Distribution and environmental requirements of stream habitat with Ranunculion fluitantis and Callitricho-Batrachion vegetation in lower Belgium (Flanders)

1. Streams with Ranunculion fluitantis and Callitricho-Batrachion vegetation – or habitat type 3260 according to
the European Habitats Directive – require particular conservation at biogeographic level but Member States carry
individual responsibility. Within this framework, the environmental requirements of this habitat type in lower
Belgium (Flanders) were analysed.
2. Overall, current vegetation composition was not significantly related to adjacent land-use but correlated
mainly with physical–chemical conditions and to a lesser extent with distance to source and channel width.
Even though sites with habitat 3260 generally showed lower levels of human impact, their abiotic features
overlapped considerably with those of sites without habitat 3260 but still showing hydrophyte development.
3. Thresholds occurred in the distribution of responsive macrophyte taxa, including the more common
characteristic species of the habitat type, along gradients of increasing solutes and nutrients. Comparison with
water quality standards proposed so far to support good ecological status for the European Water Framework
Directive in lowland rivers suggests that compliance would probably allow this habitat to persist in most cases,
although some discrepancies occur. This implies that more stringent objectives may be required in some water bodies.
4. The present analysis focuses on the conditions delimiting occurrence of HT 3260, and therefore its range and
area in lower Belgium. A comprehensive understanding of its favourable conservation status remains difficult in
lowland regions where most rivers are subject to strong human impact and will require a more long-term
perspective that also considers management regime, physical habitat structure and connectivity.