Quantification of the organic carbon pool of a large Indonesian peatland using an airborne geophysical method and comparison to an empirical topographic approach

The precise quantification of peat deposits at local to global scale is of key importance for the implementation of adequate conservation policies of peatlands. To this end, new remote sensing applications are needed, that provide high resolution data sets at regional scale. In this presentation, we present the results obtained using Airborne Electromagnetics (AEM) to estimate peat thickness and carbon content of a large peatland site located in Indonesia. The effectiveness of the AEM method for assessing peat thickness and volumes, and in turn carbon stocks, is tested by comparing the results to ground-truth measurements. Our results show that the AEM method can detect both the top and the bottom of a peatland profile over a clay substrate at high spatial resolution, allowing for an accurate three-dimensional morphological description of the peat body. The AEM method performs extremely well along the flight lines, where the instrument clearly detects the peat layer and differentiates it from the underlying mineral substrate. Moving away from the flight lines, the accuracy slightly decreases because the interpolation of the AEM data does not fully capture the highly variable morphology of the peat bottom. We conclude that in varying dome conditions, a high flight line density is preferable to describe the spatial distribution of the peat layer. Once the volume of the peatland is determined, the average organic carbon content by soil volume retrieved from field campaigns and laboratory analyses is used to estimate the total organic carbon stored in the peatland.

The results obtained with the AEM method are compared to those obtained with an empirical method that uses the soil topography to predict the thickness of the peatland. This empirical approach is based on the analyses of several previous studies available from the literature that show how it is common for some dome-shaped peatlands to present a linear correlation between peat thickness and soil topography. In this study, we show that the linear correlation is site-specific, and when used for prediction purposes, it provides incorrect peat volume estimates when it is extended to other sites or over large territories. When compared to the AEM method, our results show that the AEM method is superior in detecting the peat morphology and volume.