Combining Isotopic Techniques to Assess Historical Sediment Delivery in a Forest Catchment in Central Chile

Abstract

The purpose of this research was to determine the historical evolution of different sources of sediment by land uses in a forest catchment, through the combination of two isotopic techniques: (i) fallout radionuclides (FRNs) for dating sediment cores and (ii) compound-specific stable isotope (CSSI). Ten 30-cm-deep sediment cores (taken in a meander at the outlet of the forest catchment) were used to reconstruct the sediment delivery history for around 67 years before present (BP), i.e., 2012. Five land uses were considered as potential sources in this analysis: forest roads, pine trees, eucalyptus trees, native forest (buffer or riparian zone), and wheat. Forestry activities incremented the sedimentation rate by about 17% compared to wheat production. Results were consistent with the historical land uses in the catchment. The analysis showed an important sediment contribution of farmland used for wheat from 1945 to about 1974 (~ 20–80%). After the implementation of the public bill, the sediment source changed into the exotic plantations (pine and eucalyptus trees) until present, where harvesting periods were clearly seen as an increment of sediment delivery from the source.