Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 7 2009 10.5194/bg-6-1311-2009 http://www.biogeosciences.net/6/1311/2009/ http://www.biogeosciences.net/6/1311/2009/bg-6-1311-2009.html http://www.biogeosciences.net/6/1311/2009/bg-6-1311-2009.pdf 1311 1324 2009-07-30 Soil, plant, and transport influences on methane in a subalpine forest under high ultraviolet irradiance D. R. Bowling bowling@biology.utah.edu J. B. Miller M. E. Rhodes S. P. Burns R. K. Monson D. Baer Department of Biology, 257 South 1400 East, University of Utah, Salt Lake City, UT, 84112-0840, USA National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Boulder, CO, 80305, USA Cooperative Institute for Research in Environmental Science, University of Colorado, Boulder, CO, 80309, USA National Center for Atmospheric Research, Boulder, CO, 80305, USA Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, 80309, USA Los Gatos Research, Mountain View, CA, 94041, USA Recent studies have demonstrated direct methane emission from plant foliage under aerobic conditions, particularly under high ultraviolet (UV) irradiance. We examined the potential importance of this phenomenon in a high-elevation conifer forest using micrometeorological techniques. Vertical profiles of methane and carbon dioxide in forest air were monitored every 2 h for 6 weeks in summer 2007. Day to day variability in above-canopy CH₄ was high, with observed values in the range 1790 to 1910 nmol mol^−1. High CH₄ was correlated with high carbon monoxide and related to wind direction, consistent with pollutant transport from an urban area by a well-studied mountain-plain wind system. Soils were moderately dry during the study. Vertical gradients of CH₄ were small but detectable day and night, both near the ground and within the vegetation canopy. Gradients near the ground were consistent with the forest soil being a net CH₄ sink. Using scalar similarity with CO₂, the magnitude of the summer soil CH₄ sink was estimated at ~1.7 mg CH₄ m^−2 h^−1, which is similar to other temperate forest upland soils. The high-elevation forest was naturally exposed to high UV irradiance under clear sky conditions, with observed peak UVB irradiance >2 W m^−2. 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