Enige waterplantengemeenschappen in Zeeland

The paucity of the waterplant flora of the province of Zeeland is ascribed to the difficult access by fresh-water species. The islands are surrounded by sea water, and the inland waters are for the larger part more or less brackish. Fresh water occurs only in a narrow sandy strip along the inner side of the dune ridge and in a few small enclaves elsewhere in the area. Moreover, in this limited area fresh water is only found in small drinking pits and small ditches, the larger waters being without exception brackish. The 20 phanerogams found (Table 1) are grouped in 6 different vegetation-units. 1. The Lemno-Spirodeletum is only fragmentarily represented. 2. The Lemnetum trisulcae, a community of small, free floating hydrophytes, is only present in Zeeland in the form of a Lemna trisulca-facies. 3. The Ceratophyllum submersum-sociation is in the Netherlands more or less confined to the coastal area, where it occurs in small ditches and ponds, filled with fresh water or brackish water with a salinity maximum up to 3 ‰ Cl’. The maritime distribution of C. submersum in the northern part of its area depends on the relatively high winter temperatures near the coast. 4. The Callitricho-Ranunculetum baudotii is limited to the coastal area, and inhabits fresh water as well as brackish water with a salinity maximum up to 3 ‰ Cl’. The faithful species are Callitriche obtusangula and Ranunculus baudotii, which both show a mediterranean-atlantic distrib- ution pattern. The association is more or less amphibious and occurs only in very shallow water which may dry up completely during the summer. The dominant species of the asso- ciation, Zannichellia pedicellata, does not develop landforms, but dies off in time of drought; its seeds, however, are drought-resistent. 5. The Potamogeton pectinatus-sociation occurs in deeper water and extends also in considerably more saline waters (up to 8 ‰ Cl’!) than the above mentioned vegetation unit. 6. The Ruppietum spiralis is characteristic for brackish ponds with an average salinity between 7—8 and 15 ‰ Cl’; at lower salinities Ruppia spiralis coexists with other phanerogams, but is then only a subordinate member of the Potamogeton pectinatus-sociation.