CONTROLS ON CH4 FLUX FROM AN ALASKAN BOREAL WETLAND

Factors controlling the flux of the radiatively important trace gas me thane (CH4) from boreal wetlands were examined at three sites along a moisture gradient from a treed low-shrub bog to an open floating grami noid bog in Fairbanks, Alaska. In the summer of 1992 average static ch amber flux measurements were -0.02, 71.5, and 289 mg CH4/m(2)/d in dry , wet, and floating mat communities, respectively. In contrast, the wa rmer, drier 1993 field season flux measurements were -0.02, 42.9 and 4 07 mg CH4/m(2)/d. The data indicate that despite net oxidation of CH4 in the dry regions of the bog, the wetland is a net source of CH4, wit h fluxes ranging across three orders of magnitude between different pl ant communities. Comparison with water levels suggests that CH4 flux i s turned on and off by changes in site hydrology. In sites where suffi cient moisture is present for methanogenesis to occur, CH4 flux appear s to be temperature limited, responding exponentially to soil temperat ure changes. The combined effects of hydrology and temperature create hot spots of CH4 flux within boreal wetlands. The plant communities wi thin Lemeta Bog respond differently to changes in temperature and mois ture availability, creating both positive and negative feedbacks to po tential global climate change.