Suess Effect on Biomarkers Used to Determine Sediment Provenance from Land Use Changes

A compound-specific stable isotope (CSSI) technique developed to positively identify the source of soil by landuse provides a tool to determine the provenance of sediment from watershed erosion. The CSSI technique uses the carbon-13 (¹³C) isotopic signatures of plant-derived fatty acid biomarkers in the source soils and a mixing model to deconstruct the sediment isotopic signatures into contributing source soils by land use. While the CSSI technique provides qualitative information on where the sediment is coming from, for quantitation it requires erosion rate information from the fallout radionuclide (FRN) techniques. Together, the CSSI and FRN techniques can identify landuse practices that are exacerbating soil erosion i.e. hot spots. These tools can provide the information that allow managers to target the resources available to mitigate soil erosion. The data can also be used to map the dispersion of contemporary terrigenous sediments through an estuary and to identify land use changes through time from sediment cores. However, when the CSSI technique is used to look back in time using contemporary source libraries, the ¹³C isotopic signatures of the biomarkers need to be corrected for the Suess effect, i.e. the isotopic depletion of the δ¹³C signature of atmospheric carbon dioxide (CO₂) due to the admixing of isotopically depleted CO₂ from the burning of fossil fuels. (author)