PARENT SESSION
Poster Session #45: Gas Exchange.
Friday, August 10, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Simultaneous Measurement of CO₂, N₂O, and NO_x Fluxes from Cryptobiotic Soil Crusts.

Bradley, Kimberly¹, Weber, Jeffrey², Stedman, Donald², Sanford, Robert², ^{1 2}

ABSTRACT- In order to better understand the role of the biosphere in the formation and removal of atmospheric trace gases, we have developed two measurement systems designed to quantify the surface emission and deposition rates of CO₂, CO, CH₄, N₂O, NH₃, and NO_x. These measurement systems are based on Fourier transform infrared (FTIR) spectroscopic techniques coupled with multipass optics, a NO_x detector, and either an automated flux chamber or a large, chamber-like enclosure. Such systems have several advantages over other flux measurement techniques, including: (1) the ability to make simultaneous measurements of a variety of trace gases; (2) the ability to make continuous measurements during the closed-chamber period, allowing detection of nonlinear concentration changes and system disturbances; (3) the ability to monitor the results of measurements in real-time while in the field; and (4) good sensitivity, precision, and accuracy for most species. Here, we present results from studies of trace gas fluxes from soils with cryptobiotic surface crusts at Canyonlands National Park, Utah. Using the automated flux chamber design prototype, we have measured daytime CO₂ and CH₄ fluxes (emission of 3.82±1.25 g CO₂-C m^-2 s^-1 and uptake of 14.7±5.4 ng CH₄-C m^-2 s^-1) that are in good agreement with previous studies of desert soils. In addition, we have determined an upper bound on the N₂O flux (emission less than 7.1 ng N₂O-N m^-2 s^-1), and identified a substantial NO_x pulse (emission of 4.37±1.64 ng NO_x-N m^-2 min^-1) following wetting.

KEY WORDS: gas exchange, cryptobiotic crust, FTIR, chamber