Potential role of propagule banks in the development of aquatic vegetation in backwaters along navigation canals

The diversity and abundance of plant species in propagule banks of backwaters along two navigation canals in The Netherlands were studied in order to assess the relationship with the standing vegetation and the potential role of propagule banks in the establishment of (submerged) aquatic vegetation. At five sites, varying in vegetation composition and age, 180 samples were collected: 100 from surface sediment and 80 from the interface between original soil and sediment (=subsediment). In total, 113 species emerged of which Juncus spp. and Lythrum salicaria L. were the most abundant. Seven submerged species occurred at low densities. On average, there were 10.8-17.8 species l(-1) in the surface sediment, and 8.5-10.2 l(-1) in the subsediment. The mean number of propagules in samples ranged from fewer than 200 l(-1) in 3-year-old to over 3000 l(-1) in 10-year-old sites. There was little correspondence between propagule bank and standing vegetation. Vegetation establishment 2 months after sediment removal in six plots revealed 10 species; submerged species, however, hardly occurred. It is concluded that propagule banks cannot play a significant role in the (re-)establishment of diverse submerged aquatic vegetation along these canals. After creation of bare sites as a result of cutting and dredging in narrow zones along the water line, however, propagule banks may contribute to the development of species-rich emergent vegetation. (C) 2003 Elsevier B.V. All rights reserved.