High Water Turnover Research Articles

A comprehensive evaluation of heat stress and heat strain in a sample of sugarcane cutters in Brazil.

Sugarcane cutters are vulnerable to extreme heat and are at risk for heat-related illness and chronic kidney disease, potentially due to high heat strain. We performed a comprehensive assessment of the physiological demands of sugarcane cutters via measurements of metabolic, thermal, and cardiovascular responses. In addition, we assessed cross-shift changes in markers of kidney function. Nine male sugarcane cutters were monitored while working during the spring harvest season in Brazil. Core temperature (Tcore) and heart rate (HR) were continuously recorded, and oxygen consumption was measured during the work shift. Urine and blood samples were collected pre- and postwork shifts. Total sweat loss was calculated using body weight changes and adjusting for water ingestion and urine output. A wet-bulb globe temperature (WBGT) station was used to monitor environmental heat stress. WBGT was ≥30°C on 7 of the 8 study days. Mean and peak Tcore during the work shift were 37.96 ± 0.47°C and 38.60 ± 0.41°C, respectively, with all participants surpassing a Tcore of 38°C. Mean and peak HR during the work shift were 137 ± 14 and 164 ± 11 beats/min, respectively. Percent of maximal oxygen consumption was, on average, 53 ± 11%. Workers had a total sweat loss of 7.63 ± 2.31 L and ingested 6.04 ± 1.95 L of fluid. Kidney function (estimated glomerular filtration rate) was reduced from pre- to postwork shift (Δ -20 ± 18 mL·min·1.73 m2). We demonstrated that sugarcane cutters performing prolonged work during a period of high environmental heat stress display high levels of heat strain, high water turnover, and reduced kidney function.NEW & NOTEWORTHY We demonstrate that a shift of sugarcane cutting performed outdoors during the spring harvest season results in a high level of heat strain. In fact, all the studied workers sustained core temperatures above 38°C and heart rates above 75% of the measured maximum heart rate. Additionally, workers displayed a high water turnover with sweat loss close to 10% of their body weight. Finally, we report elevated muscle damage and reductions in kidney function following the work shift.

Variation in human water turnover associated with environmental and lifestyle factors.

Water is essential for survival, but one in three individuals worldwide (2.2 billion people) lacks access to safe drinking water. Water intake requirements largely reflect water turnover (WT), the water used by the body each day. We investigated the determinants of human WT in 5604 people from the ages of 8 days to 96 years from 23 countries using isotope-tracking (2H) methods. Age, body size, and composition were significantly associated with WT, as were physical activity, athletic status, pregnancy, socioeconomic status, and environmental characteristics (latitude, altitude, air temperature, and humidity). People who lived in countries with a low human development index (HDI) had higher WT than people in high-HDI countries. On the basis of this extensive dataset, we provide equations to predict human WT in relation to anthropometric, economic, and environmental factors.

Influence of Fluid Delivery Schedule and Composition on Fluid Balance, Physiologic Strain, and Substrate Use in the Heat

