Oxygen and carbon dioxide transport by the haemocyanin of an amphibious crab,Holthuisana transversa

Summary The oxygen and carbon dioxide transporting properties of the haemolymph from an amphibious Australian crab,Holthuisana transversa were investigated. Within the temperature range 15 to 35°C increasing temperature markedly decreased oxygen affinity (H=–54 kJ·mol^–1). The Bohr effect was small at all temperatures with a mean value of –0.13. Over the temperature range 15–35°C there was a significant increase in the cooperativity of oxygen binding. Changing the concentration of Ca,l-lactate or haemocyanin in the haemolymph could elicit no significant change in either O₂ affinity or cooperativity of O₂ binding. There was no evidence in support of a specific effect of CO₂ on oxygen affinity of either non-dialysed or dialysed haemolymph.The amount of CO₂ that could be carried byH. transversa haemolymph was significantly reduced by increased temperature (approx. 14 to 12.5 mmol·l^–1 CO₂). Comparisons of oxygenated and deoxygenated haemolymph at a fixed pH were unable to demonstrate the presence of a significant Haldane effect. Combining data from oxygenated and deoxygenated haemolymph the buffer value was calculated to be in the range –6.2 to –8.5 mmol·l^–1 HCO ₃ ^– ·pH unit^–1.The insensitivity ofH. transversa haemocyanin function to all modulating influences except temperature is discussed with respect to the ecology of this crab.     

Cardiovascular and respiratory physiology of tuna: adaptations for support of exceptionally high metabolic rates

Synopsis Both physical and physiological modifications to the oxygen transport system promote high metabolic performance of tuna. The large surface area of the gills and thin blood-water barrier means that O₂ utilization is high (30–50%) even when ram ventilation approaches 101 min^–1kg^–1. The heart is extremely large and generates peak blood pressures in the range of 70–100 mmHg at frequencies of 1–5 Hz. The blood O₂ capacity approaches 16 ml dl^–1 and a large Bohr coefficient (–0.83 to –1.17) ensures adequate loading and unloading of O₂ from the well buffered blood (20.9 slykes). Tuna muscles have aerobic oxidation rates that are 3–5 times higher than in other teleosts and extremely high glycolytic capacity (150 mol g^–1 lactate generated) due to enhanced concentration of glycolytic enzymes. Gill resistance in tuna is high and may be more than 50% of total peripheral resistance so that dorsal aortic pressure is similar to that in other active fishes such as salmon or trout. An O₂ delivery/demand model predicts the maximum sustained swimming speed of small yellowfin and skipjack tuna is 5.6 BL s^–1 and 3.5 BL sec^–1, respectively. The surplus O₂ delivery capacity at lower swimming speeds allows tuna to repay large oxygen debts while swimming at 2–2.5 BL s^–1. Maximum oxygen consumption (7–9 × above the standard metabolic rate) at maximum exercise is provided by approximately 2 × increases in each of heart rate, stroke volume, and arterial-venous O₂ content difference.Paper from International Union of Biological Societies symposium The biology of tunas and billfishes: an examination of life on the knife edge, organized by Richard W. Brill and Kim N. Holland.     

Oxygen binding properties,capillary densities and heart weights in high altitude camelids

Summary The oxygen binding properties of the blood of the camelid species vicuna, llama, alpaca and dromedary camel were measured and evaluated with respect to interspecific differences. The highest blood oxygen affinity, not only among camelids but of all mammals investigated so far, was found in the vicuna (P₅₀=17.6 Torr compared to 20.3–21.6 Torr in the other species). Low hematocrits (23–34%) and small red blood cells (21–30 m³) are common features of all camelids, but the lowest values are found in theLama species. Capillary densities were determined in heart and soleus muscle of vicuna and llama. Again, the vicuna shows exceptional values (3720 cap/mm² on average in the heart) for a mammal of this body size. Finally, heart weight as percent of body weight is higher in the vicuna (0.7–0.9%) than in the other camelids studied (0.5–0.7%). The possibility that these parameters, measured in New World tylopodes at sea level, are not likely to change considerably with transfer to high altitude, is discussed.In the vicuna, a unique combination of the following features seems to be responsible for an out-standing physical capability at high altitude: saturation of blood with oxygen in the lung is favored by a high blood oxygen affinity, oxygen supply being facilitated by low diffusion distances in the muscle tissue. Loading, as well as unloading, of oxygen is improved by a relatively high oxygen transfer conductance of the red blood cells, which is due to their small size and which compensates the negative effect of a low hematocrit on the oxygen conductance of blood. Blood oxygen transport is presumably favored by two factors: a relatively large heart mass and, as a result of low hematocrit, a low blood viscosity. Both are advantageous for achieving a high maximal cardiac output.     

