Mapping of soil organic carbon and nitrogen in two small adjacent Arctic watersheds on Herschel Island, Yukon Territory


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Hugues.Lantuit [ at ] awi.de

Abstract

Permafrost soils are particularly vulnerable to global climate change, and warming air temperatures could turn them from carbon sinks into carbon sources. Estimates of Arctic carbon stocks are still highly uncertain, despite their importance to predict the magnitude of CO2 and CH4 release to the atmosphere, a process termed the Permafrost Carbon Feedback. Because most of the Arctic is difficult to access and survey, remote sensing techniques bear the capacity to fill spatial gaps and map the changing landscape at wider scales. Recent studies have attempted to use multispectral images, such as Landsat, to estimate soil total organic carbon (TOC) and total nitrogen (TN) storage. Yet, most studies worked on a regional to global scale and used relatively coarse landscape classes. Since TOC and TN storage is known to be highly spatially variable in the landscape, high resolution estimates of TOC and TN storage are necessary to estimate the potential impact of thawing permafrost (and the subsequent release of CO2 and CH4) to the atmosphere. This project is one of the first to use high resolution images (1.65m GeoEye (4 spectral bands: blue‐infrared), 2m DEM) to predict SOC and TN storage within different Tundra vegetation classes in a small (3 km²) twin watershed (Ice Creek) on Herschel Island, Yukon, Canada. Vegetation classes were based on indicator species and geomorphic disturbance levels. Remote sensing detection accuracy varied strongly between classes. Field based moisture measurements were most strongly correlated with the carbon to nitrogen (CN) ratio, TOC and TN (ρ =0.84, ρ =0.74 ρ =0.65, p<0.05). However, slope and the normalized difference vegetation index (NDVI) also had a statistically significant relationship to CN and TOC. This suggests that fine scale estimates of carbon and nitrogen stocks are possible using few spectral bands from high resolution images. The active layer of Ice Creek watershed contains 33391 tonnes of TOC and 3635 tonnes of TN, which is lower than the average value reported for Herschel Island by the Northern Circumpolar Soil Carbon Database. Carbon and nitrogen are not evenly distributed within the watershed. Flat upland terrain and tall erect bush areas contained the largest amount TOC and TN. Lowest contents could be found in the steep and frequently eroded zones. High carbon accumulation along the stream banks suggests that fluvial processes do not remove all the eroded sediments from the watershed. An intensification of summer rainfall and warmer temperatures could alter the hydrological patterns of the watershed and current accumulation sites may release more carbon from the catchments to the Beaufort Sea. High correlation between soil moisture and TOC and TN contents found in this thesis shows that moisture information retrieved from satellite radar data could provide additional information on soil properties. This thesis also shows that detailed studies on remobilization of carbon in the catchments and atmospheric losses of carbon are crucial to understand the role small watersheds play in the face of a changing climate.



Item Type
Thesis (Master)
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Not peer-reviewed
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Published
Eprint ID
40199
Cite as
Eischeid, I. (2015): Mapping of soil organic carbon and nitrogen in two small adjacent Arctic watersheds on Herschel Island, Yukon Territory Master thesis,


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