Regional, vertical and seasonal distribution of phytoplankton and photosynthetic pigments in Lake Baikal

A 3-year phytoplankton study was carried out in Lake Baikal (Siberia) as part of the CONTINENT project and in conjunction with a 60-year long monitoring programme by the Irkutsk State University. A combination of microscopy and high performance liquid chromatography (HPLC) pigment analysis was used. All over the lake, the dominant functional group (by biovolume) was the vernal diatom blooms, due to the dominance of endemic Cyclotella species. Chlorophyll a (Chl a) was significantly highest at the Selenga and Barguzin inflows (2.39 +/- 0.34 and 2.49 +/- 0.18 nmol L-1, mean +/- 95% CI, respectively) and higher in the South than in the North (1.43 +/- 0.26 and 0.96 +/- 0.13 nmol L-1). This variation of Chl a reflected changes in the phytoplankton composition. Diatoms and Chrysophyceae were the major contributors to the total Chl a except in the South (Chlorophyceae) and Selenga Delta (cyanobacterial picoplankton). There were also indications of species composition changes due to enhanced P-loading from the Selenga River. However, canonical analyses indicated that temperature and stratification were the major driving forces for regional distribution patterns and seasonal succession. It seems likely that further global warming will cause a shift in the species and group composition towards small cells at the expense of the large endemic diatom flora.