Search

Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Journal of Paleolimnology 50 (2013): 41-56, doi: 10.1007/s10933-013-9703-0., Patagonia is commonly seen as an exceptionally pristine area because of its wildlife and practically unpolluted waters. However, during the twentieth century the burning of natural forests was one of the most important human activities in Northern Chilean Patagonia. Some estimations indicate that three million hectares were burned during the first three decades of the century being its impacts rarely assessed. Hence the objective of this study was to evaluate the impacts of the historical fires in Lake Burgos (45º42’S) and Lake Thompson (45º38’S) in Chilean Patagonia. The impact was measured by evaluating chironomid assemblage since they are sensitive enough to be used as an indicator of aquatic ecosystem health. Fires have a direct and drastic effect on a lake watershed but also indirectly affect a lake ecosystem, changing sedimentation patterns or increasing nutrient inputs. In the studied lakes the periods with higher prevalence of fires were identified by charcoal analysis, while organic matter and magnetic susceptibility allowed to confirm the pre-fire and post-fire periods. The chironomid composition was evaluated through a PCA and an analysis of similarity (ANOSIM) to test the significance among periods while a DCA was applied to the chironomid assemblage downcore to assess compositional structure and taxa turnover. In Lake Burgos the ANOSIM test indicated significant differences between the pre-fire and fire periods (p<0.05), while in Lake Thompson differences were not significant. However, in Lake Thompson the PCA clearly separated the pre-fire from the fire period but not the fire from the post-fire periods. In both lakes chironomid composition changed in relation to the period of higher prevalence of fires, which in turn implies catchment changes, pollution, and other anthropogenic impacts. Particularly a marked change in mesotrophic/eutrophic taxa was detected, reflecting an increase in nutrient input due to deforestation. Our findings point out that the, Funding for this research is from the Fondecyt project Nº 11080158 and partially from Fondecyt project 1120765., 2014-03-30

Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Journal of Paleolimnology 50 (2013): 41-56, doi: 10.1007/s10933-013-9703-0., Patagonia is commonly seen as an exceptionally pristine area because of its wildlife and practically unpolluted waters. However, during the twentieth century the burning of natural forests was one of the most important human activities in Northern Chilean Patagonia. Some estimations indicate that three million hectares were burned during the first three decades of the century being its impacts rarely assessed. Hence the objective of this study was to evaluate the impacts of the historical fires in Lake Burgos (45º42’S) and Lake Thompson (45º38’S) in Chilean Patagonia. The impact was measured by evaluating chironomid assemblage since they are sensitive enough to be used as an indicator of aquatic ecosystem health. Fires have a direct and drastic effect on a lake watershed but also indirectly affect a lake ecosystem, changing sedimentation patterns or increasing nutrient inputs. In the studied lakes the periods with higher prevalence of fires were identified by charcoal analysis, while organic matter and magnetic susceptibility allowed to confirm the pre-fire and post-fire periods. The chironomid composition was evaluated through a PCA and an analysis of similarity (ANOSIM) to test the significance among periods while a DCA was applied to the chironomid assemblage downcore to assess compositional structure and taxa turnover. In Lake Burgos the ANOSIM test indicated significant differences between the pre-fire and fire periods (p<0.05), while in Lake Thompson differences were not significant. However, in Lake Thompson the PCA clearly separated the pre-fire from the fire period but not the fire from the post-fire periods. In both lakes chironomid composition changed in relation to the period of higher prevalence of fires, which in turn implies catchment changes, pollution, and other anthropogenic impacts. Particularly a marked change in mesotrophic/eutrophic taxa was detected, reflecting an increase in nutrient input due to deforestation. Our findings point out that the, Funding for this research is from the Fondecyt project Nº 11080158 and partially from Fondecyt project 1120765., 2014-03-30

Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Quaternary Geochronology 12 (2012): 23-29, doi:10.1016/j.quageo.2012.06.003., The offset between AMS radiocarbon ages obtained on bulk lake sediments and the true age of deposition was evaluated at four sites in Northern Chilean Patagonia. Our results show that the bulk radiocarbon ages are systematically older by 300 to 1100 years. In this region free of carbonate and carbonaceous rocks, we argue that this difference results from variable inputs of terrestrial organic carbon from the Holocene soils that cover the lake watersheds. For the four studied lakes, the age offset is clearly related to the fraction of terrestrial carbon preserved in the lake sediments, which was estimated using the N/C ratio of the bulk organic matter. We propose that N/C measurements can be used to significantly improve chronologies based on radiocarbon dating of bulk lake sediments., This research was partly funded by Fondecyt grant #1070508 to R. Urrutia, by FNRS grant R.FNRS.1360 and ULg grant R.CFRA.1060 to N. Fagel, and by an EU FP6 Marie Curie Outgoing Fellowship to S. Bertrand.

Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Quaternary Geochronology 12 (2012): 23-29, doi:10.1016/j.quageo.2012.06.003., The offset between AMS radiocarbon ages obtained on bulk lake sediments and the true age of deposition was evaluated at four sites in Northern Chilean Patagonia. Our results show that the bulk radiocarbon ages are systematically older by 300 to 1100 years. In this region free of carbonate and carbonaceous rocks, we argue that this difference results from variable inputs of terrestrial organic carbon from the Holocene soils that cover the lake watersheds. For the four studied lakes, the age offset is clearly related to the fraction of terrestrial carbon preserved in the lake sediments, which was estimated using the N/C ratio of the bulk organic matter. We propose that N/C measurements can be used to significantly improve chronologies based on radiocarbon dating of bulk lake sediments., This research was partly funded by Fondecyt grant #1070508 to R. Urrutia, by FNRS grant R.FNRS.1360 and ULg grant R.CFRA.1060 to N. Fagel, and by an EU FP6 Marie Curie Outgoing Fellowship to S. Bertrand.

En esta investigación se estudian, mediante geocronología radioisotópica (Pb210), las variaciones históricas en el proceso de erosión-sedimentación en Laguna Chica de San Pedro, VIII Región. Las estimaciones cronológicas indican que, durante los últimos 100 años, el aporte de sedimentos desde la cuenca de drenaje osciló drásticamente en un orden de magnitud. Se concluye que las variaciones son producto de los cambios históricos en el uso del suelo. Finalmente, se proponen tres períodos históricos que habrían provocado el aumento de la erosión de los suelos en la cuenca. In this study, the historical variations in the erosional-sedimentation process in the "Laguna Chica de San Pedro" (VIII Region), are studied using lead210 geochronology. The results indicate that over the last century, the sediment supply from the drainage basin fluctuated drastically in an order of magnitude. It is concluded that this variations are the result of the historical changes in the land use. Finally, three historic periods are proposed which would have caused an increase in the erosion in the basin soils.

En esta investigación se estudian, mediante geocronología radioisotópica (Pb210), las variaciones históricas en el proceso de erosión-sedimentación en Laguna Chica de San Pedro, VIII Región. Las estimaciones cronológicas indican que, durante los últimos 100 años, el aporte de sedimentos desde la cuenca de drenaje osciló drásticamente en un orden de magnitud. Se concluye que las variaciones son producto de los cambios históricos en el uso del suelo. Finalmente, se proponen tres períodos históricos que habrían provocado el aumento de la erosión de los suelos en la cuenca. In this study, the historical variations in the erosional-sedimentation process in the "Laguna Chica de San Pedro" (VIII Region), are studied using lead210 geochronology. The results indicate that over the last century, the sediment supply from the drainage basin fluctuated drastically in an order of magnitude. It is concluded that this variations are the result of the historical changes in the land use. Finally, three historic periods are proposed which would have caused an increase in the erosion in the basin soils.