Ockenfeld, K. Institute of Freshwater Ecology and Inland Fisheries, ockenfeld@igb-berlin.de
Koehler, J. Institute of Freshwater Ecology and Inland Fisheries, koehler@igb-berlin.de

We often observed a strong reduction of phytoplankton biomass along a stretch of the lowland river Spree in Germany in 1997 and 1998. As this sektion of the river originates from the flushed through lake Neuendorfer See, we tested the hypothesis, that the phytoplankton was damaged by the swich from lake to river conditions. Primary production of phytoplankton from the lake outflow and of several stations along the river was measured in bottles with different light transparancy. These bottles were continously moved through the water column in order to provide the enclosed algae with a comparable frequency of fluctuation as experienced by the phytoplankton transported downstream. On one hand this method gave us some information about the light adaption of phytoplankton, on the other hand chlorophyll- or biomassspecific produktion between different points along the river could be compared. The specific production usually declined down the stream and reduction ranged between 9 and 95 % of the specific production measured at the lake outflow. This indicates that losses of phytoplankton could not only be explained by sedimentation and grazing activity of benthic filter feeders.
Day: Wednesday, Feb. 3
Time: 11:00 - 11:15am
Location: Eldorado Hotel
Code: SS03WE1100E