Soil organic carbon and total nitrogen on the Herschel Island

jaroslav.obu [ at ]


Organic carbon and nitrogen are two of the basic elements that control primary production and organism growth in Arctic Environments. They control geochemical and biological processes including potential release of carbon dioxide, methane, and nitrous oxide, both in the terrestrial and marine environments. They accumulated with organic matter and stored in deeper permafrost layers of soil. Predicted temperature rise in Arctic can cause organic matter to thaw and decompose. That could mobilise carbon and nitrogen and cause potential emissions of greenhouse gasses. Knowing the exact amounts of carbon and nitrogen that are available for activation is therefore crucial for estimating gas and nutrient fluxes. The study area is Herschel Island and is situated in the northern part of Yukon Coast. It is a push moraine with abundance of massive ice and continuous permafrost. Its undulating terrain is characterised by numerous valleys, steep coasts and retrogressive thaw slumps which is a reason for highly variable ecological settings. The goal of this study is to produce maps of soil organic carbon (SOC) and total nitrogen (TN) to provide numbers and spatial distribution on their stocks. Twelve permafrost cores up to two meters depth were drilled from different ecological units on Herschel Island during summer field work in 2013. The samples were analysed for CNS and TOC contents with combustion method. Additionally, bulk density was calculated from volume and dry weight of samples in order to provide reliable organic carbon and nitrogen volumetric contents. Volumetric sample contents were extrapolated to the first metre of core in order to get SOC and TN storage values. Ecological units on Herschel Island were defined with soil and vegetation survey in 1989. We used this classification and delineated training units that were recognised in the field. They were used for maximum-likelihood supervised classification that we performed on RapidEye multispectral imagery with slope layer added as additional band. Comparison between classification result and ground truth points yielded a 75% agreement. The core data were upscaled to the ecological units in order to get spatial distribution of SOC and TN. Results showed a lot of variability in SOC and TN values between ecological units. The highest storages are in wet polygonal terrain (SOC 0-100cm ~ 80 kgm-2), moderate in undisturbed uplands (SOC 0-100cm ~ 40 kgm-2) and lowest in disturbed areas (SOC 0-100cm ~ 20 kgm-2). There is 3.9 Tg of SOC and 0.4 Tg of TN in first meter of soil in total on Herschel Island. Statistical analysis of variables influencing SOC storage showed a positive correlation with moisture and negative correlation with slope.

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CAPP workshop, 12 May 2014 - 14 May 2014, Stockholm University.
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Obu, J. , Lantuit, H. , Fritz, M. , Heim, B. , Myers-Smith, I. , Sachs, T. and Helm, V. (2014): Soil organic carbon and total nitrogen on the Herschel Island , CAPP workshop, Stockholm University, 12 May 2014 - 14 May 2014 .

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