Effects of bottom-up and top-down interactions on the productivity of Iyieke Lake, Afikpo North, Ebonyi State, south-east Nigeria

Abstract

The bottom-up and top-down interactions of the abiotic and biotic components of Iyieke Lake were studied for eleven months covering a pre-flood, flood and post-flood periods. During the study, some water quality parameters were measured while plankton samples were collected for identification in the laboratory using standard method. The results of the water quality parameters measured showed that water temperature was highest (35.00R”C) in February. pH (7.10) and transparency (0.98 m) were highest in August. Highest TDS (28.0 mg/L) and conductivity (56.00 μS/cm) were recorded in March (pre-flood period) while dissolved oxygen level was lowest (4.00 mg/L) in the pre-flood period (February and March). Nitrate (0.18 mg/L) was highest in August (flood period) and phosphate (0.25 mg/L) at the two extreme periods (pre-flood and post flood). The depth of the lake was highest (3.2 m) in August which was the period of inundation. The phytoplankton (Bacillariophyta, Chlorophyta, Cyanobacteria) and zooplankton (Rotifera, Cladocera, Copepoda) of the lake were made of three divisions and taxa each, respectively. Bacillariophyta dominated among the phytoplankton while Rotifera was the most abundant among the zooplankton. The study revealed that nutrients and zooplankton grazing were the major factors that affected phytoplankton abundance and biomass during the study.

Keywords: Flood; phytoplankton; Iyieke; water quality; zooplankton