The UK Biodiversity Action Plan and the EC Habitats Directive aim to conserve specific types of habitat by means of action plans and site protection measures. In order to set natural resources in context, to enable planning to be effective and to facilitate the costing of proposals for action, it is necessary to know the extent of each habitat type. The total surface area of standing fresh water in Great Britain is estimated at 2400 km². The aim of the investigation described here is to estimate the extent of the different types of standing freshwater habitat that make up this total.

 

Freshwater habitat classification systems used in Britain and the European Union incorporate the concept of trophic levels. The current British system, based on the results of a nationwide botanical survey of standing waters, groups ten standing water site types under the broad habitat categories dystrophic, oligotrophic, mesotrophic, eutrophic and brackish. Data collected by the statutory nature conservation agencies on site type (and therefore habitat type) and surface area are available for 3500 water bodies, mostly in Scotland. In England and Wales, survey has been much more selective and patchy than in Scotland. Therefore, it was not considered possible to estimate the areas of habitat types in England and Wales (or in Britain as a whole) simply by direct extrapolation from the survey sample to the total resource of standing water.

 

Computerised national datasets available to the Centre for Ecology and Hydrology (CEH) include Ordnance Survey (OS) statistics on the area of standing water in each kilometre square in Great Britain and records of the occurrence of aquatic plant species in the Biological Records Centre (BRC) database. A system of Trophic Ranking Scores (TRS) has been developed for aquatic plant species. Using BRC data, a mean TRS for each 10x10 km square in Britain was produced and the country was divided into TRS bands. For each of these bands the percentage by surveyed area of each freshwater habitat type (dystrophic, oligotrophic, mesotrophic and eutrophic) was calculated. These percentages were applied to the total area of standing water in each TRS band and the extent of these habitats in Britain as a whole could then be calculated.

 

 

The estimated extent (with an approximation of error) and percentage of each freshwater habitat type is:

 

	Dystrophic	Oligotrophic	Mesotrophic	Eutrophic
		Area (km2)
England	1 ± 0.1	93 ± 9	62 ± 6	518 ± 52
Scotland	10 ± 1	1294 ± 65	180 ± 18	121 ± 6
Wales	0.4 ± 0.04	59 ± 6	25 ± 3	40 ± 4
Great Britain	11 ± 1	1445 ± 80	267 ± 27	679 ± 62
		Area (%)
England	0.2	14	9	77
Scotland	0.6	80	12	7
Wales	0.4	47	20	32
Great Britain	0.5	60	11	28