Habitat account - Freshwater habitats
3260 Water courses of plain to montane levels with the Ranunculion fluitantis and Callitricho-Batrachion vegetation
Background to selection
|Distribution of SACs/SCIs/cSACs with habitat 3260 Water courses of plain to montane levels with the Ranunculion fluitantis and Callitricho-Batrachion vegetation. Click image for enlarged map.|
Description and ecological characteristics
This habitat type is characterised by the abundance of water-crowfoots Ranunculus spp., subgenus Batrachium (Ranunculus fluitans, R. penicillatus ssp. penicillatus, R. penicillatus ssp. pseudofluitans, and R. peltatus and its hybrids). Floating mats of these white-flowered species are characteristic of river channels in early to mid-summer. They may modify water flow, promote fine sediment deposition, and provide shelter and food for fish and invertebrate animals.
There are several variants of this habitat in the UK, depending on geology and river type. In each, Ranunculus species are associated with a different assemblage of other aquatic plants, such as water-cress Rorippa nasturtium-aquaticum, water-starworts Callitriche spp., water-parsnips Sium latifolium and Berula erecta, water-milfoils Myriophyllum spp. and water forget-me-not Myosotis scorpioides. In some rivers, the cover of these species may exceed that of Ranunculus species. Three main sub-types are defined by substrate and the dominant species within the Ranunculus community.
Sub-type 1: This variant is found on rivers on chalk substrates. The community is characterised by pond water-crowfoot Ranunculus peltatus in spring-fed headwater streams (winterbournes), stream water-crowfoot R. penicillatus ssp. pseudofluitans in the middle reaches, and river water-crowfoot R. fluitans in the downstream sections. Ranunculus is typically associated in the upper and middle reaches with Callitriche obtusangula and C. platycarpa.
Sub-type 2: This variant is found on other substrates, ranging from lime-rich substrates such as oolite, through soft sandstone and clay to more mesotrophic and oligotrophic rocks. There is considerable geographic and ecological variation in this sub-type. Faster-flowing western rivers on harder rocks, for example in Wales and south-west England, support stream water-crowfoot Ranunculus penicillatus ssp. penicillatus, while western and northern rivers on sandstone or alluvial substrates often support both R. penicillatus ssp. penicillatus and river water-crowfoot R. fluitans. Sub-type 2 rivers elsewhere in the UK contain a mixture of species, and often hybrids, but rarely support R. penicillatus ssp. penicillatus or R. fluitans. Associated species which may be present include lesser water-parsnip Berula erecta, blunt-fruited water-starwort Callitriche obtusangula, and, in more polluted rivers, curled pondweed Potamogeton crispus, fennel pondweed P. pectinatus and horned pondweed Zannichellia palustris. Flowering-rush Butomus umbellatus is an occasional bank-side associate.
Sub-type 3: This variant is a mesotrophic to oligotrophic community found on hard rocks in the north and west. Rivers in Wales, Northern Ireland and south-west England are significant for the occurrence of stream water-crowfoot Ranunculus penicillatus ssp. penicillatus. Other typical species include the aquatic moss Fontinalis squamosa, alternate water-milfoil Myriophyllum alterniflorum and intermediate water-starwort Callitriche hamulata. More oligotrophic examples of this community lack Ranunculus spp. and are dominated by M. alterniflorum, C. hamulata and bog pondweed Potamogeton polygonifolius.
European status and distribution
This habitat type is widespread in Europe, though examples on chalk (sub-type 1) are rare.
UK status and distribution Click to view UK distribution of this habitat
The habitat type is widespread in rivers in the UK, especially on softer and more mineral-rich substrates. It is largely absent from areas underlain by acid rock types (principally in the north and west). It has been adversely affected by nutrient enrichment, mainly from sewage inputs and agriculture, and where agriculture has caused serious siltation. It is also vulnerable to artificial reductions in river flows and to unsympathetic channel engineering works. Consequently, the habitat has been reduced or has disappeared from parts of its range in Britain.
The main variants have very different distributions and have different significance for conservation in a European context.
Sub-type 1 has a limited distribution in the UK, being found only in those areas where chalk is present, and is therefore restricted to southern and eastern England.
Sub-types 2 and 3 are widespread in those parts of the UK where the substrate is suitable. In general, sub-type 2 is commoner in the south and east, whereas sub-type 3 is largely restricted to south-west England, Wales, northern England, Northern Ireland, and parts of Scotland. A few southern rivers show a transition from one substrate to another, as geology changes from chalk to clay.
