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https://doi.org/10.5194/bg-2019-500
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-500
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 11 Mar 2020

Submitted as: research article | 11 Mar 2020

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This preprint is currently under review for the journal BG.

Assessing branched tetraether lipids as tracers of soil organic carbon transport through the Carminowe Creek catchment (southwest England)

Jingjing Guo1, Miriam Glendell2, Jeroen Meersmans3, Frédérique Kirkels1, Jack J. Middelburg1, and Francien Peterse1 Jingjing Guo et al.
  • 1Department of Earth Sciences, Utrecht University, 3584 CBUtrecht, the Netherlands
  • 2The James Hutton Institute, Aberdeen, AB15 8QH, UK
  • 3TERRA Teaching and Research Centre, Gembloux Agro-Bio Tech, University of Liege, 5030 Gembloux, Belgium

Abstract. Soils represent the largest reservoir of organic carbon (OC) on land. Upon mobilization, this OC is either returned to the atmosphere as carbon dioxide (CO2), or transported and ultimately locked into (marine) sediments, where it will act as a long-term sink of atmospheric CO2. These fluxes of soil OC are, however, poorly quantified, mostly due to the lack of a soil-specific tracer. In this study, a suite of branched glycerol dialkyl glycerol tetraethers (brGDGTs), which are membrane lipids of soil bacteria, is tested as specific tracers for soil OC from source (soils under arable land, ley, grassland and woodland) to sink (Lake Loe Pool sediments) considering a small catchment located in southwest England (i.e. Carminowe Creek draining into Lake Loe Pool). The analysis of brGDGTs in catchment soils reveals that their distribution is not significantly different across different land use types (p > 0.05), and thus does not allow tracing land use-specific soil contributions to Lake Loe Pool sediments. Furthermore, the significantly higher contribution of 6-methyl brGDGT isomers in creek sediments (isomerization ratio (IR) = 0.48 ± 0.10; mean ± s.d., standard deviation; p < 0.05) compared to that in catchment soils (IR = 0.28 ± 0.11) indicates that the initial soil signal is substantially altered by brGDGT produced in situ. Similarly, the riverine brGDGT signal appears to be overwritten by lacustrine brGDGTs in the lake sedimentary record, indicated by remarkably lower Methylation of Branched Tetraethers (MBT'5ME = 0.46 ± 0.02 in creek bed sediment and 0.38 ± 0.01 in lake core sediment; p < 0.05) and higher Degree of Cyclization (DC = 0.23 ± 0.02 in creek bed sediment and 0.32 ± 0.08 in lake core sediment). Thus, in this small catchment, brGDGTs do not allow us to trace soil OC transport. Nevertheless, the downcore changes in the degree of cyclization and the abundance of isoprenoid GDGTs produced by methanogens in the Lake Loe Pool sediment do reflect local environmental conditions over the past 100 years, and have recorded the eutrophication history of the lake.

Jingjing Guo et al.

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Jingjing Guo et al.

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Short summary
The fluxes of soil organic carbon (OC) transport from land to sea are poorly constrained, mostly due to the lack of a specific tracer for soil OC. Here we evaluate the use of specific molecules derived from soil bacteria as a tracer foil soil OC in a small river catchment. We find that the initial soil signal is lost upon entering the aquatic environment. However, the local environmental history of the catchment is reflected by these molecules in the lake sediments that act as their sink.
The fluxes of soil organic carbon (OC) transport from land to sea are poorly constrained, mostly...
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