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71.
A survey of oligotrophic Lake Rara, the biggest lake in Nepal, was carried out from 1982 till 1984. Mean depth is 100 m, and
maximum depth is 167 m. The surface area covers 9.8 km2, and the lake contains 0.98 km3 volume of water.
Transparency was about 16 m, photoquantum yield decreased exponentially with depth below 5 m, and the extinction coefficient
was 8.3 × 10−2. The concentration of Chl.-a was in the range of 0.06–0.46 mg m−3, and total nitrogen was 18–30 μg 1−1. The whole water column was well oxygenated. Primary productivity was extremely low. It has more than 30 inflowing brooks
and one outlet. The water quality of the brooks changes drastically with their location. The pH, electrical conductivity,
and EDTA hardness in the waters from a landslide area were high. In the waters from a rich pine forest they were extremely
low.
The zooplankton consisted of two species of protozoa, five species of rotifers, two species of Cladocera, and two species
of Copepoda. The zooplankton density range was 6200–16200 individuals m−3. The minimum was on November 11th, 1983 and the maximum on August 19th, 1983. 相似文献
72.
M. A. Khan 《Hydrobiologia》1986,135(3):233-242
L. Naranbagh (alt. 1587 m) is a polymictic, shallow marl lake in the flood-plain valley of Kashmir, India. Macrofloral affinities resemble Potamogeton Type of Forsberg (1965) with alkaline waters, not rich in phosphorus. CaCO3 precipitation coupled with decline in Ca2+ and alkalinity values are characteristic of the lake. Fluctuations in Mg2+, Na+, K+, and Cl– were relatively conservative. The levels of PO
inf4
sup3–
-P and NO
inf3
sup–
-N indicate moderate fertility of the lake water.Persistence of a summer-autumn planktonic algal pulse is related to favourable irradiance, high water temperatures, and increased photosynthetic efficiency values. The most striking seasonality in photosynthetic rates (m–2 h–1) between winter minimum (3 mg Cassim) and summer maximum (75.4 mg Cassim) is determined by mainly climatic changes. Energy flow gave annual phytoplankton production of 51.95 × 102 KJ m–2 for the ecosystem.The nutrient levels and productivity rates suggest mesotrophic status of L. Naranbagh in classic oligoeutrophic classification of lake types. 相似文献
73.
Osmotic properties of human red cells 总被引:2,自引:0,他引:2
Summary When an osmotic pressure gradient is applied to human red cells, the volume changes anomalously, as if there were a significant fraction of nonosmotic water which could not serve as solvent for the cell solutes, a finding which has been discussed widely in the literature. In 1968, Gary-Bobo and Solomon (J. Gen. Physiol.
52:825) concluded that the anomalies could not be entirely explained by the colligative properties of hemoglobin (Hb) and proposed that there was an additional concentration dependence of the Hb charge (zHb). A number of investigators, particularly Freedman and Hoffman (1979,J. Gen. Physiol.
74:157) have been unable to confirm Gary-Bobo and Solomon's experimental evidence for this concentration dependence of zHb and we now report that we are also unable to repeat the earlier experiments. Nonetheless, there still remains a significant anomaly which amounts to 12.5±0.8% of the total isosmotic cell water (P0.0005,t test), even after taking account of the concentration dependence of the Hb osmotic coefficient and all the other known physical chemical constraints, ideal and nonideal. It is suggested that the anomalies at high Hb concentration in shrunken cells may arise from the ionic strength dependence of the Hb osmotic coefficient. In swollen red cells at low ionic strength, solute binding to membrane and intracellular proteins is increased and it is suggested that this factor may account, in part, for the anomalous behavior of these cells. 相似文献
74.
Summary The osmotic water permeabilityP
f of brush border (BBM) and basolateral (BLM) membrane vesicles from rat small intestine and renal cortex was studied by means of stopped-flow spectrophotometry. Scattered light intensity was used to follow vesicular volume changes upon osmotic perturbation with hypertonic mannitol solutions. A theoretical analysis of the relationship of scattered light intensity and vesicular volume justified a simple exponential approximation of the change in scattered light intensity. The rate constants extracted from fits to an exponential function were proportional to the final medium osmolarity as predicted by theory. For intestinal membranes, computer analysis of optical responses fitted well with a single-exponential treatment. For renal membranes a double-exponential treatment was needed, implying two distinct vesicle populations.P
f values for BBM and BLM preparations of small intestine were equal and amount to 60 m/sec. For renal preparations,P
f values amount to 600 m/sec for the fast component, BBM as well as BLM, and to 50 (BBM) and 99 (BLM) m/sec for the slow component. The apparent activation energy for water permeation in intestinal membranes was 13.3±0.6 and in renal membranes, 1.0±0.3 kCal/mole, between 25 and 35°C. The mercurial sulfhydryl reagentpCMBS inhibited completely and reversibly the highP
f value in renal brush border preparations. These observations suggest that in intestinal membranes water moves through the lipid matrix but that in renal plasma membranes water channels may be involved. From the highP
f values of renal membrane vesicles a transcellular water permeability for proximal tubules can be calculated which amounts to 1 cm/sec. This value allows for an entirely transcellular route for water flow during volume reabsorption. 相似文献
75.
