Spatial patterns of greenhouse gas emission in a tropical rainforest in Indonesia

Spatial patterns of CO2, CH4, and N2O flux were analyzed in the soil of a primary forest in Sumatra, Indonesia. The fluxes were measured at 3-m intervals on a sampling grid of 8 rows by 10 columns, with fluxes found to be below the minimum detection level at 12 points for CH4 and 29 points for N2O. All three gas fluxes distributed log-normally. The means and standard deviations of CO2 and CH4 fluxes calculated by the maximum likelihood method were 3.68 ± 1.32 g C m-2 d-1 and 0.79 ± 0.60 mg C m-2 d-1, respectively. The mean and standard deviation of N2O fluxes using a maximum likelihood estimator for the censored data set was 2.99 ± 3.26 microgram N m-2 h-1. The spatial dependency of CH4 fluxes was not detected in 3-m intervals, while weak spatial dependency was observed in CO2 and N2O fluxes. The coefficients of variation of CH4 and N2O were higher than that of CO2. Some hot spots where high levels of CH4 and N2O were generated in the studied field may increase the variability of these gases. The resulting patterns of variability suggest that sampling distances of >10 m and > 20 m are required to obtain statistically independent samples for CO2 and N2O flux in the studied field, respectively. But because of weak or no spatial dependency of each flux, a sampling distance of more than 10 m intervals is enough to prevent a significant problem of autocorrelation for each flux measurement.