Standing open water

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Abridged version taken from the Wiltshire Biodiversity Action Plan (BAP)

Importance

Standing open water includes natural features such as oxbow lakes, woodland ponds and temporary pools in hollows; and artificial features such as gravel pits, ornamental lakes, canals, farm ponds, dew ponds, garden ponds and ditches. Temporary and permanent ponds and pools created in tank tracks on Salisbury Plain are also an important feature.

Open water is a relatively scarce habitat in the county, and apart from the Cotswold Water Park, its conservation importance has not been fully assessed.

The Cotswold Water Park contains over 140 lakes formed by mineral extraction in the upper Thames floodplain in north west Wiltshire and south east Gloucestershire. The water is lime rich and there are often calcium carbonate or marl deposits on the lakebeds. Marl lakes support distinctive aquatic plant communities and are nationally scarce. The Water Park is the most extensive marl lake system in Britain. The Water Park has its own biodiversity action plan, implemented by a partnership of organisations including Wiltshire Council and the Cotswold Water Park Society.

The water park, along with a few larger man-made lakes in the county, is also important for wintering and breeding birds, particularly wildfowl, and as a migration stopover point for a variety of bird species.

White-clawed crayfish, water voles and otters can also be spotted in the water park, although the white-clawed crayfish is declining, principally due to the introduced American signal crayfish.

Seasonal water bodies on Salisbury Plain, in particular flooded tank tracks, are known to be important for invertebrates and amphibians such as the fairy shrimp Charocephalus diaphanous and the smooth newt.

Elsewhere farm ponds, dewponds and some winterbourne ponds on the MoD’s Salisbury Plain Training Area (SPTA) support a range of wildlife including the great crested newt.

The three canals in Wiltshire are known to be important for water voles and occasionally great crested newts as well.

Extent and distribution

The Cotswold Water Park is the largest area of open water in the county, with part of its area located within Wiltshire. Average lake size is 7ha.

The Wiltshire and Swindon Biological Record Centre (WSBRC) records almost 600ha of open water identified as Site of Special Scientific Interest (SSSI) or County Wildlife Site (CWS) in Wiltshire. In addition to this are:

• Those elements of the Wilts & Berks Canal that have water;
• Many SSSIs and CWSs that have an open water element in them, such as a small pond, the areas of which are not separately measured;
• A large number of farm and village ponds. This may range between 4,000 and 12,000.

Apart from those open water sites identified as SSSI or CWS, the distribution of the remaining areas of standing open water is not currently known. However, it is likely to reflect the underlying geology as well as current and historic land use.

Trends

There is considerable evidence to suggest that smaller areas of open water, such as farm ponds, may be in decline. For example:

• A survey of the Salisbury area in 1994 estimated that over the last 100 years 43% of ponds had been lost (Wiltshire Wildlife Trust (WWT) survey);
• A comparison between loss and gain for a series of sample 5km squares across all the natural areas in Wiltshire showed an average pond loss of 46% over the last 30 years (WWT desk exercise).

The above figures may, however, be offset to some extent by the creation of new ponds in the landscape, and more particularly in private gardens.

A brief comparison by the BAP project suggests that perhaps 20-40 ponds a year are created or restored with the help of a variety of grant schemes including Wiltshire Council’s Biodiversity Improvement Grant Scheme. In addition it is assumed that there are a large number of garden ponds in the county as well as a number of private individuals who have created water bodies by their own efforts. The Environment Agency has also undertaken a number of standing open water creation schemes in the county.

Last updated: 23 June 2009