Increased decomposition of subsurface peat in Swedish raised bogs:are temperate peatlands still net sinks of carbon?

• Main Author: L.G. Franzén
• Format: Article
• Language: English
• Published: International Mire Conservation Group and International Peat Society 2006-02-01
• Series: Mires and Peat
• Subjects: anthropogenic dust; carbon balance; net CO2 source; fertilizing; secondary decomposition
• Online Access: http://www.mires-and-peat.net/map01/map_1_3.pdf

An increased rate of decomposition has been observed in a large number of raised bogs in southern Sweden and elsewhere since the 1970s. The effect is manifest as a discoloured and mucous subsurface peat layer, and there is associated subsidence of mire surfaces. This paper reports the results of a systematic investigation of the phenomenon in 14 raised bogs in southern Sweden, which was carried out between 1997 and 2005. Degree of decomposition, bulk density and ash content were measured and evidence of surface subsidence over recent decades was collected. Shallow peat layers of ‘normal’ appearance could not be found anywhere within the study sites, and all showed the same signs of secondary decomposition. In particular, the ombrotrophic parts of the Komosse Bog Complex appeared to have subsided by at least 150 mm over the last 35 years, i.e. at a rate of approximately 4.3 mm per annum, which is more than four times the average rate of peat formation in circumboreal raised bogs. The changes observed could have been caused by change in any one of a number of factors, e.g. climate, hydrology and rate of nutrient supply; or by a combination of such factors. However it seems most likely that they are attributable to the heavy modern nutrient load, e.g. of dust from anthropogenic sources. There is cause for concern that many high-latitude peatlands may consequently have switched over from being net sinks, to net sources, of atmospheric carbon.