From ‘third pole’ to north pole: a Himalayan origin for the arctic fox

The ‘third pole’ of the world is a fitting metaphor for the Himalayan–Tibetan Plateau, in allusion to its vast frozen terrain, rivalling the Arctic and Antarctic, at high altitude but low latitude. Living Tibetan and arctic mammals share adaptations to freezing temperatures such as long and thick winter fur in arctic muskox and Tibetan yak, and for carnivorans, a more predatory niche. Here, we report, to our knowledge, the first evolutionary link between an Early Pliocene (3.60–5.08 Myr ago) fox, Vulpes qiuzhudingi new species, from the Himalaya (Zanda Basin) and Kunlun Mountain (Kunlun Pass Basin) and the modern arctic fox Vulpes lagopus in the polar region. A highly hypercarnivorous dentition of the new fox bears a striking resemblance to that of V. lagopus and substantially predates the previous oldest records of the arctic fox by 3–4 Myr. The low latitude, high-altitude Tibetan Plateau is separated from the nearest modern arctic fox geographical range by at least 2000 km. The apparent connection between an ancestral high-elevation species and its modern polar descendant is consistent with our ‘Out-of-Tibet’ hypothesis postulating that high-altitude Tibet was a training ground for cold-environment adaptations well before the start of the Ice Age.     

Dietary variation in arctic foxes (Alopex lagopus)-an analysis of stable carbon isotopes

We used stable carbon isotopes to analyse individual variation in arctic fox diet. We extracted collagen from bones (the lower jaw), and measured stable carbon isotopes. The foxes came from three different localities: Iceland, where both microtines and reindeer are rare; west Greenland, where microtines are absent; and Sweden, where scat analyses showed the primary food to be microtine rodents and reindeer. The Icelandic samples included foxes from both coastal and inland habitats, the Swedish sample came from an inland area, and the Greenland sample from coastal sites. The spatial variation in the isotopic pattern followed a basic division between marine and terrestrial sources of protein. Arctic foxes from inland sites had ¹³C values of –21.4 (Iceland) and –20.4 (Sweden), showing typical terrestrial values. Coastal foxes from Greenland had typical marine values of –14.9, whereas coastal foxes from Iceland had intermediate values of –17.7. However, there was individual variation within each sample, probably caused by habitat heterogeneity and territoriality among foxes. The variation on a larger scale was related to the availability of different food items. These results were in accordance with other dietary analyses based on scat analyses. This is the first time that stable isotopes have been used to reveal individual dietary patterns. Our study also indicated that isotopic values can be used on a global scale.     

Oxygenation properties of haemoglobins from the flatfish plaice (Pleuronectes platessa) and flounder (Platichthys flesus)

Summary The oxygen binding properties and some haematological data of haemoglobins of plaice (Pleuronectes platessa) and flounder (Platichthys flesus) were measured and compared, with the view of discerning their adaptations to the benthic habitat.Compared to plaice, flounders posses higher haematocrit and haemoglobin levels, and their haemoglobin has a higher oxygen affinity, smaller Bohr and Root effects and appears to have a greater ATP sensitivity. At pH 7.6, the half-saturation oxygen tensions,P ₅₀, of stripped plaice and flounder haemoglobins amount to about 5.9 and 4.2 torr, and the Bohr shifts (logP ₅₀/ pH) to –0.51 and –0.34, respectively. The species differences in the oxygen binding patterns occur after stripping the haemoglobin in solution, from dissolved ions and thus appear to be inherent in the pigment molecules. The differences suggest that the haemoglobin of flounder is better adapted to hypoxic and hypercarbic environments than plaice haemoglobin, in accordance with the more inshore occurrence of the former species.The molar ratios of ATP to haemoglobin tetramers are low in plaice and flounder (about 1.6); in plaice this ratio corresponds to that where the cofactor effect is most pronounced. In contrast to previous evidence for an adaptive reduction in the temperature dependence of the haemoglobin of flounder but not of plaice from the Baltic Sea (Friedrich, 1935), the same temperature effects were found in representatives of the two species both from the Dutch North Sea and the Danish Kattegat.     

