Positive Water Balance Research Articles

The sensitivity of a Tanzanian crater lake to catastrophic tephra input and four millennia of climate change

Diatom genera in many large East African lakes change little throughout the Holocene period suggesting relatively stable ecological conditions and some resilience to environmental change. Ecosystem stability is less common in smaller, more sensitive lakes, such as those within volcanic craters, where external impacts can cause abrupt and rapid fluctuations. A 4100-year diatom and cyanobacteria pigment record from Lake Massoko, a volcanic crater lake in southern Tanzania, is used to illustrate important switches in resource ratios following tephra deposition 1190 years ago. It is hypothesized that the tephra reduced the rate of P diffusion from the sediments and increased the Si:P ratio in the lake. A period of acute change in planktonic diatom communities resulted from the tephra impact and lasted c. 110 years. The magnitude of the change shown by the diatoms and their slow recovery from the tephra may be due in part to a coincident fall in lake level caused by a reduction in regional rainfall. The statistical significance of the tephra impact relative to that of catchment and climate change has been tested using variance partitioning and rate-of-change analysis. Multiproxy indicators show an important period of positive water balance 1700 ago and a relatively dry episode persisting between 1000 and 400 years ago. The lake ecosystem is shown to be highly sensitive to both climate change and tephra deposition.

The impact of human activities in the Malia coastal area (Crete) on groundwater quality

The evaluation of the long-term effects of seawater intrusion into the aquifers due to negative water balance and nitrate pollution of drinking-water quality due to human activities requires detailed knowledge of both the transport of the chemical constituents and the geochemical processes within aquifers. Hydrogeological and hydrochemical studies in the unconfined aquifer of Malia have provided the necessary data to define the areas at increased risk from these phenomena. The solution of the second Fick's low under given boundary conditions gave an estimate of the propagation of groundwater pollution by NO3 –. Additionally, in order to simulate the ion concentration changes during a period, for example a period of positive water balance or refreshening, groundwater transport and cation exchange reactions were modelled using the code PHREEQM.

Water Economy of Granivorous Birds: California House Finches

A water economy model for granivorous birds has been proposed that assumes equality between exogenous water intake and excretory (fecal + renal) water loss, with the variables of metabolic water production (MWP) and evaporative water loss (EWL) representing the determinants of states of water balance. The model further states that for each species employing seeds as the primary foodstuff, some ambient temperature (T a ) exists at and below which MWP ≥ EWL, and positive water balance is achieved. We tested this model with California coastal and desert populations of House Finches (Carpodacus mexicanus), both of which conform to the model, but the desert forms invariably are more economical in water regulation than are the coastal forms. We also compared both populations while fully hydrated and while subsisting on minimal water rations (dehydrated), and during both daytime and night-time. Under these treatments the gradient of water economy from most to least economical is night-time/dehydrated > night-time/hydrated > daytime/ dehydrated > daytime/hydrated. Ecologically, our studies confirm that House Finches under most circumstances are dependent upon exogenous water supplies; although more economical, the desert forms approach water independence only during the night, when the T a at MWP = EWL in hydrated birds is 4.9°C and that for dehydrated birds is 11.5°C. These temperatures are frequently encountered in their desert habitat during winter nights.

Mechanisms of thermal balance in flying Centris pallida (Hymenoptera: Anthophoridae).

