Influence of water table levels on CO 2 emissions in a Colorado subalpine fen: an in situ microcosm study

Abstract

We quantified the relationship between water table position and CO 2 emissions by manipulating water table levels for two summers in microcosms installed in a Colorado subalpine fen. Water levels were manipulated in the microcosms by either adding water or removing water and ranged from +10 cm above the soil surface to 40 cm below the soil surface, with ambient water levels in the fen averaging +3 and +2 cm above the soil surface during 1998 and 1999, respectively. Microcosm installation had no significant effect on CO 2 efflux; the 2 year means of natural and reference CO 2 efflux were 205.4 and 213.9 mg CO 2-C m −2 h −1, respectively ( p=0.80). Mean CO 2 emissions were lowest at the highest water tables (water +6 to +10 cm above the soil surface), averaging 133.8 mg CO 2-C m −2 h −1, increased to 231.3 mg CO 2-C m −2 h −1 when the water table was +1 to +5 cm above the soil surface and doubled to 453.7 mg CO 2-C m −2 h −1, when the water table was 0–5 cm below the soil surface. However, further lowering of the water table had little additional effect on CO 2 emissions, which averaged 470.3 and 401.1 mg CO 2-C m −2 h −1 when the water table was 6–10 cm, and 11–40 cm beneath the soil surface, respectively. The large increase in CO 2 emissions as we experimentally lowered the water table beneath the soil surface, coupled with no increase in CO 2 emissions as we furthered lowered water tables beneath the soil surface, suggest the presence of an easily oxidized labile carbon pool near the soil surface.