Conceptualizing catchment processes affecting stream chemistry

Maintaining good surface water quality is recognized as one of the greatest challenges for future generations. In northern-latitudes, it is predicted that aquatic ecosystems may experience a large climatic change. This could have dramatic consequences for the hydrological cycle, which influences many biogeochemical process and ultimately stream water quality. Additionally, increasing demand for forest resources can increase the pressure on water resources in the boreal forest that already experience large scale industrialized forestry. However, before the combined effects of climate change and forestry on stream chemistry can be understood, the basic principles of how catchments function are first a prerequisite. In this thesis, investigating the natural variability of stream water quality in a meso-scale boreal catchment showed that temporal and spatial variation in hydrology within catchment landscape types was the main regulator of stream water quality. Shallow groundwater from the dominant landscape types regulated stream chemistry during high and intermediate flows, while large inputs of deep groundwater regulated the chemistry during base flow when the connectivity between landscape types decreased. Additionally, specific landscape attributes reflected different processes occurring in the catchment. By identifying the areal coverage, riparian soils, and connectivity of the catchment landscapes, this work has led to an improved understanding of dissolved organic carbon (DOC), conservative elements, redox sensitive elements as well as those with high affinity for organic matter, and elements derived from atmospheric deposition. Applying the new conceptual understanding to predict future effects showed that warmer and wetter conditions, as indicated by future climate and forestry scenarios, suggest there may be increased DOC concentrations and fluxes in streams which will be driven by both climate change and forestry effects. Further applications of this new catchment biogeochemical processes understanding to forest management showed that a more cost effective solution for forest management can be achieved by strategically targeting the most vulnerable and sensitive areas of the riparian zone by using a hydrologically adapted buffer zone strategy