Meromixis, stratification and internal waves in Kigoma waters of Lake Tanganyika

Abstract

Meromixis, stratification and internal waves were observed 4 km NW of Kigoma Port, Lake Tanganyika. Meromixis occurred during the cool, dry season, from June to August; its end was marked by upward displacement of some isotherms. From September to early November, the water temperature increased but the thermocline was still not distinct. From November onwards, stratification was enhanced and the thermocline became well defined and oscillated about 40 m. From February, while still oscillating, it gradually descended to a maximum depth of 70 m, in June. In July 1994, the cycle of meromixis started again. Oscillations of the thermocline indicated the existence of internal waves. The periodicity and duration of the oscillations implied that they were seiches similar to those already observed elsewhere on the lake, thus indicating their lake-wide existence. Other parameters, such as conductivity, pH, turbidity, ammonia and nitrate appeared to vary in response to these oscillations; thus the oscillations probably play a vital role in the biological production in Lake Tanganyika.