Wildfire suppression is characterized by high total energy expenditure and water turnover rates. Hydration position stands outline hourly fluid intake rates. However, dose interval remains ambiguous. We aimed to determine the effects of microdosing and bolus-dosing water and microdosing and bolus-dosing carbohydrate-electrolyte solutions on fluid balance, heat stress (physiologic strain index [PSI]), and carbohydrate oxidation during extended thermal exercise. In a repeated-measures cross-over design, subjects completed four 120-min treadmill trials (1.3 m·s-1, 5% grade, 33°C, 30% relative humidity) wearing a US Forest Service wildland firefighter uniform and a 15-kg pack. Fluid delivery approximated losses calculated from a pre-experiment familiarization trial, providing 22 doses·h-1 or 1 dose·h-1 (46±11, 1005±245 mL·dose-1). Body weight (pre- and postexercise) and urine volume (pre-, during, and postexercise) were recorded. Heart rate, rectal temperature, skin temperature, and steady-state expired air samples were recorded throughout exercise. Statistical significance (P<0.05) was determined via repeated-measures analysis of variance. Total body weight loss (n=11, -0.6±0.3 kg, P>0.05) and cumulative urine output (n=11, 677±440 mL, P>0.05) were not different across trials. The micro-dosed carbohydrate-electrolyte trial sweat rate was lower than that of the bolus-dosed carbohydrate-electrolyte, bolus-dosed water, and microdosed water trials (n=11, 0.8±0.2, 0.9±0.2, 0.9±0.2, 0.9±0.2 L·h-1, respectively; P<0.05). PSI was lower at 60 than 120 min (n=12, 3.6±0.7 and 4.5±0.9, respectively; P<0.05), with no differences across trials. The carbohydrate-electrolyte trial's carbohydrate oxidation was higher than water trial's (n=12, 1.5±0.3 and 0.8±0.2 g·min-1, respectively; P<0.05), with no dosing style differences. Equal-volume diverse fluid delivery schedules did not affect fluid balance, PSI, or carbohydrate oxidation during extended thermal work.

Detoxification and elimination of nicotine by nectar-feeding birds.

Many dilute nectars consumed by bird pollinators contain secondary metabolites, potentially toxic chemicals produced by plants as defences against herbivores. Consequently, nectar-feeding birds are challenged not only by frequent water excess, but also by the toxin content of their diet. High water turnover, however, could be advantageous to nectar consumers by enabling them to excrete secondary metabolites or their transformation products more easily. We investigated how the alkaloid nicotine, naturally present in nectar of Nicotiana species, influences osmoregulation in white-bellied sunbirds Cinnyris talatala and Cape white-eyes Zosterops virens. We also examined the metabolic fate of nicotine in these two species to shed more light on the post-ingestive mechanisms that allow nectar-feeding birds to tolerate nectar nicotine. A high concentration of nicotine (50µM) decreased cloacal fluid output and increased its osmolality in both species, due to reduced food intake that led to dehydration. White-eyes excreted a higher proportion of the ingested nicotine-containing diet than sunbirds. However, sugar concentration did not affect nicotine detoxification and elimination. Both species metabolised nicotine, excreting very little unchanged nicotine. Cape white-eyes mainly metabolised nicotine through the cotinine metabolic pathway, with norcotinine being the most abundant metabolite in the excreta, while white-bellied sunbirds excreted mainly nornicotine. Both species also utilized phase II conjugation reactions to detoxify nicotine, with Cape white-eyes depending more on the mercapturic acid pathway to detoxify nicotine than white-bellied sunbirds. We found that sunbirds and white-eyes, despite having a similar nicotine tolerance, responded differently and used different nicotine-derived metabolites to excrete nicotine.

Daily micro particle distribution of an experimental recirculating aquaculture system—A case study

The particle size distribution (PSD) in a recirculating aquaculture system (RAS) was investigated during a 24-h cycle. PSD was analyzed in water sampled at several locations in a recirculation loop containing a 60-μm drum filter, a submerged fixed-bed biofilter and a trickling filter.In relation to total counts, the system was dominated by micro-particles with particles smaller than 20μm comprising >94% of the distribution in all samples. However, the system presented a substantial volumetric influence of larger particles, reflected by a PSD derivate β-value of 3.40±0.18. Overall β-values throughout the compartments (p=0.584) and experimental period (p=0.217) were not significantly different, although specific components seemed to marginally affect the PSD.A high internal water turnover rate (one system passage every 50min) promoted the rapid removal of large particles from the system. Permanent volumetric particle removal above 60μm (31% reduction in the relative contribution from each size by the drum filter) per passage, but marginal production and removal of particles throughout the rest of the system further support the β-value stability and consequent PSD equilibrium.The results showed a stable β-value in the mature RAS. The β-value is influenced by the contained compartments and system configuration, and may be used as a system performance-predicting tool. Mechanisms of particle influence on system and fish performance should be addressed in future studies, and are herein discussed.

