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Universitaet Wien (1999)

Spatio-temporal variations in physicochemical factors and stream fauna abundance and composition in the zones of transition between Baharini Springbrook, Njoro River and Lake Nakuru, Kenya

Shivoga, W.A.

Titre : Spatio-temporal variations in physicochemical factors and stream fauna abundance and composition in the zones of transition between Baharini Springbrook, Njoro River and Lake Nakuru, Kenya

Auteur : Shivoga, W.A.

Akad. Grad : Thesis.Doctoral 1999

Université de soutenance : Institut fuer Zoologie ; Formal- und Naturwissenschaftliche Fakultaet ; Universitaet Wien

Résumé
This study investigates the spatio-temporal variations in physicochemical factors, faunal abundance and composition in the transition zones between Baharini Springbrook, Njoro River and Lake Nakuru. Fauna and sediment sampling was carried out with a modified Hess sampler and a small shovel, respectively. During each sampling, physicochemical parameters were measured. Baharini and Njoro have significantly different flow regimes and consequently discharge-related factors influencing their fauna. Baharini is perennial, slow-flowing with low and steady discharge, high conductivity and low conductivity gradient. Njoro is intermittent, faster- flowing with higher and variable discharge, lower conductivity and higher conductivity gradient. Discharge, substrate characteristics and conductivity explain most of the variations in the faunal communities in Baharini and Njoro. The fauna of the two streams consists mainly of ostracods, copepods, corixids and chironomids. Due to the permanent and steadier flow, Baharini has higher abundance and number of taxa than Njoro. The faunal composition in the two streams is similar despite the intermittent nature of Njoro. At the onset of flow after a drought, fast colonization of the intermittent stretch of Njoro occurs by drift from upstream perennial sections. Initial small spates at the onset of flow seem not to affect invertebrate abundance. But later, bigger spates during and after heavier rains reduce the abundance significantly. Taxon richness is not affected by the spates. The recovery of abundance to pre- flood levels in Njoro was completed in 27 days. The streams’ substrata are predominantly fine-grained and the relative proportions of larger grain size classes are important determinants of the faunal distribution in the streams. Abundance and number of taxa decline with increasing conductivity, though this relationship is not significant over the intermediate conductivity ranges and a number of species show a wide distribution with respect to conductivity.

Mots clé : physikochemische Faktoren / Uebergangszone / Fauna / Fluss / Kenia / raeumlich-zeitliche Veraenderungen — stream fauna / conductivity / substrate nature / flow regimes / Kenya / spatio-temporal variations

Présentation : Österreichische Dissertationsdatenbank

Page publiée le 11 juin 2008, mise à jour le 14 mars 2019