MACROINVERTEBRATE-BASED BIOMONITORING AND PHYSICO-CHEMICAL CHARACTERIZATION OF WATER QUALITY IN A TROPICAL RIVER SYSTEM: A CASE STUDY OF OLORI RIVER, SOUTHWESTERN NIGERIA
NJE Vol. 42(2) : 1-17, 2026
DOI.10.36108/NJE/6202/24.0210
Adeleke S. O.1; Amusan B. O.2; Adeosun O. J.2*; Adeleke N. A.3; Okeowo O. P.4
1Department of Biology, Adeyemi Federal University of Education, Ondo State, Nigeria.
2Department of Zoology, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria.
3Department of Biology, Osun State University, Osogbo, Osun State, Nigeria.
4Salford Business School, University of Salford, United Kingdom
Abstract
Assessment of freshwater ecosystems using biological indicators provides valuable insights into their ecological integrity and pollution status. This study evaluated the water quality and macroinvertebrate assemblages of Olori River, Oke-Igbo, Southwestern Nigeria, to determine the ecological condition of the river. Water and macroinvertebrate samples were collected bi-monthly from six sampling stations between December 2023 and October 2024. Physico-chemical parameters including temperature, dissolved oxygen (DO), pH, total dissolved solids (TDS), electrical conductivity (EC), and biological oxygen demand (BOD) were measured using standard methods. Macroinvertebrates were sampled using a D-frame net and direct hand-picking technique and preserved in 70% ethanol for identification. The results showed that most physico-chemical parameters did not vary significantly among sampling stations (p > 0.05), except for temperature. A total of 2,002 macroinvertebrate specimens belonging to 12 orders, 31 families, and 51 genera were recorded. Melanoides sp. was the most dominant species, while Philaccolus sp. was the least abundant. Station 1 exhibited the highest taxa richness and diversity indices, whereas the lowest diversity was observed in Station 6. The dominance of pollution-tolerant taxa, particularly dipterans and gastropods, alongside moderate BOD levels, suggests that Olori River is experiencing moderate anthropogenic pollution, likely from agricultural runoff and domestic waste inputs. Despite this, the presence of some pollution-sensitive taxa indicates localized areas of relatively good water quality. The study highlights the importance of integrating physico-chemical analysis with macroinvertebrate bioassessment for effective monitoring and management of freshwater ecosystems. Appropriate conservation and pollution control strategies are recommended to safeguard the ecological integrity and biodiversity of Olori River.
Keywords: Water Quality, Macroinvertebrate, River, Abundance, Diversity