Tracing Crop-Specific Sediment Sources in Agricultural Catchments with Compound-Specific Stable Isotope (CSSI) and Geochemical Markers

Compound specific stable isotopes (CSSI) in soils have the potential to trace suspended sediment in river channels back to source areas determined by specific crop type. As such they offer to provide support for soil resource management policies and also to inform sediment risk assessment for the protection of aquatic habitats and water resources. This manuscript summarises a study which aimed to assess the potential for CSSI tracers to provide information on sediment sources in mixed land use agricultural catchments in the United Kingdom (UK). Source discrimination was undertaken in two ways using: (i) CSSI properties and (ii) more conventional geochemical markers. The properties of the source areas were compared with those of suspended sediment collected during a major storm event using established unmixing models. Results from both methods suggested that grassland was an important source of sediment (ca. 0.13 ± 0.02 t/ha) but the geochemical fingerprinting method appeared to be slightly biased to cultivated sources owing to the influence of prior ploughing on the geochemical signals in soil of temporary pasture fields (ley pasture) that were in rotation. With prior knowledge of ley and permanent pasture management practice, analysis of the discrepancies between the two sets of tracers highlights the importance of damaged permanent pasture as an erosion hotspot. Compound specific stable isotopes offer a powerful means of addressing the impacts of land management on soil erosion and downstream sediment problems, but further research is required into the influence of crop rotations on CSSI signature development and implications for downstream interpretation. (author)