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  • 1
    Electronic Resource
    Electronic Resource
    The thermal, oxygen and light regimes in isolated columns of water in a turbid impoundment (1980)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 10 (1980), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. Temperature, oxygen and secchi disc transparency were measured in 5-m diameter isolation columns positioned in water approximately 4 m deep. In general the difference in thermal conditions between the adjacent open water and columns was slight. Oxygen levels in bottom waters in the enriched columns were often slightly lower than in the open water but never dropped below 50% saturation. It seems unlikely that sufficient depletion occurred to markedly increase release of phosphorus from the sediment. Light penetration in the columns was more varied than in the open water but was seldom sufficient to permit the development of large stands of benthic algae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.1980.tb01195.x
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of epiphyton onPotamogeton crispus L. leaves (1981)
    Springer
    Microbial ecology 7 (1981), S. 351-363 
    Details
    ISSN: 1432-184X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Potamogeton crispus L. grows as a winter producing annual in the shallow lakes of the Pongolo Floodplain, South Africa. Colonization of leaves by algal and bacterial epiphytes, as seen by scanning electron microscopy, followed the established pattern of increasing diversity and density with leaf age. It was apparent from the micrographs that the primary and subsequent colonizers were present even after death of the host leaf. Cross sections of leaves, viewed by transmission electron microscopy, illustrated that bacterial attachment did not damage the surface of young leaves. There was, however, extensive inward swelling and disorganization of the epidermal walls, characteristic of a reaction to invasion by pathogens. In older leaves the swelling was also present in mesophyll cells, while bacteria had invaded and degraded the epidermal cell wall. The bacterial invasion was concomitant with signs of senescence, and in dead leaves the organisms had penetrated and degraded the epidermis and mesophyll cell walls. The epiphyton/ host relationship may therefore be considered necrotrophic with important consequences for the transfer of energy from producers to consumers during decomposition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02341430
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  • 3
    Electronic Resource
    Electronic Resource
    The aluminium signal: New dimensions to mechanisms of aluminium tolerance (1991)
    Springer
    Plant and soil 134 (1991), S. 153-166 
    Details
    ISSN: 1573-5036
    Keywords: aluminium ; calcium ; cap secretions ; roots ; stress physiology ; tolerance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The physiological basis of plant reaction to and tolerance of aluminium (Al) is poorly understood. We review the results of investigations into Al toxicity and root physiology to develop a theoretical basis for explaining the reaction of the root to Al, including suggested roles for Ca2+, mucilaginous cap secretions and endogenous growth regulators in mediating a transmitted response between Al-damaged cap cells and the interacting cell populations of the cap and root. This information is used to identify possible mechanisms of Al tolerance, notably involving signal transduction, Al uptake pathways and root morphogenesis; and to briefly discuss how procedures selecting for Al tolerance may be improved by incorporating the concept of stimulus-response coupling. Similarities in the responses of roots to Al and other signals (e.g. gravity, light, mechanical impedance) are used to develop the hypothesis that roots respond to environmental signals by way of a common regulatory system. New research prospects for extending our perception of Al tolerance mechanisms are identified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010728
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  • 4
    Electronic Resource
    Electronic Resource
    An assessment of the importance of water stress in seasonally floodedC. dactylon on the Pongolo River floodplain in the formulation of guidelines for controlled flooding (1986)
    Springer
    Hydrobiologia 137 (1986), S. 175-184 
    Details
    ISSN: 1573-5117
    Keywords: Cynodon dactylon ; water stress ; floodplain ; flood management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Daily variation in water potential was measured inCynodon dactylon in seasonally flooded areas of the Pongolo river floodplain. Soil moisture declined during the dry winter season when the plants were exposed, causing them to experience increasing water stress. Fog and mist appeared to relieve stress but it is concluded that water stress is sufficient to reduce production during exposure. The results are discussed in relation to the timing of flood releases from the upstream Pongolapoort dam and it is concluded that the period of exposure is of less significance than the duration and frequency of inundation in the formulation of guidelines for flood releases from the dam.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00004213
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  • 5
    Electronic Resource
    Electronic Resource
    Interactions between period of exposure, grazing and crop growth rate of Cynodon dactylon (L.) Pers. in seasonally flooded areas of the Pongolo River floodplain (1985)
    Springer
    Hydrobiologia 126 (1985), S. 65-73 
    Details
    ISSN: 1573-5117
    Keywords: floodplain ; Cynodon dactylon ; grazing ; production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cynodon dactylon (L.) Pers. forms extensive meadows on seasonally inundated areas of the Pongolo river floodplain. As floodwaters receded during winter, the shoots of C. dactylon which had not decomposed during submergence sprouted. Crop growth rate was high (up to 23 kg/ha/d dry mass) and the meadows were heavily grazed by domestic stock which removed up to 15 kg/ha/d. The high crop growth rate was not maintained because as exposure period increased, soils became dry and water stress conditions developed. This caused the C. dactylon to become less palatable and brought about a shift in grazing which allowed a build-up of the grazeable and ungrazeable fraction standing crop. Maximum standing crop occurred at the onset of the next flood. Grazing is shown to have a net negative effect on production, although at different times during exposure defoliation had either a depressing or stimulating effect on growth. It is postulated that the duration of the inundation period is more significant than the duration of the exposure period in maintaining the C. dactylon meadows.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00008389
