Environmental variables and benthic macroinvertebrates of Temidire Stream associated with an oil depot, Ibadan, southwest Nigeria

Abstract

Streams are often recipients of pollution from agricultural, domestic and industrial sources though they are important sources of water supply and habitats of several aquatic species. Regular monitoring is required to protect this fragile but important ecosystem. Therefore, some physico-chemical parameters and macroinvertebrate assemblages of Temidire Stream, a perennial stream that flows through the Nigeria National Petroleum Corporation (NNPC) depot and Temidire community in Apata, Ibadan metropolis were investigated in order to determine the pollution status of the water and sediment and its impact on the biological community. Water and sediment samples were collected from five stations in the stream and from an adjacent stream monthly between August, 2019 and January, 2020 for physico-chemical parameter and benthic macroinvertebrate analyses. Dissolved oxygen, conductivity and total dissolved solids (TDS), and pH were determined in situ using EXTECH EC400 and C933 pH meters, respectively. Heavy metals were determined by atomic absorption spectrophotometry. Benthic macroinvertebrates were collected by kick sampling method. The results showed that TDS and conductivity of station 1 differed significantly from the other stations (p< 0.05). The concentrations of Pb, Ni and Cd exceeded the recommended levels for surface water and Pb and Cd in water and sediment correlated mostly with PC 1. The average Igeo class for the heavy metals in all the stations was >2 indicating uncontaminated to moderately/heavily contaminated sediment. Ninety-six (96) individuals of macroinvertebrates from seven families and six orders were encountered and aquatic insects were dominant (75%). Taxa richness (0-0.82) and diversity (0-0.59) were lower in all the stations compared to the control site. Exceedance of WHO limits by some heavy metals and paucity of macroinvertebrates, especially pollution-sensitive species in the stream suggests that it is polluted. Regular   monitoring of the stream is advocated to minimize pollution.