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Volume 12, issue 2
Biogeosciences, 12, 307–322, 2015
https://doi.org/10.5194/bg-12-307-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 12, 307–322, 2015
https://doi.org/10.5194/bg-12-307-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 19 Jan 2015

Research article | 19 Jan 2015

Historical TOC concentration minima during peak sulfur deposition in two Swedish lakes

P. Bragée1, F. Mazier2, A. B. Nielsen1,5,6, P. Rosén3, D. Fredh1, A. Broström1,*, W. Granéli4, and D. Hammarlund1 P. Bragée et al.
  • 1Quaternary Sciences, Department of Geology, Lund University, Sweden
  • 2GEODE, UMR5602, Jean Jaures University, Toulouse-Le Mirail, France
  • 3Department of Ecology and Environmental Science, Umeå University, Sweden
  • 4Department of Biology, Aquatic Ecology, Lund University, Sweden
  • 5Department of Physical Geography and Ecosystem Science, Lund University, Sweden
  • 6Department of Biology and Environmental Science, Linnæus University, Sweden
  • *now at: Swedish National Heritage Board, Contract Archaeology Service, Sweden

Abstract. Decadal-scale variations in total organic carbon (TOC) concentration in lake water since AD 1200 in two small lakes in southern Sweden were reconstructed based on visible–near-infrared spectroscopy (VNIRS) of their recent sediment successions. In order to assess the impacts of local land-use changes, regional variations in sulfur, and nitrogen deposition and climate variations on the inferred changes in TOC concentration, the same sediment records were subjected to multi-proxy palaeolimnological analyses. Changes in lake-water pH were inferred from diatom analysis, whereas pollen-based land-use reconstructions (Landscape Reconstruction Algorithm) together with geochemical records provided information on catchment-scale environmental changes, and comparisons were made with available records of climate and population density. Our long-term reconstructions reveal that inferred lake-water TOC concentrations were generally high prior to AD 1900, with additional variability coupled mainly to changes in forest cover and agricultural land-use intensity. The last century showed significant changes, and unusually low TOC concentrations were inferred at AD 1930–1990, followed by a recent increase, largely consistent with monitoring data. Variations in sulfur emissions, with an increase in the early 1900s to a peak around AD 1980 and a subsequent decrease, were identified as an important driver of these dynamics at both sites, while processes related to the introduction of modern forestry and recent increases in precipitation and temperature may have contributed, but the effects differed between the sites. The increase in lake-water TOC concentration from around AD 1980 may therefore reflect a recovery process. Given that the effects of sulfur deposition now subside and that the recovery of lake-water TOC concentrations has reached pre-industrial levels, other forcing mechanisms related to land management and climate change may become the main drivers of TOC concentration changes in boreal lake waters in the future.

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