Assessment of surface water quality using phytoplankton as base-line indicator organisms in Ilorin, Kwara state, Nigeria

Abstract

Timely and accurate water quality monitoring is crucial to ensure their sustainable use and safeguard public health. Therefore, this study assessed surface water quality in Mubo River (SP1) and Sobi Dam (SP2) in Ilorin, using phytoplankton as base-line indicator organisms. Water samples were collected on July 20th (rain season) and December 20th (dry season), 2023, at 0.3 meters from the mid-water column. The physicochemical parameters of the water samples were determined using standard methods. The standard microscopic techniques were used to enumerate and identify phytoplankton genera. The findings showed that the pH and DO (mg/l) levels were within the permissible limit stipulated by the National Environmental Standard and Regulation Enforcement Agency for Surface Water in Nigeria (NESREA). The BOD (mg/l) and COD (mg/l) levels were above the permissible limit for SP1 for both seasons. The 8 genera of pollution-tolerant phytoplankton recorded were Cyclotella, Chlorella, Closterium, Chlamydomonas, Micractinium, Microcystis, Euglena, and Phacus, with Chlorella having the highest abundance percentage in all the sampling sites. The Shannon diversity indices values indicate lower phytoplankton species diversity (H ≤ 1.99) in all the water samples. The Palmer’s pollution index (PPI) scores ranged from 14 to 18 in the sampling sites. Palmer's index suggests likely high organic pollution in Mubo Rivers' in both sampling periods. A notable high level of organic pollution was recorded in Sobi Dam only during the rainy season. The relatively high turbidity, BOD (mg/l), and COD (mg/l) values support the index pollution scores and confirm the suitability of phytoplankton as baseline indicators for organic pollution assessment in surface water.