Thermoregulation of the thorax is critical for bees and other endothermic insects to achieve high rates of flight muscle power production. However, the mechanisms allowing insects to regulate thorax temperatures during flight are not well understood. To test whether variations in metabolic heat production, evaporation or heat transfer from the thorax to the abdomen contribute to the maintenance of stable body temperatures during flight in the bee Centris pallida, we measured CO2 production, water vapor loss, wingbeat frequency and body segment temperatures during flight at varying air temperatures (Ta). While hovering in the field and while flying in the respirometer, C. pallida males maintain extremely stable, elevated thorax temperatures (45+/-2 degrees C; mean +/- S.E.M.). Measurements of head, thorax and abdomen temperatures as a function of Ta during hovering flight in the field indicated that C. pallida males were not actively increasing heat transfer from the thorax to the head or abdomen at high Ta values. As Ta increased from 26 to 35 degrees C, increases in evaporative water loss were relatively small compared with the decrease in carbon dioxide emission. As Ta values increased from 26 to 35 degrees C, the factorial decreases in metabolic heat production and the elevation of thorax temperature above Ta were closely matched (35 %), suggesting that variation in metabolic heat production is the major mechanism of thermoregulation in flying C. pallida. The thermal effects on rates of water loss and metabolic water production resulted in a strong positive water balance at cooler Ta values, but a strong negative water balance at Ta values above 31 degrees C. During the first minute of flight in the respirometry chamber, wingbeat frequency was independent of Ta. However, by the fourth minute, there was a significant negative relationship between Ta and wingbeat frequency, which was similar to the thermal relationship observed for wingbeat frequency in the field. These data suggest that, either through homeostatic regulation or resulting secondarily from thermal effects on flight motor properties, variation in metabolic heat production may occur via altered wingbeat kinematics.

EFFECTS OF WATER TABLE MANAGEMENT ON GROUNDWATER CONTAMINATION FROM THE USE OF PROMETRYN IN ORGANIC SOILS

In 1990, a two year study was undertaken to determine the effects of water table management on the movement of the herbicide prometryn in an organic soil in southern Québec. Three water table management systems were used: controlled drainage, subsurface irrigation, and subsurface drainage. Results indicate that most of the prometryn movement through soil and into groundwater occurred during the first few months following application. In the subsurface drainage field, the concentrations of herbicide in groundwater were mostly higher than the drinking water quality standard of 10 μg/L. When subirrigation or controlled drainage was used, the concentration fell significantly below this level, indicating their usefulness in reducing the amount of prometryn reaching the groundwater. The study also demonstrated that, in an organic soil, pesticide movement was affected mainly by the water balance. The negative water balance during dry periods caused the soil water and pesticide to move upwards. This phenomenon was enhanced when the water table was close to the soil surface and the contaminant was positioned higher in the soil profile, which improved the opportunity for degradation of the chemical before it reached the drains. On the other hand, during high rainfall events and periods of positive water balance, the contaminant was readily leached through the soil profile.

Seasonal variability in sea surface oceanographic conditions in the Aegean Sea (Eastern Mediterranean): an overview

Seasonal variability and the spatial distribution of sea surface temperatures (SST) and salinities (SSS) are reviewed, in relation to the prevailing climatological conditions, heat fluxes, water budget and general water circulation patterns. Within this context, consideration is given to: sea surface temperatures; air temperatures; precipitation; evaporation; wind speeds and directions; freshwater (mainly riverine) discharges throughout the Aegean; and the exchange of water masses with the Black Sea and eastern Mediterranean Sea. The investigation of satellite images, covering a 6-yr period (1988–1994), has enabled a synthesis of the monthly sea surface thermal distribution to be established. The climate of the Aegean Sea is characterised by annual air temperatures of 16–19.5°C, precipitation of about 500 mm yr −1 and evaporation of some 4 mm d −1. The Aegean has a negative heat budget (approximately −25 W m −2) and positive water balance (+ 1.0 m yr −1), when inflow from the Black Sea is considered. During the summer, the (northerly) Etesians are the dominant winds over the Sea. Mean monthly sea surface temperatures (SST) vary from 8°C in the north during winter, up to 26°C in the south during summer. SST depends mainly upon air temperature; there is a month's delay between the former and latter maxima. The sea surface salinity (SSS) varies also spatially and seasonally, ranging from less than 31 psu, in the north, to more than 39 psu, in the southeast; lower values (< 25 psu) occur adjacent to the river mouths. SSSs present their maximum differences during summer, whilst during winter and autumn the distribution of SSS is more uniform. The overall spatial SST and SSS distribution pattern is controlled by: distribution of the (colder) Black Sea Waters; advection of the (warmer) Levantine Waters, from the southeastern part of the Aegean; upwelling and downwelling; and, to a lesser extent, but locally important, freshwater riverine inflows.

Hyponatremia in the rat in the absence of positive water balance.

