Fen Management Handbook - Scottish Natural Heritage

LIDAR maps can provide a general understanding of the topographical setting of a proposed fen creation site, highlighting the main high and
low sports or areas. In this example, the sea bed is shown on the left of the dunes (green) and the low areas behind the dunes (machair)
are shown in blue/grey (top right), and may indicate in general ecological terms where wetland habitats are most likely to develop and be
maintained. (Courtesy of the Western Isles Data Partnership)
9.7.3 Geology
Underlying bedrock (chalk, sandstones, shales etc.) and superficial geology (clays,
sands, gravels etc.) will largely determine the hydrochemistry of a site in terms
of water quality and acidity/alkalinity (pH) (see Section 4: Understanding Fen
Nutrients). Localised base-rich tills or drift deposits can enable the development of
rich-fens in areas with principally siliceous bedrock which will normally give rise to
acidic waters. Calcite veins in some metamorphosed rocks, e.g. Silurian gritstones,
can also give rise to very small, but floristically diverse base-rich springs and flushes
in a generally acidic environment.
The type of bedrock and superficial deposits will also dictate whether water will
issue from an aquifer or whether water will be held on site by an impervious layer
and consequently affect the hydrology/hydrogeological regime of any proposed fen
(see Section 3: Understanding Fen Hydrology). Spring-head mires and seepage
fens depend on presence of a suitable aquifer.
Maps of solid and superficial geology are available at a scale of
1:50,000 from the British Geological Survey) either as paper copies or
in digital format compatible with MapInfo and ESRI.
Alternatively, LandIS, (www.landis.org.uk) the 'Land Information System',
is a substantial environmental information system operated by Cranfield
University, UK, designed to contain soil and soil-related information for
England and Wales including spatial mapping of soils at a variety of
scales as well as corresponding soil property and agro-climatological
data.
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