Journal des sciences de la Terre et du changement climatique

Abstrait

Water Column Characteristics and Analysis of Conductivity, Temperature and Dissolved Oxygen (CTD) Data from Modern Rift Lake Tanganyika

Januarius Matata Bishanga* and Jin Qiang

Conductivity, temperature and dissolved oxygen profiles from modern Lake Tanganyika, a rift basin lake in East Africa, give an insight of the water column physical characteristics and implications for water quality and primary production. The profiles cover both arid and wet seasons for 2013/2014. Temperature and dissolved oxygen concentration of the water column decrease with depth from 29°C and over 80% (6.5 mg/l) saturation at the surface to 23.5°C below a thermocline. The lake permanently stratified between 50 m to 150 m, creating stable anoxic conditions. Specific conductance decreases from 688 µS cm-1 at surface to 677 µS cm-1 at 100 m of water column (thermocline) and gradually increase below the anoxic waters. Increase in salinity complements increase in water density that inhibits vertical mixing. Increase in dissolved organic matter attributed by increased anthropogenic activities, thus more terrestrial sediments transported into Lake Tanganyika by runoff rivers. Raised levels of dissolved organic matter have inhibited the growth of phytoplankton, limit photosynthesis, hence damaging ecosystem and impend primary productivity in the lake basin. As a result, anoxic bottom-water conditions substantially increase the preservation potential of organic-rich sediments because of the adverse effects on benthic scavenging and particle mixing and by supporting anaerobic processes. Climate variability has contributed to the regular changes in Lake Tanganyika water conditions and affect ecosystem.