Limnological studies of the pelagic zone of Lake Tanganyika at Kigoma, Tanzania.

Abstract

Some limnological parameters and chlorophyll a were determined for twelve months at a pelagic station near Kigoma. Temperatures ranged between 25.7 ºC and 27.3 ºC at the surface, and 24.1 oC and 24.7 oC at100 m. Thermal stratification persisted throughout the year with the thermocline oscillating between 15 m in October and 60 m in May. Dissolved oxygen concentrations were high at the surface, ranging between 6.59 mg l-1 and 8.15 mg l-1, while at 100 m the concentrations ranged from less than 0.20 mg l-1 to 1.94 mg l-1. Nitrate-nitrogen concentrations in surface water ranged between 26 µg N l-1 in May and 74 µg N l-1in December. Nitrate -nitrogen concentrations generally increased with depth to 80 m, after which they decreased. Soluble reactive phosphorus concentrations in the photosynthetic zone were always very low, ranging between 0.30 µg P l-1 and 4.0 µg P l-1. The concentrations increased with depth. Total phosphorus concentrations in the surface water were also low, ranging between 2.0 µg P l-1 in March and 12.0 µg P l-1 in August. The concentrations increased with depth. Chlorophyll a concentrations were generally low throughout the year, except for October and April-May when high concentrations were found. In October the mean concentration was 4.52 µg Chl a l-1, while January had the lowest concentrations with a mean of 0.36 µg Chl a l-1. Chlorophyll a concentrations decreased with depth.