Comparison of bacterial and phytoplankton productivity in extremely acidic mining lakes and eutrophic hard water lakes

Abstract

Two types of standing waters are important in Brandenburg (Germany): eutrophic hard water lakes of glacial origin (about 2.800) and several hundred mining lakes, mostly highlyacidic (pH between 2 and 3 and high concentrations of dissolved iron). A trophic gradient can be used, describing the nutrient situation in these lakes from oligo- to mesotrophic mining lakes to eutrophic to polytrophic natural hard water lakes. Bacterial and algal production in some typical lakes of these two types are compared. Whereas bacterial productivity in acidic mining lakes is comparable with eutrophic hard water lakes, primary production is very low. It does not exceed the level of bacterial production considering volume related daily carbon production. Mining lakes are thereby characterised as heterotrophic ecosystems. Reasons for the production differences in both types of lakes can be looked for in the resource availability and top down control. Contrary to the eutrophic natural lakes, phytoplankton productivity in mining lakes is controlled by carbon limitation. Consequences for the structural classification of pelagic bacterial and phytoplankton communities are shown concerning the course of ecosystem succession from pioneer initiation in mining lakes to high-biomass maturation stage in eutrophic hard water lakes.