meant that soil water is more correlated with landscape pattern characteristics, and the effect of soil water change on landscape heterogeneity is more obvious. The study of the relationship between hydrological processes and landscape pattern characteristics in this paper enriches and expands the theoretical method system of ecological hydrology and ecological environmental protection in arid/semi-arid regions in our country.

Assessing Tree Drought Resistance and Climate-Growth Relationships under Different Tree Age Classes in a Pinus nigra Arn. ssp. salzmannii Forest

The magnitude of drought impact in forest ecosystems depends on which group of trees are more severely affected; greater mortality of smaller trees can modulate the trajectories of succession, while the mortality of larger trees can disproportionately offset the ecosystem’s carbon balance. Several studies have documented a greater vulnerability of large trees to extreme droughts while some other studies reported a greater growth reduction in smaller trees during droughts. We tested these hypotheses by comparing tree basal area increment (BAI), drought resistance (i.e., magnitude of growth decline during drought), and resilience (i.e., magnitude of growth recovery after drought) across five different age-classes in black pine (Pinus nigra Arn. ssp. salzmannii) forests in Spain. Our results showed that the BAI patterns, drought resistance, and resilience were strongly influenced by tree age-classes. In addition, the effect of climatic water balance (precipitation minus potential evapotranspiration) on BAI significantly varied among age-classes. The effect of water balance on BAI was lower for younger age-classes (1–39 years of age) compared to older age-classes. We observed a greater growth reduction (i.e., lower resistance) in older trees (>40 years of age) during droughts compared to younger trees (<40 years of age). However, all trees, irrespective of their ages, were able to recover the growth rates after the drought. In general, younger trees showed a greater capacity in recovering the growth rate (i.e., more resilient) than older trees. We detected no significant effects of stand basal area and stand density on BAI, drought resistance, and resilience. Overall, our results indicated that growth of older trees was more negatively affected during drought. Therefore, these older/larger trees can be selected for commercial thinning, or can be released from competition, which can minimize the potential impacts of future droughts in black pine forests in Spain.

Height growth-related competitiveness of oak (Quercus petraea (Matt.) Liebl. and Quercus robur L.) under climate change in Central Europe. Is silvicultural assistance still required in mixed-species stands?

Sessile oak (Quercus petraea (Matt.) Liebl.) and pedunculate oak (Quercus robur L.) play an important role in increasing the resistance of central European forests to severe droughts. But outside their real niche the competitiveness of both oak species can be low in mixed-species stands. This paper examines the height growth of oaks depending on environmental conditions and inter-specific competition. Height growth of trees was analysed using data from forest inventories covering monospecific and mixed-species stands within the German federal state of Bavaria. By means of regression analyses of 23,607 height measurements, we found that site conditions and stand structure have strong effects on the height growth of oak. Summer temperature, water balance in the vegetation period and base saturation were the main explanatory site variables. The first positive effect of summer temperature had no influence at warmer sites with mean summer temperatures above 16.4 °C, while the effect of water balance was positively linear. In addition, stand density modified the height growth of oak in a mainly positive manner. Vertical structure also had a positive effect, which was found for most species compositions, except monospecific stands and oak-hornbeam mixture. In most mixtures, oaks height growth seemed to be less climate-sensitive compared to monocultures. A currently warmer and drier climate seemed to favour the height growth superiority of European beech, whereas it decreased the superiority of Scots pine. The results indicated that even if the climate changes as predicted, the growth of oak will depend upon silvicultural promotion. Our findings can be used to improve regional guidelines for oak silviculture with special regard to climate-sensitive height growth. For example, a regionally delayed introduction of admixed species can reduce silvicultural treatments by ensuring oak vitality in mixed forests at the same time.

Effect of Water Balance in Ionomer Solution for Novel Membrane Electrode Assembly of Polymer Electrolyte Membrane Fuel Cells

The performance of membrane electrode assemblies (MEA) is considerably affected by water balance or content in ionomer solution. The three-dimensional structure of the ionomer in electrode is very important for getting higher current density in MEA. In this study, some representative water-based and alcohol-based commercial ionomers were compared for getting higher MEA performance under different humidity level. The contact angle of the catalyst layer was measured to determine the variation in wetting properties with different ionomer solution. Various MEAs with different electrode combination were tested in single cell station. And some electrochemical techniques were applied to this MEA such as polarization curve, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The results show that a MEA of water-based ionomer as anode and alcohol-based ionomer as cathode exhibits higher performance at most humidity levels.

Soil compaction and water availability affect growth and survival of Quercus ilex subsp. ballota seedlings under different light environments

We examined the effect of abiotic characteristics (soil compaction, water availability and photosynthetic photon flux density (PPF) on the germination, emergence, growth and survival of Quercus ilex subsp. ballota seedlings. To determine the importance of these characteristics on the growth and development of the seedlings, we simulated two levels of water availability [650 mm year−1 (W650) and 1000 mm year−1 (W1000)], two levels of light [representing full (PPF100) and low sunlight (80 % reduction of sunlight, PPF20) conditions] and three soil compaction depths [soil compaction at depth 60 cm (C60), 25 cm (C25) and 10 cm (C10)]. Seedling emergence and survival were determined, along with various biometric characteristics. Emergence rate was only significantly affected by the water availability treatment, being significantly lower in W650. No differences were found in the other treatments. Seedlings grown under high PPF presented an increase in biomass. Seedlings grown in the deeper soils (C60) showed deeper and thinner roots. The results show increased survival of seedlings grown under low PPF and high water availability. Our results obtained in this greenhouse study support the hypothesis of facilitation, which considers that under drought conditions the promoting effect of water balance induced by the shade is more positive for the survival of the seedlings. We cannot say whether there are one or more independent factors that will limit or enhance the natural regeneration of Q. ilex, which implies that the effects of some can be mitigated, compensated for or amplified depending on the interaction with other elements. Knowledge of these interactions and the environmental variability of habitats at a smaller scale can be a powerful tool for promoting the growth of native vegetation and conservation of the Mediterranean area and dry environments.

