Net ecosystem CO2 exchange measured by autochambers during the snow-covered season at a temperate peatland

✍ Scribed by Jill Bubier; Patrick Crill; Andrew Mosedale

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 873 KB
• Volume: 16
• Category: Article
• ISSN: 0885-6087
• DOI: 10.1002/hyp.1233

✦ Synopsis

Abstract

Net ecosystem exchange of CO~2~ was measured at a temperate peatland in southeastern New Hampshire. Classified as a mineral‐poor fen owing to deep, water‐logged peats that are influenced to a limited extent by groundwater, the ecosystem is dominated by plants such as sedges (Carex spp.) and evergreen shrubs. Ten automatic chambers measured fluxes every 3 h by sampling changes in headspace concentration of CO~2~ from November 2000 through March 2001. The fen was covered in snow for most of this period and CO~2~ was emitted from the snow pack throughout the winter. The largest fluxes were associated with ground temperatures of 0°C and with declining atmospheric pressure. CO~2~ effluxes up to 3 µmol m^−2^ s^−1^ were recorded when the ground temperature reached the thaw point. Fluxes were lower when the ground temperature rose above 0°C, however, suggesting that the large fluxes were associated with a build up and release of stored CO~2~ degassing as soon as the ground thawed, or by enhanced microbial activity associated with freeze–thaw dynamics. The large number of thaw events coupled with frequent short‐term releases of CO~2~ suggest that degassing occurred on a regular basis with changes in atmospheric pressure and/or microbial decomposition occurred beneath the snowpack. The extent of soil freezing prior to thaw was also an important factor, with colder soils yielding smaller CO~2~ emissions upon thaw. Although most of the observed CO~2~ flux was efflux from the ecosystem, occasional CO~2~ uptake by the ecosystem of up to 1 µmol m^−2^ s^−1^ was also observed, indicating small rates of photosynthesis even during winter. Photosynthesis occurred only when the ground temperature was >0°C. The implications for a warmer climate are unclear. If warmer winter temperatures yield less snow in the temperate region, then soils could freeze more deeply and result in lower CO~2~ emissions. However, if less snow results in a higher frequency of freeze–thaw events, then winter CO~2~ emissions could be larger with a warmer climate. Copyright © 2002 John Wiley & Sons, Ltd.