Respiration and oxygen transport functions of the blood from an intertidal fish,Helcogramma medium (Tripterygiidae)

Synopsis Aquatic and aerial oxygen uptake (̇O₂), ventilation frequency, and oxygen transport properties of the blood were determined for the intertidal fish Helcogramma medium. Ventilation frequency increased in response to decreased environmental PO₂ and aquatic ̇O₂ was maintained down to a critical PO₂ of 30–40 mm Hg. Below PO₂ 30 mm Hg fish intermittently gulped air and finally emerged into air at PO₂ 18 mm Hg. After 1 h exposure to air ̇O₂ decreased to 60% of the aquatic rate and this was accompanied by an increase in blood lactate. Aerobic expansibility was reduced in air (×1.2) compared to water (× 5.5). The Hb concentration was 0.47 ± 0.13 mmol 1^–1 and hematocrit 11.55 ± 3.61% indicating a moderate O₂-carrying capacity. Oxygen affinity was not especially high (P₅₀ = 19 mm Hg at pH 7.7 and 15°C) and ATP was the predominant acid-soluble phosphate regulating P₅₀. The equilibrium curve was essentially hyperbolic (Hill's n = 1.2) with a marked Bohr effect = –1.06) and Root effect (saturation depressed by 50% at pH7.1). The pattern of respiration and the respiratory properties of the blood together with observations of the behaviour of the fish during aerial exposure indicated that Helcogramma is adapted to living in a well-aerated environment yet can adequately tolerate short term exposure to low aquatic PO₂ or air.     

Oxygen equilibria and structural characteristics of the tetrameric and polymeric intracellular hemoglobins from the bivalve molluscBarbatia reeveana

Summary The arcid bivalveBarbatia reeveana contains within its erythrocytes two hemoglobins with remarkably different structures and oxygen equilibrium properties. A tetrameric hemoglobin (M _r about 60,000) with non-identical subunits (₂₂) constitutes about 60% of the erythrocytic heme protein. This hemoglobin has a relatively low oxygen affinity (P ₅₀=19 Torr at 20°C, pH 7.2), shows cooperativityn _H=2.2, shows no Bohr effect between pH 6.8 and 7.6 and a heat of oxygenation (H) of –5.4 kcal/mole between 15 and 35°C. Its oxygen affinity appears to be insensitive to ATP.B. reeveana erythrocytes also contain another hemoglobin withM _r=430,000, the largest intracellular hemoglobin known in any organism. The subunit of this hemoglobin is unusual, having aM _r of 32–34,000 and two heme oxygen binding sites per polypeptide chain. The large hemoglobin has a very low oxygen affinity (P ₅₀=33 Torr at 20°C, pH 7.2), shows slight cooperativity,n _H=1.8, and no Bohr effect (Grinich and Terwilliger 1980). The H at pH 7.2 equals –2.9 kcal/mole, a low value for most hemoglobins, and its O₂ affinity appears to be insensitive to ATP. The two hemoglobins ofB. reeveana, so different in their structure, are also different in their functional properties.     