Effects of dietary protein intake on lactation performance of the laboratory mouse, &lt;i&gt;Mus musculus&lt;/i&gt;

Laboratory mice (strain MF1) were used to investigate the effects of dietary protein content on lactation performance to test the heat dissipation limit hypothesis. The specific dynamic action (SDA) for high protein (HP) and high carbohydrate (HC) diets was measured using open-flow respirometry at 9.4% and 6.1%, respectively. The same two diets were fed ad libitum to mice during lactation. Mice fed on HP and HC diets at 21 ºC reached a plateau in their daily food intake at 12.3±0.2 g day-1 and 16.6±0.2 g day-1, respectively between days 12-17 of lactation. HP-fed mice had a significantly higher daily energy expenditure (DEE) measured by doubly labelled water and higher water turnover than HC-fed mice but the energy they exported as milk was significantly lower than that of HC-fed mice and therefore resulted in poor growth rate of their offspring. The urea production of HP-fed mice from their daily protein intake of 7.1 g was estimated at 1994 mg which required 10.2 mls of water per day to be cleared. The mice increased their urine production by 14.4 mls probably to eliminate this urea. High protein diet had negative effects on lactation, indicating the growth of pups in previous studies was not protein limited. The negative effects of the HP diet were due to the high DEE that greatly reduced the energy available for milk production, rather than a toxicity effect of the urea production. The different DEE of the two diets suggests that other factors were involved in the delivery of energy to the offspring.KEY WORDS: Laboratory mouse, dietary protein, specific dynamic action, and daily energy expenditure

Effect of Diet Quality and Housing on Water Status in Sudanese Desert Sheep and Goats

Two independent experiments were carried out using Sudanese Desert sheep and goats to investigate water metabolism (total body water, TBW and water turnover, WTO) and internal water compartments using radioactive water (tritium), under natural grazing conditions in a semi-desert area. The second trial was carried out on confined sheep, fed high (Lucerne) and poor quality (desert grasses) diets. The body weights, rectal temperature and water parameters were monitored in both trials and species under the Sudanese summer conditions. The grazing animal’s body weights were reduced compared to confined ones. Hyperthermia was pronounced in goats (9%) compared to sheep (6%). The goat hyperthermia was associated with high water turnover, indicating the poor heat tolerance of this species of high evaporative cooling. The confined animals, however, maintained their body weights and did not show signs of hyperthermia. The poor diet (desert grasses) was associated with reduced water intake whereas the Lucerne was associated with high water turnover and high feed intake. The extracelluar compartment (ECV) was higher with the poor diet but was lower than the grazing group. The intracellular compartment (ICV) was higher in the Lucerne group. The study indicated that Sudanese Desert sheep are more tolerant to high temperatures and grazing system than goats.

Cyclomorphosis in Tardigrada: adaptation to environmental constraints

Tardigrades exhibit a remarkable resilience against environmental extremes. In the present study, we investigate mechanisms of survival and physiological adaptations associated with sub-zero temperatures and severe osmotic stress in two commonly found cyclomorphic stages of the marine eutardigrade Halobiotus crispae. Our results show that only animals in the so-called pseudosimplex 1 stage are freeze tolerant. In pseudosimplex 1, as well as active-stage animals kept at a salinity of 20 ppt, ice formation proceeds rapidly at a crystallization temperature of around -20 degrees C, revealing extensive supercooling in both stages, while excluding the presence of physiologically relevant ice-nucleating agents. Experiments on osmotic stress tolerance show that the active stage tolerates the largest range of salinities. Changes in body volume and hemolymph osmolality of active-stage specimens (350-500 microm) were measured following salinity transfers from 20 ppt. Hemolymph osmolality at 20 ppt was approximately 950 mOsm kg(-1). Exposure to hypo-osmotic stress in 2 and 10 ppt caused (1) rapid swelling followed by a regulatory volume decrease, with body volume reaching control levels after 48 h and (2) decrease in hemolymph osmolality followed by a stabilization at significantly lower osmolalities. Exposure to hyperosmotic stress in 40 ppt caused (1) rapid volume reduction, followed by a regulatory increase, but with a new steady-state after 24 h below control values and (2) significant increase in hemolymph osmolality. At any investigated external salinity, active-stage H. crispae hyper-regulate, indicating a high water turnover and excretion of dilute urine. This is likely a general feature of eutardigrades.

