Tidal river, upstream from the estuary

This habitat includes portions of large rivers subject to the tide, upstream from the estuary. The water level is subject to tidal influence, but the water is mainly freshwater or slightly brackish (1-2 psu).  Several aquatic macrophytes and helophytes are characteristic of this habitat, and some of them are endemic to specific river floodplains. In this habitat, the submerged aquatic vegetation is especially developed in shallow parts of the river system, where the water level is only about 20 cm at low tide. Here, submerged macrophytes can form extensive beds. The banks are covered by extensive helophyte vegetation, usually dominated by Phragmites australis that is tolerant to periodical water table fluctuations. More characteristic for the lower zones are Schoenoplectus triqueter and Bolboschoenus maritimus. The helophyte dominated vegetation growing on the permanently flooded part of the beds is included in this habitat, however the emergent vegetation growing on the periodically flooded banks, with characteristic species like Leucojum aestivum and Senecio fluviatilis, is included in the habitat type C5.1.Some endemic species occur in tidal freshwater areas, like Oenanthe conioides and Deschampsia wibeliana in the Elbe floodplain, and Caltha palustris ssp. araneosa  in the Scheldt, Rhine-Meuse and Elbe floodplains.

Vegetation zonation is highly dependent on flooding frequency. In sheltered parts of the tidal creeks, which almost never dry completely, Nuphar lutea, Potamageton pusillus and Potamageton perfoliatus may locally dominate. Potamogeton pectinatus, Zannichellia palustris ssp. palustris, Sagittaria sagittifolia, Veronica anagallis-aquatica, Veronica catenata and Sparganium emersum sometimes also occur in or near the gullies. Special (semi)aquatic species that occur in tidal freshwater habitats are those of the genus Elatine. Although extreme rare and not completely associated with tidal freshwater habitats, Elatine hydropiper and Elatine triandra occur in this system in The Netherlands.

Tidal freshwater wetlands have become scarce in Europe because of drastic human alterations of estuarine geomorphology. The habitat is restricted to the Atlantic and North Sea coast of Europe, where tidal fluctuation is relatively large. In the current situation, the main tidal freshwater wetlands are distributed directly upstream from the estuaries of the Thames, Trent (UK), Weser (DE), Elbe (DE/NL), Rhine-Meuse (NL), Scheldt (B), Garonne, Loire, Seine, Charente (FR) and Mondego (PT).

Indicators of good quality:

• Submerged, open fields of sediment-rooted aquatic macrophytes
• Absence of or only limited alterations of estuarine hydromorphology
• Tidal amplitude unchanged
• Freshwater to slightly brackish water
• Good water quality in terms of nutrient content and water clarity supporting submerged macrophyte growth

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats