Int. J. Biosci

In the aim of evaluating the impact of a dam construction on the biodiversity of aquatic organisms, physicochemical variables coupled to benthic macroinvertebrates communities were analysed at the upstream and downstream of the Mefou stream dam from September 2009 to March 2010. Physicochemical results revealed a slightly acidic and well oxygenated water of the Mefou stream, being appropriated for the development of benthic macroinvertebrates organisms. Significant differences were observed for temperature and oxygen between the stations (P < 0.05). Of the 1801 individuals collected (4 phyla, 6 classes, 13 orders, and 47 families), Arthropods (99.25%) dominated, while Annelids, Nemathelminths and Mollusca were less represented (2 %). The Correspondence Canonic analysis (CCA) distinguished two sections on the stream: a superior section at the upstream of the dam which is characterised by much oxygenation and abundance of Atyidea (excellent bioindicators of good quality water) (r = 0.04; P < 0,05); an inferior section at the downstream of the dam, dominated by rheophil organisms (odonates). The relative abundance of odonates correlated with the values of water flow rates of each station (r = 0.94 ; P < 0.01). The presence of polluo-tolerant organisms (Chironomidae and Haplotaxidae) at station 3 could reflect anthropic action at the downstream of the dam. Shannon and Weaver (H = 4.1±0.5 bits) and Pielou index (J = 0.8 ± 0.1bits) revealed favourable conditions for the coexistence of benthic macroinvertebrates. This results could provide viable information used in evaluating the water quality of lotic systems subjected to dam construction in Cameroon. *Corresponding Author: Foto Menbohan Samuel  sfotomen@yahoo.fr International Journal of Biosciences (IJB) ISSN: 2220-6655 (Print) 2222-5234 (Online) Vol. 2, No. 11, p. 137-145, 2012 http://www.innspub.net