Seasonal thermoregulatory responses in mammals

This study examined the proportional seasonal winter adjustments of total and mass-specific basal power (watts and watts g^–1, respectively), thermal conductance (watts g^–1 °C^–1), non-shivering thermogenesis capacity (ratio of NST/basal power), body temperature (°C), and body mass (g) of mammals. The responses are best summarized for three different body size classes; small mammals (<100 g), intermediate-sized mammals (0.1–10 kg), and large mammals (>10 kg). The principal adjustments of the small mammals center on energy conservation, especially the Dehnel Effect, the winter reduction in body size of as much as 50%, accompanied by reductions in mass-specific basal power. On average, these reductions reduce the total basal power approximately in direct proportion to the mass reductions. Reductions in mass-specific basal power are matched by concomitant reductions in conductance to maintain the setpoint body temperature during winter. The overall thermoregulatory adjustments in small mammals serve to (a) lower overall winter power consumption, (b) maintain the setpoint body temperature, and (c) lower the lower critical limit of thermoneutrality and hence thermoregulatory costs. In intermediate-size mammals, the seasonal response is centered more on increasing thermogenic capacity by increasing basal power and NST capacity, accompanied by predictable and large reductions in conductance. The Dehnel effect is negligible. Very large mammals undergo the largest reductions in total and mass-specific basal power and conductance. However, there are too few data to resolve whether the reductions in total basal power can be attributed to the Dehnel effect, because the moderate decreases in body mass may also be caused by nutritional stress. Apart from the seasonal changes in basal power, these observations are consistent with the predictions of Heldmaiers seasonal acclimatization model.     

Respiratory adaptations to diving in the nile monitor lizard,Varanus niloticus

Summary The objectives of this study included directin vivo measurements of circulating blood gases, pH, heart rate, and blood pressure during voluntary dives of unrestrained Nile monitor lizards. A Radiometer flow-through cuvette was employed for continuous recording of arterial PO₂, PCO₂ and pH. Hematological properties revealed no particular adaptations for diving. Mean values were: hematocrit = 24%; hemoglobin concentration = 7.1 g %; oxygen capacity = 9.3 vol %; red cell dimensions = 22×12 ; red cell count = 0.67 million/l. The respiratory properties of the blood, studiedin vitro andin vivo, show distinct adaptations to habitual diving. Oxygen affinity of blood is low (P₅₀ = 42.4 mm Hg at pH 7.45, 25 °) and the dissociation curve is markedly sigmoid (n = 3.1). These features, coupled with a Bohr factor ( logP ₅₀/pH) of –0.48, ensure increased utilization of oxygen while maintaining relatively high tissue PO₂. Arterial pH decreases during diving from about 7.5 to 7.1 due to combined respiratory and metabolic acidosis. High plasma bicarbonate (30 mM/l at PCO₂ = 25 mm Hg) and a buffering capacity of H C₃ ^–O/ pH = 18.9 mM/l increase the tolerance to this acidosis and prolong diving time. Thein vivo oxygen dissociation curve shows a 90 % depletion of arterial oxygen content during typical dives. Diving elicited a rapidly developing bradycardia with maximum of 85 % reduction in heart rate. The temperature sensitivity of HbO₂ binding was very low (H = –3kcal). This would minimize the HbO₂ affinity increase accompanying the decrease in body temperature likely to occur in lizards going from sun basking to submergence in water.Supported by a grant from the Danish Natural Science Research Council.     

Thermal acclimation of aerobic metabolism and O2-Hb binding in the snake,Vipera berus

Summary Snakes,Vipera berus, were acclimated to 5 and 25 °C for 3 months preceding measurements of O₂ uptake and blood respiratory properties. O₂ uptake measured at the lower acclimation temperature (5 °C) shows lower values for the cold-acclimated snakes. Measured at 25 °C cold-acclimation results in O₂ uptakes slightly higher than in warm-acclimated snakes. The temperature sensitivity (Q₁₀) of aerobic metabolism in thus higher for the cold-acclimated snakes being 3.17 compared to 2.11 for the warmacclimated.O₂-Hb dissociation curves of whole blood from the two acclimation groups show a marked increase in O₂ affinity associated with cold-acclimation independent of blood pH. The shift in O₂ affinity correlates with a marked decrease in red cell organic phosphate concentration (ATP) in cold-acclimated snakes. The temperature sensitivity of the O₂-Hb binding expressed by the H values was rather uniform at about –11 kcal·mol^–1 (O₂) for both acclimation groups. The CO₂ Bohr factor in cold-acclimated blood at –0.55 was about double that in warm-acclimated. Then value for both acclimation groups increased with higher temperatures. Hematocrit and blood O₂ capacity were higher in the cold-acclimated snakes.The acclimation effects on O₂ uptake, O₂-Hb affinity and the Bohr effect, are opposite to those obtained earlier on reptiles at lower latitudes. It is discussed how a downward translation of the O₂ uptake-temperature curve and a high thermal sensitivity (Q₁₀) may be adaptive for species at latitudinal extremes where the active season is short and diurnal temperatures fluctuate widely. It is further discussed how a change in O₂ affinity by its influence on the capillary to cellular O₂ gradients may affect the aerobic metabolism.     

