Mitigation of Greenhouse Gas Fluxes from Cultivated Organic Soils by Raised Water Table

MITIGATION OF GREENHOUSE GAS FLUXES FROM CULTIVATED ORGANIC SOILS BY RAISED WATER TABLE

Kristiina Regina

Agrifood Research Finland, Plant Production Research, Finland

E-mail:

Cultivated organic soils are a remarkable source of greenhouse gases (GHG) in some countries

and raised ground water table has been suggested as a mitigation measure on these soils.

Drainage of the peat increases mineralization of the organic matter and causes high emissions

of carbon dioxide (CO2) and nitrous oxide (N2O) while emissions of methane (CH4) are lowered

compared to pristine peatlands. In countries with a large area of organic soils these GHG

emissions can be remarkable. In Finland, the area of cultivated organic soils is 12% of the

agricultural area but they cause 30% of the N2O emissions of agricultural soils reported under

the Climate Convention of the UNFCCC. Organic croplands are also the largest single emission

source of CO2 among the emissions reported in the land use sector. Best and Jacobs (1997)

reported a decrease in CO2 emissions and an increase in CH4 emissions with a WT raise from

30-54 cm to 7-27 cm in a grassland. Renger et al. (2002) estimated that by maintaining the

WT at 30 cm the peat mineralization could be reduced to 30-40% and the total GHG emissions

to 50-60% of the maximum.

Emissions of CO2 and N2O are known to be lower from grass cultivation than from arable crops

(Maljanen et al., 2007). A new form of agri-environmental subsidy encourages farmers to

change from cereal cultivation to grass cultivation on organic soils from 2009 on in Finland.

The proportion of cultivated organic soils used for grass cultivation was 45% in 2008. Increase

in the area under grass cultivation would enable larger areas with a higher WT since grass

cultivation is possible with a less effective drainage. We studied the effect of raised water table

on the emissions of N2O, CO2 and CH4 from undisturbed peat soil profiles of six different

cultivated organic soils. We hypothesized that it would be possible to determine an optimum

WT that would suit for grass cultivation but have lower than normal emissions of N2O and CO2

without an accompanying increase in CH4 emissions.

Raised water table decreased the greenhouse gas emissions from every peat type ranging

from weakly decomposed Sphagnum peat to highly humified Carex peat. The average

reduction of emissions with a raise of water table from 70 cm to 30 cm below the surface was

30% for CO2 and 74% for N2O. The sink of CH4 declined but the significance of that is small

and high emissions of CH4 are not expected unless the water table reaches 20 cm. The results

suggest that raising the WT could be used as a greenhouse gas mitigation tool in a wide range

of cultivated organic soils.

References

Best E.P.H & Jacobs F.H.H. (1997) The influence of raised water table levels on carbon dioxide

and methane production in ditch-dissected peat grasslands in the Netherlands. Ecological Engineering

8: 129-144.

Maljanen, M., Hytönen, J., Mäkiranta, P., Alm, J., Minkkinen, K., Laine, J. & Martikainen, P. J.

(2007) Greenhouse gas emissions from cultivated and abandoned organic croplands in Finland.

Boreal Env. Res. 12: 133–140.

Renger, M., Wessolek, G., Schwärzel, K., Sauerbrey, R. & Siewert, C. (2002) Aspects of peat

conservation and water management. J. Plant Nutr. Soil Sci. 165: 487-493. 69

NJF Report • Vol 6 • No 1 • Year 2010

NJF Seminar 430

Climate Change and Agricultural Production in the Baltic SeaRegion

- Focus on Effects, Vulnerability and Adaptation

Uppsala, Sweden, 4-6 May 2010

Nordic Association of Agricultural Scientists