Validation of the use of doubly labeled water for estimating metabolic rate in the green turtle (Chelonia mydas L.): a word of caution

Marine turtles often have extremely high water turnover accompanied by a low field metabolic rate (FMR), a combination that can contraindicate the use of doubly labelled water (DLW). Therefore, we conducted a validation study to assess the suitability of the DLW technique for determining FMR of marine turtles. Six green turtles (22.42+/-3.13 kg) were injected with DLW and placed in a tank of seawater with a respirometer for continuous monitoring of oxygen consumption (MR) over a 5-day period. Trials were conducted for turtles in both fed and fasted states. Respiratory exchange ratio (RER) was determined in a dry respirometer and used to calculate energy expenditure. For fed and fasted turtles, total body water (TBW) was 66.67+/-3.37% and 58.70+/-7.63% of body mass, and water flux rates were 9.57+/-1.33% and 6.14+/-0.65% TBW day(-1), respectively. Water turnover in fasted turtles was 36% lower than that of fed turtles but MR (from oxygen consumption) of fasted turtles (13.77+/-1.49 kJ kg(-1) day(-1)) was 52% lower than in fed turtles (28.66+/-5.31 kJ kg(-1) day(-1)). Deuterium to oxygen-18 turnover rate (k(d):k(o)) ratios averaged 0.91+/-0.02 for fed turtles and 1.07+/-0.16 for fasted turtles. Fed turtles had a mean group difference of 8% and a mean individual difference of 53% between DLW and respirometry. The DLW method gave negative MR values in fasted turtles and could not be compared with respirometry data. Researchers should use caution when applying the DLW method in marine reptiles, especially when high water flux causes >90% of the labeled oxygen turnover to be due to water exchange.

Water homeostasis in bees, with the emphasis on sociality

Avenues of water gain and loss in bees are examined here at two levels of organisation: the individual and the colony. Compared with the majority of terrestrial insects, bees have a high water turnover. This is due to their nectar diet and, in larger species, substantial metabolic water production during flight, counteracted by high evaporative and excretory losses. Water fluxes at the colony level can also be very high. When incoming nectar is dilute, honeybees need to remove large volumes of water by evaporation. On the other hand, water is not stored in the nest and must be collected for evaporative cooling and for feeding the brood. Water regulation has many similarities at individual and colony levels. In particular, manipulation of nectar or water on the tongue is extensively used by bees to increase evaporation for either food-concentrating or cooling purposes.

EXPERIENCES FROM A BIOMARKER STUDY ON FARMED RAINBOW TROUT (ONCORHYNCHUS MYKISS) USED FOR ENVIRONMENTAL MONITORING IN A SWEDISH RIVER

Biomarkers in fish may serve as a useful tool for evaluating the pollution load in the environment and for early warning signals about new environmental threats. By employing a strategy with fish that are caged or reared in tanks, problems linked to migration and feeding status can be reduced or eliminated. Such a strategy, however, also may introduce other confounding factors linked to, for example, hierarchical behavior or disease outbreaks. In the present study, rainbow trout (Oncorhynchus mykiss) were reared in plastic tanks at four sites in the Göta älv river system (plus one external reference) in western Sweden during 2006 and 2007. Because of low population density and high water turnover in the area, pollution levels are expected to be low. Therefore, this should be a good test for the sensitivity of the methodology. Several significant differences were found between sites as well as between years, such as ethoxyresorufin-O-deethylase (EROD) activity, polycyclic aromatic hydrocarbon (PAH) metabolites in bile, and concentration of inorganic ions in blood plasma, but it also was seen that factors other than pollution could be contributing to these differences. The condition factor (CF) varied between sites, possibly because of differences in feeding resulting from variations in water turbidity. Furthermore, even the small differences in CF that were found within sites correlated significantly to several of the biomarkers. It was shown that PAHs likely are the most important EROD inducers in Göta älv and that variation over time is greater than variation between sites. Because CF differed between sites despite a standardized feeding ration, starving of the fish during the exposure period should be considered for future studies.

