CHEMICAL OXYGEN DEMAND AND METAL (CHROMIUM AND IRON) CONCENTRATIONS AS KEY DRIVERS CONTROLLING THE PHYTOPLANKTON COMPOSITION OF FISH PONDS IN OSOGBO, NIGERIA

Abstract

There is an alarming increase in industrialization and anthropogenic activities in many parts of the world, which raises concern as to the roles they play in the aquatic ecosystems. The study was conducted to investigate chemical oxygen demand (COD) and metal concentrations as key drivers of the phytoplankton community of selected fish ponds in Osogbo, Nigeria, from February 2021 to July 2021. Water samples were collected monthly and analysed for physicochemical parameters, phytoplankton composition and abundance. Analysis of variance (ANOVA) was performed on linear regression models to assess their prediction of phytoplankton community diversity. Mean water temperature was 27.57±0.14 °C, pH 6.91±0.16, Biological Oxygen Demand (BOD) 1.30±0.13 mg/l, Chemical Oxygen Demand (COD) 345.1±75.0 mg/l, phosphate-phosphorus 7.518±1.75 mg/l, electrical conductivity 594.9±97.75 µs/cm, DO 2.37±0.29 mg/l and alkalinity 129.0±47.25 mg/l in the investigated ponds. The dominant phytoplankton group was Chlorophyceae (74%), followed by Bacillariophyceae (11%), Cyanobacteria (9%) and Euglenophyceae (6%). Canonical correspondence analysis (CCA) revealed that COD, chromium (Cr) and iron (Fe) were the key parameters controlling the phytoplankton composition of the investigated ponds. Analysis of variance performed on the CCA model revealed that the most significant environmental determinants controlling the occurrence and abundance of phytoplankton in the investigated ponds were COD (p = 0.009), Fe (p = 0.023) and Cr (p = 0.024). Results of the phytoplankton composition in the ponds indicated that physicochemical parameters play a very important role in their distribution and abundance.