Dissolved organic carbon concentrations and fluxes along the Moisie River, Quebec

SUMMARY. 1. The main stream and tributaries of a 145 km reach of the Moisie River, Quebec, were examined for temperature, conductivity, pH, dissolved organic carbon (DOC),%DOC>100,000 nominal molecular weight (NMW), optical density (OD₃₅₀), and the ratio of OD₄₀₀ to OD₆₀₀ (E4:E6).
2. Dissolved organic carbon concentrations correlated closely with OD₃₅₀ ( r ²=0.92, P <0.001). However,%DOC>100,000 NMW did not correlate with the E4:E6 ratio.
3. Except for a slight increase in%DOC> 100,000 NMW ( r ²=0.37, P <0.05), no change in any characteristic occurred down the length of the Moisie River, despite consistently higher levels of DOC in the tributaries.
4. Results suggest that high concentrations of DOC in tributary waters are rapidly removed within the main river channel. These results are discussed in terms of both biotic and abiotic models of in-strcam processing.     

Potassium dependence and phytoplankton ecology: an experimental study

SUMMARY 1. Unialgal cultures of three species common in the freshwater phytoplankton were used to test limitation of specific growth rate and final yield in defined media of low K⁺ concentration (range <0.3–6 μmol L⁻¹ or mmol m⁻³).
2. Growth rate of the diatom Asterionella formosa was independent of K⁺ concentration above 0.7 μmol L⁻¹. Final yield was dependent on initial concentration when accompanied by K⁺ depletion below this concentration, but not by lesser depletion with more residual K⁺. Analyses of particulate K in the biomass indicated a mean final cell content of 2.8 μmol K 10⁻⁸ cells, approximately 1.0% of the organic dry weight.
3. Less detailed work with the diatom Diatoma elongatum showed no dependence of growth rate or final yield upon the initial K⁺ concentration in the range 0.8–3.2 μmol L⁻¹. The phytoflagellate Plagioselmis nannoplanctica suffered net mortality in the lowest concentration tested, 0.8 μmol L⁻¹.
4. Comparison with the range of K⁺ concentration in natural fresh waters, including a depletion induced by an aquatic macrophyte, suggests that K⁺ is unlikely to limit growth of phytoplankton. Nevertheless, there can be correlation of K⁺ with lake trophy.     

Immobilization of dissolved organic matter from groundwater discharging through the stream bed

SUMMARY. 1. In laboratory experiments, 9.7–25.7% of dissolved organic carbon (DOC) in groundwater (at concentrations of 18.7–24.8 mg 1-⁻¹) was immobilized after perfusion through 8-cm-deep (22-cm-diameter) cores of stony stream-bed substratum.
2. This represented immobilization rates of 7.1–23.5 mg m⁻² h⁻¹ or, extrapolated across the year, potential immobilization rates within the stream bed of 62.2–205.9g m⁻² yr⁻¹. Actual rates in the entire stream bed were probably higher because perfusion through the experimental cores did not reduce groundwater DOC concentrations to levels measured in the adjacent stream.
3. Natural concentrations of dissolved free amino acids (DFAAs) in groundwater were generally unchanged following perfusion through the cores, suggesting the maintenance of a dynamic equilibrium in their concentrations.
4. Selective enrichments of amino acids in groundwater (up to 20-fold) were entirely immobilized following perfusion, indicating their rapid retention and flux in this environment. Thus, immobilization of the bulk DOC in stream-bed cores probably did not reflect net reductions in dissolved free, low-molecular-weight material, with higher molecular weight, more 'refractory' material being immobilized instead.
5. We conclude that groundwater can contribute substantial amounts of DOC, both high and low molecular weight, to a stream ecosystem. The stream bed is the site at which much of this material could be initially immobilized and made available to the stream trophic structure.     

Removal of heavy metals using a brewer's yeast strain of Saccharomyces cerevisiae: advantages of using dead biomass

Aim:  The capacities of live and heat-killed cells of Saccharomyces cerevisiae at 45°C for the removal of copper, nickel and zinc from the solution were compared.
Methods and Results:  Kinetic studies have shown a maximum accumulation of Ni²⁺ and Zn²⁺ after 10 min for both types of cells, while for Cu²⁺ this was attained after 30 and 60 min for dead and live cells, respectively. Equilibrium studies have shown that inactivated biomass displayed a greater Zn²⁺ and Ni²⁺ accumulation than live yeasts. For Cu²⁺, live and dead cells showed similar accumulation. Fluorescence, scanning electron microscopy and infrared spectroscopy studies have shown that no appreciable structural or molecular changes occurred in the cells during the killing process. The increased metal uptake observed in dead cells can be most likely explained by the loss of membrane integrity, which allows the exposition of further metal-binding sites present inside the cells.
Conclusions:  Heat-killed cells showed a higher degree of heavy metal removal than live cells, being more suitable for further bioremediation works.
Significance and Impact of the Study:  Dead flocculent cells can be used in a low cost technology for detoxifying metal-bearing effluents as this approach combines an efficient metal removal with the ease of cell separation.     

