INSITU PHOSPHORUS RELEASE EXPERIMENTS IN THE WARNOW RIVER (MECKLENBURG, NORTHERN GERMANY)

Results are presented of in situ benthic phosphorus release experiments in an undercut bank of an impounded river. Due to high sedimentation of phytoplankton biomass high oxygen consumption rates between 259.4 and 947.0 Mg O2 m-2 d-1 developed, leading to almost anaerobic conditions and phosphorus releases between 175.2 and 236.3 mgP m-2 d-1 over a period of 18 days. In a second series of experiments the water column overlying the sediment was aerated, resulting in much lower P release rates (1.1 to 32.9 mgP m-2 d-1) over a period of 30 days. The influence of pH and nitrate was studied by adjusting pH and adding NO3- to the overlying water. Increasing pH positively affected P release rates and enhanced NO3- levels led to an increase of benthic P release, too.