Biological Water Quality Assessment of Shallow Urban Streams Based on Abundance and Diversity of Benthic Macroinvertebrate Communities: The Case of Nima Creek in Ghana

The phenomenon of water pollution constitutes a massive threat to the very existence of freshwater bodies and can potentially eliminate vital benefits otherwise associated with these resources. In several countries such as Ghana, initial steps to salvage existing freshwater bodies have given rise to the need for effective water quality assessment and biological monitoring. This study was conducted with the aim of assessing the abundance, composition, and diversity of benthic macroinvertebrate fauna in the Nima Creek, situated in Accra, Ghana. On the basis of findings in relation to identified macroinvertebrate types, we further determine the quality of water in the creek. Samples were collected at 8 different riffles with a Surber sampler. The benthic macroinvertebrates sampled consisted of 6 taxa and 5891 individuals belonging to Nematoda, Oligochaeta, Gastropoda, and Insecta classes. Chironomini were the predominant group with 99.04% on the average, followed by Psychoda sp (0.44%), Rhabitidae (0.26%), and Tubifex (0.26%) at the upstream stretch of the creek. The downstream was dominated by Chironomini forming 97.30% on the average, followed by Tubifex (1.52%), Rhabitidae (1.08%), and Psychoda sp (0.05%). The estimated diversity of the sampling area for both upstream and downstream was assessed by using the Simpson Diversity Index and was found to be 0.53, indicative of a fairly diversified community structure. Family Biotic Index (FBI) was used to determine the water quality of the creek and found to be 9.92, which indicates severely polluted water. One-way analysis of variance (ANOVA) revealed no significant differences between upstream and downstream abundances at both 95% and 99% confidence levels. However, Melanoides tuberculata was found only at the downstream reach due to low current, the formation of rocky substratum, and the absence of riparian vegetation making it a suitable habitat.