<p>Wildfires are the major disturbance in boreal ecosystems, and are of great importance for the biogeochemical cycles of carbon (C) and nutrients. However, these fire-induced impacts are hard to quantify and rarely assessed together at an ecosystem level incorporating both aquatic and terrestrial environments. Following a wildfire in Sweden in an area with ongoing monitoring, we conducted a pre- and post-fire multi-catchment investigation of element losses (combustion and leaching), and impacts on water quality. Direct C and nitrogen (N) losses through combustion were ca. 4500 g m<sup>−2</sup> and 100 g m<sup>−2</sup>, respectively. Net CO<sub>2</sub> loss associated with soil and biomass respiration was ~ 150 g C m<sup>−2</sup> during the first year, but the ecosystem started to show net CO<sub>2</sub> uptake in June three years post-fire. Aquatic C and N losses during the first 12 months were 7 g m<sup>−2</sup> and 0.6 g m<sup>−2</sup>, respectively. Hence, soil respiration comprised a non-negligible part of the post-fire C loss, whereas aquatic C losses were minor, and did not increase post-fire. However, other elements (e.g., Ca, S) exhibited ecologically relevant increases in fluvial export and concentration, with large peaks in the immediate post-fire period. The temporal dynamics of stream concentrations suggest the presence of faster- and slower-release nutrient pools with half-lives of around 2 weeks and 4 months, which we attribute to physicochemically and biologically mediated mobilisation processes, respectively. Three years after the fire, it appears that biogeochemical cycles have largely returned to pre-fire conditions, but there is still net release of CO<sub>2</sub>.</p>