Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : The effect of ecological factors on algae in six Algerian rivers

Auteur : Al-Asadi, M.S.A

Université de soutenance : University of Wales College of Cardiff

Grade : Doctor of Philosophy (PhD) 1991

Résumé
Six sites on three different Watersheds (A, Shelif River and its Mina Tributary ; B, Habra Chaneel-Reservoir ; and C, Tafna River and its Remshy Tributary), in West Algeria were sampled at approximately bimonthly intervals, from June 1986 to March 1988. The investigation provided a baseline appraisal of phytoplankton, epipelic and epipsammic, physico-chemical aquatic conditions for the area together with notes on bank species. Biomass estimation using chlorophyll extraction and productivity studies supported work on cell numbers of the constituent algal taxa. Standard water and sediment analysis techniques were applied. All rivers were well oxygenated, light was not limiting to algal growth, and waters were slightly alkaline with very little variation in pH. Watershed B differed from the others in having higher conductivity, total residue, fixed total residue, volatile matter, total and magnesium hardness, nitrogen and phosphate values, chlorophyll a, phaeophytin a and primary productivity than the other watersheds. Conversely, silicate and calcium hardness were higher at A and C, and A was unique in having the highest suspended solids, turbidity and current velocity readings. Nutrients and algae appear to be recycled from sediments. 227 algal species were identified, the bulk being Bacillariophyta and planktonic, particularly in Watershed C. The Myxophyta were the common algae in Watershed B and the chlorophyta in A. Biological indices were applied and indicated only occasional periods of organic pollution or other stress. Ordination by Decorana separated the algae according to the environmental conditions at each Station, whereas classification of algal abundance by Twinspan separated the different Watersheds. The river banks were found to provide a habitat for 28 angiosperm species and their times of invasion into adjacent cultivated ground were noted.

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