Estimating peat thickness by using airborne geoscanning

Introduction

The conservation of peatlands is one of the main measures indicated by the Intergovernmental Panel on Climate Change to mitigate climate change (Intergovernmental Panel on Climate Change, 2014). Peatlands, in fact, are extraordinary deposits of organic carbon, and their protection is of key importance in order to avoid emissions due to degradation (Ballhorn et al., 2009; Page et al., 2002; Turetsky et al.,2015). Peat is a mixture of organic material produced by wetland plants and accumulated in the soil when continuously or cyclically anaerobic conditions are present for long periods. Peatlands can be found over a wide range of latitudes, in tropical, to temperate, to (sub)polar climates.

Despite the importance of peatlands as carbon reservoirs, a reliable methodology for the detection of peat volumes at regional scale is still missing. In this study we explore for the first time the use of airborne electromagnetic (AEM) to detect and quantify peat thickness and extension of two bogs located in Norway, where peat lays over resistive bedrock. Our results show that when calibrated using a small amount of field measurements, AEM can successfully detect peat volume even in less ideal conditions, that is, relatively resistive peat over resistive substrata. We expect the performance of AEM to increase significantly in presence of a conductive substratum without need of calibration with field data.

Conclusion

Conservation actions targeted at avoiding potential greenhouse gas emissions from peatlands require accurate assessment of the carbon stored in peatlands at the regional to the global scale, and hence, a reliable method to quantify peat thickness and volume is essential. However, despite their importance, the accurate quantification of peatlands extension and volume is still lacking.

Airborne Electromagnetic has been used in this study to determine the presence, thickness and extension of peat deposits in a Norwegian territory rich in wetlands. We found that peat resistivity of bogs is variable, increasing from the surface to the bottom of the bogs.

Despite peat deposits are often located over clay (which is characterized by extremely low resistivities), in this study the AEM did not detect any significant conductive strata indicative of clay layers underneath the peats. On the contrary, the resistivity of the bottom layers has been found to be higher than the resistivity of the peat, corresponding to bedrock or moraine material. If an underlying layer of clay was present, as suggested by some samples collected during the field survey, we speculate it was too thin to be detected by the AEM system. However, further inspections are needed to confirm this hypothesis.

Acknowledgement

This research is part of the project CReScenDo (Combining Remote Sensing Technologies for Peatland Detection and Characterization) that has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska‐Curie grant agreement 747809.  We thank the National Norwegian Railroad Authorities for having kindly provided the SkyTEM data that were collected as part of the InterCity Project. We also thank Arne Grønlund and Knut Bjørkelo of the Norwegian Institute of Bioeconomy Research for having provided the map of the distribution of peatlands in the study area. This research would have not been possible without the precious help of Anita, Emma, and Marco, who gave a fundamental support with the field survey. Comments from Valeriy Ivanov, Lee Slater, Neal J. Pastick, and anonymous reviewers have greatly improved the clarity of this paper.

References

The full paper can be requested through the download link above or found directly at: www.zenodo.org.

Silvestri, S., Christensen, C. W., Lysdahl, A. O. K., Anschütz, H., Pfaffhuber, A. A., and Viezzoli, A. 2019. Peatland volume mapping over resistive substrates with airborne electromagnetic technology, Geophysical Research Letters, 46, 6459–6468.