A coupled hydrological-biogeochemical model to simulate DOC dynamics in a sub-arctic headwater catchment underlain by permafrost

Abstract:

Sub-arctic regions are currently undergoing climate induced changes, with projections of widespread degradation or loss of permafrost in these regions. While many studies have focussed on the controls of DOC exports in sub-arctic systems and many large scale models were applied, very few studies have investigated these processes in sub-arctic alpine, headwater catchments. With increasing air-temperatures it is predicted that the permafrost will be reduced and the depth of the thawing active layer may increase. The effect of these changes on the quantity and timing of DOC exports under these changes is still unclear. Therefore, it is important to understand the controls of DOC in these systems. These regions are characterised with high DOC concentrations during early spring melt when the thaw depth is shallow and the highly labile organic layer is the dominant flow pathway. As the season progresses and the active layer deepens, maximum soil water storage increases and DOC comes into contact with and is sorbed by less permeable mineral soils. Using a parsimonious coupled conceptual model to simulate stream discharge and DOC production and export for a small (c.a. 8 km²) sub-arctic alpine headwater catchment, this study aims to improve the understanding of stream discharge and DOC dynamics and the main underlying processes of DOC exports. Using a coupled process-based model to simulate DOC production and hydrological processes allows to integrate additional information gained concerning the controls of these processes. Model complexity is balanced with the complexity of the system to allow for the identification of the main controlling processes of DOC exports. Based on the HBV model, the model includes additional components to reflect the effect of slope aspect and the permafrost active layer dynamics and the production and loss of DOC. The results of the model provide valuable information on the dominant controlling processes of DOC in the catchment.