Quantification of Peat Thickness and Stored Carbon at the Landscape Scale in Tropical Peatlands: A Comparison of Airborne Geophysics and an Empirical Topographic Method

Abstract

Peatlands play a key role in the global carbon cycle, sequestering and releasing large amounts of carbon. Despite their importance, a reliable method for the quantification of peatland thickness and volume is still missing, particularly for peat deposits located in the tropics given their limited accessibility, and for scales of measurement representative of peatland environments (i.e., of hundreds of km2). This limitation also prevents the accurate quantification of the stored carbon as well as future greenhouse gas emissions due to ongoing peat degradation. Here we present the results obtained using the airborne electromagnetic (AEM) method, a geophysical surveying tool, for peat thickness detection at the landscape scale. Based on a large amount of data collected on an Indonesian peatland, our results show that the AEM method provides a reliable and accurate 3‐D model of peatlands, allowing the quantification of their volume and carbon storage. A comparison with the often used empirical topographic approach, which is based on an assumed correlation between peat thickness and surface topography, revealed larger errors across the landscape associated with the empirical approach than the AEM method when predicting the peat thickness. As a result, the AEM method provides higher estimates (22%) of organic carbon pools than the empirical method. We show how in our case study the empirical method tends to underestimate the peat thickness due to its inability to accurately detect the large variability in the elevation of the peat/mineral substrate interface, which is better quantified by the AEM method.

Global peatland area and carbon dynamics from the Last Glacial Maximum to the present – a process-based model investigation

“…Despite their global importance, peat research has long focused almost exclusively on northern high-latitude peatlands with about 80 % of dated peat cores taken in Europe and North America, which only covers roughly 40 % of global peat area (Xu et al, 2018;Treat et al, 2019). Although research on tropical peatlands has increased in recent years (e.g., Page et al, 2011;Dommain et al, 2011Dommain et al, , 2014Lawson et al, 2015;Silvestri et al, 2019;Gumbricht et al, 2017;Cobb and Harvey, 2019;Leng et al, 2019;Illés et al, 2019), our understanding about tropical peatlands, including their dynamics and life cycles, is still limited. This also entails ongoing new discoveries of previously unknown peatland complexes such as in the Congo Basin (Dargie et al, 2017).…”

Airborne Electromagnetic and Radiometric Peat Thickness Mapping of a Bog in Northwest Germany (Ahlen-Falkenberger Moor)

“…The next step was to analyze the airborne electromagnetic (HEM) data in order to derive estimates for the location of the peat base. This interface should be detectable, if the resistivity of peat differs significantly from the resistivity of the substrate [11][12][13][14]. The resulting peat thickness could then be used to scale the HRD data (exposure rate).…”

“…Puranen et al [11] and Airo et al [7] published results from Finland, and Beamish and Farr [12] from Wales, using fixed-wing frequency-domain systems. More recently, Silvestri et al [13,14] presented peat thickness results acquired by helicopter-borne time-domain electromagnetic devices in Norway and Indonesia.…”

The Least Square Adjustment for Estimating the Tropical Peat Depth Using LiDAR Data

“…Another method used to characterize bedrock is to use a geophysical (radiometric) method that include both airborne and ground-based geophysical systems. The newest example in the use of airborne systems is the application Airborne Electromagnetic (AEM) to quantify peat thickness of tropical peatlands [15]. Ground-based systems include the use of Gamma-Ray Spectrometer (GRS) and…”

“…The use of GPR produced peat depth data that give an excellent correlation to the manual drilling method [17], which can reduce the survey time. However, the use of ground-based systems does not provide information about surface elevation [15]. This method does not disturb the peat ecosystem, but this measurement is considered expensive and time consuming [17].…”