Benthic diatom assemblages in mountain streams: community structure in relation to environmental and human pressures

摘要

The objective of this study was to determine the environmental factors that best explain the distribution and community composition of benthic diatoms in undisturbed mountain streams in the Eastern Highlands of Zimbabwe. Benthic diatoms were sampled during the dry season from 21 sampling sites established along altitudinal gradient of the study rivers. A total of 119 diatom species belonging to 38 genera and twelve families were recorded for all the 21 sites sampled. No significant differences were observed in species diversity and equitability amongst the three river systems. However, species richness, diversity and equitability decreased significantly along the longitudinal gradient of the rivers, with the highest richness, diversity and evenness being recorded in the upper reaches. Temperature, velocity, NO3- and Ca2+ levels were strongly associated with changes in diatom communities in the three rivers. Inventory of diatom communities has applications in many fields of biological research including conservation and biological monitoring of ecosystem changes. Resume Cette etude visait a determiner quels facteurs environnementaux expliquent le mieux la distribution et la composition des communautes de diatomees benthiques dans les cours d'eau montagneux intacts des hauts-plateaux de l'est du Zimbabwe. Des echantillons de diatomees benthiques furent preleves pendant la saison seche en 21 lieux situes le long d'un gradient altitudinal sur les cours d'eau etudies. Au total, 119 especes de diatomees appartenant a 38 genres et a 12 familles furent enregistrees pour les 21 sites. Aucune difference significative ne fut observee dans la diversite et l'equitabilite des especes pour les trois systemes aquatiques etudies. Cependant, la richesse en especes, leur diversite et leur equitabilite diminuaient significativement le long du gradient altitudinal des cours d'eau, les valeurs maximales etant enregistrees dans les parties les plus hautes. La temperature, la velocite, le taux de NO3 et Ca2+ etaient fortement associes a des changements des communautes de diatomees dans les trois rivieres. L'inventaire des communautes de diatomees peut avoir des applications dans de nombreux domaines de la recherche biologique, comme la conservation et le suivi biologique des changements ecosystemiques.