Combined use of stable isotopes and fallout radionuclides as soil erosion indicators in a forested mountain site, South Korea

[摘要] The aim of this study is to assess and to validate the suitability of thestable nitrogen and carbon isotope signature as soil erosion indicators in amountain forest site in South Korea. Our approach is based on the comparisonof the isotope signature of "stable" landscape positions (reference sites),which are neither affected by erosion nor deposition, with eroding sites. Forundisturbed soils we expect that the enrichment of δ¹⁵N andδ¹³C with soil depth, due to fractionation during decomposition,goes in parallel with a decrease in nitrogen and carbon content. Soil erosionprocesses potentially weaken this correlation. The ¹³⁷Cs method and theRevised Universal Soil Loss Equation (RUSLE) were applied for the soil erosionquantification. Erosion rates obtained with the ¹³⁷Cs method range from0.9 t ha⁻¹ yr⁻¹ to 7 t ha⁻¹ yr⁻¹. Considering thesteep slopes of up to 40° and the erosive monsoon events (R factor of6600 MJ mm ha⁻¹ h⁻¹ yr ^–1), the rates are plausible andwithin the magnitude of the RUSLE-modeled soil erosion rates, varying from0.02 t ha⁻¹ yr⁻¹ to 5.1 t ha⁻¹ yr⁻¹. The soilprofiles of the reference sites showed significant (p < 0.0001)correlations between nitrogen and carbon content and its correspondingδ¹⁵N and δ¹³C signatures. In contrast, for the erodingsites this relationship was weaker and for the carbon not significant. Theseresults confirm the usefulness of the stable carbon isotope signature as aqualitative indicator for soil disturbance. We could show further that theδ¹⁵N isotope signature can be used similarly for uncultivatedsites. We thus propose that the stable δ¹⁵N and δ¹³Csignature of soil profiles could serve as additional indicators confirmingthe accurate choice of the reference site in soil erosion studies using the¹³⁷Cs method.

[学科分类] 地球化学与岩石