Nontuberculous Mycobacteria in Aerosol Droplets and Bulk Water Samples from Therapy Pools and Hot Tubs

Hot tub exposure has been causally associated with a steroid-responsive, granulomatous lung disease featuring nontuberculous mycobacterial (NTM) growth in both clinical and environmental samples. Little is known regarding prevalence of and risk factors for NTM-contamination and associated illness in these settings. In this study, the frequency of NTM growth and aerosolization in 18 public hot tubs and warm water therapy pools and the factors associated with mycobacterial growth were analyzed. Each site was characterized by water chemistry analysis; a questionnaire on maintenance, disinfection, and water quality; and air and water sampling for quantitative NTM culture. NTM were detected in air or water from 13/18 (72%) sites; a strong correlation was found between the maximum air and water NTM concentrations (rho 0.49, p = 0.04). Use of halogen (chlorine or bromine) disinfection was associated with significantly lower air and water concentrations of NTM compared with disinfection using ultraviolet light and hydrogen peroxide (p = 0.01–0.04). Higher water turnover rates were also associated with lower air and water NTM concentrations (p = 0.02–0.03). These findings suggest that NTM are frequently detectable in the air and water of spas and therapy pools and that particular maintenance and disinfection approaches affect NTM bioaerosol concentrations in these settings.

Routes of water loss in South African abalone ( Haliotis midae) during aerial exposure

South African abalone, Haliotis midae, were exposed to air at 12 °C for 36 h to simulate the extent and rate mass loss experienced by animals during long distance live exports. Animals lost 15.1 ± 0.94% of their mass during the 36 h air exposure, an approximation of the highest mass losses sustained by industry. The total mass loss was attributed to water loss, as the contribution of dry mass to the total mass remained constant under all conditions. Water content decreased from 64.8% of the body mass ( M b) under control conditions to 58.8% M b after 36 h in air. In real terms, however, animals had lost 22% of the body water pool. Abalone exhibited a typically high water turnover rate when in water (125 μL g − 1 h − 1 ), which decreased markedly during air exposure (2.2 μL g − 1 h − 1 ). Haemolymph volume decreased from 43% M b in water to 14% M b in air. The concomitant decrease in haemolymph pressure probably limited the first step in urine formation (ultra-filtration through the pericardium). Thus we observed that while urine flow represented about 26% of the total water loss when the animals were in water, urine flow ceased during air exposure. The decrease in haemolymph volume in air represents a redistribution of water to the tissues and not a bulk loss of haemolymph. This is supported by the concentration of haemolymph ions by a factor of 1.2 during aerial exposure, which was predicted based on the 22% decrease in water content. Under the same conditions, evaporation from water containers with similar surface to volume dimensions as abalone, accounted for only an 8.25% mass loss. As all other water loss routes were accounted for, we measured pedal mucus production rates of abalone in water and air. During 36 h aerial exposure, the pedal mucus production represented a loss of 6.8% M b. We conclude that water loss during 36 h air exposure is attributable to evaporation (8.25% M b) and pedal mucus production (6.8% M b). This paves the way for directed research into mitigating water loss during the live export process.