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  • 6
    Electronic Resource
    Electronic Resource
    Ionic content as a factor influencing turbidity in two floodplain lakes after a flood (1988)
    Springer
    Hydrobiologia 160 (1988), S. 19-31 
    Details
    ISSN: 1573-5117
    Keywords: conductivity ; floodplain lakes ; inorganic suspensoids ; ionic content ; turbidity ; underwater light
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationship between ionic content, measured as electrical conductivity, and turbidity resulting from inorganic suspensoids was investigated experimentally on the Ponogolo river floodplain. Turbid floodwaters were mixed in various proportions with clear lake water of high conductivity and settling rates determined. For the conductivity range 215–1084 μS cm−1 there was an increase in the maximum settling rate from 3.3–20.6% h−1. These data were compared with observations made, in a turbid lake of low conductivity and a clear water lake of high conductivity, during and after a flood. The importance of lake morphology, flushing and conductivity as determinants of turbidity and light attenuation in the floodplain lakes is discussed. The relevance of these observations to the understanding of turbidity in other systems is considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00014275
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  • 7
    Electronic Resource
    Electronic Resource
    The application of growth kinetics to the control of Eichhornia crassipes (Mart) solms. Through nutrient removal by mechanical harvesting (1977)
    Springer
    Hydrobiologia 53 (1977), S. 165-171 
    Details
    ISSN: 1573-5117
    Keywords: Eichhornia crassipes production ; growth kinetics ; nutrient removal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The growth of Eichhornia crassipes (water hyacinth) under nitrate-nitrogen limiting conditions can be explained by the Monod rectangular model. The kinetic constants maximum specific growth rate, half saturation constant and yield coefficient were determined under nitrate-nitrogen limiting conditions in nutrient culture at an air temperature of 25°C. The practical application of these constants for the possible control of water hyacinth through nutrient limitation is illustrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00029295
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  • 8
    Electronic Resource
    Electronic Resource
    The study of phosphorus and nitrogen fluxes in enriched isolation columns (1981)
    Springer
    Hydrobiologia 77 (1981), S. 49-60 
    Details
    ISSN: 1573-5117
    Keywords: Phosphorus ; sediments ; isolation columns ; nutrient enrichment ; enclosures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Isolation columns positioned in approximately 3.5 m of water in Midmar Dam, were enriched with PO4-P and NO3-N, singly and in combination. Increased chlorophyll concentration resulted from all enrichment treatments. Responses showed marked seasonality and varied in intensity and duration. Despite the PO4-P fixing potential of the sediments, SRP concentrations increased markedly at times and possible reasons for this discussed. The marked response to addition of NO3-N alone suggested a flux of phosphorus from the sediment through the water to the algal component. The significance of periphyton within the columns is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00006387
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  • 9
    Electronic Resource
    Electronic Resource
    A comparison of nutrient availability measured by chemical analysis and calculated from bioassay yields (1982)
    Springer
    Hydrobiologia 94 (1982), S. 247-255 
    Details
    ISSN: 1573-5117
    Keywords: Selenastrum ; available phosphorus ; available nitrogen ; bioassay ; eutrophication ; southern Africa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The concentrations of soluble biologically available nitrogen and phosphorus were determined using Selenastrum capricornutum bioassays and compared with analytically measured soluble nitrate (NO3-N) and soluble reactive phosphorus concentrations during enrichment studies in a South African impoundment. The NO3-N analyses consistently underestimated the soluble biologically available nitrogen and the extent of the discrepancy decreased with increasing NO3-N concentration. Biological availability of soluble organic nitrogen during the bioassays is suggested as a reason for the discrepancies. At low soluble reactive phosphorus concentrations the analytical measurements underestimated the soluble biologically available phosphorus while at high soluble reactive phosphorus concentrations the analytical measurements were considerable overestimates of soluble biologically available phosphorus. Possible reasons for the observed trend are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00016406
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  • 10
    Electronic Resource
    Electronic Resource
    The influence of site and position in the plant community on the nutrient distribution in, and content of Eichhornia crassipes (Mart.) Solms (1977)
    Springer
    Hydrobiologia 53 (1977), S. 67-72 
    Details
    ISSN: 1573-5117
    Keywords: Eichhornia crassipes ; nutrient content ; growth forms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Concentrations of Na, K, Ca, Mg, total organic N and P were determined in roots, petioles and pseudolaminae of water hyacinth plants sampled from the margins and centres of plant communities growing at three sites. Significant differences in the concentrations of most nutrients were found between the various plant parts and between marginal and central plants, whereas between site differences were only significant in the case of Na, Mg, and P. The differences in nutrient content in plants occupying different positions in the plant community are not readily explained, but suggest that interactions between plants in the centre of a community influence both their physiology of nutrient uptake and growth form.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00021233
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