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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 18 (1987), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY 1. The occurrence, composition and invertebrate fauna of naturally-occurring leaf packs were studied over 24 months in Langrivier, a second-order mountain stream in the south-western Cape, South Africa. Langrivier is shallow and fast-flowing and stores very low levels of allochthonous detritus, although natural leaf packs form an obvious part of the energy base in the stream throughout the year.2. The occurrence and size of the packs were influenced mainly by stream discharge and by the timing and character of leaf fall from riparian trees. Packs were smallest (minimum dry mass 17 g, minimum volume 1.7–10−5 m3) in winter when discharge was high, and largest (maximum dry mass 191 g, maximum volume 4.2–10−3 m3) in spring when discharge decreased and leaf fall from the evergreen riparian trees began. Through the year the packs covered a mean 0.41 % of the stream bed and had a mean abundance of 0.46 packs m−2 of stream bed. They were ephemeral, lasting on average 〈1.7 months and yet accounted for 29% of the stored detritus in the system. Wood was the dominant component of packs, and leaves at ali stages of decomposition were present throughout the year.3. The ratio of numbers of invertebrates in packs: numbers of individuals in the benthos was very low (0.002–0.030), presumably because of the rarity and small size of the packs. Nevertheless, the density of invertebrates per unit area covered by leaf packs was consistently much higher than the density in an equivalent area of the benthos, except during peak leaf fall (October to December).4. Experiments were undertaken with artificial leaf packs in order to determine the extent to which these simulated natural packs. Although both natural and artificial leaf packs contained a high proportion of Plecoptera (46% and 29% respectively), the natural packs contained high numbers of simuliid larvae (33% of total), whereas artificial packs had a high percentage of chironomid larvae (62%), Several other taxa regularly occurred in both types of pack but in very low numbers. In addition,
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 216 (1967), S. 1097-1099 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Fig. 1. Number of film fragments, counted from photographs taken in the cloud chamber, plotted as a function of bubble film area (or bubble diameter). Lines represent loci of counts made at constant maximum supersaturations, S. Supersaturation vertical profiles in the cloud chamber are extremely ...
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 160 (1988), S. 141-153 
    ISSN: 1573-5117
    Keywords: desert limnology ; gypsous crusts ; mineral springs ; physicochemistry ; stratification ; reversed temperature gradients ; salinity gradients ; solar pond
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Hosabes is a small mineralized spring lying in a gypsous crust in the central Namib Desert on the south-western coast of Africa. It is fed by virtually fresh groundwater that wells to the surface at this and other similar fracture lines. The extremely high rates of evaporation and solar radiation result in intense concentration of the salts and the formation of strong salinity and therefore density gradients in the deeper parts of the system. These in turn produce a “solar pond” effect with a reversed temperature gradient; temperatures reach 50°C within the water column. The deeper parts of the system appear to be monomictic. Although the surrounding crust is largely gypsous, the water in the spring is dominated by NaCl as a result of precipitation of CaS04 in the highly concentrated water.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 267 (1993), S. 37-59 
    ISSN: 1573-5117
    Keywords: Southern Africa ; Namib Desert ; hydrochemistry ; saline waters ; major ions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Africa south of about 23° S has few natural athalassic lakes, saline or freshwater. South Africa, however, is rich in temporary pans, many of which are saline, while permanent saline springs occur along the coastal strip of the Namib Desert in Namibia. This paper examines the chemistry of the major ions in 67 Namibian waters, 47 of which have not previously been reported in the literature, and compares them with 66 South African waters, five of which have not previously been reported, and with saline lakes in East Africa. The highest value for total dissolved solids in South African waters was 276 g l−1 (Koekiespan, south-western Cape) and the highest for Namibian waters were 160 g l−1 (Hosabes, a small spring on a gypsous crust) and 302 g l−1 (a salt pan at Oranjemund at the mouth of the Orange River). The dominant ions in fresh waters in the region are Ca2+ and HCO inf3 − /CO inf3 2− in the interior and in Namibia, and Na2+ and Cl+ on the south and east coasts. Regardless of the geochemistry of their substrata, the dominant ions in the saline waters throughout the region are Na+ and Cl−. Thus differential precipitation of CaCO3 and CaSO4, as a result of evaporative concentration at high salinities, appears to be the determinant of the proportions of the major ions in these systems. The permanent springs on gypsous crusts along the coast of Namibia, although dominated by Na+ and Cl− ions, contain considerable quantities of both Ca2+ and SO 4 2− ions.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-5117
