Abstract. 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 are
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-fire (9 years) and post-fire (4 years)
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 and 100 g m−2, respectively. Net
CO2 loss associated with soil and biomass respiration was
∼ 150 g C m−2 during the first year, but the ecosystem
started to show net CO2 uptake in June 3 years post-fire. Aquatic C
and N losses the first 12 months post-fire were 7 and 0.6 g m−2, 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 (Ca2+, Mg2+, K+ ,SO4-2,
Cl− ,NH4+, total organic N) 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
mobilization processes, respectively. Three years after the fire, it appears
that dissolved fluxes of nutrients have largely returned to pre-fire
conditions, but there is still net release of CO2.