The purpose of this report is to determine the mechanisms that lead to hyponatremia when isotonic saline was the only fluid infused into rats given antidiuretic hormone (ADH), and what might minimize the degree of this hyponatremia. Normal rats were deprived of food and water for the 24-hr study period. They received an infusion of isotonic saline to expand their extracellular fluid (ECF) volume with and without exogenous ADH administration (N = 8 in each of the four groups). Similar studies were also carried out in 32 rats fed a low electrolyte diet for 72 hr before the experiment. An additional control group was fed the low electrolyte diet supplemented with sodium (Na), potassium (K), and chloride (Cl). Hyponatremia developed over 24 hr in rats fed their usual diet if treated with ADH and isotonic saline (fall, 13 +/- 2 mM, P < 0.01). The hyponatremia was caused by negative balance for Na + K salts. Hyponatremia did not develop after the saline + ADH treatment if rats were pretreated for 3 days with a low electrolyte diet. Two factors were required to develop this hyponatremia--generation of electrolyte-free water as a result of the excretion of a large quantity of Na + K salts at a high concentration in the urine, and prevention of the excretion of this electrolyte-free water by ADH. Increasing the avidity for Na reabsorption by the kidney prevented this type of hyponatremia from developing.

What is the impact of potassium excretion on the intracellular fluid volume: Importance of urine anions

Hyponatremia is a common electrolyte abnormality that causes symptoms as a result of swelling of brain cells. We evaluated the impact of a negative balance for sodium (Na) and potassium (K) salts on the intracellular fluid (ICF) volume, emphasizing the role of anions excreted with K. Rats (N = 10) were deprived of food and water for 24 hours. They received half-isotonic saline to expand their extracellular fluid (ECF) volume by 20%; a long acting antidiuretic hormone (DDAVP) preparation was given to prevent the excretion of electrolyte-free water. The concentration of Na in plasma fell from 139 +/- 1 mM to 120 +/- 2 mM 24 hours after the infusion of hypotonic saline (P < 0.01). Since these rats had a small negative balance for water (4 +/- 1 ml), hyponatremia was due to their negative balances for Na (2.2 +/- 0.3 mmol) and K (2.2 +/- 0.1). There were negative balances for Cl (2.4 +/- 0.2 mmol) and phosphate (0.7 +/- 0.05 mmol). Despite the negative balance for NaCl, the ECF volume as assessed by 3H-inulin space was not contracted. In this model for acute hyponatremia, its basis was electrolyte loss, but the ECF volume was not contracted, suggesting that water shifted from the ICF to the ECF. Hyponatremia is associated with cell swelling only if its cause is positive water balance and/or is loss of Na from the ECF. It is critical to examine the urine anions to determine the compartment of origin of particles excreted with K and thereby whether hyponatremia will result in overall expansion or contraction of the ICF volume.

Rates of Metabolism and Water Flux in Free-Ranging Racers, Coluber constrictor

A combination of temperature-sensitive radiotelemetry and doubly labeled water was used to determine daily activity periods, thermal profiles, water flux rates, and field metabolic rates (FMR) of free-ranging racers (Coluber constrictor) in a temperate mesic habitat during summer. Results were compared to published values on the closely related, ecologically similar coachwhip (Masticophis fla- gellum). Racers were active from about 0900-1800 h. Most snakes were in positive water balance. Rates of water influx (9.49 ml/d) and efflux (9.13 ml/d) were related to rates of body mass change (mean = 0.35%/d ) and were about four times greater than those of Masticophis inhabiting a more xeric habitat. Mean activity temperature (32C), FMR (0.157 ml C02/g/h), mass-specific daily meta- bolic energy expenditure (94.5 kJ/kg/d), calculated values of resting metabolism (20.3 kJ/kg/d), and activity metabolism (74.2 kJ/kg/d) in Coluber were all similar to those of Masticophis. We did not detect any relationship between FMR and either distance moved per day, frequency of activity, or body temperature. Water flux rates were greater in females than in males, but we observed no differences between sexes in body temperature or FMR. Compared to intermolt racers, molting racers had higher body temperatures and FMRs (2%, 15%) and lower water fluxes (17%, 25%), but none of these differences was significant. Compared to early in the activity season, racers in late season had lower body temperatures, were less active, and moved less. Water flux and FMR also decreased (13%, 21%), but the differences were not significant.

