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: Developing ow paths or expanding existing pathways in deep geological strata is generally referred to as "stimulation". To extract heat from geothermal reservoirs, stimulation treatments are carried out by injecting water at high pressure into the formation (hydraulic stimulation), by dissolution of certain mineral components, mostly carbonates, thus increasing the hydraulic pathways (chemical stimulation), or by cooling of the rock to induce tensile stresses which helps the fracture expansion (thermal stimulation). The achieved factor of productivity increase by conventional stimulation treatments is reported to be between 1.3 and 25. In petrolium industry a significant decline of the production increase occurs already during the first year after stimulation. The time to refracturing is typically 4 to 7 years. It is not clear whether these values are also appropriate for geothermal applications. The sustainability of the increase in permeability due to thermal stimulation depends on the situation: for an injection well the increase remains for few years. For production wells, the longevity of the stimulation depends on the self-propping ability of the rock. After reviewing the current situation in the field of deep geothermal energy in Europe, dierent stimulation techniques are discussed. Furthermore, case studies of stimulation treatments in deep geothermal reservoirs are presented. In the subsequent chapters the authors present the methods of stimulation treatment in deep geothermal wells to show the increase of productivity, to explain the potential benefits and risks and estimate the economic performance.