wise use of mires and peatlands - Peatland Ecology Research Group

MIRES AND PEATLANDS35decay in the catotelm. However, LORCAprovides insight into the balance betweenlong-term input and decay. The true net rateof C accumulation (ARCA) can be determinedby peat accumulation models 87 , and has beenestimated as 2/3 of LORCA 88 . Therelationship of these three different measuresof peat accumulation rate is illustrated inFigure 2/4. The differences between thesethree different measures increase with time.The mineral subsoil under mires is anadditional C sink that may account forapproximately 5% of the unaccounted C inthe global carbon budget 89 .The present-day sequestering rate of C inglobal mires is estimated to be 40-70 ·10 12 g y -1(= 40 – 70 million tonnes C y -1 ) 90 .270-370·10 15 g of carbon (C) is stored in thepeats of boreal and sub-boreal peatlandsalone 92 . This means that globally peatrepresents about one third of the total globalsoil carbon pool (being 1395·10 15 g) 93 . Itcontains an equivalent of approximately 2/3of all carbon in the atmosphere and the sameamount of carbon as all terrestrial biomasson the earth 94 .Peat extraction is presently responsible foroxidative peat losses of approximately 15·10 12g of carbon per year 95 , while agriculture andforestry consume 100 – 200 ·10 12 g C per year 96 .As global peat accumulation is about 40 - 70·10 12 g C per year, the world’s peatlands havechanged from a carbon sink to a carbonsource, with an annual global loss of the peatcarbon resource of about 0.5‰ 97 .2.6 CHARACTERISTICS OFMIRES AND PEATLANDSThe essential features of mires and peatlands– peat accumulation and peat storage – areassociated with a number of othercharacteristics 98 that distinguish them frommost other ecosystem types. As peatlandslargely consist of water 99 , hydrologicalcharacteristics play a central role. Therefollow four characteristics or processes whichlie at the basis of many peatland-specificconflicts. They are therefore especiallyrelevant to the rest of this document. (Thecharacteristics of mires and peatlands thatrelate directly to “benefits”, “resources” and“services” are dealt with in extenso inChapter 3).i) Their principal characteristic is that thewater level should - on average in thelong-term - be near the surface 100 for amire to exist, i.e. to make peataccumulation possible.Water levels which are too low 101 and toohigh 102 are detrimental to peat accumulation.This means that activities which substantiallylower or raise the water level in peatlands,including their use for many production andcarrier functions, negatively affect their peataccumulation capacity and the associatedfunctions.ii) Oxidation processes 103 change thephysical, chemical, hydraulic, andbiological properties of peats and peatsoils, and these changes are oftenirreversible 104 .Drainage of mires brings about changes inthe properties of the peat and hence in thefunctioning of the peatland ecosystem.Processes induced by drainage includeamong others 105 :● subsidence, i.e. the lowering of the surface,● shrinkage and swelling, and increased soilloosening by soil organisms,● increased mineralisation (conversion oforganic material to mineral substances).As peat largely consists of water 106 , drainageof peatlands leads to subsidence 107 and peatoxidation 108 and compaction. Consequentlythe hydraulic properties 109 (those whichgovern water movement) of the peats change.This may decrease the peatland’s capacities