Site selection rationale
Sites have been selected to represent the geographical distribution of the habitat, the range of substrates on which it occurs, and its ecological variation. The presence of characteristic plant communities (for example, association with water-starworts Callitriche) is considered important, and the selected sites also include the biologically richest examples in the UK. Rivers that show a transition from one substrate to another, e.g. as geology changes from chalk to clay, have also been included. Chalk rivers (sub-type 1) belonging to this habitat type have a very restricted distribution in the UK and Europe, and so have received particular attention; sites have been selected to represent the characteristic communities of both ephemeral (winterbourne) and perennial river sections.
|Afon Gwyrfai a Llyn Cwellyn||West Wales and The Valleys|
|The Gwyrfai is a good example of the small, steep rivers that occur in north-west Wales. It is dominated by base-poor rock and contains extensive beds of the most oligotrophic end of sub-type 3 of this habitat, dominated by stream water-crowfoot Ranunculus penicillatus ssp. penicillatus, intermediate water-starwort Callitriche hamulata, aquatic mosses Fontinalis spp. and bulbous rush Juncus bulbosus. The conservation value of the site is enhanced by the presence of good adjacent river corridor habitat, and by the presence of Llyn Cwellyn, a good example of a Littorella – Lobelia – Isoetes oligotrophic lake.|
|Afon Teifi/ River Teifi||West Wales and The Valleys|
|The Teifi in west Wales is a large river flowing over hard rock, with some spectacular gorges in the lower section. It is mainly mesotrophic but also has oligotrophic sections in the upper reaches, and represents an outstanding example of a sub-type 3 river with water-crowfoot Ranunculus vegetation in western Britain. The river has a spatey flow regime, and in-stream vegetation is dominated by stream water-crowfoot Ranunculus penicillatus ssp. penicillatus, water-starworts Callitriche hamulata and C. obtusangula and the aquatic moss Fontinalis squamosa in a diverse macrophyte community characteristic of oligo-mesotrophic base-poor rocks. A small amount of R. penicillatus ssp. pseudofluitans is present where one tributary flows over base-rich rocks. The river is also noteworthy for an unusually low-gradient section flowing through Cors Caron, a large area of 7110 Active raised bog that is an SAC in its own right.|
|Owenkillew River||Northern Ireland|
|The Owenkillew River rises in the Sperrin Mountains in Northern Ireland and flows westwards, forming part of the Lough Foyle system. It is a large river, being ultra-oligotrophic in its upland reaches, and then gradually becoming oligotrophic and oligo-mesotrophic through its middle and lower reaches. The Owenkillew River is notable for the physical diversity and naturalness of the bank and channel, and the richness and naturalness of its plant and animal communities. Beds of stream water-crowfoot Ranunculus penicillatus ssp. penicillatus occur throughout its middle and lower reaches, typically in association with intermediate water-starwort Callitriche hamulata and large-leaved pondweeds such as broad-leaved pondweed Potamogeton natans and shining pondweed P. lucens.|
|River Avon||Dorset and Somerset, Gloucestershire, Wiltshire and Bristol/Bath area, Hampshire and Isle of Wight|
|The Avon in southern England is a large, lowland river system that includes sections running through chalk and clay, with transitions between the two. Five aquatic Ranunculus species occur in the river system, but stream water-crowfoot Ranunculus penicillatus ssp. pseudofluitans and river water-crowfoot R. fluitans are the main dominants. Some winterbourne reaches, where R. peltatus is the dominant water-crowfoot species, are included in the SAC.|
|The Axe is a south-western example of sub-type 2. Only the lower reaches of the main river have been designated, where the mixed catchment geology of sandstones and limestones gives rise to calcareous waters where R. penicillatus ssp. pseudofluitans dominates, giving way to R. fluitans further downstream. Short-leaved water-starwort Callitriche truncata is an unusual addition to the Ranunculus community and gives additional interest.|
|River Dee and Bala Lake/ Afon Dyfrdwy a Llyn Tegid||Cheshire, East Wales, Shropshire and Staffordshire, West Wales and The Valleys|
|Habitat occurrence account not yet available.|
|River Eden||Cumbria, North Yorkshire, Northumberland and Tyne and Wear|
|The Eden is a north-western representative of sub-type 2. The river flows over both calcareous limestone and sandstone, giving a diversity of ecological conditions, ranging from oligotrophic to mesotrophic. This river has 184 recorded plant species, more than any other river in the UK. The Ranunculus species of the river system include stream water-crowfoot Ranunculus penicillatus ssp. penicillatus occurring here at the edge of its range, and others, such as R. penicillatus ssp. pseudofluitans and river water-crowfoot R. fluitans.|