Ammonium and phosphate regenerationby the zooplankton of an Amazon floodplain lake

SUMMARY. 1. Regeneration of ammonium and phosphate by macro-zooplankton (Cladocera. adult copepods. and copepodites) was measured in Lake Calado. an Amazon floodplain lake, Macrozooplanktonabundances ranged between 1×10⁴ and 3×10⁵ individuals m⁻².
2. Phosphate regeneration ranged from 0.2 to 1.3 μ mol PO₄ m⁻² b⁻¹at station 1. located 2 km from the Solimoes River, and from 1.6 to8.3 μ mol PO₄ m⁻² h ⁻¹ at station 3, located 7 km from the SolimoesRiver. Ammonium regeneration at stations 1 and 3 ranged from 1.7 to11.9 and from 13.4 to 77.2 μ mol NH₄ m⁻² h⁻¹. respectively.
3. Zooplankton regenerated ammonium and phosphate at similarrates during rising and falling waier. Regeneration by macrozooplankton was low compared to other tropical lakes and compared to microbesand microzooplankton in Lake Calado.     

Effect of disk rotational speed on heavy metal accumulation by rotating biological contactor (RBC) biofilms

The efficiency of a rotating biological contactor (RBC) in the treatment of waters contaminated with cadmium, copper and zinc, in particular the effect of rotational speed, namely 3, 15 and 25 rev min⁻¹, on heavy metal reclamation was evaluated. Atomic absorption spectrophotometric analysis indicated > 92% and < 20% removal of copper (Cu²⁺) and zinc (Zn²⁺), respectively. Cadmium (Cd²⁺) levels, however, remained constant. Similar results were obtained at all three rotation speeds tested.     

Effects of soil frost on nitrogen net mineralization, soil solution chemistry and seepage losses in a temperate forest soil

Freezing and thawing may alter element turnover and solute fluxes in soils by changing physical and biological soil properties. We simulated soil frost in replicated snow removal plots in a mountainous Norway spruce stand in the Fichtelgebirge area, Germany, and investigated N net mineralization, solute concentrations and fluxes of dissolved organic carbon (DOC) and of mineral ions (NH₄⁺, NO₃⁻, Na⁺, K⁺, Ca²⁺, Mg²⁺). At the snow removal plots the minimum soil temperature was −5 °C at 5 cm depth, while the control plots were covered by snow and experienced no soil frost. The soil frost lasted for about 3 months and penetrated the soil to about 15 cm depth. In the 3 months after thawing, the in situ N net mineralization in the forest floor and upper mineral soil was not affected by soil frost. In late summer, NO₃⁻ concentrations increased in forest floor percolates and soil solutions at 20 cm soil depth in the snow removal plots relative to the control. The increase lasted for about 2–4 months at a time of low seepage water fluxes. Soil frost did not affect DOC concentrations and radiocarbon signatures of DOC. No specific frost effect was observed for K⁺, Ca²⁺ and Mg²⁺ in soil solutions, however, the Na⁺ concentrations in the upper mineral soil increased. In the 12 months following snowmelt, the solute fluxes of N, DOC, and mineral ions were not influenced by the previous soil frost at any depth. Our experiment did not support the hypothesis that moderate soil frost triggers solute losses of N, DOC, and mineral ions from temperate forest soils.     

Salinity response of a freshwater charophyte, Chara vulgaris

Abstract. Chara vulgaris L. growing in an oligohaline lake was adapted to laboratory conditions and subjected to long-term salinity treatments ranging from 0 to 350 mol m ³ NaCl added to the lake water (40–680 mosmol kg ¹). Osmotic potential and concentration of the main osmotically active solutes (K⁺, Na⁺, Mg²⁺, Cl and sucrose) in the vacuolar sap of the central internodal cells were estimated. C. vulgaris did regulate turgor but incompletely. Turgor decreased from 335 mosmol kg ¹ under control conditions to 52–111 mosmol kg ¹ at 350 mol m ³ NaCl. The enhancement of πⁱ was achieved by increase in both ions and sucrose. Sterile and fertile plants differed in their response to osmotic stress. In sterile plants, the ions accounted for about 87% of the vacuolar osmotic potential. The increase of πⁱ under osmotic stress was exclusively due to an accumulation of Na⁺ and Cl^-. In fertile plants, sucrose accounted for about 35% of πⁱ and ions for about 51% Under osmotic stress, sucrose content increased together with the ionic content of Na⁺ and Cl^-.     

