MITIGATION OF GREENHOUSE GAS FLUXES FROM CULTIVATED ORGANIC
SOILS BY RAISED WATER TABLE
Kristiina Regina
Agrifood Research Finland, Plant Production Research, Finland
E-mail: kristiina.regina@mtt.fi
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 N 2O 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