Fen Management Handbook - Scottish Natural Heritage

Farm effluent run-off has been recognised as a significant diffuse source of
pollution for many years. Both UK and European legislation now seeks to protect
against such contamination, for example under the EU Nitrates Directive 91/676/
EEC and the Water Framework Directive (2000/60/EC). The value of the nitrate
treatment potential of wetlands can therefore be promoted for inclusion in,
and realisation through, the Programmes of Measures which are developed for
achieving good status under the Directive.
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A constructed farm
wetland at Oldhamstocks
Farm, Scottish Borders
(A.McBride)
The Coal Authority in the UK describes reedbeds as the ‘most ecologically
friendly’ and visually attractive way of treating mine water, in particular the pollution
of watercourses with iron ochre as groundwater levels rebound. The roots of
common reed, bulrush and yellow iris filter particles of ferric hydroxide (ochre).
Settlement then occurs when these particles collect together and fall to the base
of the reedbed. Currently, 10 mg/l ferrous hydroxide entering the Coal Authority’s
reedbeds will be reduced to less than 1 mg/l. Examples include Kames in Ayrshire,
which is a passive wetland system to treat gravitational flow to the River Ayr, and
treatment of acid mine drainage from colliery spoils (including iron, aluminium,
manganese and zinc) at Quaking Houses, County Durham (a ‘CoSTaR’ project,
based at Newcastle University). Reedbeds for mine water treatment are often
combined with public amenity use incorporating picnic areas, paths, benches and
viewing points.
Valuation of this service can be through comparison with the cost of an equivalent
waste water treatment facility. In the United States it was calculated that the natural
Congaree Bottomland Hardwood Swamp in South Carolina avoids the need for a
$5 million waste water treatment plant.
12.2.3 Carbon sequestration
Another key role of peat-based wetlands is the regulation of global CO 2
concentrations, and therefore climate change, through storage of a major proportion
of fixed carbon in the biosphere. Peatlands cover only an estimated 3-4% of
the world’s land area, but are estimated to hold 540 Gt of carbon, equivalent to
around 74% of the 730 Gt of carbon held in the atmosphere as CO 2. If the world’s
peatlands lost only 5% of their carbon store through respiration, global CO 2
concentration would rise from its current value of 386 ppm to around 400 ppm.
Carbon is stored in peat by accumulation of dead organic matter under anaerobic
conditions, where the soil water level is at or close to the ground surface. Where
water levels have been lowered, for example by drainage for agricultural production,