Evaluation of surface water quality characteristics in Ogun watershed of south western Nigeria using principal component analysis

Abstract

Utilization of water resources across watersheds in Nigeria has been without commensurate at-tention to protection from degradation at the basin level. One of the strategies in river basin management is effective monitoring and assessment of pollution levels, patterns and identifica-tion of major variables driving such degradation most importantly at the watershed scale. Therefore, it is important to evaluate how critical a quality indicator is in its contribution as well as its spatial extent within and across the entire water basin. Twenty six water quality indicators were assessed in Ogun watershed, Nigeria. The nitrogen forms; TN, NO₃^- and NH_4-N were significantly low in the watershed while TP and PO₄^3- were higher (p<0.05). The BOD₅ and COD were significantly high which explains the low DO observed in the watershed. High levels of Fe, Cd, Pb, Mn as well as E-coli and Fecal Coliform were recorded. Using Principal Component Analysis (PCA), 77% (20 out of 26) of the water quality indicators examined were found to be critical. These explained more than 90% of the observed water quality variation across the watershed. The variable inclusion level showed that these parameters were critical in 70% of the locations across the watershed. The selection of 77% of the parameters investigated by PCA over 70% of the locations revealed high levels of diffused pollution that calls for urgent attention.

Keywords: Principal Component Analysis, Ogun watershed, Water Quality, Pollution, Nigeria