Scanner derived colour parameters to determine suspended sediment sources in burned catchments
Authors: García-Comendador Julián , Martínez-Carreras Núria , Fortesa Josep , Borràs Antoni , Calsamiglia Aleix , Estrany Joan 
Published: March 2020

&lt;p&gt;After a wildfire, total or partial removal of vegetal biomass and changes in physicochemical soil properties can lead to an increase in overland flow and sediment yield. Eventual damage must be counteracted urgently identifying erosion hotspots, implementing post-fire management programmes and sampling campaigns to check its effectiveness. Under this context, the sediment source fingerprinting technique is widely used for determining the origin of suspended sediments in catchments and can be useful to evaluate the effectiveness of sediment management programmes. It traditionally relies on the use of physical, biochemical and geochemical properties as tracers. However, measuring these tracers in the laboratory often entails a high economic cost and time consuming. Colour tracers were proven to greatly reduce this cost and measuring time, especially if measurements are done using a common office scanner. Here we propose that colour parameters can be used to investigate SS origin in burned catchments. To this end, we created artificial mixtures of sediment and ash to verify the colour linear additivity and the ash influence on colour parameters. We then used colour parameters for source-ascription of SS samples (n=9) collected during two years after a fire in small Mediterranean catchment (4.8 km&lt;sup&gt;2&lt;/sup&gt;; Mallorca, Spain). Furthermore, reflectance-derived colour parameters were compared with those obtained using a current office scanner. The high correlation between most chromatic indexes (obtained using both methods; p &lt; 0.01) suggested that scanning is a good alternative for measuring soil and sediment colour. A Bayesian tracer mixing model (MixSIAR) was applied to determine the relative contribution of each source. The type of mixing models allowed to appropriately represent natural and sampling uncertainty in tracer data. During the first events, suspended sediment was mainly originated in burned surfaces, whereas its contribution decreased throughout the study period. Tracing results obtained using colour parameters were compared with estimations using &lt;sup&gt;137&lt;/sup&gt;Cs and &lt;sup&gt;210&lt;/sup&gt;Pb&lt;sub&gt;ex&lt;/sub&gt;, as recognized tracers to discriminate between surface and subsurface sediment sources after wildfires. Estimated source ascriptions with both methods (i.e. reflectance-derived colour parameters and radionuclides) matched in 88% of the samples measured. Colour tracers have been proved to be useful to discriminate between burned and unburned sources, making them suitable for suspended sediment source ascription and monitoring as part of post-fire management strategies.&lt;/p&gt;&lt;p&gt;&lt;em&gt;This work was supported by the research project CGL2017-88200-R &amp;#8220;Functional hydrological and sediment connectivity at Mediterranean catchments: global change scenarios &amp;#8211;MEDhyCON2&amp;#8221; funded by the Spanish Ministry of Science, Innovation and Universities, the Spanish Agency of Research (AEI) and the European Regional Development Funds (ERDF)&lt;/em&gt;&lt;/p&gt;