Computationally efficient modeling of the dynamic behavior of a portable PEM fuel cell stack

A numerically efficient mathematical model of a proton exchange membrane fuel cell (PEMFC) stack is presented. The aim of this model is to study the dynamic response of a PEMFC stack subjected to load changes under the restriction of short computing time. This restriction was imposed in order for the model to be applicable for nonlinear model predictive control (NMPC). The dynamic, non-isothermal model is based on mass and energy balance equations, which are reduced to ordinary differential equations in time. The reduced equations are solved for a single cell and the results are upscaled to describe the fuel cell stack. This approach makes our calculations computationally efficient. We study the feasibility of capturing water balance effects with such a reduced model. Mass balance equations for water vapor and liquid water including the phase change as well as a steady-state membrane model accounting for the electro-osmotic drag and diffusion of water through the membrane are included. Based on this approach the model is successfully used to predict critical operating conditions by monitoring the amount of liquid water in the stack and the stack impedance. The model and the overall calculation method are validated using two different load profiles on realistic time scales of up to 30 min. The simulation results are used to clarify the measured characteristics of the stack temperature and the stack voltage, which has rarely been done on such long time scales. In addition, a discussion of the influence of flooding and dry-out on the stack voltage is included. The modeling approach proves to be computationally efficient: an operating time of 0.5 h is simulated in less than 1 s, while still showing sufficient accuracy.

Investigation of water transport through membrane in a PEM fuel cell by water balance experiments

Water balance in a polymer electrolyte membrane fuel cell (PEMFC) was investigated by measurements of the net drag coefficient under various conditions. The effects of water balance in the PEMFC on the cell performance were also investigated at different operating conditions. Experimental results reveal that the net drag coefficient of water through the membrane depended on current density and humidification of feed gases. It was found that the net drag coefficient (net number of water molecules transported per proton) ranged from −0.02 to 0.93, and was dependent on the operating conditions, the current load and the level of humidification. It was also found that the humidity of both anode and cathode inlet gases had a significant effect on the fuel cell performance. The resistance of the working fuel cell showed that the membrane resistance increased as the feed gas relative humidity (RH) decreased. The diffusion of water across Nafion membranes was also investigated by experimental water flux measurements. The electro-osmotic drag coefficient was evaluated from the experimental results of water balance and diffusion water flux measurements. The value of electro-osmotic drag coefficient, ranging from 1.5 to 2.6 under various operating conditions, was in agreement with literature values. The electro-osmotic drag coefficient, the net flux of water through the membrane and the effective drag as a function of operating conditions will also provide validation data for the fuel cell modeling and simulation efforts.

Effects of water balance, diet and antidiuretic-hormone administration on the renal excretion of water.

Enuresis is the result of multifactorial processes. Enuretic patients often exhibit an abnormal diurnal rhythm of plasma vasopressin in addition to high nocturnal urine production. Renal function is considered to be a core factor in influencing the volume of fluid delivered to the bladder. Animal studies have suggested that the amount of fluid delivered to the bladder is dependent upon the state of hydration and/or the amount of protein present in the animal's diet. The state of hydration, or diuresis, may also influence the permeability of the terminal collecting ducts to water and urea and the hydro-osmotic response of the kidney to desmopressin. Multiple agents, including vasopressin, glucagon, calcitonin, parathyroid hormone, beta-adrenergic agonist, insulin, angiotensin II, prostaglandins and calcium and magnesium ions influence sodium transport in the thick ascending limb, indicating that all of these factors may potentially play a role in enuresis.

Effect of Water Balance on Growth and Calcium Mobilization of Embryonic Painted Turtles (Chrysemys picta)

Flexible-shelled eggs of painted turtles (Chrysemys picta) were incubated in wet (-150 kPa water potential) and dry (-750 kPa water potential) substrates to elicit different patterns of net water exchange between eggs and their environment. Embryos exposed to wet substrates consumed yolk more rapidly, grew faster, and incubated longer than did embryos exposed to dry substrates. As a result, hatchlings emerging in wet environments were larger and contained less residual yolk than hatchlings emerging in dry environments. Embryos exposed to wet and dry conditions relied on both yolk and eggshell to supply the calcium required for development. However, embryos exposed to wet substrates used the eggshell for a larger proportion of their calcium (56%) than did embryos exposed to dry substrates (40%). Residual yolk of hatchlings in both experimental groups contained less than 1 mg of calcium. Consequently, residual yolk cannot support growth of neonates at or near levels characteristic of late-term embryos. Thus, the larger energy reserve available to small hatchlings in the form of a large residual yolk probably can be used only to support maintenance metabolism, and young presumably must begin to forage soon after emerging from the nest if growth of both soft and hard tissues is to continue.

Effect of Water Balance on Ability to Perform in High Ambient Temperatures

Abstract To determine the effects of water balance on ability to perform in high temperatures, 18 male subjects were subjected to exhaustion runs on the treadmill under three experimental conditions: normal water balance, dehydration, and superhydration. All three runs were performed in an ambient temperature of 120°F. No statistical difference was found between performance under conditions of superhydration and normal water balance, but performance in the dehydrated state was significantly reduced. The performance of a subgroup of 11 athletes under the condition of superhydration was significantly superior to their corresponding performance under the condition of normal water balance. The seven nonathletes did not exhibit this tendency.