BACTERIAL AND PHOSPHORUS DYNAMICS IN PROFUNDAL LAKE ERKEN SEDIMENTS FOLLOWING THE DEPOSITION OF DIATOMS - A LABORATORY STUDY

The benthic microbial response to the deposition of natural seston and the microbial impact on nutrient dynamics was studied in an experimen tal system using whole sediment cores equipped with flow-through syste ms for the overlying water. For 20 days, changes in sediment bacterial activity, total metabolic activity (heat production), bacterial bioma ss, phosphorus fractions and basic chemistry were followed, as well as the exchange of nutrients between sediment and water. Microbial activ ity and biomass increased immediately in response to the deposition of seston, peaked after seven days and then decreased linearly over the remaining time of the experiment. Co-settled bacteria were suggested t o play an important role in the microbial response. Changes in bacteri al biomass production, bacterial biomass and the NaOH-nrP extractable phosphorus fraction were concurrent in response to seston additions. T he sediment acted as a trap for SRP from the overlying water when bact erial activity was high and as a source when the bacterial activity de creased. Altogether, the results suggest an important role of bacteria in the regeneration of seston P. Mineralization rates estimated from sediment heat production showed that ca. 11% of the added seston carbo n was oxidized in the sediments during the experiment.