Preprints
https://doi.org/10.5194/bg-2020-363
https://doi.org/10.5194/bg-2020-363

  07 Oct 2020

07 Oct 2020

Review status: a revised version of this preprint was accepted for the journal BG and is expected to appear here in due course.

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

Gustaf Granath1, Christopher D. Evans2,3, Joachim Strengbom4, Jens Fölster3, Achim Grelle4, Johan Strömqvist5, and Stephan J. Köhler3 Gustaf Granath et al.
  • 1Department Ecology and Genetics, Uppsala University, Norbyvägen 18D, Uppsala, Sweden
  • 2Centre for Ecology and Hydrology, Bangor, LL57 2UW, UK
  • 3Department of aquatic sciences and assessment, Swedish university of agricultural sciences, Box 7050, Uppsala, Sweden
  • 4Department of Ecology, Swedish University of Agricultural Sciences, Box 7044, SE-750 07 Uppsala, Sweden
  • 5Swedish Meteorological and Hydrological Institute (SMHI), SE-601 76 Norrköping, Sweden

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 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−2 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 three years post-fire. Aquatic C and N losses during the first 12 months were 7 g m−2 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 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 CO2.

Gustaf Granath et al.

 
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Gustaf Granath et al.

Gustaf Granath et al.

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Short summary
We measured element losses and impacts on water quality following a wildfire in Sweden. We observed the largest carbon and nitrogen losses during the fire, and a strong pulse of elements 1–3 months after the fire that showed a fast (weeks) and a slow (months) release from the catchments. Total carbon export through waters did not increase post-fire. Overall, we observed a rapid recovery of the biogeochemical cycling of elements within three years, but still annual net release of carbon dioxide.
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