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Late Holocene environmental reconstruction in Empadadas Norte Lake (Azores archipelago, Portugal) based on diatom ssemblages.

AuthorsSousa Marques, Helena; Raposeiro, P. M.; Hernández, Armand ; Rubio de Inglés, Maria Jesús ; Sáez, Alberto; Giralt, Santiago ; Bao, Roberto; Gonçalves, V.
KeywordsNE Atlantic
Environmental reconstructions
Volcanic lakes
Issue Date10-Jul-2017
CitationConference program and abstracts of the VI Regional Committee on Neogene Atlantic Stratigraphy: RCANS 2017, 10-13 July 2017, Ponta Delgada, Azores, Portugal
AbstractEnvironmental reconstructions using lacustrine sedimentary sequences are a useful tool to both identify long term changes in lake conditions and correlate these changes with environmental and climate drivers. Here we present a diatom-based environmental reconstruction from a 270-cm long sediment core of Empadadas Norte Lake (São Miguel island, Azores archipelago), corresponding to the last ca. 700 years, integrated with other proxy records. Diatom assemblages along the Empadadas sequence show changes in species composition and diversity, resulting from climatic and anthropogenic forcings. The lower part of the sequence (ca. 1350 to 1450 AD) is dominated by macrophyte associated species, typical of low nutrient conditions, such as Stauroforma exiguiformis and Encyonema neogracile, indicative of an oligotrophic lake rich in macrophytes. These findings are supported by the high TOC/TN ratios indicative of organic matter (OM) mainly derived from lake macrophytes and external inputs. From 1450 to 1750 AD, a replacement of S. exiguiformis by Encyonema gaeumannii and Brachysira brebissonii, two benthic epipelic species, suggests lower lake levels probably associated with more arid climate conditions. This period also displays the shrink of trees and increase of shrubs and grasslands percentages owing to the increasing of human population in São Miguel island. Lower TOC and TOC/TN values during this phase also suggest a reduction in allochthonous OM inputs to the lake due to vegetation changes and reduced runoff. This stage is followed by a period (1750 to 1980 AD) of significant anthropogenic impact in lake ecosystem (replacement of native vegetation by exotic tree species, fish introductions, water consumption and impermeabilization of the littoral zone) that were reflected in the diatom assemblages with changes in species dominance. The major shift in diatom assemblages is observed from 1980 AD to present, with a drastic reduction of species richness and diversity, due to the high dominance of Staurosira sp., a tychoplanktonic diatom. This drastic shift also coincides with the recent global warming and could be associated to higher water level and productivity resulting from increases in precipitation and temperature.
Publisher version (URL)http://fundacion.usal.es/rcans/images/stories/documentos/2017_6thRCANS_Azores_Abstracts.pdf
Appears in Collections:(ICTJA) Comunicaciones congresos
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