Photosynthetic potential of phytoplankton in the deep water of Lake Baikal, Russia

We examined the photosynthetic activity of the phytoplankton community collected from the surface to a depth of 1000 m in the south basin of Lake Baikal. Experiments were conducted in June (mixing period) and August (stratified period). The carbon fixation rate was measured by the use of a 13C tracer after the incubation of samples under light conditions in the upper water column. Photosynthetic fixation of 13C was detected for samples collected from a depth of 500 m, indicating the viability of phytoplankton in deep water. The community composition was dominated by Bacillariophyceae in deep water. The finding of lower activity at a depth of 200 m than that at a depth of 500 m in August suggests that the spring diatom bloom could be a significant source of viable populations at a depth of 500 m. Photosynthetic activity was not detected in samples collected at a depth of 1000 m.