A bacteriological survey of an oyster-growing area: The Oualidia Lagoon,Morocco

A 3-year bacteriological survey of an oyster-growing area in Morocco, where the Japanese oyster (Crassostrea gigas) is grown, showed that the contamination of this lagunar ecosystem was not continuous but intermittent and that animal manure and human recreational activities were important sources of pollution. The major source of contamination was of animal origin, except during the summer, when human contamination prevailed.     

Phosphatases; origin,characteristics and function in lakes

Phosphatases catalyze the liberation of orthophosphate from organic phosphorus compounds. The total phosphatase activity in lake water results from a mixture of phosphatases localized on the cell surfaces of algae and bacteria and from dissolved enzymes supplied by autolysis or excretion from algae, bacteria and zooplankton. External lake water phosphatases usually have pH optima in the alkaline region. Acid phosphatases generally seem to be active in the internal cell metabolism. The synthesis of external alkaline phosphatases is often repressed at high phosphate concentrations and derepressed at low phosphate concentrations. Phosphatase activity has therefore been used as a phosphorus deficiency indicator in algae and in natural plankton populations. The possibilities for this interpretation of phosphatase activity in lake water are limited, however, and this is discussed. The in situ hydrolysis capacity, i.e. the rate by which orthophosphate is released from natural substrates, is unknown. However, we advocate that this process is important and that the rate of substrate supply, rather than phosphatase activity, limits the enzymatic phosphate regeneration.     

Water hyacinth productivity and detritus accumulation

Water hyacinth [Eichhornia crassipes (Mart) Solms] productivity and detritus accumulation were evaluated in eutrophic lake water with and without added nutrients (fertilized and control reservoirs, respectively). Seasonal changes in plant productivity and detritus accumulation were determined at monthly intervals for one year. Significant differences were observed in plant productivity between seasons and nutrient additions. Seasonal plant productivity ranged from 1.9 to 23.1 mg (dry wt) ha⁻¹ for the fertilized reservoir and −0.2 to 10.2 mg ha⁻¹ for the control reservoir. Detritus accumulation was not significantly different between seasons or nutrient additions. Seasonal N assimilation by plants ranged from 34 to 242 kg N ha⁻¹ for plants in the fertilized reservoir and < 0 to 104 kg N ha⁻¹ for plants in the control reservoir. Annual net N recovered in detritus represented 21 and 28% of the total N removed by plants in the fertilized and control reservoirs, respectively. Net N loading to the reservoirs from detritus was 92 to 148 kg N ha⁻¹ yr⁻¹.     

Morphology,physics, chemistry and biology of Lake Rara in West Nepal

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.     

Hydrobiology and organic production in a marl lake of Kashmir Himalayan Valley

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 C_assim) and summer maximum (75.4 mg C_assim) 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.     

Osmotic properties of human red cells

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 (z_Hb). 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 z_Hb 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.     

Osmotic water permeabilities of brush border and basolateral membrane vesicles from rat renal cortex and small intestine

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.     

Biomanipulation and its feasibility for water quality management in shallow eutrophic water bodies in The Netherlands

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.