INFLUENCE OF WATER-TABLE ON CARBON-DIOXIDE, CARBON-MONOXIDE, AND METHANE FLUXES FROM TAIGA BOG MICROCOSMS

Hydrological changes, particularly alterations in water table level, may largely overshadow the mole direct effects of global temperature increase upon carbon cycling in arctic and subarctic wetlands. Frozen cores (n=40) of intact soils and vegetation were collected from a bog near Fairbanks, Alaska, and fluxes of CO2, CH4, and CO in response to water table variation were studied under controlled conditions in the Duke University phytotron. Core microcosms thawed to a 20-cm depth over 30 days under a 20 hour photoperiod with a day/night temperature regime of 20/10 degrees C. After 30 days the water table in 20 microcosms was decreased from the soil surface to -15 cm and maintained at the soil surface in 20 control cores. Outward fluxes of CO2 (9-16 g m(-2) d(-1)) and CO (3-4 mg m(-2) d(-1)) were greatest during early thaw and decreased to near zero for both gases before the water table treatment started. Lower water table tripled CO2 flux to the atmosphere when compared with control cores. Carbon monoxide was emitted at low rates from high water table cores and consumed by low water table cores. Methane fluxes were low (<1 mg m(-2) d(-1)) in all cores during thaw. High water table cores increased CH4 flux to 8-9 mg m(-2) d(-1) over 70 days and remained high relative to the low water table cores (<0.74 mg m(-2) d(-1)). Although drying of wetland taiga soils may decrease CH4 emissions to the atmosphere, the associated increase in CO2 due to aerobic respiration will likely increase the global warming potential of gas emissions from these soils.