Water quality and biodiversity of potamoplankton in an African sacred grove and world heritage site

Abstract

Despite the increasing awareness of sacred groves as potential biodiversity hotspots, freshwater systems that drain such environments are not being duly explored for their biodiversity values. In a bid to fill this information gap, plankton and water samples were collected along the longitudinal stretch of the Osun River within the Osun-Sacred Grove from June 2015 to March 2016. This was with a view to assessing the water quality and trophic status of the river. Phytoplankton diversity (111 species) was high, with no previous similar records in any lotic system within the region. Phytoplankton biodiversity was high in the dry season with zooplankton being high in the wet season. Physical and chemical parameters were within the optimal range for sustainability of aquatic life. Plankton indicator species of trophic condition suggest that the river shifted from oligotrophic/mesotrophic (e.g. Tabellaria fenestrata) in the wet season to eutrophic (e.g. Anabaena circinalis, A. spiroides, Aphanizomenon flos-aquae, Microcystis aeruginosa, Euglena oxyuris and Brachionus falcatus) in the dry season. High concentrations of nutrient parameters (NO₃⁻ and PO₄³⁻) were concomitantly recorded at the peak of eutrophic indicator species. Water quality and plankton biodiversity values of the river were indicative of a healthy lotic freshwater system with high primary production. It is recommended that the physicochemical and biological water quality of freshwater systems within protected areas be periodically assessed to ensure sustainability of terrestrial and freshwater biodiversity in such environments.

Keywords:

• Conservation
• phytoplankton
• protected area
• Osun River
• water quality
• zooplankton

Acknowledgement

We are grateful to the National Commission for Museums and Natural Monuments for their kind approval to carry out this study on the historic river. The logistic input and kind assistance of the curator (Mr. Williams Olakunle) as well as Messrs Adeyinka Adesiyan and Mukaila Ayorinde are particularly appreciated.