Fen Management Handbook - Scottish Natural Heritage

Although shallow excavations are preferred because of the ease with which the
required plants can become established, depth may be dictated by the degree to
which the roots of the existing plants have penetrated. The rhizomes of reed can
potentially descend to a metre or more, but most grow 20 - 50 cm below the peat
surface. Rhizome depth depends on fluctuations in water levels at a site as well as
plant size, with larger species generally having deeper rhizomes. Sedge rhizomes
(Carex spp.) are generally much shallower (5 - 10 cm deep) than those of sawsedge
which are usually present at depths of about 20 cm below the surface of the
substrate (Conway 1942).
Looking at the rhizomes and seeds at the depth which will form the new surface
provides a guide as to what might regenerate. Seeds can be extracted from
approximately 300 - 500 ml of substrate by mixing with water and sieving the
resulting slurry through 2mm, 500 μm and 125 μm sieves. Material retained on
the sieves can be washed off with tap water for examination under a low power
dissecting microscope and identification by comparison to reference material and/
or published reference works. Leaving the seeds on a damp substrate or in a
shallow layer of water in a warm location will reveal which will germinate readily.
7.2.5 Silt traps
The rapid terrestialisation of some fens may be due to the input of large quantities
of silt from streams and other watercourses. Installation of an appropriately sized
and designed silt trap where the offending watercourse enters the fen can help
reduce sediment input, but the long-term goal should be to identify and eliminate
the high concentrations of suspended solids in the watercourse.
For silt traps to work effectively, the velocity of water must be reduced sufficiently
so that silt will fall out of suspension faster than it will be carried into the fen or body
of water downstream. Installation of the silt trap and/or disposal of sediment may
require a licence (see Appendix V).
Construction of a silt
trap can help intercept
water-borne silt to reduce
terrestrialisation of fens.
The two surface baffles
pictured extend 15cm
under the surface help
reduce the flow
(A. McBride).
155