Spatial evolution of the diversity of macroinvertebrate-Odonate larva population dynamics in relation to the environmental variables of the Niete hydrosystem (South Cameroon)

Abstract

A study was carried out in the Niété, a tributary of the Lobé, to evaluate the quality of it's water through a follow-up of the longitudinal evolution of the various abiotic (physico-chemical) and biotic (Odonate larva) parameters of this aquatic ecosystem. The results of the physico-chemical analysis of the water of the Niété, according to the grid of the water evaluation system (SEQ-Eau), show that, with the exception of aquaculture production, the rate of oxygen saturation (79.39±0.54%) electrical conductivity (42.59±, 16.52 µS/cm), sulphate (2.78±0.71 mg/L), suspended solids (10.88±0.54 mg/L), and nitrate ions (1.10±0.21mg/L) are in the very good quality range, whatever the intended use. This is not the case for orthophosphate ions (12.32±0.35 mg/L), which are rather in the range of poor quality water requiring complex treatment for drinking water production and likely to cause lethal effects on the most sensitive species, leading to a decrease in abundance. Out of 92 individuals collected, 09 genera were identified: 4 genera of Coenagrionidae (44.44%), 4 genera of Libellulidae (44.44%) and 1 genus of Corduliidae (11.12%). The genera Orthetrum (family Libellulidae), Coenagrion and Nehalennia (family Coenagrionidae) have a relative abundance of 65.22%. Sörensen's similarity coefficient reveals high dissimilarities between the populations of stations N1 and N2 (36.36%), N1 and N3 (28.57%) and N2 and N3 (25%). The diversity indices of Shannon and Weaver, Simpson and Piélou show that station N2 is the most diversified and favours the installation of polluotolerant Odonata, whereas station N1 is more balanced and favours a better development of Odonata larvae. This is confirmed by the Hilsenhoff index, which shows that station N2 has low water quality, compared to stations N1 and N3, which have very good water quality, reflecting the self-purifying action of the Niété river.