The effect of aeration on stratification and phytoplankton populations in Lake Tegel, Berlin

The Lake number is used as an indicator for the degree of stability and mixing in Lake Tegel, Berlin. It is shown that aeration during late spring and summer reduces the stability of the water column but does not overturn the lake as long as the stability due to meteorological forcing is strong enough. The increased mixing due to aeration during summer affected species composition by favoring population growth of some cyanobacterial species - Microcystis spp. and Aphanizomenon flos-aquae in competition against dinoflagellates - Ceratium spp. Further, it enabled growth of some large centric diatoms - Aulacoseira spp. - already during summer. Asterionella formosa, Planktothrix agardhii and Anabaena spp. grew better under more stably stratified conditions. The Lake number proved to be a useful tool for assessing the impact of stability and mixing upon phytoplankton population growth.