A flux-gradient system for simultaneous measurement of the CH4, CO2, and H2O fluxes at a lake-air interface.
Inland lakes play important roles in water and greenhouse gas cycling in the environment. This study aims to test the performance of a flux-gradient system for simultaneous measurement of the fluxes of water vapor, CO2, and CH4 at a lake-air interface. The concentration gradients over the water surface were measured with an analyzer based on the wavelength-scanned cavity ring-down spectroscopy technology, and the eddy diffusivity was measured with a sonic anemometer. Results of a zero-gradient test indicate a flux measurement precision of 4.8 W m(-2) for water vapor, 0.010 mg m(-2) s(-1) for CO2, and 0.029 μg m(-2) s(-1) for CH4. During the 620 day measurement period, 97%, 69%, and 67% of H2O, CO2, and CH4 hourly fluxes were higher in magnitude than the measurement precision, which confirms that the flux-gradient system had adequate precision for the measurement of the lake-air exchanges. This study illustrates four strengths of the flux-gradient method: (1) the ability to simultaneously measure the flux of H2O, CO2, and CH4; (2) negligibly small density corrections; (3) the ability to resolve small CH4 gradient and flux; and (4) continuous and noninvasive operation. The annual mean CH4 flux (1.8 g CH4 m(-2) year(-1)) at this hypereutrophic lake was close to the median value for inland lakes in the world (1.6 g CH4 m(-2) year(-1)). The system has adequate precision for CH4 flux for broad applications but requires further improvement to resolve small CO2 flux in many lakes.
Yale-NUIST Center on Atmospheric Environment, ‡Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, and §Jiangsu Key Laboratory of Agricultural Meteorology, Nanjing University of Information Science & Technology , Nanjing, Jiangsu 210044, China.
Wei
W
Xiao
Shoudong
S
Liu
Hanchao
H
Li
Qitao
Q
Xiao
Wei
W
Wang
Zhenghua
Z
Hu
Cheng
C
Hu
Yunqiu
Y
Gao
Jing
J
Shen
Xiaoyan
X
Zhao
Mi
M
Zhang
Xuhui
X
Lee
D002138:Calibration; D002245:Carbon Dioxide / Q000032:analysis*; D002681:China; D004784:Environmental Monitoring / Q000379:methods; D005068:Eutrophication; D060106:Lakes; D055904:Meteorology / Q000379:methods; D008697:Methane / Q000032:analysis*; D013057:Spectrum Analysis / Q000295:instrumentation / Q000379:methods*; D014867:Water / Q000032:analysis*
D014867:Water; D002245:Carbon Dioxide; D008697:Methane