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Response of macrophytes to restoration from eutrophication in the shallow softwater
lake Kraenepoel (Belgium)
Van Wichelen J.1, Denys L.2, Packet J.2, Hoste I.3 & Vyverman W.1
1. Ghent University, Department of Biology, Section Protistology and Aquatic Ecology,
Ghent, Belgium
2. Research Institute for Nature and Forest (INBO), Brussels, Belgium
3. National Botanic Garden of Belgium, Meise, Belgium
Keywords: 3130 Oligotrophic to mesotrophic standing waters with vegetation of the
Littorelletea uniflorae and/or the Isoëto-Nanojuncetea, eutrophication, nutrient removal
During the last decades, efforts were made to restore at least 200 standing shallow waters in
the Flemish part of Belgium. Often, reduction of external nutrient loading proved insufficient
to induce a reversal from turbid to clear water, indicating that additional measures are usually
needed. The restoration project of Lake Kraenepoel is one of the most extensive ones ever
carried out in Flanders. Since its creation in the Middle-Ages, this 22 ha lake was managed
for traditional pisciculture. Regular water-level drawdown (± every 5 years) for harvesting
fish prevented foddering and accumulation of organic matter from leading to ecological
degradation. However, since World War II, supply of nutrient-rich surface water, polluted
atmospheric deposition and cessation of water-level drawdown accelerated the eutrophication
process. Consequently, the regionally exceptional softwater vegetation with priority species
such as Lobelia dortmanna and Luronium natans declined. Restoration started in 2000 within
the frame of a LIFE project and included phased implementation of complementary measures.
Changes in the vegetation were recorded by means of complete surveys and transect relevés.
Abiotic conditions for the specific flora improved considerably and a marked increase in
aquatic macrophyte abundance and structural diversity occurred. Yet, former species
composition was only partially restored. Species with a viable seed bank and relic populations
that persisted until restoration (Elatine hexandra, Eleocharis acicularis, Hypericum elodes)
were most successful. The quality of available surface water is insufficient to allow its use as
a source of buffering capacity, whilst atmospheric N-deposition, accumulation of leaf litter
and large numbers of exotic geese remain items of concern. Regular drawdown can mitigate
some of their effects.
Corresponding author: Jeroen Van Wichelen, Ghent University, Protistology and Aquatic Ecology, Krijgslaan
281 (S8), B-9000 Gent, Belgium
tel: 0032 (0)9 264 85 05
fax: 0032 (0)9 264 85 99
[email protected]