Physicochemical characterization of the waters of the Lep'oo river in Mbanda (Bot-Makak) and structuring of the benthic macroinvertebrate community

Abstract

A study on the characterisation of the Lep'oo stream waters in Mbanda (BotMakak) by physicochemical parameters and benthic macroinvertebrates community was conducted from February to July 2016. Physicochemical parameters were measured according to Rodier's recommendations, while benthic macroinvertebrates were collected using the multihabitat approach. The physicochemical analysis showed that the waters of the Lep'oo stream were well oxygenated (71.16%), slightly acidic (6.36 UC), with low values of nitrogen and orthophosphates reflecting litter decomposition. A total of 2019 benthic macroinvertebrates were collected, divided into 4 phyla, 7 classes, 15 orders, 40 families and over 60 genera. The phylum Arthropoda was the most abundant with 98.61% relative abundance, followed by Molluscs (0.99%) and Annelids (0.29%). The greatest number of organisms collected belonged to the class Hexapoda, which represented 56.76% of relative abundance, followed by Malacostraca (41.75%). Within the Hexapoda class, the order Hemiptera predominated with 18.22% relative abundance and in the Malacostraca class, the order Decapoda predominated with 41.75% relative abundance. These two orders were dominated by the families Atyidae, Libellulidae, Gerridae, Leptophlebidae and Hydroptilidea. In the upper part of the Lep'oo stream, the families Libellulidae and Belostomatidae were dominant. The station Lep2 was most colonised by the families Atyidae, Libellulidae, Belostomatidae, Hydrometridae, and Gerridae, while station Lep3 was dominated by the families Atyidae, Hydroptilidae and Leptophlebidae. The Shannon and Weaver (H') and Piélou equitability (J) index showed a greater diversity of taxa downstream of the stream at station Lep3, where conditions seem more favourable to the development of benthic macroinvertebrates as indicated by the physicochemical results. The NGBI index characterized water quality from mediocre to excellent. Finaly, the Lep'oo watercourse had a poor and diversified population of benthic macroinvertebrates, showing a relative good ecological quality of water.