Identifying and Classifying Sites and Macroinvertebrate Taxa into Pollution Categories in an Afrotropic Riverine System: A Multivariate Approach

Abstract

Measuring the level of degradation in riverine systems is paramount to assessing their current health status. In this study, we identified pollution classes and the sensitivities of macroinvertebrates in River Ringim, northwestern Nigeria. We marked four sites in the study area based on their level of human influence and accessibility. Physicochemical variables and macroinvertebrates were sampled monthly for a period of five months between November 2018 and March 2019. Physicochemical variables were used to categorize the four sites into pollution categories, while the 12 taxa of macroinvertebrates recorded were also classified into biological categories. The constructed principal component analysis (PCA) showed that physicochemical variables, such as total dissolved solids, conductivity, and pH, were positively associated with Site 2, whereas Sites 3 and 4 were negatively associated with water temperature, air temperature, and flow velocity. Further analysis based on the extracted coordinate scores from the PCA showed that Sites 2-4 were heavily polluted, whereas Site 1 was slightly polluted. The result of the canonical correspondence analysis (CCA) revealed that macroinvertebrate taxa, such as Leuctridae and Hydrometridae, were positively associated with conductivity, flow velocity, water depth, water temperature, air temperature, dissolved oxygen, and pH. Of the 12 taxa we categorized, nine were highly vulnerable based on our further analysis using the extracted coordinates from the CCA. The classified sites and macroinvertebrate taxa can be used for biomonitoring the ecological health of River Ringim and other river systems subjected to similar stressors within the northwestern region of Nigeria by river managers. Our study provides baseline information on the current state of River Ringim, and we recommend sampling rivers and sites within the northwestern region of Nigeria to confirm our present results.