摘要:

Active turbulence in lakes is confined to the surface mixed layer, to boundary layers on the lake sides and bottom, and to turbulent patches in the interior. The density stratification present in most lakes fundamentally alters the pathways connecting external mechanical energy inputs, for example by wind, with its ultimate fate as dissipation to heat; the density stratification supports internal waves and intrusions that distribute the input energy throughout the lake. Intrusions may be viewed as internal waves with zero horizontal wavenumber and are formed each time localised mixing occurs in a stratified fluid. Intrusions are also formed in the epilimnion by differential heating or cooling and by differential deepening. The fraction of lake volume below the diurnal mixed layer that is subject to active turbulence is very small, probably of the order of 1% or less in small to medium‐sized lakes. By contrast, in the surface mixed layer, turbulence is less intermittent and maintains phytoplankton in suspension and controls their exposure to the underwater solar flux. Nutrient transport to individual cells depends not only on the cell Reynolds number but also on the Peclet number, which, if large, implies enhanced mass transfer above purely diffusive values.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516233

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The interactions of size, shape, and density of cyanobacteria result in a 5‐order of magnitude difference in flotation or sinking rates which, in turn, influence the extent of their dispersion in turbulent water masses. Active mixing through resource‐replete waters of high clarity favours fast‐growing, small‐celled species. Where photosynthetically active radiation is severely attenuated through the wind‐mixed layer, species may rely on turbulent entrainment but must be adapted toward efficient light harvesting (morphological attenuation, enhanced pigmentation). In both strongly segregated waters (light‐ and nutrient‐rich layers separated vertically) and waters experiencing high‐frequency fluctuations in vertical mixing and optical depth, emphasis is placed on the ability to make rapid, buoyancy‐adjusted vertical movements, favoured by large size. The cyanobacterial 1ife‐forms respectively typical of these contrasted limnological systems — unicellular coccoids (e.g.,Synechococcus), solitary filaments (e.g.,Oscillatoria) and colonial forms (e.g.,Microcystis) — illustrate the diversity of evolutionary adaptations to be discerned among the planktonic cyanobacteria and which contributes to their reputation as a prominent and successful group of organisms.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516234

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The literature was reviewed to determine the direct temperature effects on photosynthetic capacity (Pmax), specific respiration rate (Rest), and growth rate of bloom‐forming cyanobacteria(Anabaena, Aphanizomenon, Microcystis, Oscillatoria) and to assess the importance of direct tern‐perature effects on cyanobacterial dominance in lakes. This analysis is supported by field studies ofMicrocystis aeruginosain a hypertrophic lake. The literature and field data show that Pmax, Rest, and growth rate are temperature‐dependent with optima usually at 25 °C or greater. The four genera varied in their response to low temperatures withMicrocystisbeing most severely limited belw about 15 °C.Oscillatoriatended to tolerate the widest range of temperatures. However, an examination of field data from representative lakes around the world indicated that direct temperature effects were secondary to indirect temperature effects (mixing) and nutrients in determining the dominance of bloom‐forming cyanobacteria in lakes, direct tern‐perature effects probably act synergistically with other factors in this process.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516235

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

In eutrophic lakes cyanobacteria are favoured relative to other phytoplankton, both under stratified and mixed conditions. During stratification, gas vacuole formation allows the accumulation of dense surface scums which attain the highest possible area‐specific photosynthetic rates in aquatic environments owing to high irradiances, near‐complete harvesting of impinging light, and minimal light inhibition and photo‐oxidation. During moderate mixing, high yields of biomass can be achieved by effective light harvesting for photosynthesis (aided by phycobilin pigments) and low maintenance energy requirements at low mean irradiances. Howevrr, nitrogen fixation competes for energy and reductant with photosynthesis, and leads to a decline of light‐saturated maximum growth rates. Wind‐driven vertical mixing and lateral advection are the main causes for the instability of cyanobacterial blooms in hyper‐eutrophic lake ecosystems.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516236

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Experiments described in the literature have demonstrated that additions of N, Fe, and occasionally P, influence planktonic cyanobacterial nitrogen fixation in lakes and estuaries throughout the world. Increase in abundance of cyanobacteria which can fix nitrogen did not necessarily indicate that N2fixation had occurred. In natural plankton assemblages, N2fixation was normally stimulated by low total inorganic nitrogen (TIN) and depressed by additions of TIN. Nitrogenase was often stimulated by addition of Fe but soluble reactive phosphate (SRP) alone only stimulated nitrogenase activity occasionally. Luxury consumption and storage of P, but not N, explains the lack of P stimulation in nature. Nitrogenase activity was usually repressed at TIN oncentrations of >50–100 μg l‐1. Additions of N + P had variable effects which may depend on the balance between nitrogenase inhibition by N and general growth stimulation by N + P (which reduces ambient N).