Mg2+-free buffer elevates transformation efficiency of Vibrio parahaemolyticus by electroporation

Aims:  The ability to transform Vibrio spp. is limited by the extracellular nuclease that their cells secrete. The reported transformation efficiency of this organism is 10²–10⁵ transformants per microgram DNA. We tried different buffers and conditions, aiming to elevate its transformation efficiency.
Methods and Results:  MgCl₂ and sucrose are often included in the washing and/or electroporation buffers to stabilize the cell membrane. However, Mg²⁺ is required for production and activity of the extracellular nuclease. A simple electroporation buffer lacking Mg²⁺ was found to increase transformation efficiency dramatically, to levels 50-fold more than the buffers containing Mg²⁺. To maintain the stability of the cell membranes, Mg²⁺ was replaced with high concentrations of sucrose, from 272 to 408 mmol l⁻¹. With the new buffers, the transformation efficiency of Vibrio parahaemolyticus was increased to 2·2 × 10⁶ transformants per microgram DNA.
Conclusions:  Mg²⁺ in the buffer adversely affected transformation of V. parahaemolyticus by electroporation. The cell membranes of vibrio can be stabilized by high concentration of sucrose when Mg²⁺ is absent.
Significance and Impact of the Study:  A greater transformation efficiency can facilitate the genetic analysis of an organism and its pathogenicity. Buffers lacking Mg²⁺ can be used for other nuclease-producing organisms.     

Time-course of inorganic nitrogen uptake and incorporation by natural populations of freshwater phytoplankton

SUMMARY. 1. Time-course measurements of NH₄⁺ and NO₃⁻uptake were made on the natural phytoplankton populations in a eutrophic lake at a time when these nutrients were at their lowest annual concentration.
2. Both NH₄⁺ and NO₃⁻ uptake was increased at least five-fold during the first 5 min of incubation following near saturating pulses of these nutrients.
3. Elevated uptake was also observed following low level (∼2μg N 1⁻¹) pulses of NH₄⁺ and NO₃⁻, but substrate depletion during the first hour of incubation may have been partially responsible for this apparent enhancement.
4. Incorporation of ^I5N into TCA-insoluble material (protein) following the saturating NH₄⁺ pulse was increased less than total cellular ¹⁵N uptake, whereas no elevation of ¹⁵N incorporation into protein was observed following a saturating NO₃⁻pulse.
5. The percentage of ^I5N incorporated into protein, with respect to total cellular uptake, was ∼32% and ∼12% for NH₄⁺ and NO₃⁻, respectively, following 5 h of incubation.     

Input, movement and exchange of organic matter within a subtropical coastal black water river-flood plain system

SUMMARY. 1. Inputs, movements and exchanges of particulate organic matter were measured on two contrasting floodplains of the Ogeechee River, Georgia, U.S.A. A model, which incorporated measurements of standing crop, respiration, litterfall, inundation, and litter processing rates, was used to estimate annual exchanges of organic matter between the river and floodplains.
2. Annual litterfall was higher on the East floodplain than on the lower elevation West floodplain (902 v. 784 g ash-free-dry-mass [AFDM] m⁻²).
3. Experiments with tagged leaves and sticks demonstrated that litter was readily displaced during floods. The distance and direction of displacement varied within and between floodplains but tended to be higher closer to the river and was generally parallel to the river.
4. The model indicated that both floodplains lost organic matter to the river. The lower elevation floodplain (East) lost more organic matter to the river (208 g AFDM m⁻² year⁻¹) than did the higher elevation (West) floodplain (79g AFDM m⁻² year⁻¹).
5. Inputs of organic matter from the floodplain to the river exceeded the amount of litterfall typically entering heavily forested high gradient headwater streams (5.5 v. 0.4-0.6 kg AFDM m⁻² year⁻¹).
6. Floodplain organic matter inputs may exert a greater influence upon structure and function within these streams than do upstream inputs or primary production. Consequently, current conceptualizations of stream structure and function need to be modified to account for the effects of floodplain inputs on stream channel processes within large, low-gradient rivers.     

