Assessment of water quality and primary productivity characteristics of Volta Lake in Ghana
Physico-chemical and primary productivity studies were undertaken at the northern reverine segment of the Volta Lake, Yeji, at two southernmost lacustrine areas (Kpando-Tokor and Dzemeni) and one below the dam (Kpong Headpond). The studies were conducted from June 2006 to April 2008 at different depths (0, 2, 4, 6 and 8 m). The mean surface dissolved oxygen levels at the 4 stations were comparable and varied between 7.3 and 8.1 mgL-1. Dissolved oxygen decreased with increasing depth but with considerable amount of oxygen detected even at 12 m depth, indicating a well oxygenated Lake. Mean pH values ranged from 6.8 to 7.7. Transparency values ranged from 20 to 320 cm with Yeji recording relatively low values. Compared with earlier studies, transparency had reduced over the years at Yeji due to increase in suspended particles as a result of human activities. Concentrations of chemical constituents at 100 m from the shores of the Lake were similar to that of 500 m, suggesting a well-mixed Lake. Generally, the nutrient levels in the Volta Lake were low indicating that the Lake is not eutrophic. The average values of temperature, pH and dissolved oxygen are considered suitable for normal aquatic life. A total of 73 algal taxa were encountered during the study. These include 37 Green algae (Chlorophyta), 50.68%; 16 Blue-Green algae (Cyanophyta) 21.92% and 20 Diatoms (Bacillariophyta) 27.40%. Yeji was richer in Green algae (27 taxa) compared to Dzemeni and Kpando-Tokor (24 and 23 each) which were similar in green algae diversity. The Blue-Green algae and the Diatoms were about evenly occurring at the three stations on the Lake. Kpong Headpond was richer in Green and Blue-Green algae compared to stations on the main lake.