|River Foyle and Tributaries||Northern Ireland|
|Habitat occurrence account not yet available.|
|River Itchen||Hampshire and Isle of Wight|
|The Itchen is a classic example of a sub-type 1 chalk river. The river is dominated throughout by aquatic Ranunculus spp. The headwaters contain pond water-crowfoot Ranunculus peltatus, while two Ranunculus species occur further downstream: stream water-crowfoot R. penicillatus ssp. pseudofluitans, a species especially characteristic of calcium-rich rivers, and river water-crowfoot R. fluitans.|
|River Lambourn||Berkshire, Buckinghamshire and Oxfordshire|
|The Lambourn is an example of sub-type 1 in central southern England, a chalk stream discharging into the middle reaches of the Thames system. For part of its length it is a winterbourne, drying through the summer months. It is one of the least-modified rivers of this type, with a characteristic flora dominated by pond water-crowfoot Ranunculus peltatus. In the downstream perennial sections R. peltatus is replaced by stream water-crowfoot R. penicillatus var. pseudofluitans.|
|River Tweed||Eastern Scotland, Northumberland and Tyne and Wear|
|The Tweed represents sub-type 2 in the north-eastern part of its range. It is the most species-rich example, by far, of a river with Ranunculus in Scotland, and is the only site selected for this habitat in Scotland. The river has a high ecological diversity which reflects the mixed geology of the catchment. Stream water-crowfoot Ranunculus penicillatus ssp. pseudofluitans, a species of southern rivers and streams, here occurs at its most northerly location as does fan-leaved water-crowfoot R. circinatus, along with river water-crowfoot R. fluitans, common water-crowfoot R. aquatilis, pond water-crowfoot R. peltatus and a range of hybrids. The Tweed is also the most northerly site for flowering-rush Butomus umbellatus.|
|River Wensum||East Anglia|
|The Wensum represents sub-type 1 in lowland eastern England. Although the river is extensively regulated by weirs, Ranunculus vegetation occurs sporadically throughout much of the river’s length. Stream water-crowfoot R. penicillatus ssp. pseudofluitans is the dominant Ranunculus species but thread-leaved water-crowfoot R. trichophyllus and fan-leaved water-crowfoot R. circinatus also occur.|
|River Wye/ Afon Gwy||East Wales, Gloucestershire, Wiltshire and Bristol/Bath area, Herefordshire, Worcestershire and Warwickshire, West Wales and The Valleys|
|The Wye, on the border of England and Wales, is a large river representative of sub-type 2. It has a geologically mixed catchment, including shales and sandstones, and there is a clear transition between the upland reaches, with characteristic bryophyte-dominated vegetation, and the lower reaches, with extensive Ranunculus beds. There is a varied water-crowfoot Ranunculus flora; stream water-crowfoot R. penicillatus ssp. pseudofluitans is abundant, with other Ranunculus species – including the uncommon river water-crowfoot R. fluitans – found locally. Other species characteristic of sub-type 2 include flowering-rush Butomus umbellatus, lesser water-parsnip Berula erecta and curled pondweed Potamogeton crispus. There is an exceptional range of aquatic flora in the catchment including river jelly-lichen Collema dichotum. The river channel is largely unmodified and includes some excellent gorges, as well as significant areas of associated woodland.|
|Upper Ballinderry River||Northern Ireland|
|The Upper Ballinderry River rises in the Sperrin Mountains in Northern Ireland and flows eastwards into Lough Neagh. It is a moderately large river and ranges in type from oligo-mesotrophic to mesotrophic. The river is notable for the physical diversity and naturalness of the bank and channel, and the richness and naturalness of its plant and animal communities. In the middle reaches, common aquatic bryophytes are Chiloscyphus polyanthos, Amblystegium fluviatile, Fontinalis antipyretica and Rhynchostegium riparioides. In addition, beds of stream water-crowfoot Ranunculus penicillatus ssp. penicillatus are abundant in the river channel, often growing in association with intermediate water-starwort Callitriche hamulata and large-leaved pondweeds Potamogeton spp.|
SACs/SCIs/cSACs where this Annex I habitat is a qualifying feature, but not a primary reason for site selection
|Afonydd Cleddau/ Cleddau Rivers||West Wales and The Valleys|
|Cladagh (Swanlinbar) River||Northern Ireland|
|Coedydd Derw a Safleoedd Ystlumod Meirion/ Meirionnydd Oakwoods and Bat Sites||West Wales and The Valleys|
|River Derwent||North Yorkshire|
|River Derwent and Bassenthwaite Lake||Cumbria|
|River Mease||Derbyshire and Nottinghamshire, Leicestershire, Rutland and Northamptonshire, Shropshire and Staffordshire|
|River Roe and Tributaries||Northern Ireland|
|River Usk/ Afon Wysg||East Wales, West Wales and The Valleys|
Many designated sites are on private land: the listing of a site in these pages does not imply any right of public access.