Ecological health status of some watercourses in the Mfoundi Watershed, Yaoundé (Central Cameroon): Structure of the benthic macroinvertebrate community and water quality

Abstract

In Cameroon, as in many developing countries, urban aquatic environments are subject to increasing degradation of their quality. This phenomenon results from a multitude of extrinsic factors, stemming from rapid population growth coupled with anarchic urban sprawl. In this context, watercourses serve as final receptacles for domestic and industrial waste, as well as latrine drainage channels, significantly contributing to water pollution. The Mfoundi basin and its tributaries perfectly illustrate this situation, currently acting as dumping grounds and ultimate receptacles for various wastes. These discharges directly affect water quality and the biodiversity of these ecosystems. The present study aims to assess the impact of anthropogenic pressures on the biodiversity of benthic macroinvertebrates in three rivers of the Mfoundi basin (Odza, Akeu, and Olézoa), as well as in the upstream part of the Mfoundi River, in order to determine their current ecological status. To achieve this, hydro-morphometric parameters were measured using standardized methods, and benthic macroinvertebrates were collected following a multi-habitat approach. Hydro-morphometric analyses revealed that the structure of the banks of the different watercourses is, in places, marked by a loss of natural sinuosity in favour of channel reconfiguration. This phenomenon affects the natural transport of solid and liquid flows, as well as riparian vegetation, which has been replaced by crops and constructions, thereby increasing the vulnerability of the watercourses. On the biological level, a total of 3,467 benthic macroinvertebrate specimens were recorded, distributed across three phyla, twelve orders, and more than thirty families. The community is dominated by insects and characterised by low diversity, with a predominance of pollution-tolerant organisms such as Chironomidae, Belostomatidae, and Anthomyiidae, which are saprobionts and saprophiles. A canonical correspondence analysis indicated that the main groups of benthic macroinvertebrates identified were associated with the poor hydro-morphometric conditions observed. The Shannon-Weaver diversity and Piélou’s evenness indices confirmed the low diversity of organisms within the studied aquatic ecosystems, as well as their poor evenness. This situation is primarily explained by the dominance of saprobiont and saprophile groups. Finally, the weakening, and in some cases complete destruction, of natural riparian vegetation observed along the watercourses of Yaoundé, combined with their role as dumping grounds, constitutes a key factor in the degradation of water quality and the loss of ecological stability. Benthic macroinvertebrates, an essential link in water quality monitoring due to their diversity and variable sensitivity to pollution, thus reflect the extent of disturbances experienced by these ecosystems.