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516237

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Cyanobacteria are the only group of phytoplankton to show a clear increase both in bio‐mass and relative contribution to total phytoplankton biomass as temperate lakes become eutrophic. Correlative studies indicate that this increase begins at total phytoplankton biomass levels of 3–5 mg fresh weight l‐1or spring total phosphorus (TP) concentrations of 25–30 μg l‐1. Above TN : TP ratios of 30, cyanobacteria tend to become rare, but below this value they may or may not dominate. Better predictions may be possible by attempting to remove the influence of the refractory dissolved organic nitrogen and phosphorus fractions by using the TN‐DON : TP‐DOP ratio. While experimental manipulation of N : P ratios in enclosures or entire lakes may often stimulate or suppress relative cyanobacterial biomass, laboratory studies do not clearly link low N : P ratios with cyanobacteria. Evidence from correlative studies, long‐term records of individual lakes, and experimental manipulations of nutrient loads suggest that other factors such as temperature, mixing regimes, transparency, and iron or carbon availability may influence cyanobacterial dominance in lakes.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516238

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Trace metals play crucial roles in the carbon and nitrogen metabolism of cyanobacteria. Physiological responses to metal limitation and toxicity in culture have shown that iron is important for photosynthesis and energy distribution in the cell while both iron and molybdenum are biochemically involved in nitrate reduction and nitrogen fixation. Nitrogen fixation is also relatively sensitive to copper toxicity. Consequently, factors that affect the supply rate, chemical speciation, or the recycling of trace metals can alter patterns of primary productivity and nitrogen metabolism. Overall, three trace metal dependent processes may contribute towards dominance: efficient use of limiting light, nitrogen fixation, and production of extracellular iron binding compounds.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516239

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The growth of cyanobacteria in natural waters may be dependent on an efficient ammonium transport system. Such a system may also play a role in the retention of internally generated ammonium from N2fixation, nitrate reduction, and photorespiration. Methylammonium is commonly used as an ammonium analogue to study transport. The kinetics of methylammonium uptake by cyanobacteria are biphasic with a first rapid phase representing transport into the cells and a second slower phase dependent on metabolism by the primary ammonia assimilating enzyme glutamine synthetase. At high external pH values (pH > 9) diffusion of the uncharged species becomes increasingly dominant while at neutral pH values the uptake is thought to be an active process dependent on membrane potential.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516240

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The most common storage products of cyanobacteria are polyphosphate as a phosphorus storage compound, cyanophycin or phycobilin protein pigment as nitrogen storage products, and glycogen as a storage product of both carbon and energy. Nutrient uptake kinetics are regulated by the storage pools, and the patterns of regulation have a feedback effect on the amount of accumulated nutrient in the cells. Besides having a storage function the nutrient storage products are likely to act as metabolic sinks during conditions of energy stress. Regulation of storage products is especially strict in light‐limited cultures. By increasing the rate of polysaccharide formation during growth with short photoperiods, cyanobacteria are able to sustain relatively high growth rates. This effect is enhanced by keeping respiratory losses very low.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516241

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Correlative field evidence suggests that large grazers such asDaphnia pulexpromote the growth of colonial cyanobacteria by selectively eating competitive phytoplankton. This is supported by experimental evidence that (1) in eutrophic lakes dominated by cyanobacteria grazing by zooplankton on small particles is often > 100% day‐1, and (2) colonial cyanobacteria are generally not grazed as rapidly as smaller phytoplankton. Cyanobacteria generally have deleterious effects on grazing zooplankton. Filamentous cyanobacteria such asAnabaenaandOscillatoriacan inhibit filtering by cladocerans, reducing growth and reproduction. Detrimental effects on zooplankton via nutritional deficiencies and toxins of cyanobacteria have been demonstrated in the laboratory but not in the field. Grazing on colonial cyanobacteria by zooplankton appears to be an important trophic link in tropical lakes. Generally, calanoid copepods seem best adapted to utilising large cyanobacteria. The generalisation that, with increasing eutrophication, zoo‐plankton communities tend to shift from a dominance of calanoid copepods to cladocerans, does not apply to lakes in New Zealand.

ISSN:0028-8330    

DOI:10.1080/00288330.1987.9516242

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor