Fen Management Handbook - Scottish Natural Heritage

10.8 Monitoring surface water flows
Measurement of surface water flow in wetlands can be challenging because
channel gradients and flow velocities are often very low. Surface water flows also
vary more than soil water levels over the short-term, and it is often difficult to devise
a measurement scheme which captures the full range of this variation.
Manual measurements range from straightforward volumetric measurement,
using a container of known volume and a stopwatch, through to the use of a
current meter. The techniques described in publications such as Shaw (1994)
and Brassington (2006), are relatively simple and cheap, and usually within the
capabilities of site staff or volunteers.
Automated techniques include a rated channel section (for example a ‘flume’)
or structure (for example a ’v-notch weir’), where the relationship between water
level and flow is established and water levels are measured continuously. These
techniques are described in publications such as Shaw (1994) and Herschy
(2008), but they are more involved and demanding technically and it might therefore
be necessary to seek third-party advice on installation and operation.
10.9 Monitoring water quality
The value of regular field measurement of water quality parameters is high: the
temporal variation of base-richness (pH), mineralisation (electrical conductivity) and
dissolved oxygen, which can all be measured using hand-held meters, can provide
valuable information on the seasonal variation of water sources to a site. Regular
meter maintenance and calibration is important to ensure precision of measurement.
Concentrations of a wide range of determinants (major and minor anions and
cations, trace elements, contaminants) can be found through laboratory analysis of
water samples. More comprehensive information on water quality is more powerful
in terms of development of the conceptual understanding of the functioning of, and
pressures on, a site, but there is a trade-off in terms of cost. A common strategy
is regular (e.g. weekly or fortnightly) field measurements, supplemented by much
lower frequency (e.g. annual) laboratory analysis of samples.
10.10 Measuring and monitoring enrichment – detailed information gathering
For fen sites with limited enrichment problems or where the source of enrichment
is easily identifiable, looking at fen type and catchment land use and broad
assessments of water sources and vegetation communities can be sufficient to
inform management. However, in some cases greater detail of water and peat
chemistry of a site is needed in order to understand what might be causing
enrichment and how to tackle it. Detailed assessments are also useful as a
monitoring tool, as changes in water and soil chemistry are likely to be identified
sooner after management begins than changes in the fen vegetation itself, which
might take several seasons to respond.
Changes in nutrient status could be gauged initially by the encroachment of nutrient
tolerant species including great willow herb, bulrush, scrub etc. The occurrence
of some key undesirable species may be sufficient to warrant a more detailed
investigation of nutrient levels in the fen.
More detailed analysis relatively cheaply undertaken by commercial laboratories
include chemical nutrients such as total and available (sometimes termed
‘extractable’) N, P and K along with pH and EC. Most laboratories will supply
sterilised water bottles for sample collection. Soil samples can be stored in sealable
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