wise use of mires and peatlands - Peatland Ecology Research Group
wise use of mires and peatlands - Peatland Ecology Research Group
wise use of mires and peatlands - Peatland Ecology Research Group
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APPENDIX 2197A2.3 THE ROLE OF PEATLANDSDRAINED FOR AGRICULTUREWhen virgin peatl<strong>and</strong>s are converted toagriculture, the natural biomass is replacedby crop biomass. This may result insubstantial changes in the biomass carbonstore, e.g. when tropical forested peatl<strong>and</strong>sare converted to vegetable or rice fields. Areclamation <strong>of</strong> non-forested virgin peatl<strong>and</strong>to grassl<strong>and</strong>s <strong>and</strong> arable fields will generallynot lead to large biomass or litter changes 39 .The dominant effect <strong>of</strong> peatl<strong>and</strong> drainage foragriculture is that the peat gets exposed tooxygen which leads to peat mineralisation,i.e. a decrease in the peat carbon store, <strong>and</strong>an increased emission <strong>of</strong> carbon dioxide,especially in the summer months 40 .Under grassl<strong>and</strong>, drained bogs <strong>and</strong> fens inthe boreal <strong>and</strong> temperate zones emit about2,500 <strong>and</strong> 3,500 kg C ha -1 year -1 as CO 2respectively (Table A2/6). Water table depthdoes not substantially influence themagnitude <strong>of</strong> these emissions. The highestmineralisation rate is observed with a watertable depth <strong>of</strong> 80 - 90 cm 41 , whereas depths <strong>of</strong>17 - 60 cm already lead to 80 % <strong>of</strong> the maximumvalue 42 . At water levels deeper than 90 cm,drought inhibits peat mineralisation again 43 .Under tillage, peat mineralisation isaccelerated as compared to grassl<strong>and</strong> due tomore intensive aeration. CO 2emission ratesin arable fens are higher than in bogs (TableA2/7).Methane emissions from drained peatl<strong>and</strong>sare generally very low (Table A2/8), thoughemissions <strong>of</strong> up to 21 kg CH 4-C ha -1 year -1have been observed in bogs. Drained fensemit less methane than bogs <strong>and</strong> functionmore frequently as net sinks for atmosphericmethane.Region CO 2emission in kg C ha -1 y. -1bogsfensFinl<strong>and</strong> 44 1500 – 2500 3140Canada 45 1910North-east Germany 46 2800 - 6580North-west Germany 47 0 – 4840 2 4119 - 4318Sweden 48 3500Median 2350 3465Table A2/6: CO 2emissions from drained peatl<strong>and</strong>s <strong>use</strong>d as grassl<strong>and</strong>.Region CO 2emission in kg C ha -1 y. -1bogsfensNorth West Germany 50 4400 13200South Germany 51 6600-9900Pol<strong>and</strong> 52 11220Median 4400 10560Table A2/7: CO 2emissions from drained peatl<strong>and</strong>s <strong>use</strong>d as arable l<strong>and</strong> 49 .
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