Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 14, 1773-1792, 2017
https://doi.org/10.5194/bg-14-1773-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
03 Apr 2017
Spatial variability of organic matter molecular composition and elemental geochemistry in surface sediments of a small boreal Swedish lake
Julie Tolu1, Johan Rydberg1, Carsten Meyer-Jacob1, Lorenz Gerber2, and Richard Bindler1 1Department of Ecology and Environmental Science, Umeå University, 901 87 Umeå, Sweden
2Umeå Plant Science Center, Swedish University of Agricultural Sciences, Department of Forest Genetics and Plant Physiology, 901 83 Umeå, Sweden
Abstract. The composition of sediment organic matter (OM) exerts a strong control on biogeochemical processes in lakes, such as those involved in the fate of carbon, nutrients and trace metals. While between-lake spatial variability of OM quality is increasingly investigated, we explored in this study how the molecular composition of sediment OM varies spatially within a single lake and related this variability to physical parameters and elemental geochemistry. Surface sediment samples (0–10 cm) from 42 locations in Härsvatten – a small boreal forest lake with a complex basin morphometry – were analyzed for OM molecular composition using pyrolysis gas chromatography mass spectrometry for the contents of 23 major and trace elements and biogenic silica. We identified 162 organic compounds belonging to different biochemical classes of OM (e.g., carbohydrates, lignin and lipids). Close relationships were found between the spatial patterns of sediment OM molecular composition and elemental geochemistry. Differences in the source types of OM (i.e., terrestrial, aquatic plant and algal) were linked to the individual basin morphometries and chemical status of the lake. The variability in OM molecular composition was further driven by the degradation status of these different source pools, which appeared to be related to sedimentary physicochemical parameters (e.g., redox conditions) and to the molecular structure of the organic compounds. Given the high spatial variation in OM molecular composition within Härsvatten and its close relationship with elemental geochemistry, the potential for large spatial variability across lakes should be considered when studying biogeochemical processes involved in the cycling of carbon, nutrients and trace elements or when assessing lake budgets.

Citation: Tolu, J., Rydberg, J., Meyer-Jacob, C., Gerber, L., and Bindler, R.: Spatial variability of organic matter molecular composition and elemental geochemistry in surface sediments of a small boreal Swedish lake, Biogeosciences, 14, 1773-1792, https://doi.org/10.5194/bg-14-1773-2017, 2017.
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In this study, we demonstrated that the composition of sediment organic matter can vary significantly within a single lake, in a close relationship with the spatial patterns of elemental inorganic geochemistry. This results from a combination of different bio-, geo- and physicochemical lake factors, and our results highlight that the potential for large spatial variability across lakes should be considered when studying carbon, nutrient and trace element cycling at lake and global scales.
In this study, we demonstrated that the composition of sediment organic matter can vary...
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