PRELIMINARY ASSESSMENT OF THE DISTRIBUTION, CHEMICAL-COMPOSITION AND VARIABILITY OF POTENTIAL NUTRIENTS IN SPATE-GENERATED FOAM FROM WESTERN CAPE BLACK-WATER RIVERS

In order to test the hypothesis that the foam, generated during spates by the black-water mountain streams of the western Cape, constitutes an energy base for invertebrate communities during the months of winte r rainfall, a preliminary study of foam and water samples collected fr om various streams at different stages of the winter season was undert aken. Samples found by micro-analysis to contain organic matter were a nalysed to determine their carbohydrate, protein and polyphenolic cont ents. The proportions of neutral sugar and amino-acid constituents in the carbohydrate and protein components, respectively, were determined by chromatographic analysis of hydrolysates. Major differences in tot al carbohydrate content as well as proportions of constituent sugars w ere evident for samples collected at different stages of the winter-ra infall season. The proportions of amino acids in the proteinaceous com ponents did not vary significantly. Steric-exclusion chromatography of foam samples collected at the same location at the beginning and end of winter demonstrated wide variation in the molecular-weight distribu tion of the carbohydrate and protein components. The observed concentr ation of nutrients in the foams affords evidence in favour of their po stulated importance in the energy system of western Cape rivers. Varia tion in foam composition, especially with respect to the propertion, c omposition and molecular-weight distribution of carbohydrate component s, during the winter-rainfall season is clearly important in this cont ext.