Make your own free website on
Physical and limnological aspects
Physical aspects

Lake Tanganyika (3°30'-8°50' S; 29°05'-31°15'E) has a surface of 32900 km², is about 650 km long and is situated at an altitude of 773 m, with a maximum and mean depth of respectively 1435 m and 700 m.
The Lake is shared by four riparian states: Burundi, Tanzania, Zambia and Zaire (now called Congo again).

Limnological aspects

The chemical composition of Lake Tanganyika and other African lake waters varies and includes features rarely found elsewhere. The studies carried out on this lake by several researchers, and the information published, are very scattered and of varying details and reliability. Most comparative studies resulting on compilation concern only limited areas and periods. Lake Tanganyika has been described as having sodium- potassium-magnesium-bicarbonate waters.

Conductivity was generally between 660 (µS/cm near the surface and 700 µS/cm at 300 m). Conductivity at Kigoma was often slightly lower than at both ends of the lake. Greatest variability of conductivity was measured at Bujumbura/Uvira in the upper layer (values between 520 and 728 µS/cm have been recorded). The changes of conductivity were relevant as they could be used as indicators of metalimnion movements.

Sodium is dominant and its concentration increases with conductivity. Magnesium is the principal cation and its origin might be due to volcanic activities. The concentrations of calcium and potassium are relatively low, but the concentration of potassium increases with increasing salinity.

The anions are constituted principally by (bi)carbonates. These ions have an impact on the pH, which is around 9 at  the surface (follow this link for more details). When the surface pH is 9.0, the pH at 300 m depth is 8.7 (pH decreases with depth). As such, the pH seems to be an excellent 'tracer' of vertical water movements.
The sulfate ion concentration is low in surface layers with a large concentration in the hypolimnion. This ion is reduced to sulfide by Desulfivibrio and precipitated also in sediments.

Water temperature ranges between 23.35 and 29 °C and the temperature of surface water depends on the daily solar radiation. Thermal stratification was observed at each station during the whole year except in the south in the dry season (upwelling). The epilimnion generally extended from the surface to depths between 20 and 105 m. The upper metalimnion including the thermocline extended generally from 50 to 120 m. The thermocline was occasionally detected in the upper 20 m. The lower metalimnion reached at least a depth of 300 m. Hypolimnion water (<23.5 °C) was measured at c. 300 m except during upwelling in the south. Internal waves, indicated by temperature fluctuations were noted at all depths including below the thermocline down to 300 m all the year. They were not clear from 0 to 30 m due to mixing of the epilimnion.

The oxygen concentration in surface waters were often saturated or supersaturated in dissolved oxygen. Dissolved oxygen was present down to c. 80 m at Bujumbura/Uvira and c. 200 m at Mpulungu.

The transparency fluctuated between 5.0 and 23.5 m at site A. The northern station at Bujumbura/Uvira had the lowest transparency (mean = 9.1 m). Higher mean values were recorded at Kigoma (13.8 m) and pulungu (12.4 m.). Transparency varied considerably on a daily basis. Variations in transparency (up to 5 m) were noted in a few hours in the south on 17/9/94, 18/11/94 and 16/12/94. Turbulent mixing may have been responsible for a high level of heterogeneity in nutrients, plankton and transparency. Water temperature and transparency showed a positive correlation.

Average turbidity at Bujumbura/Uvira was highest (0.40 NTU) compared to Mpulungu (0.35 NTU) and Kigoma (0.25 NTU). Turbidity decreased with depth at each station. The lake was usually more transparent in deep waters than on the surface. This was probably due to a higher abundance of living organisms in the epilimnion. However, in some months turbidity increased in deeper water suggesting deeper pulses of production. During the dry season, turbidity was significantly higher at the north and the south ends of the lake compared to Kigoma. During the wet season, a turbidity layer developed near the thermocline at Bujumbura/Uvira and was probably caused by communities of deep-living organisms.

The lake receives water from different rivers with different chemical compositions. The most important one is the Ruzizi river in the north which supplies more than 50 % of the total of dissolved salts.