The impact of wildfire on biogeochemical fluxes and water quality in boreal catchments

[摘要] 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 CO 2 loss associated with soil and biomass respiration was ∼  150 g C m −2 during the first year, but the ecosystem started to show net CO 2 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 (Ca 2+ , Mg 2+ , K + ,SO 4 - 2 , Cl − ,NH 4 + , 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 CO 2 .

[学科分类] 大气科学