ALBERT

Description: Recent mobilisation of soil organic matter (SOM) in permafrost of the northern high latitudes is thought to have a significant impact on the carbon balance in the atmosphere. However, the environmental processes which influence SOM accumulation and remobilisation still need to be investigated more accurately. This study investigates the quantity and quality of SOM on Herschel Island in the western Canadian Arctic in relation to various landscape characteristics. To reach this goal, soil moisture, total organic carbon (TOC) and total nitrogen (TN) contents, stable carbon isotopes (∂¹³C) and TOC/TN ratios (C/N) were determined on 128 samples from twelve sediment cores reaching up to 250 cm depth. Drilling locations were chosen based on morphology, vegetation and soil properties and supported by satellite imagery and air photos. Seasonal thaw depths (active layer depths) correlate with ground disturbance and vegetation cover and lie between 20 and 100 cm. Well-preserved SOM is accumulated in the active layer and subjacent ice-rich permafrost of wet polygonal tundra. Uplands, hummocky tussock tundra and alluvial fans cover more than 50 % of the island and show heterogeneous SOM storage characteristics with considerable TOC contents being limited to the active layer. Disturbed areas with slope gradients greater than 6° show strong SOM degradation with low TOC contents throughout the active layer and permafrost strata. Linear regression and principal component analysis (PCA) shows that a decreasing SOM content is driven by increasing ground disturbance and reduced vegetation cover. Improved drainage decreases the preservation of SOM in the active layer. Future deepening of the active layer because of increasing temperatures and ground disturbance will remobilise SOM stored in ice-rich permafrost. This might increase carbon dioxide and methane emissions from permafrost landscapes.

Description: Organic matter in soils of northern high latitudes show a high lability to recent permafrost thaw. Mobilisation and release of soil organic matter (SOM) in permafrost areas might have a significant impact on the carbon and nitrogen flux into the marine environment and in the atmosphere which motivated scientists in the past to quantify carbon and nitrogen stocks. However, the determination of environmental factors and their influences to SOM storage still need to be investigated more accurately. This thesis seeks to contribute to an improvement of this issue. This study investigates the SOM in the active layer and surficial permafrost on Herschel Island in the western Canadian Arctic. It evaluates the preservation and degradation status of SOM in relation to different landscape phenomena. To reach this goal, soil moisture, total organic carbon (TOC) and total nitrogen (TN) contents were analysed on 128 samples from twelve sediment cores. The stable carbon isotope (∂¹³C) composition on organic carbon and TOC/TN ratios (C/N) were determined. Drilling locations were chosen based on of morphology, vegetation and soil properties and supported by satellite imagery and air photos which classify the surface of Herschel Island into seven ecological units. Regression analyses and principal component analysis (PCA) were used to work out possible correlations and significant differences between environmental factors. Seasonal thaw depths (active layer depths) increase with disturbance and a decreasing vegetation cover and show depths between 20 and 100 cm. Results on organic matter show that consistently wellpreserved SOM is accumulated in the active layer and subjacent ice-rich permafrost of depressional polygonal tundra. Waterlogging leads to reduced organic matter decomposition and an enrichment of the TOC and TN content characterising depressional polygonal tundra as a peatland environment. Upland plateaus, gently rolling terrain and alluvial fans represent more than 50 % of the island and show heterogeneous SOM storage characteristics with mostly considerable TOC contents being limited to the active layer. SOM storage in subjacent permafrost is reduced. Disturbed areas with slope gradients greater than 6° show strong SOM degradation with consistently low SOM contents throughout the active layer and permafrost strata. Stabilised slopes show a reestablishment of a vegetation cover and indicate initiation of SOM accumulation. This study highlights the heterogeneity in SOM storage on Herschel Island which is mainly due to local morphology, soil type, vegetation and moisture content. Principal component analysis shows that a gradient of reduced SOM content is evident with increasing ground disturbance. Improved drainage decreases the preservation of SOM in the active layer and ice rich permafrost can hold considerable SOM contents. Future deepening of the active layer with increasing air temperatures in the Arctic might remobilise SOM stored in ice-rich permafrost, especially in peatland environment.