A SYSTEM FOR MEASURING INSITU CO2 AND CH4 FLUX IN UNMANAGED ECOSYSTEMS - AN ARCTIC EXAMPLE

1. A passive, rapid response, closed system was developed to measure in situ ecosystem CO2 and CH4 flux in 0.5-m2 plots over diurnal, seasonal, and annual time scales in arctic tundra ecosystems. The system consists of a chamber measuring 0.75 m on a side, 0.3 m in height, with acrylic sides, a mylar top, and 6-10 cm radial fans to ensure thorough mixing of the chamber environment. 2. CO2 concentration and flux rates were measured using a Li-Cor 6200 Portable Photosynthesis System, which is capable of measuring 0.1 p.p.m. s-1 changes in CO2 concentration. CH4 flux rates were measured by sequential sampling of the CH4 concentration in the chamber over the duration of a 15-20-min incubation period. 3. Performance analyses indicate that light attenuation was less-than-or-equal-to 10% of ambient light. The rate of temperature increase within the chamber over the duration of the measurement period was approximately 1-5-degrees-C and 0.2-degrees-C for the majority of the sampling days at tussuck tundra and wet coastal tundra sites, respectively. The maximum increase in thaw depth due to the bases was approximately 10%, and was a function of the site water balance and the amount of time that the bases were in place. Generally, thaw depth in plots with bases was greater when the bases were in place for a longer period of time (greater-than-or-equal-to 1 year), while the bases that were installed during the current growing season had a small effect on plot thaw depths. 4. The system had a minimal effect on ecosystem CO2 flux, compared to plots that lacked bases in a wet coastal tundra and southern California turf ecosystem. 5. The system was successfully used to measure the effect of light intensity, soil temperature, and water balance on ecosystem CO2 flux. 6. Due to the rapid response of the system, high sensitivity to low flux rates, high portability, low cost, potential for use in field experiments, and non-invasive sampling design, the system allows for the reliable measurement of CO2, CH4, and other trace gas flux rates in a variety of ecosystem types.