Comparative investigation provides further insights on how riparian deforestation and different land uses impact the distribution of freshwater macroinvertebrates in Nigerian streams.

Abstract

Riparian forest loss and various land use impacts on macroinvertebrate communities in Nigerian streams remain poorly understudied. To fill this knowledge gap, a study was conducted on five streams in the southwest ecoregion of Nigeria between December 2019 and October 2021. A total of 2,077 macroinvertebrates were sampled, comprising 16 orders, 40 families, and 80 species. Aquatic insects were the most abundant, constituting 85 % of species and 73.13 % of individuals. Other specimens included Mollusca, Crustacea, Arachnida, and Annelida. Notably, Olumirin stream exhibited the highest macroinvertebrate abundance, including the stress-sensitive Ephemeroptera-Plecoptera-Trichoptera (EPT) members. The site also had the highest degree of naturalness, widest channel and dissolved oxygen (DO), but lowest electrical conductivity (EC) and total dissolved solids (TDS) compared to the other streams (Abirunmu, Awoosun, Mogimogi, and Aboto), that harbored facultative and stress-tolerant species, indicating varying degrees of disturbances. The bivariate regression analysis confirms that riparian deforestation and land use impact macroinvertebrate distribution in streams as there was an inverse relationship between EPT abundance and forest cover. Also, DO positively correlates with EPT taxa richness but inversely correlates with Coleoptera richness and Hemiptera abundance. As a result, Olumirin stream is proposed as a benchmark for evaluating freshwater ecological integrity in the region. Given the escalating anthropogenic activities in the tropics, urgent collaborative efforts are required to safeguard freshwater biodiversity, protect the riparian corridor of Olumirin stream, and restore impaired streams in the region.