Use of environmental radionuclides in estimation of the relative contribution of fine sediment sources in forest plantation basins

The need to control sediment delivery to watercourses during and after forest harvest operations is attracting increasing attention in Chile, particularly as a result of the introduction of Forest Certification requirements. The aim of this investigation is to pioneer the development and application of sediment source fingerprinting techniques in Chile for establishing the relative apportionment of fine sediment sources to the total sediment load previous and after harvest operations and after the establishment of the new plantation. The study was conducted between 2009 and 2011 in paired forest catchments (control and treatment) in Nacimiento, Bio Bio, Chile. During the study period, the control catchment was not intervened and the treatment catchment was clear-cutted and afterwards reforested. For sediment accumulation and collection weirs were installed at each catchment outlet. The tracers able to discriminate between the source zones, established using Kruskal-Wallis and DFA tests, were mainly fallout and environmental radionuclides. The relative apportionments of the different zones were estimated using a multivariate mixing model and Monte Carlo analysis. The maximum relative fine sediment contributions were originated in the stream channel (86-90%) during the pre- harvest period, along the forest slopes (59%) during harvest and post-harvest period and again in the stream channel (77%) during and after the establishment of the new plantation. The study contributed to develop and demonstrate the application of sediment source fingerprinting procedures in Chile and provide a basis for expanding such work into other regions and agricultural areas and into studies linked to other sediment-related environmental problems