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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-205
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-205
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 Jun 2019

Submitted as: research article | 04 Jun 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Understanding the effects of early degradation on isotopic tracers: implications for sediment source attribution using compound-specific isotope analysis (CSIA)

Pranav Hirave1, Guido L. B. Wiesenberg2, Axel Birkholz1, and Christine Alewell1 Pranav Hirave et al.
  • 1Environmental Geosciences, Department of Environmental Sciences, University of Basel, Basel, Switzerland
  • 2University of Zurich, Department of Geography, Soil Science and Biogeochemistry, Zurich, Switzerland

Abstract. Application of compound-specific isotope analysis (CSIA) in sediment fingerprinting source apportionment studies is becoming more frequent, as it can potentially provide robust land-use based source attribution of suspended sediments in a freshwater system. Isotopic tracers such as δ13C values of vegetation-derived organic compounds are considered to be suitable for CSIA based fingerprinting method. However, a rigorous evaluation of tracer conservativeness in terms of the stability of isotopic signature during detachment and transport of soil during erosion process is essential for the suitability of the method. With the aim to identify potential fractionation and shifts in tracer signature during early degradation of organic matter in surface soils, we measured concentrations and δ13C values of long-chain fatty acids and n-alkanes from fresh plant biomass (as vegetation is a direct source of these compounds to the soils), degraded organic horizon (O horizon) as well as mineral soil (A horizon) from various forest types with different humus forms (five sites). The bulk δ13C values showed continuous 13C enrichment through the degradation stages from fresh plant material to the O and A horizon, ranging between 3.5 and 5.6 ‰. Compound-specific δ13C values showed a general 13C enrichment for both, long-chain fatty acids (up to 5 ‰) as well as n-alkanes (up to 3.9 ‰) from fresh plant biomass to the O horizon overlying the A horizon. However, only slight or no further changes occurred from the O to the A horizon. We also compared compound-specific δ13C values between two soil particle-size classes (< 2 mm and < 63 µm) from four sites and found no significant differences of tracer values between them, with even less fractionation for the long-chain n-alkanes within the soil particle fractions, which points to the conclusion that sampling and analysing bulk soil material might be valid for the isotopic tracer applications. We further conclude, that our results support the suitability of studied isotopic tracers as representative source soil signature in CSIA based sediment source attribution, as they demonstrated necessary stability in plant-soil system during organic matter degradation.

Pranav Hirave et al.
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Data from isotopic and molecular measurements for: Understanding the effects of early degradation on isotopic tracers: implications for sediment source attribution using compound-specific isotope analysis (CSIA) P. Hirave, G. L. B. Wiesenberg, A. Birkholz, and C. Alewell https://doi.org/10.5281/zenodo.3228446

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Short summary
Sediment input into water bodies is a prominent threat to freshwater ecosystem. We tested the stability of tracers employed in compound-specific isotope analysis based sediment tracing method during early degradation in soil. While bulk δ13C values showed no stability, δ13C values of plant-derived fatty acids and n-alkanes were stably transferred to the soil without particle-size dependent changes after an early degradation in organic horizons, thus indicating their suitability as tracers.
Sediment input into water bodies is a prominent threat to freshwater ecosystem. We tested the...
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