Stimulation of phototrophic pelagic and benthic metabolism close to sediments in acidic mining lakes

Young, very acidic mining lakes have ecological potentials that are quite different from those of natural lakes: Whereas their primary production and hence their algal biomass is mostly limited by carbon and phosphate, their species composition is largely controlled by the extreme chemical composition of their water (low pH, high metal and sulfate concentrations). As a consequence, their phytoplankton biomass corresponds to the oligo- to mesotrophic level and the dominant taxa of plankton belong to Chrysophyceae, Chlorophyceae, Dinophyceae, Bacillariophyceae and Euglenophyceae whereas the benthic communities are dominated by euglenoids and diatoms. In some lakes, all these taxa are found permanently or sporadically in considerably high quantities either in their hypolimnion or at the sediment surface, indicating a remarkable ecological potential for primary production of these environments. We therefore hypothesize that input of inorganic carbon and phosphorus by groundwater or the replenishment of these nutrients by microbial processes at the sediment/water interface are the main stimulants of primary production in mining lakes.