Water level fluctuations for managing excessive plant biomass in shallow lakes

The importance of water level fluctuations (WLF) and a suite of linked factors in lake management has been the focus of active research in the past decades. The interest of WLF as a method to limit excessive macrophyte development is addressed in this paper. For this, we assessed the response of three common nymphaeid species (Nymphaea alba, Nuphar lutea and Nymphoides peltata) in terms of biomass to slight changes in water regime (<50 cm) in a large shallow eutrophic lake in the frame of a long-term study (1995-2007). The modelled response of the plants to several descriptors of WLF (water level (WL) and duration of exposure to high water levels (D) in the course of various plant life cycle stages) varied between species. Significant negative correlations (r2 ranging from 58.1 to 75.4%) were found between changes in N. alba biomass (until 50%) and high water regimes occurring in all life stages of the plant. Such relationships were also observed for N. lutea, but to a lesser degree, and variations in N. peltata biomass were poorly explained by WLF. Support for the importance of the period in the life cycle of the plant in which high water regimes occur is provided to explain the successful limitation in plant biomass, despite the known tolerance of nymphaeids to large WLF. Results also reflect the importance of lake size, and the supposed factors associated with WLF, in the management of dense macrophyte-covered aquatic ecosystems. Additional research on this issue is needed to generate more widespread application of WLF under different environmental conditions (trophic state, morphology and size of lakes).