Eaux dormantes, eaux courantes (Still waters, running waters...)

Abstract. - The volume of continental liquid waters is very small, compared with other reservoirs (oceans, for instance). Nevertheless, they are of particular importance to human societies. Still waters and running waters are the consequence of a positive water balance, which varies with space and time. They induce an original kind of ecosystems, changing and fleeting. Taking into account natural and technical processes on long periods allows the perpetuation of those geosys- tems based on the exploitation of such environments.

Effects of sodium chloride on growth, tissue elasticity and solute adjustment in two Acacia nilotica subspecies

The objective of this study was to compare whole plant growth and physiological responses to salt stress of two Acacia nilotica subspecies (ssp. cupressiformis and ssp. tomentosa). Salt stress was induced by adding NaCl at different concentrations to the nutrient solution: 0, 75, 100 and 200 mM. After one month under such stress, plants were still healthy and actively growing in both subspecies up to 100 mM NaCl. Water potential (Ψ) and osmotic potential (π) decreased with salinity and the lower π enabled the plants to maintain turgor. Höfler diagrams confirmed that osmotic adjustment had occurred under all treatments. Furthermore, the point of zero turgor occurred at a higher relative water content. An increase in the elastic modulus (ɛ) was observed under stress (low elasticity of the cell wall). Both osmotic adjustment and a high ɛ modified the capacity of both subspecies to maintain a positive water balance. Accumulation of ions (Na+, K+ and Cl−) and proline could explain such osmotic adjustment. Acacia nilotica ssp. cupressiformis showed a higher absorption of K+ than ssp. tomentosa up to 100 mM NaCl treatment.

Tubular Reverse Osmosis Treatment of Secunda Mine Water: A Pilot Plant Investigation

Secunda Collieries experience a positive water balance. Because of the zero discharge principle applied by Sasol and because it is rather difficult to build storage dams, desalination using a tubular reverse osmosis pilot plant was investigated. The objectives were to prove the technical feasibility of the process and to obtain enough information:to design a full-scale plant andto subsequently do economic evaluations regarding operating and capital costs. With pretreatment consisting of flocculation/clarification and dual media filtration, excellent results were obtained. Average standard flux was 700 ℓ/m2.d at pressures of ca 4 MPa and at a water recovery of 70% (which was the maximum that could be obtained even with the addition of scale inhibitor). The importance of operating the system at feed water temperatures of ca 25°C was demonstrated. Salt rejection based on conductivity was very constant at ca 96% resulting in permeate conductivity values of ca 20 mS/m. Fouling, which was mainly inorganic in nature, was reversible and could be removed by citric acid washes and regular replacement of sponge balls. Treatment of mine water using tubular reverse osmosis is a technically feasible process. However, further research is needed to improve overall water recovery.

The influence of calorie source on water and sodium balances during intravenous refeeding of malnourished rabbits

34 New Zealand rabbits were starved until a mean weight loss of 15% to 20% was achieved and then were parenterally re-fed with four different total parenteral nutrition (TPN) formulae for 6 days. Regimens were isocaloric (85 kcal/kg/day) and isonitrogenous (0.52 gN/kg/day) with the following formulae: group S-GLU-70 (water 100 ml/kg/day, Na 7 mEq/day and 70 30 % of calories as glucose/lipids, n = 9), group S-GLU-50 (water 100 ml/kg/day, Na 7 mEq/day and 50 50 % of calories as glucose/lipids, n = 9), group L-GLU-30 (water 70 ml/kg/day, no sodium and 30 70 % of calories as glucose/lipids, n = 8) and group L-GLU-50 (water 70 ml/kg/day, no sodium and 50 50 % of calories as glucose/lipids, n = 8). The group S-GLU-70 showed the highest water and sodium balances (p = 0.001 respectively, ANOVA test). Group S-GLU-70 showed also a greater weight gain (p = 0.0001) and, although not statistically significant, the lowest albumin at the end of the TPN. Glucose load appears to be responsible for the rapid weight gain and positive water and sodium balances during TPN in depleted non-stressed animals.

