Evaluation of the relaxed eddy accumulation coefficient at various wetland ecosystems

Abstract

Field measurements at various wetland ecosystems were conducted to investigate the coefficients b for different scalars in the relaxed eddy accumulation method. These measurements were performed at paddy, marsh and lagoon fields using the eddy covariance system to collect data with a sampling rate of 10 Hz. Without the application of a wind deadband, the mean median values of b were found to be 0.55 for paddy, 0.57 for marsh and 0.56 for lagoon for all scalar quantities under unstable and near-neutral conditions. However, the median values of b under stable conditions steadily increase with stability. The results of estimated b were well described by proposed relationships as a function of the dimensionless stability parameter z/L. Scalar similarity between carbon dioxide, temperature and water vapor showed a distinct diurnal pattern and change within the day where good scalar correlations were observed at paddy and marsh during daytime, but poor scalar correlations were observed at lagoon. With the application of wind deadband, the reductions of the normalized b factors, bREA, related to the increase of deadband values were evaluated and the results were compared with the reported relationships in the literature. The relative minimal variability of the normalized bREA was found when the wind deadband was equal to 0.8. From the diurnal variation of bREA, the relative maximum values of bREA factors occurred around noon, and lower values were observed in the early morning and late afternoon. Daily median b0 values for various scalars under unstable and neutral conditions over paddy from the beginning to the end of the study period were used to verify the independence of the variations in surface roughness.