Oxygen affinities of maternal and fetal hemoglobins of the viviparous seaperch,Embiotoca lateralis

Summary The striped seaperch,Embiotoca lateralis, is a viviparous teleost. The hemoglobins of adult and fetal seaperch are both tetrameric proteins which in their native state appear to be indistinguishable from one another by electrophoresis. However, differences in the subunit structure of maternal versus fetal seaperch hemoglobins can be detected by electrophoresis in urea with a reducing agent, amino acid analyses and peptide maps of the respective proteins. Furthermore, stripped adult and fetal hemoglobins have different oxygen binding affinities at all pH's tested between pH 6.8 and 8.0. Mid-gestation fetal hemoglobin has a higher oxygen affinity than late-gestation fetal hemoglobin which in turn has a higher affinity than that of the adult hemoglobin. All three stripped hemoglobins show a similar Bohr effect (=–0.9). These data suggest that a difference in oxygen affinities exists in vivo between the adult and fetal blood of the seaperchEmbiotoca lateralis and that it can be explained in part by the presence of a structurally unique fetal hemoglobin. This report is the first to provide evidence for a mechanism of maternal-fetal oxygen transfer in a teleost fish.Abbreviations A adult - LF late-gestation fetal - MF mid-gestation fetal (hemoglobins)     

Determination of the overall volumetric mass transfer coefficient kLa,by a temperature dependent change of gas solubility

Summary The solubility of oxygen in the liquid phase of a bioreactor was changed by a ramp change of temperature, and k_La was determined from the resulting return to equilibrium of dissolved oxygen activity. The maximum k_La that can be measured by this method in a standard laboratory scale bioreactor is 145 h^–1 corresponding to a temperature change rate of 320°C h^–1.Nomenclature p Difference between p_G and p_L (% saturation) - T Ramp change of temperature (°C) - E Temperature-compensated output from the oxygen electrode (A) - E_u Uncompensated output from the oxygen electrode (A) - k_La Overall volumetric mass transfer coefficient (h^–1) - k_La_Tm Overall volumetric mass transfer coefficient at temperature T_m (h^–1) - P_G Dissolved oxygen activity in equilibrium with the gas phase (% saturation) - p_L Dissolved oxygen activity (% saturation) - p_Lm Dissolved oxygen activity at time t_m (% saturation) - t Time (h) - t_m Time of maximum p (h) - T Temperature (°C) - T_cal Calibration temperature of the oxygen electrode (°C) - T_m Final temperature after a temperature shift (°C) - T_n Temperature at time t_n     

Variability of macroinvertebrate community composition in an arctic and subarctic stream

The macroinvertebrate community composition was compared in two Alaskan streams (USA) for numeric and species constancy during the ice-free period from 1981 to 1983. Imnavait Creek is a first order arctic stream (60° 39 N, 149° 21 W) draining upland tundra in the foothills of the Brooks Range. Caribou-Poker Creek is a 4th order subarctic stream (65° 08 N, 147° 28 W) draining the taiga forest north of Fairbanks, Alaska. The aquatic insect larvae and other macroinvertebrates were sampled with drift nets and Hess bottom samplers for four periods, each 1 week long in the ice free season of three years. We found 112 species in the arctic stream and 138 species in the subarctic stream in a chironomid-dominated community. In any sample period the communities contained 51–60 species in the arctic and 49–92 species in the subarctic. Between the four sample periods on average 39% and 50% of the species were present in two sequential samples in the arctic and subarctic stream, respectively. New immigrants, never before found in the system, averaged 37% and 31% of the community, respectively. These systems are exposed to several intermediate disturbances: prolonged and variable freeze-up, extreme variation in discharge, wide diel and seasonal changes in temperature, and erosion by frazil and anchor ice. The dipterans that compose the most numerous and variable taxa must have variable diapause, ability to grow in cold waters, and good dispersal powers, even migrating across drainages in the arctic. Much of the seasonal dominance pattern appears therefore to be stochastic.     

