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Abstract TD46
Plisnier P.-D., Langenberg V., Mwape L., Chitamwebwa D., Tshibangu K. & E.J. Coenen, 1996, Limnological sampling during an annual cycle at three stations on Lake Tanganyika (1993-1994). GCP/RAF/271/FIN-TD/46 (En): 136p.

SUMMARY

This report presents the results of the first year of limnological sampling by LTR. Layers identified in the water column of Lake Tanganyika, parameter profiles and rhythmic patterns regulating the distribution of the nutrients are described.

Upwelling was observed in the south of the lake during the dry, windy season. Stratification was variable in strength but always present in the north. The lake showed a marked tilting of the epilimnion during the dry season from June to September. This period was followed by oscillations of water masses towards an equilibrium when the strong winds from the south east stopped. Conductivity and pH fluctuations indicated dampened oscillations, particularly at both 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 or physical characteristics of the lake.

Ten parameters were measured frequently near Bujumbura, Kigoma and Mpulungu over one year. Variation in the concentration of several parameters was commonly by a factor of 3 or more. The time of long-period internal waves was estimated to be approximately 28 to 33 days. Pulse production caused by internal waves is suggested. It could be linked to "non-random patchiness" in nutrients and organisms.

Turbulence may have explained the presence of dissolved oxygen in deep water, sometimes detectable at 300 m, or ammonia in the epilimnion. Turbulence resulting from highly dynamic physical events might induce "random-patchiness" in water composition.

The results of the first year of sampling showed that the productivity of Lake Tanganyika, like that of the oceans, seemed to depend largely on regeneration processes.