Carbon Stored as Large Wood in the Mackenzie River Delta, Northwest Territories, Canada

Abstract:

The Mackenzie River, draining 1/5 of Canada, is the largest exporter of carbon to the Arctic Ocean, making it a significant contributor to global carbon cycling. The basin also supports a natural large wood regime (wood > 10 cm diameter and 1 m length) as the area is largely undisturbed by human activities. Before reaching the Beaufort Sea, the Mackenzie basin flows through the Mackenzie River Delta (MRD), a 13,000km² depositional landscape containing complex channels and over 45,000 lakes. While storing large amounts of carbon in underlying permafrost, the MRD may also contain a large carbon reservoir stored as large wood. However, we lack estimates of carbon storage and transport in this form. In the face of permafrost thaw and subsequent landscape alteration due to climate change, there is a need to generate accurate estimates of carbon storage across size domains of carbon storage pools.

In this work, we use remote sensing and field work to quantify carbon stored as large wood in the MRD. We measure the distribution of large wood deposits by applying machine learning classification algorithms to very high-resolution satellite imagery of the region. Algorithms tested include Support Vector Machines (SVM) and Convolutional Neural Networks (CNNs), resulting in accurate wood capture in the landscape. Using targeted field work, we transform wood extents into wood volume and carbon stock. We find extensive wood deposit sites across the delta that have residence times spanning decades to centuries, making them long-term carbon storage pools. Measured wood coverage over the delta results in 26e6 m³ of wood stored with carbon storage estimates of greater than 6600 Mg-C. Results from field work also suggest extensive wood deposits under the canopy that cannot be captured by imagery, making total estimated carbon stored as large wood over 13e3 Mg-C. We compare these results to carbon stocks found in other landscapes.