De gevolgen van de wateronttrekking voor de flora van de „Groote Meer” onder Ossendrecht

Up to a few years ago the “Groote Meer” in Ossendrecht (south of Bergen op Zoom, prov. N.-Brabant) was known as the largest and soundest Littorellion-pool in the Netherlands. In consequence of withdrawal of water for a neighbouring water-company the pool was drained during extreme long periods in summer. Moreover a supply of reclamation water intensified the disturbance of the vegetation. Lobelia dortmanna, Isoëtes tenella, Luronium natans, and Sparganium angustifolium vanished. Sphagna diminished. In the Littorella-vegetation on the banks, in the zone of mud deposit, Agropyro-Rumicion crispi and Bidention-communities developed. In the lower zone with less mud deposit, communities of the Nanocyperion flavescentis settled. Meanwhile the waterlevel was raised by unrefined water rich in minerals, pumped up from the depth. The problem is now how to aim at the stabilization of the rhythmical dynamic which is characteristic of the ecology of the pool.