76.
77.
Biomanipulation and its feasibility for water quality management in shallow eutrophic water bodies in The Netherlands 总被引:5,自引:0,他引:5
A. F. Richter 《Aquatic Ecology》1986,20(1-2):165-172
Biomanipulation as a tool for lake restoration is discussed mainly using literature data. It is based on the exploitation of the interactions both within and between the trophic levels in an aquatic ecosystem. Important among the interactions are: competition for light and nutrients between aquatic macrophytes and phytoplankton and among different phytoplankton species; grazing by planktonic and benthic filter feeders; and size-selective predation by fish. In several case studies biomanipulation has proved to be successful in restorating mildly eutrophic small waterbodies. However, for long-term stability of the restored ecosystems supplementary measures like reducing the external nutrient loadings are needed. The feasibility of the different biomanipulation measures to improve the water quality in shallow Dutch lakes is discussed. Preliminary results on biomanipulation experiments in enclosures withOscillatoria agardhii and the benthic filter feederDreissena polymorpha are given. 相似文献
78.
Summary A stopped-flow nephelometric technique was used to examine osmotic water flow across small intestinal brush-border membranes. Brush-border membrane vesicles (BBMV) were prepared from rat small intestine by calcium precipitation. Scattered 500 nm light intensity at 90° to incident was a linear function of the number of vesicles in suspension, and of the reciprocal of the suspending medium osmolality. When BBMV were mixed with hyperosmotic mannitol solutions there was a rapid increase in the intensity of scattered light that could be fit to a single exponential function. The rate constant for vesicle shrinking varied with temperature and the size of the imposed osmotic gradient. At 25°C and an initial osmotic gradient of 50 mOsm, the rate constant was 1.43±0.044 sec–1. An Arrhenius plot of the temperature dependence of vesicle shrinking showed a break at about 25°C with an activation energy of 9.75±1.04 kcal/mole from 11 to 25°C and 17.2±0.55 kcal/mole from 25 to 37°C. The pore-forming antibiotic gramicidin increased the rate of osmotically driven water efflux and decreased the activation energy of the process to 4.51±0.25 kcal/mole. Gramicidin also increased the sodium permeability of these membranes as measured by the rate of vesicle reswelling in hyperosmotic NaSCN medium. Gramicidin had no effect on mannitol permeability. Assuming spherical vesicles of 0.1 m radius, an osmotic permeability coefficient of 1.2×10–3 cm/sec can be estimated for the native brush-border membranes at 25°C. These fesults are consistent with the solubility-diffusion model for water flow across small intestinal BBMV but are inconsistent with the existence there of large aqueous pores. 相似文献
79.
Two species of jute plants Corchorus capsularis L. (cv. JRC 212) and C. olitorius L. (cv. JRO 632) were subjected to water stress for 2 and 4 days by withholding water. The relative water content (RWC) decreased in both plants under water stress but to a greater extent in C. olitorius . The C. olitorius seedlings also showed greater membrane injury than C. capsularis seedlings under water stress as was evident from injury index data. Water stress increased glycolate oxidase (EC 1.1.3.1.) activity more in C. olitorius than in C. capsularis . The activity of superoxide dismutase (SOD, EC 1.15.1.1.) and catalase (EC 1.11.1.6.) decreased under water stress and their decrease was higher in C. olitorius than in C capsularis . The level of hydrogen peroxide and lipid peroxidation also increased in both plants under water stress and the increase was higher in C. olitorius than in C. capsularis seedlings. Under comparable external water stress, C. capsularis seedlings showed lower membrane damage, lower H2 O2 accumulation and lower lipid peroxidation than C. olilorius which may be taken as indicative of higher water stress tolerance capacity of the former. 相似文献
80.
Interdependence of growth, water relations and abscisic acid level in Phaseolus vulgaris during waterlogging 总被引:3,自引:0,他引:3
The interdependence between changes in growth and water relations after waterlogging was investigated by recording simultaneously growth, transpiration, water potential, turgor, leaf diffusion resistance and abscisic acid content in Phaseolus vulgaris L. cv. bruine Noord-Hollandse. Growth was inhibited immediately after flooding, whereas transpiration decreased gradually to a low level in about three days. The first two days after flooding a small increase in abscisic acid content in the leaves was observed which was accompanied by an increase in diffusion resistance. The increase in abscisic acid content could result from an inhibited export from the leaves. After the first two days a decrease in water potential and turgor was accompanied by a drastic increase in both abscisic acid content and diffusion resistance. This large increase in abscisic acid content occurred before the turgor had reached its minimum value. The change in diffusion resistance kept showing a lag of about one day with the change in abscisic acid content. The possibility is discussed that besides abscisic acid also its metabolite phaseic acid is involved in stomatal closure. After the formation of adventitious roots on the hypocotyl, abscisic acid level, diffusion resistance, water potential and turgor returned to the control values. Transpiration showed a slow recovery from the sixth day after flooding, whereas growth was inhibited for at least nine days. A remarkable similarity exists between our observations on the responses of bean plants to flooding and the well known responses to drought. 相似文献