PARENT SESSION
Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.

Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Comparison of closed-path and open-path eddy covariance systems over a Florida scrub oak ecosystem.

Powell, Thomas^*,1, Bracho, Rosvel², Hinkle, Ross³, Drake, Bert¹, ¹ Smithsonian Environmental Research Center, Edgewater, MD² National Research Council, Kennedy Space Center, FL³ Dynamac Corporation, Kennedy Space Center, FL

ABSTRACT- Eddy covariance using a closed-path infrared gas analyzer (IRGA) has been a useful tool for making composite measurements of ecosystem gas exchange. Recently an open-path IRGA has become available as an alternative to the closed-path IRGA to circumvent concerns over flux loss associated with sampling tubes and sensor response. From November 2002 through February 2003, measurements comparing the two different eddy covariance systems were made above a scrub oak ecosystems in central Florida. System one was comprised of a Gill R3 anemometer and a LI-COR closed-path IRGA (LI-6262). System two was comprised of a Campbell Scientific CSAT3 anemometer and a LI-COR open-path IRGA (LI-7500). Wind statistics and mean maximum half-hour fluxes for daytime net ecosystem exchange (NEE) and sensible heat were all within 2% between the two systems. However, latent energy (LE) for the open-path system was 35% greater (R² = 0.89) than the closed-path system. The open-path system also achieved a greater level of energy closure, a problem chronic to eddy covariance measurements, when compared to an independent measurement of net radiation. When the two IRGAs where collocated on the CSAT3 anemometer, there was less than a 1% difference (R² = 0.99) in NEE, but the difference in LE was still considerable at 18% (R² = 0.90). These results provide a benchmark for comparing eddy covariance measurements from multiple sites by enabling us to ensure that any differences in ecosystem fluxes are attributable to ecological differences and not to instrumentation.

Key words: infrared gas analyzer, net ecosystem exchange, eddy covariance, latent energy