Estimation of Water Turnover Rate in Captive Dugongs (&lt;I&gt;Dugong dugon)&lt;/I&gt;

Water turnover rate was measured for two captive dugongs (Dugong dugon) using deuterated water. Body water content of 69.5% in a dugong was high compared to other marine mammals. A water turnover of 257.2 ml kg -1 day -1 measured in one dugong was almost twice as high as the highest rates measured in studies of captive West Indian manatees (Trichechus manatus) and was high compared to those measured in carnivorous marine mammals. The other dugong’s estimated water turnover rate of 134 ml kg -1 day -1 was comparable to the highest rates in manatees. Two alternative explanations are offered for the high water turnover: (1) the incidence of mariposia or voluntary drinking of sea water by the dugong or (2) a metabolic rate that is significantly higher than predicted, based on its phylogeny.

Water balance and kidney function in the least shrew ( Cryptotis parva)

We assessed renal function in least shrews ( Cryptotis parva, body mass 4.7 g) within the context of overall water balance. The glomerular filtration rate (GFR) of shrews with unlimited food and water was 2.4 ml/h, about 60% of the rate predicted from body mass. Of this, about 3% (0.075 ml/h) was excreted as urine with an osmolality of 1944 mmol/kg, 5.5 times plasma osmolality. Shrews had a total water turnover (5 ml/day) two to three times higher than expected from allometry for a small mammal of this size. Water influx was partitioned among preformed water from food (65%), drinking (16%), and metabolic water (20%). Water efflux was divided among urine flow (35%), fecal water loss (estimated as 23%), and evaporation (by difference, 42%). Least shrews had a high water turnover rate and relatively high urine flow rate (UFR); this likely reflects a combination of factors, including high metabolism, active lifestyle, and wet diet.

Spatial and temporal scales for monitoring coastal aquatic ecosystems

1. Coastal ecology is mostly regulated by hydro-meteorological factors and human disturbances. The spatial and temporal scales of variation of the processes associated with these factors may not correlate. 2. Monitoring of water and ecosystem quality in the coastal zone must be performed at spatial and temporal scales that adequately address the objectives. They range between two extreme states, i.e. high water turnover due to surface water exchanges and evaporation driven turnover, and can cover a range of ecological situations depending on hydrological variables. 3. The spatial scale for monitoring coastal aquatic ecosystems may be better related to water masses circulation than to physiographic features. Biologically mediated processes require monitoring taking account of meteorological, seasonal and interannual time scales. 4. Variables to be monitored must be in accordance with objectives. They may range from intra-compartment variables (e.g. demography of a biological population) to inter-zone relationships (e.g. budgets of nutrient exchange with the sea). Larger and longer scales, such as including buffer zones around lagoons and the continental and sea basins, and the consideration of interdecadal and secular time scales are required for wider monitoring perspectives. 5. Monitoring the impacts of global changes (both direct, such as urbanization and eutrophication of the coastal zone, and indirect, through relative sea-level rise due to climate change) requires a wider conceptual scale of approach to coastal zone ecology and even longer monitoring programmes. Copyright © 2004 John Wiley & Sons, Ltd.

Comparison of nutrient and contaminant fluxes in two areas with different hydrological regimes (Empordà Wetlands, NE Spain)

Nutrient (N and P), heavy metal (Ni, Cd, Cr, Cu and Pb) and pesticide (DDT, DDD, DDE, lindane, aldrin, endrin, dieldrin, permethrin, atrazine and simazine) concentrations in water and sediment were analysed in the Empordà Wetlands, a Mediterranean wetland area in NE Spain. Mean nutrient and contaminant concentrations and input and output loads via tributaries were compared in two marshes with different water turnover: a freshwater marsh (FWM), with a high water turnover rate due to continuous surface water inputs and outputs, and a brackish water marsh (BWM), with lower turnover and no continuous surface output, where water remains confined during dry periods. Mean concentrations of most heavy metals exceeded the maximum permissible concentration (MPC) in BWM, whilst only some pesticides reached MPC in FWM. The confined waters of BWM showed higher sensitivity to contaminant input loadings than FWM due to the lack of continuous water outputs. Non-point source pollution inputs during runoff (mainly in FWM) and concentration during confinement (mainly in BWM) showed as the main environmental problems related to nutrients and contaminants in these ecosystems. Thus, the importance of confinement and its effect on pollutant concentrations must be borne in mind to achieve correct management of Mediterranean wetlands.