The ecology and taxonomy of anaerobic halophilic eubacteria

Abstract A number of obligately anaerobic chemoorganotrophic moderately halophilic bacteria have been isolated from the bottom sediments of the Dead Sea and the Great Salt Lake, Utah: (1) Halobacteroides halobius , a long motile rod from the Dead Sea, fermenting sugars to ethanol, acetate, H₂ and CO₂; (2) Clostridium lortetii , a rod-shaped bacterium from the Dead Sea, producing endospores with attached gas vacuoles; (3) a spore-forming motile rod-shaped bacterium, fermenting sugars, isolated from the Dead Sea; (4) Haloanaerobium praevalens , isolated from the Great Salt Lake, fermenting carbohydrates, peptides, amino acids and pectin to acetate, propionate, butyrate, H₂ and CO₂.
Analysis of their 16S rRNA shows that these organisms are related to each other, but unrelated to any of the other subgroups of the eubacterial kingdom, to which they belong.
Ha. praevalens and Hb. halobius regulate their internal osmotic pressure by the accumulation of salt (Na⁺, K⁺, Cl⁻) rather than by organic osmotic solutes.     

Sinking rates of planktonic diatoms in an unstratified lake: a comparison of field and laboratory observations

SUMMARY. 1. Natural population sinking rates were calculated by fitting an exponential regression to 6 years'observations on declining crops of Melosira italica subarctica O. Müll. and Stephanodiscus astraea (Ehr.) Grun.
2. Losses were described by an exponential model which yielded still water sinking rates of 0.86 md⁻¹ for M. italica and 0.45md⁻¹ for S. astraea.
3. Laboratory measurements of the sinking rate of natural populations showed that the rate increased abruptly from less than 0.2 m d⁻¹ in growing populations to 0.4 m d⁻¹ after silica depletion.
4. The measured sinking rate of S. astraea agreed well with that observed in the field. Where as populations of M. italica appeared to sink more quickly in the lake than could be accounted for by laboratory observations.     

Life cycle, growth, mortality and production of Ephemerella major Klapalek (Ephemeroptera) in a trout stream in Belgium

SUMMARY. 1. The life cycle of Ephemerella major Klapalek in a chalk trout stream in Belgium took 1 year. Emergence was highly synchronized with a flight period from mid-May to mid-June. Tiny nymphs occurred from June to late August.
2. The mean instantaneous growth rate was high in autumn (3.6% wet wt day⁻¹), very low from November to February (0.8% wet wt day⁻¹) and high until emergence (2.3% wet wt day⁻¹); short day length seemed to be the major factor reducing growth rate during winter.
3. Mortality was close to zero during winter and 1.4—1.7% day⁻¹during other seasons. Total mortality from egg to adult was 99.6%.
4. The annual production was about 9g wet wt m⁻² year⁻¹ and the annual P/ ratio was 7.5. There was good agreement between the production values estimated by four methods. Production rate was highest in May (13 mg wet wt m⁻² day⁻¹) and zero in February.     

A LIGHT-SCATTERING TECHNIQUE FOR THE STUDY OF THE PERMEABILITY OF RAT BRAIN SYNAPTOSOMES IN VITRO

Abstract— (1) Swelling of synaptosomes was measured spectrophotometrically by recording changes in extinction at 520 nm.
(2) Synaptosomes behaved as osmometers in NaCl solutions. When the tonicity of the medium was changed, synaptosome volume changed in accordance with Boyle and van't Hoff's Law. These changes were reversed on restoring the tonicity of the medium.
(3) The rate at which a solute entered the synaptosome was determined from the rate of swelling in the presence of that solute. Permeability of synaptosomes to non-electrolytes was in the order glucose ≪ glycerol < thiourea = formamide < propylene glycol = dimethylsulphoxide.
(4) Synaptosomes were freely permeable to ammonium and acetate ions and impermeable to Ca²⁺, Mg²⁺, PO₄²⁻, SO₄²⁻ and oxalate ions.     

Real-time quantification of Pseudomonas fluorescens cell removal from glass surfaces due to bacteriophage varphiS1 application

Aims:  To study the efficacy of the lytic phage φS1 in eliminating Pseudomonas fluorescens in the early stage of biofilm formation, using an in situ and real time methodology for cell quantification.
Methods and Results:  Cell adhesion and phage infection studies were carried out in a parallel plate flow chamber under laminar conditions. Cells were allowed to adhere until reaching 1·7–1·8 × 10⁶ cells cm⁻² and phage infection was performed with two different phage concentrations (2 × 10⁹ PFU ml⁻¹ and 1 × 10¹⁰ PFU ml⁻¹). Phage concentration clearly affects the speed of infection. The less concentrated phage solution promoted a three times slower rate of cell removal but did not affect the overall percentage of cell removal. In fact, after a longer infection period the less concentrated phage solution reached the same 93% cell removal value.
Conclusions:  Phages are efficient in the eradication of bacterial cells at the early stage of biofilm formation and their presence at the surface did not allow bacterial recolonization of the surface.
Significance and Impact of the Study:  To date, no published studies have been made concerning in situ and real time quantification of cell removal from surfaces due to phage action.     