Emergence Periodicity of Six Summer Annual Weed Species

Emergence periodicity of common purslane, hemp sesbania, horse purslane, prickly sida, spurred anoda, and velvetleaf was determined from March to October during 5 yr at Stoneville, MS, in the absence of reseeding. In early March of each year prior to emergence determinations, plots were not tilled or tilled to depths of 0, 5, 10, or 15 cm. Yearly emergence periodicity of the six weed species was not affected by tillage. In each year, weeds of all species emerged in identifiable flushes and very few emerged at other times during the growing season. Velvetleaf emerged mainly during the early growing season from March through May. Peak periods of emergence for the other species varied slightly over the 5 yr, but conformed generally to the early or the midseason peak period (June, July, and August) or both. In most years, common purslane, horse purslane, hemp sesbania, prickly sida, and spurred anoda emerged during the midseason period. Annual patterns of temperature fluctuations were similar during the 5 yr, but relatively warm soil temperatures during the early growing season of 1977 may have caused earlier emergence of velvetleaf, prickly sida, and hemp sesbania. Weekly water balance (rainfall minus open-pan evaporation) varied during March through May of each year but was negative during each June, July, and August. Apparently the main effect of a positive water balance during most of the year was to cause merger of the early and midseason peak emergence periods in 1979. Early and midseason emergence peaks were possibly due to different populations of seeds able to germinate in cooler soil temperatures of the early season and warmer soil temperatures of the midseason, respectively.

Peripheral p-chloroamphetamine is an unsuitable probe for investigation of central serotoninergic control on renal renin secretion in the rat

Intraperitoneal application of p-chloroamphetamine (PCA) is considered a suitable probe for investigation of central serotoninergic control on renin release in the rat, although it causes several behavioral and autonomic changes including negative water balance (increased urination and loss of body weight). The possibility that PCA-induced renin release is secondary to the alterations in water balance was investigated 1 hour after intraperitoneal PCA in male Wistar (Wi) (Experiment I), Long-Evans (LE) and diabetes insipidus (DI) (Experiment II), DI rats pretreated by the inhibitor of angiotensin I-converting enzyme captopril (Experiment III), and water-loaded or propranolol-pretreated Wi rats (Experiment IV). PCA treatment induced significant body weight loss, increase in hematocrit, stimulation of renin-aldosterone system (RAS) and elevation of plasma creatinine level. A toxic damage of the kidney and liver was documented histologically 72 h after 5 mg/kg PCA in Wi rats. The blockade of PCA-induced stimulation of RAS (by captopril or propranolol) markedly potentiated the attendant negative water balance, whereas positive water balance (oral water load) abolished PCA-induced renin secretion. In conclusion, intraperitoneal PCA is an unsuitable probe for investigation of central serotoninergic control on renin release in the rat since PCA-induced renin release is caused by the attendant negative water balance.

Evidence of density currents with the potential to promote meromixis in ice-covered saline lakes

Ice covers all but the most saline of the Vestfold Hills' lakes for about 8–12 months of each year and precludes wind-induced turbulent mixing over the winter, when strong winds are most frequent. Nevertheless, the progressive growth of ice volume through the austral winter and spring months generates haline convection capable of mixing the water column to a depth at least as great as that achieved by wind-induced turbulence in the summer ice-free period. Further, cold and very saline brines may form at the shallow periphery of a lake and flow downslope, penetrating to the lake centre below the convectively mixed layer. Detailed temperature profiles of hypersaline Organic Lake provide the first evidence for these density currents in saline lakes of the Vestfold Hills. These data indicate a dynamic responsiveness to periods of relatively cold weather, and that the resulting density currents may be sufficiently small in volume to have little effect on the anoxia of bottom layers in these meromictic lakes. Alternating periods of negative and positive water balance may also be significant in the formation and destruction of meromixis in these saline lakes, which lack outflow streams. If a lake has been through a period of negative water balance, becoming relatively more saline, and then begins to be diluted during a subsequent period of positive water balance, the winter haline convection will penetrate to progressively shallower depths and deeper layers may stagnate, marking the onset of meromixis. An increase in the water level of Organic Lake over ten years indicates the speed with which the Vestfold Hills' lakes may experience significant change in salinity despite the generally small catchments of these lakes.

