Browsing by Author "Abarzua, Ana M."

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    Linking sedimentological and spatial analysis to assess the impact of the forestry industry on soil loss: The case of Lanalhue Basin, Chile
    (2021) Alaniz, Alberto J.; Abarzua, Ana M.; Martel-Cea, Alejandra; Jarpa, Leonora; Hernandez, Marjorie; Aquino-Lopez, Marco A.; Smith-Ramirez, Cecilia
    Soil loss has become one of the main problems associated with global change over the last decades. New assessments are needed in order to improve our understanding of the real impacts of human productive activities on the natural dynamics linked to erosion in lake basins. We analyzed the recent and historical dynamics of soil loss in a coastal lake basin of central Chile (Lanalhue lake), evaluating land use impacts and proposing management changes to control erosion and restore the soil. We implemented two approaches: A) Using a high-resolution sedimentological proxy and a high-accuracy chronology of cores to determine the sediment accumulation rate, organic/inorganic matter and granulometry for the last 120 years; and B) applying the Universal Soil Loss Equation to estimate erosion of soil from hills during the last 32 years, considering a combination of satellite, climate, soil, and land-cover topographic data. We found that the sedimentation rates, as well as the concentration of organic matter in lake sediments, were relatively constant from 1900 to 1950; after that, they experienced a significant increase. The same pattern of rapid increase was found for sand content. We found that erosion during the last 30 years has been high and constant, especially in bare soil (mainly clear-cutting areas) and exotic forest plantations. Erosion has been significantly higher within exotic forest plantations, reaching 31 ton/ha/yr in clear-cutting areas. Three industrial forestry companies accounted for 61.5% of the basin surface where urgent erosion control is needed. Our findings support the indication that industrial forestry is the main activity affecting erosion dynamics in the basin; secondarily, earthquakes have been important modulators of the sediment dynamics in Lanalhue during these last 120 years.
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    Vegetation, glacier, and climate changes before the global last glacial maximum in the Isla Grande de Chiloe, southern Chile (42° S)
    (2022) Gomez, Gabriel A.; Garcia, Juan-Luis; Villagran, Carolina; Luethgens, Christopher; Abarzua, Ana M.
    Climatic and vegetation features of the mid-latitudes of the Southern Hemisphere before the global Last Glacial Maximum (gLGM) are still a matter of discussion. The signatures of Marine Isotope Stage (MIS) 3 show strong variability at the poles that has not yet been resolved at lower latitudes. This work discusses one of the first terrestrial records that reflects the vegetation, glacier, and climate conditions in southern South America during this period. The stratigraphic, palynological, and geomorphological features of the Punta Pihuio, Rio Huicha, Punta Pirquen and Punta Detico sites (41-42 degrees S) on the Isla Grande de Chiloe (southern Chile) are described and discussed. Glacially sourced sediment intercalated with peat soils constrained by single-grain feldspar (SGIR50) luminescence and radiocarbon (C-14) dating show that the Late MIS 5 and the MIS 3 were periods of high environmental variability at these locations. Pollen records from peat layers indicate an open forest with conifers, Nothofagus and thermophilic elements, such as Myrtaceae, representing interstadial conditions that were abruptly interrupted by glacial expansions during stadials. High variability between arboreal and herbaceous taxa is also interpreted as environmental instability. Moreover, we show that the Patagonian Ice Sheet (PIS) reached full glacial extent during Early to Middle MIS 3, as is also observed in other Southern Hemisphere glacier records on both sides of the Pacific Ocean. Our data support that millennial-to multi-millennial-scale climate changes characterized the pre-gLGM not only at the poles, but also at the southern mid-latitudes. (C) 2021 Elsevier Ltd. All rights reserved.