Temporal scales of variability in pelagic environments and the response of phytoplankton

SUMMARY. 1. Pelagic environments are inherently and continuously variable. Time scales relevant to phytoplankton behaviour are identified as ranging from the time taken for light to penetrate a cell (10-⁻¹⁵ s) to the creation and disappearance of lakes (10¹² s). Each scale invokes characteristic responses in algae, spanning the activation of biochemical pathways to the extinctions of species.
2. With special, though not exclusive, reference to the Freshwater Biological Association's activities through its first 60 years, scientific investigation has touched each point on the scale. The existing knowledge is used to produce simulations of the behaviour of model planktonic species at every level in the series.
3. Emphasis is placed on scale interaction, upon how variability at one level collapses into the steady state of higher levels and, equally, how the ultimate texture or 'grain' of biological systems is determined by the structure at finer scales.     

Salinity adaptation in the snakehead, Ophiocephalus maculatus Lacépède: changes in oxygen consumption, branchial Na+-K+-ATPase and body composition

Snakeheads were adapted to fresh water (1 mOsm kg⁻¹), 25% sea water (230 mOsm kg⁻¹), 33% sea water (320 mOsm kg⁻¹) and 40% sea water (380 mOsm kg⁻¹) for 20 days. Exposure to salt water resulted in tissue dehydration, elevations of plasma osmolality, Na⁺, Mg²⁺, Cl⁻and protein concentrations and stimulation of branchial Na⁺-K⁺-ATPase activity. These changes were accompanied by concomitant decline of the hepatosomatic index and liver glycogen concentration. The routine rate of oxygen consumption was increased in snake-heads adapted to 33% sea water. These data were taken to indicate a stressful effect of salinity to the snakehead despite documentation of its ability to penetrate into brackish waters.     

EFFECTS OF POTASSIUM AND GLUTAMATE ON BRAIN CORTEX SLICES: UPTAKE AND RELEASE OF GLUTAMIC AND OTHER AMINO ACIDS

Abstract— Effects of an increased concentration of K⁺ (55 m m ) in the medium on fluxes of glutamate and other amino acids in the presence and absence of 10 m m -glutamate were studied. The following observations were made:
(1) The efflux of glutamate is slightly increased by excess K⁺. The glutamate efflux is smaller than the potassium fluxes.
(2) The K⁺-induced increase of glutamate efflux is enhanced under anoxia or in glutamate-containing media.
(3) The influx of glutamate is unaffected or slightly increased by excess K⁺.
(4) The efflux of GABA is increased by excess K⁺, both in the absence and in the presence of glutamate.
(5) Efflux of glutamine, leucine and lysine is increased by excess K⁺, but only provided that glutamate is also present in the medium.
(6) Efflux of glutamate and of GABA is increased by addition of 10 m m -glutamate.     

GRAMICIDIN INDUCED ION TRANSPORT IN BRAIN MITOCHONDRIA PREPARATIONS

Abstract— —(1) Gramicidin at low concentrations induces an uptake of K⁺ and Na⁺ in brain mitochondria in a manner similar to that observed with liver mitochondria.
(2) The cation uptake is energy dependent, and is accompanied by an ejection of H⁺ ions and a slight increase in respiration in the absence of added permeant anion.
(3) The cation uptake and hydrogen ion release are both inhibited by agents which inhibit electron transport. Barbiturates and chlorpromazine inhibit the transport phenomenon by inhibiting electron transport.
(4) In the presence of permeant anions (phosphate and acetate) respiration is stimulated quite significantly.
(5) At high gramicidin concentrations there is a release of Na⁺ and K⁺ from the mitochondria and uptake of H⁺. There is also a cyclic reduction-oxidation of the nicotinamide adenine dinucleotides, which is believed to be due to the release from the mitochondria of the reduced dinucleotides followed by their subsequent oxidation.
(6) The effect of high gramicidin on the mitochondrial nicotinamide-adenine dinucleotides and cation distribution is irreversible and is not blocked by individual inhibitors of respiration and of phosphorylation, but is prevented by prior addition of a mixture of these inhibitors.
(7) Gramicidin is therefore believed to have a bimodal function; one on the mitochondrial membrane per se , and the other on the energy dependent ion accumulation apparatus.
(8) A model of induced mitochondrial ion accumulation is presented.