Addressing spatial and temporal variability of soil CO2 flux using an automated 16-chamber multiplexed system.
Madsen, Rodney1, Xu, Liukang1, McDermitt, Dayle*,1, Burba, George1, Garcia, Rick1, Demetriades-Shaw, Tanvir1, Scoby, David2, Arkebauer, Timothy2, 1 LI-COR Biosciences, Lincoln, NE2 University of Nebraska, Lincoln, NE
ABSTRACT- High spatial and temporal variability of soil CO2 flux information is essential to understanding how environmental (soil moisture, rain events, temperature, etc.) and biological (photosynthesis, LAI, etc.) factors regulate soil CO2 flux. We have developed a 16-port automated multiplexing system. It can cover an area with a radius of 17 m. As we know soil CO2 flux is driven primarily by the CO2 diffusion gradient across the soil surface. The flux measurement should be made without affecting the diffusion gradient and without having any chamber induced pressure perturbation. An improperly designed chamber may have the problem of chamber induced pressure perturbation during the measurement under windy conditions, due to the Venturi effect. This could lead to a magnitude high overestimation of the flux. We are presenting a new chamber vent design capable of maintaining pressure equilibrium between the inside and outside of the chamber under both calm and windy conditions. Also, to minimize the impact of decreased CO2 diffusion gradient on the CO2 flux measurement, the chamber CO2 concentration vs. time is fitted with an exponential function. The soil CO2 flux is estimated by calculating the initial slope from the exponential function at time zero when the chamber closes. Our results indicate that the flux estimated from a linear function can significantly underestimate CO2 flux as compared with the exponential function. High spatial and temporal resolution soil CO2 flux data obtained with our Multiplexing System in an agricultural field at the University of Nebraska Agricultural Experimental Station in Mead NE will be presented.
Key words: soil co2 flux, exponential function, multiplexing system
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