Freshwater systems across the globe are experiencing increased sediment delivery. Anthropogenic activities including intensification of land management are primary causes of increased sediment delivery to freshwater systems. Excessive input of suspended sediments in freshwater systems can substantially alter physical, chemical, and biological properties of the water bodies, which can have detrimental effects on the aquatic flora and fauna. Changing climate scenarios are expected to further increase soil erosion and associated increase of sediment load to freshwater systems due to frequent extreme weather events and changing land use practices. Hence, information on the sources of the suspended sediments is invaluable for efficient, focused, and cost-effective implementation of land management strategies.

Recently introduced sediment source fingerprinting technique using compound-specific isotope analysis (CSIA) can potentially identify major erosion sources and quantify their contribution to the stream suspended sediments based on the land uses in the catchment. Compound-specific stable isotope (CSSI) values of carbon (δ13C values) and hydrogen (δ2H values) of plant lipid components such as long-chain fatty acids (LCFAs) and n-alkanes are primarily used as tracers in the CSIA-based sediment source fingerprinting. However, a rigorous evaluation of tracer conservativeness in terms of stability of isotopic signatures during detachment and transport of soil during erosion is essential to validate suitability of the fingerprinting method. Potential fractionation and shifts in the isotopic signatures of long-chain fatty acids and n-alkanes during early degradation in soils after their production by plants was studied to assess the stability of the isotopic tracers during early degradation. Increasing degradation stages across the plant–soil systems (fresh plant biomass–organic horizons–mineral soil) from forests with different vegetation, soil, climatic zones, and humus forms were sampled. A clear increase in δ13C values for both compound classes from aboveground plant biomass to the O horizon overlaying the mineral soil was observed; however only slight or no further changes were observed during the further degradation in the mineral soil. The latter was in clear contrast to bulk δ13C values, which continued to become enriched in 13C through all the degradation stages from fresh plant biomass to mineral soil. This finding emphasizes the suitability of studied compounds as tracers used in CSIA-based sediment source fingerprinting.

Analysis of the effect of particle size on the isotopic composition of LCFAs and n-alkanes is crucial to validate conservative behaviour of isotopic tracers during soil erosion processes. Compound-specific carbon isotope values were compared between the two particle sizes which are frequently used for characterizing source tracer signatures from soils (