Diurnal and seasonal variation of carbon dioxide exchange from a former true raised bog

Abstract

Carbon dioxide exchange was measured, using the eddy covariance technique, during a one and a half year period in 1994 and 1995. The measurements took place over a former true raised bog, characterized by a shallow peat layer and a vegetation dominated by Molinia caerulea. The growing season extended from May until late October, with a maximum LAI in August of 1.7. The carbon balance shows a net release of 97 g C m–2 y–1 (265 kg C ha–1 y–1) from the peat bog ecosystem to the atmosphere. During June, July and August there is net consumption of CO2, while during the rest of the year there is net production of CO2. The average daytime assimilation rates ranged between – 0.2 and – 0.5 mg CO2 m–2 s–1 (– 45 and –11.3 μmol CO2 m–2 s–1), in a period where the LAI ranged between 1 and 1.7. A high vapour pressure deficit (> 15 hPa) corresponding with high temperatures was found to reduce the assimilation rate by on average 50%. Apart from these factors, LAI and the soil temperature codetermine the net exchange of CO2. The total nocturnal respiration during the growing season lies within the same order as the average daytime net assimilation rate. Temperature was found to be the main factor controlling soil respiration, with a Q10 of 4.8.

A lysimeter study on the effect of temperature on CO2 emission from cultivated peat soils

“…Conditions in the New Zealand experiment were very similar to those in the present experiment in that watertable depth ranged between 0.2 and 0.8 m (in our experiment between 0.4 and 0.8 m) and the vegetation at their site was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). Other studies with water-logged conditions (Nieveen et al, 1998) report a lower R 10 of 1.3 µmol m -2 s -1 , indicating anaerobic conditions.…”

“…When the temperature increased from 10 to 23°C, Moore and Dalva (1993) recorded a 2.3-fold increase in CO 2 emissions from peat soil in a laboratory experiment. Q 10 values (the Q 10 temperature coefficient is a measure of the rate of change of a biological or chemical system as a consequence of increasing the temperature by 10 °C) between 2 and 3 have been reported by Blodau (2002), but both smaller (Scanlon and Moore, 2000;Waddington et al, 2001) and larger Thurlow, 1996,1998;Nieveen et al, 1998) values have been reported. Many emission studies have been conducted on disturbed peat samples, without vegetation or under uncontrolled conditions in the field, as pointed out by Blodau et al (2004), but none on undisturbed soil with vegetation cover and under controlled conditions.…”

Variability of annual CO<sub>2</sub> exchange from Dutch grasslands

“…peat) are often found to be sources for carbon dioxide (Nieveen et al, 1998;Nieveen et al, 2005;Lloyd, 2006;Veenendaal et al, 2007), while grasslands on mineral soils (for example, clay and sand) often show a net uptake for carbon dioxide (Gilmanov et al, 2007). Clearly it can be observed that the Fochtelooërveen, Haastrecht, Oukoop and Stein sites follow this rule for organic soils and the Haarweg and Horstermeer sites for mineral soils.…”

“…CO 2 fluxes were measured between June 1994 and October 1995. More details about this site can be found in Nieveen et al (1998) and Jacobs et al (2003b).…”

“…In peat areas where the water table is usually close to the ground surface, this phenomenon may then result in a close relation between the water table depth and respiration (Lloyd, 2006). In places with a less direct coupling between soil moisture content of the upper layer and the depth of the groundwater table, such a relation may be very weak or absent (Lafleur et al, 2005;Nieveen et al, 2005). For the Haarweg and Cabauw sites, observations from four complete years (2002)(2003)(2004)(2005) are available.…”