Internal waves; Lake Tanganyika; Limnology; Patchiness; Upwelling; annual cycle; lake dynamics; stratification; trophic status; turbidity; upwelling; Africa
Abstract :
[en] Ten variables were measured at least twice per month at three locations of Lake Tanganyika (East Africa) over one year (1993-94). Upwelling was observed in the south of the lake during the dry, windy season from May to September. Stratification was variable in strength but always present in the north. The lake showed a marked tilting of the epilimnion during the dry season (0-20 m in the South, 60-70 m in the North). This period was followed by oscillations of water masses towards an equilibrium when the strong winds from the south east ceased. Conductivity and pH fluctuations indicated dampened oscillations, particularly at the ends of the lake. Movements of the epilimnion toward an equilibrium position generated and/or re-inforced internal waves. These waves were inferred from fluctuations of chemical and physical characteristics of the lake. The concentrations of inorganic P and N commonly fluctuated by a factor of 3 or more in the epilimnion. The period of long-period internal waves was estimated to be ca. 28-33 days. Turbidity changes suggested pulse production caused by internal waves linked to non-random patchiness in nutrients and organisms. Turbulence resulting from highly dynamic physical events also induce random-patchiness in water composition. The lake water generally showed oligotrophic characteristics near the surface but had high concentrations of nutrients in deep water. The results showed that the trophic state of Lake Tanganyika, like that of the oceans, seems to depend largely on regeneration processes. The annual limnological cycle in Lake Tanganyika appears closely linked to the climatic conditions.
Disciplines :
Aquatic sciences & oceanology
Author, co-author :
Plisnier, Pierre-Denis ; Université de Liège - ULiège > Département d'astrophysique, géophysique et océanographie (AGO) > Chemical Oceanography Unit (COU) ; Royal Museum for Central Africa, Geology and Mineralogy Department, Leuvensesteenweg, 13, B-3080 Tervuren, Belgium
Chitamwebwa, D.; Royal Museum for Central Africa, Geology and Mineralogy Department, Leuvensesteenweg, 13, B-3080 Tervuren, Belgium
Mwape, L.; Royal Museum for Central Africa, Geology and Mineralogy Department, Leuvensesteenweg, 13, B-3080 Tervuren, Belgium
Tshibangu, K.; Royal Museum for Central Africa, Geology and Mineralogy Department, Leuvensesteenweg, 13, B-3080 Tervuren, Belgium
Langenberg, V.; Royal Museum for Central Africa, Geology and Mineralogy Department, Leuvensesteenweg, 13, B-3080 Tervuren, Belgium
Coenen, E.; Royal Museum for Central Africa, Geology and Mineralogy Department, Leuvensesteenweg, 13, B-3080 Tervuren, Belgium
Language :
English
Title :
Limnological annual cycle inferred from physical-chemical fluctuations at three stations of Lake Tanganyika
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