Presently a storm-surge barrier is under construction in the mouth of the Oosterschelde. After its completion tidal conditions in the estuary can be controlled. In order to indicate the limiting conditions for conceivable uses of the storm-surge barrier a number of the most prominent salt-marsh species were tested in their various life stages against immersion times of 2, 4 and 8 days.
Most of the species were able to withstand an extended immersion fairly well, although some of them showed reduced growth during-and after immersion. No evident relation was found between the position of the species on the salt-marsh ecotone and their inundation tolerance. Only one taxon from the upper marsh, Festuca rubra ssp. litoralis, showed a total die-back after an 8 day summer inundation. Most of the species involved showed a decreasing immersion tolerance with increasing water temperatures. Limonium vulgare and Juncus gerardii, however, exhibited a significant growth increase after extended immersion, even at a temperature of the inundation water of 36 Β°C.
In contrast herewith flowers and flower buds started to decay after as little as a 2 day immersion. For Aster tripolium prolonged immersion reduced seed weight and germination capacity of the seeds. Germination and seed weight of Salicornia dolichostachya were not affected by prolonged immersion.
It is concluded that prolonged summer inundations will cause an overall negative effect on the salt-marsh vegetation.
* Nomenclature follows Tutin et al., (1964Tutin et al., ( 1980)). ** Communication nr 295 of the Delta Institute for Hydrobiological Research *** Thanks are due to Mrs. M. A. Vink, Miss M. Bouts and Miss H. Geltink for their assistance. The study was funded by the Ministry of Transport and Public Works, Rijkswaterstaat Delta Department, Environmental Division (project VEGIN).