Changes in sub-fossil chironomid assemblages in two Northern Patagonian lake systems associated with the occurrence of historical fires

Abstract

2Patagonia is commonly seen as an exceptionally pristine area because of its wildlife and practically unpolluted 3 waters. However, during the twentieth century the burning of natural forests was one of the most important 4 human activities in Northern Chilean Patagonia. Some estimations indicate that three million hectares were 5 burned during the first three decades of the century being its impacts rarely assessed. Hence the objective of this 6 study was to evaluate the impacts of the historical fires in Lake Burgos (45º42'S) and Lake Thompson (45º38'S) 7 in Chilean Patagonia. The impact was measured by evaluating chironomid assemblage since they are sensitive 8 enough to be used as an indicator of aquatic ecosystem health. Fires have a direct and drastic effect on a lake 9 watershed but also indirectly affect a lake ecosystem, changing sedimentation patterns or increasing nutrient 10 inputs. In the studied lakes the periods with higher prevalence of fires were identified by charcoal analysis, 11 while organic matter and magnetic susceptibility allowed to confirm the pre-fire and post-fire periods. The 12 chironomid composition was evaluated through a PCA and an analysis of similarity (ANOSIM) to test the 13 significance among periods while a DCA was applied to the chironomid assemblage downcore to assess 14 compositional structure and taxa turnover. In Lake Burgos the ANOSIM test indicated significant differences 15 between the pre-fire and fire periods (p<0.05), while in Lake Thompson differences were not significant.

Remobilization of trace elements by forest fire in Patagonia, Chile

“…Chilean Patagonia is renowned for its relatively pristine environment, extensive freshwater resources, and wildlife (Araneda et al 2013). However, human activities associated with development in the region began impacting its ecosystems during the last century (Vince 2010;Araneda et al 2013).…”

“…However, human activities associated with development in the region began impacting its ecosystems during the last century (Vince 2010;Araneda et al 2013). Most notably, settlers burned approximately three million hectares of forest between 1930 and 1950 in the Aysén region of Northern Patagonia in Chile, resulting in a loss of *23 % of its original vegetation (Araneda et al 2013).…”

“…However, human activities associated with development in the region began impacting its ecosystems during the last century (Vince 2010;Araneda et al 2013). Most notably, settlers burned approximately three million hectares of forest between 1930 and 1950 in the Aysén region of Northern Patagonia in Chile, resulting in a loss of *23 % of its original vegetation (Araneda et al 2013). The impacts of those deliberate wildfires on ecosystems were, and continue to be, substantial, including the replacement of native species (Coffman et al 2010;Moreira et al 2013) and the eutrophication of water bodies (Falcon-Lang 1998)-in addition to the previously noted mobilization of contaminants.…”

“…1). The lake has a surface area of *1.18 km 2 , maximum depth of *15 m, and drainage area of *15.43 km 2 (Araneda et al 2013).…”

“…Radiocarbon dating was done on a parallel core collected from the lake, and depths of both cores were correlated using magnetic susceptibility and organic content profiles. The dating, organic content measurement, and charcoal analysis are described in detail elsewhere (Bertrand et al 2012;Araneda et al 2013). The macrocharcoal particles ([125 lm) in sediment subsamples were disaggregated in hot (70°C) 10 % KOH solution for 20 min, sieved through a 125-lm mesh, and the retained particles were counted under a stereomicroscope as detailed by Araneda et al 2013.…”