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Large N₂O emissions from cryoturbated peat soil in tundra.

Nitrous oxide is a potent greenhouse gas whose concentration is increasing in the atmosphere; the highest emissions have been observed from agricultural and tropical soils. Now, measurements in subarctic East European tundra show that bare surfaces on permafrost peatlands, known as peat circles, release large quantities of nitrous oxide.

Repo Maija E, Susiluoto Sanna, Lind Saara, Jokinen Simo, Elsakov Vladimir,  Biasi Christina, Virtanen Tarmo &. Martikainen Pertti J. 2009. Nature Geoscience. doi:10.1038/ngeo434

The results were also published in Helsingin Sanomat 18.2.2009

http://www.hs.fi/kuvat/iso_webkuva/1135243612807.gif

This study explores the variability in concentrations of dissolved CH4 and annual flux estimates in the pelagic zone in a statistically defined sample of 207 lakes in Finland. We found that CH4 concentrations and fluxes to the atmosphere tended to be high in nutrient rich calcareous lakes, and that the shallow lakes had the greatest surface water concentrations. Methane concentration in the hypolimnion was related to oxygen and nutrient concentrations, and to lake depth or lake area. The surface water CH4 concentration was related to the depth or area of lake. Methane concentration close to the bottom can be viewed as proxy of lake status in terms of frequency of anoxia and nutrient levels.The mean pelagic CH4 release from randomly selected lakes was 49 mmolm−2 a−1. The sum CH4 flux (storage and diffusion) correlated with lake depth, area and nutrient content, and CH4 release was greatest from the shallow nutrient rich and humic lakes. Our results support earlier lake studies regarding the regulating factors and also the magnitude of global emission estimate. These results propose that in boreal region small lakes have higher CH4 fluxes per unit area than larger lakes, and that the small lakes have a disproportionate significance regarding to the CH4 release.

S. Juutinen, M. Rantakari, P. Kortelainen, J. T. Huttunen, T. Larmola, J. Alm, J. Silvola, and P. J. Martikainen. Biogeosciences, 6, 209–223, 2009

Cultivation of perennial grass for bioenergy use on a boreal organic soil – carbon sink or source?

The area under the cultivation of perennial bioenergy crops on organic soils in the northern countries is fast increasing. To understand the impact of reed canary grass (RCG, Phalaris arundinaceae L.) cultivation on the carbon dioxide (CO₂) balance of an organic soil, net ecosystem CO₂ exchange (NEE) was measured for four years in a RCG cultivated cutover peatland in eastern Finland using the eddy covariance technique. There were striking differences among the years in the annual precipitation. The annual precipitation was higher during 2004 and 2007 and lower during 2005 and 2006 than the 1971-2000 regional mean.  During wet growing seasons, moderate temperatures, high surface soil moisture and low evaporative demand favored high CO₂ uptake. During dry seasons, owing to soil moisture and atmospheric stress, photosynthetic activity was severely restricted. The CO₂ uptake (GPP) was positively correlated with soil moisture, air temperature and inversely with vapor pressure deficit. Total ecosystem respiration (TER) increased with increasing soil temperature but decreased with increasing soil moisture.  The relative responses of GPP and TER to moisture stress were different. While changes in TER for a given change in soil moisture were moderate, variations in GPP were drastic. Also, the seasonal variations in TER were not as conspicuous as those in GPP implying that GPP is the primary regulator of the interannual variability in NEE (net ecosystem CO₂ exchange) in this ecosystem. The ecosystem accumulated a total of 398 g C m^-2 from the beginning of 2004 until the end of 2007. It retained some carbon during a wet year such as 2004 even after accounting for the loss of carbon in the form of harvested biomass. Based on this CO₂ balance analysis, RCG cultivation is found to be a promising after-use option on an organic soil.

Shurpali N.J., Hyvönen N., Huttunen J.T., Clement R., Reichestein M., Nykänen H., Biasi C. & Martikainen P.J. 2009.  Global Change Biology Bioenergy. doi: 10.1111/j.1757.2009.01003.x