The blood oxygen binding properties of hypoxicSalmo gairdneri

Summary The blood oxygen binding properties of rainbow trout responded to environmental hypoxia (the oxygen saturation of water 30% at 11°C) in three ways. The quickest response was a moderate acidosis, leading to slightly lowered blood oxygen loading due to the Bohr effect. The second response, an increase of blood oxygen carrying capacity, was completed with 6 h from the onset of hypoxia. The speed of the response suggests that the formation of new haemoglobin played no practical role, the increase being caused either by a decrease of plasma volume or the liberation of erythrocytes from a storage organ. The slowest response, a 25% increase of the blood oxygen affinity within a week of hypoxia, was probably caused by the concurrent decrease of the erythrocyte ATP concentration from 4.45 to 2.51 mol/ml erythrocytes.     

Methane and oxygen dynamics in a shallow floodplain lake: the significance of periodic stratification

Temperature, dissolved oxygen and dissolved methane profiles were measured during autumn and summer, in a shallow floodplain lake in south-eastern Australia to determine the effects of water-column stability on methane and oxygen dynamics. The water column was well mixed in autumn. Strong thermal stratification developed in the late afternoon in summer, with top-to-bottom temperature differences of up to 6 °C. Methane concentrations in surface waters varied over a daily cycle by an 18-fold range in summer, but only by a 2-fold range in autumn. The implication of short-term temporal variation is that static chambers deployed on the water surface for short times (less than a day) in summer will significantly underestimate the diffusive component of methane emissions across the water–atmosphere interface. There was a marked diel variation in dissolved oxygen concentrations in summer, with the highest oxygen values (commonly 5–8 mg l^–1) occurring in the surface waters in late afternoon; the bottom waters were then devoid of oxygen (< 0.2 mg l^–1). Because of high respiratory demands, even the surface water layers could be nearly anoxic by morning in summer. The concentration of dissolved oxygen in the surface waters was always less than the equilibrium value. When the water column became thermally stratified in summer, the dissolved oxygen and methane maxima were spatially separated, and planktonic methanotrophy would be limited to a moving zone, at variable depth, in the water column. In summer the whole-wetland rates of oxygen production and respiration, calculated from long-term (5 h) shifts in dissolved oxygen concentrations over a diel period, were approximately 6–10 and 3–6 mmol m^–3 h^–1, respectively. These values correspond to net and gross primary production rates of 0.7–1.2 and 1.0–1.9 g C m^–3 day^–1, respectively.     

Ancient ecology of 15-million-year-old browsing mammals within C3 plant communities from Panama

Middle Miocene mammals are known from ~15 million-year-old sediments exposed along the Panama Canal of Central America, a region that otherwise has an exceedingly poor terrestrial fossil record. These land mammals, which represent a part of the ancient terrestrial herbivore community, include an oreodont Merycochoerus matthewi, small camel-like protoceratid artiodactyl Paratoceras wardi, two horses Anchitherium clarencei and Archaeohippus sp., and two rhinos Menoceras barbouri and Floridaceras whitei. Bulk and serial carbon and oxygen isotope analyses of the tooth enamel carbonate allow reconstruction of the ancient climate and ecology of these fossil mammals. Ancient Panama had an equable climate with seasonal temperature and rainfall fluctuations less than those seen today. The middle Miocene terrestrial community consisted predominantly, or exclusively, of C₃ plants, i.e., there is no evidence for C₄ grasses. Statistically different mean carbon isotope values for the mammalian herbivores indicate niche partitioning of the C₃ plant food resources. The range of individual carbon isotope analyses, i.e., ¹³C from –15.9 to –10.1, indicates herbivores feeding on diverse plants from different habitats with extrapolated ¹³C values of –29.9 to –24.2, possibly ranging from dense forest to more open country woodland. The ecological niches of individual mammalian herbivore species were differentiated either by diet or body size.     

