Seasonal dynamics in water quality and phytoplankton of four tropical rivers in Ebonyi State, southeastern Nigeria

Abstract

This study assessed the impacts of human activities and naturogenic processes on the water quality and phytoplankton of four rivers proximal to rice farms in Ebonyi State, south-eastern Nigeria. A range of water quality parameters were measured in conjunction with phytoplankton samples that were collected and identified in the laboratory using microscope and standard keys. The results showed that mean water temperature (30.32 ± 3.34 °C), conductivity (199.11 ± 118.70 μS cm⁻¹) and total dissolved solids (102.60 ± 58.5 mg l⁻¹) were highest in the dry season, while mean flow rate (0.7 ± 0.1 ms⁻¹) and dissolved oxygen (6.15 ± 1.88 mg l⁻¹) were highest in the wet season. Bacillariophyta had the highest mean abundance (6 611 ind. l⁻¹) and biomass (5.52 μg l⁻¹) in the dry season, whereas Chlorophyta had the highest mean diversity (Hʹ = 4.55) and species richness (MI = 1.1) in the wet season. Canonical correspondence analysis showed that hydrologic and climatic factors (temperature, water clarity and discharge) predominantly controlled phytoplankton community structure during the wet season while anthropogenic related factors (phosphate, nitrate and conductivity) regulated phytoplankton during the dry season. Consequently, sustainable management plans for these rivers must prioritise these factors in order to succeed.