Understanding the effects of early degradation on isotopic tracers: implications for sediment source attribution using compound-specific isotope analysis (CSIA)
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Published:2020-04-20
Issue:8
Volume:17
Page:2169-2180
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Hirave Pranav,Wiesenberg Guido L. B.,Birkholz Axel,Alewell Christine
Abstract
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 freshwater and marine systems.
Isotopic tracers such as δ13C values of vegetation-derived
organic compounds are considered to be suitable for the 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 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), and 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 horizons, 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 ‰) and 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. This 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 a representative source soil
signature in the CSIA-based sediment source attribution, as they demonstrated
necessary stability in the plant–soil system during organic matter degradation.
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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