1. Arne Grønlund and Daniel P. Rasse Norwegian Institute for Agricultural and Environmental Research Division for Soil and Environment Carbon loss from cultivated peat soils in Norway

2. Cultivated peat soils in Norway Cover 7-10 % of agricultural soils in Norway Uneven distribution due to climate conditions: –2-3 % in south-east –12-15 % in north and west Subsidence and C-loss has been known for a century –An agricultural problem –Relation to climate change and greenhouse gas emission the last 2 years in Norway No systematic/extensive survey of C-loss from cultivated peat soils in Norway Rough estimates can be obtained

3. Estimates from 3 methods are compared 1.Long-term monitoring of peat subsidence 2.Changes in ash contents 3.Soil CO 2 flux measurements

4. 1. Monitoring of peat subsidence Subsidence includes: –Compaction –Soil loss Data required for calculating C loss: –Initial and final bulk density –Initial and final C-concentration Not always available Assumptions: 50 % of the subsidence due to C loss Mean C concentration 40 % Estimated loss: 0.77 kg C (2.85 kg CO 2 ) m -2 y -1 Material from a study in western Norway: 11 fields – 1300 observation points – 30 years Mean annual subsidence 1.86 cm

5. 2. Changes in ash (mineral) contents Assumption: Increase in mineral content is due to: –C loss –Lime and fertilizer application

6. 2. Changes in ash contents The OM loss can be calculated from the equation: MF fin = measured final mineral content MF ini = measured initial mineral content (can be estimated from adjacent uncultivated peat) BD fin = final bulk density Thick = layer thickness Not required: Initial bulk density Bulk density of deeper layers Subsidence measurements

7. 2. Changes in ash contents Calculations based on material from the mentioned study in western Norway: 11 fields – 1300 observation points – 30 years Available data: –Final mineral content –Initial mineral content –Final bulk density Assumptions: –Thickness of the influenced layer was assumed to be 20 cm –Correction for increase of lime content: 0.4 % CaO (mean value from the soil database) Results: Final mineral content: 11.1 % - Initial mineral content 4.5 % - Increased lime content: 0.4 % = Increase due to degradation: 6.2 % Estimated carbon loss:0.75 kg C (2.75 kg CO 2 ) m -2 y- 1

8. 3. Soil CO 2 flux measurements Small chambers (25 x 25 cm) Sampling interval: 2 weeks Period: August 2003 – November 2004 (Not December- March)

9. 3. Soil CO 2 flux measurements Results kg C m -2 y -1 Gross respiration (emission)1.15 + Yield removed0.38 - Gross photosynthesis*0.94 = Net C loss (ecosystem balance)0.6 (2.2 kg CO 2 ) *Estimated from: net plant producivity/above ground net plant productivity (NPP/ANPP=1.4) net plant productivity/gross plant productivity (NPP/GPP=0.55)

10. Assessment of the 3 methods 1.Monitoring of peat subsidence 2.Changes in ash contents 3.Soil CO 2 flux measurements Advantages Disadvantages High precision of total long-term C loss Initial data and long term monitoring required Cheap – few parameters required Less precision expected Uniform peat layer a precondition Temporal variability of CO 2 loss Relation to other greenhouse gases More expensive Many replicates necessary Photosynthesis estimates required

11. Comparison of the results 1.Monitoring of peat subsidence: 0.77 kg C m -2 y -1 2.Changes in ash contents: 0.75 kg C m -2 y -1 3.Soil CO 2 flux measurements: 0.6 kg C m -2 y -1 Likely estimate:0.6 – 0.8 kg C m -2 y -1

12. Total losses fram cultivated peat soils Cultivated peatlands the last 100 years in Norway: –150,000 – 200,000 ha (15-20 % of cultivated area) From the soil database: –Organic soils: 6.3 % of soil samples, whereof 2/3 have 20-40 % SOM (mixed mineral-organic soil) Estimated peat area in agricultural use: 70,000- 100,000 ha Estimated total annual carbon loss from cultivated peatlands: –2 - 4 million tons CO 2 y -1, –5 - 10 % of the total human induced CO 2 emission The emission will be reduced as the peat is converted to mineral soils

13. Mitigation measures Limited options for areas under cultivation: –>90 % used for grass production –Raising ground water table hardly feasible Restoration of abandoned cultivated peatland Natural processes –Shallow peat soils over bedrock or stone rich moraine –Too low slope for further drainage –Difficult drainage because of low permeability Deliberate actions –Commitments to WTO can lead to surplus of cultivated land - Unfavourable climate conditions –Encouragements for set aside land and C sequestration Options –No management - high ground water table –Deep/shallow drainage –Afforestation/bioenergy production Main challenge: –minimize CH 4 emission

14. Conclusions Little attention to cultivated peat soils as a source of CO 2 emission No systematic survey of C loss has been conducted Calculations by three methods indicate a loss of –0.6 – 0.8 kg C m 2 y -1 –2 - 4 million tons CO 2 y -1 –5-10 % of the total human induced CO 2 emission in Norway Future challenge: –Restoration of abandoned cultivated peatlands –Maximize C accumulation and minimize CH 4 emission

15. Thank you for your attention