Why 'very shallow' lakes are more successful opposing reduced nutrient loads

There are different approaches for classifying deep and shallow waters using physically and ecologically derived parameters. Nevertheless, transition states make it difficult to define border crossing points between the two types of limnetic ecosystems and to distinguish more precisely between different types of shallow, especially highly eutrophicated lakes. We contribute a detailed analysis of different characteristics of shallow waters from lakes in the Berlin/Brandenburg-region. In the catchment area of the river Dahme in Eastern Brandenburg (Scharmutzelseeregion) we find mainly shallow and highly eutrophicated lakes, dominated by Cyanobacteria. 'Very shallow' lakes of different morphometry and topography are compared with 'medium shallow' or deeper lakes in the region with similar loading characteristics for the following properties: morphometry, topography, theoretical retention time, mixing intensity, nutrient dynamics, external and internal loading, underwater light climate, z(eu)/z(mix), phytoplankton development and oxygen budget. We found that 'very shallow' lakes in the region are more efficient in converting the available phosphorus into phytoplankton biomass because of the constant and sufficient underwater light climate due to the favourable relation of z(eu) and z(mix). We conclude that the regular mixing regime guarantees a stable and near optimum light/dark rhythm as well as higher heterotrophic activities, stimulating primary production up to the upper limit of algal development.