Anthropogenic impact on macroinvertebrates distribution and physicochemical characteristics of a tropical stream in north-central Nigeria

Abstract

Emu is a tropical stream in Northcentral Nigeria that serves as the water source for drinking and other domestic activities for Kusotachin communities, Niger State, Nigeria. This study evaluates the impact of anthropogenic activities on the ecological health of the stream using physicochemical parameters and macroinvertebrate assemblages. Macroinvertebrates were collected for a period of 8 months (July 2021 to February 2022) using modified kick sampling techniques, and the physicochemical parameters were determined using standard sampling and analytical procedures. Samples were collected from four different stations which are characterized by various anthropogenic activities across the stream bed. With the exception of depth, the measured physicochemical parameters showed no significant (P>0.05) difference between the sampling stations. However, there were significant (P<0.05) differences in air temperature, pH, electrical conductivity, total alkalinity, total hardness, dissolved oxygen, chemical oxygen demand, phosphate, and nitrate between the sampling months. A total of 506 individuals, from 30 species in eight groups of macroinvertebrates were identified. Hemiptera were the most represented group with 57.07% abundance, followed by Odonata with 27.44%, Arachnida (4.14%), Coleoptera (3.93%), Ephemeroptera (2.55%), Diptera (2.17%), Mollusca (1.38) % and the least abundance was 0.19% observed in Decapoda and Oligochaeta. The Canonical correspondence analysis (CCA) showed little or no correlations between the determined macroinvertebrates and physicochemical parameters. CCA axis 1 accounted for 44.94% of the variation of the macroinvertebrates data set with an Eigenvalue of 0.30. CCA axis 2 accounts for 30.5% of data set of macroinvertebrates and an Eigenvalue of 0.20 while CCA axis 3 accounts for 24.55% variation in data set with an Eigenvalue of 0.16. Overall, the low abundance of Ephemeroptera and the absence of other pollution-sensitive macroinvertebrate groups such as Plecoptera and Trichoptera, combined with deteriorating surface water quality, is an indication of pollution stress caused by various anthropogenic activities as the vegetative nature of the stream was the primary factor responsible for the macroinvertebrate assemblage structure.