Effects of time of day, gender, and menstrual cycle phase on the human response to a water load.

Estrogen and progesterone interference with renal actions of arginine vasopressin (AVP) has been shown. Thus we hypothesized that women will have a higher water turnover than men and that the greatest difference will be during the luteal phase of the menstrual cycle. Seven men (32 +/- 3 yr) and six women (33 +/- 2 yr) drank 12 ml water/kg lean body mass on different days at 0800 and at 2000 following 10 h of fast and a standardized meal at 0600 and 1800. Women participated on days 4-11 and 19-25 of the menstrual cycle. Initial urine and plasma osmolalities and urine flow rates were similar in all experiments. The cumulative urine voided over 3 h following the morning drink was less in men (73 +/- 12% of the water load) compared with women in either the follicular (100 +/- 3%) or luteal phases (102 +/- 10%) of the menstrual cycle. Nighttime values (30-43% of the water load) were lower in all experiments and were not different between sexes or menstrual cycle phases. Plasma AVP was higher at night and may contribute to this diurnal response. The data are generally consistent with the stated hypothesis; however, possibly owing to the greatly reduced urine flow in both sexes at night, a difference between sexes was not observed at that time.

Nutrientes y renovación del agua en aiguamolls de l’Empordà. (NE de la península Ibérica). Uso potencial de agua residual para la inundación de zonas húmedas

The monitoring of the ecological water quality of “Aiguamolls de l’Emporda” Natural Park was carried out between September 1996 to August 1997. The aim was to evaluate the impact of effluent from a nearby wastewater treatment plant, on the flooding of marshes in the Natural Park. In this paper we present physical and chemical data together nutrient concentrations and its changes in the lentic system of the “Aiguamolls de l’Emporda”. The ultimate aim was to evaluate the effect of reclaimed wastewater on the salt marsh system. Seasonal variation in nutrients concentrations and their relationship to turnover and source of water were analysed. Significant variation in the N/P ratio was related to water turnover. Confined systems presented lower values for this ratio. Taking into account the nutrient concentrations of the reclaimed water, which is rich in nitrogen, it is recommended flooding applied in zones with high water turnover and higher N/P ratios.

Wintering Tufted Ducks Aythya fuligula Diving for Zebra Mussels Dreissena polymorpha Balance Feeding Costs within Narrow Margins of Their Energy Budget

Diving ducks face the strongly cooling properties of aquatic environments. In experiments with Tufted Ducks Aythya fuligula feeding on zebra mussels Dreissena polymorpha in outdoor cages, we measured changes in food consumption and diving behaviour in relation to water temperature (3-22 degrees C). Water efflux and daily energy expenditure (DEE) were measured using doubly-labelled water. Tufted Ducks swallow mussels whole and crush the shells in the gizzard. Due to the low flesh content of mussels, daily mussel consumption was extremely high in winter (up to 3 times the duck body mass of 600 g). Water efflux was 6.5 to 13 limes higher than allometrically predicted, with a maximum of 1.1 1 d(-1). Because of high water turnover rates, DEE estimates from doubly-labelled water measurements were variable, but on average agreed with DEE estimates obtained from food consumption and time-energy budgets (ca. 5% higher values). DEE increased with lower temperatures from 2.5 (summer, 20 degrees C) to more than 4 times the basal metabolic rate (winter, 3 degrees C). Costs of thermoregulation and heating up ingested mussels (as estimated from the theoretical caloric heat) primarily explained the high DEE in winter. At lower temperatures, dive duration was shorter and less time was spent selecting small mussels at the bottom, while more larger mussels were brought up and were ingested at the water surface. Thereby, the energy costs of crushing shells probably increased in favour of reducing diving costs. The narrow margins of the energy budget, wherein feeding costs must be balanced, imply that food availability and water temperature are important attributes to winter distributions of diving ducks.