The role of periphyton during the re-colonization of a shallow lake with submerged macrophytes

Abstract

The development of periphyton on artificial substrate exposed for 1, 2 or 2–20 weeks was followed during two subsequent vegetation periods (2000 and 2001) in shallow Lake Müggelsee. Mean periphyton biomass was found to be higher than in 1962, when submerged plants were abundant. Periphyton development differed considerably between 2000 and 2001. Seasonal biomass minima occurred at different times in the two years due to phosphorus, silica and nitrogen limitation. Grazing was assumed to play a role in July. Periphyton was generally dominated by diatoms, whereas green algae became abundant with increasing water temperature in summer. 1-, 2-, and 2–20-week periphyton absorbed, on average, 19, 63, and 82% PAR, respectively. When combined with the attenuation of a 0.5 m water column these values increased to 60, 82 and 92% PAR, respectively. Minimum light requirements of submerged macrophytes are close to or higher than the remaining PAR, indicating that light limitation is an important factor for their growth in Lake Müggelsee. It was concluded that shading by periphyton shortens the clear-water phase with optimum growth conditions for the submerged plants. In combination with herbivorous activities of waterfowl and fish, periphyton shading prevents P. pectinatus plants from growing to the water surface to survive periods with low light availability during summer cyanobacteria blooms.