van de Bund, W. J. Netherlands Institute of Ecology, Centre for Limnology,
van Donk, E. Netherlands Institute of Ecology, Centre for Limnology,

In shallow lakes submersed vegetation is a crucial factor for plankton dynamics; phytoplankton and macrophytes compete for similar resources. Within a certain nutrient range either macrophytes or algae may dominate; both situations appear to be self-reinforcing. Various processes have been identified that may be responsible for this phenomenon, but it is difficult to study these simultaneously under natural conditions. Mesocosm experiments can be a tool to provide such insights, although processes occurring on longer time scales (months to years) can't be adequately studied. In the summer of 1998 identical mesocosm experiments were performed in shallow, macrophyte-dominated lakes at five European locations as a part of the EU-project SWALE. The aim was to study how nutrients and fish affect the development of algal dominance. The Dutch enclosure experiment was performed in Lake Naardermeer, with charophytes dominating the macrophyte community. During the first four weeks both nutrients and fish greatly enhanced phytoplankton chlorophyll, with only little within-treatment variability. Then all Chara was removed and the experiment continued for another four weeks. Chlorophyll concentrations generally increased, but interpretation of the data became much more difficult due to increased within-treatment variability; possibly comparison of the data of all five European experiments will reveal more general trends.
Day: Thursday, Feb. 4
Time: 02:00 - 02:15pm
Location: Hilton of Santa Fe
Code: SS51TH0200E