The Distribution of Diatoms Near a Thermal Bar in Lake Baikal

Studies of the spatial distribution of suspended matter and of diatoms across a thermal bar in Lake Baikal revealed that waters sinking at the thermal bar front (2 km off-shore) move to the bottom along the underwater slope, and may be traced to a depth of at least 700 m, 5 km off-shore. The distributions of 11 diatom species across the thermal bar were significantly different, reflecting their different ecological requirements. Maximum concentrations of Asterionella formosa, Nitzschia acicularis, Aulacoseira islandica occur near the shore. The distribution of Stephanodiscus hantzschii, a species characteristic of the Selenga River, suggests that riverine waters penetrate far into the lake along its eastern shore. Another species typical of the Selenga River, Stephanodiscus minutulus, was found both near the shore, and in the surface waters of the open lake. Endemic spring baikalian diatoms Aulacoseira baicalensis and Cyclotella baicalensis were found at highest concentrations in the deep waters far off-shore, beyond the thermal bar. Another endemic diatom, the autumn species Cyclotella minuta was evenly distributed over the open lake at all depths. The data obtained shed new light on the dynamics of water masses near thermal bars, and on the ecology of the diatom species studied.