    Keywords: fynbos biome ; mountain stream ; spring leaf fall ; allochthonous detritus retention ; discharge ; calorific values ; C:N ratios ; annual cycles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The quality and quantity of allochthonous inputs and of benthic organic matter were investigated in a second-order, perennial mountain stream in the south-west Cape, South Africa, between April 1983 and January 1986. Although the endemic, riparian vegetation is sclerophyllous, low and evergreen, inputs of allochthonous detritus to the stream (434 to 500 g m−2y−1) were similar to those recorded for riparian communities worldwide, as were calorific values of these inputs (9548 to 10 032 KJ m−2y−1). Leaf fall of the riparian vegetation is seasonal, occurring in spring (November) as discharge decreases, resulting in retention of benthic organic matter (BOM) on the stream bed during summer and early autumn (maximum 224 g m−2). Early winter rains (May) scoured the stream almost clean of benthic detritus (winter minimum 8 g m−2). Therefore, BOM was predictably plentiful for about half of each year and predictably scarce for the other half. Coarse BOM (CBOM) and fine BOM (FBOM) constituted 46–64% of BOM standing stock, ultra-fine BOM (UBOM) 16–33% and leaf packs 13–24%. The mean annual calorific value of total BOM standing stock was 1709 KJ m−2. Both standing stocks and total calorific values of BOM were lower than those reported for streams in other biogeographical regions. Values of C:N ratios decreased with decrease in BOM particle size (CBOM 27–100; FBOM 25–27; UBOM 13–19) with no seasonal trends. The stream is erosive with a poor ability to retain organic detritus. Its character appears to be dictated by abiotic factors, the most important of which is winter spates.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-5117
    Keywords: storms ; stream chemistry ; antecedent conditions ; fire ; South Africa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The influence of different antecedent conditions on hydrochemical response during storm events was investigated in a small, south-western Cape mountain catchment. Winter and summer storms (four in total) were sampled both before and after the catchment was deliberately burnt. During winter storms, discharge responded rapidly to rainfall, and direct runoff represented the major component of streamflow. Marked lags were observed between rainfall and discharge peaks during the summer storms, and streamflow was dominated by delayed interflow. Chloride, PO inf4 sup3− -P and NO inf3 sup− -N exhibited variable response to discharge according to seasonal variations in soil-moisture levels, whereas the response of HCO inf3 sup− , H+ and NH inf4 sup+ -N was not influenced by season. The movement of ions appears to be affected more by geochemical processes operating within the soil than by plant-uptake dynamics, as the prescribed burn appeared to have little effect on relationships between ionic concentration and discharge. The findings of the study highlight the complexity of relationships between solute concentration and discharge.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-5117
    Keywords: uptake ; Al ; Cu ; Mn ; amphipod ; acidic waters ; interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Experiments were performed on the freshwater amphipod Paramelita nigroculus to determine the route of uptake for Al, Cu and Mn. The extent of correlation between the concentrations of Al, Cu and Mn and those of macro-cations Na, Ca and Mg was investigated in order to determine appropriate strategies of water quality management. Indeed, active uptake of toxicants can be controlled by disturbing the active pump used. After 21 days of exposure to different combined concentrations, survivors were analysed chemically by ICP-S after depuration, drying, ashing and digestion with concentrated nitric acid.The results showed significant correlations between the concentrations of major cations and the three metals under study (i.e. Al, Cu and Mn) at p 〈 0.05. These are Ca vs Al, Ca vs Mg, Na vs Mg, Na vs Mn, Al vs Mg, Al vs Cu, and Mg vs Mn. No other combination showed significant correlation. High r-values for Na vs Mg (r=0.7194) and for Na vs Mn (r=0.6253), as well as low concentrations of Mg and Mn, suggest interactions between the active uptake of Mn and Mg, although there may be interferences due to the use of Na pump. Additional experiments examined the type of interaction occurring when Mn and Mg were present in 1:1 mixtures in water. The Student's t test showed that observed differences in bioaccumulation of Mn, when alone and when combined, were not statistically significant at p 〈 0.05. These differences may be attributed to chance but not to the presence of Mg in the medium; while differences in bioaccumulation of Mg, when alone and when combined, were statistically significant at p 〈 0.002. These were attributed to Mn, which lowers Mg uptake by P. nigroculus.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 224 (1991), S. 167-174 
    ISSN: 1573-5117
    Keywords: Berzelia lanuginosa ; Elegia thyrsifera ; laboratory experiment ; leaching ; decomposition ; ‘black’ waters ; sclerophyllous plants ; fynbos ; oligotrophic lakes ; south-western Cape
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In vivo leaching is described for dried leaf litter of Berzelia lanuginosa (Bruniaceae) and dried stem material of Elegia thyrsifera (Restionaceae), two species of sclerophyllous fynbos (Cape ‘macchia’) plants. The process in B. lanuginosa was characterised by darkening of the water owing to the release of humic substances, which were quantified as polyphenols using the Folin-Ciocalteau reaction. Very little leaching or colouration of the water took place during the immersion period of E. thyrsifera. After an initial decrease in both species, the pH of the water containing B. lanuginosa increased to slightly above the initial level. Early (〈 12 h) pulses of ammonium were detected from both species and of phosphorus from B. lanuginosa, while in both species, nitrate levels began to rise only after about 48 h. Subsequent trends in nutrient releases substantiated our hypothesis that little or no decomposition (as opposed to leaching) took place during the experiment.
    Type of Medium: Electronic Resource
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