Chemical modelling applications to experimental recirculating streams

Chemical models describing the precipitation of calcium carbonate, coprecipitation of inorganic phosphate, carbon dioxide and oxygen transfer through the air-water interface have been applied to results from a recirculating experimental stream. The transfer velocities for carbon dioxide and oxygen transfer for the experimental stream were determined as 1.00 × 10^–4 m s^–1 and 0.0058 m min^–1 (at 20°C) respectively. During a 24-hour long experiment the stream, containing a varied biota dominated by the macro-algae Zygnema, was monitored to evaluate changes in the water chemistry. The calcite precipitation rate varied during the experiment reflecting changes in temperature, supersaturation of the water and local variation in the solution chemistry at the growth sites. The rate constant was evaluated from a chemical mechanistic model as 516.7 ± 27.2 mol h^–1 at 10 °C. The coprecipitation of inorganic phosphate, which accompanied calcite growth, accounted for < 6% of the total phosphorus loss. The constant uptake of phosphorus by plants and algae was estimated as 0.22 mol h^–1 g^–1 dry weight). The rates of production of oxygen and consumption of inorganic carbon in the experimental stream, after taking account of gas transfer and calcite precipitation, were also computed and found to be in good agreement during the experiment. The maximum rate of production of oxygen was 3.5 × 10^–4 mol h^–1 g^–1 (dry weight).     

Benthic oxygen flux in the highly productive subarctic Lake Myvatn, Iceland: In situ benthic flux chamber study

In situ paired light and dark-stirred benthic flux chambers were used to estimate dissolved oxygen flux across the sediment–water interface in Lake Mývatn, Iceland. Three sampling stations were selected, each station reflecting a specific sedimentary environment, benthic communities, and water depth. During this study the phytoplankton density was low. Spatial and seasonal variations of bottom DO concentration and DO flux have been observed during this study. The oxygen consumption rate at all study sites had a mean of –89 (±44) mmol m^–2 d^–1 while the oxygen production rate due to benthic algae had a mean of 131 (±103) mmol m^–2 d^–1. There was a strong correlation (r=0.91) between oxygen consumption rate and temperature. This was presumably because of the temperature influence on rates of microbial and macrobenthic processes. The mean benthic primary production rate at all study sites was 1216 (±957) mg C m^–2 d^–1 between June 2000 and February 2001. Annual gross benthic primary production was estimated from the gross mean daily benthic DO production (P) and Redfield's C:O₂ ratio of 106:138 to be 420 g C m^–2 y^–1 at station HO, 250 g C m^–2 y^–1 at B2 and 340 g C m^–2 y^–1 at station 95. Thus, the mean gross benthic primary production was estimated as 1151 mg C m^–2 d^–1 at station HO, 685 mg C m^–2 d^–1 at station B2, and 932 mg C m^–2 d^–1 at station 95.     

Respiratory adaptations in carp blood influences of hypoxia, red cell organic phosphates, divalent cations and CO2 on hemoglobin-oxygen affinity

Summary This study concerns the adaptation of oxygen transporting function of carp blood to environment hypoxia, tracing the roles played by erythrocytic cofactors, inorganic cations, carbon dioxide and hemoglobin multiplicity.Carp acclimated to hypoxia ( 30 mmHg) display striking increases in blood oxygen affinity compared to normoxic ( =120–150 mm) specimens (P ₅₀'s are 3.0 and 7.0 mm, respectively, at pH 7.9 and 20°C). This correlates with a marked decrease in erythrocytic concentrations of NTP (nucleoside triphosphates) (Figs. 1, 2, Table 1), permitting investigation of the time-course of the response (Fig. 3). That GTP (guanosine triphosphate) plays a greater role than ATP in the allosteric regulation of blood oxygen affinity, follows from greater decreases in its concentration during hypoxia, and its greater effect on oxygen affinity of the hemoglobin (Figs. 1, 5). It is furthermore shown that divalent cations (which complex with NTP) inhibit the regulatory role of GTP on O₂ affinity to a lesser extent than that of ATP (Fig. 7). However, the divalent cation, Mg²⁺, occurs in similarly high concentrations in the erythrocytes of hypoxic and normoxic fish (Table 1). CO₂ specifically depresses the O₂ affinity of carp hemoglobin, but below pH 8.3, its effect is obliterated by ATP and GTP suggesting that the chains are the main sites for CO ₂ ^– binding. Four carp hemoglobin components are isolated and their oxygen-binding properties compared with those of the cofactor-free hemolysate (Figs. 4, 8, 9). The results are discussed comparatively with special reference to hemoglobin function in fish and mammals.