Atrial natriuretic peptide and exercise-induced fluid retention in man

Previous studies have shown that day-long hill walking exercise results in significant sodium and water retention, followed during a recovery/rest period by natriuresis and diuresis. The purpose of this study was to assess the role of atrial natriuretic peptide (ANP) during the post-exercise natriuretic phase. Five subjects ate a fixed diet for 13 days. A period of 4 rest days preceded 5 days of strenuous hill walking, followed by a 4-day recovery period. Daily measurement of aldosterone, ANP and haematocrit, and sodium and water balances were performed. Exercise was associated with sodium retention and a positive cumulative balance, mean 268 mmol (SD 17) after 5 days. There was a mean cumulative positive water balance of 700 ml (sd 34). Haematocrit was reduced from 44.6% to 39.3%, indicating an increase in plasma volume of 22%. Plasma aldosterone concentration during exercise was elevated. Plasma ANP concentrations were raised significantly throughout the exercise period (mean 20.3 pmol I −1 [sd 6.4], control 9.4 pmol I −1 [sd 5.4], P −1 [sd 9.1]) but levels were significantly higher than control ( P

Effects of chronic intraventricular sodium on blood pressure and fluid balance.

To examine if chronic sodium loading on the brain produces sustained increases in blood pressure, water intake, and sodium excretion, hypertonic (0.5 M and 1.5 M) and isotonic (0.15 M) NaCl solutions were infused into the third ventricle of Sprague-Dawley rats at a rate of 5.5 microliters/hr for 7 days. Intracerebroventricular infusion of 1.5 M NaCl significantly increased systolic blood pressure during the entire infusion period (+23 +/- 5 mm Hg on day 1 and +15 +/- 2 mm Hg on day 7, n = 10, mean +/- SEM). Blood pressure rose insignificantly in the 0.5 M NaCl group, whereas it remained at the baseline levels in the 0.15 M NaCl group. The increases in water intake (day 2), positive water balance (day 2), and negative sodium balance (day 3) were observed in the 1.5 M NaCl group. On day 7, the 1.5 M NaCl group showed hyponatremia and low plasma osmolality and had higher plasma norepinephrine but not vasopressin compared with the 0.15 M NaCl group. In another series of study, depressor response to intravenous hexamethonium (20 mg/kg) in the 1.5 M NaCl group was greater than that in the 0.15 M NaCl group on both day 1 and 7. The depressor response to d(CH2)5Tyr(Me)-arginine vasopressin (10 micrograms/kg) in the 1.5 M NaCl group was greater on day 1 but not on day 7. These results indicate that sustained sodium stimulus on the central nervous system causes mild hypertension and alters water and sodium balance. The sympathetic nervous system but not vasopressin may play an important role in the chronic phase of central NaCl-induced hypertension.

The anatomy and morphology of four Tasmanian cushion species

A study of the anatomy and morphology of four Tasmanian cushion plant species showed that anatomical convergence was not as well developed as the obvious morphological convergence. The lack of well-developed xeromorphic features in the Tasmanian species is not consistent with the hypothesis previously suggested that the cushion form evolved primarily as a strategy to maintain a positive water balance.

Water relations of tiger beetle larvae (Cicindela marutha): correlations with habitat microclimate and burrowing activity

Rates of water loss/gain for third instar larvae of the tiger beetle Cicindela marutha Dow were measured at various temperatures and humidities. The larvae occupy burrows in exposed hot, dry sand ridges. They are active at the surface at midday during spring and fall, but plug their burrows during the summer day and become active only at night. Water loss rates increase moderately with increasing temperatures (25 to 40°C) and show a consistent decline with increasing relative humidity (0 to 97·5%). The larvae do not absorb sufficient atmospheric moisture at any of the high humidities to offset water lost via transpiration; however, they ingest moist sand while burrowed and absorb the water from their digestive tract. This uptake mechanism supplements water obtained from prey, whose availability is limited, and also enables them to remain in positive water balance during times that microclimatic conditions prevent them from feeding on the surface.