Bacterial activities in shallow lakes – a comparison between extremely acidic and alkaline eutrophic hard water lakes

Abstract

Bacterial abundance and activity were investigated by DAPI-staining and 3H-thymidine incorporation method in samples from a very shallow, hypertrophic hard water lake and from acidic mining lakes in north-eastern Germany. Bacterial cell numbers in the acidic lakes were about one order of magnitude less than in the hypertrophic natural lake but are probably underestimated due to methodological problems. Bacterial activity in the shallow acidic mining lakes was high and comparable with that of hypertrophic hard water lakes. By application of microautoradiography, we checked whether these high thymidine uptake rates in acidic waters were caused by artefacts due to the complex chemistry. It was shown by this qualitative analysis that in addition to small cocci and rods, large filamentous bacteria in the shallow acidic lakes also contribute to the high thymidine uptake. We observed clearly lower bacterial activities in deep and dimictic acidic mining lakes. This phenomenon cannot be explained by the trophic state alone. It is assumed that shallowness in combination with the groundwater input, intense sediment–water interaction, the poor zooplankton colonization and photolytic processes favours the development of large bacterial cells with high specific activity in shallow acidic mining lakes.