Constructed shallow zones along navigation canals: vegetation establishment and change in relation to environmental characteristics

1. In recent decades shallow zones have been constructed along navigation canals in the Netherlands which form a potential new habitat for aquatic macrophytes and helophytes absent from traditional canals. 2. The aim of this Study was to examine the relationships between the aquatic plant vegetation that becomes established and the physical and chemical characteristics of water and sediment, in order to find the determinants of species composition and the changes therein. Data were collected in 1998 and 1999 from 80 plots in bank zones at varying stages of development since construction along two navigation canals. 3. Plots 3-5 years old were partly dominated by rooting submerged macrophytes such as Potamogeton pectinatus, Elodea nuttallii and Potamogeton pusillus; locally non-rooting species occurred such as Ceratophyllum demersum, Lemna minor and Spirodela polyrhiza. Older plots contained Phragmites australis, locally mixed with free-floating species. Hydrological isolation from the eutrophic canals was indicated by the presence of Chara vulgaris. 4. Characteristics of both water layer and sediment could explain the variation in vegetation composition. Rooting submerged macrophytes predominantly occurred in sites with a thin (<2cm) layer of sediment with relatively low concentrations of organic matter; moreover, ammonium concentrations in the water layer and sediment pore water were relatively low. Stands of non-rooting macrophytes and of Phragmites australis were characterized by a relatively thick sediment layer and high ammonium levels in the pore water. Light limitation:in turbid water, associated with navigation and eutrophication, may also play a role. 5. Although submerged aquatic macrophytes persist for a relatively short time, shallow zones nevertheless function as a habitat for helophyte communities and contribute to a higher aquatic biodiversity than is associated with traditional banks along navigation canals. Copyright (C) 2001 John Wiley Sons, Ltd.