Fen Management Handbook - Scottish Natural Heritage

is, however, significant disruption to the fen, including exposure of underlying peat
(and possible erosion), loss of the peat pollen/macrofossil archive and damage to
any archaeology. This technique should therefore only be undertaken on small areas
of fen at a time (generally less than 2 ha, or no more than 10% of the site area) and
advice from an archaeologist sought before starting.
Before embarking on costly and potentially controversial work such as turf stripping,
it is crucial to remove the original source of nutrient enrichment or take measures to
ensure nutrients no longer reach the site. See Case Study 8.1.
8.4.4 Dredging
Mechanical dredging by a machine with a long-reach arm and a bucket can be used
to remove nutrient rich sediments which have accumulated over time in ditches,
ponds, lakes, reedbeds and other wetlands. However disposal of the spoil is
problematic.
8.4.5 The role of re-wetting and water management in nutrient management
Retaining high water levels is important for overall fen management, but in terms
of nutrient management keeping peat wet reduces oxidation and mineralisation
and subsequent release of nutrients. Therefore, any of the techniques used to
retain water on a fen site, or stabilise water-levels (see Section 7: Fen Water
Management) will benefit nutrient management and, in particular, reduce the
likelihood of nitrogen mineralisation and release. However, there is also potential for
re-wetting (i.e. raising water levels to re-wet or flood the soil) to result in a ‘flush’ of
phosphorus from enriched soils under anaerobic (waterlogged) conditions.
Re-wetting can result in additional nutrient enrichment problems if eutrophic water
is used, or if the natural water inputs to a fen are from a eutrophic source, such as a
nutrient enriched river.
8.4.6 Soil inversion
The principal of soil inversion is to bury the top layers of nutrient-enriched soils
deeply enough to prevent the nutrients being readily accessed by plant roots. The
technique has been used successfully for species-rich grassland restoration, where
the top 30cm of soil was buried under around 40cm of sub-soil using a deep plough
(Glen et al, 2007). Unlike soil stripping, there is no material to dispose of, but the
technique relies on heavy machinery and is therefore only likely to be suitable for
drier fens, such as those previously used for agriculture. There is also a risk that
phosphorus will be re-mobilized, and careful consideration is required as to whether
any phosphorus release is likely to be a short ‘flush’ or a more long-term release of
nutrients which would negate the benefits of soil inversion.
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Soil inversion is a relatively new technique which has not yet been tried
on fens. Effectively the nutrients are still on site, and could be released
by inappropriate future management or utilised by vegetation such as
trees which root to sufficient depth to access the buried nutrient store.
There is also a risk of ploughing or other soil inversion techniques
damaging archaeological remains.
Soil inversion should therefore only be considered as a last resort for
nutrient management on fens.