Hydrology and water chemistry in a heterogeneous landscape : process-based modelling of coupled surface water and groundwater flow across contrasting boreal catchments

Surface water and groundwater are connected, and the exchange between them is a vital part of a catchment’s hydrology. Along the flow paths through the catchment, biogeochemical processes can change the water’s chemical composition. The degree of the chemical change depends largely on the water pathways and travel times through the subsurface environment. This thesis describes the application of a 3D coupled surface water and groundwater model to the well-studied Krycklan catchment to investigate the impact of hydraulic properties, landscape variability, and seasonal changes on the hydrology and water quality across nested catchments in a heterogeneous boreal landscape. The results show that variability in specific discharge and surface water and groundwater interactions can be linked to catchment characteristics such as soil properties and spatial variability in winter soil frost. Spatial variability of water quality, including weathering of base cations and locations of dissolved organic carbon-rich sources along the streams, was linked to different catchment characteristics affecting hydrology (including travel times and water pathways). Some catchment characteristics, such as soil frost, were found to not necessarily impact the modelling of streamflow dynamics from a large-scale perspective. However, soil frost was still important for the flow dynamics on smaller scales, and an important part of the spatial variability of stream water quality. This research highlights the importance of expanding our knowledge of the flow dynamics of different landscape components, surface water and groundwater interactions, and how hydrology can be linked to water quality across temporal and spatial scales.